Influence Factors On Dimensions Of Precision Casting Parts
Precision casting parts are affected by many factors such as casting structure, casting material, mould making, shell making, roasting, pouring etc generally, any unreasonable operation or setting on the links will make the shrinkage rate of castings change, which will lead to the deviation on dimension of precision casting parts and requirement. Below are some factors that can cause precision casting parts parts to be defective in size:
1.Casting structure: 1) thick casting wall, big shrinkage rate;thin casting wall, small shrinkage rate.2)Big freedom shrinkage rate, small hinder shrinkage rate.
2.Casting material:1) The higher carbon content in the material, the smaller the line shrinkage rate, The lower carbon content, the greater the line shrinkage rate. 2) The normal material casting shrinkage rate is as follows: the casting shrinkage rate k= (LM-LJ)/LJx100%, LM is the cavity size, LJ is the casting size. K is affected by the following factors: Wax mold K1, casting structure K2, Alloy type K3, pouring temperature K4.
3.Mould making: 1) Influence of wax temperature, wax pressure and holding time on the dimension of the molten mold, obvious influence is wax temperature,following is wax shooting, holding time has small impact on the final size of molten mold 2)The line shrinkage rate of wax (die) material is about 0.9-1.1%. 3) When the molten mold is deposited, it will shrink further, with a shrinkage value of about 10% of the total shrinkage, but after 12 hours of storage, the size of the molten mold is basically stable. 4)The radial shrinkage rate of wax mould is only 30-40% of length direction shrinkage, the effect of wax temperature on the free shrinkage rate is much greater than hinder shrinkage rate (the optimum wax temperature is 57-59 ℃, the higher the temperature is, the greater the shrinkage rate).
4. Shell making: Use zircon sand, zircon powder, Gioba Stone sand,Gioba Stone powder in precision casting parts, because of its small expansion coefficient, only 4.6×10-6/℃, so which can be negligible.
5.Roasting:Because of small expansion coefficient on shells, when the temperature of shells is 1150℃, it is 0.053%, which can be negligible.
6.Pouring:Pouring temperature must be suitable, As the higher temperature of pouring, the bigger shrinkage rate, the lower temperature of pouring, the smaller shrinkage rate it is.