Mathematical modeling of tundish operation and flow control to reduce transition slabs
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INTRODUCTION
THE tundish can play very important roles in improving steel quality and achieving high productivity in continuous casting of steel. It primarily acts as a distributor of liquid metal between the ladle and molds to make continuous casting possible. It also provides additional opportunities for inclusion removal, especially with large capacities. Tundish structures and sizes, therefore, have been modified greatly over the past decade, since a tundish with large capacity and flow controls has been identified to be more advantageous than a plain tundish with low capacity. Casting different grades of steel sequentially is increasingly required to achieve satisfactory productivity for a modem caster as steel grades to be cast by this steel-making technique expand. The tundish, therefore, also presents a problem associated with sequential casting which causes chemistry mixing to occur within the resulting transition slabs, especially when tundish capacity is large.[ ~-4] Hundreds of thousands of tons of steel slabs from grade changes have to be downgraded each year as a result. This problem has been receiving more and more attention and is being addressed through several remedies. (a) Scheduling the steel production of different grades within allowable time limits to mitigate chemistry contradiction between the grades. This is an ideal circumstance and only feasible when a plant produces a narrow range of compositions often with overlapping compositional requirements. (b) Changing the tundish for a new grade of steel. This will significantly increase the refractory material consumption and slow down or even stop the casting process. (c) Draining the molten steel left in the tundish. This approach often results in molten steel contamination and also greatly reduces casting yield. (d) Utilizing grade separators in the mold. This measure may easily result in inclusion entrapment and strand
HUIQING SARAH CHEN, formerly Graduate Student Research Assistant, The University of Michigan, is Advanced Process Modeling Engineer, AMCAST Automotive, Southfield, MI 40304. ROBERT D. PEHLKE, Professor, is with the Department of Materials Science and Engineering, The University of Michigan, Ann Arbor, IVll 4810%2136. Manuscript submitted December 13, 1994.
METALLURGICAL AND MATERIALSTRANSACTIONS 13
breakouts and has even been reported to be harmful to the mold. However, none of these approaches addresses tundish flow and mixing phenomena for reduction of transition slabs. In fact, the number of transition slabs is principally determined by tundish flow patterns and mixing characteristics (mixing in the mold is much less extended, since the mold is usually much smaller than the tundish, and molten steel stays there for a much shorter time before solidifying into solid slabs). The tundish behavior is defined by tundish geometry and operating level patterns which are overlooked in the aforementioned approaches. Therefore, in this work, tundish flow and mixing with various tundish configurations and different tundish oper
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