The following are several factors that can cause dimensional accuracy defects in precision casting:
1. Influence of casting structure. The thickness of the casting is large, the shrinkage is large, the casting is thin, and the shrinkage is small; the free shrinkage is large, and the hindrance shrinkage is small.
2, the influence of casting material. The higher the carbon content in the material, the smaller the linear shrinkage, and 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 It is the cavity size, LJ is the size of the casting, and K is affected by several factors such as wax mold K1, casting structure K2, alloy type K3, and pouring temperature K4.
3. The influence of mold making on the linear shrinkage of castings. The impact of wax injection temperature, wax injection pressure, and dwell time on the size of the investment mold is most obvious with the temperature of the injection wax, followed by the pressure of the wax injection. The dwell time has a small effect on the final size of the investment mold after the investment is formed; The linear shrinkage of the (mold) material is about 0.9-1.1%; when the investment mold is stored, it will further shrink, 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 radial shrinkage of the wax mold is only 30-40% of the shrinkage in the length direction. The effect of the wax injection temperature on the free shrinkage is much greater than the effect on the hindered shrinkage. The higher the high shrinkage).
4. The influence of the shell material is zircon sand, zircon powder, Shangdian sand, Shangdian powder, which has a small expansion coefficient of only 4.6 × 10-6 / ℃, so it can be ignored.
5. Due to the small shell's expansion coefficient, 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 larger the shrinkage rate, the lower the pouring temperature, the smaller the shrinkage rate, so the pouring temperature should be appropriate.