IMPROVING THE INGOT QUALITY BY UNDERSTANDING THE BEHAVIOR OF THE MOLD FLUX DURING CASTING PROCESS USING A 3D FLUID/STRUCTURE NUMERICAL SIMULATION MODEL

摘要

It is well known now that the ingot defects like hot tears or cracks are rooted at the first beginning of the solid shell birth. Damages result from the competition between hydrostatic pressure within the turbulent flow of the liquid zone and the solidifying skin under tensile stresses and strains state. In addition, the thermal energy extracted from the cast product by the mold has huge impact of the thickness of the shell. It depends on the air gap growth issued from the shrinkage of the solidifying metal together with the deformation of the mold components. In addition, within the pouring phase, the mold flux can be inserted between mold and ingot shell that is also impacting the heat exchanges. Numerically speaking, the method able at taking all that phenomena into account through an accurate way is a fluid/structure model. Indeed, a standard CFD method does not represent the solid behavior, so that the stresses, strains, air gap evolution due to the shrinkage of the shell are not reachable. In this paper, a new 3D fluid/structure model involving the turbulent fluid flow and the solid constitutive equation is described. The management of the dedicated "liquid time step" allowing high velocity motion into the liquid phase of the alloy coupled with the "solid time step" dealing with the solid phase and the corresponding slow motion, is presented. The model considers as well added bags of mold flux on top of ingot surface impacting not only the heat exchanges with ambient but also with mold during casting process. An application on an ingot casting process taking into account the coupling with the deformation of the mold is presented. Moreover, based on that model, it is shown that the segregation within the ingot is tracked. In addition, the top powder is accounted as deformable body following the shrinkage of the top surface of the ingot. The exothermic reaction is considered as well in order to estimate its impact on the cooling time and the final quality of the cast product