Power transmission elements BASIC MECHANICAL ENGINEERING SEM-II
- 1. Prof. A.B. Humbe HOD, Applied science Department ICEEM Aurangabad
- 2. Machine element is an individual component or a group of components of a machine which performs a specific function. Its function may be of holding the components together, to transmit power or to give supports. Depending upon these functions only, the machine elements are following types. 1) Machine elements used for holding the components. 2) Machine elements used for transmitting the power. 3) Machine elements used for support of other components.
- 3. Shaft:- It is rotating, circular cross section member used to transmit the power from one point to another point. The shaft is rotated by the application of tangential force applied by fitting components like belt, pulleys, gears etc. Types of shafts : 1.Transmission shaft : It is used to transmit power between power source and machine absorbing power. e.g. Line shaft , counter shafts. 2.Machine shaft : It is integral part of the machine itself. e.g. Crank shaft , camshaft in automobile , main shaft of turbine. Axle :- An axle is member which is used to support rotating wheels. It carries load. Spindle:-A spindle is short shaft used to give motion to a cutting tool or work piece on a machine tool.
- 4. Sr .No Shaft Axle 1 Rotating member Non-Rotating member 2 Used to transmit the torque and support the transmission elements, like: gears, pulleys Only used to support the transmission elements, like: wheels, pulleys etc 3 It is subject to torque, bending moment and axial force It is subjected to bending moment and axial force 4 Example- line shaft, counter shaft, spindle, crankshaft Example:- front axle of car, wheel axle of motorcycle etc.
- 5. It is mechanical device which is used to connect or disconnect the driving shafts from the driven at the will of operator. It is mounted between driving shaft. The flow of mechanical power from prime mover to the driven machine is controlled by means of clutch. In automobiles in order to change the gears or to temporarily stop the vehicle, the requirement is that the driven shaft should stop but the engine should continue to run. This is achieved by means of clutch mounted between engine and the gear box which is operated by lever.
- 6. 1. Positive 2. Friction a. Plate i) Single Plate ii) Multi Plate b. Cone c. Centrifugal
- 8. • It consist of two flanges. One is connected rigidly to a driving shaft with the help of key. The other flange is free to move along the driven shaft. • A spring is used to provide an actuating force. The sliding plate is forced to remain in contact with fixed plate with spring force and power transmitted from driving shaft to driven shaft. • Driving shaft flange is lined with friction material such as ferredo ( friction plate) • It makes perfect contact between two flanges because of spring force. No slipping occurs because of friction plate. • Power is transmitted smoothly when driven shaft is to be disconnected the force is applied by the operator against the spring force and the flange on the driven shaft is moved along the axis away from the friction plate. • Used in automobiles
- 10. • It is used to transmit large torque. • The working principle is same as single plate clutch but the contact area is increased by providing more number of plates. • It consist of outside plate connected to casing of the flange keyed to the driving shaft. • The inside plates are fastened to driven shaft through splines can have axial motion. • The axial force which is required to hold the disk together is provided by means of spring. • When driving shaft rotates resulting in rotation of discs and through inside plates driven shaft transmit the power due to friction. • Multi plate clutch are usually oil cooled. • Use motor cycle scooters also in machine tools.
- 11. It is the mechanical device used to slow down or completely stop the motion of moving system such as machine, vehicle or rotating drum, by applying an artificial frictional resistance . It is also used to hold the system under load at rest. In the process of performing this function , the brake absorbs the energy given by the moving system. The energy absorbed by the brake can either kinetic energy or potential energy or both. The energy absorbed by the brake is converted into heat and dissipated to the surrounding air .
- 12. On configuration On mode of actuation Block or shoe brake Drum and shoe brake Disk brake Band brake Band and block brake Mechanical brakes Pneumatic brakes Hydraulic brakes Electrical brakes Automatic brakes.
