Processing technology characteristics of precision foundry
The mechanical properties of precision castings are hig […]
The mechanical properties of precision castings are higher than those of cast iron, but their casting properties are worse than those of cast iron. They belong to investment casting or precision casting. Its melting point is high, molten steel is easy to oxidize, molten steel has poor fluidity and large shrinkage. Precision casting is not only suitable for casting of various types and alloys. Processing technology characteristics:
1. Since the shrinkage of precision casting greatly exceeds that of cast iron, in order to prevent shrinkage and shrinkage defects in castings, most of the measures used in the casting process are feeders, cold iron and subsidies to achieve sequential solidification. In order to prevent the casting from generating shrinkage, shrinkage, porosity and crack defects, the wall thickness should be uniform, and sharp and right angle structures should be avoided. Sawdust is added to the foundry sand, coke is added to the core, and hollow cores and oil sand cores are used to improve the yield and air permeability of the sand or core.
2. Due to the poor fluidity of molten steel, in order to prevent cold insulation and insufficient pouring of steel castings, the wall thickness of steel castings must not be less than 8mm; dry or hot casting molds are used; the pouring temperature is appropriately increased, generally 1520 ° ～ 1600 ℃, because the pouring temperature is high, the molten steel has a high degree of superheat, and the liquid is kept for a long time, and the fluidity can be improved. However, if the temperature is too high, defects such as coarse grains, thermal cracking, pores and sticky sand will be caused. Therefore, for general small-scale, thin-walled and complex-shaped precision castings, the casting temperature is about 150 ° C, the melting point of steel; the structure of the casting system is simple, and the cross-sectional size is larger than that of cast iron; large, thick-walled The casting temperature of the casting is about 100 ° C higher than its melting point.