Research status of interfacial heat transfer coefficient in sand mold casting abroad

Since the 1950s, casting engineers have found that the interfacial heat transfer coefficient has a great influence on the change of temperature field during metal solidification, which affects the final microstructure and properties of sand mold castings. Since the late 1970s, computer simulation technology has been applied to the field of sand mold casting. The interfacial heat transfer coefficient between casting and mold is an essential boundary parameter in the process of sand mold casting simulation. Researchers have made a lot of exploration on the factors affecting the interfacial heat transfer coefficient.

Tillman and berry were early scholars who determined the interfacial heat transfer coefficient through experiments. They designed the graphite mold, placed the cold iron at the bottom of the graphite mold, and then poured the liquid steel into the graphite mold. The temperature change data of corresponding positions of cold iron and sand mold castings during solidification were measured by using thermocouples with fixed discharge in sand mold castings and molds. Then these temperature data are used to calculate the temperature gradient at the interface, so as to calculate the interface heat flow of casting / mold. Through the macro interface heat transfer coefficient formula and the iteration of time step, the curve of interface heat transfer coefficient with time is obtained. The results show that the interfacial heat transfer coefficient ranges from 550 to 1300 w / (M2 · K).

In 1976, Sully studied the interfacial heat transfer coefficient between low carbon steel casting and copper mold. He used thermocouples to measure the internal temperature field data of sand mold castings and copper molds, took the experimental temperature data as the input variable, and established the calculation program by using one-dimensional finite difference method. In the study, the interfacial heat transfer coefficient is simplified as a linear piecewise relationship with time, and the average interfacial heat transfer coefficient between low carbon steel casting and copper mold is about 400 W / (M2 · K). At the same time, he also found that the oxidation of the surface of coatings and sand mold castings will reduce the interfacial heat transfer coefficient.

Matsubara and Nishida studied the effect of pressure on interfacial heat transfer coefficient. They use pure aluminum as the casting material, and the cast steel mold that can apply pressure is selected. Similarly, the measured data of thermocouple are calculated by finite difference method. Considering the thermal radiation, the variation relationship of interfacial thermal resistance with time is obtained. In the paper issued in 1986, it is explained that the range of interfacial heat transfer coefficient is 0 ~ 3000 w / (M2 · K).

Jacobi conducted an experimental study on the solidification of pure iron castings in water-cooled functional molds in a vacuum furnace to determine the change of interfacial heat transfer coefficient with time. According to his experience, he expressed the heat flow at the mold interface as a piecewise function of time, and solved the interface heat transfer coefficient through the ratio of interface heat flow to interface temperature gradient. The interface heat transfer coefficient varies in the range of 2200 ~ 3400W / (M2 · K).

Professors Ho and pehlke have done a lot of research on the inverse problem of heat transfer in the solidification process and made outstanding contributions to the inverse calculation of interfacial heat transfer coefficient. They are the first to use Beck inverse algorithm to study the inverse problem of metal solidification heat conduction, and obtain the variation law of heat transfer coefficient of casting / metal mold interface with time. Pehlke research team also further studied the mechanism of interfacial heat transfer between castings / molds. The inverse heat conduction problem solving method and interface gap method are used to solve the interface heat transfer coefficient. He ignores the influence of convective heat transfer in the research process of interface gap method.

Sahai selected ceramic mold to study the relationship between interfacial heat transfer coefficient and interfacial gap. Beck estimation method is used to solve the interfacial heat transfer coefficient. The results show that the interfacial heat transfer coefficient changes with time and temperature, and the variation range is 200-60w / (M2 · K).

Compared with metal mold, sand mold casting has the characteristics of low casting cost, simple production process, short production cycle and wide application range. This makes workers begin to pay attention to the study of interfacial heat transfer coefficient in sand mold casting. Huang et al. Studied the interfacial heat transfer coefficient of ZL101 and solidification in resin sand mold. They measured the temperature data of sand castings and sand molds, regarded the thermophysical parameters of castings and sand molds as constants, and solved the interfacial heat transfer coefficient through the inverse heat conduction problem method. They calculated that the interfacial heat transfer coefficient between aluminum alloy and sand mold varied from 250 to 700W / (M2 · K).

Woodbury studied the heat transfer process between sand mold castings and resin sand. He regarded the thermophysical parameters of materials as the quantity varying with temperature, and solved the inverse problem of heat conduction by using Beck estimation method with future time. The greatest significance of this study is that it is the first to reverse calculate the interface heat transfer coefficient only by using the temperature measurement data of thermocouple in sand mold, which avoids the error of aluminum alloy thermophysical parameters at high temperature, simplifies the experimental device, reduces the calculation time and improves the estimation accuracy. At the same time, Woodbury and Ke also estimated the heat transfer process between sand mold casting and green sand, which is the first time to use the inverse heat conduction algorithm to solve the interfacial heat flow between sand mold casting and green sand mold.

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