Machine elements

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 Flange Flange 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

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

21. Types of Friction Clutches Disc or plate clutches Cone clutches Centrifugal clutches

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

23. 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

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

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

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

27. 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 = μ Wr m cosec α w

28. Centrifugal clutch Driving shaft Driven shaft Friction lining Total friction torque , T = nµR(F-P) F=mr ω 2 ω ω P R