Subtopic: Design and selection of machine elements – gears, pulleys, chains and sprockets and belts
Question Statement:
While testing a wheat thresher at the recommended throughput, 80 N m torque is recorded at 750 rpm at the main shaft of the threshing cylinder, which is operated by a 200 mm diameter v-pulley. The overload factor and unit mass of the v-belt are 1.2 and 0.9 kg m⁻¹, respectively. At the condition of maximum power transmission, the maximum tension in the v-belt in N is ______
Official Answer Key:
165 to 168
Step-by-Step Solution & Explanation
Pulley angular speed ω = 2πN/60 = 2π×750/60 = 78.54 rad/s; belt (pitch-line) velocity V = ω×D/2 = 78.54×0.1 = 7.854 m/s. Centrifugal tension Tc = m·V² = 0.9×7.854² = 55.52 N. For maximum power transmission, the classical belt-drive condition is that the centrifugal tension equals one-third of the maximum (tight-side) tension: Tc = T_max/3, i.e. T_max = 3×Tc = 3×55.52 = 166.5 N, within the accepted band 165–168. (The torque, rpm and overload factor confirm the design power requirement is compatible with this belt/pulley combination but the T_max = 3Tc relation directly gives the requested maximum tension.)
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