Blowholes are one of the common precision casting defects. Blowholes refer to smooth hole defects in individual positions of precision castings. Pores are usually found after machining. Yanzi precision casting technicians combined with many years of workshop production experience, summarized the reasons and prevention methods of air holes in precision casting as follows:
1. Reasons for formation: 1. Porosity occurs in most cases mainly due to insufficient roasting of the precision casting mold shell. When casting molten steel, the mold shell instantly generates a large amount of gas that cannot be smoothly discharged, and then invades into the molten metal to form pores; 2. Because the shell is made Due to the process or shell material, the air permeability of the shell is too poor, and the gas in the cavity is difficult to be discharged, and it enters the molten metal to form pores; 3. The air that is caught in the molten steel during pouring fails to be discharged and the pores in the casting are caused.
Second, preventive methods 1. In the case of precision casting conditions, the exhaust hole is set at the highest part of the casting with complex structure. 2. When designing the pouring system, the exhaust requirements of the shell must be fully considered. 3. The baking temperature and time of the shell should be reasonable, and the holding time should be sufficient. 4. When dewaxing, wax should be completely eliminated. 5. Properly reduce the distance between the ladle nozzle and the gate cup, and the pouring speed should be uniform to ensure that the molten steel fills the cavity smoothly and the air in the molten steel is as little as possible so that the gas in the cavity and molten steel can be smoothly discharged.