MULTIPHASE MODELLING OF THE STEEL GRADE TRANSITION IN A CONTINUOUS CASTING TUNDISH

Nowadays, continuous casting is extremely conditioned by sequences of different steel grades that produce a large amount of intermixed steel. Due to customer requirements, steel producers are forced to deliver a few slabs of high-specialized steels, so the number of castings handling steels of dissimilar grades has been significantly increased in recent years. As a consequence, manufacturers are particularly concerned with the development of practical methods to know exactly where the mixed regions begin and end, in order to make a precise classification of the steel grade that has been produced and avoid further downgrading. Pioneering works by Huang and Thomas introduced a 1-D model to estimate the intermixed region during a grade transition. This model reached a notable popularity because of its ability to provide on-line predictions, though it is assumed that mixing inside the tundish is globally determined with a number of fixed parameters. Recently, Cho and Kim have introduced a modification reducing the number of parameters required, but with the full unsteady description of the tundish flow still unresolved. Moreover, all these models require experimental calibration, using the results from full-scale water models. Additionally, other researchers have been focused on the development of numerical simulations to analyze the flow structures and mixing features of the tundish, mainly during stable operation, but using limiting simplifications and/or steady schemes. In the present investigation, to the author's knowledge, a 3D, unsteady numerical simulation using a volume-of-fluid formulation is carried out for the first time. With this technique, the transient behavior of the tundish during the ladle change can be fully modelled, tracking the free surface and extending the computations towards the steady state. A transport equation is resolved for a non-reactive scalar, representing a dimensionless concentration, so it is possible to predict the mixing degree of the steel at the tundish exit for different operating conditions. The final objective is the development of an off-line methodology to estimate precise intermixing periods during grade transition in continuous casting.