Unit 1

1. Unit 1 Machine Elements

2. Introduction to Machine • A machine is device, consisting of various elements arranged • together, so as to perform the prescribed task to satisfy • human needs. INPUT (Source of Energy) MACHINE (Arrangement of elements) OUTPUT (Prescribed task) • A machine is capable of doing some useful work. It converts • and transfers energy. • Examples:- pump set, I.C. engines, turbine, screw jack etc.

3. Introduction to machine

4. Machine elements • Any machine is made up of number of different components. • An individual component of the machine is known as • machine element. • Each component performs a specific function. • The functions of machine elements:- • Holding the different components of machine. • Supporting the different components of machine. • Transmitting the power from one machine component to • another.

5. Types of machine elements Machine elements Holding Type Element Supporting Type Element Power transmitting element • Keys • Nuts and bolts • Cotters • Rivets • Axles • Bearings • Brackets • Body or Frame • Shafts • Pulleys and belts • Sprockets and chains • Gears

6. Machine Elements • The machine elements which we are studying: • Shaft • Axle • Key • Couplings • Bearings • Clutches • Brakes • Belts • Gears

7. Shaft • A shaft is a rotating member which transmits power from • one point to another. • The shaft is rotated by application of tangential force which is • applied through pulleys and gears mounted on the shaft. • As tangential force is acting on shaft, they are generally made • round in cross section. • Types of shaft:- • A. Transmission Shaft: B. Machine shaft: • i. Line shaft i. Spindle. • ii. Counter shaft ii.Crank shaft

8. Types of shaft • Transmission shaft :- • A shaft which is used to transmit the power between the • machine generating power and absorbing power. • e.g: Fire Pump, Portable Agriculture Pump. • The transmission shafts supports transmission elements like, • gears, pulleys, sprockets etc. • The transmission shaft are subjected to torque, bending • moment and axial force. • The examples of transmission shaft are line shaft and counter • shaft.

9. Explain here with Diagram

10. Types of shaft • 2. Machine shaft :- • A machine shaft is the short rotating shaft which is an • integral part of machine itself. • The machine shaft are also subjected to torque, bending • moment and axial force. • The examples of transmission shaft are spindle and crankshaft. • e.g: Spindle, crank shaft

11. Types of Shaft A) Solid shaft • Solid shaft are used in all types of • machines. • Hollow shafts are lighter in weight than • solid shafts. • Hollow shafts provide more strength per • kg weight of the shaft. • The shaft is also made stepped for fixing • transmitting elements like pulleys, gears • and bearings. B) Hollow shaft C) Stepped shaft

12. Shaft material and their properties • The material used for shaft should have following properties:- • It should have high strength and good machinability. • It should have high wear resistance and good heat treatment • properties. • iii. It must be hard enough and posses good corrosive resistance. • iv. It should be ductile. • The material used for shaft are:- • i. The common material used for shaft is mild steel. • The Plain Carbon steel (containing 0.4 to 0.6 % carbon) is preferred where • high strength and wear resistant is required. e.g: 40C8,45C8,55C8 • iii. Alloy steels such as nickel, chromium and molybdenum steels are used • where very high strength and corrosive resistance are needed. e.g: 40Cr1. • Manganese = Improving Hardenability

13. Axle • Axle is an non rotating machine element which is used to • support rotating machine elements like wheels, pulleys etc. • An axle does not transmit torque. It is subjected to bending • moment and axial force. • The purpose of axle is to secure the wheels or gears to specific • locations relative to other wheels or gears. • There are three different kinds of axles in vehicles:- • Straight axle • Split axle • Tandem axle

14. Axle

15. Difference Between shaft and axle

16. Keys • Key is an element used to prevent relative motion between a shaft and the part mounted on it, such as pulley and gear wheel. • A groove/recess/slot is cut on surface of the shaft, parallel to its axes and in the hub of the part to be mounted. They are called keyways. • The material used for keys are plain carbon steels and alloy steels. • The material used for key are is of lesser strength than the shaft material. • Function of keys:- • Prevent the relative motion between the shaft and hub of • rotating element like gear, pulley or sprocket. • To transmit the torque from the shaft to rotating elements.

17. Keys

18. Types of keys • The keys are broadly classified into six types:- • Sunk Key • Square sunk key • Rectangle sunk key • Parallel sunk key • Gib-head sunk key • Feather sunk key • Woodruff key. • 2. Saddle key • Flat saddle key • Hollow saddle key • 3. Round key and taper pins • 4. Kennedy key • 5. Tangent key • 6. Splines

19. Types of keys • Sunk Key :- • The sunk keys are provided half in the keyway of the shaft and half in the • keyway of the hub or boss of the rotating element. Square sunk Key:- w = t = d/4 Taper of 1:100 is provided on hub side. Square sunk key Rectangular sunk key:- w = d/4, t = d/6 or 2/3 w. Taper of 1:100 is provided on hub side. Parallel sunk key:- No taper is provided. Application: Gearbox Rectangular sunk key

