Too high pouring temperature will cause the sand mold to swell, especially for gray cast iron parts with complex sand cores. When the pouring temperature is ≥1420℃, the waste will increase. When the pouring temperature is 1460℃, the waste will reach 50%. In production, the use of induction electric furnace smelting can better control the temperature of molten iron.
Defects that may be formed when the pouring temperature is too low
(1) Manganese sulfide pores These pores are located below the surface of gray cast iron parts and are mostly on the top. They are often exposed after processing. The diameter of the pores is about 2-6mm. Sometimes the holes contain a small amount of slag. Metallographic studies have shown that this defect investment casting china is caused by the mixture of MnS segregation and slag. The reason is the low pouring temperature and the high content of Mn and S in the molten iron.
Such S content and suitable Mn content (0.5%~0.65%) can significantly improve the purity of molten iron, thereby effectively preventing such defects.
(2) Porosity caused by sand core gas Pores and multi-cavity pores are often caused by poor exhaust of sand core. Because the sand core is hardened in the core box during core making, the number of sand core vent holes is often insufficient. In order to form vent holes, drill holes can be added after the core is hardened.
(3) Liquid slag inclusion After processing, individual small holes will be found under the surface of the gray cast iron. The diameter of the holes is generally 1~3mm. In some cases, there are only 1 to 2 small holes. Metallographic studies have shown that these small holes appear together with a small amount of liquid slag, but no S segregation is found there. Studies have shown that this defect is related to the pouring temperature. When the pouring temperature is higher than 1380℃, no such defects are found in the investment casting china, so the pouring temperature should be controlled at 1380-1420℃. It is worth mentioning that changing the design of the pouring system failed to eliminate this defect. Therefore, this defect can be considered to be caused by the low pouring temperature and the molten iron pouring under a trace reduction atmosphere.
The most common reason for low pouring temperature is that before pouring, the molten iron is transported and stayed in the open ladle for a long time to dissipate heat. Using a ladle cover with thermal insulation material can significantly reduce heat loss.