Subtopic: Design and selection of machine elements – gears, pulleys, chains and sprockets and belts
Question Statement:
In the design and selection of V-belt drives for agricultural machinery, which of the following statements are CORRECT?
Options:
(A) V-belts utilize the wedging action in the pulley groove, significantly increasing the effective coefficient of friction
(B) The groove angle of a V-pulley is made slightly smaller than the nominal belt angle to compensate for belt cross-section distortion during bending
(C) Centrifugal tension reduces the maximum power transmitting capacity of a belt drive at very high speeds
(D) Slip in a V-belt drive is entirely eliminated due to the wedging action in the groove
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
1. The effective coefficient of friction for a V-belt in a groove of angle $2\beta$ is $\mu' = \frac{\mu}{\sin \beta} > \mu$. (Statement A is True)
2. When a V-belt bends around a sheave, its outer section stretches and its inner section compresses, reducing the trapezoidal wedge angle. Thus sheave groove angle is cut to $34^\circ - 38^\circ$ instead of $40^\circ$. (Statement B is True)
3. Centrifugal tension $T_c = m v^2$ decreases effective tight and slack side tensions $(T_1 - T_c)$ and $(T_2 - T_c)$, limiting power capacity at high speeds. Maximum power occurs when $T_c = T/3$. (Statement C is True)
4. V-belt drives are friction-dependent flexible drives and can experience creep and slip under heavy overload; they are not positive drives like timing belts or chains. (Statement D is False)