20. Types of Keys • d) Gib-Headed sunk Key:- • Rectangular tapered sunk key with gib head • provided at one end. • Easy removal and installation of key. • Flywheel, pulley, gear, overhaging shaft Gib-Headed Key • e) Feathered sunk key:- • It is parallel key fasten either to shaft • or hub. • It prevents relative rotary motion • but Permits axial relative motion between • shaft and hub. e.g: clutch & gear shifting device. Feathered Key • f) Woodruff key:- • The key is a piece of cylindrical disc segment of • uniform strength. • Used to transmit small torques. Woodruff Key

21. Types of keys • 2. Saddle Key :- • The saddle key is a tapered key which completely fits in the keyway • provided in the hub of rotating element. • The torque is transmitting due to the friction between the key and the • shaft. Hence the torque transmitting capacity of saddle is low. • The different saddle keys are: • Flat saddle key:- • It is a taperless key which sits on a flat • surface provided on shaft and fits • in a keyway provided in the hub. • Hollow saddle key:- • It is a tapered key which fits in a • keyway provided in the hub. • The key is hollow so as to sit on the • curved surface of the shaft.

22. Types of keys • Round Keys:- • Circular in cross section. • Fitted into the partly drilled holes in shaft • and hub. • Used for low power transmission. Round Key • Tapered pins:- • Taper of 1:50 is provided. • Used for low power transmission. Tapered pin • Splined shaft:- • Consist of multiple integral keys in 4,6,10 • or 16 in number. • Strength is more than single keyway shaft. • Used for large power transmission. • Used in automobile gear box. Splines

23. Types of keys • Tangent key:- • Consist of two tapered rectangular keys • placed at 900 apart. • Each key withstands torque in one direction. • Used in heavy duty industrial application. Tangent Key • Kennedy Key:- • Consist of two tapered square keys placed • at 900 apart. • Used in heavy duty industrial application. Kennedy Key

24. Couplings • Coupling is an important mechanical element used to connect two shafts or to couple driver shaft with driven shaft. • Shafts are usually available up to 7 meters length due to inconvenience in transport. • Inorder to have greater length, it is necessary to join two or more pieces of shaft by means of couplings. • So a coupling is a device used to connect two shafts permanently so that necessary power and torque can be transmitted. • The coupling can be used when, • - When axes of shaft are collinear. • - When two shafts are intersecting. • - When two shafts are parallel and some distance apart.

25. Requirements of Couplings • The requirements of good couplings are, • It must transmit full power of the driving shaft. • It should keep the shaft in perfect alignment or it should absorb the slight mis-alignment between the shaft. • It should be easy to connect and disconnect the coupling. • It should be able to operate in any type of operating condition. • It should not transmit shock loads. • vi It should be easily available at low cost. • vii. It should not have any projected part.

26. Types of shaft couplings • The shaft couplings are classified into two types:- • Rigid coupling:- • Rigid couplings are used to connect two shafts which are perfectly aligned. • These couplings has no flexibility hence the shafts need to be in good alignment, in order to avoid excessive loads on coupling or shaft bearing. • Following are types of rigid couplings:- • Flange coupling • Sleeve or Muff coupling • Clamp or compression coupling

27. Types of shaft couplings • Flexible coupling:- • Flexible coupling used to connect two shafts consisting of small amount of mis-alignment which may be lateral or angular. • The shock and vibration absorption capacity of these couplings is more. • Following are types of flexible couplings:- • Bushed pin type flexible coupling • Oldham’s coupling • Universal coupling or Hook’s joint

28. Types of Rigid coupling • Rigid flange coupling:- • It consist of two separate cast iron flanges, which are mounted on shaft with the help of key. • The two flanges are coupled together by means of nut and bolts. • Advantages: • It is simple in construction. • It is easy to assemble and disassemble. • It has high torque transmitting capacity. • Disadvantage: • If there is small misalignment between shafts, then flange coupling can not be used. • This coupling is used when the motion is free from shocks and vibrations.

29. Types of Rigid coupling • Applications: • Used to connect electric motor to pump or electric motor to compressor. • Flange coupling is generally used for heavy loads and in long shafts. Rigid flange Coupling

30. Types of Rigid coupling • 2. Sleeve or muff coupling:- 3. Clamp or compression spring

31. Types of flexible coupling • Bush pin type coupling:- • In bush pin type flexible • coupling, rubber bushes are • used which are inserted into • the flanges. • It can tolerate very small • amount of lateral or angular • misalignment.

32. Types of flexible couplings • 2. Oldham coupling:- • Used for connecting two shafts whose axes are parallel and at a small distance(lateral) apart. • There is a relative sliding motion between flanges and intermediate circular disk.

33. Types of flexible coupling 3. Universal coupling or Hook Joint:- • Used for connecting two non parallel and intersecting shafts having small angle between them. • It consist of two U shaped yokes or forks and a cross or connecting link. • This is used to transmit power from the gear box of automobile engine to the rear axle.

