Page 165 - Analysis and Design of Machine Elements

Belt Drives
3 A belt drive can transmit a maximum power of P = 3 kW. The driving sheave has a 143
−1
diameter of d = 150 mm, rotating at n = 1420 r min .Thecontact angleonthe
1 1
∘
driving sheave is = 160 . The coefficient of friction between the belt and belt
1
sheave is 0.3. Decide the maximum effective force F and tight side tension F .
ec 1
4 A single belt drive with an initial tension of F = 300 N has a contact angle of
0
∘ −1
= 150 on the small drive. The belt speed is v = 8ms . If the equivalent coef-
1
ficient of friction between the belt and belt drive is f = 0.5, neglecting centrifugal
force, decide the maximum power P thebeltdrive cantransmit.
∘
5 A belt drive has contact angles of 180 on the driving and driven sheaves with an
initial tension of F = 150 N. The equivalent coefficient of friction is 0.5. Neglecting
0
centrifugal force, if the transmitted effective force is F = 180 N, decide whether the
e
belt will slip and explain why.
Design Problems
1 Design a V-belt drive for a 5.5 kW motor running at 1440 rpm driving an air com-
pressor at 520 rpm. Ensure it has the shortest possible centre distance.
2 A single V-belt is selected to deliver 3 kW engine power to a tractor. Approximately
70% of this power is transmitted to the belt. The maximum engine speed is 3000 rpm.
The driving sheave has a diameter of 150 mm, the driven, 300 mm. The belt selected

should be as close to a 2300 mm datum length as possible. Select a satisfactory belt.
3 A 1.5 kW electric motor running at 1460 rpm is to drive a blower at a speed of
240 rpm. Select a V-belt drive for this application and specify standard V-belts,
sheave sizes and centre distance.
4 The compressor of a small air-conditioning unit requires a 1.5 kW, 1200 rpm motor.
The speed of compressor is 300 rpm. The centre distance should be minimized to
provide a compact design. Design a suitable V-belt drive.

Structure Design Problems

1 On a V-belt drive in Figure P6.1, the angle between the two working surfaces of
∘
the V-belt is = 40 , then the corresponding angle on the sheave groove is
1
∘
________40 .
(a) >
(b) <
(c) =
2 In Figure P6.2, which one best depicts the position of a V-belt in a sheave groove?
______.
3 Figure P6.3 is a layout of power transmission. Find the errors and correct them.

4 For the tensioning scheme shown in Figure P6.4, part (a) is for a flat belt, while
(b) is for a V-belt. Make corrections where you see the errors occur.