Subtopic: Design and selection of machine elements – gears, pulleys, chains and sprockets and belts
Question Statement:
Which of the following statements regarding mechanical belt drives used in agricultural machinery is/are correct?
Options:
(A) In a crossed flat belt drive, the driving and driven pulleys rotate in opposite directions.
(B) The angle of contact for an open belt drive is always smaller on the smaller pulley.
(C) Centrifugal tension reduces the effective belt tension available for power transmission at high speeds.
(D) V-belts utilize the wedging action inside pulley grooves, permitting higher torque transmission at smaller wrap angles compared to flat belts.
Answer Key:
A, B, C, D
Step-by-Step Solution & Explanation
• Crossed belts reverse rotation direction (A is correct).
• In an open drive with unequal pulley diameters, wrap angle on smaller pulley is $\theta = 180^\circ - 2\arcsin((D-d)/2C) < 180^\circ$ (B is correct).
• Centrifugal tension $T_c = mv^2$ acts radially outward, reducing net normal contact pressure and effective grip (C is correct).
• V-belt groove wedging increases apparent friction coefficient to $\mu/\sin\beta$, substantially enhancing traction (D is correct).