Introduction to Mechanical Engineering_BME_Unit 1

Unit I
Introduction to Mechanical
Engineering
Basic Mechanical Engineering –
102013
F.E-Semester II

UNIT I
 Mechanical Elements: Function, Sketch, Description, Uses and
Classification of – Shaft, Axle, Parallel Key, Rigid Flange Coupling, Ball
Bearing, Single Plate Clutch & Disc Brake
 Power Transmission Devices: Construction, Working, Comparison ,
Application and Classification of – Belt Drives (Flat & V-Belt), Chain
Drives and Spur Gear Drive arranged with Simple Gear Train
Introduction to Mechanical Engineering
Book Referred – Design of Machine Elements by V. B. Bhandari

Mechanical Machine Elements
Machine Elements
Holding Type
Nuts and Bolts
Keys
Couplings
Rivets
Cotters
Supporting Type
Body Frame
Axle
Bearings
Frames
Power Transmitting
Elements
Gears
Shafts
Pulleys and Belts
Sprockets and Chains
Clutches

Automobile Transmission System
www.Wikipedia.org

Shaft
The shaft is a rotating bar generally of circular cross
section, which is used to transmit torque or rotational
motion.
Common Terms Associated with Shafts:
 Transmission Shaft
 Line Shaft
 Counter Shaft
 Jackshaft
 Spindle
 Crankshaft

The shaft which is directly connected power is called
transmission shaft
Transmission Shaft

Line shaft is a very long transmission shaft which is directly
driven by the prime mover (or power source) and which is used
distribute power from main source to different power consuming
devices.
Line Shaft

Counter shaft is a secondary shaft which is not directly
connected to power source but driven by it through belt,
chain or gear drive.
Counter Shaft

The shaft which used in multi cylinder IC
engine to which cranks are embedded is called
crankshaft.
Crankshaft
www.Wikipedia.org

Spindle is peculiar terminology
associated with shafts of machine tools
which provide rotary motion either to a
cutting tool or to a work piece.
.
Spindle

AXLE
BFF Design Ltd Wikipedia.com
The axle is a non rotating bar which doesn’t transmit any
torque but only used to supports rotating machine elements
like wheels, pulleys etc.

Difference between Axle and Shaft
Axle Shaft
Axle is a non rotating member Shaft is rotating member
Primary function is to provide support to
elements like wheel, pulley etc.
Primary function is to transmit torque.
Axle is primarily subjected to bending . Shaft is subjected to bending, torque, as
well as vibrations
Design of axle is relatively simple
compared to shaft
Design of shaft is complex as compared
axle because shaft is simultaneously
subjected to torque, bending, and
vibrations
Depending upon loading condition, cross
sectional area of axle can be different e. g.
Rectangular, Circular, I-section, T-section
etc.
Cross sectional area of shaft is generally
circular because it causes minimum
vibrations and stress as compared to
other shapes of same cross sectional area.
Examples: Axles of automobiles, railway
buggies.
Examples: Shaft of electric motor, shaft of
IC engine

The key is machine element which is used to prevent
free relative rotation between shaft and the element
mounted on the shaft
 Key transmits the torque from the shaft to the rotating
element or vice-versa.
Classification:
 Saddle or Sunk Keys
 Parallel or Taper Key
 Key with or without Gib Head
Mechanical Keys

Saddle Key
The saddle key is a key which fits
in key way of hub only and
transmits torque between hub
and shaft by means of friction
 Saddle key doesn’t sink inside the
shaft hence it is NOT a sunk key
 Saddle keys have low torque
transmitting capacity
 As key way on shaft is avoided saddle
keys don’t weaken the shaft

Sunk Key
The sunk key is a key in which
some portion of its thickness fits
in keyway on shaft and
remaining portion of the
thickness sits in key way of hub.
 The torque is transmitted by means of
shear force within the key.
 As key way on shaft is required sunk
keys weaken the shaft

Tapered Keys
 As compared to parallel keys, the
tapered keys are more tight because of
wedge action
 Tapered keys are easy to remove as
compared parallel keys
The thickness of the tapered key changes along the length

Parallel Key
Technifast.com
The parallel keys have uniform thickness along
their length

Gib Headed Keys
The key which is provided with head for easy
removal is called Gib headed key

Tangent Keys
The tangent key transmits the torque
only in one direction by means of
compressive force alone
• Tangent key is subjected to compressive
stress
• Two tangent keys separated by 900 angle force
hub and shaft to concentric position
• Example: Kennedy Key

Feather Key
The feather key is a key which
allows relative axial motion
between hub and shaft but
prevents relative rotational
motion between them
 The key is permanently fixed to the
shaft generally
 Clearance is provided between hub
and key so that hub slides freely
over the key
 Sometimes double Gib headed key is
provided so that hub will not come
out completely

Woodruff Key
 The curved portion of key sits inside slot
made on shaft whereas flat portion sits
inside slot made on hub
 The extra depth of Woodruff key prevents its
tendency of slip over during heavy load
condition.
 The Woodruff key is extensively used in
tapered shafts because it can align easily
with the hub slot by slight rotations
 Woodruff keys weaken the shaft because of
their extra depth
The Woodruff key is sunk key, almost in the form of
semicircular disc of uniform thickness

Couplings
Coupling is the mechanical element used to connect two
shafts of a transmission system and transmit the torque
from one shaft to another.
 Connects two shafts (transmission shaft)
 Absorb/Reduces vibrations and shocks.
Functions of Coupling :

Couplings
Rigid
Sleeve
or Muff
Split
Muff
Flange
Un-Protected
type
Protected type
Flexible
Beam/
Healical
Universal/
Hooke’s
Joint
Oldham

Rigid Couplings
 These couplings are not capable of tolerating any
misalignment between two shafts.
 These couplings are not capable of absorbing
shocks and vibrations.
 These are simple and inexpensive.

