Basiclly, a lever which is connected to the arm which carries the brake shoes are pulled in when the circuit is denergized, it releases only when the circuit is energized and the drum will become free to move. Explained operation is given below. This is a fail safe arrangement as a power failure wil ensure the braes tighted on to the drum,
The Shoes are of cast iron and other components are of fabricated steel. The lever is hinged on the main arm, which is connected to the side arm through a tie rod, and is stressed by a pre-loaded compression spring. The compression of the spring can be adjusted to set the braking torque to desired value. The brake liner of selected quality material is riveted to the shoes by aluminum rivets. A.C. solenoid with laminated magnetic sheet steel houses a copper magnetizing coil which is impregnated with Class F materials. The plunger which is connected to the lever, is drawn in to the coil, when it is energized with AC source. This loads the spring and releases the brake shoes from the brake drum. When the supply is cut off, the plunger is pulled out of the coil, and spring force clamps the brake shoes on the brake drum and the brake is applied.
Usuallt this kind of brakes are used in E/R cranes, motors and other heavy rotating machineries which needed to be stopped instantlt, and needs to hold load.
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