2. Try to design a single reducer with a cylindered worm gear driv Given the rated power of electric motor P=7.5KW, rotational spee n=1440r/min, speed ratio i=24(for reducing applications), uniform driven load, life expectancy 10 years, 16 hours per day, under unidirectional operating condition.

A 15KW and 1200r.p.m motor drives a compressor at 300r.p.m through a pair of spur gears having 20° stub teeth .the centre to centre distance between the shafts is 400mm.the motor pinion is made to forged steel having an allowable static stress 210MPa while the gear is made of cast steel having an allowable static stress as 140MPa.Assuming that the drive operates 8 to 10 hours per day under light shock conditions,find from the standpoint of strength (a) Module;(b)face width and (c)number of teeth an pitch circle diameter of each gear.check the gears thus designed from the consideration of wear .the surface endurance limit may be taken as 700MPa.

XY=11 By examine the parameters given, evaluate the maximum power-transmitting capacity, based on AGMA bending strength for both gears.

• HOME WORK Design the elliptical cross-section of a belt pulley arm near the hub for the following specifications: The mean pulley diameter is (300 mm) and the (number of pulley arms are 4). The elliptical section has major axis twice the minor axis length. The tight and slack sides tension in the belt are (600 N and 200 N) respectively. Assume half number of arms transmit torque at any time and the load factor of 1.75 to account for dynamic effects on the pulley while transmitting torque. The permissible tensile stress for cast iron pulley material is 15 MPa. The pulley hub diameter is 60 mm. [Ans. a=40 mm, b₁= 20 mm]