Category: Advance Concept Mechanical Eng

Figure 13.12 shows the schematic diagram of double purchase winch crab. In this device, velocity ratio is increased by using two pairs of gears. There are three axles as effort axle, intermediate, and load axle, two pinion gears as P1 and P2, two spur gears as S1 and S2. Pinion P1 mounted on effort axle, pinion P2 and spur gear S1 are mounted on the intermediate axle while…

Figure 13.11 shows the schematic diagram of single purchase winch crab. There are two axles: effort axle and load axle. On the effort axle, a small toothed wheel of small diameter known as pinion is mounted. The pinion is a driving gear and is meshed with a large gear known as spur gear. Spur gear is…

Figure 13.10 shows a worm and worm wheel arrangement. It consists of a threaded screw B called worm and a toothed wheel C called worm wheel. The worm B is in mesh with worm wheel C and their axes are perpendicular to each other. Figure 13.10 Worm and Worm Wheel On the axis of worm B, an…

Figure 13.9 shows Weston’s differential pulley block arrangement consisting of two blocks A and B. Upper block A is provided with two pulleys 1 and 2, having differential diameters. Both pulleys behave as one pulley. Lower block B carries a movable to which load W is attached. One string passes over all the pulleys. The effort is applied…

First Order Pulley: VR = 2n where n is number of movable pulleys, only one pulley is fixed. Second Order Pulley: Three fixed and three movable pulleys are in the system. Single string passes over all the pulleys. VR = n where n is total number of pulleys. Third Order Pulley: One pulley is fixed; one end of each string is connected to load. VR…

Figure 13.7 shows a single fixed pulley arrangement which consists of a wheel with a groove around its circumference to receive a rope or chain. It is mounted on an axle about which it can rotate freely. The ends of the axle are supported by a frame called block. Block may be fixed or movable, if…

Figure 13.6 shows the arrangement of differential wheel and axle. It is used to lift the heavier loads. In this lifting machine, the axle is made up of two cylindrical axles B and C of different diameters d1 and d2, respectively. Wheel A has larger diameter, D. The wheel A and axles B and C are keyed to the…

Figure 13.5 shows the working of simple wheel and axle. It consists of a wheel A of larger diameter and axle B of smaller diameter. Both wheel A and axle B are keyed to the same shaft. There are two strings—first is wound around the wheel A to which effort is applied and second is wound…

In the case of self-locking machine, after load removal friction force overcomes the work done by the load in reverse direction. Thus for an irreversible of self-locking machine efficiency should be less than 50%. Example 13.1: In a lifting machine, it was found that the effort was moved by 300 mm to lift a load by…

  Frictional loss = Input – Output = P × y – W × x   When effort is removed, i.e., P = 0. The work done by the load exceeds the frictional loss and load starts to move in reverse direction. Thus for a reversible machine the efficiency must be greater than 50%.