Chain drives are the most important drives for the transmission of power. It is a positive drives system unlike self-drives. The velocity ratio of chain drives, i.e., ratio of angular velocity of the driving sprocket wheel remains constant with no slip and no creep. The velocity ratio in this case is as high as 8 which are quite high.
Figure 9.14 shows a complete assembly of chain drive system. It has two toothed sprockets and a chain. Chain drives are very much suitable for the power transmission for small center-to-center distance and can be suitably used up to 2.5 m but, however; the distance can be increased in most special application.
A single chain can be used to drive a number of shafts to get the power transferred. These chains have a longer life as compared to belt drive but the operation is not so smooth. Chain drive produces noise in operation due to impact when the chain roller contacts the sprocket tooth. There is a variation of speed of chain from one tooth to another. It may cause vibration.
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The lubrication of chain is essentially done to work smoothly, with a noiseless operation and to ensure a long and trouble-free life of chain. In regards to this, the arrangement for transmission chain drive system will essentially have an endless chain and two wheels called sprockets.
Sprockets are the toothed wheels, as shown in Figs. 9.15(a) and 9.15(b), on which endless chain is fitted. The endless chains are formed in different sizes on the basis of center-to-center distance of wheel. The most important applications of chain drive system in power transmission are bicycles, motorcycles, scooters, machine tools, conveyors, etc.
There are two important types of chains which are commonly used:
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(a) Roller Chain and
(b) Silent Chain.
(a) Roller Chain:
Roller chains are simple chains which are used in bicycle, motor cycle, scooter, machine tools, etc. Figure 9.16 shows a portion of a roller chain with pin links. A roller link consists of two rollers which roll on two bushings which are press fitted into two link plates. A pin link consists of two pins which are press fitted into two link plates.
(b) Silent Chain:
Figure 9.17(a) shows several laminations of the links pinned together. The bush is fitted into each hole of the lamination of links. The chain is made by joining these links through pins. These are silent chains. Each link plate has two teeth with a space in between them to accommodate the mating tooth of sprockets.
Silent chains are used for smooth and noiseless operations. Figure 9.17(b) shows a portion of silent chain running on a portion of sprockets.
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Advantages of Silent Chain:
(a) Effective transmission of power.
(b) Positive drive in the absence of slip.
(c) System is useful for small center-to-center distance up to 2.5 m.
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(d) Velocity ratio is found as high as 8.
(e) System is compact and occupies less space.
Disadvantages of Silent Chain:
(a) More lubrication is required.
(b) Initial cost is high.
(c) Velocity of chain is fluctuating periodically.
(d) Alignment of driving and driven shaft should be properly done.