Effect of Stopper-Rod Misalignment on Fluid Flow in Continuous Casting of Steel R. CHAUDHARY, GO-GI LEE, B.G. THOMAS, SEONG-MOOK CHO, SEON-HYO KIM, and OH-DUCK KWON Misalignment of metal-delivery systems can cause asymmetric fluid flow in the mold region of continuous casters, leading to abnormal surface turbulence, insufficient superheat transport to the meniscus, slag entrainment, inclusion entrapment, and other quality problems. This work investigates the effect of stopper-rod misalignment on nozzle and mold flow velocities in a conventional continuous casting process using both a water model and a computational model. Three stopper-rod configurations are studied (aligned, front misaligned by 2 mm, and left misaligned by 2 mm). The 3-D steady k–e finite-volume model matched well with impeller probe measurements of both velocity and its fluctuations. Negligible asymmetry was found near the narrow faces. Asymmetry close to submerged entry nozzle is the main cause of vortex formation observed in all cases. The left-misaligned stopper-rod produces a shallower jet with a higher flow rate from the right port, leading to higher surface velocities on the right surface. This produced substantially more large vortices on the left side. The asymmetry produced by the nozzle length bore diameter ratio of ~21 in this work is consistent with the theoretical critical entrance length of ~24 for turbulent pipe flow. DOI: 10.1007/s11663-011-9478-5 Ó The Minerals, Metals & Materials Society and ASM International 2011 I. INTRODUCTION CONTINUOUS casting solidifies most steel world- wide. [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 sub- merged entry nozzle (SEN) and the mold, leading to surface defects, vortex formation, slag entrapment, and other defects. [5,6] In addition to aggravating turbulent 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 that front–back asymmetry caused by a 90-deg slide-gate was responsible for particle entrapment on the inner radius. Mahmood [12] computed the asymmetric flow caused by nozzle clogging based on clog samples collected at the steel plant. A two-fold difference in surface velocity between opposite sides of the SEN leading to vortex formation was found. Asymmetric effects were enhanced by increasing casting speed and reducing SEN depth. [5,6,12] Modeling by Zhang et al. [13] found a similar great effect of SEN clogging on 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: bgthomas@illinois.edu GO-GI LEE, Senior Research- er, is with the Non-Ferrous Refining Project Team, Research Insti- tute 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 Technol- ogy, 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 METALLURGICAL AND MATERIALS TRANSACTIONS B