强制风冷在大型铸钢件砂芯上的应用

Application of Forced Air Cooling in the Sand Core of Large Steel Casting

通过活动横梁铸件简化模型研究了冷铁、自然风冷和强制风冷对厚壁回转体大型铸钢件凝固时间和砂芯温度场的影响。砂芯采用强制风冷铸件凝固时间最短,而采用冷铁不能缩短铸件凝固时间。通过对比不同冷却条件砂芯的温度场发现无强制冷却砂芯和冷铁砂芯分别在13 h和12 h出现热饱和现象,随后砂芯中心到铸件的温度梯度转为负值,砂芯向铸件输送热量;而砂芯采用自然风冷和强制风冷时从砂芯中心到铸件建立了正的温度梯度,能有效吸收铸件凝固期间释放的热量而改善其冷却条件;强制风冷对流换热系数高,冷却作用明显。对活动横梁铸件原始工艺改进,砂芯采用强制风冷;模拟结果与原始工艺相比缩孔位置上移,表明冒口补缩能力增强;同时砂芯实测温度场与模拟温度场相吻合,验证了模拟结果的可行性,由于砂芯在高温热作用下的时间短,经改进工艺所生产的活动横梁铸件中心孔表面无机械粘砂。

The solidification time of the large steel casting with thick section and the temperature field of the sand core cooled by chill, natural air and forced air are studied by the simplified model of a movable crossbeam. The casting solidification time is the shortest when sand core are cooled by forced air, while chill cannot shorten solidification time of the casting. By comparing the temperature fields in different sand core cooling conditions we find that both the no cooling sand core and the sand core with chill appear to be thermal saturation when solidification times are 13 and 12 hrs, respectively. Furthermore the heat come from thermal saturation will be transferred to the casting due to negative temperature gradient from center of the sand core to the casting. However, when the sand core is cooled by natural air or forced air, A positive temperature gradient from center of the sand core to the casting can effectively be established and therefore the heat come from the release of casting solidification can be absorbed to improve its cooling condition because the higher of convective heat transfer coefficient of forced air cooling, the more obvious of the cooling effect on the casting. The original casting technique of the movable crossbeam is improved by adopting forced air cooling to the sand core. The simulation results show that the feeding ability of the riser is enhanced due to the effect of forced air cooling on the shrinkage defect in the riser departing away from the casting. Furthermore the monitoring temperature field is coincided with that obtained by simulation indicating that the simulation results are credible. No mechanical bonding is found between sand and the surface of the center hole of the movable crossbeam for the refined technique due to the reduced time of the sand core exposed in the high temperature.