The layout of a shaft carrying two pulleys 1 and 2, and supported on two bearings A and B is shown in Fig (1). The shaft transmits 7.5 kW power at 360 rpm from the pulley 1 to the pulley 2. The diameters of pulleys 1 and 2 are 250 mm and 500 mm respectively. The masses of pulleys 1 and 2 are 10 kg and 30 kg respectively. The belt tensions act vertically downward and the ratio of belt tensions on the tight side to slack side for each pulley is 2.5:1. The shaft is made of plain carbon steel 40C8 (σyt = 380 N/mm2) and the factor of safety is 3. A. Estimate suitable diameter of shaft according to ASME Code if (kb = 1.5 and kt = 1.0) . B. If the permissible angle of twist is 0.5° per meter length, calculate the shaft diameter on the basis of torsional rigidity. Assume G = 79300 N/mm2.
