The air hole is the main defect in the production of the brake drum of the bimetal automobile, and is mainly distributed on the inner wall and the outer wall of the brake drum. How can I prevent it in order to get a complete brake drum casting? 1. When casting the brake drum castings, it is necessary to reduce the overheating temperature during the financialization and minimize the contact time between the alloy liquid and the gas during the melting. Second, we must pay attention to the treatment of oxides and stains on the surface of steel parts, so the steel plate should be sandblasted; remember to dry the steel. Third, in the place where the cast iron and steel parts are combined, it is necessary to pay attention to the brushing of the gettering paint. Fourth, open the exhaust (overflow) riser in the process to make the gas in the cavity timely