1. Mechanics of Materials
Mechanical properties of materials, tensile, compressive and shear stress &
strain, stress strain relationship,

The force per unit area, or intensity of the forces distributed over a given section, is called
the stress on that section

a uniform distribution of stress is possible only if the line of action of the concentrated
loads P and P9 passes through the centroid of the section considered

Since the distribution of these forces—and of the corresponding stresses—is quite
complicated, one uses in practice an average nominal value sb of the stress, called the
bearing stress, obtained by dividing the load P by the area of the rectangle representing
the projection of the bolt on the plate section

For most materials the ultimate stress decreases as the number of load applications is
increased.

In the case of an eccentric axial loading, the distribution of stresses is not uniform.

The ultimate load of a given structural member or machine component is the load at
which the member or component is expected to fail; it is computed from the ultimate
stressor ultimate strength of the material used

The ultimate load should be considerably larger than the allowable load, i.e., the load that
the member or component will be allowed to carry under normal conditions.

the normal strain Pin a member will be defined as the deformation of the member per unit
length.

The normal strain in a rod under axial loading as the deformation per unit length of that
rod

The difference between the engineering stress s 5 PyA0 that we have computed and the
true stresss obtained by dividing P by the cross-sectional area A of the deformed
specimen becomes apparent in ductile materials after yield has started.

the stress distribution may be assumed independent of the actual mode of application of
the loads. This statement, which applies not only to axial loadings, but to practically any
type of load, is known as Saint Venant‘s principle,

Maximum stress over the average stress computed in the critical (narrowest) section of
the discontinuity. This ratio is referred to as the stress-concentration factor of the given
discontinuity.

The value of s for which failure does not occur, even for an indefinitely large number

of cycles, is known as the endurance limit of the material used in the test.

This strain is referred to as the lateral strain, and the ratio of the lateral strain over the
axial strain is called Poisson‘s ratio

The change in volume per unit volume is referred to as the dilatation
Hooke’s law

The largest value of the stress for which Hooke‘s law can be used for a given material is
known as the proportional limit of that material.

Materials whose properties depend upon the direction considered are said to be
anisotropic.

An important class of anisotropic materials consists of fiber reinforced composite
materials

The largest value of the stress for which the material behaves elastically is called the
elastic limit of the material.

The fact that P does not return to zero after the load has been removed indicates that a
permanent set or plastic deformation of the material has taken place.

The stress-dependent part of the plastic deformation is referred to as slip, and the timedependent part—which is also influenced by the temperature—as creep.

rupture will occur at a stress much lower than the static breaking strength; this
phenomenon is known as fatigue.

A fatigue failure is of a brittle nature, even for materials that are normally ductile.

As the magnitude of the maximum stress is reduced, the number of cycles required to
cause rupture increases, until a stress, known as the endurance limit, is reached.

the fatigue limit as the stress corresponding to failure after a specified number of loading
cycles

All materials considered will be assumed to be both homogeneous and isotropic, i.e.,
their mechanical properties will be assumed independent of both position and direction.

Under the given multi axial loading, the element will deform into a rectangular
parallelepiped of sides equal, respectively

The constant G is called the modulus of rigidity of the material and the relations obtained
express Hooke‘s law for shearing stress and strain

The ratio of the maximum value of the stress occurring near the discontinuity over the
average stress computed in the critical section is referred to as the stress-concentration
factor

The plastic deformations which occur in structural members made of a ductile material
when the stresses in some part of the member exceed the yield strength of the material.
Thermal stresses, torsion of circular bars,

When a circular shaft is subjected to torsion, every cross section remains plane and
undistorted because a circular shaft is axisymmetric, i.e., its appearance remains the same
when it is viewed from a fixed position and rotated about its axis through an arbitrary
angle.

the shearing strain varies linearly with the distance from the axis of the shaft

The principal specifications to be met in the design of a transmission shaft are the power
to be transmitted and the speed of rotation of the shaft.

This value of the torque, which corresponds to a fully plastic deformation (Fig. 3.35d), is
called the plastic torque of the shaft considered.

The distribution of stresses in the cross section of a circular shaft is statically
indeterminate.

A circular shaft subjected to torsion, every cross section remains plane and undistorted
shearing force and bending moment, pure bending of beams, shear stresses
in beams, beam deflection using various methods

Equal and opposite couples M and M9 acting in the same longitudinal plane. Such
members are said to be in pure bending.

Plastic deformations in bending, i.e., the deformations of members which are made of a
material which does not follow Hooke‘s law and are subjected to bending.

The moment M of that couple is referred to as the bending moment in the section

the longitudinal normal strain Px varies linearly with the distance y from the neutral
surface

in the elastic range, the normal stress varies linearly with the distance from the neutral
surface

For a member subjected to pure bending, and as long as the stresses remain in the elastic
range, the neutral axis passes through the centroid of the section.

The normal stress sx caused by the bending or ―flexing‖ of the member is often referred
to as the flexural stress.

The deformation of the member caused by the bending moment M is measured by the
curvature of the neutral surface.

The reciprocal of the radius of curvature r9represents the curvature of the transverse cross
section and is called the anticlastic curvature.

The new cross section obtained in this way is called the transformed section of the
member

The distribution of stresses when the line of action of the loads does not pass through the
centroid of the cross section, i.e., when the loading is eccentric.

since the vertical plane is not a plane of symmetry, we cannot expect the member to bend
in that plane, or the neutral axis of the section to coincide with the axis of the couple will
be zero if these axes are the principal centroidal axes of the cross section

The neutral axis of the cross section will coincide with the axis of the couple M
representing the forces acting on that section if, and only if, the couple vector M is
directed along one of the principal centroidal axes of the cross section

In a curved member, the neutral axis of a transverse section does not pass through the
centroid of that section

Transverse sections remain plane as a member is deformed

Member in pure bending has a neutral surface along which normal strains and stresses are
zero and that the longitudinal normal strain P x varies linearly with the distance y from
the neutral surface

normal stress sx varies linearly with the distance from the neutral axis

Neutral axis passes through the centroid of the cross section of a member in pure
bending.

the neutral axis does not pass through the centroid of the composite cross section

Permanent deformations and residual stresses remain in a member after the loads that
caused yielding have been removed.

Such a transverse loading causes only bending and shear in the beam.

The properties of the beams with regard to their resistance to deformations must be taken
into consideration. Such beams are said to be statically indeterminate

The bending couple M creates normal stresses in the cross section, while the shear force
V creates shearing stresses in that section.

the design of non-prismatic beams ,i.e., beams with a variable cross section

The shear at any given point of a beam is positive when the external forces (loads and
reactions) acting on the beam tend to shear off the beam at that point

The bending moment at any given point of a beam is positive when the external forces
acting on the beam tend to bend the beam at that point

The horizontal shear per unit length q is also referred to as the shear flow.

the distribution of shearing stresses in a transverse section of a rectangular beam is
parabolic

The member is observed to bend and twist at the same time, except when the load is
applied at a specific point, called the shear center.

shear center, where the loads should be applied if the member is to bend without twisting

the corresponding values smax and smin of the normal stress exerted on these planes are
called the principal stresses at Q

The planes of maximum shearing stress are at 458to the principal planes.

When the shearing stress exerted on a given face tends to rotate the element clockwise,
the point on Mohr‘s circle corresponding to that face is located above the s axis.

When the shearing stress on a given face tends to rotate the element counterclockwise,
the point corresponding to that face is located below the s axis

Von Mises criterion, a given structural component is safe as long as the maximum value
of the distortion energy per unit volume in that material remains smaller than the
distortion energy per unit volume required to cause yield in a tensile-test specimen of the
same material.

The hexagon associated with the initiation of yield in the material is known as Tresca‘s
hexagon

The maximum-normal-stress criterion, also known as Coulomb‘s criterion on the
assumption that the ultimate strength of the material is the same in tension and in
compression.

The normal stresses s1and s2 shown in Fig. 7.47 are therefore principal stresses. The
stress s1 is known as the hoop stress, because it is the type of stress found in hoops used
to hold together the various slats of a wooden barrel, and the stress s2 is called the
longitudinal stress.

2. Engineering Drawing and Graphics
Types of lines, lettering, dimensioning, planning of drawing sheet
1. The projection showing the front in the true shape and size is




(a) isometric
(b) perspective
(c) oblique
(d) axonometric
Ans: (c)
2. What type of line has precedence over all other types of lines?




(a) hidden line
(b) centre line
(c) visible line
(d) none of the above
Ans: (c)
3. Which is not a principal view?




(a) front
(b) bottom
(c) auxiliary
(d) left side
Ans: (c)
4. Inclined planes in a three-view drawing will appear as




(a) two surfaces and one edge
(b) one surface and two edges
(c) three edges
(d) foreshortened in each view
Ans: (d)
5. When a surface of an object is inclined to a plane of projection, it will appear in the view




(a) foreshortened
(b) in true size and shape
(c) as a line
(d) as a point
Ans: (a)
6. The top view of an object should typically be drawn




(a) to the right of the front view
(b) directly below the front view
(c) anywhere on the same page
(d) on a separate piece of paper
Ans: (b)
7. The top and right side views have common dimensions of




(a) height and width
(b) width and depth
(c) height
(d) depth
Ans: (d)
8. This type of projection is when projectors are parallel to each other, but are at an angle other
than 90 degrees to the plane of projection:




(a) perspective
(b) oblique
(c) aesthetic
(d) angular
Ans: (b)
9. This is how axonometric, oblique, and perspective sketches show objects




(a) Orthographically
(b) Pictorially
(c) Obliquely
(d) Parallel
Ans: (b)
10. The primary unit of measurement for engineering drawings and design in the mechanical
industries is the




(a) millimeter
(b) centimeter
(c) meter
(d) kilometer
Ans: (a)
11. This type of solid has two bases that are parallel equal polygons:




(a) pyramid
(b) prism
(c) cone
(d) torus
Ans: (b)
12. The solid having a polygon for a base and triangular lateral faces intersecting at a vertex is




(a) pyramid
(b) prism
(c) cone
(d) torus
Ans: (a)
13. This is formed where three or more surfaces intersect:




(a) oblique
(b) line
(c) edge
(d) vertex
Ans: (b)
14. These types of projectors converge at a vanishing point




(a) perspective
(b) parallel
(c) orthographic
(d) oblique
Ans: (a)
15. In oblique sketches, the most commonly used angles for receding lines are




(a) 15 or 60 degrees
(b) 15 or 75 degrees
(c) 45 or 60 degrees
(d) 45 or 75 degrees
Ans: (c)
16. Objects that are symmetric can be shown effectively using this type of section




(a) quarter section
(b) half section
(c) full section
(d) symmetric section
Ans: (b)
17. In this type of section, one quarter of the object is removed




(a) revolved section
(b) removed section
(c) quarter section
(d) half section
Ans: (d)
18. This type of section is limited by a break line




(a) removed section
(b) revolved section
(c) broken-out section
(d) half section
Ans: (c)
19. This type of section is not in direct projection from the view containing the cutting plane




(a) revolved section
(b) removed section
(c) broken-out section
(d) full section
Ans: (a)
20. An axonometric projection in which three perpendicular edges of the object make different
angles with the plane of projection is called




(a) isometric projection
(b) diametric projection
(c) trimetric projection
(d) oblique projection
Ans: (c)
1. Hidden lines are drawn as




(a) dashed narrow lines
(b) dashed wide lines
(c) long-dashed dotted wide line
(d) long-dashed double dotted wide line
Ans: (a)
2. Line composed of closely and evenly spaced short dashes in a drawing represents




(a) visible edges
(b) hidden edges
(c) hatching
(d) pitch circle of gears
Ans: (b)
3. Lettering on a drawing sheet should have




(a) all alphabets in capital letters
(b) all alphabets in small letters
(c) In a sentance only first alphabet in capital letter
(d) In a sentance only abbreviations are capital letter
Ans: (a)
4. The line connecting a view to note is called




(a) dimension line
(b) projection line
(c) leader
(d) arrowheads
Ans: (c)
5. The dimension figure for radius of a circle should be preceded by




(a) R
(b) CR
(c) SR
(d) RAD
Ans: (b)
6. The recommended method of dimensioning a sphere with diameter 80 mm is




(a) 80фS
(b) ф80S
(c) S80ф
(d) Sф80
Ans: (d)
7. Methods of arrangement of dimensions includes




(a) Parallel, continuous and combined
(b) Perpendicular, parallel and combined
(c) Perpendicular, continuous and combined
(d) Perpendicular, parallel and continuous
Ans: (a)
8. Superimposed dimensioning is a simplified method of




(a) chain dimensioning
(b) parallel dimensioning
(c) combined dimensioning
(d) tabular dimensioning
Ans: (b)
9. A curve drawn for Boyle‘s law (PV = constant) on a P-V chart has a characteristic shape of




(a) ellipse
(b) parabloa
(c) oblique hyperbola
(d) rectangular hyperbola
Ans: (d)
10. The profile of a gear teeth is in the form of




(a) parabola
(b) involute
(c) spiral
(d) helix
Ans: (b)
11. When two angles together make 90º, they are called




(a) obtuse angle
(b) reflex angle
(c) complementary angles
(d) supplementary angles
Ans: (c)
12. The included angle of a hexagon is




(a) 30º
(b) 60º
(c) 120º
(d) 150º
Ans: (c)
13. The curve generated by a point on the circumference of a circle, which rolls without slipping
along outside of another circle is known as




(a) Hypocycloid
(b) Epicycloid
(c) Cycloid
(d) Trochoid
Ans: (b)
14. In orthographic projections, the rays are assumed to




(a) diverge from station point
(b) converge from station point
(c) be parallel
(d) None of these
Ans: (c)
15. If an object lies in third quadrant, its position with respect to reference planes will be




(a) infront of V.P, above H.P
(b) behind V.P., above H.P.
(c) behind V.P., below H.P.
(d) infront of V.P., below H.P.
Ans: (c)
16. If the Vertical Trace (V.T.) of a line lies 30 mm above reference line (XY), then its position
will be




(a) 30 mm infront of V.P.
(b) 30 mm behind V.P.
(c) 30 mm above H.P.
(d) 30 mm below H.P.
Ans: (c)
17. When an object is cut by a section plane parallel to H.P and perpendicular to V.P, then the
sectional view of the object is obtained in




(a) top view
(b) front view
(c) left side view
(d) right side view
Ans: (a)
18. Which of the following object gives a circular section, when it is cut completely by a section
plane (irrespective of the angle of the section plane)




(a) Cylinder
(b) Sphere
(c) Cone
(d) Circular lamina
Ans: (b)
19. Comparative scale is a pair of scale having a common




(a) units
(b) representative fraction
(c) length of scale
(d) least count
Ans: (b)
20. An angle can be set off and measured with the help of




(a) plane scale
(b) diagonal scale
(c) comparative scale
(d) Scale of chords
Ans: (d)
1. In an isometric projection, the included angle between the edges of a cube is




(a) 30º
(b) 60º
(c) 90º
(d) 120º
Ans: (d)
2. The axonometric drawing having equal foreshortening along two axis directions and a
different amount on the third axis is called




(a) dimetric
(b) trimetric
(c) isometric
(d) multiview
Ans: (a)
3. In an isometric drawing, lines that are not parallel to the isometric axes are called




(a) dimetric lines
(b) trimetric lines
(c) non-isometric lines
(d) multiview lines
Ans: (c)
4. The axonometric drawing having different ratios of foreshortening for all the three axes is
called




(a) dimetric
(b) trimetric
(c) isometric
(d) multiview
Ans: (b)
5. When the projectors are at 45º to the plane of projection and the receding lines are true length,
it is called




(a) cabinet projection
(b) cavalier projection
(c) axonometric projection
(d) perspective projection
Ans: (b)
6. Perspective drawings are classified according to their number of these features




(a) station points
(b) picture planes
(c) vanishing points
(d) ground lines
Ans: (c)
7. In offset sections, offsets or bends in the cutting plane are all:




(a) 90 degrees
(b) 180 degrees
(c) Either 90 or 180 degrees
(d) 30, 60, or 90 degrees
8. These breaks are used to shorten the view of an object:




(a) Section breaks
(b) Aligned breaks
(c) Conventional breaks
(d) Full breaks
ENGINEERING DRAWING
SECTION OF SOLIDS
1.
Drafters should use a ________ in a section view of a mechanical part that includes the
cylindrical view of a threaded hole.
A. Center line
B. Hatch line
C. Poly line
D. Dimension line
ANSWER: A
2.
The section view drawing in which one fourth of an object has been marked for removal is
known as a ________ section.
A. Full
B. Half
C. Quarter
D. none of the above
ANSWER: B
3.
In offset sections, offsets or bends in the cutting plane are all:
A. 90 degrees
B. 180 degrees
C. Either 90 or 180 degrees
D. 30, 60, or 90 degrees
ANSWER: A
4. When filling an area with a hatch pattern in AutoCAD the drafter needs to be able to ________.
A. see the entire bounding area to hatch
B. set Ortho on
5.
6.
7.
8.
9.
10.
11.
C. turn ISO grid off
D. set the layer to Defpoints
ANSWER: A
To avoid having to dimension to a hidden feature the drafter can utilize a ________ section.
A. Whole.
B. Half
C. broken out
D. all of the above
ANSWER: D
Objects that are symmetric can be shown effectively using this type of section:
A. Quarter section
B. Half section
C. Full section
D. Symmetric section
ANSWER: B
This type of section is not in direct projection from the view containing the cutting plane:
A. Revolved section
B. Removed section
C. Broken-out section
D. Full section
ANSWER: B
By using a ________ section of a cylindrical mechanical part the drafter should be able to show
only one view of the part.
A. Half
B. Whole
C. Revolved
D. broken out
ANSWER: C
In the section view, the areas that would have been in actual contact with the cutting plane are
shown with:
A. A cutting plane line
B. Section lining
C. Visible lines
D. Lines and arrows
ANSWER: B
These breaks are used to shorten the view of an object:
A. Section breaks
B. Aligned breaks
C. Conventional breaks
D. Full breaks
ANSWER:C
In architectural drawing ________ are often used to illustrate and detail structural components.
A.
B.
C.
D.
12.
13.
14.
15.
16.
Foundation beam detail sections
Wall sections
Building sections
All of the above
ANSWER: D
When only a small section of an interior area needs to be revealed the drafter can use a
________ section.
A. Half
B. Quarter
C. Full
D. broken out
ANSWER: D
In this type of section, one quarter of the object is removed:
A. Revolved section
B. Removed section
C. Quarter section
D. Half section
ANSWER: D
A ________ section allows the drafter to create a Cutting Plane line which is not in a straight line
across the part.
A. Offset
B. Half
C. Whole
D. broken out
ANSWER: A
The ________ is a standard element of a section view in a technical drawing.
A. Cutting Plane line
B. Section lines
C. Material hatch pattern
D. All of the above
ANSWER: D
When creating a Cutting Plane line with AutoCAD it is customary to use a ________ to create the
line.
A. center line
B. polyline
C. dashed line
D. hatch line
17. The type of section is limited by a break line is
A. Removed section
B. Revolved section
C. Broken-out section
D. Half section
ORTHOGRAPHIC PROJECTION
1. The top, front, and bottom views align in this manner:
A. Horizontally
B. Vertically
C. According to the planar views
D. Parallel to the frontal plane
ANSWER: B
2. If a plane is parallel to the plane of projection, it appears:
A.
B.
C.
D.
True Size
As a line or edge
Foreshortened
As an oblique surface
ANSWER: A
3. This line pattern is composed of three dashes, one long dash on each end with a short
dash in the middle:
A. Object
B. Hidden
C. Center
D. Phantom
ANSWER: C
4. This is the plane upon which the top view is projected:
A. Horizontal
B. Frontal
C. Profile
D. Base
ANSWER: A
5. An advantage of this type of view is that each view shows the object all the way through
as if it were transparent:
A. Planar
B. Horizontal
C. Auxiliary
D. Orthographic
ANSWER: D
6. This type of surface is tipped to all principal planes of projection and does not appear true
size in any standard view:
A. Foreshortened
B. Parallel
C. Orthographic
D. Oblique
ANSWER: D
7. Visible lines always take precedence over hidden lines or centerlines
A. True
B. False
ANSWER: A
C.
8. Any object can be viewed from six mutually perpendicular views
A. True
B. False
ANSWER: A
9. A total of three principal views are arranged in a standard way.
A. True
B. False
ANSWER: B
10. Height is shown in the left-side, top, right-side, and bottom views.
A. True
B. False
ANSWER: B
11. A plane surface always projects either on edge or as a surface in any view.
A. True
B. False
ANSWER: A
12. If an edge is perpendicular to a plane of projection, it appears as a point.
A. True
B. False
ANSWER: A
13. The depth dimensions in the top and side views do not necessarily correspond.
A. True
B. False
ANSWER: B
14. The profile plane is the plane upon which the side view is projected.
A. True
B. False
ANSWER: A
15. The rear, left-side, front, and right-side views align horizontally.
A. True
B. False
ANSWER: A
16. Width is shown in the rear, top, front, and bottom views.
A. True
B. False
ANSWER: A
ISOMETRIC PROJECTION
17. Isometric drawings are often used by ________ to help illustrate complex designs.
A. mechanical engineers
B. piping drafters
C. aerospace engineers
D. all of the above
ANSWER: D
18. In order to create an isometric circle to represent a hole through the top surface of a box,
the drafter must insure that the correct isoplane has been selected by scrolling through the
isoplanes using the ________ key.
A. F1
B. F3
C. F5
D. F8
ANSWER: C
19. A fillet is a rounded surface on the ________ corner of a part.
A. Inside
B. Outside
C. Radial
D. Isoplane
ANSWER: A
20. Before starting an isometric drawing in AutoCAD the drafter needs to ________.
A. set the grid to isometric
B. set the current layer to Defpoints
C. turn Object Snap off
D. turn Ortho off
ANSWER: A
21. A round is a rounded surface on the ________ corner of a part.
A.
B.
C.
D.
Inside
Outside
Radial
Isoplane
ANSWER: B
22. Architectural drafters generally prefer to use ________ drawings to help illustrate 3-
dimensional views of a structure.
A. Isometric
B. Perspective
C. Orthographic
D. Auxiliary
ANSWER: B
23. The bounding box method for setting up an isometric drawing helps the drafter
________.
A. confine the isometric drawing to its maximum size
B. figure what lines are to be illustrated vertical and horizontal
C. position the isometric drawing in paper space
D. none of the above
ANSWER: A
24. The Offset tool should only be used for placing ________ in an isometric drawing.
A. Circles
B. horizontal lines
C. vertical lines
D. none of the above
ANSWER: C
25. When creating an isometric drawing in AutoCAD the drafter can utilize the Dynamic
Input and Polar Coordinate system to place both vertical and horizontal lines. A line
created from one point 3 inches at 180 degrees would be a ________ line.
A.
B.
C.
D.
Horizontal
Vertical
Inclined
none of the above
ANSWER: B
26. AutoCAD refers to isometric ellipses as ________.
A. Ellipses
B. Isoellipses
C. Isocircles
D. Circles
ANSWER: C
27. In an isometric drawing all horizontal lines are drawn on a 60 degree angle away from a
given point.
A. True
B. False
ANSWER: B
28. An isometric drawing is a type of technical drawing used to illustrate a mechanical part in
true 3-dimensional form.
A. True
B. False
ANSWER: B
29. When using AutoCAD to create an isometric drawing it is best to set the grid to ISO.
A. True
B. False
ANSWER: A
30. The Offset command can be used on vertical lines but not on horizontal lines.
A. True
B. False
ANSWER: A
PERSPECTIVE DRAWINGS
1. Two-point perspective is also known as:
A. Two-view perspective
B. Regular perspective
C. Parallel perspective
D. Angular perspective
ANSWER: D
2. This is the intersection of the ground plane with the picture plane:
A. Vanishing point
B. Ground line
C. Station point
D. Horizon
ANSWER: B
3. In perspective drawings this is placed between the observer and the object:
A. Vanishing point / horizon
B. Station point
C. Ground line
D. Plane of projection / picture plane
ANSWER: D
4. When positioning this feature of perspective projection, the centerline of the cone of
visual rays should be directed toward the approximate center of the object:
A. Station point
B. Vanishing point
C. Horizon
D. Ground line
ANSWER: A
5. Perspective drawings are classified according to their number of these features:
A. Station points
B. Picture planes
C. Vanishing points
D. Ground lines
ANSWER: C
3. Mechanics of Machines
Linkages:
synthesis
and
analysis,
position, velocity
and
acceleration
analysis,

The term inertial reference frame is used to denote a system which itself has no
acceleration.








Counterclockwise angles, angular velocities, and angular accelerations are positive in
sign.


The general case of complex motion is the sum of the translation and rotation
components

Euler Theorem The general displacement of a rigid body with one point fixed is a
rotation about some axis.

Chasles' theorem: Any displacement of a rigid body is equivalent to the sum of a
translation of any one point on that body and a rotation of the body about an axis through
that point.

The transmission angle is defined as the angle between the output link and the coupler.

Chase and Mirth[2] define a circuit in a linkage as "all possible orientations of thelinks
that can be realized without disconnecting any of the joints" and a branch as "a
continuous series of positions of the mechanism on a circuit between two stationary
configurations .... The stationary configurations divide a circuit into a series of branches."

A mechanism that must change circuits to move from one desired position to the other
(referred to as a circuit defect) is not useful as it cannot do so without disassembly and
reassembly.

A mechanism that changes branch when moving from one circuit to another (referred to
as a branch defect) may or may not be usable depending on the designer's intent.

FUNCTION GENERATION is defined as the correlation of an input function with an
output function in a mechanism.

PATH GENERATION is defined as the control of a point in the plane such that it follows
some prescribed path.

MOTION GENERATION is defined as the control of a line in the plane such that it
assumes some sequential set of prescribed positions.

The points, or positions, prescribed for successive locations of the output (coupler or
rocker) link in the plane are generally referred to as precision points or precision
positions

there will be an infinite number of sets of center-point and circle-point circles.

The circle-point and center-point circles of the

three-position problem become cubic curves, called Burmester curves, in the fourposition problem.

In a four bar function generator, the coupler exists only to couple the input link to the
output link.

Our function generator uses link 2 as the input link and takes the output from link 4. The
"function" generated is the relationship between the angles of link 2 and link 4 for the
specified three-position positions, PJ, P2, and P3.

the solution equations are the same for all three types of kinematic synthesis,function
generation, motion generation, and path generation with prescribed timing. This is why
Erdman and Sandor called equation 5.35 the standard form equation.

The type labeled equation in Table 5-5 refers to methods that solve the tricircular,
trinodal sextic coupler curve to find a linkage that will generate an entire coupler curve
that closely approximates a set of desired points on the curve.

The type labeled optimized in Table 5-5 refers to an iterative optimization procedure that
attempts to minimize an objective function that can be defined in many ways, such as the
least-squares deviation between the calculated and desired coupler point

Recent developments in the mathematical theory of polynomials have created new
methods of solution called continuation methods (also called homotopy methods) which
do not suffer from the same convergence problems as other methods and can also
determine all the solutions of the equations starting from any set of assumed values.

The coupler curve equation itself is very complex and as far as is known in the study of
mechanics (or for that matter elsewhere) no other mathematical result has been found
having algebraic characteristics matching those of the coupler curve.

The lengths of all the links, the angular positions of all the links, and the instantaneous
input velocity of any one driving link or driving point.

If the rotation component relates two points in the same rigid body, then that velocity
difference component is always perpendicular to the line connecting those two points

The link simply has an angular velocity, just as does a frisbee thrown and spun across the
lawn.


Kennedy's rule: Any three bodies in plane motion will have exactly three instant centers,
and they will lie on the same straight line.

All pin joints are permanent instant centers.

A sliding

joint is kinematically equivalent to an infinitely long link, "pivoted" at infinity.

a slider joint will have its instant center at infinity along a line perpendicular to the
direction of sliding

The angular velocity ratio m Vis defined as the output angular velocity divided by the
input angular velocity.

