Ⅰ. The characteristics of pores in stainless steel castings
Pores are holes that exist on the surface or inside of the casting, which are round, oval or irregular. Sometimes multiple stomata form an air mass, generally pear-shaped under the skin. The choking hole has irregular shape and rough surface. The air pocket is a recessed part on the surface of the casting, and the surface is relatively smooth. Bright holes can be found as soon as they are inspected, and subcutaneous pores can only be found after machining.
Ⅱ. Reasons for pores in stainless steel castings:
1. The mold preheating temperature is too low, and the liquid metal cools too fast when passing through the pouring system.
2. The mold exhaust design is poor, and the gas cannot be discharged smoothly.
3. The paint is not good, its own exhaust is not good, and it even volatilizes or decomposes gas.
4. There are holes and pits on the surface of the mold cavity of casting components. After the liquid metal is injected, the gas in the holes and pits expands rapidly, compressing the liquid metal, and forming choking holes.
5. The surface of the mold cavity is corroded and not cleaned up.
6. The raw materials (sand cores) are stored improperly and have not been preheated before use.
7. Poor deoxidizer, insufficient dosage or improper operation, etc.
Ⅲ. The method of preventing the generation of pores in stainless steel castings:
1. The mold of the stainless steel casting should be fully preheated, the particle size of the coating (graphite) should not be too fine, and the air permeability should be good.
2. Use inclined pouring method for pouring.
3. The raw materials of castings should be stored in a ventilated and dry place, and should be preheated during use.
4. Choose a deoxidizer (magnesium) with better deoxidizing effect.
5. Pouring temperature should not be too high.