Unit-I Introduction to Mechanical Engineering A) Machine Elements B) Power Transmitting Devices

1. MACHINE ELEMENTS
Prof.A.J.More
AISSMSIOIT,Pune

2. Introduction
• A machine is a device which recieves energy in some
available form and utilises it to do some particular type of
work.
• Machine elements is an individual component or group of
components to perform a specific function.
• These elements are used for-
• 1. power transmission
• 2. holding the components
• 3. providing support

3. Power transmitting elements
• These are used to transmit power from one part to
another part of the machine.
• These are—
• Shafts
• Gears
• Pulleys
• Cams
• Chains,etc

4. Examples of power transmitting elements

5. Shafts
• A shaft is a rotating power component which is used to
transmit power from one component to the other.
• It provides the axis of rotation for elements like gears,
pulleys,flywheel,etc
• The cross section may be solid or sometimes hollow.
• Types—
• 1. transmission shafts
• 2. machine shafts

6. Transmission shaft

7. Holding elements
• These elements are used to hold various parts of the
machine.
• These includes---
• Nuts
• Bolts
• Pins
• Rivets

8. Holding elements

9. Supporting elements
• These elemens are used to support various parts of the
maachine.
• These are –
• Bearings
• Brackets
• keys, etc

10. Bearings
• Bearing is a machine element which supports another
moving machine element called as journal.
• It permits the relative motion between the contact
surfaces
• There is friction and wear
• Lubricant may provided.
• Types ---
• 1. sliding contact bearing
• 2. rolling contact bearing

11. Bearing and its types

12. Spring 2006 ENSC305/440 12
Bearing types
Ball bearing
Tapered roller
bearing
Needle roller
bearing
Thrust bearing

13. Keys
• Key is a machine element usually made of mild steel
which is inserted between the shaft and hub in order to
prevent relative motion.

14. Couplings
Coupling is a device used to connect two shafts together at their
ends for the purpose of transmitting power
Motor
Coupling
Pump

15. Uses of coupling
• To provide connection of shafts of units made separately
• To allow misalignment of the shafts or to introduce
mechanical flexibility.
• To reduce the transmission of shock loads
• To introduce protection against overloads.
• To alter the vibration characteristics

16. Types of coupling
• Rigid
• Flexible
• Universal
Rigid coupling
Flexible coupling
Universal coupling

17. Rigid coupling
Flange
Driven Shaft
Driving
Shaft
Key Hub
•Rigid couplings are used when precise shaft alignment is required
•Simple in design and are more rugged
• Generally able to transmit more power than flexible couplings
•Shaft misalignments cannot be compensated
Flanged Coupling

18. Flexible Coupling
Bush
FlangeFlange
Driving
Shaft
Driven Shaft
Pin
•A flexible coupling permits with in certain limits, relative rotation and
variation in the alignment of shafts
•Pins (Bolts) covered by rubber washer or bush is used connect flanges
with nuts
•The rubber washers or bushes act as a shock absorbers and insulators.

19. A Clutch is a machine member used to connect
the driving shaft to a driven shaft, so that the
driven shaft may be started or stopped at will,
without stopping the driving shaft. A clutch thus
provides an interruptible connection between two
rotating shafts. Clutches allow a high inertia load
to be stated with a small power.
Clutch

21. A clutch enables two co-axial shafts to be
engaged or disengaged while at rest or in
relative motion.
Friction Clutches

22. TYPES OF FRICTION
CLUTCHES
1. Disc or plate clutches
2. Cone clutches
3. Centrifugal clutches

23. T
T
W (axial thrust)W
Friction
plate
Friction
liningPressure
plates
springs
Single-plate Friction Clutch (Disengaged position)
Driving
shaft
Driven
shaft
Flat-plate friction clutches

24. Single-plate Friction Clutch (Engaged position)
T
T
W (axial
thrust)
W
Friction plate
Friction
lining
Pressure
plates
springs
Driving
shaft
Driven
shaft
Flat-plate friction clutches

25. An example is the clutch found in most
automobiles.
Flat-plate friction clutches

26. Torsional
springs
Splined boss
(hub)
Friction
lining
Clutch plate or friction plate

27. Pressure
plate
Diaphragm
spring
Clutch
housing
Pressure plate and housing

29. Driving
shaft
Driven
shaft
Friction
lining
α
The maximum torque transmitted =
α = semi-apex angle of
the cone
Only one pair of driving
surfaces is possible, n =1
Cone clutch
T = μWrm cosecα
w

30. Centrifugal clutch
Driving
shaft
Driven
shaft
Friction lining
Total friction torque , T = nµR(F-P)
F=mrω2
ω
ω
P