Final Review
Mech 1200
Mech 1200
• Some types of maintenance techniques:
- Preventative maintenance: Performing scheduled
and unscheduled tasks on an equipment for
optimization and preventing failure.
- Predictive maintenance: condition monitoring of
an equipment in comparison to a preset standard or
baseline.
- Proactive maintenance
Mech 1200
Examples of Predictive maintenance
1. Vibration analysis: Analysis of the
oscillatory motion in a cyclic manner.
2. Oil Analysis: Investigation of the physical
properties and presence of contaminants in oil
samples.
3. Thermography: Analysis of the temperature
of an equipment at different operating
conditions.
Mech 1200
Lockout Requirements
1. Use a positive means to keep the energy-isolating device
in the safe position.
2. The lockout device must be able to withstand the
environment it is exposed to, such as excessive heat,
radiation, freezing..etc.
3. The lockout and tagout devices must be standardized in
the facility in size and/or color and/or shape.
4. The lockout device must be strong enough to prevent
removal without excessive force.
5. Notification of employees before the application and
after removal of the lockout/tagout.
6. Only the employee who applied it can remove it.
Mech 1200
Tagout Requirements
1. Must contain a clear warning. For example: Danger.
2. Must state clearly that moving the energy-isolating
device from the safe mode is not allowed.
3. Must be placed in the place a lock device would be
placed, or if not possible, as close as safely possible in a
position obvious to anyone who attempts to operate
the device.
4. Must be able to withstand the environment.
5. Must be standardized in the facility.
6. Must have a nonreusable type of attachment.
For more Lockout/Tagout requirements, please read pages
27 and 28 of the text.
Topics:
MECH1200
• Introduction to Chapter 3: Mechanical Power
Transmission Fundamentals
• Energy
• Force
• Inertia
• Acceleration
• Friction
• Work
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• Usually mechanical systems consist of the
following elements:
- A prime mover: such as en electric motor
or an internal combustion engine.
- Linking components: such as shafts, gears,
belts, joints..etc.
- Driven components such as wheels.
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Newton’s Laws of Motion
Newton’s First Law (Law of Inertia):
A body in rest will stay in rest and a body in motion will
stay in motion unless an external force is acted upon it.
Newton’s Second Law (conservation of momentum):
The net force acting on an object is equal to the rate of
change of its momentum.
Forcenet = mass × acceleration
Newton’s Third Law (action-reaction law):
For every action there is a reaction equal in magnitude
and opposite in direction.
FA = - FB
Force
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Force: causes an object that has a mass to
change velocity.
• A vector quantity: It has direction and
magnitutde.
• Some common units of force:
Newton (N)
Pound force (lbF) = 4.45 N
Inertia
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• Inertia: the resistance of an object to any change
in its motion state.
• Example 1: Object A (1 kg) and object B (10 kg) are
each acted upon by a force of 1 N to the right. which
would move at a higher acceleration?
1N
A
1kg
1N
B
10 kg
Object B has a larger inertia, thus more resistance to
change in its rest state, so it has a lower acceleration.
Angular Speed
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• Angular speed: a measurement to describe an object rotating
about an axis.
• Units of measurement:
 RPM
 Rad/s
Surface velocity (ft/min) = RPM× π × diameter (ft)
= RPM ×0.262 × diameter (in inches)
Example 4: what is the surface velocity of a 20 in diameter rotor
that rotates at 1500 rpm?
Solution:
𝑆𝑝𝑒𝑒𝑑 = 1500
1
𝑚𝑖𝑛
× 𝜋 × 20 𝑖𝑛 ×
1 𝑓𝑡
12 𝑖𝑛
= 1500 × 0.262 × 20 = 7860 ft/min
Viscosity
• Viscosity: A measure of the fluid’s resistance to
flow.
• The best lubricant is that which has the lowest
viscosity possible to maintain a film that
separates the metal parts.
• Viscosity Index (VI): a measure of the change in
viscosity with temperature. As VI increases, the
less is the change of the lubricant’s viscosity with
temperature.
• Kinematic viscosity: is the measure of inertial
force to viscous force.
• Units of kinematic viscosity are:
• m2/s (the SI unit)
• the Stoke (1 m2/s = 10,000 stokes )
• Saybolt Universal Seconds (SUS)
Source: Wikimedia
Commons.
12
Gear Drives
The pitch diameter is the diameter of the pitch circle and is used to
calculate the speed and torque to the driven shaft.
The pitch circle is only significant in determining the pitch diameter.
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Gear Drives
Pressure Angle: The angle at which power is passed
from the tooth of one gear to the tooth of the other.
Commonly pressure angle is 20o
Backlash: the space between the non-driving sides of
the adjacent teeth of two meshing gears.
Backlash prevents gear binding and wearing.
Root Clearance: the radial distance between the top of
the tooth of the pinion and the bottom of the tooth of the
gear.
Gear Drives
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Diametral Pitch - The ratio of the
number of teeth on the gear to the
pitch diameter
It indicates the relative size of the
teeth on the gear.
