Analysis of back calculation results of interface heat transfer coefficient in sand casting

Based on the temperature field data measured by pouring experiment and the established matlab inverse calculation program, the interface heat flow, interface heat transfer coefficient and temperature field are inversely calculated. The changes of internal and external interface heat flow and interface heat transfer coefficient with the temperature of sand casting were compared between flat sand casting and ring sand casting, and the change law of interface heat transfer coefficient caused by the change of geometric parameters of sand casting was explored.

It mainly arranges and analyzes the measured and back calculated data, calculates the interface heat flow and interface heat transfer coefficient through the measured temperature data, and analyzes the variation law.

(1) The measured data were collected and processed into a form that can be calculated by MATLAB back calculation program. The changes of sand mold temperature field of flat sand casting and sand mold and sand core of ring sand casting with different sizes were compared.

(2) The changes of interfacial heat flux and interfacial heat transfer coefficient with time are inversely calculated. For the ring sand castings with equal thickness, the peak values of interfacial heat flux and interfacial heat transfer coefficient decrease 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 largest at the initial stage of solidification, and 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 ring size, the interfacial heat transfer coefficient of sand mold and sand core will decrease;

(3) The change of interfacial heat transfer coefficient with temperature can be regarded as an “s” curve similar to temperature. 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 shrinkage of sand casting is blocked and the heating time of sand core increases, which will increase the maximum and minimum values of “s” curve, and the “s” curve will extend to the solidus temperature direction.

(4) By comparing the temperature difference between the measured temperature and the back calculation temperature of 50 / 100mm ring sand castings TC2 and TC6 and flat sand castings TC2 thermocouple position, it is found that the back calculation error is large in the first 100s. With the increase of the back calculation iteration time, the back calculation error will gradually reduce to less than 2 โ„ƒ after 200s, which verifies the convergence and stability of the back calculation program.

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