Matters Needing Attention in the Operation of Precision Investment Casting Technology
1. What materials are commonly used in precision investment casting?
In precision investment casting, we can use stainless steel, carbon steel, alloy steel, etc., all of which can be used for precision investment casting. However, the specific materials can be selected according to different situations. The precision investment casting, which can be referred to as precision casting for short, is a special casting method. Generally speaking, the parts obtained by precision investment casting do not need to be processed, because it can obtain a more accurate shape and a relatively high casting accuracy. However, we can also perform heat treatment and cold processing on the product according to the needs of the product. The types of precision investment casting mainly include investment casting and pressure casting.
The precision investment casting adopts silica sol precision investment casting technology, and the whole process of processed products is automatically controlled from wax melting, injection, dewaxing, roasting, to casting. For each furnace of molten steel of different materials, a spectrometer is used to perform on-site material composition determination and analysis. If the material composition is insufficient or too high, precision investment castings manufacturers are not allowed, which fundamentally guarantees the quality and reliability of the product.
2. Matters needing attention in the operation of precision investment casting technology
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 of precision investment casting should not be less than 8mm; the structure of the pouring system should be simple and the cross-sectional size is larger than that of cast iron; dry casting or hot casting is used; appropriately increase the pouring temperature, generally 1520°C to 1600°C, because the pouring temperature is high, the molten steel has a high degree of overheating, and the liquid stays for a long time, and 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.
Therefore, the casting temperature of small, thin-walled and complex-shaped castings is generally about the melting point temperature of steel + 150°C; the casting temperature of large, thick-walled castings is about 100°C higher than its melting point. Since the shrinkage of cast steel greatly exceeds that of cast iron, in order to prevent shrinkage cavities and shrinkage defects in castings, risers, chilled iron and subsidies are mostly used in the precision investment casting technology to achieve sequential solidification.
In addition, in order to prevent the occurrence of shrinkage cavities, shrinkage porosity, pores and cracks 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 hollow cores and oil sand cores are used to improve the retreatability and air permeability of sand molds or cores.
Cast steel has a high melting point and correspondingly its pouring temperature is also high. The interaction between molten steel and mold material at high temperature can easily produce sticky sand defects. Therefore, artificial quartz sand with higher refractoriness should be used as the mold, and the surface of the mold should be brushed with a coating made of quartz powder or zircon sand powder.