What are the factors that cause the dimensional accuracy defects of heat-resistant steel precision castings?
1. The influence of casting structure
The wall thickness of the casting is large, the shrinkage rate is large, the wall thickness of the casting is thin, and the shrinkage rate is small;
2. The influence of casting material
The higher the carbon content in the material, the smaller the linear shrinkage, the lower the carbon content, the greater the linear shrinkage;
3. The influence of mold making on the linear shrinkage rate of castings
The influence of wax injection temperature, wax injection pressure and holding pressure time on the size of the investment mold is more obvious with the wax injection temperature, followed by the wax injection pressure. The holding pressure time has little effect on the final size of the investment mold after ensuring the investment molding; The linear shrinkage rate of the material is about 0.9-1.1%; when the investment mold is stored, further shrinkage will occur, and its shrinkage value is about 10% of the total shrinkage, but after 12 hours of storage, the size of the investment mold is basically stable; The shrinkage rate in the longitudinal direction is only 30-40% of the shrinkage rate in the length direction, and the influence of the wax injection temperature on the free shrinkage rate is much greater than that on the hindered shrinkage rate.
4. Influence of shell material
The use of zircon sand, zircon powder, Shangdian sand and Shangdian powder is negligible because of its small expansion coefficient, which is only 4.6×10-6/℃.
5. The influence of shell roasting
Due to the small expansion coefficient of the shell, when the shell temperature is 1150 ℃, it is only 0.053%, so it can be ignored.
6. The influence of casting temperature
The higher the pouring temperature, the greater the shrinkage rate, the lower the pouring temperature, the smaller the shrinkage rate, so the pouring temperature should be appropriate.