Abstract: 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.

Key words: forced air cooling, large steel casting, sand core, temperature gradient, thick section