Electromagnetic brakes slow down or stop a moving machine by using an electromagnetic force to apply friction to its wheels. These brakes receive the electromagnetic force they require from a magnetic field comprised of a magnetic coil and a coil shell that is bolted to the machine frame.
A typical electromagnetic brake has three elements in its construction – a magnetic field comprising of a coil and a shell, an armature and the hub. When the brakes are applied, the armature is attracted to the magnetic field developed by the coil.
Simultaneously, a torque working in the opposite direction is transferred into the field to counteract the effect of the magnetic field. As the strength of the field falls, the vehicle begins to slow down and eventually stops. The disengagement process begins as soon as the vehicle stops. As the magnetic flux degrades rapidly, the armature is brought to its initial position ready to work again. This process is quite rapid and usually takes less than three seconds to complete. The smooth working of the coil is crucial to the effective functioning of the electromagnetic brake as it produces the magnetic field. The whole assembly has to be protected against extremes of temperature as well as wear and tear, as both these factors are detrimental to the functioning of the brakes.
Electromagnetic brakes are now used in airplane braking systems in addition to extensive use in train and tram braking systems.