Precision control during precision casting
The following are several factors that can cause dimensional accuracy defects in Precision casting:
- 1. The influence of the casting structure. The wall thickness of the casting is large, the shrinkage rate is large, the casting wall is thin, and the shrinkage rate is small; the free shrinkage rate is large, and the shrinkage rate is hindered.
- 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; the casting shrinkage of common materials is the casting shrinkage K=(LM-LJ)/LJ×100%, LM For the cavity size, LJ is the casting size, and K is affected by several factors such as the wax pattern K1, the casting structure K2, the alloy type K3, and the casting temperature K4.
- 3. The influence of mold making on the shrinkage rate of castings. The effect of wax temperature, wax pressure and dwell time on the size of the investment is the most obvious temperature of the wax, followed by the pressure of the wax, and the pressure retention time has little effect on the final size of the investment after the investment is formed. The linear shrinkage of the (mold) material is about 0.9-1.1%; when the investment mold is stored, the shrinkage is further generated, and the shrinkage value is about 10% of the total shrinkage amount, but after 12 hours of storage, the investment size is substantially stable; The radial shrinkage of the wax mold is only 30-40% of the shrinkage in the longitudinal direction. The effect of the wax temperature on the free shrinkage is far greater than the effect on the shrinkage shrinkage (the optimum wax temperature is 57-59 ° C, the temperature is higher. The higher the shrinkage is).
- 4. The influence of the shell material is zircon sand, zircon powder, Shangdian sand and Shangdian powder. Because of its small expansion coefficient, it is only 4.6×10-6/°C, so it is negligible.
- 5, the influence of shell roasting, because the expansion coefficient of the shell is small, when the shell temperature is 1150 ° C, only 0.053%, it is also negligible.
- 6. The influence of casting temperature, the higher the pouring temperature, the larger the shrinkage rate, the lower the pouring temperature and the smaller the shrinkage rate, so the pouring temperature should be appropriate.