The ambient temperature control for precision casting usually refers to the ambient temperature of cemented carbide steel in the static furnace, which is 60-120 ℃ higher than that of alloy liquidus. For the alloy with excessive primary crystal tendency of oxide between cemented carbides, the ambient temperature of precision casting should be raised as much as possible. For the alloy with high crack tendency, such as the flat ingot of LC4 type alloy, the ambient temperature of precision casting can be appropriately reduced. For industrial pure aluminum, the ambient temperature control for precision casting is usually adjusted in the range of 690-710 ℃, the low value in summer and the high value in winter.
When the temperature of investment casting environment is raised, the length of liquid phase cavity will be increased, the tendency of columnar crystal structure expansion will be formed, the crack waste will be raised, and the degree of segregation floating will often appear on the surface of expanded ingot. As a matter of fact, the average temperature in the liquid phase cavity increases only 1-2 ℃ every 30 ℃ rise in the ambient temperature of precision casting. Although the ambient temperature of molten steel in the liquid phase cavity is only increased by 2 ℃, it has a great influence on the structure and defects of ingot. When manufacturing the aluminum rod with a diameter of about 10 mm, because of the rapid investment casting speed, when the temperature of the investment casting environment is too high, the upper surface of the aluminum rod is prone to the problem of double skin, such as fish scale, or even leakage of aluminum liquid due to the failure of condensation.
The low ambient temperature of stainless steel precision casting will promote the expansion of the dry solid area of meniscus, and then promote the formation of cold shut on the surface of ingot and expand its deep layer; and may cause the sequential crystallization of volume, make the ingot structure form obvious heterogeneity, and reduce the physical properties of ingot. When the ambient temperature of precision casting is lowered, the width of liquid-solid transition area increases, the viscosity of molten steel increases, the exhaust and feeding conditions of cemented carbide are deteriorated, and the shrinkage porosity, oxide film and slag inclusions are increased. In the production of aluminum rod with a diameter of about 10 mm, although the investment casting speed is too fast, when the temperature of the investment casting environment is too low, the lower surface of the aluminum rod is still very easy to have cold insulation problems, even if the condensation front enters into the asbestos plate guide mouth, the aluminum rod can not be pulled or torn off.
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