The definition of effective link pairs is two lines, mutually parallel, drawn through the
fixed pivots and intersecting the coupler extended,

Just as with a two-force member in which a force applied at one end transmits only its
component that lies along the link to the other end, this velocity component can be
transmitted along the link to point B. This is sometimes called the principle of
transmissibility.

two ratios, angular velocity ratio and mechanical advantage, provide useful,
dimensionless indices of merit by which we can judge the relative quality of various
linkage designs which may be proposed as solutions.

the successive positions of an instant center (or centro) form a path of their own. This
path, or locus, of the instant center is called the centrode.

If a coupler point is chosen to be on the moving centrode at one extreme of its path
motion (i.e., at one of the positions ofh,3), then it will have a cusp in its coupler curve

This axis of transmission is the only line along which we can transmit motion or force
across the slider joint, except for friction.

axis of slip called the velocity of transmission. This lies along the axis of transmission
which is the only line along which any useful work can be transmitted across the sliding
joint.

the lengths of all the links, the angular positions of all the links, the angular velocities of
all the links, and the instantaneous input acceleration of any one driving link or driving
point.


If the two points are in the same rigid body, then that acceleration difference centripetal
component has a magnitude of rm2 and is always directed along the line connecting the
two points, pointing toward the reference point as the center

We had to understand the concept of angular acceleration as a free vector, which means
that it exists everywhere on the link at any given instant. It has no particular center. It has
infinity of potential centers. The link simply has an angular acceleration. It is this
property that allows us to solve equation 7.4 for literally any point on a rigid body in
complex motion referenced to any other point on that body.

When a sliding joint is present on a rotating link, an additional component of acceleration
will be present, called the Coriolis component

This vector is both rotating and changing length as the system moves.

The time derivative of acceleration is called jerk, pulse, or shock. The name is apt, as it
conjures the proper image of this phenomenon. Jerk is the time rate of change of
acceleration
Cam and follower

Cam-follower systems can be classified in several ways: by type of follower motion,
either translating or rotating (oscillating); by type of earn, radial, cylindrical, threedimensional; by type of joint closure, either force- or fonn-closed; by type of follower,
curved or flat, rolling or sliding; by type of motion constraints, critical extreme position
(CEP), critical path motion (CPM); by type of motion program, rise-fall (RF), rise-falldwell (RFD), rise-dwell-fall-dwell (RDFD).

Force closure, as shown in Figure 8-1 (p. 347), requires an external force be applied to
the joint in order to keep the two links, cam and follower, physically in contact.

Form closure, as shown in Figure 8-2, closes the joint by geometry.

another variety of form-closed earn-follower arrangement, called conjugate cams. There
are two cams fixed on a common shaft which are mathematical conjugates of one
another. Two roller followers, attached to a common arm, are each pushed in opposite
directions by the conjugate cams. When form-closed cams are used in automobile or
motorcycle engine valve trains, they are called desmodromic cams.

The roller follower has the advantage of lower (rolling) friction than the sliding contact of
the other two but can be more expensive. Flat-faced followers can package smaller than
roller followers for some earn designs and are often favored for that reason as well as cost
for automotive valve trains. Roller followers are more frequently used in production
machinery where their ease of replacement and availability from bearing manufacturers'
stock in any quantities are advantages.

Flat-faced or mushroom followers are usually custom designed and manufactured for
each application.

The direction of the follower's motion relative to the axis of rotation of the earn
determines whether it is a radial or axial earn.

Open radial cams are also called plate cams

An axial carn whose follower moves parallel to the axis of earn rotation. This
arrangement is also called a face earn if open (force-closed) and a cylindrical or barrel
earn if grooved or ribbed (form-closed).\

A three-dimensional cam or camoid (not shown) is a combination of radial and axial
cams. It is a two-degree-of-freedom system.

There are two general categories of motion constraint, critical extreme position (CEP;
also called endpoint specification) and critical path motion (CPM).

Critical extreme position refers to the case in which the design specifications define the
start and finish positions of the follower (i.e., extreme positions) but do not specify any
constraints on the path motion between the extreme positions.

Critical path motion is a more constrained problem than CEP because the path motion,
and/or one or more of its derivatives are defined over all or part of the interval of motion.
This is analogous to function generation in the linkage design case except that with a cam
we can achieve a continuous output function for the follower.

The motion programs rise-fall (RF), rise-fall-dwell (RFD), and rise-dwell-fall-dwell
(RDFD) all refer mainly to the CEP case of motion constraint and in effect define how
many dwells are present in the full cycle of motion,

Dwells, defined as no output motion for a specified period of input motion,

A machine's cycle is defined as one revolution of its master driveshaft.

The cam function must be continuous through the first and second derivatives of
displacement across the entire interval (360 degrees)

The jerk function must be finite across the entire interval

As a general rule we would like to minimize the number of segments in our polynomial
cam functions.

A high-degree function may have undesirable oscillations between its BCs.

Spline functions, of which polynomials are a subset, offer even more flexibility in
meeting boundary constraints and other cam performance criteria

There are two general types of automated production machinery in common use,
intermittent motion assembly machines and continuous motion assembly machines.

Intermittent motion assembly machines carry the manufactured goods from work station
to work station, stopping the work piece or subassembly at each station while another
operation is performed upon it.

Continuous motion assembly machines never allow the work piece to stop and thus are
capable of higher throughput speeds.

There are two major factors which affect cam size, the pressure angle and the radius of
curvature.

The base circle is defined as the smallest circle which can be drawn tangent to the
physical cam surface

The prime circle is defined as the smallest circle which can be drawn tangent to the locus
of the centerline of the follower

The locus of the centerline of the follower is called the pitch curve.

The pressure angle <\> is the angle between the direction of motion (velocity) of the
follower and the direction of the axis of transmission

There is an eccentricity E defined as the perpendicular distance between the follower's
axis of motion and the center of the cam.

For a positive co, a positive value of eccentricity will decrease the pressure angle on the
rise but will increase it on the fall.

The radius of curvature is a mathematical property of a function.

The cam contour is actually defined as the locus of the center of the roller follower, or the
pitch curve.

The cutter creates a perfect sharp point, or cusp, on the cam surface.

Plunge-cutting to refer to plunging the spinning milling cutter down through the work
piece.

FOLLOWER JUMP The principal advantage of a form-closed (track) cam is that it does
not need a return spring, and thus can be run at higher speeds than a force-closed cam
whose spring and follower mass will go into resonance at some speed, causing potentially
destructive follower jump.

CROSSOVER SHOCK Though the lack of a return spring can be an advantage, it comes,
as usual, with a trade-off.
Gear trains

When two gears are placed in mesh to form a gear set such as this one, it is conventional
to refer to the smaller of the two gears as the pinion and to the other as the gear.

The fundamental law of gearing which, if followed, provides that the angular velocity
ratio between the gears of a gear set remains constant throughout the mesh.

The torque ratio (mr) was shown in equation 6.12 (p. 259) to be the reciprocal of the
velocity ratio (my); thus a gearset is essentially a device to exchange torque for velocity
or vice versa.

Since there are no applied forces as in a linkage, but only applied torques on the gears,
the mechanical advantage mA of a gear set is equal to its torque ratio mr.

The surfaces of the rolling cylinders will become the pitch circles, and their diameters the
pitch diameters of the gears. The contact point between the cylinders lies on the line of
centers as shown in Figure 9-3a, and this point is called the pitch point

The cycloid still is used as a tooth form in watches and clocks, but most other gears use
the involute curve for their shape.

The string is always tangent to the cylinder.

The center of curvature of the involute is always at the point of tangency of the string
with the cylinder.

A tangent to the involute is then always normal to the string, the length of which is the
instantaneous radius of curvature of the involute curve.

The gear tooth must project both below and above the rolling cylinder surface (pitch
circle) and the involute only exists outside of the base circle. The amount of tooth that
sticks out above the pitch circle is the addendum,

There is a common tangent to both curves at the contact point, and a common normal,
perpendicular to the common tangent.

Thus the common normal, which is also the axis of transmission, always passes through
the pitch point regardless of where in the mesh the two teeth are contacting

law of gearing the common normal of the tooth profiles, at all contact points within the
mesh, must always pass through a fixed point on the line of centers, called the pitch
point.

The points of beginning and leaving contact define the mesh of the pinion and gear

The distance along the line of action between these points within the mesh is called the
length of action, Z, defined by the intersections of the respective addendum circles with
the line of action,

The distance along the pitch circle within the mesh is the arc of action, and the angles
subtended by these points and the line of centers are the angle of approach and angie of
recess.

The pressure angle in a gear set is similar to that of the cam and follower and is defined
as the angle between the axis of transmission or line of action (common normal) and the
direction of velocity at the pitch point

with an involute tooth form, center distance errors do not affect the velocity ratio.

Backlash is defined as the clearance between mating teeth measured along the
circumference of the pitch circle

Such applications need anti backlash gears which are really two gears back-to-back on
the same shaft which can be rotated slightly at assembly with respect to one another, and
then fixed so as to take up the backlash.

The tooth height is defined by the addendum (added on) and the dedendum (subtracted
from) which are referenced to the nominal pitch circle.

The dedendum is slightly larger than the addendum to provide a small amount of
clearance between the tip of one mating tooth (addendum circle) and the bottom of the
tooth space of the other (dedendum circle).

The tooth thickness is measured at the pitch circle, and the tooth space width is slightly
larger than the tooth thickness.

The difference between these two dimensions is the backlash.

The face width of the tooth is measured along the axis of the gear.

The circular pitch is the arc length along the pitch circle circumference measured from a
point on one tooth to the same point on the next.

The tooth pitch can also be measured along the base circle circumference and then is
called the base pitch

module which is the reciprocal of diametral pitch with pitch diameter measured in
millimeters.

In order to avoid interference on small pinions, the tooth form can be changed from the
standard, full-depth shapes of Figure 9-10 (p. 442) that have equal addenda on both
pinion and gear to an involute shape with a longer addendum on the pinion and a shorter
one on the gear called profile-shifted gears.

For contact ratios between 1 and 2, which are common for spur gears, there will still be
times during the mesh when one pair of teeth will be taking the entire load. However,
these will occur toward the center of the mesh region where the load is applied at a lower
position on the tooth, rather than at its tip. This point is called the highest point of singletooth contact (HPSTC).

SPUR GEARS are ones in which the teeth are parallel to the axis of the gear.

HELICAL GEARS are ones in which the teeth are at a helix angle \jf with respect to the
axis of the gear

crossed helical gears of the same hand can be meshed with their axes at an angle

HERRINGBONE GEARS are formed by joining two helical gears of identical pitch and
diameter but of opposite hand on the same shaft.

If the helix angle is increased sufficiently, the result will be a worm, which has only one
tooth wrapped continuously around its circumference a number of times, analogous to a
screw thread. This worm can be meshed with a special worm gear (or worm wheel),
whose axis is perpendicular to that of the worm

Single enveloping means that the worm gear teeth are wrapped around the worm.

Double enveloping sets also wrap the worm around the gear, resulting in an hourglassshaped worm.

Perhaps the major advantage of the worm set is that it can be designed to be impossible to
back drive.

If the "string" wrapped around this base circle to generate the in volute were still in place
after the base circle's enlargement to an infinite radius, the string would be pivoted at
infinity and would generate an involute that is a straight line. This linear gear is called a
rack

An example of its use is in rack-and-pinion steering in automobiles.

For right-angle drives, crossed helical gears or a wormset can be used.

Just as spur gears are based on rolling cylinders, bevel gears are based on rolling cones

If the teeth are parallel to the axis of the gear, it will be a straight bevel gear

If the teeth are angled with respect to the axis, it will be a spiral bevel gear (see Figure 922), analogous to a helical gear.

HVPOIDGEARS If the axes between the gears are nonparallel and also nonintersecting,
bevel gears cannot be used.

Vee belts are made of elastomers (synthetic rubber) reinforced with synthetic or metallic
cords for strength.

The synchronous belt solves the phasing problem while retaining the advantages of quiet
running of vee belts and can cost less than gears or chains.

CHAIN DRIVES are often used for applications where positive drive (phasing) is needed
and large torque requirements or high temperature levels preclude the use of timing belts.

One unique limitation of chain drive is something called "chordal action."

A gear train is any collection of two or more meshing gears. A simple gear train is one in
which each shaft carries only one gear, the most basic,

A single gearset of spur, helical, or bevel gears is usually limited to a ratio of about 10: 1

compound train is one in which at least one shaft carries more than one gear.

Such a gearbox, whose input and output shafts are not coincident, is called a nonreverted
compound train.

The design of a reverted compound train is more complicated because of the additional
constraint that the center distances of the stages must be equal.

Another class of gear train has wide application, the epicyclic or planetary train. This is a
two-DOF device.

This has become an epicyclic train with a sun gear and a planet gear orbiting around the
sun, held in orbit by the arm.

At the left is a turbinelike fluid coupling between engine and transmission, called a
torque converter. This device allows sufficient slip in the coupling fluid to let the engine
idle with the transmission engaged and the vehicle's wheels stopped.

A differential is a device that allows a difference in velocity (and displacement) between
two elements.
Balancing

static balance does apply to things in motion

Another name for static balance is single-plane balance,

Dynamic balance is sometimes called two-plane balance.

the condition of static balance can also be defined as one of making the mass center
stationary.

The net shaking force is the vector sum of these two sets of forces for each time step
flywheels,

Gyroscopes




Bands And Shoe Brakes Dynamometers.




Governors


Friction
Of Pivot,
Centrifugal Clutch,




Collar
And
Conical
Bearing,
Cone,
Plate
And











Belts And Rope Drives, Chains















The primary function of a belt or chain drive is identical to that of a gear drive.

Belt and chain drives are commonly referred to as flexible connectors.

The function of a belt drive is to transmit rotational motion and torque from one shaft to
another, smoothly, quietly, and inexpensively.

A flat belt is shown in Figure 11.1a. This belt is the simplest type but is typically limited
to low-torque applications because the driving force is restricted to pure friction between
the belt and the pulley

AV-belt is shown in Figure 11.1b. This is the most widely used type of belt, particularly
in automotive and industrial machines.

A multi-V-belt is shown in Figure 11.1c. This belt design is identical to several V-belts
placed side by side but is integrally connected.

A cog belt is shown in Figure 11.1d. This belt design is similar to a V-belt but has
grooves formed on the inner surface.

A timing belt is shown in Figure 11.1e. This belt design has gear-like teeth that engage
with mating teeth on the pulleys.

Pulleys, more appropriately referred to as sheaves, are the wheels that are connected to
the shafts and carry the belt.

Sheaves are classified with a pitch diameter, which is the diameter slightly smaller than
the outside of the groove, corresponding to the location of the center of the belt.

An idler pulley is used to maintain constant tension on the belt.

A belt drive is intended to provide a constant velocity ratio between the respective shafts

As stated, the pitch diameter, d, of the sheave is measured to the point in the groove
where the center of the belt sits.

The center distance, C, is the distance between the center of the driver and driven
sheaves.

The belt length, L, is the total length of the belt

The angle of contact, θ, is a measure of the angular engagement of the belt on each
sheave.

In a manner identical to gear drives, the velocity ratio,VR,is defined as the angular speed
of the driver sheave (sheave 1) divided by the angular speed of the driven sheave (sheave
2)

The belt speed, vb, is defined as the linear velocity of the belt.

As with belts, chain drives are used to transmit rotational motion and torque from one
shaft to another, smoothly, quietly, and inexpensively.

Chain drives provide the flexibility of a belt drive with the positive engagement feature of
a gear drive.

A roller chain is shown in Figure 11.8a. This is the most common type of chain used for
power transmission.

A multiple-strand roller chain is shown in Figure 11.8b. This design uses multiple
standard roller chains built into parallel strands. This increases the power capacity of the
chain drive

An offset sidebar roller chainis shown in Figure 11.8c. This is less expensive than a roller
chain but has slightly less power capability

An inverted tooth, silent chainis shown in Figure 11.8d.

This is the most expensive chain to manufacture. It can be efficiently used in applications
that require high speed, smooth, and quiet power transmission.

Roller chains are classified by a pitch,p, which is the distance between the pins that
connect the adjacent links.

Sprockets are the toothed wheels that connect to the shaft and mate with the chain. The
teeth on the sprocket are designed with geometry to conform to the chain pin and link.

Sprockets are commonly referenced by the corresponding chain size and the number of
teeth.

The number of teeth, N, in the sprocket is a commonly referenced property.

As stated, the pitch diameter, d, of the sprocket is measured to the point on the teeth
where the center of the chain rides.

The center distance, C, is the distance between the center of the driver and driven
sprockets.

The angle of contact, θ, is a measure of the angular engagement of the chain on each
sprocket.

Once again, the velocity ratio, VR, is defined as the angular speed of the driver sprocket
(sprocket 1) divided by the angular speed of the driven sprocket (sprocket 2).

Similar to belts, the linear velocity of the chain, or chain speed, is defined as vc. The
magnitude of this velocity corresponds to the magnitude of the linear velocity of a point
on the pitch diameter of each sprocket.
4. Machine Design
Basic criteria of design of machine parts, determination of permissible and
actual stresses, factor of safety,

The reliability method of design is one in which we obtain the distribution of stresses and
the distribution of strengths

In the reliability method of design, the designer‘s task is to make a judicious selection of
materials,

A very common state of stress occurs when the stresses on one surface are zero. When
this occurs the state of stress is called plane stress.

Shear stresses tending to rotate the element clockwise (cw) are plotted above the saxis.

Shear stresses tending to rotate the element counterclockwise (ccw) are plotted below the
s axis.

Any moment vector that is collinear with an axis of a mechanical part is called a torque
vector, because the moment causes the part to be twisted about that axis. A bar subjected
to such a moment is said to be in torsion.

When the median wall line is not closed, the section is said to be an open section

Such discontinuities are called stress raisers, and the regions in which they occur are
called areas of stress concentration.

The stress-concentration factor depends for its value only on the geometry of the part.
That is, the particular material used has no effect on the value of Kt. This is why it is
called a theoretical stress-concentration factor.

In ductile materials (f $0.05), the stress-concentration factor is not usually applied to
predict the critical stress, because plastic strain in the region of the stress concentration is
localized and has a strengthening effect.

In brittle materials(f ,0.05), the geometric stress- concentration factor Kt is applied to the
nominal stress before comparing it with strength.

For dynamic loading, the stress concentration effect is significant for both ductile and
brittle materials and must always be taken into account

Under these conditions the tangential stress, called the hoop stress

The stresses expressed by Eqs. (3–61) and (3–62) are called thermal stresses. They arise
because of a temperature change in a clamped or restrained member. Such stresses, for
example, occur during welding, since parts to be welded must be clamped before
welding.

The axial force is located at the centroidal axis of the section and the bending moment is
then computed at this location.

Elasticity is that property of a material that enables it to regain its original configuration
after having been deformed.

A spring is a mechanical element that exerts a force when deformed.

The force is not linearly related to the deflection, and hence this beam can be described as
a nonlinear stiffening spring.

The force necessary to flatten the disk increases at first and then decreases as the disk
approaches a flat configuration, as shown by the graph. Any mechanical element having
such a characteristic is called a nonlinear softening spring

The external work done on an elastic member in deforming it is transformed into strain,or
potential, energy

Castigliano‘s theorem states that when forces act on elastic systems subject to small
displacements, the displacement corresponding to any force, in the direction of the force,
is equal to the partial derivative of the total strain energy with respect to that force

A system is over constrained when it has more unknown support (reaction) forces and/or
moments than static equilibrium equations. Such a system is said to be statically
indeterminate and the extra constraint supports are called redundant supports.

The term column is applied to all such members except those in which failure would be
by simple or pure compression.

Elastic instability can also occur in structural members other than columns.

Compressive loads/stresses within any long, thin structure can cause structural
instabilities (buckling).

The maximum-shear-stress (MSS) theory predicts that yielding begins whenever the
maximum shear stress in any element equals or exceeds the maximum shear stress in a
tension-test specimen of the same material when that specimen begins to yield.

As a strip of a ductile material is subjected to tension, slip lines (called Lüder lines)\

The distortion-energy theory predicts that yielding occurs when the distortion strain
energy per unit volume reaches or exceeds the distortion strain energy per unit volume
for yield in simple tension or compression of the same material

The shear stresses on these surfaces are equal and are called the octahedral shear stresses

failure is assumed to occur whenever the octahedral shear stress for any stress state
equals or exceeds the octahedral shear stress for the simple tension-test specimen at
failure

A variation of Mohr‘s theory, called the Coulomb-Mohr theory or the internal friction
theory

The maximum-normal-stress (MNS) theory states that failure occurs whenever one of the
three principal stresses equals or exceeds the strength.

The term relatively brittle is rigorously defined in the test procedures,10 but it means,
roughly, fracture without yielding occurring throughout the fractured cross section.

The critical stress intensity factor KIc is a material property that depends on the material,
crack mode, processing of the material, temperature, loading rate, and the state of stress
at the crack site

The body of knowledge available on fatigue failure from N 51 to N 51000 cycles is
generally classified as low-cycle fatigue

Residual stresses may either improve the endurance limit or affect it adversely.

the existence of a torsional steady-stress component not more than the torsional yield
strength has no effect on the torsional endurance limit, provided the material is ductile,
polished, notch-free, and cylindrical.

The endurance limit obtained by the rotating-beam test is frequently called the flexural
endurance limit, because it is a test of a rotating beam. In this section we shall study a
property of mating materials called the surface endurance shear.

Buckingham defined a load-stress factor, also called a wear factor, which is derived from
the Hertz equations.
Design codes and standards

A standard is a set of specifications for parts, materials, or processes intended to achieve
uniformity, efficiency, and a specified quality.

A code is a set of specifications for the analysis, design, manufacture, and construction of
something.

It is important to observe that safety codes do not imply absolute safety.

Tolerance. The difference between the two limits

Clearance. A general term that refers to the mating of cylindrical parts such as a bolt and
a hole.

Interference. The opposite of clearance, for mating cylindrical parts in which the internal
member is larger than the external member

Allowance. The minimum stated clearance or the maximum stated interference for
mating parts

Fit. The amount of clearance or interference between mating parts.

the cumulative effect of the individual specified tolerances must be allowed to
accumulate somewhere This is known as tolerance stack-up
Design of brakes and clutches, flywheel

In braking systems, the internal-shoe or drum brake is used mostly for automotive
applications.

A brake shoe is self-energizing if its moment sense helps set the brake, self-deenergizing
if the moment resists setting the brake.

Flexible clutch and brake bands are used in power excavators and in hoisting and other
machinery.

Caliper brakes (named for the nature of the actuating linkage) and disk brakes (named for
the shape of the unlined surface) press friction material against the face(s) of a rotating
disk.

The drawing of a cone clutch in Fig. 16–21 shows that it consists of a cup keyed or
splined to one of the shafts, a cone that must slide axially on splines or keys on the
mating shaft, and a helical spring to hold the clutch in engagement.

The woven-cotton lining is produced as a fabric belt that is impregnated with resins and
polymerized.

A woven-asbestos lining is made in a similar manner to the cotton lining and may also
contain metal particles.

Molded-asbestos linings contain asbestos fiber and friction modifiers

Molded-asbestos pads are similar to molded linings but have no flexibility

Sintered-metal pads are made of a mixture of copper and/or iron particles with friction
modifiers

Cermet pads are similar to the sintered-metal pads and have a substantial ceramic content.

One of these surfaces usually is the rear face of the engine flywheel, and the other is a
heavy, flat ring with one side machined and surfaced. This part is known as the pressure
plate.

In the helical-spring clutches, a system of levers pivoted on the cover forces the pressure
plate away from the driven disk and against the pressure of the springs whenever the
clutch release bearing moves forward against the inner ends of the levers.

The hydraulic clutch operating system moves the fork by hydraulic pressure.

The transmission Is driven by a single friction plate that is sandwiched between the
flywheel and an Iron pressure plate.

When the clutch Is engaged fully, the driven disk Is clamped firmly between the flywheel
and the pressure plate by the pressure of the springs

In some clutches, a diaphragm Is used Instead of coil springs

In a wet-type clutch, the disks and the entire internal assembly run In an oil bath.

The fluid coupling consists of an impeller, or driving torus, driven by the engine and a
turbine, or driven torus, mounted on the driven shaft.

In actual practice, the torque converter is used with a gear system (including planetary
gears) to provide a high range (for normal operation), a low range (for steep hills, or
pulling out of mud), reverse, and neutral

All torque converters have a driven member (called the turbine) and a driving member
(called the pump).

In actual operation, the secondary stator and primary stator are stationary when there is a
great difference between pump and turbine speed.
Design of welded, riveted and bolted joints

The lead l, not shown, is the distance the nut moves parallel to the screw axis when the
nut is given one turn.

For a single thread, as in Fig. 8–1, the lead is the same as the pitch.

A multiple-threaded product is one having two or more threads cut beside each other

a double-threaded screw has a lead equal to twice the pitch, a triple-threaded screw has a
lead equal to 3 times the pitch, and so on

All threads are made according to the right-hand rule unless otherwise noted. That is, if
the bolt is turned clockwise, the bolt advances toward the nut.

When a positive torque is obtained from this equation, the screw is said to be selflocking.

A power screw lifting a load is in compression and its thread pitch is shortened by elastic
deformation. Its engaging nut is in tension and its thread pitch is lengthened.

This clamping force is called the pretension or bolt preload.

The grip l of a connection is the total thickness of the clamped material.

The proof load is the maximum load (force) that a bolt can withstand without acquiring a
permanent set.

The proof strength is the quotient of the proof load and the tensile-stress area.

The snug-tight condition is the tightness attained by a few impacts of an impact wrench,

indicator of yielding that is

Sometimes used is a load factor, which is applied only to the load Pas a guard against
overloading.

Calculation of this stress, which is usually called a bearing stress, is complicated by the
distribution of the load on the cylindrical surface of the rivet.

the force F9is called the direct load, or primary shear.

The moment load, or secondary shear, is the additional load on each bolt due to the
moment M1.

The arrow side of a joint is the line, side, area, or near member to which the arrow points.
The side opposite the arrow side is the other side

The shear force produces a primary shear in the welds of magnitude

The moment at the support produces secondary shear or torsion of the welds

The resulting second moment of area is then a unit second polar moment of area.

The heating and consequent welding that occur when an electric current is passed through
several parts that are pressed together is called resistance welding.

Spot welding and seam welding are forms of resistance welding most often used.

Structural adhesives are relatively strong adhesives that are normally used well below
their glass transition temperature

These include contact adhesives, where a solution or emulsion containing an elastomeric
adhesive is coated onto both adherends, the solvent is allowed to evaporate, and then the
two adherends are brought into contact

Pressure-sensitive adhesives are very low modulus elastomers that deform easily under
small pressures, permitting them to wet surfaces.

Anaerobic adhesives cure within narrow spaces deprived of oxygen

Volkersen presented an analysis of the lap joint, known as the shear lag model.

Adhesives can be used in conjunction with spot welding. The process is known as weld
bonding.
Mechanical springs

A spring with plain ends has a non-interrupted helicoid; the ends are the same as if a long
spring had been cut into sections. A spring with plain ends that are squared or closed is
obtained by deforming the ends to a zero-degree helix angle.

Set removal or presetting is a process used in the manufacture of compression springs to
induce useful residual stresses.

The same effect occurs in helical springs, and it is called spring surge.

the maximum alternating stress that may be imposed without causing failure is constant

Springs are free of notches and surfaces are often very smooth. This failure criterion is
known as the Sines failure criterion in torsional fatigue

When extension springs are made with coils in contact with one another, they are said to
be close-wound.

When a helical coil spring is subjected to end torsion, it is called a torsion spring.

The strain-strengthening locks in residual stresses opposing working stresses provided the
load is always applied in the winding sense.

