In general, precision cast
ing parts dimensional accuracy is influenced by structure of casting, casting material, moulding, shell making, roasting, pouring the influence of various factors, such as any one link set, unreasonable operation can make the casting shrinkage rate of change, has led to the deviation of dimension accuracy of castings and requirements.
Here are factors can result in the precision casting dimension accuracy defects: (
The influence of the casting structure: a.
Casting wall thickness, shrinkage rate is large, thin wall castings, the shrinkage rate is small.
Free shrinkage, hinder the little shrinkage.
The influence of the casting material: a.
Materials in the carbon content is higher, the line of the smaller shrinkage rate, the lower the carbon content, the line, the greater the shrinkage rate.
Common material casting shrinkage rate is as follows: casting shrinkage ratio K = (
100%, LM for cavity size, LJ for casting size.
K by the following factors: the wax models K1, K2, alloy casting structure types K3, K4 pouring temperature.
The influence of the molding shrinkage of casting line: a.
Wax wax temperature, pressure, the influence of the holding time of molten mould size to wax mould temperature is the most obvious, followed by radiation pressure of wax, the holding time in melt after mould for casting the influence of the final size is very small.
The line of shrinkage is about 0.
Deposit moudle, will further produce contraction, the shrinkage value is about 10% of the total shrinkage, after 12 hours, but when stored moudle size basically stable.
Wax models of radial shrinkage rate was only about shrinkage rate of 30 - length direction
Shoot 40%, wax temperature effect on the free shrinkage rate is much greater than stuck to the influence of shrinkage,
Optimum temperature for 57 - wax
59 ℃, the higher the temperature the greater the shrinkage)
The influence of shell making material: using zircon sand, zircon powder, shop on the sand, shop on powder, because of its small expansion coefficient, just 4.
6 / ℃, so can be neglected.
Shell roasting effect: as the shell of the small expansion coefficient, when the shell temperature of 1150 ℃, is only 0.
As a result, 053%, and can be neglected.
The influence of pouring temperature, the higher the pouring temperature, the shrinkage rate, the greater the pouring temperature is low, the smaller the shrinkage rate, thus pouring temperature should be appropriate.
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