Page 189 - Analysis and Design of Machine Elements

Calculation Questions Chain Drives 167
1 A chain drive with pitch p = 25.4 mm rotates at n = 750 rpm. The number of teeth
1
of driving sprocket is z = 23. Determine the average speed v, the maximum speed
1
v max and the minimum speed v min .
2 A single-strand roller chain is used to transmit power between a 23-tooth driving
sprocket and a 69-tooth driven sprocket. The rotational speed of driving sprocket
is 960 rpm. If the rotational speed of driven sprocket is reduced to 210 rpm:
(a) What is the number of teeth of driving sprocket if the teeth number of the
driven sprocket is kept unchanged? What will be the power transmitted?
(b) What is the number of teeth of a driven sprocket if the teeth number of the
driving sprocket is kept unchanged? What will be the power transmitted?
(c) Compare the two approaches: which one is better?

3 A single-strand 08A chain operates on a 20-tooth sprocket at 750 rpm. The small
sprocket is applied to the shaft of an electric motor and the output sprocket to a
conveyor. Determine the power rating for the single-strand chain. What would be
the rating for four strands?

4 A four strand 08A roller chain is proposed to transmit power from a 21-tooth driv-
ing sprocket that rotates at 1200 rpm. The driven sprocket is to rotate at one-third
the speed of the driving sprocket.
(a) Determine the power that can be transmitted by the chain drive;
(b) Estimate the centre distance if the chain length is 82 pitches;
(c) Describe the preferred method of lubrication.

Design Problems

1 Design a roller chain drive to transmit 10 kW. The rotational speed of motor is
n = 970 rpm. The speed ratio of the chain drive is i = 3, uniform power transmission
and centre distance no less than 550 mm.

2 A 5 kW 750 rpm electric motor is to drive an agitator at 325 rpm. The motor shaft
will be in approximately the same horizontal plane as the agitator shaft. Specify the
chain size, the sizes and number of teeth of sprockets, the number of chain pitches
and the centre distance.

3 A heavy conveyor is to be driven at 250 rpm by a 30 kW six-cylinder engine with an
input speed of 500 rpm. The centre distance is approximately 1000 mm. Moderate
shock loading is expected. Select a suitable roller chain and associated sprockets for
this application.