New Algorithm to Calculate Liquid – Solid Shrinkage and Graphite Expansion

Abstract:

Meanwhile the calculation of cooling and solidification is a well introduced tool into the foundry industry for calculating gating and riser systems. However, knowing the areas of last solidification is often no answer to the question if there are any defects in the casting or not. Of course one requirement is an exact description of the heat flow and the heat transfer between melt and mould. But furthermore the liquid/liquid and liquid/solid shrinkage influence the temperature fields due to a convective heat flux. Also auxiliary material influence the liquid/solid behaviour. Auxiliary materials can be on one hand the inoculation material and on the other chills with and without coating. This is the reason, why defects near the gating often can not be detected by a conventional solidification calculation, which doesn’t take into account the impact of the auxiliary material on the convective flow. With new algorithms within the FEM program SIMTEC/WinCast it is possible to respect this behaviour during the simulation of solidification. Special attention was turned to the expansion of graphite in ductile irons. The graphite first nucleates in the liquid, and then continues to grow in the solid phase depending on the alloy compositions and the solidification parameters. With the knowledge about the physical properties of the alloy the location and the size of defects can be predicted precisely.