In the process of metal solidification, the interfacial heat transfer coefficient is affected by many factors, such as sand casting and mold material, sand mold casting structure, sand mold casting process and so on. Due to the complexity of sand mold casting / mold interface, it is impossible to directly calculate the interface heat transfer coefficient with the definition formula. At present, there are four methods to solve the interface heat transfer coefficient:
(1) Interface gap method
Interface air gap method is to measure the displacement of a specific point at the interface between sand mold casting and die with time through displacement sensor. This method ignores the convective heat transfer in the gap, and the heat transfer between sand mold castings and molds is only radiation heat transfer and heat conduction of gas in the gap layer. In addition, the complexity of the composition of the air gap layer can not correctly estimate the average thermal conductivity of the air gap layer, which limits the wide use of this method.
(2) Interface temperature difference function
From the point of view of interfacial heat exchange, considering the temperature difference on both sides of the interface, the heat flux is calculated. Finally, the interfacial heat transfer coefficient is calculated by using the relationship between the cooling rate of sand mold casting and the interfacial heat flux.
(3) Interfacial heat flow method
Design experiments and measure the temperature curve of sand mold castings and measuring points inside the mold with time, and use numerical calculation to deduce the interface situation, so as to obtain the interface temperature difference. The heat flow through the interface can be calculated by using the linear slope of the interface cooling curve, and then the interface heat transfer coefficient can be obtained by deriving the interface heat flow and the interface temperature difference.
(4) Numerical inverse algorithm
Numerical inverse algorithm is the most common and effective method to calculate the heat transfer coefficient of sand mold casting / mold interface. The temperature variation law of sand mold castings or specific points in the mold is measured by experimental method, and the interface heat transfer coefficient is calculated by establishing the back calculation mathematical model and using the sensitivity coefficient judgment iterative method. This method has been widely used.