Porosity is one of the common precision casting defects, which refers to smooth hole defects in individual locations of precision castings. The stomata are usually not found after machining. Scorpion precision casting technicians combined with years of workshop production experience, the reasons for the occurrence of pores in precision casting and prevention methods are summarized as follows:
First, the reasons for formation:
1. In most cases, the occurrence of pores is mainly due to the insufficient calcination of the precision casting shell. When the molten steel is poured, a large amount of gas is instantaneously discharged from the shell, and the pores are intruded into the molten metal to form pores;
2. Because of the shell-making process or shell-type material, the gas permeability of the shell is too poor, the gas in the cavity is difficult to discharge, and the pores are formed in the molten metal;
3. The air that is blown into the molten steel during pouring fails to be discharged to cause the casting porosity.
Second, the prevention method
1. Where the precision casting conditions permit, vent holes are provided at the highest part of the casting with complex structure.
2. When designing the gating system, fully consider the casing exhaust requirements.
3. The calcination temperature and time of the shell should be reasonable, and the holding time should be sufficient.
4. The wax should be completely removed when dewaxing.
5. Properly reduce the distance between the pouring spout and the sprue 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 trapped as little as possible, so that the gas in the cavity and the molten steel can be smoothly discharged.
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