The inset of Fig. 10–11 shows the cross-section of a coned-disk spring, commonly called
a Belleville spring.

The force required to uncoil it remains constant; thus it is called a constant force spring.

A volute spring, shown in Fig. 10–13a, is a wide, thin strip, or ―flat,‖ of material wound
on the flat so that the coils fit inside one another.

A conical spring, as the name implies, is a coil spring wound in the shape of a cone
Design Of Spur, Helical, Bevel & Worm Gears

the contact of two circular steel cylinders along the common generating line(an analog of
a toothing friction gear

When passing through the contact area a relative point displacement of the drive and
driven cylinders is observed, i. e., relative slip, which is the cause of wear.

The smaller gear wheel is called a pinion and a larger one is called a wheel.

The intersection lines between the teeth side faces and any circumferential cylindrical
surface coaxial with the initial surface are called teeth lines.

If teeth lines are parallel to the gear wheel axis this is called a spur

If these lines are helical with constant pitch the gear wheel is described as helical

The tangent point W of the initial circumferences of the piniondw1and the wheeldw2is
called the pitch point.

The distance between analogous profile points of adjacent teeth on the pitch diameter
measured in the section normal to the teeth line is called a normal spacing p. The ratio
p/πis called a module and is designated by m

Bevel gearings transmit mechanical power between shafts with intersecting axes.

Intersection lines of the teeth side faces with the pitch cone surface are called teeth lines.

Depending on the form of the tooth line there are gearings with straight teeth

The tilt angle βn is the acute angle between the tangent to the tooth line and the
generation of the pitch cone

Another version of bevel gearings is thehypoid gearing, where the rotation axes of the
gear wheels do not intersect but cross

Heat refining treatment is a combination of quenching and high-temperature tempering

The tooth core hardness corresponds to the heat refining treatment

Cementation(surface diffusion carburizing) with subsequent quenching along with high
surface hardness also provides a high bending strength for the teeth

The load-carrying capacity of gearings corresponding to the contact strength is higher
when the surface teeth hardness is higher.

higher hardness corresponds to a more difficult manufacturing technique for the gear
wheels and moderate gearing dimensions

Core-mold casting is used in the manufacture of large gear wheels

Cast wheels are subjected to normalization

For every tooth, stresses change in time according to a zero-to-tension stress cycle, which
is the cause of fatigue damage

Fatigue flaking of the work teeth surfaces, which is the main fracture mode of teeth for
most closed well lubricated gearings, is a consequence of the cycling of the contact
stresses.

In open gearings(without lubrication) flaking is not observed; wear of the teeth surface
surpasses fatigue crack propagation.

Bearing failure of the teeth work surface occurs under the action of considerable loads or
impacts on load application.

Teeth breakdown, in comparison with work surface damage, is uncommon.

Teeth wear is the main type of teeth fracture observed in open gearings, gearings with a
solid lubrication coating, and gearings with a very small coating thickness

If the cycle operation factors are constant in time, the loading conditions are called
regular. The cycle of variable in time loading conditions is called irregular.

Stress-cycle diagrams obtained experimentally on specimen prototypes of the gear wheels
define in the coordinates

The limit number Nlim of cycles is called the abscissa of inflection of the stress-cycle
diagram

Load variability is taken into account by the choice of the allowable stresses.

Contact strength is the capability of the contacting teeth surfaces to provide the required
safety against progressive fatigue flaking.

The internal dynamic load in the toothing (the ratio KHV) is caused by impact of the
teeth on entry into the toothing due to production errors of the pitch and teeth distortion
under loading.

If the circular pitch is less than the wheel pitch, untimely meshing of the second teeth pair
occurs and edge impact(at the tooth point of the driven wheel) is observed.

The unevenness of the load distribution between the teeth (the ratio KHα) depends on
production errors (pitch errors and teeth direction).

The rotation angle of the gear wheel by the transference of the profile tangent point from
one extreme position to another is called the front overlap angle.

Stresses found without taking into account stress concentrators are called nominal.

The features of helical gearings in bending strength testing of the pinion teeth and wheel
teeth are taken into account by the factors

Bevel wheels can have straight or circular teeth.

The external and internal ends of bevel wheels form external and internal extra cones, of
which the generating lines are perpendicular to the generating line of the pitch cone

The length of the generating line from its point to its external end is called the external
cone distance Re, and the length to the middle of the face width is called the average cone
distance Rm

In bevel gearings the pinion is set as a cantilever.

In order to increase the rigidity of the bearing, the shafts are mounted on tapered roller

Seizing of soft materials is shown as a smearing(diffusion transfer) of bronze on the
worm

Globoidal worms (Fig.6.85) differ structurally from cylindrical ones in the form of the
cutting area and the diameters of the bearing journals, which are comparable to the worm
diameter.

The most commonly used ordinary single-row planetary gear

Master links are links that are loaded with the external torque.

If all the links in the planetary gear are mobile, i. e., both wheels and carrier, the gearing
is called differential.

For determination of the planetary gear transmission ratio the method of the carrier stop
(Villis‘s method) is used.

The tooth number za of the central pinion a is set based on the non-undercutting
condition of the dedendum:

Tooth number matching of the other wheels is carried out taking into consideration three
conditions: coaxiality, mounting, and adjacency.

when the same material is used for the wheels it is sufficient to calculate only the external
toothing

The number of stress cycles Nk of the teeth for the whole lifetime is calculated only for
wheel rotation relatively to each other.

Spur gears, illustrated in Fig. 13–1, have teeth parallel to the axis of rotation and are used
to transmit motion from one shaft to another, parallel, shaft.

Helical gears, shown in Fig. 13–2, have teeth inclined to the axis of rotation.

Bevel gears, shown in Fig. 13–3, have teeth formed on conical surfaces and are used
mostly for transmitting motion between intersecting shafts.

Spiral bevel gears are cut so the tooth is no longer straight, but forms a circular arc

Hypoid gears are quite similar to spiral bevel gears except that the shafts are offset and
nonintersecting.

The pitch circle is a theoretical circle upon which all calculations are usually based; its
diameter is the pitch diameter. The pitch circles of a pair of mating gears are tangent to
each other.

A pinion is the smaller of two mating gears. The larger is often called the gear.

The circular pitch pis the distance, measured on the pitch circle, from a point on one tooth
to a corresponding point on an adjacent tooth. Thus the circular pitch is equal to the sum
of the tooth thickness and the width of space.

Worm gear sets are also made so that the teeth of one or both wrap partly around the
other. Such sets are called single enveloping and double-enveloping worm gear sets.
Worm gear sets are mostly used when the speed ratios of the two shafts are quite high,
say, 3 or more.

The module m is the ratio of the pitch diameter to the number of teeth.

The diametral pitch P is the ratio of the number of teeth on the gear to the pitch diameter.

The addendum ais the radial distance between the top landand the pitch circle. The
dedendum b is the radial distance from the bottom land to the pitch circle.

The whole depth ht is the sum of the addendum and the dedendum

The clearance circleis a circle that is tangent to the addendum circle of the mating gear.

The clearance cis the amount by which the dedendum in a given gear exceeds the
addendum of its mating gear.

The backlash is the amount by which the width of a tooth space exceeds the thickness of
the engaging tooth measured on the pitch circles.

When the tooth profiles, or cams, are designed so as to produce a constant angularvelocity ratio during meshing, these are said to have conjugate action.

Circles drawn through point P from each center are called pitch circles, and the radius of
each circle is called the pitch radius. Point P is called the pitch point.

The circle on which the involute is generated is called the base circle.

If we now construct tooth profiles through point and draw radial lines from the
intersections of these profiles with the pitch circles to the gear centers, we obtain the
angle of approach for each gear.

By drawing another set of tooth profiles through b, we obtain the angle of recess for each
gear in a manner similar to that of finding the angles of approach.

The sum of the angle of approach and the angle of recess for either gear is called the
angle of action. The line ab is called the line of action

We may imagine a rack as a spur gear having an infinitely large pitch diameter

Corresponding sides on involute teeth are parallel curves; the base pitch is the constant

The addendum circle of the internal gear lies inside the pitch circle.

The contact of portions of tooth profiles that are not conjugate is called interference.

When gear teeth are produced by a generation process, interference is automatically
eliminated because the cutting tool removes the interfering portion of the flank. This
effect is called undercutting

Teeth can also be formed by using the powder-metallurgy process; or, by
extrusion,
using

Gears that carry large loads in comparison with their size are usually made of steel and
are cut with either form cutters or generating cutters.

One of the newest and most promising of the methods of forming teeth is called cold
forming, or cold rolling, in which dies are rolled against steel blanks to form the teeth.

Gears made of thermoplastics such as nylon, polycarbonate, acetal are quite popular and
are easily manufactured by injection molding.

This surface obtained when every point on the edge generates an involute is called an
involute helicoid.

A gear of the same pitch and with the radius R will have a greater number of teeth,
because of the increased radius. In helical-gear terminology this is called the virtual
number of teeth

In specifying the pitch of worm gear sets, it is customary to state the axial pitch pxof the
worm and the transverse circular pitch pt , often simply called the circular pitch, of the
mating gear.

A tooth system is a standard that specifies the relationships involving addendum,
dedendum, working depth, tooth thickness, and pressure angle.

The face width FG of the worm gear should be made equal to the length of a tangent to
the worm pitch circle between its points of intersection with the addendum circle

It is sometimes desirable for the input shaft and the output shaft of a two-stage compound
gear train to be in-line, as shown in Fig. 13–29. This configuration is called a compound
reverted gear train

Planetary trains always include a sun gear, a planet carrier or arm, and one or more planet
gears,

Failure of the surfaces of gear teeth, which is generally called wear. Pitting, as explained
in Sec. 6–16, is a surface fatigue failure due to many repetitions of high contact stresses.
Other surface failures are scoring, which is a lubrication failure, and abrasion, which is
wear due to the presence of foreign material.

Two fundamental stress equations are used in the AGMA methodology, one for bending
stress and another for pitting resistance (contact stress). In AGMA terminology, these are
called stress numbers

Transmission error is defined as the departure from uniform angular velocity of the gear
pair.

The hardness-ratio factor CH is used only for the gear.

The Zerol bevel gear is a patented gear having curved teeth but with a zero spiral angle.

Gearing similar to bevel gears but with the shafts offset. Such gears are called hypoid
gears, because their pitch surfaces are hyperboloids of revolution.

For larger offsets, the pinion begins to resemble a tapered worm and the set is then called
spiroid gearing

Since they are essentially non enveloping worm gears, the crossed helical gears,
Design of belts, ropes and chains

Crowned pulleys are used for flat belts, and grooved pulleys, or sheaves, for round and V
belts. Timing belts require toothed wheels, or sprockets.

A change in belt tension due to friction forces between the belt and pulley will cause the
belt to elongate or contract and move relative to the surface of the pulley. This motion is
caused by elastic creep and is associated with sliding friction as opposed to static friction.

The angle of contact is made up of the effective arc, through which power is transmitted,
and the idle arc.

For the driving pulley the belt first contacts the pulley with a tight-side tension F1 and a
velocity V1, which is the same as the surface velocity of the pulley.

The angle gy2, through which the link swings as it enters contact, is called the ngle of
articulation.

The regular lay, which is the accepted standard, has the wire twisted in one direction to
form the strands, and the strands twisted in the opposite direction to form the rope.

Lang-lay ropes have the wires in the strand and the strands in the rope twisted in the same
direction, and hence the outer wires run diagonally across the axis of the rope.

A wire rope tension giving the same tensile stress as the sheave bending is called the
equivalent bending load

The amount of wear that occurs depends upon the pressure of the rope in the sheave
groove. This pressure is called the bearing pressure
Design of shafts

A shaft is a rotating member, usually of circular cross section, used to transmit power or
motion.

An axle is a nonrotating member that carries no torque and is used to support

rotating wheels, pulleys, and the like

A shaft is intended for transmission of the torque along its axis,

An axle only supports the details installed on it and takes the forces acting on these
details

In contrast to a shaft an axle does not transmit torque and therefore does not experience
torsion.

An axle can be fixed or can rotate with the details placed on them.

Depending on the form of the geometrical axles, shafts are divided into
straight(Fig.6.132)and indirect crankshafts,

Depending on the form of the cross section there are solid and hollow shafts

Depending on the outer outline of the cross section the shafts are divided into a spline and
a key

Journals serve as supports for shafts and axles. Intermediate journals are called necks

Transitional sections of the shafts and axles between two stages of different diameters are
designed as follows.

Under the action of environmental stresses the rotating shafts are subjected to periodic
loading

Feather and sliding keys are sometimes used in movable joints of the hub with the shaft
in the axial direction

Splines are essentially stubby gear teeth formed on the outside of the shaft and on the
inside of the hub of the load-transmitting component.

Press and shrink fits for securing hubs to shafts are used both for torque transfer and for
preserving axial location.

Tapered fits between the shaft and the shaft-mounted device

Critical speeds: at certain speeds the shaft is unstable, with deflections increasing without
upper bound.

The resistance to axial motion of the collar or hub relative to the shaft is called holding
power.

Keys and pins are used on shafts to secure rotating elements, such as gears, pulleys, or
other wheels. Keys are used to enable the transmission of torque from the shaft to the
shaft-supported element. Pins are used for axial positioning and for the transfer of torque
or thrust or both.

Deviation is the algebraic difference between a size and the corresponding basic size.

Tolerance is the difference between the maximum and minimum size limits of a part

International tolerance grade numbers (IT) designate groups of tolerances such that the
tolerances for a particular IT number have the same relative level of accuracy but vary
depending on the basic size.

Hole basis represents a system of fits corresponding to a basic hole size.

Shaft basis represents a system of fits corresponding to a basic shaft size.

The standard uses tolerance position letters, with capital letters for internal dimensions
(holes) and lowercase letters for external dimensions (shafts).
Design Of Rolling Contact Bearings

At present, so-called thermo mechanical component joints are used more often, being
produced from shape-memory alloys

Bearings working mainly for movement with rolling friction are called rolling bearings,
and those for movement with sliding friction are called friction bearings.

Radial forces acting in the direction perpendicular to the bearing axis

Axial forces acting in the direction parallel to the bearing axis

In some structures so-called floating shafts are used. These shafts allow axial
displacement in both directions

Local loading applies when the resulting radial load acting on the bearing is always
supported by the same limited section of the rolling path

Circulating loading applies when the resulting radial load acting on the bearing is
supported

Oscillatory loading applies when the fixed race of a bearing is subjected to the influence
of the resulting radial load

Semisolid lubricants consist mainly of a liquid base, thickener, and additives to improve
their operational properties.

The commonly used term is bearing life, which is applied to either of the measures just
mentioned.

The rating life is a term sanctioned by the ABMA

Median life is the 50th percentile life of a group of bearings. The term average life has
been used as a synonym for median life,

A catalog load rating is defined as the radial load that causes 10 percent of a group of
bearings to fail at the bearing manufacturer‘s rating life.

The basic static load rating is the load that will produce a total permanent deformation in
the raceway

The bearings are identified by a two-digit number called the dimension-series code.

Two bearings can be mounted with the cone backs facing each other, in a configuration
called direct mounting, or with the cone fronts facing each other, in what is called
indirect mounting.

Elastohydrodynamic lubrication (EHD) is the phenomenon that occurs when a lubricant
is introduced between surfaces that are in pure rolling contact.

When maximum stiffness and resistance to shaft misalignment is desired, pairs of
angular-contact ball bearings (Fig. 11–2) are often used in an arrangement called
duplexing.

Felt seals may be used with grease lubrication when the speeds are low

The commercial seal is an assembly consisting of the rubbing element

The labyrinth seal is especially effective for high-speed installations and may be used
with either oil or grease.
Hydrodynamic theory of lubrication, journal bearings

Hydrodynamic lubrication means that the load-carrying surfaces of the bearing are
separated by a relatively thick film of lubricant,

Hydrodynamic lubrication is also called full-film, or fluid, lubrication.

Hydrostatic lubrication is obtained by introducing the lubricant, which is sometimes air
or water, into the load-bearing area at a pressure high enough to separate the surfaces
with a relatively thick film of lubricant.

Elastohydrodynamic lubrication is the phenomenon that occurs when a lubricant is
introduced between surfaces that are in rolling contact, such as mating gears or rolling
bearings.

The highest asperities may be separated by lubricant films only several molecular
dimensions in thickness. This is called boundary lubrication.

Absolute viscosity, also called dynamic viscosity.

The ips unit is called the reyn

A unit of force called the dyne(dyn), a unit of dynamic viscosity called the poise(P), and
a unit of kinematic viscosity called the stoke(St).

The bearing characteristic number, or the Sommerfeld number, is defined by the

The quantity r/c is called the radial clearance ratio

The dimension c is the radial clearance and is the difference in the radii of the bushing
and journal

The minimum film thickness is designated by h0 , and it occurs at the line of centers.

If the radius of the bushing is the same as the radius of the journal, it is known as a fitted
bearing.

If the bushing encloses the journal, as indicated by the dashed lines, it becomes a full
bearing.

Replace the curved partial bearing with a flat bearing, called a plane slider bearing.

Raimondi-Boyd analysis is that viscosity of the lubricant is constant as it passes through
the bearing.

Design optima are sometimes maximum load, which is a load-carrying characteristic of
the bearing, and sometimes minimum parasitic power loss or minimum coefficient of
friction.

Bearings in which the warm lubricant stays within the bearing housing will now be
addressed. These bearings are called self-contained bearings because the lubricant sump
is within the bearing housing and the lubricant is cooled within the housing. These
bearings are described as pillow block or pedestal bearings.

Because the lubricant is supplied to the bearing under pressure, such bearings are called
pressure-fed bearings.

When two surfaces slide relative to each other with only a partial lubricant film between
them, boundary lubrication is said to exist.

Fatty acids, such as stearic acid, palmitic acid, or oleic acid, or several of these, which
occur in animal and vegetable fats, are called oiliness agents.

In such cases the extreme-pressure, or EP, lubricants may be mixed with the fatty-acid
lubricant.

When a bearing operates partly under hydrodynamic conditions and partly under dry or
thin-film conditions, a mixed-film lubrication exists.

Relative motion between surfaces in contact in the presence of a lubricant is called
boundary lubrication.
5. Manufacturing Processes
Forming & shaping processes and equipment

―Forming‖ generally indicates changing the shape of an existing solid body.

Shaping processes typically involve the molding and casting of soft or molten materials,

Rolling is the process of reducing the thickness or changing the cross section of a long
work piece by compressive forces

At one point along the contact length (called the neutral point or no-slip point) the
velocity of the strip is the same as that of the roll.

The maximum possible draft is defined as the difference between the initial and final strip
thicknesses,

The rolls apply pressure on the flat strip in order to reduce its thickness, resulting in a roll
force

Although it has limited and specialized applications, rolling also can be carried out by
front tension only, with no power supplied to the rolls-a process known as Steckel rolling.

Because of the heat generated by plastic deformation during rolling, rolls can become
slightly barrel shaped (thermal camber).

Chatter, generally defined as self-excited vibration, can occur in rolling as well as in
extrusion,

Chatter in rolling has been found to occur predominantly in tandem mills.

Hot rolling converts the cast structure to a wrought structure

The product of the first hot-rolling operation is called a bloom, a slab, or a billet

Pack rolling is a flat-rolling operation in which two or more layers of metal are rolled
together,

Wavy edges on sheets (Fig. 13.8a) are the result of roll bending.

Alligatoring (Fig.13.8d) is a com plex phenomenon and typically is caused by
nonuniform bulk deformation of the billet during rolling or by the presence of defects in
the original cast material.

In tandem rolling, the strip is rolled continuously through a number of stands to thinner
gages with each pass

Cold shape rolling also can be done with the starting materials in the shape of wire with
various cross sections

A process similar to roll forging is skew rolling, typically used for making ball bearings

In ring rolling, a thick ring is expanded into a large-diameter thinner one.

Thread rolling is a cold-forming process by which straight or tapered threads are formed
on round rods or wire.

Internal thread rolling can be carried out with a flute less forming tap.

Rotary Tube Piercing. Also known as the Mannesmann process, this is a hot working
operation for making long, thick-Walled seamless pipe and tubing

The diameter and thickness of pipes and tubing can be reduced by tube rolling,

In the pilger mill, the tube and an internal mandrel undergo a reciprocating motion; the
rolls are specially shaped and are rotated continuously.

Forging is a basic process in which the work piece is shaped by compressive forces
applied through various dies and tooling.

Open-die forging is the simplest forging operation

Open-die forging can be depicted by a solid work piece placed between two flat dies and
reduced in height by compressing it (Fig. 14.3a)-a process that is also called upsetting or
flat die forging.

Barreling is caused primarily by frictional forces that oppose the outward flow of the
work piece at the die interfaces and thus can be minimized by using an effective

Cogging (also called drawing out) is basically an open-die forging operation in which the
thickness of a bar is reduced by successive forging steps (bites) at specific intervals

Preforming operations (Figs. 14.7b and c) typically are used to distribute the material
properly into various regions of the blank using simple shaped dies of various contours.

In fullering, material is distributed au/ay from an area.

In edging, it is gathered into a localized area. The part then is formed into the rough
shape (say, a connecting rod) by a process called blocking, using blocker dies.

Called sizing, this process requires high pressures.

Also called upset forging, heading is essentially an upsetting operation, usually
performed on the end of a round rod or wire in order to increase the cross section

Hubbing. This process consists of pressing a hardened punch with a particular tip
geometry into the surface of a block of metal.

Orbital Forging. In this process, the upper die moves along an orbital path and forms the
part incrementally.

Incremental Forging. In this process, a tool forge a blank into a shape in several small
steps.

Isothermal Forging. Also known as hot-die forging, this process heats the dies to the
same temperature as that of the hot work piece.

Rotary Swaging. In this process (also known as radial forging, rotary forging, or simply
su/aging), a solid rod or tube is subjected to radial impact forces by set of reciprocating
dies of the machine

In die-closing swaging machines, die movements are obtained through the reciprocating
motion of wedges

Swaging also can be used to assemble fittings over cables and wire;

Tube Swaging. In this process, the internal diameter and/or the thickness of the tube is
reduced with or without the use of internal rnandrels

Porgeability is generally defined as the capability of a material to undergo deformation
without cracking

In the upsetting test, a solid, cylindrical specimen is upset between flat dies

The second method is the hot-twist test, in which a round specimen is twisted
continuously in the same direction until it fails.

In this condition, known as end grains, the grain boundaries become exposed directly to
the environment and can be attacked by it,

Preshaping. In a properly preshaped work piece, the material should not flow easily into
the flash

For most forgings, the parting line is located at the largest cross section of the part.

Draft angles are necessary in almost all forging dies in order to facilitate removal of the
part from the die.

The process of producing a die cavity in a die block is called die sinking. The process of
hubbing

Most commonly, dies are machined from forged die blocks by processes such as highspeed milling, turning, grinding, and electrical discharge and electrochemical machining.

The speed varies from a maximum at the center of the stroke to zero at the bottom of the
stroke; thus, mechanical presses are stroke limited.

A knuckle joint mechanical press is shown in Fig. 14.17b. Because of the linkage design,
very high forces can be applied in this type of press

In extrusion, which produces the largest volume of plastics, raw materials in the form of
thermoplastic pellets,

Plastic Tubes and Pipes. These are produced in an extruder with a spider die

Rigid Plastic Tubing. Extruded by a process in which the die is rotated

coextrusion involves simultaneous extrusion of two or more polymers through a single
die.

Plastic-coated Electrical Wire. Electrical wire, cable, and strips also are extruded

Polymer Sheets and Films. These can be produced by using a specially designed flatextrusion die

Thin Polymer Films. Common plastic bags and other thin polymer film products are
made from blown film

Plastic Films. Plastic films, especially polytetrafluoroethylene (PTFE, trade name:
Teflon), can be produced by shaving the circumference of a solid

Pellets. Used as raw material for other plastic-processing methods described in this
chapter, pellets also are made by extrusion.

Most synthetic fibers used in reinforced plastics are ol mers that are extruded throu h the
tin holes of a devic P iy bl if 11 Zi f ,M cal ed a spinneret

This process of extrusion and solidification of Bobbin continuous filaments is called
spinning. The term spinning also is used for the production of natural textiles

Wet spinning is the oldest process for fiber production and is used for polymers that have
been dissolved in a solvent.

Dry spinning is used for thermosets carried by a solvent.

Gel spinning is a special process used to obtain high strength or special fiber properties.

Graphite fibers are produced from different polymer fibers by pyrolysis

Injection molding is similar to hot-chamber die casting

Multicomponent injection molding (also called coinjection or sandwich molding) allows
the forming of parts with a combination of various colors and shapes.

Insert molding involves metallic components (such as screws, pins, and strips) that are
placed in the mold cavity prior to injection and then become an integral part of the
molded product

Overmolding. This is a process for making products (such as hinge joints and ballandsocket joints) in one operation and without the need for postmolding assembly.

In ice-cold molding, the same type of plastic is used to form both components of the
joint.

In the reaction-injection molding (RIM) process, a monomer and two or more reactive
fluids are forced at high speed into a mixing chamber at a pressure of 10 to 20 MPa

In extrusion blow molding, a tube or preform (usually oriented so that it is vertical) is
first extruded.

In injection blow molding, a short tubular piece (parison) is injection molded (Fig.
19.14b) into cool dies.

A related process is stretch blow molding, in which the parison is expanded and
elongated simultaneously, subjecting the polymer to biaxial stretching and thus
enhancing its properties

Multilayer blow molding involves the use of coextruded tubes or parisons and thus
permits the production of a multilayer structure

Most thermoplastics and some thermosets can be formed into large, hollow parts by
rotational molding.

In this operation (called slush molding or slush casting), the mold is heated and rotated
simultaneously.

Thermoforming is a process for forming thermoplastic sheets or films over a mold
through the application of heat and pressure

In compression molding, a preshaped charge of material, premeasured volume of powder,
or viscous mixture of liquid-resin and filler material is placed directly into a heated mold
cavity

Transfer molding represents a further development of compression molding.

Structural Foam Molding. This is a molding process used to make plastic products with a
solid outer slain and a cellular core structure.

Solid-phase Forming. Also called solid-state forming, this process is carried out at a
temperature 10° to 20°C below the melting temperature of the plastic

Rubber and some thermoplastic sheets are formed by the calendering process (Fig.
19.20), Wherein a Warm mass of the compound is fed into a series of rolls and is
masticated.

Discrete rubber products, such as gloves, are made by dipping a metal form

In making sheet-molding compound (SMC), continuous strands of reinforcing fiber are
first chopped into short fibers

Bulk-moldzng com art; in the sgape of billets5

The simplest method of contact molding is hand layup.

In spray layup, molding is done by spraying the materials into the mold.

Filament winding is a process in which the resin and fibers are combined at the time of
curing

Long parts with various uniform cross sections (such as rods, profiles, flat strips, and
tubing) are made continuously by the pultrusion process.

Continuously reinforced products other than those with constant cross-sectional profiles
are made by pulforming.

Slurry infiltration is the most common process for making ceramic-matrix composites.
Machining Processes For Producing Various Shapes material removal, cutting
tools

Machining is a general term describing a group of processes that consist of the removal
of material and modification of the surfaces

Turning, in which the work piece is rotated and a cutting tool removes a laye of material
as the tool moves to the left

Cutting off, in which the cutting tool moves radially inward and separates the right piece
from the bulk of the blank

Slab milling, in which a rotating cutting tool removes a layer of material from the surface
of the work piece.

End milling, in which a rotating cutter travels along a certain depth in the work piece and
produces a cavity.

Orthogonal cutting, because it is two dimensional and the forces involved (as we later
show) are perpendicular to each other. The cutting tool has a rake angle of oz (positive, as
shown in the figure) and a relief or clearance angle

The deformation of the material takes place along a narrow shear zone called the primary
shear zone.

