Application of physical simulation to evaluate the impact of teeming method and rate on axial zone formation of large ingots

The article presents the results of evaluation of the impact of teeming method and rate on solidification and formation of the axial zone of large ingots. The research is based on a physical simulation. With this aim a laboratory-scale plant (a crystallization mould) was designed and built which enabled to visualize and monitor solidification and structural formation of the model ingots. Sodium thiosulphate (crystal hyposulphite) – Na2S2O3·5H2O was used as a modeling solution. Matching of the processes in the model and in real industrial conditions of ingot teeming was assessed with similarity criteria obtained on the basis of the dimension theory with consideration of the physical and chemical processes in the ingot during its teeming and crystallization. Two methods – downhill casting and uphill casting – were used to teem the melt into the mould. During teeming the geometry and technological parameters of the model ingots remained unchanged while the teeming rate was altered. Length and medium width of the model ingot axial zone were measured. The thermal profiling of the surface of the mould model was monitored over the entire period of solidification to evaluate the thermal field alteration while the ingot was teemed and crystallized. Thermal imaging processing made it possible to observe temperature changes of the surface of the model mould from top to bottom for downhill cast ingots teemed at different rates. The results obtained demonstrate that teeming rate has a noticeable impact on the axial zone length. It was established that a decreased rate leads to an increased directionality of crystallization and improvement of the ingot axial zone structure.