Generally speaking, the dimensional accuracy of metal castings is affected by the casting structure, casting material, mold and casting process. Unreasonable operation will change the shrinkage rate of castings and lead to deviations in the dimensional accuracy of metal castings.

(1) The influence of casting structure: A. Casting wall thickness, large shrinkage, thin wall, shrinkage porosity. b.. Increase free contractility and reduce obstructive contractility.

(2) The influence of the castable: the higher the carbon content of the raw material, the smaller the linear shrinkage rate, and the lower the carbon content, the greater the linear shrinkage rate.

(3) The influence of mold making on casting line shrinkage: wax injection temperature, wax injection pressure and holding time have the most obvious influence on mold size, followed by wax injection pressure. After the mold is formed, the holding time has little effect on the final size of the mold. The linear shrinkage of the wax (mold) material is about 0.8-1.2%. After welding, the weld mold will shrink further, and the shrinkage value is about 11% of the total shrinkage. But after 16 hours of storage, the size of the weld mold is basically stable. The radial shrinkage of the wax model in the length direction is only 35-40%, and the influence of wax injection temperature on free shrinkage is far greater than continuous shrinkage (temperature is about 58℃).

(4) Shell material: The influence of zircon sand and zircon powder can be ignored due to its small expansion coefficient.

(5) The influence of the baking shell: Due to the small expansion coefficient of the baking shell, the temperature of the baking shell reaches 1120℃, which is only 0.073%, which can be ignored.

(6) The influence of pouring temperature: the higher the pouring temperature, the higher the shrinkage porosity, the lower the pouring temperature, the smaller the shrinkage porosity. Therefore, the pouring temperature should be appropriate.