Solenoid brakes use an electric solenoid to actuate two or more brake shoes against a rotating member, slowing or stopping equipment. There are two types of installations, and solenoid brakes can be used alone or with mechanical brakes. The operation relies on the conversion of electromagnetic force into linear motion. The shoe sets vary in design, and the overall operation falls into two categories: on and off. Solenoid brakes are often used as a safety backup for mechanical brake systems, such as in reverse brake lockup on trailers and to prevent stationary heavy vehicles from moving inadvertently.
The term solenoid brake refers to a group of braking mechanisms that rely on an electric solenoid for their actuation. The brake mechanism usually consists of two or more brake shoes which are pushed against the rotating member by solenoid actuated linkages. Solenoid brakes are typically used to slow and stop rotating equipment, including winch drums, home wash tubs, and vehicle wheels. There are two basic types of solenoid brake installations: one that exerts braking pressure when power is applied and the other when power is removed. Solenoid brakes can be used alone or in combination with mechanical brakes.
An electric solenoid consists of a coil of wire wound around a hollow core with a spring-loaded metal plunger inside. When an electric current is passed through the coil, it creates an electromagnetic field which pulls the plunger into the core. When power is removed from the coil, the spring pushes the plunger out again. This conversion of electromagnetic force into linear motion is the basis for the operation of a solenoid brake. Typically the plunger acts through a series of links that move a set of brake shoes against whatever needs to be slowed or stopped.
These shoe sets vary greatly in design depending on the application. Drum hoists such as those used in underground mining operations use a set of half round brake shoes which are pressed against the braking collar on the drum. Other solenoid brakes pull a flat disc coated with brake material against a similar flange to stop rotation. The linkage systems employed also differ with some solenoid brake mechanisms not using physical linkages. Instead, these systems rely on a spring-loaded collar that is pulled against a brake lining on the face of the solenoid.
The overall operation of solenoid brakes falls into two basic categories: on and off. Power-on brakes rely on the actuation of the solenoid to exert the braking forces. Shut-off systems exert a braking force when power is removed and only release when power is applied to the solenoid. Shutdown systems are often used on vertical mining hoists carrying personnel as a safety measure against power outages.
Solenoid brakes are often included as a safety backup for mechanical brake systems. One such application is reverse brake lockup on trailers. These systems use the signal from the reverse light to activate a solenoid which disengages the trailer brakes when reversing. Many vehicles also have solenoid brake systems that lock the brakes until the engine is running. This prevents stationary and unattended heavy vehicles from starting to move inadvertently.
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