Casting dimensional accuracy of castings subject to what factors?
Casting dimensional accuracy influenced by many factors casting structure, materials, tooling, Shell, roasting, casting and other subject.
1) Effect of casting temperature: the higher the pouring temperature, the greater the shrinkage; pouring temperature is low, low shrinkage, thus pouring temperature should be appropriate.
2), the impact of the casting structure: (1) casting wall thickness, shrinkage; thin-walled castings, shrinkage is small; (2), the free shrinkage hinder small shrinkage.
3), the impact of the system shell material: the use of zircon sand, zircon powder, sand on the shop, the shop because the powder expansion coefficient of only 4.6 × 10-6 / ℃, therefore, may or may not count a little.
4) shell firing: Since expansion coefficient of small shell, the shell when the temperature is 1150 ℃, the only 0.053%, therefore, may be slightly or not count.
5), the impact of material:
(1), the higher the carbon content of the material, the smaller the linear shrinkage rate, the lower the carbon content, the greater the linear shrinkage;
(2) casting shrinkage common materials are as follows: casting shrinkage K = (LM-LJ) / LJ × 100% LM- cavity dimensions; LJ- casting size. K affected by the following factors: the wax mold K1, casting structure K2, the type of alloy K3, pouring temperature K4.
6), casting mold on shrinkage of the casting line:
(1) wax radial (blocked) in the longitudinal direction shrinkage rate was 30-40% (free) shrinkage, the impact of temperature on wax injection free shrinkage is far greater than the impact of the disruption shrinkage. (Best wax injection temperature is 57-59 ℃, the higher the temperature the greater the contraction.)
(2) Wax (mold) material linear shrinkage of about 0.9 to 1.1%;
(3) melting mold storage, further shrinkage, shrinkage values of about 10% of the total amount of shrinkage, but after 12 hours storage, melt stable mode size;
(4) wax injection temperature, wax injection pressure, dwell time to melt mode size to shoot wax temperature most obvious, followed by wax injection pressure, dwell time on the investment casting final size is in the guarantee melt molding small.
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