In the natural environment, the specifications of casting are reasonable layout of carbon steel castings, casting materials, combustion, mold production, shells, aspects of identity, one set of all stages, and improper control of large cities makes the indivisible casting shortening rate change, resulting in There are certain deviations in casting precision specifications and regulations. The following are some of the characteristics related to the inevitable casting specification accuracy defects:

(1) Influence of casting materials: a. The higher the carbon content of the material, the smaller the line shortening ratio; the lower the carbon content, the greater the line shortening ratio. B. The shrinkage rate of general materials after calcining: forging shrinkage rate K=(LM-LJ)/LJ×100%, the mold specification is LM, and the casting specification is LJ. K is affected by the following identities: wax type K1, reasonable casting arrangement K2, aluminum alloy type K3, and casting temperature K4.

 (2) The influence of mold making on the shrinkage rate of the sub-casting line: a. The influence of injection temperature, injection working pressure and holding pressure on the investment specifications at that time is very important, followed by the working pressure of the injection wax. At this time, after the investment mold at the entrance is formed, the holding pressure has little effect on the specifications of the investment mold. The line shortening rate of wax (mold) material is about 0.90% -1.1%. C. After the investment is deposited, it will be further shortened, and the shortening value is about 10% of the total shortening, but the cornerstone of the investment specifications will not change after 12 hours. d. The axial shortening rate of the wax model is only 30-40% of the short-term and short-term target shortening rate, and the impact of shooting temperature satisfies the shortening rate far greater than the shortening rate on the resistance (the shooting temperature is 57-59°C, the higher the temperature, The greater the shortening rate).

(3) Reasonable casting layout has an inseparable effect on castings: a. The wall thickness of castings has a high reduction rate, while the wall thickness reduction rate of the castings is low. B. High complacency rate and low obstruction rate.

(4) The influence of shell culture and burning: Due to the small folding index of shells, when the shell temperature is 1150℃, it is only 0.053%, which can be ignored.

(5) The influence of pouring temperature: the higher the pouring temperature, the greater the shortening ratio; the lower the pouring temperature, the smaller the shortening ratio. The pouring temperature should be appropriate.

(6) The influence of shell-making materials: zircon sand, zircon powder, shop sand, shop powder are used, and the aggregation index is small, 4.6×10-6/℃, and it is not suitable to record randomly.