Continuous chips usually are formed with ductile materials that are machined at high
cutting speeds and/or high rake angles

Serrated chips (also called segmented or nonhomogeneous chips, see Fig. 21.5d) are semi
continuous chips with large zones of low shear strain

Discontinuous chips consist of segments that may be attached firmly or loosely to each
other

Infrared radiation from the cutting zone may be monitored with a radiation pyroineter.

Flank wear occurs on the relief (flank) face of the tool

Mechanical shock (i.e., impact due to interrupted cutting, as in turning a splined shaft on
a lathe)

Thermal fatigue (i.e., cyclic variations in the temperature of the tool in interrupted
cutting).

Thermal cracks usually are perpendicular to the cutting edge of the tool,

Thermosetting plastics are brittle and sensitive to thermal gradients during cutting;
machining conditions generally are similar to those of thermoplastics.

Rake angle is important in controlling both the direction of chip flow and the strength of
the tool tip.

Cutting-edge angle affects chip formation, tool strength, and cutting forces to various
degrees.

Side rake angle is more important than the back rake angle,

Relief angle controls interference and rubbing at the tool-work piece interface.

Nose radius affects surface finish and tool-tip strength.

The bed supports all major components of the lathe.

The carriage, or carriage assembly, slides along the ways and consists of an assembly of
the cross-slide, tool post, and apron.

The headstock is fixed to the bed and is equipped with motors, pulleys, and V-belts

The tailstock, which can slide along the ways and be clamped at any position,

The feed rod is powered by a set of gears through the headstock.

Closing a split nut around the lead screw engages it with the carriage; the split nut is also
used for cutting threads accurately.

Its swing, the maximum diameter of the work piece that can be machined

A chuck usually is equipped with three or four jaws.

A collet is basically a longitudinally-split, tapered bushing.

Face plates are used for clamping irregularly shaped work pieces.

Mandrels (Fig. 23.8) are placed inside hollow or tubular work pieces

Form tools are used to produce various shapes on solid, round work pieces

Boring on a lathe is similar to turning.

Drilling (Section 23.5 ) can be performed on a lathe by mounting the drill bit in a chuck
in the tailstock quill.

Toolroorn lathes have high precision, enabling the machining of parts to close
dimensional tolerances.

Tracer Lathes. These lathes have special attachments that are capable of turning parts
with various contours. Also called a duplicating lathe or contouring lathe

Single-spindle automatic bar machines are similar to turret lathes

Multiple-spindle automatic bar machines typically have from four to eight spindles
arranged in a circle on a large drum,

Turret Lathes. These machine tools are capable of performing multiple cutting
operations, such as turning, boring, drilling, thread cutting

The turret lathe shown in Fig. 23.9 is known as a ram-type turret lathe-on in which the
ram slides in a separate base on the saddle.

Spade drills (Fig. 23.21a) have removable tips or bits and are used to produce largediameter and deep holes.

Developed originally for drilling gun barrels, gun drilling is used for drilling deep holes
and requires a special drill

Drilling machines with multiple spindles (gang drilling) are used for high-production-rate
operations.

Worleholding dei/ices for drilling are essential to ensure that the work piece is located
properly.

Tapered taps are designed to reduce the torque required for the tapping of through holes

Chip less tapping is a process of internal thread rolling using a forming tap

In peripheral milling (also called plain milling), the axis of cutter rotation is parallel to
the work piece surface

When the cutter is longer than the width of the cut, the process is called slah milling.

In conventional milling (also called up milling), the maximum chip thickness is at the end
of the cut as the tooth leaves the work piece surface.

In climb milling (also called down milling), cutting starts at the surface of the work piece
where the chip is thickest.

For a straight-tooth cutter, the approximate undeformed chip thickness (chip depth of cut)

In face milling, the cutter is mounted on a spindle having an axis of rotation
perpendicular to the work piece surface

When the cutter rotation is as shown in Fig. 24.4b, the operation is climb milling; when it
is in the opposite direction (Fig. 24.4c), the operation is conventional milling.

End milling is an important and common machining operation because of its versatility
and capability to produce various profiles and curved surfaces.

The cutter, called an end mill (Fig. 24.2c) has either a straight shank (for small cutter
sizes) or a tapered shank (for larger sizes) and is mounted into the spindle of the milling
machine.

Hollow end mills have internal cutting teeth and are used to machine the cylindrical
surfaces of solid, round work pieces.

High-speed end milling has become an important process with numerous applications,
such as the milling of large aluminum-alloy aerospace components and honeycomb

The production of cavities in metalworking dies (die sinking)-such as in forging or in
sheet-metal forming

In straddle milling, two or more cutters are mounted on an arbor and are used to machine
two parallel surfaces on the work piece (Fig. 24.l1a).

Form milling produces curved profiles using cutters that have specially shaped teeth (Fig.
24.11b)

Slotting and slitting operations are performed with circular cutters,

Key seat cutters are used to make the semi cylindrical (or Woodruff) key seats for shafts.

Angle milling cutters (single-angle or double-angle) are used to produce tapered surfaces
with various angles

Shell mills are hollow inside and are mounted on a shank; this allows the same shank to
be used for -l-'Slot different-sized cutters.

The use of shell mills is similar to that of end mills.

Milling with a single cutting tooth mounted on a high-speed spindle is known as fly
cutting; generally, generally, it is used in simple face-milling and boring operations.

Arbor cutters are mounted on an arbor (see Figs. 24.11 and 24.15a), for operations such
as peripheral, face, straddle, and form milling.

In shank-type cutters, the cutter and the shank are made in one piece-the most common
examples being end mills.

Back striking involves double feed marks made by the trailing edge of the cutter.

Used for general-purpose milling operations, column-and-knee-type machines are the
most common milling machines.

Plain milling machines have three axes of movement, with the motion usually imparted
manually or by power.

In universal column-and-knee milling machines, the table can be swiveled on a horizontal
plane.

In hed-type machines, the worktable is mounted directly on the bed, which replaces the
knee and can move only longitudinally

Planer-type milling machines, which are similar to bed-type machines, are equipped with
several heads and cutters to mill different surfaces.

Rotary-tahle machines are similar to vertical milling machines and are equipped with one
or more heads for face-milling operations

prohle milling machines, which have five axes of movement

The accessory that has been used most commonly in the past, typically in job shops, is
the universal dividing (index) head.

In a planet, the work piece is mounted on a table that travels back and forth along a
straight path.

Horizontal shaper, the cutting tool travels back and forth along a straight path.

Vertical shapers (slotters) are used to machine notches, keyways, and dies.

In a broach (Fig. 24.21a), the total depth of material removed in one stroke is the sum of
the depths of cut of each tooth of the broach.

The rake (hook) angle depends on the material cut

The pitch of the teeth depends on factors such as the length of the work piece (length of
cut), tooth strength, and size and shape of chips

Turn broaching is a combination of shaving and skiving

Push broaches usually are shorter, generally in the range from 150 to 350 mm.

Pull broaches tend to straighten the hole, Whereas pushing permits the broach to follow
any irregularity of the leader hole.

Hacksaws have straight blades and reciprocating motions.

Hand hacksaw blades are thinner and shorter than power hacksaw blades,

Circular saws (also called cold saws in cutting metal) generally are used for highproduction-rate sawing, a process called cutting off

Band saws have continuous, long, flexible blades and thus have a continuous cutting
action

Vertical band saws are used for straight as well as contour cutting of flat sheets and other
parts supported on a horizontal table

Blades and high-strength wire can be coated with diamond powder (diamond edged
blades and diamond-wire saws) so that the diamond particles act as cutting teeth

Friction sawing is a process in which a mild-steel blade or disk rubs against the work
piece

The heat generated in the work piece produces a heat-affected zone on the cut surfaces

Filing involves the small-scale removal of material from a surface, corner, edge, or hole

Rotary files and burs (Fig. 2428) are used for such applica- High speed Stem Carbide
Rotary tions as deburring, removing scale from surfaces,

In form cutting, the cutting tool is similar to a form-milling cutter made in the shape of
the space between the gear teeth

Broaching also can be used to machine gear teeth and is particularly suitable for
producing internal teeth

A pinion-shaped cutter can be considered as one of the two gears in a conjugate pair, with
the other being the gear blank

On a rack shaper, the generating tool is a segment of a rack

A hob (Fig. 24.31) is basically a gear-cutting worm, or screw, made into a gear

M1/iltinxis computer-controlled machines are capable of generating many types and sizes
of gears using indexable milling cutters.

several finishing processes are available to improve the surface quality of the gears.

In generating, the grinding Wheel acts in a manner similar to the gear generating cutter
described previously

The honing tool is a plastic gear impregnated with fine abrasive particles.

To further improve the surface finish, ground gear teeth are lapped,

It can be highly automated in order to increase productivity, and it is indeed the principle
behind transfer lines

pallet (carrying another work piece to be machined) is brought into position by an
automatic pallet changer

The maximum dimensions that the cutting tools can reach around a work piece in a
machining center is known as the work envelop

The tool-exchange arm shown in Fig. 25.5 is a common design; it swings around to pick
up a particular tool and places it in the spindle.

Machining centers may be equipped with a tool-checking and/or part-checking station
that feeds information to the machine control system so that it can compensate for any
variations in tool settings or tool wear.

Touch probes(Fig. 25.6) can be installed into a tool holder to determine work piecereference surfaces

Vertical machining centers (VMC), these are capable of performing various machining
operations on parts with deep cavities, as in mold and die making.

Horizontal machining centers (HMC), these are suitable for large as well as tall work
pieces that require machining on a number of their surfaces.

Universal machining centers are equipped with both vertical and horizontal spindles.

Welded steel structures are lighter than cast-iron structures

Ceramic components are used in advanced machine tools for their strength, stiffness,
corrosion resistance,

Composites may consist of a polymer matrix,

Polymer concrete is a mixture of crushed concrete and plastic

Stiffness is a major factor in the dimensional accuracy of a machine tool

Damping is a critical factor in reducing or eliminating vibration and chatter in machining
operations.

An important factor in machine tools is the thermal distortion of their components,

Resin bonding is being used to assemble machine tools,

Low stiffness can cause vibration and chatter of the cutting tools and the machine
components

Forced vibration generally is caused by some periodic applied force present in the
machine tool,

Generally called chatter, self-excited vibration is caused by the interaction of the chipremoval process with the structure of the machine tool.

The most important type of self-excited vibration is regenerative chatter, which is caused
when a tool is cutting a surface that has a roughness or geometric disturbances

Dynamic stiffness is defined as the ratio of the applied-force amplitude to the vibration
amplitude

Damping is defined as the rate at which vibrations decay.

Internal damping results from the energy loss in materials during vibration

External damping is accomplished with external dampers that are similar to shock
absorbers on automobiles or machines.

Called hard machining or bard turning, this process produces machined parts with good
dimensional accura

The cutting tool for ultra precision machining applications is almost exclusively a singlecrystal diamond, and the process is called diamond turning.

With depths of cut in the nm range, hard and brittle materials produce continuous chips in
a process known as ductile-regime cutting.

An abrasive is a small, hard particle having sharp edges and an irregular shape

an important characteristic of abrasives is friability defined as the ability of abrasive
grains to fracture (break down) into smaller pieces

Essentially a glass, a 1/it1'i}9ed bond (also called a ceramic bond) is the most common
and widely used bond material.

Resinoid bonding materials are thermosetting resins and are available in a wide range of
compositions

Reinforced Wheels. These wheels typically consist of one or more layers of fiberglass
mats of various mesh sizes.

ln addition to thermosetting resins, thermoplastic bonds are used in grinding wheels.

The grade of a bonded abrasive is a measure of its bond strength,

Grinding is a chip-removal process that uses an individual abrasive grain

An excessive temperature rise in grinding can cause tempering and softening of the work
piece surface.

High temperatures in grinding may cause the work piece surface to develop cracks; this
condition is known as heat checking.

Truing, which is producing a true circle on a wheel that has become out of round

Dressing is necessary when excessive attritious wear dulls the wheel (called glazing
because of the shiny appearance of the wheel surface)

Loading of a grinding wheel occurs when the porosities on the wheel surfaces become
filled or clogged with chips from the work piece.

Surface grinding is one of the most common operations (Fig. 26.13), generally involving
the grinding of flat surfaces.

in plunge grinding, the wheel is moved radially into the Work piece

In cylindrical grinding (also called center-type grinding, Fthe external cylindrical
surfaces and shoulders of work pieces such as crankshaft bearings, spindles, pins, and
bearing rings are ground.

In roll grinders used for large and long work pieces

Thread grinding is done on cylindrical grinders

Center less grinding is a high-production process for continuously grinding cylindrical
surfaces

In through-feed grinding, the work piece is supported on a work-rest blade and is ground
between two wheels.

The regulating wheel (which is rubber bonded) is tilted and runs at a speed of only about
one-twentieth of the grinding-wheel speed.

as In internal center less grinding, the work piece is supported between three rolls and is
ground internally;

Universal tool and cutter grinders are used for grinding single-point or multipoint tools
and cutters, including drills.

Tool-post grinders are self-contained units and usually are attached to the tool post of a
lathe

Rough grinding of castings is called snagging

Bench and pedestal grinders are used for the routine offhand grinding of tools and small
parts.

Chatter is particularly important in grinding operations because it adversely affects
surface finish and wheel performance.

Damage to a grinding Wheel can reduce its bursting speed severely.

In ultrasonic machining (UM), material is removed from a surface by micro chipping

Coated abrasives also are used as belts for high-rate material removal With good surface
finish.

In alternative surface is produced by micro replication, in which abrasives in the shape of
tiny aluminum-oxide pyramids are placed in a predetermined orderly arrangement on the
belt surface.

Wire Brushing. In this process, also called power brushing, the work piece is held against
a circular wire brush that rotates at speeds

Honing is an operation that is used to improve the surface finish of holes produced by
processes such as boring, drilling, and internal grinding.

Lapping. This is an operation used for finishing flat, cylindrical, or curved surfaces.

Polishing is a process that produces a smooth, lustrous surface finish.

Burrs are thin ridges, usually triangular in shape,

Micro abrasive blasting consists of small-scale polishing and etching, using very fine
abrasives, on bench-type units

In micro abrasive-flow machining, a process mechanics similar to that used in ordinary
abrasive-flow machining is used,

Thermal Energy Deburring. This process consists of placing the part in a chamber that is
then injected with a mixture of natural gas and oxygen.

Deburring and flash removal from finished products are being performed increasingly by
programmable robots

Chemical blanking is similar to the blanking of sheet metals in that it is used to produce
features which penetrate through the thickness of the mate

P/ootoclveniical blanking (also called plvotoetclving) is a modification of chemical
milling.

The reduced negative of the design is called artwork.

The sheet blank is coated with a photosensitive material (photoresist) by dipping,
spraying, spin casting, or roller coating and is then dried in an oven. This coating is often
called the emulsion

Tool wear can be minimized by reversing the polarity and using copper tools-a process
called no-wear EDM.
Extrusion and drawing

―forming‖ generally indicates changing the shape of an existing solid body

Rapid-prototyping processes can be classified into three major groups: subtractive,
additive, and virtual. As the names imply, subtractive processes involve material removal
from a work piece that is larger than the final part. Additive processes build up a part by
adding material incrementally to produce the part. Virtual processes use advanced
computer-based visualization technologies.

Cutting, typically involving single-point or multipoint cutting tools, each with a clearly' '
defined shape

The maximum possible draft is defined as the difference between the initial and final strip
thicknesses, or (loo - hf)

In extrusion, a cylindrical billet is forced through a die

A characteristic of extrusion (from the Latin extrudere, meaning ―to force out‖) is that
large deformations can take place without fracture

Extrusion at room temperature often is combined with forging operations, in which case
it generally is known as cold extrusion

The term drawing also is used to refer to making cup-shaped parts by sheet-metalforming operations

The distinction between the terms rod and Wire is somewhat arbitrary, with rod taken to
be larger in cross section than wire.

In indirect extrusion (also called reverse, inverted, or backward extrusion), the die moves
toward the unextruded billet (

In hydrostatic extrusion (Fig. 15 .3b), the billet is smaller in diameter than the chamber

A less common type of extrusion is lateral (or side) extrusion

In coaxial extrusion, or cladding, coaxial billets are extruded together provided that the
strength and ductility of the two metals are compatible

Stepped extrusions are produced by extruding the billet partially in one die and then in
one or more larger dies

Square dies (shear dies) are used in extruding nonferrous metals

Tubing is extruded from a solid or hollow billet

Hollow cross sections (Fig. 15 .9a) can be extruded by welding-chamber methods and
using various dies known as a porthole die, spider die, and bridge die

Ina process developed inthe 19405 and known as the Séjournet process (after ].
Séjournet), a circular glass or fiberglass pad is placed in the chamber at the die entrance.

For metals that have a tendency to stick to the container and the die, the billet can be
enclosed in a thin-walled container, or jacket, made of a softer and lower strength metal,
such as copper or mild steel. This procedure is called jacketing or canning.

cold extrusion is a general term that often denotes a combination of operations, such as
direct and indirect extrusion and forging

Lubrication is critical, especially with steels, because of the possibility of sticking
(seizure) between the work piece and the tooling

The most effective means of lubrication is the application of a phosphate-conversion
coating on the work piece, followed by a coating of soap or wax,

Impact extrusion is similar to indirect extrusion, and the process often is included in the
cold-extrusion category.

In hydrostatic extrusion, the pressure required in the chamber is supplied via a piston
through an incompressible fluid medium surrounding the billet

There are three principal extrusion defects: surface cracking, pipe, and internal cracking.

If extrusion temperature, friction, or speed is too high, surface temperatures can rise
significantly, which may cause surface cracking and tearing (Hrtree cracking or speed
cracking). These cracks are intergranular (i.e., along the grain boundaries; see Fig. 2.27)
and usually are caused by hot shortness

Surface cracking also may occur at lower temperatures, where it has been attributed to
periodic sticking of the extruded product along the die land. Because of the similarity in
appearance to the surface of a bamboo stem, it is known as a bamboo defect.

The center of the extruded product can develop cracks, called center cracking, centerburst, arrowhead fracture, or c/vez/ron cracking

The basic equipment for extrusion is a horizontal hydraulic press

Vertical hydraulic presses typically are used for cold extrusion.

Crank-joint and /enuc/cle-joint mechanical presses are used for cold extrusion and for
impact extrusion to mass-produce small components.

In drawing, the cross section of a long rod or wire is reduced or changed by pulling(hence
the term drawing) it through a die called a draw die

The wall thickness, diameter, or shape of tubes that have been produced by extrusion or
by other processes described in this book can be reduced further by tube-drawing
processes

Wedge-shaped dies are used for the drawing of flat strips and are used only in specific
applications. However, the principle behind this process is the fundamental deformation
mechanism in ironing, used extensively in making aluminum beverage cans

A light reduction (sizing pass) also may be taken on rods to improve their surface finish
and dimensional accuracy.

A light reduction (sizing pass) also may be taken on rods to improve their surface finish
and dimensional accuracy.

Drawn copper and brass wires are designated by their temper

High-carbon steel wires for springs and for musical instruments are made by heat treating
(patenting)

One method employed to increase productivity is to draw many wires (a hundred or
more) simultaneously as a bundle.

A set of dies is required for profile drawing, which involves various stages of
deformation to produce the final profile.

Wet drawing, in which the dies and the rod are immersed completely in the lubricant

Dry drawing, in which the surface of the rod to be drawn is coated with a lubricant by
passing it through a box filled with the lubricant (stuffing box)

Metal coating, in which the rod or wire is coated with a soft metal, such a scopper or tin,
that acts as a solid lubricant

Ultrasonic vibration of the dies and mandrels; in this process, vibrations reduce forces,
improve surface finish and die life, and allow larger reductions per pass without failure.

Typical defects in a drawn rod or wire are similar to those observed in extrusion
especially center cracking

Another major type of defect in drawing is seams, which are longitudinal scratches or
folds in the material.

Moreover, they cause the component to warp if a layer of material subsequently is
removed (see Fig. 230),such as by slitting, machining, or grinding.

A draw bench contains a single die, and its design is similar to that of a long, horizontal
tension-testing machine

Very long rods and wire (many kilometers) and wire of smaller cross sections, usually
less than 13 mm, are drawn by a rotating drum (bull block or capstan
Sheet metal forming

the term press working or press forming is used commonly in industry to describe general
sheet-forming operations, because they typically are performed on presses

A sheet-metal part produced in presses is called a stamping

Note that this is a term similar to forging or casting, commonly used to describe parts
made by those individual processes using dies or molds

Before a sheet-metal part is made, a blank of suitable dimensions first is removed from a
large sheet (usually from a coil) by shearing

A burr is a thin edge or ridge,

The most common shearing operations are punching-where the sheared slug is scrap (Fig.
16.4a) or may be used for some other purpose-and blanking-where the slug is the part to
be used and the rest is scrap.

Perforating: punching a number of holes in a sheet

Parting: shearing the sheet into two or more pieces

Notching: removing pieces (or various shapes) from the edges

Lancing: leaving a tab without removing any material.

In slitting, the blades follow either a straight line, a circular path, or a curved path.

Soft metals (as Well as paper, leather, and rubber) can be blanked with a steel-rule die.

In nibbling, a machine called a nibbler moves a small straight punch up and down rapidly
into a die.

If the sheared edge is rough and not acceptable, it can be subjected to a process called
shaving

Several operations on the same sheet may be performed in one stroke at one station with
a compound die.

Parts requiring multiple operations to produce can be made at high production rates in
progressive dies.

ln a transfer-die setup, the sheet metal undergoes different operations at different stations
of the machine that are arranged along a straight line or a circular path.

Laser-beam cutting is an important process (Section 26.7) typically used with computercontrolled equipment to cut a variety of shapes

Water-jet cutting is effective on many metallic as well as nonmetallic material

Cutting with a band saw; this method is a chip-removal process

Friction sawing involves a disk or blade that rubs against the sheet or plate at high surface
speeds

Flame cutting is another common method, particularly for thick plates;

The true strain at which necking begins is numerically equal to the strain-hardening
exponent

Necking may be localized or it may be diffuse, depending on the strain-rate sensitivity

Low-carbon steels and some aluminum-magnesium alloys exhibit a behavior called yieldpoint elongation: having both upper and lower yield points (Fig. 16.12a). This behavior
results in Liider‘s bands

The usual method of avoiding Luder‘s bands is to eliminate or reduce yield point
elongation by reducing the thickness of the sheet 0.5 to 1.5% by cold rolling (temper or
skin rolling).

An important factor that influences sheet-metal forming is anisotropy

In the Erichsen test, the sheet specimen is clamped between two circular, flat dies and
steel ball or round punch is forced into the sheet until a crack begins to appear on the
stretched specimen.

The punch depth, d, at which failure occurs is a measure of the formability of the sheet.

Bending is one of the most common industrial forming operations.

The bend allowance, Lb, is the length of the neutral axis in the bend; it is used to
determine the length of the blank for a part to be bent.

Anisotropy of the sheet is another important factor in bendability.

Cold rolling results in anisotropy by preferred orientation or by mechanical #bering due
to the alignment of any impurities, inclusions, and voids that may be present,

Another method is to coin the bend area by subjecting it to highly localized compressive
stresses between the tip of the punch and the die surface

Another method is stretch bending, in which the part is subjected to tension while being
bent

Die materials for press brakes range from hardwood (for low-strength materials and
small-production runs) to carbides for strong and abrasive sheet materials and also are
chosen to improve die life.

In beading, the periphery of the sheet metal is bent into the cavity of a die

Flanging. This is a process of bending the edges of sheet metals, usually to 90°.

In stretch flanging, the flange periphery is subjected to tensile stresses that, if excessive,
can lead to cracking along the periphery.

Roll Forming. This process, which is also called contour-roll forming or cold-roll
forming, is used for forming continuous lengths of sheet metal and for large production
runs.

In dimpling (Fig. 16.25b), a hole first is punched and then expanded into a flange.

Flanges also may be produced by piercing with a shaped punch

When the bend angle is less than 90° (as in fittings with conical ends),the process is
called flaring.

In the hemming process (also called flattening), the edge of the sheet is folded over itself

Seaming involves joining two edges of sheet metal by hemming

Bulging. This process involves placing a tubular, conical, or curvilinear part into asplitfemale die

In stretch forming, the sheet metal is clamped along its edges and then stretched over a
male die

process in which a punch forces a flat sheet-metal blank into a die cavity (Fig.
16.31a).Although the process generally is called deep drawing

In the basic deep-drawing process, a round sheet-metal blank is placed over a circular die
opening and is held in place with a blank holder, or bold-down ring

Deep drau/ability generally is expressed by the limiting drawing ratio (LDR)

Whether a sheet metal can be deep drawn successfully into a round cup-shaped part has
been found to be a function of the normal anisotropy,

Earing is caused by the planar anisotropy

In deep drawing, the edges of cups may become wavy-a phenomenon called earing

lf they are too small, they can cause fracture at the corners; if they are too large, the cup
wall may wrinkle-a phenomenon called puckering.

Draw beads (Fig. 1635) often are necessary to control the flow of the blank into the die
cavity.

Containers that are too difficult to draw in one operation generally undergo redrawing

in rubber forming (also known as the Guerin process), one of the dies in a set is made of a
flexible material,

In the hydro form, or fluid-forming process (Pig. 16.39), the pressure over the rubber
membrane is controlled throughout the forming cycle with a maximum pressure of up to
100 MPa.

In tube hydroforming (Fig. 16.40), metal tubing is formed in a die and pressurized
internally by a fluid, usually water.

Spinning is a process that involves the forming of axisymmetric parts over a mandrel by
the use of various tools and roller

In conventional spinning, a circular blank of flat or preformed sheet metal is placed

Shear Spinning. Also known as pou/er spinning, Hou/ turning, hydro spinning, and spin
forging, this operation produces an axisymmetric conical or curvilinear shape

The spinnability of a metal in this process generally is defined as the maximum reduction
in thickness to which a part can be subjected by spinning without fracture.

In tube spinning, the thickness of hollow, cylindrical blanks is reduced or shaped by
spinning them on a solid, round mandrel using rollers

Incremental forming is a term applied to a class of processes that are related to
conventional metal spinning.

n explosive forming, first utilized to form metals in the early 19005, the sheet-metal
blank is clamped over a die and the entire assembly is lowered into a tank filled with
Water

In electromagnetically assisted forming, also called magnetic-pulse forming, the energy
stored in a capacitor bank is discharged rapidly through a magnetic coil.

The corrugation process (Fig. 16.54b) is similar to the process used in making corrugated
cardboard.
Forming & Shaping Plastics & Composite Materials

In extrusion, which produces the largest volume of plastics, raw materials in the form of
thermoplastic pellets

Feed section: Conveys the material from the hopper into the central region of the barrel.

Melt section (also called compression or transition section): Where the heat generated by
the viscous shearing of the plastic pellets and by the external heaters causes melting to
begin.

Metering or pumping section: Where additional shearing (at a high rate) and melting
occur, with pressure building up at the die.

Between the screen and the die is a breaker plate,

Defects observed in extruding plastics are similar to those observed in metal extrusion

Plastic Tubes and Pipes. These are produced in an extruder with a spider die

Extruded by a process in which the die is rotated, rigid plastic tubing causes the polymer
to be sheared and biaxially oriented during extrusion

Common plastic bags and other thin polymer film products are made from blown film

Most synthetic fibers used in reinforced plastics are ol mers that are extruded through h
the tin holes of a device called spinneret

This process of extrusion and solidification of Bobbin continuous filaments is called
spinning.

In melt spinning (shown in Fig. 19.6), the polymer is V melted for extrusion through the
spinneret and then solidified directly by cooling

Wet spinning is the oldest process for fiber production and is used for polymers that have
been dissolved in a solvent.

Dry spinning is used for thermosets carried by a solvent.

Gel spinning is a special process used to obtain high strength or special fiber properties.

Graphite fibers are produced from different polymer fibers by pyrolysis.