34. Bearing • Bearing is a machine element used for supporting rotating shaft and carry loads applied to them. • It permits relative motion between bearing surface and shaft surface and facilitate smooth running. • Relative motion, sets up frictional force and certain amount of power loss to overcome this frictional force. • The frictional force generates heat. • So lubrication is provided between two surfaces to avoid wear, power loss and heat generation.

35. Types of Bearings • The bearings are generally classified into sliding contact bearings and rolling contact (antifriction) bearings. • Sliding Contact bearings • The bearing in which the contacting surface makes sliding contact or are seperated by a film of lubricant are known as sliding contact bearings. • a. Journal Bearing • b. Thrust Bearing • Rolling contact bearings • The bearings in which the contacting surfaces make a rolling contact are known as rolling contact bearings. • a. Ball bearing • b. Roller bearing

36. Sliding contact bearings • The Sliding contact bearings are: • Journal Bearing • The relative sliding motion between the two parts is rotary. • The load is acting perpendicular to axis of the shaft. • Journal bearing supports radial loads. Load Journal Bearing • Thrust Bearing • The relative sliding motion between the two parts is rotary. • The load is acting parallel to axis of the shaft. • Thrust bearing supports axial (Thrust) loads. Thrust Bearing

37. Rolling contact bearing • The rolling contact bearings are ball bearing and roller bearings. • The ball and roller contact bearing consist of an inner race which is mounted on shaft or journal and an outer race which is carried out by the housing or casing. • In between inner and outer race there are balls or rollers, these are held at proper distances so that they will not touch each other. • In ball bearings the contact between balls and inner & outer race is point contact. • Where as in roller bearings the contact between rollers and inner & outer race is line contact.

38. Rolling contact type Ball Bearing Balls Outer Race Cage Inner Race Ball Bearing

39. Rolling contact type Roller Bearing Rollers Outer Race Cage Inner Race Roller Bearing

40. Types of Ball Bearing • The different types of ball bearings are: • Single row deep groove ball bearing:- • Take radial as well as thrust load. • Carry high radial load and moderate • thrust (axial) load. • Double row deep groove ball bearing:- • Carries heavier radial and axial loads. • Used instead of using two single row deep groove • ball bearings. • Angular contact ball bearing:- • Carries substantial thrust (axial) load in • addition to radial load. • Thrust ball bearing:- • Used to take pure thrust (axial) loads.

41. Types of Roller Bearing • The different types of roller bearings are: • Cylindrical roller bearing:- • Take greater radial load. • Cannot take thrust (axial) load. • Needle roller bearing:- • Carries heavier radial loads. • Used where radial space is limited. • Taper roller bearing:- • Carries high radial and thrust (axial) load. • Taper roller Thrust roller bearing:- • Used to take pure thrust (axial) loads.

42. Comparison between Ball & Roller bearing

43. Clutch

44. CLUTCH • Clutch Introduction • 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. • A popularly known application of clutch is in automotive vehicles where it is used to connect the engine and the gear box.

45. Clutch • Clutch is mechanical device used to connect or disconnect driving shaft from the driven shaft at the will of operator. • It is mounted between driving shaft and driven shaft. • Mostly clutch is used in • Automobiles.

46. Classification of clutch • The clutch is classified into general two types: • Positive clutch • Positive clutch are used when positive drive is required. • a. Square jaw clutch • Friction clutch • Friction clutch is a non positive drive clutch. • a. Disc or plate clutch • i. Single plate clutch • ii. Multi plate clutch • b. Cone clutch • c. Centrifugal clutch

47. Classification of clutch

48. Positive clutch • Positive clutches are used when • positive drive is required. • The Jaw clutch is the simplest type • of positive clutch. • It permits one shaft to drive another • shaft through a direct contact of • interlocking jaws. Square jaw toothed clutch

49. Positive clutch Advantages of positive clutch 1) They do not slip. 2) No heat is generated. 3) Requires little or no maintenance. 4) Design is simple. Disadvantages of positive clutch 1) They cannot be engaged at high speeds. 2) Sometimes, they cannot be engaged when both shafts are at rest unless the jaws are aligned. 3) Engagement at any speed is accompanied by shock. 4) Frequent engagement and disengagement cause wearing of jaws, which affects their performances. Applications of positive clutch : Automotive transmission, presses, punches and household appliances like kitchen grinding machine.

50. Friction clutch • Transmit power or motion by friction between contacting surfaces. • Uses: • Transmission of power of shaft and machines which must be started and stopped frequently. • When power is to be delivered to machines partially or fully loaded. • Requirements: • The contact surface should develop sufficient frictional force that may pick up and hold the load. • The heat of friction should be rapidly dissipated and tendency to grab should be minimum. • The surface should be backed by a material stiff enough to ensure a reasonably uniform distribution of pressure.