Determine (a) the normal stress, in lb/in.2, at the end of the wire as function

Question

Determine (a) the normal stress, in lb/in.2, at the end of the wire as function of the length of the wire and (b) the work done in stretching ti wire, in ft lb 1.27 What is the rate of work output of a press that delivers 120 strokes pe minute, each stroke providing a force of 8000 N throughout a distance o 18 mm? If the press efficiency is 90%, what average torque must be pro vided by a 1750-rpm driving motor? The crankshaft of a single-cylinder air compressor rotates 1800 rpm. The piston area is 2000 mm2, and the piston stroke is 50 mm. Assume a simple "idealized" case where the average gas pressure acting on the piston during the compression stroke is 1 MPa, and pressure during the intake stroke is 28 negligible. The compressor is 80% efficient. A flywheel provides adequate control of speed fluctuation. (a) What motor power (kW) is required to drive the crankshaft? (b) What torque is transmitted through the crankshaft? (Ans.: 3.75 kW, 19.9 N·m) 1.29 A punch press with flywheel adequate to minimize speed fluctuations pro- duces 120 punching strokes per minute, each providing an average force of 2000 N over a stroke of 50 mm. The press is driven through a gear reducer by a shaft rotating 300 rpm. Overall efficiency is 80%.

Explanation / Answer

1.28)

As mentioned in question pressure is 1 Mpa

Let's find pressure = 1Mpa* 2000 mm square= 2000 N

Now let's find torque =efficiency* 2000 * (50/4) in N/ mm square = 19.9 N m

Now let's find power = 2 * pi * 1800* torque /60= 3.76 Kw

1.26)

Power=8000*120*0.018/60= 288

Power= torque * angular velocity/ efficiency

Torque = 288/ 0.9/183.16= 1.415 Nm

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