Blowholes are one of the most common precision casting defects, and the stomata refers to the appearance of smooth holes in the individual positions of the precision castings. The pores are usually found after machining. The causes and prevention methods of gas holes in precision casting are summarized as follows: Yan Zi precision casting technicians combined with many years of workshop production experience.
1.the cause of formation:
◆ in most cases, the pores appear mainly because the precision casting shell is not baked enough. When pouring molten steel, the shell can not discharge smoothly, and then form pores in the molten metal.
◆ because of the reason of shell making or shell material, the air permeability of the shell is too poor, the gas in the cavity is difficult to expel and into the metal liquid to form the gas hole.
◆ the air in the molten steel is not discharged from the casting of the molten steel, resulting in the porosity of the casting.
2. prevention method
◆ exhaust holes are set at the top of the complex castings with the permissible conditions of the precision casting.
◆ when designing the gating system, it is necessary to take full account of the exhaust demand of the shell.
◆ shell calcination temperature and time should be reasonable, and the heat preservation time should be sufficient.
◆ the wax should be completely removed when dewaxing.
◆ reduce the distance between the ladle mouth and the gate cup properly, and the pouring speed should be uniform, so as to ensure that the steel is stable and full of cavity, and as little as possible is involved in the air in molten steel, so that the gas in the mold cavity and molten steel can be discharged smoothly.
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