Numerical study of steady turbulent flow through bifurcated nozzles in continuous casting
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I.
INTRODUCTION
SEVERAL million tons of liquid metal flow through nozzles every year during the processing of semifinished metal products. The continuous casting mold for solidifying steel slabs is one example of a process in which the bifurcated nozzle plays a critical role. This process is important because, over the past decade, the fraction of steel produced in the United States through continuous casting has grown from 29 pct to over 67 pct.ll] Continued viability of the steel industry depends upon improved efficiency and consistent quality of steel production. Improving the submerged entry nozzle (SEN), which controls the delivery of steel into the mold, is one step toward this goal. A schematic of part of the continuous casting process is depicted in Figure 1. Steel flows through the "tundish," and then it exits down through a ceramic SEN and into the mold. Here, the steel freezes against the water-cooled copper walls to form a solid shell, which is continuously withdrawn from the bottom of the mold at a rate or "casting speed" that matches the flow of incoming metal. Flow through the SEN is gravity driven by the pressure difference between the liquid levels of the tundish and mold top free surfaces. Thus, the flow rate depends upon the amount of steel in the tundish and the flow characteristics inside the SEN. The flow rate of molten steel is controlled to maintain a constant liquid level in the mold in several ways. In one method, a simple "stopper rod" pushes down through the tundish to partially plug the exit (not pictured). Alternatively, a "slide gate" blocks off a portion of the SEN pipe section by moving a disk-shaped plate through a horizontal slit across the entire SEN, as pictured in Figure
FADY M. NAJJAR, formerly Research Assistant, Department of Mechanical and Industrial Engineering, is with the National Center for Supercomputing Applications, University of Illinois, Urbana, IL 61801. BRIAN G. THOMAS, Associate Professor, is with the Department of Mechanical and Industrial Engineering, University of Illinois, Urbana, IL 61801. DONALD E. HERSHEY, formerly Research Assistant in the same department, is with G.E. Aircraft Engines, Cincinnati, OH 45215. Manuscript submitted June 23, 1994. METALLURGICALAND MATERIALSTRANSACTIONS B
slag layer Liquid Steel
Slide Gale " (flow contzol) Copper Mold
~dEntryNozzle (SEN)
Solid Mold Powder I Liquid MoldFlux [
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Depth
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ContinuousWithdrawal Fig. 1--Schematic of the continuous casting process showing tundish, SEN, and mold.
1. This flow-adjustment method allows for independent control of casting speed and metal level and is also essential for stopping the flow of molten steel if the operation must be abruptly terminated. The primary functions of the SEN are to protect the molten steel from reoxidation as the steel is delivered from the tundish to the mold and to control the flow of steel within VOLUME 26B, AUGUST 1995--749
the mold. The SEN has an important influence on steel quality through its effect on the flow patter
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