Heat Transfers Law Of Annular Castings Under Sand Mold And Forced Air Cooling

Today,casting alloy composition,casting cavity materials,casting auxiliary external field conditions(such as air cooling,water cooling,centrifugal,negative pressure,ultrasonic vibration,etc.)is becoming more complex and diversified,in this case the solidification and cool process of the casting and the quality and performance of the casting product also become more difficult to predict.Although the rise of simulation software for the casting process and the results of the prediction provides a convenient condition.However,the lack of research base on solidification theory and physical parameters of complex and diversified casting processes seriously limits the accuracy of simulation results.Among the physical parameters of casting,the interfacial heat transfers coefficient between the casting and the cavity film of the casting directly determines the heat dissipation efficiency of the metal liquid and the high temperature casting after solidification,strongly influences the cool rate of the casting,which in turn determines the defect distribution,stress state,grain organization coarseness and mechanical properties of the casting.Therefore,it is of great scientific significance and application value to study the theoretical basis of interfacial heat transfers coefficient in casting process and its change trend under diversified casting methods.This thesis takes cast aluminum and cast steel as casting materials,furan resin selfhardening sand and water glass self-hardening sand as core materials,with/without air cool in the sand core as external field conditions,and ring-like castings as objects,and systematically investigates the change law of interfacial heat transfers coefficient between castings and cores under different conditions by jointly using the optimized Beck inverse algorithm,numerical simulation method and temperature field measurement data,and explores the change mechanism.In this way,the necessary data base and theoretical basis are provided for the application of forced cool technology in the casting industry.The results show that the interfacial heat transfers coefficients between cast steel and aluminum parts and sand/core are different,and the addition of forced air cooling will increase the value of the interfacial heat transfers coefficient and change its curve shape.When the casting temperature is higher than 575 ℃,the value increases steadily as the casting temperature decreases,decreases steadily when it is lower than 575 ℃,and decreases abruptly when it is 575 ℃.When air-cooling is added,the change curve of the interfacial heat transfers coefficient with the decrease of temperature or the increase in time still keeps the "s" curves,and its value is greatly increased compared with the condition without air-cooling,and the process of slow decrease of the interfacial heat transfers coefficient occurs before the casting temperature decreases to 575 ℃.In the overall casting process,with the extension of time,the interfacial heat transfer coefficient first increases rapidly to the maximum value,and then decreases stepwise to the minimum value and then shows a slow rise and finally decreases slowly.Under air-cooled condition,the interfacial heat transfers coefficient of cast steel still maintains the "bimodal" form,and its average value can reach more than twice that of the nonair-cooled condition.Forced air cooling has an enhanced effect on the interfacial heat transfers coefficient in sand casting as ring castings,and can improve the value of interfacial heat transfers coefficient.Forced air cooling can shorten the cooling time of the casting and increase the cooling rate of the casting.