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INTRODUCTION MAGNETIC SHOE BRAKES
Application Shoe brakes are used for both stopping and holding loads. Some of the most common applications include cranes, hoists, conveyors and machine tools.   Design These magnetic shoe brakes were originally designed and built by Westinghouse and have a proven record of reliability. Consult GEMCO if a cross reference to the old Westinghouse part numbers are needed.	Operation Magnetic shoe brakes are spring set, electrically released.   The brake is set when power is removed from the brake's coil. As a safety feature, if power is lost, the brake resets automatically.   The Type TM brake's electrical mechanism consists of one or two DC magnets, while an AC solenoid and plunger comprise the Type CB brake's electrical mechanism.	Both the Type TM and Type CB brakes operate similarly, although the CB brake's electrical operating mechanism is a solenoid, as opposed to the TM brake's DC magnets. The mechanical operation is identical for both brakes.   The Type TM brake's operation is illustrated below.

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Brake Set (De-energized)	Brake Released (Energized)
When the twin magnets (A and B) become de-energized, spring C simultaneously moves tie rod D to the left and magnet B to the right, forcing both brake shoes (E and F) to apply brake torque to the wheel at the same time.	When the twin magnets (A and B) are energized, they pull together compressing spring C. This action simultaneously moves tie rod D to the right freeing shoe E. At the same instant, the motion of magnet B to the left frees shoe F.

 

Selection Torque Rating: The normal practice is sizing a brake's torque rating is to equal or exceed the full load torque of the motor. The formula to calculate full load motor is as follows:   T=5250 HP RPM   T=Full load motor torque in lb.ft.   HP=Motor horsepower   RPM=Speed of motor shaft   In some applications the brake may be subjected to unusual operating conditions against which the brake must be sized to exceed this maximum torque.

The thermal capacity of the magnetic shoe brakes are adequate foremost applications. However, some applications which require frequent stopping of high inertia loads requiring long deceleration periods may extend the thermal capacity of the linings and cause the brake to fade. Such applications should be referred to MagneTek with the WR of the connected load, RPM, and frequency of operation.   CB AC brakes are available with either continuous or intermittent time ratings. Continuous rated brakes can be used on all applications. The intermittent rated brakes indicate that the solenoid can be placed across the line

for one hour maximum without damage. It is equivalent to 1/2 time on and 1/2 time off. Since the coil is on for shorter periods of time, the allowable torque rating is higher on the intermittent rating.   TM DC brakes are also available with two torque ratings per frame size. TM brakes with shunt coils have higher one hour ratings than continuous ratings. The TM brakes with series coils are available with either 1/2 hour or 1 hour ratings.