Causes of insufficient precision of precision castings
1. Structural influence: 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 hindrance shrinkage rate is small. The effect of the material: the higher the carbon content in the material, the smaller the linear shrinkage, and the lower the carbon content, the larger the linear shrinkage; the casting shrinkage of common materials: casting shrinkage K = (LM-LJ) / LJ100% , LM is the size of the cavity, and LJ is the size of the casting. K is affected by the following reasons: wax mold K1, casting structure K2, alloy type K3, and pouring temperature K4.
2. The influence of mold making on the linear shrinkage of Lost wax casting: The impact of wax injection temperature, wax injection pressure, and holding time on the specifications of the investment mold is the most significant. In addition, the wax injection pressure and the holding time are guaranteed to melt. After molding, the impact on the final specifications of the investment mold is not significant; the linear shrinkage of the wax (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 However, after 12 hours of storage, the specifications of the investment mold are generally stable; the radial shrinkage of the wax mold is only 30-40% of the shrinkage in the length direction, and the effect of the wax injection temperature on the free shrinkage rate is far more than that of the hindered shrinkage rate. Influence, the best wax injection temperature is 57-59 ℃, the higher the temperature, the greater the shrinkage.
3, the effect of shell material: zircon sand, zircon powder, Shangdian sand, Shangdian powder, because its expansion coefficient is small, only 4.610-6 / ℃, so it can be ignored; the impact of shell roasting: Due to the small expansion coefficient of the shell, when the shell temperature is 1150 ° C, it is only 0.053%, so it can be ignored; the effect of the Carbon Steel casting temperature of precision castings: the higher the casting temperature, the greater the shrinkage, and the lower the casting temperature. The smaller the shrinkage, the better the pouring temperature.