Effect of casting conditions and clogging on fluid flow in metal delivery system and thermo-mechanical behavior of solidifying shell in continuous casting of steel

Abstract

In continuous casting of steel, it is very important to quantify the pressure distribution and flow rate in the metal delivery system, which starts from the tundish, then into the Upper Tundish Nozzel (UTN), Submerged Entry Nozzle (SEN), and finally to the mold. It is, also, crucial to understand the effect of turbulent flow on thermo-mechanical characteristics of the solidifying shell inside the mold, since both can directly affect the quality of the final product. To that end, two MATLAB-based state-of-the-art one-dimensional pressure energy models are developed and applied in this work to calculate pressure distribution and flow rate in slide-gate, PFSG, and stopper-rod nozzle systems, PFSR, for argon-molten steel flow systems by solving a 1D system of Bernoulli equations which can be used in commercial steel casters and water models. Both models are validated and verified with experimental plant measurements and computational fluid dynamics simulations with errors of less than 8 pct. Additionally, PFSG is used to investigate the effect of different casting conditions on the flow rate and pressure distribution. It is shown that increasing some casting conditions such as tundish height and nozzle bore diameter can decrease minimum pressure in the system, which in turn increases the possibility of air aspiration. As for the PFSR, it is concluded that two more phenomena, cavitation and non-primed flow, are needed to capture the real physics existing in the plant. Finally, a transient thermo-mechanical model is developed to understand the strength of the turbulent flow on the solidifying shell inside the mold in continuous casting of steel using ABAQUS. The model is able to account for the superheat flux, which is the heat transfer across the interface near the solidification front between the turbulent flowing liquid and the solidifying steel shell. The predictions of the model include temperature distribution, shell growth, stress, and strain (including elastic, inelastic, thermal, and fluid components) distribution for temperature-varying thermo-mechanical and composition-based properties. It is, then, verified with existing models, CON1D and analytical solutions, and validated with experiments. Ultimately, a case study is conducted to investigate the effect of the turbulent flow caused by the asymmetric clogging inside one of the ports on the thermo-mechanical behavior of the solidifying shell inside the mold. It is shown that the effect of mold heat flux is far more important than the superheat flux.