Measurements of molten steel surface velocity and effect of stopper-rod movement on transient multiphase fluid flow in continuous casting

Surface velocity of the molten steel in the mold is critical to final product quality during continuous casting of steel, and is one of the few flow parameters that can be measured in the plant to validate fluid flow models. Surface velocity was measured using two different sensors: Sub-meniscus Velocity Control (SVC) devices and nail dipping, to evaluate their performance, and to quantify surface velocities in a commercial steel caster under different casting speeds, argon gas fractions, and mold widths. A correlation between the height difference of the solidified lump on the nail and surface velocity is confirmed and extended. Reasonable agreement between the two sensing methods was obtained, both in trends and magnitudes for both time-averaged velocity and transient flows. Transient CFD models are applied to simulate multiphase flow of steel and gas bubbles in the Submerged Entry Nozzle (SEN) and mold and are validated with nail dipping measurements. To obtain the transient inlet boundary conditions for the simulation, two semi-empirical models, a stopper-position-based model and a metal-level-based model, predict the liquid steel flow rate through the SEN based on recorded plant data. The model system was applied to study the effects of stopper rod movements on transient flow in the SEN and mold. Mold level fluctuations were calculated using a simple pressure method and compared with plant measurements. The results show that severe stopper rod movements cause significant disturbances of the meniscus level, which may cause slag entrapment, leading to sliver defects in the final product.