Study on heat transfer characteristics of lost foam casting

At the front of the lost foam casting filling mold, due to the reaction of metal liquid and foam, the foam is decomposed and vaporized, which leads to a decrease in the temperature of the front metal liquid. Because of the existence of pattern surface coating, the heat transfer of liquid metal is affected at the mold wall; In addition, compared with ordinary cavity casting, the heat transfer in mold filling process of the lost foam casting is different. This is due to the characteristics of lost foam casting. Because of the reaction of molten metal and foam pattern in the process of lost foam casting, gas will be generated. The study of these processes is of great significance in preventing shrinkage cavity, wrinkle skin, cold shut and microstructure defects of castings.

In order to test the change law of sand mold temperature in aluminum alloy cavity casting and lost foam casting, Fu et al. Embedded thermocouples at different distances from the interface between metal and mold. The test results show that in the place close to the interface between metal and mold, the heating speed of lost foam casting sand mold is higher than that of cavity sand mold, while in the distance, the heating speed of cavity sand mold is higher than that of lost foam casting sand mold. This phenomenon is caused by the transport of decomposition products in the sand mold. Because the lost foam casting mold is compacted by negative pressure, the decomposed hot products will pass through the coating due to negative pressure and then enter the closer dry sand.

Due to the characteristics of lost foam casting, the outer layer of foam pattern has a coating. Because of the existence of this coating, the heat transfer process between casting and mold will be affected. The influence of heat transfer process can be understood as the change of heat exchange coefficient. In the whole process, the heat transfer process between casting and mold is changing, so the heat exchange coefficient is also changing, and the different pouring temperature and coating thickness also have an important impact on the heat transfer process.

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