Injection molding is similar to hot-chamber die casting

Multicomponent injection molding (also called coinjection or sandwich molding) allows
the forming of parts with a combination of various colors and shapes.

Insert molding involves metallic components (such as screws, pins, and strips) that are
placed in the mold cavity prior to injection and then become an integral part of the
molded product

Over molding. This is a process for making products (such as hinge joints and ball andsocket joints) in one operation and without the need for post molding assembly.

In ice-cold molding, the same type of plastic is used to form both components of the
joint.

Solidification of the outer layers in thick sections can cause porosity or 1/oids due to
shrinkage,

A defect known as sink marks (or pull-in) similar to that shown in Fig. 19.31c also is
observed in injection-molded parts

In the reaction-injection molding (RIM) process, a monomer and two or more reactive
fluids are forced at high speed into a mixing chamber at a pressure of 10 to 20 MPa

In extrusion blow molding, a tube or preform (usually oriented so that it is vertical) is
first extruded.

In injection blow molding, a short tubular piece (parison) is injection molded (Fig.
19.14b) into cool dies.

A related process is stretch blow molding, in which the parison is expanded and
elongated simultaneously, subjecting the polymer to biaxial stretching and thus
enhancing its properties

Multilayer blow molding involves the use of coextruded tubes or parisons and thus
permits the production of a multilayer structure

Most thermoplastics and some thermosets can be formed into large, hollow parts by
rotational molding.

In this operation (called slush molding or slush casting), the mold is heated and rotated
simultaneously.

Thermoforming is a process for forming thermoplastic sheets or films over a mold
through the application of heat and pressure

thermoforming is a combination of drawing and stretching operations

In compression molding, a preshaped charge of material, premeasured volume of powder,
or viscous mixture of liquid-resin

Transfer molding represents a further development of compression molding.

lntricate shapes can be produced using flexible molds,

Products such as styrofoam cups, food containers, insulating blocks, and shaped
packaging materials (such as for shipping appliances, computers, and electronics) are
made by foam molding, using expandable polystyrene beads as the raw material.

This is a molding process used to make plastic products with a solid outer slain and a
cellular core structure.

Rubber and some thermoplastic sheets are formed by the calendering process

Discrete rubber products, such as gloves, are made by dipping a metal form (such as in
the shape of a hand for making gloves) repeatedly into a liquid compound that adheres to
the form.

Reinforced especially creep resis plastics) are engineered materials with unique
mechanical properties high strength-to-Weight ratio, stiffness-to-weight ratio, fatigue
strength, tance, and directional ro erties.

A variation of this process is pressure-bag molding

This is a series of processes that use a single male or female mold made of such materials
as reinforced plastics, wood, metal, or plaster (Fig. 19.26 ); it is also referred to as openmold processing.

Contact molding is used in making laminated products with high surface area-tothickness ratios; hence, the process is also called contact lamination

The simplest method of contact molding is hand layup.

In spray layup, molding is done by spraying the materials into the mold.

Filament winding is a process in which the resin and fibers are combined at the time of
curing

Long parts with various uniform cross sections (such as rods, profiles, flat strips, and
tubing) are made continuously by the pultrusion process.

Continuously reinforced products other than those with constan cross-sectional profiles
are made by pulforming.

Liquid-phase processing basically consists of casting together the liquid-matrix material

Solid-phase processing consists basically of powder-metallurgy techniques, including
cold and hot isostatic pressing.

Two-phase (liquid-solid) processing involves technologies that consist of rheocasting

Slurry infiltration is the most common process for making ceramic-matrix composites.

Chemical-synthesis processes involve the sol-gel and the polymer-precursor techniques.

In chemical-vapor infiltration, a porous fiber preform is infiltrated with the matrix phase
using the chemical vapor deposition technique
Joining Process & Equipment

Joining is an all-inclusive term covering processes such as welding, brazing, soldering,
adhesive bonding, and mechanical fastening.

Fusion Welding is defined as the melting together and coalescing of materials by means
of heat, usually supplied by chemical or electrical means;

In solid-state welding, joining takes place without fusion; consequently, there is no liquid
(molten) phase in the joint.

Adhesive bonding has unique applications that require strength, sealing, thermal and
electrical insulating, vibration damping, and resistance to corrosion between dissimilar
metals.

Mechanical fastening involves traditional methods of using various fasteners, especially
bolts, nuts, and rivets.

The joining of plastics can be accomplished by adhesive bonding, fusion by various
external or internal heat sources, and mechanical fastening.

The transfer of atoms across an interface; thus, applying external heat improves the
strength of the bond between the two surfaces being joined, as occurs in diffusion
bonding.

The higher the pressure, the stronger is the interface (as in roll bonding and explosion
welding), where plastic deformation also occurs.
Solid State Welding Process

In cold welding (CW), pressure is applied to the work pieces through dies or rolls

During the joining of two dissimilar metals that are mutually soluble, brittle intermetallic
compounds may form

The pressure required for welding can be applied through a pair of rolls (Fig. 31.1); this
process is called roll bonding or roll welding (ROW)

The process can be carried out at elevated temperatures (loot roll bonding).

In ultrasonic welding (USW), the faying surfaces of the two components are subjected to
a static normal force and oscillating shearing (tangential) stresses.

Proper coupling between the transducer and the tip (called-by analogy with electrode-a
sonotrode, from the word sonic) is important for efficient operation

In friction welding (FRW), the heat required for welding is generated through (as the
name implies) friction at the interface of the two components being joined.

In linear friction welding, the components do not have to be circular or tubular in their
cross section.

In the friction stir-welding (FSW) process, developed in two surfaces to be joined.

In order to obtain a strong bond in the weld nugget, pressure is applied until the current is
turned off and the weld has solidified.

Rocker-arm-type spot-welding machines normally are used for smaller parts; press-type
machines are used for larger work pieces.

Resistance seam welding (RSEW) is a modification of spot welding wherein the
electrodes are replaced by rotating wheels or rollers

In roll spot welding, current to the rollers is applied only intermittently, resulting in a
series of spot welds at specified intervals along the length of the seam

In mash seam welding (Fig. 31.1Od), the overlapping welds are about one to two

times the sheet thickness, and the welded seam thickness is only about 90% of the
original sheet thickness. This process is also used in producing tailor welded sheet-metal
blanks,

High-frequency resistance welding (HFRW) is similar to seam welding typical
application is the production of butt-welded tubing or pipe where the current is conducted
through two sliding contacts

In another method, called high-frequency induction welding (HFIW), the roll-formed
tube is subjected to high-frequency induction heating

In resistance projection welding (RPW), high electrical resistance at the joint is
developed by embossing one or more projections

In flash welding (FW), also called flash butt welding, heat is generated very rapidly from
the arc as the ends of the two members begin to make contact and develop an electrical
resistance at the joint

The mechanism is called hot upsetting, and the term upset welding (UW) also is used for
this process

Some molten metal is expelled from the joint as a shower of sparks during the processhence the name flash welding.

Stud welding (SW) is also called stud are welding and is similar to flash welding.

In capacitor-discharge stud welding, a DC arc is produced from a capacitor bank.

the electrical energy for welding may be stored in a capacitor. Percussion welding (PEW)
utilizes this technique

In explosion welding (EXW), pressure is applied by detonating a layer of explosive that
has been placed over one of the components being joined, called the flyer plate

Diffusion bonding, or diffusion welding (DFW) is a process in which the strength of the
joint results primarily from diffusion

he principle of diffusion bonding dates back centuries to when goldsmiths bonded gold
over copper to create a product called filled gold.

the assembly is placed in a furnace and left until a strong bond is obtained; hence, the
process is also called hot-pressure welding (HPW)
Soldering, Brazing

Brazing is a joining process in which a #Her metal is placed between the faying surfaces
to be joined

In braze welding, filler metal (typically brass) is deposited at the joint by a technique
similar to oxyfuel-gas welding (see Fig. 3O.1d); the major difference is that the base
metal does not melt.

Filler Metals. Several filler metals (braze metals) are available with a range of brazing
temperatures

Because of diffusion between the filler metal and the base metal, the mechanical and
metallurgical properties of a joint can change as a result of subsequent process

The use of a flux is essential in brazing; a flux prevents oxidation and removes oxide
films.

Wetting agents may be added to improve both the wetting characteristics of the molten
filler metal and the capillary action.

The heat source in torch brazing (TB) is oxyfuel gas with a carburizing flame

The parts in furnace brazing (PB) are first cleaned and preloaded with brazing metal in
appropriate configurations

The source of heat in induction brazing (IB) is induction heating by high-frequency

In resistance brazing (RB), the source of heat is the electrical resistance of the
components to be brazed.

Dip brazing (DB) is carried out by dipping the assemblies to be brazed into either a
molten filler-metal bath or a molten salt

The heat source in infrared brazing (IRB) is a high-intensity quartz lamp.

Diffusion brazing (DFB) is carried out in a furnace where, with proper control of
temperature and time, the filler metal diffuses into the faying surfaces of the components
to be joined.

For specialized and high-precision applications and with high-temperature metals and
alloys, electron-beam or laser-beam heating may be used

The joint in braze welding is prepared as it is in fusion welding

In soldering, the filler metal (called solder) melts at a relatively low temperature.

Because of the toxicity of lead and its adverse effects on the environment, lead-free
solders are being developed continuously and are coming into wider use.

Fluxes are used in soldering and for the same purposes as they are in welding and
brazing,

Solderability may be defined in a manner similar to weldability

Solder pastes are solder-metal particles held together by flux, binding, and wetting
agents.

The paste is placed directly onto the joint, or on flat objects for finer detail, and it can be
applied via a screening or stenciling process,

Stenciling is commonly used during the attachment of electrical components to printed
circuit boards.

Wave soldering is a common technique for attaching circuit components to their boards

Drag soldering - is another method used to solder circuit board connections in the
electronics industry.
Metal Casting Process & Equipment

The casting process basically involves (a) pouring molten metal into a mold patterned

After the temperature of the molten metal drops to its freezing point, its temperature
remains constant while the latent heat of fusion is given off.

The solidi/Qcation front (solid-liquid interface) moves through the molten metal from the
mold walls in toward the center.

For alloys, a short freezing range generally involves a temperature difference o less than
50°C, and a long freezing range greater than 110°C

Lack of uniformity in grain size and grain distribution results in castings with anisotropic
properties

The compositions of dendrites and the liquid metal are given by the phase diagram of the
particular alloy

Cored dendrites have a surface composition different from that at their centers, a
difference referred to as a concentration gradient.

macrosegregation involves differences in composition throughout the casting itself.

lower melting-point constituents in the solidifying alloy are driven toward the center
(normal segregation

the opposite occurs; that is, the center of the casting has a lower concentration of alloying
elements (inverse segregation)

Gravity segregation describes the process whereby higher density inclusions or
compounds sink and lighter elements

The inoculant induces nucleation of the grains throughout the liquid metal
(heterogeneous nucleation).

The molten metal is poured through a pouring basin or cup; it then flows through the
gating system (consisting of sprue, runners, and gates) into the mold cavity.

Runners are the channels that carry the molten metal from the sprue into the mold cavity
or connect the sprue to the gate

Risers (also called feeders) serve as reservoirs of molten metal to supply any molten
metal necessary to prevent porosity due to shrinkage during solidification.

an important function of the gating system in sand casting is to trap contaminants (such
as oxides and other inclusions)

Aspiration (a process whereby air is sucked in or entrapped in the liquid) may take place.

The choke slows the flow sufficiently to prevent aspiration in the sprue

Another application of the foregoing equations is in the modeling of mold Elling.

An important consideration of the fluid flow in gating systems is the presence of
turbulence, as opposed to the laminar /‗low of fluids.

Dross or slag can be eliminated only by vacuum casting

The capability of molten metal to fill mold cavities is called fluidity,

As viscosity and its sensitivity to temperature (viscosity index) increase, fluidity
decreases.

A high surface tension of the liquid metal reduces fluidity.

Because they are insoluble, inclusions can have a significant adverse effect on fluidity.

Superheat (defined as the increment of temperature of an alloy above its melting point)
improves fluidity by delaying solidification.

The term castability generally is used to describe the ease with which a metal can be cast
to produce a part with good quality.

The solidification time is a function of the volume of a casting and its surface area
(Chi/orinoz/‘s rule):

Metallic projections, consisting of fins, flash, or projections such as swells and rough
surfaces

Porosity in a casting may be caused by shrinkage, entrained or dissolved gases,

Porous regions can develop in castings because of shrinkage of the solidified metal.

Microporosity also can develop when the liquid metal solidifies and shrinks between
dendrites and between dendrite branches.

Subjecting the casting to hot isostatic pressing is another method of reducing porosity

Dissolved gases may be re- fig) Fusion moved from the molten metal by flushing or
purging with an inert gas

Gross porosity is from shrinkage and usually is called a shrinkage cavity

In the cold-box mold process, various organic and inorganic binders are blended into the
sand to bond the grains chemically for greater strength.

ln the no-bake mold process, a synthetic liquid resin is mixed with the sand and the
mixture hardens at room temperature.

Because the bonding of the mold in this and in the cold-box process takes place without
heat, they are called cold-setting processes.

A sprue, through which the molten metal flows downward

The runner system, which has channels that carry the molten metal from the sprue to the
mold cavity. Gates are the inlets into the mold cavity

Risers, which supply additional molten metal to the casting as it shrinks during
solidification.

Cores, which are inserts made from sand.

Vents, which are placed in molds to carry off gases produced when the molten metal
comes into contact with the sand in the mold and the core.

Patterns are used to mold the sand mixture into the shape of the casting and may be made
of wood, plastic, or metal.

Patterns may be made of a combination of materials to reduce wear in critical regions,
and the usually are coated with a parting agent to facilitate the removal of the casting
from the molds

One-piece patterns, also called loose or solid patterns, generally are used for simpler
shapes and low quantity production; they generally are made of wood and are
inexpensive.

Split patterns are two-piece patterns, made such that each part forms a portion of the
cavity for the casting; in this way, castings with complicated shapes can be produced.

Match-plate patterns are a common type of mounted pattern in which two-piece patterns
are constructed by securing each half of one or more split patterns to the opposite sides of
a single plate

An important development in molding and pattern making is the application of rapid
prototyping

Pattern design is a critical aspect of the total casting operation. The design should provide
for metal shrinkage,

To keep the core from shifting, metal supports (chaplets) may be used to anchor the core
in place

For most operations, however, the sand mixture is compacted around the pattern by
molding machines.

In vertical flask less molding, the halves of the pattern form a vertical chamber wall
against which sand is blown and compacted

Sand slingers fill the flask uniformly with sand under a high-pressure stream

In impact molding, the sand is compacted by a controlled explosion or instantaneous
release of compressed gases.

In vacuum molding (also known as the V process), the pattern is covered tightly with a
thin sheet of plastic.

The casting subsequently may be heat treated to improve certain properties required for
its intended use;

Finishing operations may involve machining, straightening, or forging with dies

Inspection is an important final step and is carried out to ensure that the casting meets all
design and quality-control requirements.

Shell molding was first developed in the 19405 and has grown significantly because it
can produce many types of castings with close dimensional tolerances and a good surface
finish at low cost.

Precision casting, because of the high dimensional accuracy and good surface finish
obtained.

In the plaster-molding process, the mold is made of plaster of paris

Mold permeability can be increased substantially by the Antioch process, in which the
molds are dehydrated in an autoclat/e

The ceramic-mold casting process (also called cope-and-drag investment casting) is
similar to the plaster-mold process,

Evaporative-pattern and investment casting are sometimes referred to as expendable
pattern casting processes or expendable mold-expendable pattern processes.

The evaporative-pattern casting process uses a polystyrene pattern, which evaporates
upon contact with molten metal to form a cavity for the casting; this process is also
known as lost-foam casting and falls under the trade name full-mold process.

In a modification of the evaporative-pattern process, called the Replicc1st® C-S process,
a polystyrene pattern is surrounded by a ceramic shell

The term investment derives from the fact that the pattern is invested (surrounded) with
the refractory material.

A number of patterns can be joined to make one mold, called a tree

A variation of the investment-casting process is ceramic-shell casting.

In permanent-mold casting (also called hard-mold casting), two halves of a mold are
made from materials with high resistance to erosion and thermal fatigue,

A schematic illustration of the vacuum-casting process, or countergraz/ity lowpressure
(CL) process (not to be confused with the vacuum-molding process

Hollow castings with thin walls can be made by permanent-mold casting using this
principle: a process called slush casting.

In pressure casting (also called pressure pouring or lou/-pressure casting), the molten
metal is forced upward by gas pressure into graphite or metal mold.

The die-casting process, developed in the early 1900s, is a further example of permanentmold casting. The European term for this process is pressure die casting

The hot-chamber process (Fig. 1 1.19) involves the use of a piston, which forces a certain
volume of metal into the die cavity through a gooseneck and nozzle.

In the cold-chamber process (Fig. 1120), molten metal is poured into the injection
cylinder (shot chamber).

Called insert molding, this process is similar to placing wooden sticks in popsicles prior
to freezing

Heat checking of dies (surface cracking from repeated heating and cooling of the die,

In true centrifugal casting, hollow cylindrical parts (such as pipes, gun barrels, bushings,
engine-cylinder liners, bearing rings with

In centrifuging (also called centrifuge casting), mold cavities of any shape are placed at a
certain distance from the axis of rotation.

The squeeze-casting (or liquid-metal forging) process was developed in the 1960s and
involves the solidification of molten metal under high pressure

Semisolid-metal forming (also called mushy-state processing When it enters the die, the
metal (consisting of liquid and solid components) is stirred so that all of the dendrites are
crushed into fine solids,

the process also is called thixoforming or thixomolding, meaning its viscosity decreases
when agitated.

Processing metals in their mushy state also has led to developments in mushy-state
extrusion, similar to injection molding

Composite molds are made of two or more different materials and are used in shell
molding and other casting processes.

The conventional-casting process uses a ceramic mold. The molten metal is poured into
the mold and begins to solidify at the ceramic walls.

In crystal growing, developed in 1967, the mold has a constriction in the shape of a
corkscrew or helix

It is then propelled under high gas pressure against a rotating copper disk (chill block),
which chills the alloy rapidly (splat cooling).

Pressure tightness of cast components (valves, pumps, and pipes) usually is determined
by sealing the openings in the casting and pressurizing it with Water, oil, or air.

Levitation melting involves magnetic suspension of the molten metal.

Because the cooling rate in regions with larger circles is lower, these regions are called
hot spots. They can develop shrinkage cavities and porosity

Allowances for shrinkage, known a patternmaker‘s shrinkage allowances, usually range
from about 10 to 20 mm/m

A pouring basin can be used to ensure that the metal flow into the sprue is uninterrupted

Chills can be used to speed solidification of the metal in a particular region of a casting.
Powder Metallurgy

ectrolytic deposition utilizes either aqueous solutions or fused salts. The powders
produced are among the purest available.

Particle size usually is controlled by screenin

Sedimentation, which involves measuring the rate at which particles settle in a fluid

Shape Factor. Also called the shape index, shape factor (SF) is a measure of the ratio of
the surface area of the particle to its volume

The pressed powder is known as green compact, since it has a low strength

In cold isostatic pressing (CIP), the metal powder is placed in a flexible rubber mold
typically made of neoprene rubber,

In hot isostatic pressing (HIP), the container generally is made of a high-melting-point
sheet metal

Powder-injection Molding. In this process, also called metal-injection molding (MIM),
very fine metal powders

In powder forging (PF), the part produced from compaction and sintering serves as the
preform in a hot-forging operation.

In powder rolling (also called roll compaction), the metal powder is fed into the roll gap
in a two-high rolling mill

Spray deposition is a shape-generation process

Some powder-metal parts have been produced by selective laser sintering, a rapidprototyping operation

Sintering is the process whereby green compacts are heated in a controlled atmosphere
furnace to a temperature below the melting point,

As the temperature increases, two adjacent powder particles begin to form a bond by a
diffusion mechanism

A second sintering mechanism is vapor-phase transport

If two adjacent particles are of different metals, alloying can take place at the interface of
the two particles.

An example of this mechanism, known as liquid-phase sintering, is cobalt in tungstencarbide tools and dies

In spark sintering (an experimental process), loose metal powders are placed in a graphite
mold, heated by electric current, subjected to a high-energy discharge

Another technique under development is microwave sintering, which reduces sintering
times and thereby prevents grain growth, which can adversely affect strength.

Porosity may consist either of a network of interconnected pores or of closed holes.

Coining and sizing are com actin operations performed under pressureing presses.

Preformed and sintered alloy-powder compacts subsequently may be cold or hot forged
to the desired final shapes and sometimes by impact forging.

The inherent porosity of PM components can be utilized by impregnating them with a
fluid.

Infiltration is a process whereby a slug of a lower-melting-point metal is placed in contact
with the sintered part.

Electroplating can be applied on PM parts, but special care is required to remove the
electrolytic fluid
Surface Treatment

Shot Peening. In shot peening, the work piece surface is impacted repeatedly with a large
number of cast steel, glass, or ceramic shot (small balls), which make overlapping
indentations on the surface.

Laser Shot Peening. In this process, also called laser shock peening

Water-jet Peening. In this more recently developed process, a Water jet at pressures as
high as 400 MPa impinges on the surface of the work piece

Ultrasonic Peening. This process uses a hand tool based on a piezoelectric transducer.

Roller Burnishing. In this process, also called surface rolling, the surface of the
component is cold worked by a hard and highly polished roller or set of rollers.

Internal cylindrical surfaces also are burnished by a similar process, called ballizing or
ball burnishing.

Mechanical Plating. In mechanical plating (also called mechanical coating, impact
plating, or peen plating)

Cladding. In this process, also called clad bonding, metals are bonded with a thin layer of
corrosion-resistant metal through the application of pressure by rolls or other means.

Laser cladding consists of the fusion of a different material over the substrate.

Case Hardening. Traditional methods of case hardening (carhurizing, carhonitriding,
cyaniding, nitriding, flame hardening, and induction hardening)

Hard Facing. In this process, a relatively thick layer, edge, or point of wear resistant hard
metal is deposited on the work piece surface by the fusion-welding

Spark Hardening. Hard coatings of tungsten, chromium, or molybdenum carbides can be
deposited by an electric arc in a process called spark hardening, electric spar hardening,
or electrospar deposition.

Thermal spraying is a series of processes in which coatings of various metals,

Vapor deposition is a process in which the substrate (work piece surface) is subjected to
chemical reactions.

In arc deposition (PV/ARC), the coating material (cathode) is evaporated by several arc
evaporators

Pulsed-laser deposition is a more recent, related process in which the source of energy is
a pulsed laser.

Sputtering. In sputtering, an electric field ionizes an inert gas

In reactive sputtering, the inert gas is replaced by a reactive gas (such as oxygen), in
which case the atoms are oxidized and the oxides are deposited.

lon Plating. Ion plating is a generic term that describes various combined processes of
sputtering and vacuum evaporation.

Ion-beam-enhanced (assisted) deposition is capable of producing thin films

Dual ion-beam deposition is a hybrid coating technique that combines PVD with
simultaneous ion-beam bombardment.

Chemical vapor deposition (CVD) is a thermochemical process

In ion implantation, ions (charged atoms) are introduced into the surface of the work
piece material.

When used in some specific applications, such as semiconductors (Section 283), ion
implantation is called doping-meaning ―alloying with small amounts of various
elements.‖

Diffusion Coating. This is a process in which an alloying element is diffused into the
surface of the substrate (usually steel), altering its surface properties.

Plating, like other coating processes, imparts the properties of resistance to Wear

The plating solutions are either strong acids or cyanide solutions.

In rack plating, the parts to be plated are placed in a rack

In barrel plating, small parts are placed inside a permeable barrel

In brush processing, the electrolytic fluid is pumped through a handheld brush with metal
bristles.

Chromium plating is done by first plating the metal with copper, then with nickel, and
finally with chromium.

Hard chromium plating is done directly on the base metal.

Conversion coating, also called chemical-reaction priming, is the process of producing a
coating that forms on metal surfaces as a result of chemical or electrochemical reactions.

Phospliates, chromates, and oxalates are used to produce these coatings, for purposes

In hot dipping, the work piece (usually steel or iron) is dipped into a bath of molten metal

Glazing is the application of glassy coatings onto ceramic wares to give them decorative
finishes and to make them impervious to moisture.

Diamond-like carbon (DLC) coatings, a few nanometers in thickness, are produced by a
low-temperature

In electro coating or electrostatic spraying, paint particles are charged electrostatically
and are attracted to surfaces to be painted, producing a uniformly adherent coating.

Cleaning involves the removal of solid, semisolid, or liquid contaminants from a surface

Chemical cleaning usually involves the removal of oil and grease from surfaces.
Jigs & Fixture

jigs have various reference surfaces and points for accurate alignment of parts or tools for
processing.

Fixtures generally are designed for specific purposes

Several methods of flexible jixturing, based on different principles behind what are called
intelligent fixturing systems.

Tombstone Fixtures. Also referred to as pedestal-type fixtures, tombstone fixtures have
between two and six vertical faces

A lou/-melting-point metal is used as the clamping medium.
6. Fluid Mechanics:
Fluid Properties, Idea and real fluids, viscosity and compressibility of fluids

a fluid is defined as a substance that deforms continuously when acted on by a shearing
stress of any magnitude.

they will behave as a solid if the applied shearing stress is small, but if the stress exceeds
some critical value, the substance will flow. The study of such materials is called
rheology

We thus assume that all the fluid characteristics we are interested in 1pressure, velocity,
etc.2 vary continuously throughout the fluid—that is, we treat the fluid as a continuum.

The specific weight of a fluid, designated by the Greek symbol 1gamma2, is defined as
its weight per unit volume.

The specific gravity of a fluid, designated as SG, is defined as the ratio of the density of
the fluid to the density of water at some specified temperature.

The pressure in the ideal gas law must be expressed as an absolute pressure, denoted
(abs), which means that it is measured relative to absolute zero pressure 1a pressure that
would only occur in a perfect vacuum2.

In engineering it is common practice to measure pressure relative to the local atmospheric
pressure, and when measured in this fashion it is called gage pressure. Thus, the absolute
pressure can be obtained from the gage pressure by adding the value of the atmospheric
pressure.

The properties of density and specific weight are measures of the ―heaviness‖ of a fluid.

The fluid ―sticks‖ to the solid boundaries is a very important one in fluid mechanics and
is usually referred to as the no-slip condition.

Where the constant of proportionality is designated by the Greek symbol 1mu2 and is
called the absolute viscosity, dynamic viscosity, or simply the viscosity of the fluid.

Fluids for which the shearing stress is linearly related to the rate of shearing strain 1also
referred to as rate of angular deformation2 are designated as Newtonian fluids

Fluids for which the shearing stress is not linearly related to the rate of shearing strain are
designated as non-Newtonian fluids.

The slope of the shearing stress versus rate of shearing strain graph is denoted as the
apparent viscosity,

For shear thinning fluids the apparent viscosity decreases with increasing shear rate—the
harder the fluid is sheared, the less viscous it becomes.

For shear thickening fluids the apparent viscosity increases with increasing shear rate—
the harder the fluid is sheared, the more viscous it becomes.

Bingham plastic, which is neither a fluid nor a solid. Such material can withstand a finite,
nonzero shear stress, yield, the yield stress, without motion 1therefore, it is not a fluid2,
but once the yield stress is exceeded it flows like a fluid 1hence, it is not a solid2.
Toothpaste and mayonnaise are common examples of Bingham plastic materials.

The dimensions of kinematic viscosity are and the BG units are and SI units are m2/s

Dynamic viscosity is often expressed in the metric CGS 1centimeter-gram-second2
system with units of dyne s/cm2. This combination is called poise, abbreviated P. In the
CGS system, kinematic viscosity has units of and this combination is called a stoke,
abbreviated St.

A property that is commonly used to characterize compressibility is the bulk modulus.

