1 NUMERICAL MODEL FOR THE MINIMIZATION OF INTERMIXED ROUND BARS IN A FOUR LINE CONTINUOUS CASTER Marcela B. Goldschmit * , Sergio P. Ferro * , Guillermo F. Walter + , Virginia G. Aranda + and Jorge A. Tena Morelos + * Center for Industrial Research (CINI) Fundación para el Desarrollo Tecnológico (FUDETEC) Córdoba 320, 1054 Buenos Aires, Argentina e-mail: sidgld@siderca.com + SIDERCA S.A.I.C. Dr. Simini 250, 2804 Campana, Argentina Abstract.The grade transition process in a four lines round billets continuous caster was analysed. A numerical model able to determine fast and accurately the length and location of intermixed steel in the bar was developed. The model is based on “tank in series” or “volumes” mathematical models and was calibrated with physical water model measurements and full 3D turbulent numerical calculations. Comparison of the model with measurements performed on intermixed steel bars are also presented. The good agreement between these plant measurements and the numerical results validated the model. The model was implemented on PCs with a visual interface which allows the easy input and output of data, and the program is operating in the steel shop. Finally, the code was employed to evaluate different strategies to fill the tundish during grade transitons. The “double dilution” process, which consists in filling the tundish in two steps, proved to be useful to reduce the amount of downgraded steel.