Question 4
A metal crusher requires power of 90 kW at 250 rpm for its operation. The drive is by V-belt from an electric motor running at 750 rpm. The drive system requires multi-grooved pulleys for multiple belts; number of grooves depending on number of V belts required for operation. A groove angle of 350 is used. The diameter of the pulley on the shaft of the metal crusher must not be greater than 1 meter, while the centre distance between the driver and driven pulleys is limited to 1.75 meter. The belt speed should not exceed 1600 meters per minute. Each belt has a cross sectional area of 375 mm2, density 1000 kg.m-3 and an allowable stress of 2.5 MPa. The coefficient of friction between each pulley and the belt material is 0.25.
Determine the following using the given information.
i) Diameter of the motor pulley
ii) Mass per unit length of the belt
iii) Centrifugal tension
iv) Maximum allowable tension in the belt
v) Angle of lap on smaller pulley and that on larger pulley
vi) Tensions on tight and slack sides of the belt at this given belt speed
vii) Power transmitted per belt at this speed and with the maximum allowable tension in the belt
viii) Hence, the number of belts required
ix) Length of each belt required
x) Initial tension to be set up on the belt (Initial tension, T0 = (Tt1 + Tt2)/2)
Note: Without skipping the steps above, work from i) to x).
xi) The optimum speed of the belt if maximum power is to be transmitted with the belt tension not exceeding its maximum possible limit
xii) Maximum power that can be transmitted from the belt drive