Unprotected Rigid Flange Coupling
youtube.com

grabcad.comUn – protected Flange Coupling

Protected Rigid Flange Coupling
youtube.com

engineeringdesigns.blogspot.in

Split Muff Coupling
youtube.com

Flexible Couplings
Flexible couplings allow axial and/or angular
misalignment between two shafts Universal Coupling
cornell.edu
Oldham Coupling
wikipedia.org
www.mech.uq.edu
Beam Coupling

Beam/Helical Coupling
youtube.com
 Allows angular misalignment between the two
shafts

Oldham’s Coupling
 Allows small axial misalignment between the
two shafts

Hooke’s Joint /Universal Coupling

Bearings
Bearing is a device that allows relative motion between
two parts, such as shaft and housing with low friction
as well as it restricts the motion of shaft in one desired
direction only.
Functions:
I. It ensures free rotation of the shaft or the axle with minimum
friction.
II. It supports shaft or axle and holds it in the correct position.
III. It takes the forces acting on the shaft or the axle in both working
as well rest condition and transfers them to frame on which it is
mounted.

Bearings
Rolling
Contact
Ball Bearing Roller Bearing
Tapered Roller
Bearings
Sliding
Contact
Hydrostatic
Bearing
Hydrodynamic
Bearing

 The purpose to support a load while permitting relative
motion between two elements of a machine.
 The components of a typical rolling contact bearing are
the inner race, the outer race, cage and the rolling
elements.
Ball Bearings
SHAFT
yourdictionary.com

Tapered Roller Bearing
Cylindrical Roller Bearing
Roller Bearings

Journal Bearings
Hydrostatic Bearing: Oil is Pressurized
Hydrodynamic Bearing: Oil is NOT Pressurized

Clutches
Positiv
e
Clutch
Gear Tooth
Spiral
Friction
Clutch
Plate or
Disc
Single
Plate
Multiple
Plate
Cone Centrifugal
Clutch
It connects or disconnects the source of power from the
remaining parts of the power transmission system at the
will of the operator.

Single Plate Clutch
codecogs.com

wikipedia.com
Multi- plate Clutch
Centrifugal Clutch
Cone Clutch

Positive Type Clutch
hellotrade.com

Brakes
 Brake is a mechanical device used to stop or slow
down the moving body.
Brakes
Mechanical
Block
Brake/Drum
B rake
External
Internal
Expanding
Band Brake Disc Brake
Electrical
Eddy
Current
Brakes

Disc Brake Assembly
 Absorbs more heat than a drum
brake assembly
 When the brake pedal is pushed,
brake fluid from the master
cylinder compresses the brake
pads against the rotors attached
to the vehicle's front wheels.
 The friction between the
stationary pads and the revolving
rotors causes the rotors and
wheel to slow down/ stop.

www.roymech.co.in
a) Single Block
b) Double block
c) External type
d) Internal Expanding Type
www.answers.com

Difference Between Clutch and Brake
Brake Clutch
Function Absorbs Power Transmits Power
During Normal
Operation of
Vehicle
Disengaged Engaged
Position of mating
Surfaces
One surface is always
stationary and other may
be fixed or rotating
One surface is always
rotating and other
may be fixed or
rotating
Final Condition Both members are at rest
and have no relative motion
Both members rotate
at the same speed
and have no relative
motion.

Drives
Drive is a link between Prime mover and Driven machinery.
Prime movers, power
producing devices.
Driven Machinery,
Power absorbing
devices
Power
Transmitting
link
•I.C. Engines
•Steam Engines.
•Gas Turbines.
•Steam Turbines.
•Water Turbines.
•Wind Mills.
•Electric Motors.
•Flour Mill
•Oil Mill.
•Vehicle propulsion.
•Machine Tools.
•Compressors, pumps.
•Material handling
Equipments.
•House hold gadgets.
•Chain drive.
•Belt Drive.
•Rope Drive.
•Gear Drive.

Cross Belt Drive
Cross Belt Drive
• Increased angle of contact results in increased grip
• However, rubbing of belt causes reduced belt life

• Rectangular Cross
Section
•Large center distance
between shafts (5m-10m)
• cheaper compared to ‘V’
belts.
• The slip is more.
•Crown Pulley is used.
• Cross belts are used to
reverse direction of
rotation.
• Flat belts provide only
small speed ratios.
Cross section
Flat Belt Drive

V Belt Drive • Trapezoidal Cross
Section
•Short center distance
between shafts (5m-
10m)
•The no slip .
•Grooved Pulley is
used.
•V belts provide High
speed ratios.

