Influence of Submerged Entry Nozzle Clogging on the Flow Field and Slag Entrainment in the Continuous Casting Mold by the Physical Model

Clogging of the submerged entry nozzle (SEN) is a common problem during the continuous casting of aluminum-killed steel. To visualize the flow field and quantitatively assess the variation of the steel–slag interface after the formation of clogging, this study built a 0.5-scale physical model of the mold using perspex and the clogged nozzle was fabricated by sticking perspex particles with various sizes on the internal wall. The shape of clogging was designed according to the bifurcated SEN taken from the steel plant after one sequence casting was done, and different clogging ratios were considered to investigate the influence of clogging growth on the flow field and slag entrainment in the mold. The main results indicated that, as the clogging inside nozzles grew, the flow field of molten steel changed gradually from a typical symmetrical double-roll pattern to an asymmetric pattern, either with stronger upper roll or deeper lower roll. When the clogging ratio was below 10 pct, the distribution of the oil layer and the frequency of slag entrainment at the water–oil interface were affected slightly. As the clogging ratio reached 30 or 50 pct, the oil was pushed toward the nozzle and the water surface near the narrow face was exposed to air. The water–oil interface became extremely unstable, and an obvious bulge at the interface was formed. As the clogging ratio was increased, the drag of oil into the molten steel happened continuously and the frequency of slag entrainment was beyond 20 per minute. The entrainment also became severe with the increase of casting speed and the decrease of oil viscosity.