CHAIN DRIVE Introduction Merits and demerits of chain drives Merits Demerits

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1 70 CHAIN DRIVE Introduction Chain is used to transmit motion from one shaft to another shaft with the help of sprockets. Chain drives maintain a positive speed ratio between driving and driven components, so tension on the slack side is considered is as zero. They are generally used for the transmission of power in cycles, motor vehicles, agricultural machinery, road rollers etc. Merits and demerits of chain drives Merits 1. Chain drives are positive drives and can have high efficiency when operating under ideal conditions. 2. It can de used for both relatively long centre distances. 3. Less load on shafts and compact in size as compared to belt drive. Demerits 1. Relatively high production cost and noisy operation. 2. Chain drives require more amounts of servicing and maintenance as compared to belt drives.

2 71 Velocity ratio in chain drive Let n1= speed of driver sprocket in rpm n2 = speed of driven sprocket in rpm z1= number of teeth on drivers sprocket z2 = number of teeth on driven sprocket Therefore Velocity ratio n1/n2= z1/z2 Chains for power transmission The different types of chain used for power transmission are: i. Block chain ii. Roller chain iii. Inverted-tooth chain or silent chain. ROLLER CHAIN It consists of two rows of outer and inner plates. The outer row of plates in known as pin link or coupling link whereas the inner row of plates is called roller link. A Pin passes through the bush which is secured in the holes of the inner pair of links and is riveted to the outer pair of links as shown in Fig. Each bush is surrounded by a roller. The rollers run freely on the bushes and the bushes turn freely on the pins. A roller chain is extremely strong and simple in construction. It gives good service under severe conditions. To avoid longer sprocket diameter, multi-row-roller chains or chains with multiple strand width are used. Theoretically, the power capacity multistrand chain is equal to the capacity of the single chain multiplied by the number of strand, but actually it is reduced by 10 percent. Inverted tooth chain or silent chain It is as shown Fig. these chains are not exactly silent but these are much smoother and quieter in action than a roller chain. These chains are made up of flat steel stamping, which make it easy to built up any width desired. The links are so shaped that they engage directly with sprocket teeth. In design, the silent chains are more complex than brush roller types, more expensive and require more careful maintenance.

3 72 Chordal action When a chain passes over a sprocket, it moves as a series of chords instead of a continuous arc as in the case of a belt drive. Thus the center line of a chain is not a uniform radius. When the driving sprocket moves at a constant speed, the driven sprocket rotates at a varying speed due to the continually varying radius of chain line. This variation in sped ranges from Where n 1 = Speed of the driving sprocket in rpm d 1 Pitch circle diameter of the driving sprocket in mm z1 = number of teeth on driving sprockets. It is clear from above that for the same pitch, the variation in speed and articulation angle decreases, if the number of teeth in sprocket is increased. The average speed of the sprocket as given by Where p = pitch of the chain in mm and z = number of teeth in sprocket. This chordal action of the chain is shown in Fig.

4 73 DESIGN PROCEDURE FOR ROLLER CHAIN Let p = Pitch d1 = diameter of smaller sprocket d2 = diameter of larger sprocket n1 = speed of smaller sprocket n2 = speed of larger sprocket z1 = number of teeth on smaller sprocket z2 = Number of teeth on larger sprocket L = Length of chain in pitches C = Center diameter Cp = Center distance in pitches 1. Pitch of chain Where p in mm, and n1= speed of smaller sprocket Select standard nearest value of pitch from Table Chain number Breaking load Fu Measuring load w 2. Number of teeth on the sprockets From Table for the given ratio select the number of teeth on the smaller sprocket (z1) Since Number of teeth on larger sprocket = z2 3. Pitch diameters

5 74 = pitch diameter of smaller sprocket = pitch of larger sprocket 4. Velocity 5. Required pull 6. Allowable pull 7. Number of strands in a chain 8. Check for actual factor of safety

6 75 6. Allowable pull 10. length of chain 11. Correct centre distance Select a roller chain drive to transmit power of 10 kw from a shaft rotating at 750 rpm to another shaft to run at 450 rpm. The distance between the shaft centers could be taken as 35 pitches. Data: N= 10 kw; n1 = 750 rpm; n2 = 450 rpm; C = 35 pitches

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