The velocity at which these small disturbances propagate is called the acoustic velocity or
the speed of sound.

When an equilibrium condition is reached so that the number of molecules leaving the
surface is equal to the number entering, the vapor is said to be saturated and the pressure
that the vapor exerts on the liquid surface is termed the vapor pressure,

Boiling, which is the formation of vapor bubbles within a fluid mass, is initiated when the
absolute pressure in the fluid reaches the vapor pressure.

The formation and subsequent collapse of vapor bubbles in a flowing fluid, called
cavitation, is an important fluid flow phenomenon

The intensity of the molecular attraction per unit length along any line in the surface is
called the surface tension
difference between static and dynamic pressure, flow velocity and flow rate,
Measurement of static pressure, stagnation pressure, pressure in a fluid
under the action of gravity,

Steady flow1i.e. Nothing changes with time at a given location in the flow field2; each
successive particle that passes through a given point [such as point 112 in Fig. 3.1a] will
follow the same path.

The lines that are tangent to the velocity vectors throughout the flow field are called
streamlines.

The elevation term, z, is related to the potential energy of the particle and is called the
elevation head. The pressure term, is called the pressure head and represents the height of
a column of the fluid that is needed to produce the pressure p. The velocity term, is the
velocity head and represents the vertical distance needed for the fluid to fall freely
1neglecting friction2 if it is to reach velocity V from rest.

To measure its value, one could move along with the fluid, thus being ―static‖ relative to
the moving fluid. Hence, it is normally termed the static pressure.

The second term in the Bernoulli equation is termed the dynamic pressure.

The fluid in the tube, including that at its tip, 122, will be stationary. That is, or point 122
is a stagnation point

If elevation effects are neglected, the stagnation pressure is the largest pressure
obtainable along a given streamline. It represents the conversion of all of the kinetic
energy into a pressure rise

The sum of the static pressure, hydrostatic pressure, and dynamic pressure is termed the
total pressure

the fluid leaves as a ―free jet‖ p2=0

The mass flow rate from an outlet, 1slugss or kgs2, is given by where Q is the volume
flow rate.

If the density remains constant, then and the above becomes the continuity equation for
incompressible flow

For flows of liquids, this may result in cavitation, a potentially dangerous situation that
results when the liquid pressure is reduced to the vapor pressure and the liquid ―boils.‖

Three commonly used types of flow meters are illustrated: the orifice meter, the nozzle
meter, and the Venturi meter.

Another device used to measure flow in an open channel is a weir.

The static pressure tap connected to the piezometer

tube shown, on the other hand, measures the sum of the pressure head and the elevation
head, This sum is often called the piezometric head.
One dimensional in viscid flow (flow filament theory), equation of continuity,
Euler’s equations of motion, Bernoulli’s equation,

This rate of change of the volume per unit volume is called the volumetric dilatation rate.
Thus, we see that the volume of a fluid may change as the element moves from one
location to another in the flow field. However, for an incompressible fluid the volumetric
dilatation rate is zero, since the element volume cannot change without a change in fluid
density 1the element mass must be conserved

The vorticity, is defined as a vector that is twice the rotation vector;

If then the rotation 1and the vorticity2 are zero, and flow fields for which this condition
applies are termed irrotational.

The equation 1commonly called the continuity equation2 can be applied to a finite
control volume 1cv2, which is bounded by a control surface 1cs2.

Surface forces, which act on the surface of the differential element, and body forces,
which are distributed throughout the element.

Flow fields in which the shearing stresses are assumed to be negligible are said to be
inviscid, nonviscous, or frictionless.

It should be again emphasized that the Bernoulli equation, as expressed by Eqs. 6.57 and
6.58, is restricted to the following: inviscid flow incompressible flow, steady flow flow
along a streamline

A uniform flow field 1in which there are no velocity gradients2 is certainly an example
of an irrotational flow

But this is not the case for real fluids, so we will typically have a layer 1usually very
thin2 near any fixed surface in a moving stream in which shearing stresses are not
negligible. This layer is called the boundary layer.

Thus, for this type of internal flow there will be an entrance region in which there is a
central irrotational core, followed by a so-called fully developed region in which viscous
forces are dominant.

Inviscid, incompressible, irrotational flow fields are governed by Laplace‘s equation.
This type of flow is commonly called a potential flow.

lines of constant
1called equipotential lines2 are orthogonal to lines of constant
1streamlines2 at all points where they intersect.

For any potential flow field a ―flow net‖can be drawn that consists of a family of
streamlines and equipotential lines.

The simplest plane flow is one for which the streamlines are all straight and parallel, and
the magnitude of the velocity is constant. This type of flow is called a uniform flow.

Vortex motion is irrotational

The rotational vortex is commonly called a forced vortex, whereas the irrotational vortex
is usually called a free vortex.

A combined vortex is one with a forced vortex as a central core and a velocity
distribution corresponding to that of a free vortex outside the core.

A mathematical concept commonly associated with vortex motion is that of circulation.

The so-called doublet is formed by letting the source and sink approach one another

The development of this lift on rotating bodies is called the Magnus effect.

The generalized equation relating lift to fluid density, velocity, and circulation is called
the Kutta–Joukowski law, and is commonly used to determine the lift on airfoils
Navier stokes equations of motion

The Navier–Stokes equations apply to both laminar and turbulent flow, but for turbulent
flow each velocity component fluctuates randomly with respect to time and this added
complication makes an analytical solution intractable. Thus, the exact solutions referred
to are for laminar flows in which the velocity is either independent of time 1steady flow2
or dependent on time 1unsteady flow2 in a well-defined manner.
Dimensional analysis, similitude and its applications, Buckingham- Pi theorem
Reynolds’ law of similitude,

If an equation involving k variables is dimensionally homogeneous, it can be reduce to a
relationship among independent dimensionless products, where r is the minimum number
of reference dimensions required to describe the variables.

The Reynolds number is a measure of the ratio of the inertia force on an element of fluid
to the viscous force on an element.

if the Reynolds number is very small this is an indication that the viscous forces are
dominant in the problem,

Flows at very small Reynolds numbers are commonly referred to as ―creeping flows‖

for large Reynolds number flows, viscous effects are small relative to inertial effects and
for these cases it may be possible to neglect the effect of viscosity

Froude Number is distinguished from the other dimensionless groups in Table 7.1 in that
it contains the acceleration of gravity,

Euler Number can be interpreted as a measure of the ratio of pressure forces to inertial
forces

Cauchy Number and Mach Number are important dimensionless groups in problems in
which fluid compressibility is a significant factor. Both numbers can be interpreted as
representing an index of the ratio of inertial forces to compressibility forces. When the
Mach number is relatively small 1say, less than 0.32, the inertial forces induced by the
fluid motion are not sufficiently large to cause a significant change in the fluid density,
and in this case the compressibility of the fluid can be neglected.

Strouhal Number is a dimensionless parameter that is likely to be important in unsteady,
oscillating flow problems in which the frequency of the oscillation is It represents a
measure of the ratio of inertial forces due to the unsteadiness of the flow 1local
acceleration2 to the inertial forces due to changes in velocity from point to point in the
flow field 1convective acceleration2

Weber Number may be important in problems in which there is an interface between two
fluids.

A model is a representation of a physical system that may be used to predict the behavior
of the system in some desired respect. The physical system for which the predictions are
to be made is called the prototype.

Generally, as is illustrated in this example, to achieve similarity between model and
prototype behavior, all the corresponding pi terms must be equated between model and
prototype

Models for which one or more of the similarity requirements are not satisfied are called
distorted models

The transport of a fluid 1liquid or gas2 in a closed conduit 1commonly called a pipeif it is
of round cross section or a duct if it is not round2 is extremely important in our daily
operations.
Flow through pipes

The flow in a round pipe is laminar if the Reynolds number is less than approximately
2100.

The flow in a round pipe is turbulent if the Reynolds number is greater than
approximately 4000.

For Reynolds numbers between these two limits, the flow may switch between laminar
and turbulent conditions in an apparently random fashion 1transitional flow2.

At 1the centerline of the pipe2 there is no shear stress At 1the pipe wall2 the shear
stress is a maximum, denoted the wall shear stress

A small shear stress can produce a large pressure difference if the pipe is relatively long

As a general rule for pipe flow, the value of the Reynolds number must be less than
approximately 2100 for laminar flow and greater than approximately 4000 for turbulent
flow. For flow along a flat plate the transition between laminar and turbulent flow occurs
at a Reynolds number of approximately 500,000 1see Section 9.2.42, where the length
term in the Reynolds number is the distance measured from the leading edge of the plate

For an initial time period the Reynolds number is small enough for laminar flow to occur.
At some time the Reynolds number reaches 2100, and the flow begins its transition to
turbulent conditions. Intermittent spots or bursts of turbulence appear. As the Reynolds
number is increased, the entire flow field becomes turbulent. The flow remains turbulent
as long as the Reynolds number exceeds approximately 4000.

For turbulent flow it is found that the turbulent shear stress, is positive

In a very narrow region near the wall 1the viscous sublayer2, the laminar shear stress is
dominant. Away from the wall 1in the outer layer2 the turbulent portion of the shear
stress is dominant. The transition between these two regions occurs in the overlap layer.

Completely turbulent flow1or wholly turbulent flow2, the laminar sub layer is so thin 1its
thickness decreases with increasing Re2 that the surface roughness completely dominates
the character of the flow near the wall.

When the roughness is considerably less than the viscous sub layer thickness. Such pipes
are called hydraulically smooth

Pressure recovery coefficient, which is the ratio of the static pressure rise across the
diffuser to the inlet dynamic pressure.

The hydraulic diameter defined as is four times the ratio of the cross-sectional flow area
divided by the wetted perimeter,

The governing mechanisms for the flow in multiple pipe systems are the same as for the
single pipe systems

A typical orifice meter is constructed by inserting between two flanges of a pipe a flat
plate with a hole,

Another type of pipe flow meter that is based on the same principles used in the orifice
meter is the nozzle meter,

The most precise and most expensive of the three obstruction-type flow meters is the
Venturi meters

Another quantity-measuring device that is used for gas flow measurements is the bellows
meter
Two dimensional flow between parallel plates,

The object is completely surrounded by the fluid and the flows are termed external flows.

the shear stress 1i.e., viscous effect2 is the product of the fluid viscosity and the velocity
gradient, it follows that viscous effects are confined to the boundary layer and wake
regions

The transition from a laminar boundary layer to a turbulent boundary layer occurs at a
critical value of the Reynolds number, on the order of to

We define the boundary layer thickness, as that distance from the plate at which the fluid
velocity is within some arbitrary value of the upstream velocity.

the boundary layer momentum thickness, is often used when determining the drag on an
object.

the parameter that governs the transition to turbulent flow is the Reynolds number

The variation in the free-stream velocity, the fluid velocity at the edge of the boundary
layer, is the cause of the pressure gradient in this direction.

d‘Alembert‘s paradox—the drag on an object in an inviscid fluid is zero, but the drag on
an object in a fluid with vanishingly small 1but nonzero2 viscosity is not zero.

The decrease in pressure in the direction of flow along the front half of the cylinder is
termed a favorable pressure gradient. The increase in pressure in the direction of flow
along the rear half of the cylinder is termed an adverse pressure gradient.

Friction drag, is that part of the drag that is due directly to the shear stress, on the object.

Pressure drag, is that part of the drag that is due directly to the pressure, p, on an object. It
is often referred to as form drag because of its strong dependency on the shape or form of
the object. Pressure drag is a function of the magnitude of the pressure and the orientation
of the surface element on which the pressure force acts.

Shape Dependence. Clearly the drag coefficient for an object depends on the shape of the
object, with shapes ranging from those that are streamlined to those that are blunt. The
drag on an ellipse with aspect ratio where D and are the thickness and length parallel to
the flow, illustrates this dependence.

Reynolds Number Dependence. Another parameter on which the drag coefficient can be
very dependent is the Reynolds number.

Low Reynolds number flows are governed by a balance between viscous and pressure
forces.

For extremely blunt bodies, like a flat plate perpendicular to the flow, the flow separates
at the edge of the plate regardless of the nature of the boundary layer flow. Thus, the drag
coefficient shows very little dependence on the Reynolds number

If the velocity of the object is sufficiently large, compressibility effects become important
and the drag coefficient becomes a function of the Mach number

Froude Number Effects. Another parameter on which the drag coefficient may be
strongly dependent is the Froude number

Most common lift-generating devices 1 i.e., airfoils, fans, spoilers on cars, etc.2 operate
in the large Reynolds number range in which the flow has a boundary layer character,
with viscous effects confined to the boundary layers and wake region For such cases the
wall shear stress, contributes little to the lift.

For objects operating in very low Reynolds number regimes
viscous effects are
important, and the contribution of the shear stress to the lift may be as important as that
of the pressure

The amount of swirl 1circulation2 needed to have the flow leave the trailing edge
smoothly is a function of the airfoil size and shape

The average pressure is greater on the lower half of the cylinder than on the upper half,
and a lift is generated. This effect is called the Magnus effect,

The drag coefficient is fairly independent of the rate of rotation, the lift coefficient is
strongly dependent on it.

An increase in surface roughness can increase the lift coefficient because the roughness
helps drag more fluid around the sphere increasing the circulation for a given angular
velocity.

For large Reynolds number flows a thin boundary layer forms on the surface.
Fluid machinery, Similarity relations for turbo machines, specific speed

Turbo machines are mechanical devices that either extract energy from a fluid 1turbine2
or add energy to a fluid 1pump2 as a result of dynamic interactions between the device
and the fluid.

Turbo machines are classified as axial-flow, mixed-flow, or radial-flow machines
depending on the predominant direction of the fluid motion relative to the rotor‘s axis as
the fluid passes the blades

One of the most common radial-flow turbo machines is the centrifugal pump. This type
of pump has two main components: an impeller attached to a rotating shaft, and a
stationary casing, housing, or voluteen closing the impeller.

Pump impellers can also be single or double suction.

Pumps can be single or multistage.

Pump performance curves. It is this information that is most helpful to the engineer
responsible for incorporating pumps into a given flow system

Pump characterized by the data of Fig. 12.11, the head curve continuously rises as the
flow rate decreases, and in this case the pump is said to have a rising head curve.

The head developed by the pump at zero discharge is called the shutoff head, and it
represents the rise in pressure head across the pump with the discharge valve closed.

For two identical pumps in parallel, the combined performance curve is obtained by
adding flow rates at the same head


With these so-called pump scaling lawsit is possible to experimentally determine the
performance characteristics of one pump in the laboratory and then use these data to
predict the corresponding characteristics for other pumps within the family under
different operating conditions

Specific speed varies with flow coefficient just as the other coefficients and efficiency

Centrifugal pumps typically are low-capacity, high-head pumps, and therefore have low
specific speeds

Pumps that have low-capacity, high-head characteristics will have specific speeds that are
smaller than pumps that have high-capacity, low-head characteristics.

The concept of specific speed is very useful to engineers and designers, since if the
required head, flow rate, and speed are specified, it is possible to select an appropriate
1most efficient2 type of pump for a particular application

Axial-flow pumps are essentially high-capacity, low-head pumps, and therefore have
large specific speeds compared to centrifugal pumps

Mixed-flow pumps combine features of both radial-flow and axial flow pumps and have
intermediate values of specific speed

Suction Specific Speed is useful in determining the required operating conditions on the
suction side of the pump.

Axial-flow pumps are often called propeller pumps.

Turbo machines used to produce larger changes in gas density and pressure than possible
with fans are called compressors
Classification of turbo machines, impulse turbines, reaction turbines,

Although there are numerous ingenious hydraulic turbine designs, most of these turbines
can be classified into two basic types—impulse turbines and reaction turbines‘ Reaction
is related to the ratio of static pressure drop that occurs across the rotor to static pressure
drop across the turbine stage, with larger rotor pressure drop corresponding to larger
reaction

For hydraulic impulse turbines, the pressure drop across the rotor is zero; the entire
pressure drop across the turbine stage occurs in the nozzle row.

The Pelton wheel shown in Fig. 12.22 is a classical example of an impulse turbine.

Impulse turbines are best suited 1i.e. most efficient2 for lower flow rate and higher head
operations. Reaction turbines, on the other hand, are best suited for higher flow rate and
lower head situations such as are often encountered in hydroelectric power plants
associated with a dammed river

In a reaction turbine the working fluid completely fills the passageways through which it
flows 1unlike an impulse turbine, which contains one or more individual unconfined jets
of fluid2.

Typical radial- and mixed-flow hydraulic turbines are called Francis turbines

At very low heads the most efficient type of turbine is the axial-flow or propeller turbine.

The Kaplan turbine, named after Victor Kaplan, a German professor, is an efficient axialflow hydraulic turbine with adjustable blades.

Pumps and turbines are often thought of as the ―inverse‖ of each other. Pumps add energy
to the fluid; turbines remove energy.

Compressible flow turbo machines are in many ways similar to the incompressible flow
pumps and turbines described in previous portions of this chapter. The main difference is
that the density of the fluid 1a gas or vapor2 changes significantly from the inlet to the
outlet of the compressible flow machines. This added feature has interesting
consequences, benefits, and complications.

Compressors are pumps that add energy to the fluid, causing a significant pressure rise
and a corresponding significant increase in density.

Compressible flow turbines, on the other hand, remove energy from the fluid, causing a
lower pressure and a smaller density at the outlet than at the inlet.

Radial-flow 1or centrifugal2 compressors are essentially centrifugal pumps 1see Section
12.42 that use a gas 1rather than a liquid2 as the working fluid. They are typically high
pressure rise, low flow rate, and axially compact turbo machines.

Higher pressure ratios can be obtained by using multiple stage devices in which flow
from the outlet of the preceding stage proceeds to the inlet of the following stage

The axial-flow compressor is the other widely used configuration. This type of turbo
machine has a lower pressure rise per stage, a higher flow rate, and is more radially
compact than a centrifugal compressor.

Compressible flow turbines may be impulse or reaction turbines, and mixed-, radial-, or
axial-flow turbines.
force on flat surfaces, force on curved surfaces, buoyancy of fluid at rest,
stability of a floating body, chapter 2

The pressure at a point in a fluid at rest, or in motion, is independent of direction as long
as there are no shearing stresses present. This important result is known as Pascal‘s law,

There are two types of forces acting on this element: surface forces due to the pressure,
and a body force equal to the weight of the element.

In general, a fluid with constant density is called an incompressible fluid.

H is called the pressure head and is interpreted as the height of a column of fluid of
specific weight required to give a pressure difference

We normally think of gases such as air, oxygen, and nitrogen as being compressible
fluids since the density of the gas can change significantly with changes in pressure and
temperature.

The pressure at a point within a fluid mass will be designated as either an absolute
pressure or a gage pressure. Absolute pressure is measured relative to a perfect vacuum
1absolute zero pressure2, whereas gage pressure is measured relative to the local
atmospheric pressure.

A negative gage pressure is also referred to as a suction or vacuum pressure

A standard technique for measuring pressure involves the use of liquid columns in
vertical or inclined tubes. Pressure measuring devices based on this technique are called
manometers.

The fluid in the manometer is called the gage fluid.

Capillarity due to surface tension at the various fluid interfaces in the manometer is
usually not considered, since for a simple U-tube with a meniscus in each leg, the
capillary effects cancel

The aneroid barometer is another type of mechanical gage that is used for measuring
atmospheric pressure.

Monitor a pressure that is changing with time. This type of pressure measuring device is
called a pressure transducer,

For fluids at rest we know that the force must be perpendicular to the surface since there
are no shearing stresses present.

The point through which the resultant force acts is called the center of pressure.

The forces represent the components of the force that the tank exerts on the fluid.

The resultant force that the tank exerts on the mass2 must form a concurrent force
system.

When a stationary body is completely submerged in a fluid 1such as the hot air balloon
shown in the figure in the margin2, or floating so that it is only partially submerged, the
resultant fluid force acting on the body is called the buoyant force.

The buoyant force has a magnitude equal to the weight of the fluid displaced by the body
and is directed vertically upward. This result is commonly referred to as Archimedes‘
principle

The buoyant force passes through the centroid of the displaced volume as shown in Fig.
2.24c. The point through which the buoyant force acts is called the center of buoyancy.

A body is said to be in a stable equilibrium position if, when displaced, it returns to its
equilibrium position.

Conversely, it is in an unstable equilibrium position if, when displaced 1even slightly2, it
moves to a new equilibrium position.

Conversely, it is in an unstable equilibrium position if, when displaced 1even slightly2, it
moves to a new equilibrium position.

It is to be noted that as long as the center of gravity falls below the center of buoyancy,
this will always be true; that is, the body is in a stable equilibrium position with respect to
small rotations.

a completely submerged body with its center of gravity above its center of buoyancy is in
an unstable equilibrium position.

For floating bodies the stability problem is more complicated, since as the body rotates
the location of the center of buoyancy
7. Thermodynamics
Basic concepts and definitions,

Conservation of energy principle. It simply states that during an interaction, energy can
change from one form to another but the total amount of energy remains constant

The first law of thermodynamics is simply an expression of the conservation of energy
principle, and it asserts that energy is a thermodynamic property.

The second law of thermodynamics asserts that energy has Quality as well as quantity,
and actual processes occur in the direction of decreasing quality of energy.

Study of thermodynamics that does not require knowledge of the behavior of individual
particles is called classical thermodynamics.

A more elaborate approach, based on the average behavior of large groups of individual
particles, is called statistical thermodynamics.

A closed system (also known as a control mass or just system when the context makes it
clear) consists of a fixed amount of mass, and no mass can cross its boundary.

If, as a special case, even energy is not allowed to cross the boundary, that system is
called an isolated system

An open system, or a control volume, as it is often called, is a properly selected region in
space. It usually encloses a device that involves mass flow such as a compressor, turbine,
or nozzle.

The boundaries of a control volume are called a control surface, and they can be real or
imaginary.

Properties are considered to be either intensive or extensive. Intensive properties are
those that are independent of the mass of a system, such as temperature, pressure, and
density.

Extensive properties are those whose values depend on the size—or extent—of the
system.

Extensive properties per unit mass are called specific properties.

specific gravity, or relative density, and is defined as the ratio of the density of a
substance to the density of some standard substance at a specified temperature

Mechanical equilibrium is related to pressure, and a system is in mechanical equilibrium
if there is no change in pressure at any point of the system with time.

If a system involves two phases, it is in phase equilibrium when the mass of each phase
reaches an equilibrium level and stays there.

Finally, a system is in chemical equilibrium if its chemical composition does not change
with time, that is, no chemical reactions occur.

A system is called a simple compressible system in the absence of electrical, magnetic,
gravitational, motion, and surface tension effects.

Any change that a system undergoes from one equilibrium state to another is called a
process, and the series of states through which a system passes during a process is called
the path of the process

When a process proceeds in such a manner that the system remains infinitesimally close
to an equilibrium state at all times, it is called a quasi-static, or quasi-equilibrium,
process.

An isothermal process, for example, is a process during which the temperature T remains
constant; an isobaric process is a process during which the pressure P remains constant;
and an isochoric (or isometric) process is a process during which the specific volume v
remains constant.

steady-flow process, which can be defined as a process during which a fluid flows
through a control volume steadily

At that point, the heat transfer stops, and the two bodies are said to have reached thermal
equilibrium.

The zeroth law of thermodynamics states that if two bodies are in thermal equilibrium
with a third body, they are also in thermal equilibrium with each other.

In thermodynamics, it is very desirable to have a temperature scale that is independent of
the properties of any substance or substances. Such a temperature scale is called a
thermodynamic temperature scale,

A temperature scale that turns out to be nearly identical to the Kelvin scale is the idealgas temperature scale.

The temperatures on this scale are measured using a constant-volume gas thermometer

The actual pressure at a given position is called the absolute pressure, and it is measured
relative to absolute vacuum

This difference is called the gage pressure. Pgage can be positive or negative, but
pressures below atmospheric pressure are sometimes called vacuum pressures and are
measured by vacuum gages that indicate the difference between the atmospheric pressure
and the absolute pressure.

The pressure applied to a confined fluid increases the pressure throughout by the same
amount. This is called Pascal‘s law

Atmospheric pressure is measured by a device called a barometer; thus, the atmospheric
pressure is often referred to as the barometric pressure.

The unit mmHg is also called the torr in honor of Torricelli.

A device based on this principle is called a manometer, and it is commonly used to
measure small and moderate pressure differences.

Some manometers use a slanted or inclined tube in order to increase the resolution
(precision) when reading the fluid height. Such devices are called inclined manometers.

Another type of commonly used mechanical pressure measurement device is the Bourdon
tube

Modern pressure sensors, called pressure transducers, use various techniques to convert
the pressure effect to an electrical effect such as a change in voltage, resistance, or
capacitance

Strain-gage pressure transducers work by having a diaphragm deflect between two
chambers open to the pressure inputs.

Piezoelectric transducers, also called solid-state pressure transducers, work on the
principle that an electric potential is generated in a crystalline substance when it is
subjected to mechanical pressure.

Another type of mechanical pressure gage called a deadweight tester is used primarily for
calibration and can measure extremely high pressures
Properties of a pure substance

The compressibility factor ,which accounts for the deviation of real gases from ideal-gas
behavior

A substance that has a fixed chemical composition throughout is called a pure substance

The molecules in a solid are arranged in a three-dimensional pattern (lattice) that is
repeated throughout

The molecular spacing in the liquid phase is not much different from that of the solid
phase

In the gas phase, the molecules are far apart from each other, and a molecular order is
nonexistent.

Under these conditions, water exists in the liquid phase, and it is called a compressed
liquid, or a sub cooled liquid, meaning that it is not about to vaporize.

A liquid that is about to vaporize is called a saturated liquid.

A vapor that is about to condense is called a saturated vapor.

A substance at states between 2 and 4 is referred to as a saturated liquid–vapor mixture
since the liquid and vapor phases coexist in equilibrium at these states.

A vapor that is not about to condense (i.e., not a saturated vapor) is called a superheated
vapor.

That is, the temperature at which water starts boiling depends on the pressure; therefore,
if the pressure is fixed, so is the boiling temperature

At a given pressure, the temperature at which a pure substance changes phase is called
the saturation temperature

Likewise, at a given temperature, the pressure at which a pure substance changes phase is
called the saturation pressure

The amount of energy absorbed or released during a phase-change process is called the
latent heat.

More specifically, the amount of energy absorbed during melting is called the latent heat
of fusion and is equivalent to the amount of energy released during freezing.

Similarly, the amount of energy absorbed during vaporization is called the latent heat of
vaporization and is equivalent to the energy released during condensation.

A plot of Tsat versus Psat, such as the one given for water in Fig. 3–11, is called a liquid–
vapor saturation curve

A practical way of cooling leafy vegetables is vacuum cooling, which is based on
reducing the pressure of the sealed cooling chamber to the saturation pressure at the
desired low temperature, and evaporating some water from the products to be cooled.

The vacuum cooling just described becomes vacuum freezing if the vapor pressure in the
vacuum chamber is dropped below 0.61 kPa, the saturation pressure of water at 08C.

Package icing is commonly used in small-scale cooling applications to remove heat and
keep the products cool during transit by taking advantage of the large latent heat of fusion
of water,

This point is called the critical point, and it is defined as the point at which the saturated
liquid and saturated vapor states are identical.

The saturated liquid states in Fig. 3–15 can be connected by a line called the saturated
liquid line

Saturated vapor states in the same figure can be connected by another line, called the
saturated vapor line.

All the compressed liquid states are located in the region to the left of the saturated liquid
line, called the compressed liquid region.

All the superheated vapor states are located to the right of the saturated vapor line, called
the superheated vapor region.

All the states that involve both phases in equilibrium are located under the dome, called
the saturated liquid–vapor mixture region, or the wet region.

On P-vor T-vdiagrams, these triple-phase states form a line called the triple line. The
states on the triple line of a substance have the same pressure and temperature but
different specific volumes. The triple line appears as a point on the P-T diagrams and,
therefore, is often called the triple point.

