Simulation of flow control in the meniscus of a continuous casting mold with opposing alternating current magnetic field
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I. INTRODUCTION
ELECTROMAGNETIC stirring (EMS) of the melt in continuous casting has been an integral part of industrial practice since the 1980s. The EMS parameters and stirring conditions that constitute the electromagnetic aspect of the continuous casting of molten metal have been studied through production trials, physical experiments, and numerical simulations.[1–6] Some stirrers have been evaluated by laboratory devices and computer modeling to improve the quality of castings by using various coil windings.[7–11] Stirred cylindrical pools to which a main frequency (i.e., 50 or 60 Hz) magnetic field is applied without the presence of a copper mold stand in contrast to industrial EMS systems installed on continuous billet-and-bloom casters, which are arranged around molds of predominantly square and rectangular crosssectional geometry. To increase the magnetic penetration to the center of the pool for stirring effect, the systems with cylindrical geometry never operate at the main frequency, but rather within a range below 10 Hz. Therefore, predictions of electromagnetics and fluid flow phenomena derived from theoretical and experimental simulations, despite their usefulness in elucidating the fundamentals, have limitations too restrictive for use by industrial systems. In this work, an attempt has been made to improve the theoretical representation of industrial EMS systems. Moreover, a theoretical model was developed to describe electromagnetic quantities (i.e., magnetic induction, induced current, and electromagnetic force) and fluid flow fields within pools of melt (i.e., mercury) induced by not one alternating current (AC) magnetic field, as is common in industry, but by two independent AC magnetic fields. With these two AC magnetic fields, the main electromagnetic stirrer (M-EMS) proFON-CHIEH CHANG, Staff Engineer, and JOHN R. HULL, Senior Engineer and Manager, are with the Thermal and Electromechanical Section, Energy Technology Division, Argonne National Laboratory, Argonne, IL 60439. Contact e-mail: [email protected] LEN BEITELMAN, Senior Technical Consultant, is with ABB, Ontario, Canada. Manuscript submitted March 16, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS B
duces the best metallurgical results and improves the internal quality, through in-mold stirring. The auxiliary electromagnetic field alternating current–stirring modifier (AC-SM) counterbalances the motion induced by M-EMS and reduces the meniscus instability and surface defects. The strand surface defects such as lappings and bleeds, subsurface negative segregation, and teeming stream flaring can be reduced by ACSM to control flow in the meniscus region without resorting to a reduction in the stirring power of M-EMS. The model represents a novel stirring system developed by J. Mulcahy Enterprises (Ontario, Canada)[12] The system allows flexible control of the stirring flow in the mold meniscus region independent from the stirring intensity in the remainder of the mold volume. Such a technique can ensure the compatibility of EMS with the pra
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