Effects of a Magnetic Field on Turbulent Flow in the Mold Region of a Steel Caster
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asting (CC) is the predominant method of producing cast steel and is currently used in 95 pct of the world’s production.[1] Because of the large quantities of steel produced, even small improvements in casting quality and defect reduction can result in substantial savings in the unit production cost. The mold region in the CC process contains a complex turbulent flow with large velocities and is responsible for surface defects, slag entrainment and other steel quality problems. The flow at the top surface of the mold can result in hook formation if the velocities are not sufficiently large. However, if the surface velocities are very large, turbulence and shear instabilities can entrain slag from the top surface. If the surface level fluctuates, then the defects can be caused intermittently. Tailoring mold flow provides an opportunity to improve the steel quality. Thus, it is very important to choose nozzle geometries and operating conditions that produce flow patterns within an operating window that avoids these problems. Operating conditions which control mold flow and related problems include: the mold cross section, casting speed, submergence depth, mold powder, argon gas injection, and electromagnetic forces. The application of a magnetic field is an attractive method to control mold flow because it is nonintrusive and can be adjusted during operation. There are various types of flow control mechanisms using magnetic fields, with a broad classification based on the use of static magnetic fields RAMNIK SINGH, MS Student, and BRIAN G. THOMAS and SURYA P. VANKA, Professors, are with the Department of Mechanical Science and Engineering, University of Illinois at UrbanaChampaign, Urbana IL, 61801. Contact e-mail: [email protected] Manuscript submitted April 19, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
using DC current for the electromagnets, or moving fields using AC current. Detailed description of the various types of applied magnetic fields is given in Reference 2. It is well known that the movement of conducting material under the influence of a magnetic field produces a force opposing the motion, and thus should be self-stabilizing. However, the application of a magnetic field can change the flow pattern in nonobvious ways.[3,4] Understanding how a magnetic field affects the highly turbulent mold flow in CC is both an important and challenging task. Several previous studies have attempted to understand the flow in the mold region under the influence of different static magnetic field configurations such as local,[5–9] ruler,[3,9] and flow-control (FC) mold[3,10,11] configuration. Cukierski and Thomas[5] observed that application of local electromagnetic braking (EMBr) weakens the upper recirculation region and decreases the top surface velocity. Harada et al.[9] compared the effects of local and ruler EMBr systems and claimed that both configurations increase surface velocities and dampen high velocities below the mold, and that configuring the ruler configuration below the nozzle ports has better braking efficiency and also results i
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