Effect of Stopper-Rod Misalignment on Fluid Flow in Continuous Casting of Steel
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NTINUOUS casting solidifies most steel worldwide.[1] Final product quality depends greatly on the flow pattern of molten steel in the mold, especially near the top surface. To avoid surface defects, and internal inclusions from slag entrainment, the surface velocity and turbulence levels need to be maintained within an optimum range.[2,3] Turbulent flow in the mold of a continuous caster is governed by the geometries of the nozzle, mold, and flow control surfaces (slide-gate or stopper-rod), casting speed, argon gas injection, and electromagnetic forces.[2] Asymmetric flow causes transient fluctuations and is a main cause of product defects.[4–6] Asymmetric flow causes high surface velocity on one side and causes low surface velocity on the other. This causes transient cross-flow between the narrow gap between the submerged entry nozzle (SEN) and the mold, leading to surface defects, vortex formation, slag entrapment, and other defects.[5,6] In addition to aggravating turbulent R. CHAUDHARY, Ph.D. Student, and B.G. THOMAS, Professor, are with the Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801. Contact e-mail: [email protected] GO-GI LEE, Senior Researcher, is with the Non-Ferrous Refining Project Team, Research Institute of Industrial Science and Technology, Pohang, Kyungbuk 790-784, South Korea. SEONG-MOOK CHO, Ph.D. Student, and SEON-HYO KIM, Professor, are with the Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, Kyungbuk 790-784, South Korea. OH-DUCK KWON, Quality & Technical Team Leader, is with the Magnesium Business Department, POSCO, Suncheon, Jeonnam 540-856, South Korea. Manuscript submitted February 20, 2010. Article published online February 8, 2011. 300—VOLUME 42B, APRIL 2011
fluctuations and the associated intermittent problems, asymmetric flow can create a constant flow bias on the top surface of the mold, which increases the chance for velocity on one side to exceed the critical range, leading to slag entrainment[4,5] and accompanying sliver defects.[4,5,7] At the same time, it may cause insufficient velocity on the other side, leading to meniscus freezing and associated surface defects.[2] Previous researchers have studied the effects on nozzle and mold flows of various asymmetries, including turbulence,[8] slide-gates,[9–11] nozzle clogging,[12] and misaligned nozzles.[13–17] Yuan et al.[8] performed large eddy simulation (LES) to study the natural transients and asymmetries associated with turbulent flow in otherwise symmetric ‘‘quasisteady’’ flow conditions. Flow in the mold cavity switched between double-roll and complex flow patterns with many vortices. Bai et al.[9,10] studied the effect of slide gate orientation on asymmetric flow. A 90-deg (front–back) gate orientation caused swirl in the jet leaving the nozzle, whereas a 0-deg (right–left) orientation caused severe right–left flow asymmetry, with more than 2/3 of the mass flow leaving the right port for a 50 pct open gate. Lee et al.[11] found
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