- 13. It consists of simple block or shoe which is pressed against rotating drum. The block which is rigidly attached to the lever or in some applications pivoted to the lever is lined with friction material like asbestos, leather etc. The actuating force is applied at the end of lever. Applications:- In trains
- 14. It consists of two blocks or two shoes pressed against a rotating drum by means of levers. The blocks or shoes which are pivoted to the levers, are lined with friction material like asbestos ,cork etc. The actuating force is applied at the end of actuating lever. The friction between the friction lining on the blocks and the brake drum causes the retardation of the drum. Applications :- Cranes, Trains
- 15. It consists of two shoes. The outer surface of shoes are lined with some friction material. Each shoe is pivoted at one end about hinge-pin subjected to actuating force at the other end. The actuating force on both shoes is applied by a hydraulic cylinder or a cam mechanism. When force is applied it causes the brake drum either to retard or stop completely. When actuating force is release retracting spring return the brake shoes. Applications:- Trucks, buses, cars, motorcycles.
- 16. It consists of a flexible steel band lined with the friction material, which embraces a part of the circumference of brake drum. The ends of band are joined to the lever which is pivoted at point o. In order to apply the brake, the band is tightened around the brake drum by applying force at the end of the lever. The frictional force between the band and the brake drum provides necessary braking force. This is not commonly used as shoe brakes. Applications:- Material handling equipment.
- 17. It consists of number of wooden blocks fixed insight the steel band. A steel band is fixed with wooden blocks embraces the part of circumference of the brake drum. The end of steel band are attached to lever which is pivoted at point o. When the actuating force is applied at the end of lever, the wooden blocks are pressed against the brake drum. The frictional force between wooden blocks and drum provides the braking force. It is not commonly used as shoe brake. Application:- Material handling equipment's.
- 18. The belts or ropes are used to transmit power from one shaft to another by means of pulleys which rotate at the same speed or at different speeds. The amount of power transmitted depends upon the following factors: 1. The velocity of the belt. 2. The tension under which the belt is placed on the pulley. 3. The arc of contact between the belt and the smaller pulley 4. The condition under which the belt is used. 5. The material of the belt used. Selection of the Belt Drive: 1. Speed of the driving and driven shafts. 2. Speed reduction ratio 3. Power to be transmitted 4. Centre distance between the shafts. 5. Positive drive requirements. 6. Shaft layout. 7. Space available. 8. Service conditions.
- 19. Open Belt Drive : It is used, when shafts are arranged parallel and rotating in the same direction, In this case, the driver A pulls the belt from one side (i.e. lower side) and delivers it to the other side (j,e. upper side). Thus the tension in the lower side belt will be more than that in the upper side belt. Hence lower side belt is known as tight side, whereas the upper belt is known as slack side,
- 20. Cross Belt Drive : This belt drive is used when shaft are arranged parallel and rotating in the opposite direction. A crossed belt drive can transmit more power than open belt drive, as the angle of wrap is more. However, the belt has to bend in two different planes and it wears out more.
- 21. Quarter Turn Belt Drive : The quarter turn drive always known as right angle belt drive, is used with shafts arranged at right angles and rotating in one definite direction. In order to prevent the belt from leaving the pulley, the width of the face of the pulley should be greater or equal to 1.4 b, where b- is the width of the belt. when the reversible motion is desired, then a quarter turn belt drive with guide pulley.
- 22. Belt Drive with idler Pulleys : A belt drive with an idler pulley, used with shafts arrangement parallel and when an open belt drive can not be used due to small angle of contact on the smaller pulley. This type of drive is provided to obtain in high velocity ratio and when the required belt tension cannot be obtained by other means. When it is desired to transmit motion from one shaft to several shafts, all arranged in parallel, a belt drive with many ideal pulleys can be employed. In conveyer system to avoid slackness of the belt, idler pulleys are used.
- 23. Compound Belt Drive : It is used to transmit power from one shaft to another through a number of pulleys.
- 24. Stepped or Cone Pulley Drive : A stepped or cone pulley drive, used for changing the speed of the driven shaft while the main or driving shaft runs at constant speed. This is accomplished by shifting the belt from one part of the steps to the another.
