Study On Interficial Heat Transfer Coefficients Between Casting And Sand Mold Or Core In The Sand Casting Process

In the simulation of casting process,the numerical calculation of casting temperature field is the core part.The interfacial heat transfer coefficient(IHTC)is a necessary parameter for accurate calculation of castings temperature field.IHTC is affected by the gap between the casting and the casting mold,and related to the material of the casting and the mold as well as geometric shape of the contact interface.To compare with metal mold casting process,it is difficult to measure the gap size between casting and mold in gravity sand casting process.In this experiment,the change of IHTC with casting temperature was studied by changing the shape and size of castings,so as to provide a reliable interfacial heat transfer coefficient for the simulation of sand mold gravity casting.In this experiment,the interfacial heat transfer coefficient was obtained by measuring the temperature field of casting and sand mold/core in the casting process and combining with the reverse calculation program.The thickness of the plate castings was 50mm and the width and height of the casting were 150mm geometry.The inner and outer radii of the ring castings are30mm/80mm?50mm/100mm?70mm/120mm,and the height is 150mm.The material of the casting was ZL101,The material of mold was resin bonded sand.The pouring temperature was705°C.The temperature measurement position of the casting is 2 mm from the casting/mold interface.The temperature measuring position of sand mold/core were 6 mm,14 mm,22 mm from the casting/mold interface,respectively.The plate casting is along the thickness direction,and the ring casting is along the radius direction.The interface heat flux density is calculated by the temperature field of sand mold/core.In the reverse calculation program,both plate and ring castings are regarded as one-dimensional heat transfer.Rectangular elements were used in plate castings and sector-shaped elements were used in ring castings.Based on the heat transfer calculation of finite volume method and Beck nonlinear estimation method,the inverse calculation mathematical model was established,and the reverse calculation program was programmed by MATLAB software.The IHTC was obtained from the first unit temperature and interfacial heat flux of sand mold/core and the measured casting temperature,which was transformed into the curve of IHTC with casting temperature.The results show that the maximum and minimum IHTC of plate castings are 108 W/(m~2·?)and 61 W/(m~2·?)in the high and low temperature regions,respectively.and the values are almost unchanged in the high and low temperature regions.IHTC decreases with the decrease of casting temperature in the range of liquidus and solidus and presents an approximate"S"curve.the cooling shrinkage freedom of ring castings is lower than that of flat casting,the gap between casting and mold interface is small,so the maximum and minimum IHTC of casting/sand interface in ring casting increases with the decrease of outer diameter of ring casting.The maximum and minimum values of the interfacial heat transfer coefficient of the ring casting/sand mold with minimum radius(80mm)are 131 W/(m~2·?)and 83 W/(m~2·?)respectively.The overall values and variation law are similar to the interfacial heat transfer coefficient of the plate castings.The sand core expends and casting shrinks during ring castings solidification process,so the IHTC increases with ring casting inner diameter decreases and the degree of the casting/core IHTC increasing was remarkable.The maximum and the minimum IHTC constant values are 263W/(m~2·°C)and 144 W/(m~2·°C)for high and low temperature region of the 30mm inner diameter ring casting respectively.The"S"curve can reflect the change trend of IHTC with the surface temperature of the casting,when solidification shrinkage of the casting is blocked and the heat acting time of the sand core is prolonged,The maximum and minimum values of the interfacial heat transfer coefficient are increased and the"S"curve extends to the solidus temperature.In addition,the temperature field of 60/110mm ring casting was simulated by ProCAST,and the IHTC of sand core?sand mold and flat plate are used as boundary condition to simulate the temperature field.The maximum temperature difference between the simulated temperature and the measured temperature is 17?.It is shown that the reliability and accuracy of the inverse calculation program of IHTC,and the accuracy of ProCAST simulation is also improved.