Numerical Simulation of Melt Flow, Heat Transfer and Solidification in CSP Continuous Casting Mold With Vertical-Combined Electromagnetic Braking

During continuous casting, electromagnetic braking (EMBr) is a widely used technology to improve the quality of steel product. The EMBr technology takes benefit of the generation of Lorentz forces that are induced by the interactions of melt flow with externally applied magnetic fields. In the present paper we propose and investigate a new type of EMBr, named vertical-combined electromagnetic braking (VC-EMBr) in application to the Compact Strip Production (CSP) thin slab continuous casting mold. The unique characteristic of the VC-EMBr lies in the fact that two new pairs of vertical magnetic poles (VMPs) are located adjacent to the mold narrow faces on the basis of Ruler-EMBr. To determine the braking effect of the VC-EMBr, the influence of the installation position of the VMPs on the flow, heat transfer and solidification behaviors of ultra-low carbon steel in a 1500 x 70 mm CSP funnel-type mold is numerically solved. The fluid-flow-related phenomena of three casting cases in the CSP mold, i.e., No-EMBr, Ruler-EMBr, and VC-EMBr, are further investigated numerically to evaluate the metallurgical capability of the VC-EMBr, including the quantitative evaluation of level fluctuation, heat transfer, and shell growth at a casting speed of 4.5 m/min. The parametric study shows that for the CSP mold with width of 1500 mm, the optimal braking effect of the VC-EMBr can be obtained when the VMPs are located at 50 mm from the narrow face of the mold. With this adjustment, the magnitude of the maximum surface velocity is reduced by 70 pct when compared to the case of p(1) = 0 mm. This reduction can decrease the heat loss in the upper recirculation region of the CSP mold and promote the homogeneity of the temperature field therein. In addition, the evaluation results show that the newly proposed VC-EMBr provides more obvious technological advantages than the traditional Ruler-EMBr in application to the CSP mold with a bifurcated nozzle. For the VC-EMBr, the horizontal magnetic poles (HMPs) keep the same advantage as the Ruler-EMBr in providing a good protection against excessive downward impact of the molten steel. On the other hand, the VMPs overcome the disadvantage that the Ruler-EMBr cannot well suppress the upward backflow in the CSP mold. For instance, by applying a magnetic flux density of 0.3 T, the VC-EMBr has a better capability to reduce the maximum amplitude of the level fluctuation by 83.8 pct and increase the average surface temperature of the molten steel from 1803.6 K to 1804.5 K when compared to the case of Ruler-EMBr. This variation can well prevent surface defects related to the level fluctuation, such as slag entrapment and mold powder freezing. On this basis, it can be seen that the industrial application of the VC-EMBr in the CSP mold can benefit from these findings.