Passing from the solid phase directly into the vapor phase is called sublimation.

P-T diagram of a pure substance. This diagram is often called the phase diagram since all
three phases are separated from each other by three lines.

For the sake of simplicity and convenience, this combination is defined as a new
property, enthalpy, and given the symbol h:

The quantity hfg is called the enthalpy of vaporization (or latent heat of vaporization). It
represents the amount of energy needed to vaporize a unit mass of saturated liquid at a
given temperature or pressure. It decreases as the temperature or pressure increases and
becomes zero at the critical point.

This is done by defining a new property called the quality xas the ratio of the mass of
vapor to the total mass of the mixture

The properties of the saturated liquid are the same whether it exists alone or in a mixture
with saturated vapor.

Any equation that relates the pressure, temperature, and specific volume of a substance is
called an equation of state.

Gas and vapor are often used as synonymous words. The vapor phase of a substance is
customarily called a gas when it is above the critical temperature. Vapor usually implies a
gas that is not far from a state of condensation.

The molar mass M can simply be defined as the mass of one mole(also called a grammole, abbreviated gmol) of a substance in grams, or the mass of one kmol(also called a
kilogram-mole, abbreviated kgmol) in kilograms.

This deviation from ideal-gas behavior at a given temperature and pressure can accurately
be accounted for by the introduction of a correction factor called the compressibility
factor

The Z factor for all gases is approximately the same at the same reduced pressure and
temperature. This is called the principle of corresponding states.

By curve-fitting all the data, we obtain the generalized compressibility chart that can be
used for all gases

the atmospheric pressure is the sum of the pressure of dry air Pa and the pressure of water
vapor, called the vapor pressure

Air can hold a certain amount of moisture only, and the ratio of the actual amount of
moisture in the air at a given temperature to the maximum amount air can hold at that
temperature is called the relative humidity f. The relative humidity ranges from 0 for dry
air to 100 percent for saturated air(air that cannot hold any more moisture).

In this case, there is no transformation from the liquid phase to the vapor phase, and the
two phases are in phase equilibrium. For liquid water that is open to the atmosphere, the
criterion for phase equilibrium can be expressed as follows: The vapor pressure in the air
must be equal to the saturation pressure of water at the water temperature.

The natural tendency of water to evaporate in order to achieve phase equilibrium with the
water vapor in the surrounding air forms the basis for the operation of the evaporative
coolers (also called the swamp coolers).

Evaporation occurs at the liquid–vapor interface when the vapor pressure is less than the
saturation pressure of the liquid at a given temperature.

Boiling, on the other hand, occurs at the solid–liquid interface when a liquid is brought
into contact with a surface maintained at a temperature Ts sufficiently above the
saturation temperature Tsat of the liquid.
Work and Heat, First law of Thermodynamics,

The macroscopic forms of energy are those a system possesses as a whole with respect to
some outside reference frame, such as kinetic and potential energies

The microscopic forms of energy are those related to the molecular structure of a system
and the degree of the molecular activity, and they are independent of outside reference
frames.

The sum of all the microscopic forms of energy is called the internal energy of a system
and is denoted by U.

Closed systems whose velocity and elevation of the center of gravity remain constant
during a process are frequently referred to as stationary systems.

Internal energy is defined earlier as the sum of all the microscopic forms of energy of a
system. It is related to the molecular structure and the degree of molecular activity,

The portion of the internal energy of a system associated with the kinetic energies of the
molecules is called the sensible energy

The internal energy associated with the phase of a system is called the latent energy.

The internal energy associated with the atomic bonds in a molecule is called chemical
energy.

The tremendous amount of energy associated with the strong bonds within the nucleus of
the atom itself is called nuclear energy

The only two forms of energy interactions associated with a closed system are heat
transfer and work.

In thermodynamics, however, we usually refer to those forms of energy as thermal
energy to prevent any confusion with heat transfer.

Heat is defined as the form of energy that is transferred between two systems (or a system
and its surroundings) by virtue of a temperature

A process during which there is no heat transfer is called an adiabatic process

The caloric theory asserts that heat is a fluid like substance called the caloric that is a
massless, colorless, odorless, and tasteless substance that can be poured from one body
into another

if the energy crossing the boundary of a closed system is not heat, it must be work

work is the energy transfer associated with a force acting through a distance.

Path functions have inexact differentials designated by the symbol d point functions(i.e.,
they depend on the state only, and not on how a system reaches that state)

These microscopic forces are perpendicular to any line in the surface, and the force
generated by these forces per unit length is called the surface tension

the generalized displacement is the total magnetic dipole moment; and electrical
polarization work

The first law of thermodynamics, also known as the conservation of energy principle,
provides a sound basis for studying the relationships among the various forms of energy
and energy interactions

the first law of thermodynamics states that energy can be neither created nor destroyed
during a process; it can only change forms.

For all adiabatic processes between two specified states of a closed system, the net work
done is the same regardless of the nature of the closed system and the details of the
process.

for stationary systems, the changes in kinetic and potential energies are zero

Efficiency of a water heater is defined as the ratio of the energy delivered to the house by
hot water to the energy supplied to the water heater.

heating value of the fuel, which is the amount of heat released when a unit amount of fuel
at room temperature is completely burned and the combustion products are cooled to the
room temperature

The efficiency of space heating systems of residential and commercial buildings is
usually expressed in terms of the annual fuel utilization efficiency

A generator is a device that converts mechanical energy to electrical energy, and the
effectiveness of a generator is characterized by the generator efficiency, which is the ratio
of the electrical power output to the mechanical power input.
Internal energy and enthalpy

the expansion and compression work is often called moving boundary work, or simply
boundary work

During actual expansion and compression processes of gases, pressure and volume are
often related by PV n 5 C, where n and C are constants. A process of this kind is called a
polytropic process

For a closed system undergoing a cycle, the initial and final states are identical

The specific heat is defined as the energy required to raise the temperature of a unit mass
of a substance by one degree

A substance whose specific volume (or density) is constant is called an incompressible
substance.

The specific heats of real gases at low pressures are called ideal-gas specific heats, or
zero-pressure specific heats
Second Law of Thermodynamics, Carnot Cycle

This inadequacy of the first law to identify whether a process can take place is remedied
by introducing another general principle, the second law of thermodynamics.

Irresponsible management of waste energy can significantly increase the temperature of
portions of the environment, causing what is called thermal pollution.

Heat engines and other cyclic devices usually involve a fluid to and from which heat is
transferred while undergoing a cycle. This fluid is called the working fluid

The term heat engine is often used in a broader sense to include work producing devices

The work-producing device that best fits into the definition of a heat engine is the steam
power plant, which is an external-combustion engine

The fraction of the heat input that is converted to net work output is a measure of the
performance of a heat engine and is called the thermal efficiency

The Kelvin–Planck statement can also be expressed as no heat engine can have a thermal
efficiency of 100 percent(Fig. 6–18), or as for a power plant to operate, the working fluid
must exchange heat with the environment as well as the furnace

The efficiency of a refrigerator is expressed in terms of the coefficient of
performance(COP)

Another device that transfers heat from a low-temperature medium to a high temperature
one is the heat pump

The performance of air conditioners and heat pumps is often expressed in terms of the
energy efficiency ratio(EER) or seasonal energy efficiency ratio(SEER)

The Clausius statement is expressed as follows: It is impossible to construct a device that
operates in a cycle and produces no effect other than the transfer of heat from a lowertemperature body to a higher-temperature body.

We have repeatedly stated that a process cannot take place unless it satisfies both the first
and second laws of thermodynamics. Any device that violates either law is called a
perpetual-motion machine

A device that violates the first law of thermodynamics (by creating energy) is called a
perpetual-motion machine of the first kind (PMM1), and a device that violates the second
law of thermodynamics is called a perpetual-motion machine of the second kind(PMM2).

A reversible process is defined as a process that can be reversed without leaving any trace
on the surroundings

The concept of reversible processes leads to the definition of the second law efficiency
for actual processes, which is the degree of approximation to the corresponding reversible
processes.

The factors that cause a process to be irreversible are called irreversibilities.

Friction is a familiar form of irreversibility associated with bodies in motion.

Another example of irreversibility is the unrestrained expansion of a gas separated from a
vacuum by a membrane,

A third form of irreversibility familiar to us all is heat transfer through a finite
temperature difference.

A process is called internally reversible if no irreversibilities occur within the boundaries
of the system during the process.

A process is called externally reversible if no irreversibilities occur outside the system
boundaries during the process.

A process is called totally reversible, or simply reversible, if it involves no
irreversibilities within the system or its surroundings

Probably the best known reversible cycle is the Carnot cycle, first proposed in 1824 by
French engineer Sadi Carnot. The theoretical heat engine that operates on the Carnot
cycle is called the Carnot heat engine. The

Carnot cycle is composed of four reversible processes—two isothermal and two
adiabatic—and it can be executed either in a closed or a steady flow system.

The Carnot heat-engine cycle just described is a totally reversible cycle. Therefore, all the
processes that comprise it can be reversed, in which case it becomes the Carnot
refrigeration cycle.

Two conclusions pertain to the thermal efficiency of reversible and irreversible (i.e.,
actual) heat engines, and they are known as the Carnot principles

A temperature scale that is independent of the properties of the substances that are used
to measure temperature is called a thermodynamic temperature scale.

The thermal efficiency of actual heat engines can be maximized by supplying heat to the
engine at the highest possible temperature(limited by material strength) and rejecting heat
from the engine at the lowest possible temperature(limited by the temperature of the
cooling medium such as rivers, lakes, or the atmosphere).

more of the high-temperature thermal energy can be converted to work. Therefore, the
higher the temperature, the higher the quality of the energy

A refrigerator or a heat pump that operates on the reversed Carnot cycle is called a Carnot
refrigerator, or a Carnot heat pump.
Entropy

The second law leads to the definition of a new property called entropy

Unlike energy, entropy is a non-conserved property, and there is no such thing as
conservation of entropy.

On the basis of the Kelvin–Planck statement of the second law, which states that no
system can produce a net amount of work while operating in a cycle and exchanging heat
with a single thermal energy reservoir,

the equality in the Clausius inequality holds for totally or just internally reversible cycles
and the inequality for the irreversible ones

The entropy of an isolated system during a process always increases or, in the limiting
case of a reversible process, remains constant. In other words, it never decreases. This is
known as the increase of entropy principle.

The increase of entropy principle dictates that the entropy of an isolated system increases
until the entropy of the system reaches a maximum value.

Entropy generation is a measure of the magnitudes of the irreversibilities present during
that process.

A process during which the entropy remains constant is called an isentropic process.

It should be recognized that a reversible adiabatic process is necessarily isentropic but an
isentropic process is not necessarily a reversible adiabatic process.

The term isentropic process is customarily used in thermodynamics to imply an internally
reversible, adiabatic process.

Entropy can be viewed as a measure of molecular disorder, or molecular randomness.

The entropy of a pure crystalline substance at absolute zero temperature is zero since
there is no uncertainty about the state of the molecules at that instant (Fig. 7–21). This
statement is known as the third law of thermodynamics.

The third law of thermodynamics provides an absolute reference point for the
determination of entropy. The entropy determined relative to this point is called absolute
entropy,

There is no entropy transfer associated with energy transfer as work.

The quantity of energy is always preserved during an actual process (the first law), but
the quality is bound to decrease (the second law).

Liquids and solids can be approximated as incompressible substances since their specific
volumes remain nearly constant during a process.

Bernoulli equation in fluid mechanics. It is developed for an internally reversible process
and thus is applicable to incompressible fluids that involve no irreversibilities such as
friction or shock waves

The larger the specific volume, the larger the reversible work produced or consumed by
the steady-flow device

An isentropic process (involves no cooling), a polytropic process(involves some cooling),
and an isothermal process(involves maximum cooling).

To minimize compression work during two-stage compression, the pressure ratio across
each stage of the compressor must be the same.

the isentropic or adiabatic efficiency, which is a measure of the deviation of actual
processes from the corresponding idealized ones

isentropic efficiency of a turbine is defined as the ratio of the actual work output of the
turbine to the work output that would be achieved if the process between the inlet state
and the exit pressure were isentropic

The isentropic efficiency of a compressor is defined as the ratio of the work input
required to raise the pressure of a gas to a specified value in an isentropic manner to the
actual work input

A realistic model process for compressors that are intentionally cooled during the
compression process is the reversible isothermal process.

The isentropic efficiency of a nozzle is defined as the ratio of the actual kinetic energy of
the fluid at the nozzle exit to the kinetic energy value at the exit of an isentropic nozzle
for the same inlet state and exit pressure.

The property entropy is a measure of molecular disorder or randomness of a system, and
the second law of thermodynamics states that entropy can be created but it cannot be
destroyed.

The entropy balance relation above can be stated as: the entropy change of a system
during a process is equal to the net entropy transfer through the system boundary and the
entropy generated within the system.

The only form of entropy interaction associated with a fixed mass or closed system is
heat transfer, and thus the entropy transfer for an adiabatic closed system is zero.

that work is entropy-free, and no entropy is transferred by work

An energy interaction that is accompanied by entropy transfer is heat transfer, and an
energy interaction that is not accompanied by entropy transfer is work.

only energy is exchanged during work interaction whereas both energy and entropy are
exchanged during heat transfer

For a reversible process(a process that involves no irreversibilities), the entropy
generation is zero and thus the entropy change of a system is equal to the entropy
transfer.

Energy change of a system during a process is equal to the energy transfer during that
process.

Entropy change of a system equals the entropy transfer only for a reversible process.

A closed system involves no mass flow across its boundaries, and its entropy change is
simply the difference between the initial and final entropies of the system.

The entropy change of a closed system is due to the entropy transfer accompanying heat
transfer and the entropy generation within the system boundaries.

The entropy change of a closed system during a process is equal to the sum of the net
entropy transferred through the system boundary by heat transfer and the entropy
generated within the system boundaries.
Irreversibility and availability

Exergy (also called availability), which is the maximum useful work that could be
obtained from the system at a given state in a specified environment, and we continue
with the reversible work, which is the maximum useful work that can be obtained as a
system undergoes a process between two specified states. Next we discuss the
irreversibility (also called the exergy destruction or lost work), which is the wasted work
potential during a process as a result of irreversibilities, and we define a second-law
efficiency.

it would be very desirable to have a property to enable us to determine the useful work
potential of a given amount of energy at some specified state. This property is exergy,
which is also called the availability or available energy

A system is said to be in the dead state when it is in thermodynamic equilibrium with the
environment it is in

The immediate surroundings refer to the portion of the surroundings that is affected by
the process, and environment refers to the region beyond the immediate surroundings
whose properties are not affected by the process at any point.

a system delivers the maximum possible work as it undergoes a reversible process from
the specified initial state to the state of its environment, that is, the dead state. This
represents the useful work potential of the system at the specified state and is called
exergy.

It represents the upper limit on the amount of work a device can deliver without violating
any thermodynamic laws.

exergy is a property of the system–environment combination and not of the system alone.

The work potential or exergy of the kinetic energy of a system is equal to the kinetic
energy itself regardless of the temperature and pressure of the environment.

This is because when evaluating exergy, the final state is always assumed to be the dead
state, which is hardly ever the case for actual engineering systems.

surroundings work, which is the work done by or against the surroundings during a
process

The difference between the actual work Wand the surroundings work Wsurr is called the
useful work

Reversible work Wrev is defined as the maximum amount of useful work that can be
produced (or the minimum work that needs to be supplied) as a system undergoes a
process between the specified initial and final states.

Any difference between the reversible work Wrev and the useful work Wu is due to the
irreversibilities present during the process, and this difference is called irreversibility

thermal efficiency and the coefficient of performance for devices as a measure of their
performance

second-law efficiency hII as the ratio of the actual thermal efficiency to the maximum
possible (reversible) thermal efficiency under the same conditions

For a refrigerator or heat pump, the exergy expended is the work input since the work
supplied to a cyclic device is entirely consumed.

In the case of electric resistance heating, the exergy expended is the electrical energy the
resistance heater consumes from the resource of electric grid.

The property exergy is the work potential of a system in a specified environment and
represents the maximum amount of useful work that can be obtained as the system is
brought to equilibrium with the environment.

The exergy of a closed system is either positive or zero. It is never negative.

we are about to establish an alternative statement of the second law of thermodynamics,
called the decrease of exergy principle, which is the counterpart of the increase of
entropy principle.

This equation can be expressed as the exergy of an isolated system during a process
always decreases or, in the limiting case of a reversible process, remains constant.In other
words, it never increases and exergy is destroyed during an actual process. This is known
as the decrease of exergy principle.

The exergy destroyed is proportional to the entropy generated

the exergy change of a system during a process is less than the exergy transfer by an
amount equal to the exergy destroyed during the process within the system boundaries

This relation is referred to as the exergy balance and can be stated as the exergy change
of a system during a process is equal to the difference between the net exergy transfer
through the system boundary and the exergy destroyed within the system boundaries as a
result of irreversibilities.

For a reversible process, the entropy generation and thus the exergy destruction are zero,

The energy changeof a system equals the energy transferfor any process, but the exergy
change of a system equals the exergy transfer only for a reversible process.

The quantity of energy is always preserved during an actual process (the first law), but
the quality is bound to decrease (the second law)
Vapor power and refrigeration cycles,

power generation coupled with process heating called cogeneration

The cycle that results is the Rankine cycle, which is the ideal cycle for vapor power
plants.

The boiler, together with the section where the steam is superheated (the super heater), is
often called the steam generator.

Fluid friction causes pressure drops in the boiler, the condenser, and the piping between
various components.

The other major source of irreversibility is the heat loss from the steam to the
surroundings as the steam flows through various components.

Increase the average temperature at which heat is transferred to the working fluid in the
boiler, or decrease the average temperature at which heat is rejected from the working
fluid in the condenser.

Possibility is to transfer heat to the feed water from the expanding steam in a counter
flow heat exchanger built into the turbine, that is, to use regeneration.

The device where the feed water is heated by regeneration is called a regenerator, or a
feed water heater (FWH).

An open(or direct-contact) feed water heater is basically a mixing chamber, where the
steam extracted from the turbine mixes with the feed water exiting the pump.

The condensed steam is then either pumped to the feed water line or routed to another
heater or to the condenser through a device called a trap. A trap allows the liquid to be
throttled to a lower pressure region but traps the vapor.

The ideal Carnot cycle is a totally reversible cycle, and thus it does not involve any
irreversibilities.

In general, cogeneration is the production of more than one useful form of energy (such
as process heat and electric power) from the same energy source.

all the energy transferred to the steam in the boiler is utilized as either process heat or
electric power. Thus it is appropriate to define a utilization factor

A more popular modification involves a gas power cycle topping a vapor power cycle,
which is called the combined gas–vapor cycle, or just the combined cycle.

The cooling capacity of a refrigeration system—that is, the rate of heat removal from the
refrigerated space—is often expressed in terms of tons of refrigeration.

The result is a cycle that operates in the counterclockwise direction on a T-s diagram,
which is called the reversed Carnot cycle. A refrigerator or heat pump that operates on
the reversed Carnot cycle is called a Carnot refrigerator or a Carnot heat pump

Many of the impracticalities associated with the reversed Carnot cycle can be eliminated
by vaporizing the refrigerant completely before it is compressed and by replacing the
turbine with a throttling device, such as an expansion valve or capillary tube. The cycle
that results is called the ideal vapor-compression refrigeration cycle,

In the ideal cycle, the refrigerant leaves the evaporator and enters the compressor as
saturated vapor.

The compression process in the ideal cycle is internally reversible and adiabatic, and thus
isentropic.

In the ideal case, the refrigerant is assumed to leave the condenser as saturated liquid at
the compressor exit pressure.

If no single refrigerant can meet the temperature requirements, then two or more
refrigeration cycles with different refrigerants can be used in series. Such a refrigeration
system is called a cascade system

The major problem with air-source systems is frosting, which occurs in humid climates
when the temperature falls below 2 to 58C.

One way of dealing with such situations is to perform the refrigeration process in stages,
that is, to have two or more refrigeration cycles that operate in series. Such refrigeration
cycles are called cascade refrigeration cycles

When the fluid used throughout the cascade refrigeration system is the same, the heat
exchanger between the stages can be replaced by a mixing chamber (called a flash
chamber) since it has better heat transfer characteristics. Such systems are called
multistage compression refrigeration systems.

We discuss the reversed Brayton cycle, better known as the gas refrigeration cycle.

Another form of refrigeration that becomes economically attractive when there is a
source of inexpensive thermal energy at a temperature of 100 to 2008C is absorption
refrigeration.
Air standard Power and refrigeration cycles.

Thermodynamic cycles can be divided into two general categories: power cycles, which
are discussed in this chapter and Chap. 10, and refrigeration cycles

The devices or systems used to produce a net power output are often called engines, and
the thermodynamic cycles they operate on are called power cycles

Thermodynamic cycles can also be categorized as gas cycles and vapor cycles, depending
on the phase of the working fluid.

Heat engines are categorized as internal combustion and external combustion engines,
depending on how the heat is supplied to the working fluid.

When the actual cycle is stripped of all the internal irreversibilities and complexities, we
end up with a cycle that resembles the actual cycle closely but is made up totally of
internally reversible processes. Such a cycle is called an ideal cycle

Any modification that increases the ratio of these two areas will also increase the thermal
efficiency of the cycle

Thermal efficiency increases with an increase in the average temperature at which heat is
supplied to the system or with a decrease in the average temperature at which heat is
rejected from the system.

Another assumption that is often utilized to simplify the analysis even more is that air has
constant specific heats whose values are determined at room temperature (258C, or
778F). When this assumption is utilized, the air-standard assumptions are called the coldair-standard assumptions. A cycle for which the air-standard assumptions are applicable
is frequently referred to as an air-standard cycle.

The minimum volume formed in the cylinder when the piston is at TDC is called the
clearance volume

The volume displaced by the piston as it moves between TDC and BDC is called the
displacement volume

The ratio of the maximum volume formed in the cylinder to the minimum (clearance)
volume is called the compression ratio.

Term frequently used in conjunction with reciprocating engines is the mean effective
pressure(MEP).

Reciprocating engines are classified as spark-ignition (SI) engines or compressionignition (CI) engines, depending on how the combustion process in the cylinder is
initiated

Towards the end of expansion stroke, the exhaust valve opens and the combustion gases
that are above the atmospheric pressure rush out of the cylinder through the open exhaust
valve. This process is called exhaust blow down

In two-stroke engines, all four functions described above are executed in just two strokes:
the power stroke and the compression stroke.

This premature ignition of the fuel, called auto ignition, produces an audible noise, which
is called engine knock.

In spark-ignition engines (also known as gasoline engines), the air–fuel mixture is
compressed to a temperature that is below the auto ignition temperature of the fuel, and
the combustion process is initiated by firing a spark plug.

In CI engines (also known as diesel engines), the air is compressed to a temperature that
is above the auto ignition temperature of the fuel, and combustion starts on contact as the
fuel is injected into this hot air.

We now define a new quantity, the cutoff ratio rc,as the ratio of the cylinder volumes
after and before the combustion process

The ideal cycle based on this concept is called the dual cycle

There are two other cycles that involve an isothermal heat-addition process at THand an
isothermal heat-rejection process at TL:the Stirling cycle and the Ericsson cycle. They
differ from the Carnot cycle in that the two isentropic processes are replaced by two
constant-volume regeneration processes in the Stirling cycle and by two constantpressure regeneration processes in the Ericsson cycle. Both cycles utilize regeneration, a
process during which heat is transferred to a thermal energy storage device (called a
regenerator) during one part of the cycle and is transferred back to the working fluid
during another part of the cycle

The Ericsson cycle is very much like the Stirling cycle, except that the two constantvolume processes are replaced by two constant-pressure processes.

The ideal cycle that the working fluid undergoes in this closed loop is the Brayton cycle,
which is made up of four internally reversible processes:

In gas-turbine power plants, the ratio of the compressor work to the turbine work, called
the back work ratio, is very high

the high-pressure air leaving the compressor can be heated by transferring heat to it from
the hot exhaust gases in a counter-flow heat exchanger, which is also known as a
regenerator or a recuperator.

The extent to which a regenerator approaches an ideal regenerator is called the
effectiveness

The work required to compress a gas between two specified pressures can be decreased
by carrying out the compression process in stages and cooling the gas in between (Fig. 9–
42)—that is, using multistage compression with intercooling.

The work output of a turbine operating between two pressure levels can be increased by
expanding the gas in stages and reheating it in between—that is, utilizing multistage
expansion with reheating.

The steady-flow compression or expansion work is proportional to the specific volume of
the fluid. Therefore, the specific volume of the working fluid should be as low as possible
during a compression process and as high as possible during an expansion process.

A ram jet engine is a properly shaped duct with no compressor or turbine,

A scram jet engine is essentially a ramjet in which air flows through at supersonic speeds
(above the speed of sound).

A rocket is a device where a solid or liquid fuel and an oxidizer react in the combustion
chamber.
Thermodynamic relations

the constant-pressure specific heat is always greater than or equal to the constant-volume
specific heat

The line that passes through these points is called the inversion line, and the temperature
at a point where a constant-enthalpy line intersects the inversion line is called the
inversion temperature. The temperature at the intersection of the P 50 line (ordinate) and
the upper part of the inversion line is called the maximum inversion temperature.

The difference between hand h* is called the enthalpy departure, and it represents the
variation of the enthalpy of a gas with pressure at a fixed temperature.

The difference T,P is called the entropy departure and Zs is called the entropy departure
factor.
Ideal gas mixtures

There are two ways to describe the composition of a mixture: either by specifying the
number of moles of each component, called molar analysis, or by specifying the mass of
each component, called gravimetric analysis.

The ratio of the mass of a component to the mass of the mixture is called the mass
fraction mf, and the ratio of the mole number of a component to the mole number of the
mixture is called the mole fraction

Amagat‘s law of additive volumes: The volume of a gas mixture is equal to the sum of
the volumes each gas would occupy if it existed alone at the mixture temperature and
pressure

Kay‘s rule, involves the use of a pseudocritical pressure P99 cr,m and pseudo critical
temperature

a characteristic approach for determining the intensive properties of a mixture. The
internal energy, enthalpy, and entropy of a mixture per unit mass or per unit mole of the
mixture

Chemical potential, which is the change in the Gibbs function of the mixture in a
specified phase when a unit amount of component in the same phase, is added as
pressure, temperature, and the amounts of all other components are held constant. The
symbol tilde (as in v) is used to denote the partial molar properties of the components.

When the effect of dissimilar molecules in a mixture on each other is negligible, the
mixture is said to be an ideal mixture or ideal solution and the chemical potential of a
component in such a mixture equals the Gibbs function of the pure component.

osmotic rise, which represents the vertical distance the saline water would rise when
separated from the fresh water by a membrane that is permeable to water molecules alone
(again at equilibrium).
Gas and vapor mixtures.

At temperatures below the critical temperature, the gas phase of a substance is frequently
referred to as a vapor. The term vapor implies a gaseous state that is close to the
saturation region of the substance, raising the possibility of condensation during a
process.

Air is a mixture of nitrogen, oxygen, and small amounts of some other gases. Air in the
atmosphere normally contains some water vapor (or moisture) and is referred to as
atmospheric air. By contrast, air that contains no water vapor is called dry air.

The partial pressure of water vapor is usually referred to as the vapor pressure.

The enthalpy of water vapor in air can be taken to be equal to the enthalpy of saturated
vapor at the same temperature.

The most logical way is to specify directly the mass of water vapor present in a unit mass
of dry air. This is called absolute or specific humidity

As more vapor or moisture is added, the specific humidity will keep increasing until the
air can hold no more moisture. At this point, the air is said to be saturated with moisture,
and it is called saturated air.

the comfort level depends more on the amount of moisture the air holds (mv) relative to
the maximum amount of moisture the air can hold at the same temperature (mg). The
ratio of these two quantities is called the relative humidity

the ordinary temperature of atmospheric air is frequently referred to as the dry-bulb
temperature

The dew-point temperature Tdp is defined as the temperature at which condensation
begins when the air is cooled at constant pressure.

