Matters needing attention when the precision casting process is in progress

Due to the poor fluidity of molten steel, in order to prevent cold shut and insufficient pouring of steel castings, the wall thickness of steel castings should not be less than 8mm; the structure of the gating system should be simple, and the cross-sectional size is larger than that of cast iron; dry casting or hot casting is adopted. Casting mold: Properly increase the pouring temperature, generally 1520°~1600°C, because the pouring temperature is high, the superheat of molten steel is large, and the liquid state can be maintained for a long time, so the fluidity can be improved. However, if the pouring temperature is too high, it will cause defects such as coarse grains, hot cracks, pores and sand sticking. So for general small, thin-walled and complexly shaped casting, its pouring temperature is about the melting point of steel + 150 ℃; for large, thick-walled casting, its pouring temperature should be about 100 ℃ higher than its melting point.

2. Since the shrinkage of cast steel is much greater than that of cast iron, in order to prevent shrinkage cavities and porosity defects in castings, measures such as risers, chillers and subsidies are mostly used in the casting process to achieve sequential solidification. In addition, in order to prevent shrinkage cavity, shrinkage porosity, porosity and crack defects in steel castings, the wall thickness should be uniform, sharp corners and right-angle structures should be avoided, sawdust should be added to the casting sand, coke should be added to the core, and Use hollow cores and oil sand cores to improve the yield and air permeability of sand molds or cores.

The melting point of cast steel is high, and the pouring temperature is correspondingly high. The interaction between molten steel and mold material at high temperature is very easy to produce sand sticking defects. Therefore, artificial quartz sand with high refractoriness should be used as the casting mold, and the coating made of quartz powder or zirconium sand powder should be brushed on the surface of the casting mold.