A brake drum is a cast iron shaped like a tambourine that is fixed to the tire and rotates at the same speed. When braking, oil pressure is used to push the BrakeShoes to contact the inner edge of the brake drum, and the friction force generated by the contact is used to restrain the rotation of the tire to achieve the purpose of braking. Drum brake is composed of brake bottom plate, brake sub pump, brake shoe and other related connecting rod, spring, pin and brake drum. At present, it is only commonly used in the rear wheel. Drum brakes, which have lower cost and higher absolute braking force, are widely used in the rear wheels of small cars. But its wear rate is higher, so the overall cost is higher at the same time.

If the brake drum body does not produce hot crack, casting no quality defects, so - a quality of the brake drum can be referred to as the "brake do not break" for brake drum is a kind of brittle grey cast iron material and work under the environment of high temperature and high pressure, fatigue crack is from forming on the surface physical properties of cast iron materials, is an irresistible objective laws. With the extension and penetration of the crack on the drum body, the mechanical strength of the drum body declines sharply, and the brake will be broken.