Engineering Asked by Ardalan Javadi on June 6, 2021
I have a quick question guys. I am gonna select a brake but I am not sure.
A Crane Hoist motor has a rating of 300 HP and maximum speed of 1800 rpm. This motor is attached to a gearbox with a perfect (100% efficient) reduction ratio of 53.739:1. The API 7K specifications call for a safety factor of 2:1 (200% of motor full load torque) static holding torque from the brakes. The lining coefficient of friction is 0.40 (static) and the brake shoe face is 6.0 inches wide. Two (2) brakes need to be installed diametrically opposite each other on a large disc mounted directly to the cable drum (on the output side of the gear box).
Which disc diameter, and resultant brake torque is fine?
The speed of the disk rotation is $1800/53.739=33.495$
The torque it creates is $$300*5252/1800=875.33 ft.lbf quad 875.33*53.739= 47040ft.lbfrightarrow times 2=94079ft.lbf text{at the disk}$$
R = disk Radius
If we assume the brake pad pressure $P/inch^2$ then its friction force $F_f=0.4*P$
and the disk diameter is related to this torque,
$ 94079=2*F_f*6*R^2/2 quad R^2=2*94079/2*F_f*6$
This is just the static and assuming the pads start from the center to the end of the disk. We need to calculate the torque for kinetic friction during deceleration as well.
Check my arithmetic, please.
Correct answer by kamran on June 6, 2021
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