Cause and Solution of Blowhole in Casting
The high scrap rate in the casting industry has been a problem for a long time. The scrap rate of ordinary iron castings in China is about 7%, that of complex castings is about 10% - 15%, and that of aluminum alloy die castings is about 8% - 10%. Defects are mainly concentrated in sand holes on the surface or inside of the casting.
Today, let's talk about the causes and solutions of porosity in castings. Features: Porosity is a hole on the surface or inside of the casting, which is round, oval or irregular. Sometimes multiple pores form an air mass, and the subcutaneous is generally pear shaped. The choke hole is irregular in shape and rough in surface. The air pocket is a concave piece on the surface of the casting, and the surface is smooth. The open hole can be found by visual inspection, and the subcutaneous pores can be found only after machining.
Reasons for the formation of pores:
1. The mold preheating temperature is too low, and the liquid metal cools too fast when passing through the gating system.
2. The mold exhaust design is poor, and the gas cannot be discharged smoothly.
3. The paint is not good, and its exhaust is not good, even it volatilizes or decomposes gas.
4. There are holes and pits on the surface of the mold cavity. After the liquid metal is injected, the gas in the holes and pits rapidly expands and compresses the liquid metal, forming choke holes.
5. The surface of the mold cavity is rusted and not cleaned.
6. Raw materials (sand cores) are improperly stored and not preheated before use.
7. The deoxidizer is poor, or the dosage is insufficient or the operation is improper.
Blowhole prevention methods for castings:
1. The mold shall be fully preheated, the particle size of the coating (graphite) shall not be too fine, and the air permeability shall be good.
2. Pour by tilting.
3. Raw materials shall be stored in a ventilated and dry place, and shall be preheated during use.
4. Select deoxidizer (magnesium) with good deoxidization effect.
5. The pouring temperature should not be too high.