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Sunday, January 27, 2008

Brake (1)


A brake is a device used to slow down or stop a moving object. It operate by converting the energy of motion, which is called kinetic energy, into some other form of energy, usually heat energy. A stationary part, the brake shoe, is pressed against rotating part, commonly a shaft, disk or drum, producing a large amount of friction. The brake shoe usually provided with a lining made of heat-resistance friction material, often containing asbestos. The brake shoe may be pressed against the rotating part mechanically, pneumatically, electromagnetically or hydraulically

Block, Disk, Drum, and Band Brake 

Various types of brake distinguished. The simples types is the single block brake. The concave side of a block is pressed against the rotating part, which is usually a wheel or drum fastened to a shaft. This type of brake was used in horse drawn vehicles. Vibration of the wheel shaft can be prevented by the use of a double block brake, in which two blocks are symmetrically positioned on opposite sides of the shaft. The disk brake has a block that pressed against the flat surface of a disk rather than against the wheel rim. An example is a caliper disk brake, which was originally developed for aircraft and is now used in automobiles; the same type is used in bicycles. Two opposed blocks (brake shoes) squeeze between them like a pair of calipers. Because disk brakes are not enclosed, they allow air to flow over them, dissipating heat rapidly.
A drum brake has two curved brake shoes that press against a rotating brake drum. Automobiles drum brakes have internal brake shoes that are inside a tightly closed drum and actuated by hydraulic pressure. When drum brakes heat up, they are subject to fading, a decreased in braking effectiveness during extended use of the brake. This happen because the increased temperature causes a decreased in the friction of brake-lining material. Special lining materials with reduced fading have been developed. New cars are often equipped with disk brakes especially on the front wheels. A band brake consists of a metal band lined with a friction material that can be tightened around the rotating part. Band brakes are used mainly for hoist and excavating machinery.

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