- 25. In belt drives, slipping of belt may occur. In order avoid slipping, steel chains are used, The chains are made up of rigid links which are hinged together in order to avoid the necessary flexibility for warping around the driving and driven wheels. The wheels have projecting teeth and fit into the corresponding recesses, in the links of The chain. The wheels and the chain are constrained to move together without slipping and ensures perfect velocity ratio. The toothed wheel are known as sprocket wheels or simply sprockets. These wheels resemble to spur gears
- 27. There are many different types of gear are used in various engineering applications. Some of them most commonly used are as shown below 1. Spur gears :- If teeth of the gear wheels are parallel to the axis of wheel . The gears are called spur gears. Teeth of the spur gears are cut on the circumference of the cylindrical discs. Spur gears can transmit higher power because of the contact between the mating gears is along a line. Use :- Spur gears are used for transmitting power between two shafts when the axis of the driving and driven shafts are parallel and co – planer. They commonly used in machine tools and automobile gear boxes.
- 28. 2.Helical gears :- Helical gears are similar to the spur gears. But the teeth are cut in the form of the helix around the gear . Their teeth are not parallel to the shaft axis. Two moving helical gears have identical helix angle but opposite hand . The helical gears run more smoothly and more quietly at high speeds and curvilinear contact of gear teeth giving gradual engagement. The main disadvantage of helical gears is that it produces end thrusts on the driving and driven shafts. But when double helical gears or Herringbone gears are used to connect parallel shafts, produces equal and opposite thrust on each wheel and gets balanced and do not transmit axial thrusts to the shafts, Uses :- Helical gears are used for transmitting power between two parallel , non parallel , non –intersecting shafts. Helical gears are used where smooth and quit running at high speeds is required. Generally , helical gears are used in automobile power transmission.
- 29. 3.Spiral gear :- The teeth of spiral gears are same as helical gears and it cut along helical path. In spiral gear , there is a point contact while curvilinear contact in case 0f helical gear drive. Because of the point contact in the spiral gears are more suitable for transmitting less power. Use:- Spiral gears are used to transmit power between two non – parallel , nonintersecting shafts.
- 30. 4.Bevel gears :- Teeth of the bevel gears are cut on conical surfaces . Bevel gear teeth are varying in cross section along the tooth width. The axis of two moving gears are inclined in the bevel gear. In most of cases , two bevel gears have their axes at right angle and are of equal sizes, called miter gears. Use :- Bevel gears are used for transmitting power between two shafts , when the axis of the two shafts are inclined and intersect each other. Bevel gears are widely used in automobiles.
- 31. 5.Worm and worm wheel :-A worm gear drive consists of worm and worm wheel. A worm has one or more number of helical threads of trapezoidal shape cot on it. A worm wheel is a wheel with the tooth profile consists of small segments of helix which engages with the worm. Uses :-Worm gears are used for transmitting power between two shafts having their axis at right angles and non –co-planer. Worm gears are suitable for transmission of power when a high velocity ratio is required. They are mostly used in machine tools like lathe . Milling , drilling machine etc. To get large speed reduction.
- 32. 6.Rack and pinion :- Rack is a rectangular bar consist of a series of straight teeth cut on it. Theoretically , rack is a spur gear of infinite diameter . The rack is mesh with another small gear known as pinion. Use:- The rack and pinion drive is used to convert rotary motion into linear motion . Rack and pinion arrangement , generally used in machine tools. Such as lathe , drilling , planning machines. It also used in measuring instruments.
- 33. Pitch circle :- It is an imaginary circle which produces by pure rolling action would give the same motion as the actual gear. Pitch circle diameter :- It is the diameter of the pitch circle. The size of gear is usually specified by the pitch circle diameter. Pitch Point:- It is common point of contact between two pitch circle
- 34. Pressure angle or angle of obliquity :- It is an angle between the common normal to the point of contact of two mating gear teeth and the common tangent at common point between two pitch circles. Circular pitch :- It is the distance measured on the circumference of the pitch circle from a point of one tooth to the corresponding point on the next tooth. Pc=πd /T, where T =number of teeth Module (m) :- It is ratio of the pitch circle diameter in millimeters to number of teeth. m = d/T Addendum:-It is the radial distance of a tooth from the pitch circle to the top of tooth Dedendum:-It is the radial distance of the tooth from pitch circle to the bottom of tooth Diametral Pitch:-It is the ratio of number of tooth to pitch circle diameter in mm Pd=T/d
- 35. Thank you…