Two gears must have the same
diametral pitch in order to mesh
𝑃𝐷 =
𝑁
𝑃𝐶
PD –Diametral Pitch
𝑁 – Number of Teeth
𝑃𝑐 - Pitch circle diameter (inches)
Determine if gears of different
diameters or different numbers of
teeth have the same size teeth and
can mesh properly
Common sizes are 3 - 48 DP
Gear Module (metric) =
𝑃𝑖𝑡𝑐ℎ 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 (𝑚𝑚)
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ
Gear Drives
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Idler Gears
• Idler gears are inserted
between input and
output gears
• They serve to reverse
the direction of rotation
of the output gear.
• Idler gears DO NOT
affect the gear ratio
between the input and
output gears.
Idler Gears
Gear Types
1. Spur Gears
2. Helical Gears
3. Double Helical Gears
4. Herringbone Gears
5. Bevel Gears
6. Worm Gears
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Chain Drive
3 Basic Parts:
• Chain
• Driver Sprocket
• Driven
Sprocket
The Relative number of teeth between the
driven sprocket and the driver sprocket
determines the speed and torque of the driven
shaft
Ratio of the teeth can be selected to increase or
decrease speed or torque to the driven shaft
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Four common types of chains
Belt Drive Terminology
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Driven Sheave (Pulley)
Arc of Contact
Driver Sheave (Pulley)
Belt
Tight side T1
Center Distance
Slack side T2
Source: Drawing is in the public domain and was taken from Wikimedia Commons, Wikimedia Foundation
Belt Terminology
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Effective Tension (Te):
Te = T1 – T2
Total Tension:
Ttotal = T1 + T2
Power:
𝑇𝑒 × 𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦
Power HP =
33000
Drive Ratio (also called Pulley Ratio):
𝐷𝑟𝑖𝑣𝑒𝑛 𝑠ℎ𝑒𝑎𝑣𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟
𝐷𝑟𝑖𝑣𝑒 𝑟𝑎𝑡𝑖𝑜 =
𝐷𝑟𝑖𝑣𝑒𝑟 𝑠ℎ𝑒𝑎𝑣𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟
Types of V-Belts
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Fractional Horsepower V-belts: used for light
duty applications below 7.5 Hp.
Classical V-belts: standard v-belts, used in heavy
duty applications. Notches may be added to the belt
to reduce bending stress.
How to identify classical V-belts?
1. Cross sections are designated as A, B, C, D,
and E.
2. Belt length measured on the circumference is
designated numbers following the letter prefix
3. Notched V-belts are identified by an “X”
Synchronous Belts
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• Also called Timing Belts, positive drive belts,
and gear belts.
• Slip is not allowed in synchronous belt drives
• If jamming occurs the V-belt will slip, but the
synchronous belt will shear off.
Belt Sheaves
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Introduction
• Electric Machinery:
- Electric Motors: convert electrical energy into
mechanical energy.
- Electric Generators: convert mechanical energy
to electric energy.
• The Electric machine is composed of:
Stator
Rotor
Image is in the public domain. Source: Wikimedia Commons, Wikimedia Foundation
MECH1200
Principles of Operation of Electric Motors
• Faraday’s Law is the principle of operation of electric
machines.
• There are three methods by which electric motors work:
1. Having a stationary magnetic field in the stator and an
alternating magnetic field in the rotor.
- This method is employed in all DC motors except for the
Brushless DC
2. Having a rotating magnetic field in the stator and a
stationary magnetic field in the rotor.
- This method is employed in synchronous motors, Stepper
and Brushless DC Motors
3. Having a rotating magnetic field in the stator and an
induced magnetic field in the rotor.
- This method is employed in induction motors.
Types of Electric Machines
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Electric Machines
DC Machines
Permanent Magnet
DC (PMDC) Motor
Shunt Motor
Separately Excited
motor
AC Machines
Induction
Machine
Synchronous
Machine
Stepper motor
3Ph Wound Rotor
Brushless DC
motor
3Ph Squirrel Cage
Hysteresis motor
Capacitor Start
Reluctance motor
Split Phase
Universal motor
Series Motor
Compounded
Motor
Special Motors
Capacitor Run –
Capacitor Start
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Construction of DC Machines
• Field Windings: In DC machines, this is the winding in the
stator. Note: Permanent magnet dc motors do not have field
winding but rather a permanent magnet.
• Armature Windings: The windings in the rotor .
• Commutator segments: the method to convert the dc
current to an alternating current in the rotor of the dc motor
is called commutation. They are connected to the rotor
windings, and stay in contact with the brushes.
• Brushes: pieces made of carbon or graphite and pushed
against a spring to maintain electrical contact with the
commutator segments.
• Interpole windings: A third set of windings are mounted
on the stator, and connected in series with the rotor to
reduce the sparking between brushes and the commutator.