Circular Belt Drive
• Circular Cross Section
•Large center distance between shafts (more than 8m)
•The no slip .
•Grooved Pulley is used.
•Great amount of power transmitted.

Chain Drive
• Steel Chain are used.
•The no slip .
•Sprockets (tooth wheel)
are used.
•Lubrication is required

Chain Elements
wikipedia.com
Pin
Outer Link
Bushing
Roller
Inner Link

Chain Drive
Advantages
 No slip
 High transmission efficiency (upto 98 percent)
 High power transmission capacity
 High speed ratio (8 to 10 in one step)
 It gives less load on the shafts because pretension is not
required
 It can be operated under adverse temperature and
atmospheric conditions.
Disadvantages
 High cost
 At high speed noise increases
 Requires lubrication and frequent maintenance

Belt Drive
Advantages (Over Chain Drive)
 High Operating Speed
 Allows angular misalignment between two shaft
 Need not to have exact centre distance between
two shafts
 Low Cost, Easy installation
Disadvantages (Over Chain Drive)
 Slip causes fluctuation in speed
 Low power transmission Capacity
 Low speed Ratio (upto 3)
 Less Compact
 Pretension of belts is required which increases load
on the shaft

V Belt Drive
Advantages (over Flate Belt Drive)
 Less slip
 Less noise because V belts are endless
 The high velocity ratio (maximum 10) may be
obtained.
 High power transmitting capacity
 More Compact
Disadvantages (over Flate Belt Drive)
 The centrifugal force prevents the use of V-belts at
high speeds
 Cost is high

Classification of the Gears based upon position of shaft axes
GEAR
Parallel Shaft
Spur
Rack &
Pinion
Intersecting
Shaft
Bevel
Non – parallel
and non
Intersecting
Spiral
Worm

Gears
 Gear is a toothed wheel which is used in a power
transmission system to transmit torque/power from
one shaft to other
 Spur Gears
 Helical Gears
 Bevel Gears
 Worm Gear
 Rack and Pinion

Spur Gear Terminology
Gear is a tooth profile is
either involute or cycloid.

Spur Gear Helical Gear
Rack and Pinion wikipedia.com

Spur Gear Train with Idler gear
Output
3
Idler Gear

Features of Gear Drives
• Positive drive
• No slip results to constant velocity ratio
• Compared to chain drives it is smoother in operation.
• It is suitable when the centre distances are small.
• for given amount of power transmission, the drive is most compact.
• Precise ratios are possible.
• Very long life.
• Expensive
• Compared to belt drives gear drives are Noisy.
• Comparatively Expensive and Maintenance cost is also higher.
•They require Precise Alignment of the shafts.

University Question:
YEAR 2010
1) What is the brake? How does it differ from clutch? [ 2+ 2+4]
2) Explain with neat sketch ( 4 each)
• Ball Bearing
• Transmission Shaft
YEAR 2011
Q.7)
(B) Distinguish between Kinematic Pair and Kinematic Chain with
an example for each. [06]
(C) What are the advantages and disadvantages of Belt Drives ? [04]
OR
Q.8) (A) What is a Clutch ? Explain with a neat diagram the working
of a Single Plate Clutch. [07]
(B) What is a Brake ? How brakes are classified [09]

YEAR 2009
Q.11) (A) Draw sketch of Single Plate Clutch and explain its working. [06]
(C) Compare Flat Belt and V-Belt. [06]
OR
Q.12)
(C) State advantages and disadvantages of Chain Drive over Belt
Drive. [06]
YEAR 2012
7. A) Difference between ‘Line shaft’ and ‘Counter shaft’ with diagram.
(2+2+4=8)
B) How the couplings are classified (2+3+3=8)
8. B) Define ‘Gear Ratio’ and explain with neat (2+3+3=8)

YEAR 2010
Q.11)
(B) Explain any one type of Clutch with sketch. [06]
OR
Q.12) (A) Compare Belt and Gear Drive. [06]
YEAR 2011
8. A) How gears are classified ? What are the functions of gears ? State
applications
of different types of gears. (3+2+3)

Practice Question
• State the advantages and disadvantages of V belt over Flat bet drive.
• Differentiate between Belt drives and Gear drives.
• Compare merits and demerits of Individual drive with group drive.
• Suggest suitable element for following. Shaft at right angles, Shafts with slight
misalignment, Two parallel shafts 3-4 m apart, Two parallel shafts 10 cm apart.
• Differentiate between flat belt and V belt. Show their cross-sections.
• Suggest a suitable element for the following, Non parallel non intersecting
shafts, Intersecting shafts, Parallel shafts with slight misalignment, Shafts 2-4 m
apart.
• What is a chain drive? How chains are classified?
• Draw sketches of Helical gears, Bevel gears, Worm and Worm wheel.
• Differentiate between Belt drive and Chain drive.

Introduction to Mechanical Engineering_BME_Unit 1

In this document