Grey iron casting casting temperature

In the production of gray iron castings, excessively high pouring temperatures can significantly increase the risk of rejects. When the temperature reaches or exceeds 1420°C, the sand mold, especially the area with complex sand core, will expand and deform due to high temperature baking, resulting in problems such as size out-of-tolerance and sand sticking to the casting, and the rejection rate rises sharply with the increase of temperature, and the rejection rate can reach 50% at 1460°C.

If the pouring temperature is too low (<1380°C), it is easy to produce three types of defects: (1) manganese sulfide pores, due to the Mn/S<4:1 (manganese <0.5%, sulfur ≥0.12%) in the molten iron and low temperature, which can reduce the segregation of MnS and the entrapment gas, and the control of manganese 0.5%-0.65% and sulfur ≤0.15% can reduce such defects; (2) If the sand core is poorly vented and the porosity is caused, it is necessary to drill a 3mm exhaust hole and set up an exhaust groove to enhance ventilation after the sand core is hardened; (3) Liquid slag inclusion, due to the high viscosity of low-temperature molten iron, it is difficult for the inclusion to float, and the use of adiabatic pouring cover (heat loss reduced by 60%) and deoxidation before pouring can reduce the risk of defects.

In actual production, the pouring temperature needs to be strictly controlled in the range of 1380-1420°C. Thin-walled complex castings (e.g. automobile cylinder blocks, wall thickness 3-5 mm) remove the lower limit of 1380°C to reduce the thermal expansion of the sand mold; Simple castings with thick walls (e.g. machine beds, with a wall thickness of ≥ 30 mm) should be capped at 1420°C to ensure complete filling. The transportation process needs to be insulated and capped, and the time from baking to pouring should not exceed 5 minutes to avoid excessive cooling of the molten iron. By accurately controlling the melting temperature, optimizing the composition of molten iron (Mn/S≥4:1), improving the exhaust design of the sand core (drilling the exhaust hole and opening the exhaust groove) and strengthening the transportation insulation, the defects of high and low temperature can be effectively avoided, the scrap rate can be controlled within 3%, and the high-quality production of gray iron castings can be realized.