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• Name the type of each of the motors A, B, and C
shown in the figure below:
A: Shunt motor
B: Series motor
C: Compound motor
Review: Principle of Operation of DC and AC
MECH 1200
Synchronous Machines
DC Machines
AC Synchronous Machines
Stator magnetic field: Stationary
Rotor magnetic field: Alternating
Stator magnetic field: Rotating
Rotor magnetic field: Fixed
(stationary w.r.t. rotor)
N
S
N
N
N
S
S
S
S
N
S
N
MECH 1200
Construction of AC Machines
• Induction motor:
– Stator: a rotating magnetic field exists in the stator
windings. The stator windings are connected to a three
phase power supply (except for single phase motors).
– Rotor: An induced magnetic field exists in the rotor of a
squirrel cage induction motor.
• Synchronous motor:
– Stator: a rotating magnetic field from a three phase power
supply.
– Rotor: A fixed magnetic field in the rotor from a dc power
supply. Therefore, it needs brushes, but no commutation as
in dc motors. Rather, slip rings that stay in contact with the
brushes are used.
Note: Wound rotor induction motors require slip rings as in
synchronous motors.
Terms
MECH 1200
• Synchronous speed: the speed of rotation of the magnetic
field in the stator.
120 × 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦
𝑆𝑦𝑛𝑐ℎ𝑟𝑜𝑢𝑛𝑜𝑢𝑠 𝑠𝑝𝑒𝑒𝑑 =
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑃𝑜𝑙𝑒𝑠
• Mechanical speed: this is the actual speed of the rotor
• Slip: the ratio of the difference between synchronous and
mechanical speeds to the synchronous speed.
𝑛𝑠𝑦𝑛𝑐ℎ − 𝑛𝑚𝑒𝑐ℎ𝑎𝑛𝑖𝑐𝑎𝑙
𝑆𝑙𝑖𝑝 =
× 100%
𝑛𝑠𝑦𝑛𝑐ℎ
• Example: a) what is the speed of rotation of the magnetic
field in a 3-phase induction motor that has 2 poles?
b) What is the speed of the motor if the slip is 5% ?
• Solution: synchronous speed = 120×60 / 2 = 3600 RPM
Motor speed = (1-0.05) × 3600 = 3420 RPM
Induction Motor Speed and Torque
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Relationship
• Locked rotor torque: The starting torque of the motor.
• Full load torque: the torque supplied by the motor at
rated speed, voltage and frequency.
Breakdown torque
Torque
Locked rotor
torque
Full load torque
Speed (ω)
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Other Special Purpose Motors
• Stepper Motor: A special type of synchronous motors, that
moves in steps every time a pulse is sent from its control
unit. One type of stepper motors has a permanent magnet in
its rotor.
• Reluctance Motor: A hybrid of the induction and
synchronous motors, operates at synchronous speed, with a
rotor of salient poles.
• Hysteresis Motor: a self starting synchronous motor,
torque is generated through hysteresis.
• Brushless DC motor: A combination of a permanent
magnet stepper motor with a position sensor and a control
unit that gives the motor the pulses to work. It was designed
to run off DC power when brushed motors are unacceptable
such as in artificial heart applications or when radio
frequency interference is unacceptable, or at low pressure
environment such as at high altitudes.
Couplings
MECH 1200
• Shaft couplings: Sleeves that provide a
connection between shafts rotating at high speeds
to transmit torque and power.
• Three types of couplings:
- Rigid coupling
- Flexible coupling
- Universal joints
SEALS
• Purpose:
• Keep the oil in and the dirt out
• Separate fluids or cavities
• Withstand different pressures
MECH 1200
GASKET
MECH 1200
• A pliable material that is shaped and placed
between two mating machined parts to form a
seal.
• Purpose of a Gasket
– To confine; gas, oil, water, vacuum or exhaust
– Seal out foreign objects such as dirt & water
– Must withstand heat, cold, pressure, erosion,
corrosion, moisture and oil
Stuffing Box
MECH 1200
• An assembly which is used to house
a gland seal.
• It is used to prevent leakage of fluid,
such as water or steam, between
sliding or turning parts of machine
elements.
Bearings
MECH 1200
Purpose of bearings:
- Support loads
- Reduce friction
The PV factor:
- PV factor refers to the Pressure and Velocity
ratings of the bearing.
- Pressure is the load on the bearing in pounds
divided by the projected area in square inches.
- Velocity is the surface velocity of the shaft.
Some types of Bearings
Plain (Journal) Bearings
Solid
Split
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Antifriction (rolling) Bearings
Deep Groove Ball Bearing
Angular Contact Ball Bearings
Self Aligning Ball Bearing
Pure Thrust Ball Bearing
Cylindrical Roller Bearing
Spherical Roller Bearing
Tapered Roller Bearing
Needle Roller Bearing
MECH 1200
Clutches
• Clutch – Go (or limit torque)
• Brake – Stop (or slow down)
• Backstop – Go only one direction
• Primary function: Stop, slow, or prevent
reversal of load in a mechanical system