A more practical approach is to use a thermometer whose bulb is covered with a cotton
wick saturated with water and to blow air over the wick, as shown in Fig. 14 –12. The
temperature measured in this manner is called the wet-bulb temperature

The wet-bulb temperature can also be measured by placing the wet-wicked thermometer
in a holder attached to a handle and rotating the holder rapidly, that is, by moving the
thermometer instead of the air. A device that works on this principle is called a sling
psychrometer

A wet cooling tower is essentially a semi enclosed evaporative cooler
Chemical reactions

A chemical reaction during which a fuel is oxidized and a large quantity of energy is
released is called combustion.

The fuel must be brought above its ignition temperature to start the combustion

As you may recall from your chemistry courses, chemical equations are balanced on the
basis of the conservation of mass principle(or the mass balance)

The minimum amount of air needed for the complete combustion of a fuel is called the
stoichiometric or theoretical air.

The amount of air in excess of the stoichiometric amount is called excess air.

The amount of air used in combustion processes is also expressed in terms of the
equivalence ratio, which is the ratio of the actual fuel–air ratio to the stoichiometric fuel–
air ratio

A commonly used device to analyze the composition of combustion gases is the Orsat gas
analyzer.

the molecules of a system possess energy in various forms such as sensible and latent
energy(associated with a change of state), chemical energy(associated with the molecular
structure), and nuclear energy(associated with the atomic structure)

The chosen reference state is 258C (778F) and 1 atm, which is known as the standard
reference state.

enthalpy of reaction hR, which is defined as the difference between the enthalpy of the
products at a specified state and the enthalpy of the reactants at the same state for a
complete reaction

Enthalpy of formation h#f ,which can be viewed as the enthalpy of a substance at a
specified state due to its chemical composition.

Heating value of the fuel, which is defined as the amount of heat released when a fuel is
burned completely in a steady-flow process and the products are returned to the state of
the reactants.

The heating value is called the higher heating value(HHV) when the H2O in the products
is in the liquid form, and it is called the lower heating value(LHV) when the H2O in the
products is in the vapor form

In the limiting case of no heat loss to the surroundings (Q 50), the temperature of the
products reaches a maximum, which is called the adiabatic flame or adiabatic combustion
temperature of the reaction

the adiabatic flame temperature attains its maximum value when complete combustion
occurs with the theoretical amount of air

The entropy of a pure crystalline substance at absolute zero temperature is zero.

Reversible work Wrev represents the maximum work that can be done during a process.
Chemical equilibrium.

A system is said to be in equilibrium if no changes occur within the system when it is
isolated from its surroundings.

An isolated system is in mechanical equilibrium if no changes occur in pressure, in
thermal equilibrium if no changes occur in temperature, in phase equilibrium if no
transformations occur from one phase to another, and in chemical equilibrium if no
changes occur in the chemical composition of the system.

This equation involves the stoichiometric coefficients and the molar Gibbs functions of
the reactants and the products, and it is known as the criterion for chemical equilibrium.

Free electrons in the equilibrium composition can be treated as an ideal gas.

Equilibrium calculations provide information on the equilibrium composition of a
reaction, not on the reaction rate

The number of KP relations needed to determine the equilibrium composition of a
reacting mixture is equal to the number of chemical species minus the number of
elements present in equilibrium.

There is no transformation from the liquid phase to the vapor phase, and the two phases
are in phase equilibrium. The conditions of phase equilibrium change, however, if the
temperature or the pressure is changed.

The two phases of a pure substance are in equilibrium when each phase has the same
value of specific Gibbs function.

The solubility represents the maximum amount of solid that can be dissolved in a liquid
at a specified temperature

An approximate relation in this case for the mole fractions of a species on the liquid and
gas sides of the interface is given by Raoult‘s law
8. Heat and Mass Transfer:
Conduction, heat equation, Fourier’s law

The modern view is to ascribe the energy transfer to lattice waves induced by atomic
motion.

For heat conduction, the rate equation is known as Fourier‘s law

The convection heat transfer mode is comprised of two mechanisms. In addition to
energy transfer due to random molecular motion(diffusion), energy is also transferred by
the bulk, or macroscopic, motion of the fluid.

It is customary to use the term convection when referring to this cumulative transport and
the term advection when referring to transport due to bulk fluid motion.

A consequence of the fluid–surface interaction is the development of a region in the fluid
through which the velocity varies from zero at the surface to a finite value u associated
with the flow. This region of the fluid is known as the hydrodynamic, or velocity,
boundary layer.

Moreover, if the surface and flow temperatures differ, there will be a region of the fluid
through which the temperature varies from at to in the outer flow. This region, called
the thermal boundary layer

Forced convection when the flow is caused by external means, such as by a fan, a pump,
or atmospheric winds

for free(or natural) convection the flow is induced by buoyancy forces, which are due to
density differences caused by temperature variations in the fluid.

The energy that is being transferred is the sensible, or internal thermal, energy of the
fluid.

Thermal radiation is energy emitted by matter that is at a nonzero temperature

Radiation may also be incident on a surface from its surroundings.

A portion, or all, of the irradiation may be absorbed by the surface, thereby increasing the
thermal energy of the material.

If the surface is semitransparent, portions of the irradiation may also be transmitted.

For many heat transfer problems, the first law of thermodynamics (the law of
conservation of energy) provides a useful, often essential, tool

The first law can also be applied to a control volume (or open system), a region of space
bounded by a control surface through which mass may pass.

The first law of thermodynamics addresses total energy

If the inflow and generation equal the outflow, a steady-state condition must prevail such
that there will be no change in the amount of thermal and mechanical energy stored in the
control volume

The internal energy consists of a sensible component, which accounts for the
translational, rotational, and/or vibrational motion of the atoms/molecules comprising the
matter; a latent component, which relates to intermolecular forces influencing phase
change between solid, liquid, and vapor states; a chemical component, which accounts
for energy stored in the chemical bonds between atoms; and a nuclear component, which
accounts for the binding forces in the nucleus

If the material in the control volume changes from solid to liquid (melting) or from liquid
to vapor (vaporization, evaporation, boiling), the latent energy increases. Conversely, if
the phase change is from vapor to liquid (condensation) or from liquid to solid
(solidification, freezing), the latent energy decreases.

The energy generation term is associated with conversion from some other form of
internal energy (chemical, electrical, electromagnetic, or nuclear) to thermal energy. It is
a volumetric phenomenon.

The inflow and outflow terms are surface phenomena.

The first contribution, termed flow work, is associated with work done by pressure forces
moving fluid through the boundary

For a unit mass, the amount of work is equivalent to the product of the pressure and the
specific volume of the fluid

If the fluid is an incompressible liquid, its specific heats at constant pressure and volume
are equal

Viscous dissipation is the conversion from mechanical energy to thermal energy

To use Fourier‘s law, the thermal conductivity of the material must be known. This
property, which is referred to as a transport property, provides an indication of the rate at
which energy is transferred by the diffusion process.

When viewed as a particle-like phenomenon, the lattice vibration quanta are termed
phonons.

The thermal conductivity increases as the mean free path of the energy carriers (electrons
or phonons) is increased.

When these spaces are sealed from each other, the system is referred to as a cellular
insulation.
one dimensional steady state heat conduction through plane and composite
walls, cylinders and spheres with and without heat generating sources critical
thickness of insulation, heat transfer through extended surfaces

Steady-state conduction in a plane wall with no heat generation, the heat flux is a
constant, independent of x.

The term extended surface is commonly used to depict an important special case
involving heat transfer by conduction within a solid and heat transfer by convection
(and/or radiation) from the boundaries of the solid.

A straight fin is any extended surface that is attached to a plane wall.

An annular fin is one that is circumferentially attached to a cylinder, and its cross section
varies with radius from the wall of the cylinder.

In contrast a pin fin, or spine, is an extended surface of circular cross section.

Fin effectiveness. It is defined as the ratio of the fin heat transfer rate to the heat transfer
rate that would exist without the fin.

a straight triangular fin is attractive because, for equivalent heat transfer, it requires much
less volume (fin material) than a rectangular profile.
Transient conduction, lumped capacitance method.

The essence of the lumped capacitance method is the assumption that the temperature of
the solid is spatially uniform at any instant during the transient process

The resistance to conduction within the solid is much less than the resistance to
convection across the fluid boundary layer.

Periodic heating is used in various applications, such as thermal processing of materials
using pulsed lasers, and occurs naturally in situations such as those involving the
collection of solar energy
Convection, Newton’s law of cooling, boundary layer, natural (free) and forced
convection heat transfer. coefficient of heat transfer for free and forced
convection, effects of laminar, transition and turbulent flow on coefficient of
heat transfer,

The term convection to describe energy transfer between a surface and a fluid moving
over the surface.

The boundary layer velocity profile refers to the manner in which u varies with y through
the boundary layer

The velocity boundary layer. It develops whenever there is fluid flow over a surface, and
it is of fundamental importance to problems involving convection transport.

Assuming a Newtonian fluid, the surface shear stress may be evaluated from knowledge
of the velocity gradient at the surface

In a velocity boundary layer, the velocity gradient at the surface depends on the distance
x from the leading edge of the plate.

Just as a velocity boundary layer develops when there is fluid flow over a surface, a
thermal boundary layer must develop if the fluid free stream and surface temperatures
differ.

At the leading edge the temperature profile is uniform

be a vapor that is transferred into a gas stream (species B) due to evaporation at a liquid
surface (as in the water example) or due to sublimation at a solid surface

A concentration boundary layer will develop that is similar to the velocity and thermal
boundary layers.

The molar flux associated with species transfer by diffusion is determined by an
expression that is analogous to Fourier‘s law.

The problem is not a simple one, for in addition to depending on numerous fluid
properties such as density, viscosity, thermal conductivity, and specific heat, the
coefficients depend on the surface geometry and the flow conditions.

We may speak of a viscous sub layer in which transport is dominated by diffusion and the
velocity profile is nearly linear.

There is an adjoining buffer layer in which diffusion and turbulent mixing are
comparable, and there is a turbulent zone in which transport is dominated by turbulent
mixing.

The transition from laminar to turbulent flow is ultimately due to triggering mechanisms,
such as the interaction of unsteady flow structures that develop naturally within the fluid
or small disturbances that exist within many typical boundary layers.

The onset of turbulence depends on whether the triggering mechanisms are amplified or
attenuated in the direction of fluid flow, which in turn depends on a dimensionless
grouping of parameters called the Reynolds number,

Three very important dimensionless similarity parameters are introduced in Table 6.1.
They are the Reynolds number, ReL ; Prandtl number, Pr; and Schmidt number, Sc.

Reynolds number, ReL (Equation 6.41), which may be interpreted as the ratio of inertia
to viscous forces in a region of characteristic dimension L.

The Prandtl number provides a measure of the relative effectiveness of momentum and
energy transport by diffusion in the velocity and thermal boundary layers, respectively

Similarly, the Schmidt number, which is defined by Equation 6.43, provides a measure of
the relative effectiveness of momentum and mass transport by diffusion in the velocity
and concentration boundary layers, respectively.

the Grash of number provides a measure of the ratio of buoyancy forces to viscous forces
in the velocity

The Eckert number provides a measure of the kinetic energy of the flow relative to the
enthalpy difference across the thermal boundary layer

Accordingly, heat and mass transfer relations for a particular geometry are
interchangeable.

An important application of the heat and mass transfer analogy is to the process of
evaporative cooling, which occurs when a gas flows over a liquid

Evaporation occurs from the liquid surface, and the energy associated with the phase
change is the latent heat of vaporization of the liquid.

The Reynolds analogy and it relates the key engineering parameters of the velocity,
thermal, and concentration boundary layers.
Flow over flat plates,

the pressure decreases with increasing x, the streamline coordinate, and the boundary
layer develops under the influence of a favorable pressure gradient

the pressure must eventually reach a minimum, and toward the rear of the cylinder further
boundary layer development occurs in the presence of an adverse pressure gradient

The separation point, fluid near the surface lacks sufficient momentum to overcome the
pressure gradient, and continued downstream movement is impossible. Since the
oncoming fluid also precludes flow back upstream, boundary layer separation must
occur. This is a condition for which the boundary layer detaches from the surface, and a
wake is formed in the downstream region.

The occurrence of boundary layer transition, which depends on the Reynolds number,
strongly influences the position of the separation point.

In the limit of very small Reynolds numbers (creeping flow), the coefficient is inversely
proportional to the Reynolds number and the specific relation is termed Stokes‘ law

The Reynolds number ReD,max for the foregoing correlations is based on the maximum
fluid velocity occurring within the tube bank

Within the stagnation or impingement zone, flow is influenced by the target surface and
is decelerated and accelerated in the normal (z) and transverse (ror x) directions,
respectively

The overall rate of heat (mass) transfer depends strongly on the manner in which spent
gas, whose temperature (species concentration) is between values associated with the
nozzle exit and the impingement surface, is vented from the system.

The term packed bed refers to a condition for which the position of the particles is fixed.
In contrast, a fluidized bed is one for which the particles are in motion due to advection
with the fluid.
Heat transfer for flow through pipes and ducts,

An external flow is one for which boundary layer development on a surface is allowed to
continue without external constraints,

An internal flow, such as flow in a pipe, is one for which the fluid is confined by a
surface.

Viscous effects extend over the entire cross section and the velocity profile no longer
changes with increasing x. The flow is then said to be fully developed, and the distance
from the entrance at which this condition is achieved is termed the hydrodynamic entry
length,

The fully developed velocity profile is parabolic for laminar flow in a circular tube. For
turbulent flow, the profile is flatter due to turbulent mixing in the radial direction.

The form of the velocity profile may readily be determined for the laminar flow of an
incompressible, constant property fluid in the fully developed region of a circular tube

If fluid enters the tube of Figure 8.4 at a uniform temperature T(r, 0) that is less than the
surface temperature, convection heat transfer occurs and a thermal boundary layer begins
to develop.

Moreover, if the tube surface condition is fixed by imposing either a uniform temperature
(Ts is constant) or a uniform heat flux (is constant), a thermally fully developed condition
is eventually reached.

Just as the absence of a free stream velocity requires use of a mean velocity to describe
an internal flow, the absence of a fixed free stream temperature necessitates using a
mean(or bulk) temperature.

in the thermally fully developed flow of a fluid with constant properties, the local
convection coefficient is a constant, independent of x

The problem of heat transfer in laminar flow of an incompressible, constant property
fluid in the fully developed region of a circular tube is treated theoretically.

Hence in a circular tube characterized by uniform surface heat flux and laminar, fully
developed conditions, the Nusselt number is a constant, independent of ReD, Pr, and
axial location.

For laminar, fully developed conditions with a constant surface temperature, the
assumption of negligible axial conduction is often reasonable.

Such a situation would exist if the location at which heat transfer begins were preceded
by an unheated starting length.

In contrast, the combined (thermal and velocity) entry length problem corresponds to the
case for which the temperature and velocity profiles develop simultaneously.

A classical expression for computing the local Nusselt number for fully developed
(hydrodynamically and thermally) turbulent flow in a smooth circular tube

To a good approximation, the foregoing correlations may be applied for both the uniform
surface temperature and heat flux conditions.

Correlations for the peripherally averaged Nusselt number are of little use if constant heat
flux conditions are applied.
Boiling, condensation.

We consider processes that can occur at a solid–liquid or solid–vapor interface, namely,
boiling and condensation.

After expansion in a turbine, the vapor is restored to its liquid state in a condenser,

Evaporators, in which the boiling process occurs, and condensers are also essential
components in vapor-compression refrigeration cycles.

The Jakob number is the ratio of the maximum sensible energy absorbed by the liquid
(vapor) to the latent energy absorbed by the liquid (vapor) during condensation (boiling).

The Bond number is the ratio of the buoyancy force to the surface tension force.

When evaporation occurs at a solid–liquid interface, it is termed boiling.

in pool boiling the liquid is quiescent and its motion near the surface is due to free
convection and to mixing induced by bubble growth and detachment.

In contrast, for forced convection boiling, fluid motion is induced by external means, as
well as by free convection and bubble-induced mixing.

Boiling may also be classified according to whether it is sub cooled or saturated.

In sub cooled boiling, the temperature of the liquid is below the saturation temperature
and bubbles formed at the surface may condense in the liquid.

In contrast, the temperature of the liquid slightly exceeds the saturation temperature in
saturated boiling

Transition Boiling is termed transition boiling, unstable film boiling, or partial film
boiling.

Film Boiling referred to as the Leidenfrost point, the heat flux is a minimum

The influence of the gravitational field on boiling must be considered in applications
involving space travel and rotating machinery.

If liquid in a pool boiling system is maintained at a temperature that is less than the
saturation temperature, the liquid is said to be sub cooled,

The influence of surface roughness (by machining, grooving, scoring or sandblasting) on
the maximum and minimum heat fluxes and on film boiling is negligible.

Special surface arrangements that provide stable augmentation(enhancement) of nucleate
boiling are available commercially

In pool boiling fluid flow is due primarily to the buoyancy-driven motion of bubbles
originating from the heated surface. In contrast, for forced convection boiling, flow is due
to a directed (bulk) motion of the fluid, as well as to buoyancy effects.

Internal, forced convection boiling is commonly referred to as two-phase flow and is
characterized by rapid changes from liquid to vapor in the flow direction.

Heat transfer to the sub cooled liquid that enters the tube is initially by single-phase
forced convection

Farther down the tube, the wall temperature exceeds the saturation temperature of the
liquid, and vaporization is initiated in the sub cooled flow boiling region.

This slug-flow regime is followed by an annular-flow regime in which the liquid forms a
film on the tube wall.

Condensation occurs when the temperature of a vapor is reduced below its saturation
temperature.

Film condensation is generally characteristic of clean, uncontaminated surfaces.

If the surface is coated with a substance that inhibits wetting, it is possible to maintain
drop wise condensation.
Radiation, Stefan
Boltzmann’ law,
black
body
radiation,
absorptivity,
reflectivity transmissivity. Wien’s Displacement law, Kirchhoff’s law, gray body
radiation.

his cooling is associated with a reduction in the internal energy stored by the solid and is
a direct consequence of the emission of thermal radiation from the surface.

For gases and for semitransparent solids, such as glass and salt crystals at elevated
temperatures, emission is a volumetric phenomenon

radiation is a surface phenomenon

One theory views radiation as the propagation of a collection of particles termed photons
or quanta. Alternatively, radiation may be viewed as the propagation of electromagnetic
waves.

Thermal radiation because it is both caused by and affects the thermal state or
temperature of matter.

Both the magnitude of the radiation at any wavelength and the spectral distribution vary
with the nature and temperature of the emitting surface.

a surface may emit preferentially in certain directions, creating a directional distribution
of the emitted radiation.

We formally define I as the rate at which radiant energy is emitted at the wavelength
in the (,) direction, per unit area of the emitting surface
normal to this direction, per unit solid angle about this direction per unit wavelength
interval d

about
The spectral irradiation G
(W/mm) is defined as the rate at
which radiation of wavelength
unit
area
of
the
d
is incident on a surface, per
surface
and
per
unit
wavelength
interval
about

A blackbody absorbs all incident radiation, regardless of wavelength and direction

For a prescribed temperature and wavelength, no surface can emit more energy than a
blackbody

Although the radiation emitted by a blackbody is a function of wavelength and
temperature, it is independent of direction. That is, the blackbody is a diffuse emitter.

the blackbody serves as a standard against which the radiative properties of actual
surfaces may be compared

Although closely approximated by some surfaces, it is important to note that no surface
has precisely the properties of a blackbody. The closest approximation is achieved by a
cavity whose inner surface is at a uniform temperature.

Blackbody radiation exists within the cavity irrespective of whether the cavity surface is
highly reflecting or absorbing.

The emitted radiation varies continuously with wavelength

At any wavelength the magnitude of the emitted radiation increases with increasing
temperature.

The spectral region in which the radiation is concentrated depends on temperature, with
comparatively more radiation appearing at shorter wavelengths as the temperature
increases.

the blackbody spectral distribution has a maximum and that the corresponding
wavelength

max depends on temperature
Stefan–Boltzmann law. It enables calculation of the amount of radiation emitted in all
directions and over all wavelengths simply from knowledge of the temperature of the
blackbody.

It is often necessary to know the fraction of the total emission from a blackbody that is in
a certain wavelength interval or band.

A surface radiative property known as the emissivity may then be defined as the ratio of
the radiation emitted by the surface to the radiation emitted by a blackbody at the same
temperature

We define the spectral, directional emissivity of a surface at the temperature T as the ratio
of the intensity of the radiation emitted at the wavelength

spectral
irradiation
G
as
the
rate
at
which
radiation
of
wavelength
is incident on a surface per unit area of the surface and per
unit wavelength interval d

about
In the most general situation the irradiation interacts with a semitransparent medium,
such as a layer of water or a glass plate

A surface appears ―black‖ if it absorbs all incident visible radiation, and it is ―white‖ if it
reflects this radiation.

A ―white‖ surface such as snow, for example, is highly reflective to visible radiation but
strongly absorbs IR radiation, thereby approximating blackbody behavior at long
wavelengths.

The absorptivity is a property that determines the fraction of the irradiation absorbed by a
surface

The reflectivity is a property that determines the fraction of the incident radiation
reflected by a surface.

Consider a large, isothermal enclosure of surface temperature Ts, within which several
small bodies are confined

Kirchhoff‘s law no real surface can have an emissive power exceeding that of a black
surface at the same temperature,

A form of Kirchhoff‘s law for which there are no restrictions involves the spectral,
directional properties.

a gray surface may be defined as one for which and are independent of
over the spectral regions of the irradiation and the surface
emission.

The extraterrestrial solar irradiation GS,o, defined for a horizontal surface, depends on
the geographic latitude, as well as the time of day and year. It may be determined from an
expression of the form

The change is due to absorption and scattering of the radiation by the atmospheric
constituents

Rayleigh (or molecular) scattering by very small gas molecules occurs when the ratio of
the
effective
molecule
D/
diameter
to
the
wavelength
of
the
radiation,
, is much less than unity and provides for nearly uniform
scattering of radiation in all directions.

In contrast, Mie scattering by larger dust and aerosol particles of the atmosphere occurs
when D/
is approximately unity and is concentrated in
directions that are close to that of the incident rays.

That portion of the radiation that has penetrated the atmosphere without having been
scattered (or absorbed) is in the direction of the zenith angle and is termed the direct
radiation.

Because the radiation intensity is often assumed to be independent of direction the
radiation is termed diffuse.
Mass transfer, Ficks law and its application,

Mass transfer is mass in transit as the result of a species concentration difference in a
mixture.

Just as a temperature gradient constitutes the driving potential for heat transfer, a species
concentration gradient in a mixture provides the driving potential for transport of that
species

A mixture consists of two or more chemical constituents (species), and the amount of any
species i may be quantified in terms of its mass density or its molar concentration

Since similar physical mechanisms are associated with heat and mass transfer by
diffusion, it is not surprising that the corresponding rate equations are of the same form.
The rate equation for mass diffusion is known as Fick‘s law,

Fick‘s law defines a second important transport property, namely, the binary diffusion
coefficient or mass diffusivity

We define the total or absolute flux of a species, which includes both diffusive and
adjective components.

A contribution due to diffusion (i.e., due to the motion of A relative to the mass-average
motion of the mixture) and a contribution due to advection(i.e., due to motion of A with
the mass-average motion of the mixture).

Blister packaging‘s used to limit the direct exposure of the medicine to humid conditions
until immediately before their use.

Tablets that are contained in a blister package composed of a flat lidding sheet and a
second, formed sheet that includes troughs to hold each tablet.

Another common mass transfer problem is similar to the evaporation or sublimation
problem, except mass transfer within the liquid or solid phase is of interest.

Treating the gas and solid as a solution, we can obtain the concentration of the gas in the
solid at the interface through use of a property known as the solubility
Heat exchangers & classification , overall heat transfer coefficient. LMTD and
NTU methods.

Heat exchangers are typically classified according to flow arrangement and type of
construction.

The simplest heat exchanger is one for which the hot and cold fluids move in the same or
opposite directions in a concentric tube(or double-pipe) construction.

In the parallel-flow arrangement of Figure 11.1a, the hot and cold fluids enter at the same
end, flow in the same direction, and leave at the same end.

In the counter flow arrangement of Figure 11.1b, the fluids enter at opposite ends, flow in
opposite directions, and leave at opposite ends

The two configurations are typically differentiated by an idealization that treats fluid
motion over the tubes as unmixed or mixed.

Termed compact heat exchangers, these devices have dense arrays of finned tubes or
plates and are typically used when at least one of the fluids is a gas, and is hence
characterized by a small convection coefficient.

The tubes may be flat or circular, as in Figures 11.5aand 11.5b,c, respectively, and the
fins may be plate or circular,

An essential, and often the most uncertain, part of any heat exchanger analysis is
determination of the overall heat transfer coefficient.

This effect can be treated by introducing an additional thermal resistance, termed the
fouling factor,

The overall surface efficiency or temperature effectiveness of a finned surface. It is
defined such that, for the hot or cold surface without fouling,

It is a simple matter to use the log mean temperature difference (LMTD) method of heat
exchanger analysis when the fluid inlet temperatures are known and the outlet
temperatures are specified or readily determined from the energy balance expressions,

However, if only the inlet temperatures are known, use of the LMTD method requires a
cumbersome iterative procedure. It is therefore preferable to use an alternative approach
termed the effectiveness–NTU (or NTU) method

To define the effectiveness of a heat exchanger, we must first determine the maximum
possible heat transfer rate, qmax, for the exchanger.

effectiveness,, as the ratio of the actual heat transfer rate for a heat exchanger to the
maximum possible heat transfer rate

The number of transfer units (NTU) is a dimensionless parameter that is widely used for
heat exchanger analysis heat exchanger behavior is independent of flow arrangement.

in a heat exchanger performance calculation, an existing heat exchanger is analyzed to
determine the heat transfer rate and the fluid outlet temperatures

Compact heat exchangers are typically used when a large heat transfer surface area per
unit volume is desired and at least one of the fluids is a gas.

The boundary layer velocity profile refers to the manner in which u varies with y through
the boundary layer.

The foregoing boundary layer may be referred to more specifically as the velocity
boundary layer.
Radiation shape factor and its applications.

To compute radiation exchange between any two surfaces, we must first introduce the
concept of a view factor(also called a configuration or shape factor)

The view factor Fij is defined as the fraction of the radiation leaving surface i that is
intercepted by surface

Each surface of the enclosure is assumed to be isothermal and to be characterized by a
uniform radiosityand a uniform irradiation. Opaque, diffuse, gray surface behavior is also
assumed, and the medium within the enclosure is taken to be nonparticipating.

a surface which is large relative to all other surfaces under consideration can be treated as
if it were a blackbody

openings of enclosures that exchange radiation with large surroundings may be treated as
hypothetical, nonreflecting black surfaces whose temperature is equal to that of the
surroundings

Radiation shields constructed from low emissivity (high reflectivity) materials can be
used to reduce the net radiation transfer between two surfaces.

In an enclosure, the equilibrium temperature of a reradiating surface is determined by its
interaction with the other surfaces, and it is independent of the emissivity of the
reradiating surface.

Isothermal, opaque, gray surfaces that emits and reflect diffusely and that are
characterized by uniform surface radiosity and irradiation.

For such gases matters are complicated by the fact that, unlike radiation from a solid or a
liquid, which is distributed continuously with wavelength, gaseous radiation is
concentrated in specific wavelength intervals (called bands). Moreover, gaseous radiation
is not a surface phenomenon, but is instead a volumetric phenomenon.
9. Engineering Mechanics (Statics & Dynamics)