Flow and Thermal Behavior of the Top Surface Flux/powder Layers in Continuous Casting Molds

Steady-state finite-element models have been formulated to investigate the coupled fluid flow and thermal behavior of the top-surface flux layers in continuous casting of steel slabs. The 3-D FIDAPTM model includes the shear stresses imposed on the flux/steel interface by flow velocities calculated in the molten steel pool. It also includes different temperature-dependent powder properties for solidification and melting. Good agreement between the 3-D model and experimental measurements was obtained. The shear forces, imposed by the steel surface motion towards the SEN, create a large recirculation zone in the liquid flux pool. Its depth increases with increasing casting speed, increasing liquid flux conductivity and decreasing flux viscosity. For typical conditions, this zone contains almost 4 kg of flux, which contributes to an average residence time of about 2 minutes. Additionally, because the shear forces produced by the narrowface consumption and the steel flow oppose each other, the flow in the liquid flux layer separates at a location centered 200 mm from the narrowface wall. This flow separation depletes the liquid flux pool at this location and may contribute to generically poor feeding of the mold-strand gap there. As a further consequence, a relatively cold spot develops at the wideface mold wall near the separation point. This non-uniformity in the temperature distribution may result in non-uniform heat removal, and possibly non-uniform initial shell growth in the meniscus region along the wideface off-corner region. In this way, potential steel quality problems may be linked to flow in the liquid flux pool.