Research status of carburizing defects in lost foam casting cast steel

After entering the 21st century, a large number of domestic researchers still solved the problem of carbon enhancement. According to Zhang Fuwen’s research, the process design scheme of the combination of gating and riser can greatly reduce the carburizing defects. The principle is to make most of EPS burn and produce a large amount of reductive high temperature gas through open rapid casting to prevent secondary oxidation of molten steel.

At the same time, the free carbon generated by combustion is discharged from the mold cavity with high temperature gas, which reduces the possibility of carbon addition. This process is also called “carbon removal method”. At present, it is only suitable for small and medium-sized steel castings with soft single structure, and the carbon defects can not be completely eliminated.

Su Jiyong, Jia Bailin, et al. Research found that through reasonable selection of raw materials, reasonable casting, pouring and other methods to control the carbon defect of EPC cast steel, the study pointed out that the choice of low carbon foam material, such as EPMMA (expandable polymethyl methacrylate, carbon content 60%) or STMMA (methyl methacrylate and styrene copolymer resin, carbon content) 69.6%) to replace EPS (expandable polystyrene foam with 92% carbon content) can significantly reduce carbon defect.

Professor Liu Yuman of Zhongnan Institute of casting and metallurgy materials has invented the “casting method of hollow shell after firing”, which is also known as “Guilin No.5 hollow shell casting method”. It was first published and promoted to the casting industry at home and abroad at the “2008 (8th) China Huangshan foundry industry and Trade Conference”. The process is to use ordinary EPS polystyrene foam to brush “Guilin 5”. “Super strong fire resistant paint”, igniting foam model from pouring riser under dry sand negative pressure condition and conveying a small amount of oxygen, so that the foam model is rapidly burning and vaporizing, and the flue gas generated by negative pressure is poured and drained away. When the foam model is fired into empty shell, the molten steel is poured immediately, so as to obtain basically carbon free steel castings.

As soon as it was released, many small and medium-sized enterprises in China have followed suit. It has been applied in factories in Guangdong, Guangxi, Hunan and other places, and has achieved some remarkable results. However, this process is limited to the production of steel castings with large soft unit thickness and low quality requirements, and can not completely eliminate carbon defects for complex steel castings.