Friction discs are made of friction materials and bonded, usually with rivets, to a metal plate. These make up the disc brake pads of the brake component. The other parts of a typical disc brake include calipers attached to pistons and rotors which are responsible for motion. The friction discs are used to slow or stop the motion of drive shafts which will in turn stop the wheels from rotating. As pressure is applied to the brake pedal, the calipers cause the discs to close around the rotors. This pressure can be a result of hydraulic, mechanical or pneumatic power depending on the design of the engine, but either way, when enough friction has been created, the rotors will stop moving.
The materials used in the construction of friction discs need to be durable enough to withstand the stress and tension of the friction process, as well as to maintain strength despite the high temperatures achieved. During the process of creating friction, a large amount of kinetic energy is converted into heat energy. This allows the drive shaft to stop moving, and the energy can then be dissipated as heat.
Disc design varies according to application and choice of brake material, but high quality construction will ensure longer lasting discs. Uneven wear or thickness of discs is responsible for juddering or engine vibrations, resulting in potential engine component damage or an unpleasant engine ride. Well made discs, which may be solid, slotted for ventilation or drilled for high performance vehicles, will wear at the same rate, allowing smooth breaking and gear changing even when they are almost ready to be replaced. Due to the high-stress nature of friction creation, friction discs will need to be periodically checked and replaced as the materials inevitably wear down over time.
Dust is created as the plates rub against each other and slowly break down their surfaces. This is a major reason why asbestos is no longer widely used for disc plate manufacturing or in clutch materials as asbestos dust is harmful to inhale. Other materials used for friction discs include woven fibers such as Kevlar or aramid and ceramic materials which are durable enough to withstand the pressure of friction but not so hard as to cause component damage.