Overview
Machine Elements
1
Columns
Dr. Md. Zahurul Haq, Ph.D., CEA, FBSME, FIEB
2
Springs
Professor
Department of Mechanical Engineering
Bangladesh University of Engineering & Technology (BUET)
Dhaka-1000, Bangladesh
3
Gears
http://zahurul.buet.ac.bd/
4
Beams
ME 101 : Introduction to Mechanical Engineering
http://zahurul.buet.ac.bd/ME101/
5
Bearings
© Dr. Md. Zahurul Haq (BUET)
Machine Elements
ME 101: 2024
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© Dr. Md. Zahurul Haq (BUET)
Machine Elements
ME 101: 2024
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Columns
Key Machine Elements · · ·
Columns
012345
012345
6789
6789
T1537
T1890
T1544
T1536
© Dr. Md. Zahurul Haq (BUET)
Machine Elements
T1891
T1544
Compression members are widely used in machinery of all types. A
column is a slender compression member that deforms laterally, or
buckles, before stresses reach the yield strength of the material.
In buckling, loads below a critical value can be supported, but once
the critical load is exceeded, large deformations result.
ME 101: 2024
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© Dr. Md. Zahurul Haq (BUET)
Machine Elements
ME 101: 2024
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Columns
Springs
Euler Column Formula and Critical Load
0
0
Springs
0 0
1234578
9 5
7 ;
0
1"8;
1"5;
7"1;
455 45855
4545
25753 545
./1"5
./7"1
./1"8
3 5 ./0"1
./1"65
./7"01
./1"9
33 ./0"1
3 5
T1546
2
3
2
3
2:3
2
3
h
i2
2
5
5
5
!
4
5
2
7
5
5
2
5
545!45
π
Pcr = Le /r EA
2587 3537 3537 5!" #$%&'$()'#
344735!
255855!45 *&''+$$()'#,
Le /r > 100
3537 T1543
'-&&'$()'#"
Le = KL
© Dr. Md. Zahurul Haq (BUET)
Machine Elements
ME 101: 2024
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T1545
A spring is a flexible machine element used to exert a force or a torque
and, at the same time, store energy.
Energy is stored in the solid that is bent, twisted, stretched, or
compressed to form the spring. The energy is recoverable by the
elastic return of the distorted material.
© Dr. Md. Zahurul Haq (BUET)
Springs
Machine Elements
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Gears
Automotive Springs
Gears
Gears are very popular power transmission devices, combining the attributes
of high efficiency, long and maintenance-free service life, reasonable
manufacturing cost, and relatively large torque capability in a compact size.
T1547
T1549
01
2 5273
35617389
T1556
3562891
311
T1548
© Dr. Md. Zahurul Haq (BUET)
1253
Machine Elements
32913
T1557
T1558
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Machine Elements
ME 101: 2024
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012301451637
89 Gears
Gears
Spur Gears
Helical Gears
9
012301451637
89 T1538
T1550
T1551
9
Spur gears are parallel-axis gears with straight teeth. These are the
simplest and the most common type of gear, as well as the easiest to
manufacture.
© Dr. Md. Zahurul Haq (BUET)
Machine Elements
ME 101: 2024
Helical gears are parallel-axis gears with teeth cut on helix that wraps
around cylinder. These have greater load-carrying capacity than spur gears
of the same size.
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© Dr. Md. Zahurul Haq (BUET)
Gears
Machine Elements
ME 101: 2024
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Gears
Bevel Gears
Worm Gears
T1553
T1552
Bevel gears have nonparallel axes that lie in the same plane. Usually,
bevel gears are mounted perpendicular to each other, but almost any shaft
angle can be accommodated.
© Dr. Md. Zahurul Haq (BUET)
Machine Elements
ME 101: 2024
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Worm gears are unique in that they cannot be back-driven; that is, the
worm can drive the worm gear, but the worm gear cannot drive the worm.
This is a function of the thread geometry and is referred to as self-locking.
© Dr. Md. Zahurul Haq (BUET)
Machine Elements
ME 101: 2024
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Beams
Bearings
Beams
Rolling Contact Bearing
Beams are structural members, subjected to transverse loads. Examples
include machinery shafts, building floor joists, leaf springs, automobile
frame members and numerous other machine and structural components.
T1554
(a) Deep groove ball bearing; (b) cylindrical roller bearing; (c) needle bearing
with drawn cup and no inner race. In such a circumstance, the needles roll on a
ground and hardened shaft. (d) Tapered roller bearing; (e) thrust ball bearing.
T1562
T1563
© Dr. Md. Zahurul Haq (BUET)
Machine Elements
ME 101: 2024
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© Dr. Md. Zahurul Haq (BUET)
Bearings
Machine Elements
ME 101: 2024
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Bearings
Journal Bearing
Lubrication & Lubricants
A lubricant (sometimes shortened to lube) is a substance that helps to
reduce friction between surfaces in mutual contact, which ultimately
reduces the heat generated when the surfaces move. Key functions of
lubrication systems are:
T1555
Journal bearings: the bearing surfaces are parallel to the axis of rotation,
Journal bearings are used to support shafts and to carry radial loads with
very low power loss and extremely low wear. The journal bearing can be
represented by a plain cylindrical sleeve (bushing) wrapped around the
journal (shaft) but can adopt a variety of forms. The lubricant is supplied
at some convenient location in the bearing through a hole or a groove.
© Dr. Md. Zahurul Haq (BUET)
Machine Elements
ME 101: 2024
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◮ reduce friction between mating machine parts,
◮ cools moving parts,
◮ seals the macro-gap between mating parts,
◮ reduces rust formation and the system lifetime is extended
Classifications of lubricants:
1
2
3
liquid lubricants: mineral oils and synthetic oils.
solid lubricants: graphite.
semi-liquid lubricant: grease.
© Dr. Md. Zahurul Haq (BUET)
Machine Elements
ME 101: 2024
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