NUMERICAL-SIMULATION OF METAL FLOW AND HEAT-TRANSFER DURING TWIN-ROLLSTRIP CASTING

How to start up the casting operation is one of the serious problems e ncounted in twin-roll strip casting process. During the initial pourin g stage, the metal pool should be progressively developed to reach the optimal pool level and the solidified metal layers formed on the surf aces of two opposite-rotating rolls should be welded together before t he dummy sheet is withdrawn from the minimum roll gap. Improper operat ion with inaccurate withdrawal time often results in unstable process and products as well as the breakup of cast strip, which will be detri mental to the formability and subsequent coiling of cast strip. Theref ore, the proper withdrawal time of dummy sheet plays a very important role in the initial stage of a vertical twin-roll casting process. The accurate withdrawal time is, however, very sensitive to the variation s of thermal distribution, flow conditions and metal-roll interactions . In order to elucidate the fundamental transport phenomena in twin-ro ll casting, a commerical software called ProCAST was employed to simul ate the transient fluid flow, heat transfer and solidification behavio rs during the early stage of the process in this study. The coupled se t of governing differential equations for mass, momentum and energy bl ance were solved with the finite element method and the transient free surface problem was treated with a Volume of Fluids (VOF) approach. A n enthalpy method was employed to handle the phase change during solid ification. The advantage of this model is the great capability to trea t the problems of moving boundary and free surface of fluid. With this mathematical model, the filling sequences, flow patterns and correspo nding temperature profiles in the metal pool under an actual casting c ondition of a vertical twin-roll strip casting process were simulated in this study. From the calculated results, how the metal pool progres sively develops between the rolls and how the solidified layer grows i n thickness with time on the rotating rolls are possibly revealed. Mor eover, the metal pool level, the solidification front as well as the p osition of solidification end could be obtained. With these available informations, the optimal withdrawal time of the;strip casting process can be thoughtfully determined.