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Factors affecting the accuracy of castings

Issuing time:2020-12-18 10:34Author:Joy

Factors affecting the accuracy of castings: Under normal circumstances, the dimensional accuracy of precision castings is affected by multiple factors such as casting structure, casting material, mold making, shell making, baking, pouring, etc. Any of the settings and operations of any link will cause castings. The shrinkage rate changes, resulting in deviations in the dimensional accuracy of the castings from the requirements. The following are the factors that can cause defects in the dimensional accuracy of precision castings:

(1) The influence of casting structure: a. Casting wall thickness, large shrinkage rate, thin casting wall, small shrinkage rate. b. The free shrinkage rate is large and the hindered shrinkage rate is small.

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

(3) The influence of mould making on the linear shrinkage rate of castings: a. The influence of wax injection temperature, wax injection pressure and pressure holding time on the investment size is the most obvious in the wax injection temperature, followed by the wax injection pressure, and the pressure holding time is guaranteed After investment molding is formed, it has little effect on the final size of the investment mold. b. The linear shrinkage rate of wax (mold) material is about 0.9-1.1%. c. When the investment mold is stored, there will be further shrinkage, and its shrinkage value is about 10% of the total shrinkage, but when stored for 12 hours, the investment mold size is basically stable. d. The radial shrinkage rate of the wax mold is only 30-40% of the lengthwise shrinkage rate. The wax injection temperature has a far greater influence on the free shrinkage rate than the hindered shrinkage rate (the best wax injection temperature is 57-59, The higher the temperature, the greater the shrinkage).

(4) The influence of shell-making materials: zircon sand, zircon powder, Shangdian sand and Shangdian powder are used. Because of their small expansion coefficient, only 4.6×10-6/,they can be ignored.

(5) The effect of shell baking: Because the expansion coefficient of the shell is small, when the temperature of the shell is 1150, it is only 0.053%,so it can be ignored.

(6) The influence of pouring temperature: the higher the pouring temperature, the greater the shrinkage rate, the lower the pouring temperature, the smaller the shrinkage rate, so the pouring temperature should be appropriate.

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