The variation law of interfacial heat transfer coefficient of typical ZL101 Aluminum alloy ring sand castings with height of 150 mm, thickness of 50 mm, internal and external radius of 30 mm / 80 mm, 50 mm / 100 mm and 70 mm / 120 mm and flat sand castings with height and width of 150 mm and thickness of 50 mm in the casting process was studied by sand mold gravity casting. The actual sand casting temperature measurement experiment was mainly carried out The following conclusions are obtained from the establishment of interface heat transfer back calculation program, the analysis of back calculation results and the solidification simulation of sand castings:
(1) Based on the law of conservation of energy and implicit finite volume method, the one-dimensional back calculation mathematical model of temperature field of sand mold and sand core of flat sand casting and ring sand casting is established, and the back calculation program of interface heat transfer coefficient is compiled through MATLAB software Based on the temperature field data of sand core and combined with the back calculation program, the time-varying curves of interfacial heat flow and interfacial heat transfer coefficient of casting / sand mold and casting / sand core are obtained.
(2) For ring sand castings with equal thickness, the maximum value of interfacial heat flow and interfacial heat transfer coefficient decreases with the increase of internal and external dimensions; When the core temperature reaches saturation, the interface heat flow of the inner core will produce reverse heat flow. With the increase of the ring size, the occurrence time of the reverse heat flow will be delayed; The interfacial heat transfer coefficient is the maximum at the initial stage of solidification, and the value remains basically unchanged. The interfacial heat transfer coefficient of the inner sand core of the same ring sand casting is greater than that of the outer sand mold. With the increase of the inner and outer dimensions of the ring sand mold casting, the interfacial heat transfer coefficient of the sand mold and sand core will decrease, The numerical value and variation law of interface heat transfer coefficient of flat sand casting are similar to that of ring casting.
(3) The change of interfacial heat transfer coefficient with temperature can be approximately regarded as an “s” curve. The change of interfacial heat transfer coefficient is mainly concentrated between the solid and liquid phase lines, and the high temperature area above the liquid phase line and the low temperature area below the solid phase line remain basically unchanged. For the sand core with small size, the blocked shrinkage of sand casting and too long heating time will increase the maximum and minimum values of “s” curve, and the “s” curve will extend towards the solidus temperature, and the interface heat transfer coefficient will decrease for a period of temperature lower than the solidus temperature.
(4) Compared with the measured temperature, the calculated temperature data of ring sand castings TC2 and TC6 and flat sand castings TC2 calculated by the reverse calculation program show that the temperature difference fluctuates by 10 ℃ in the first 100s, and gradually decreases with the increase of iteration time. After 200s, the temperature difference between the calculated temperature and the measured temperature of ring sand castings and flat sand castings remains within 2 ℃, Verify the convergence and stability of the inverse calculation program.
(5) The annular sand casting with inner and outer radius of 60mm / 110mm and height of 150mm is simulated by ProCAST software, and the interface heat transfer coefficient adopts the back calculation result. The temperature field of the simulated sand casting is basically consistent with the measured temperature field. Only after the solidification is complete, the maximum temperature difference is 17 ℃, indicating the reliability and accuracy of the inverse calculation result of the interface heat transfer coefficient, and improving the simulation accuracy of ProCAST.