An improved mathematical model for electromagnetic casters and testing by a physical model
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THE electromagnetic
(EM) casting of aluminum is established technology, and there have been investigations of the EM casting of other metals, r~,2] The two types of caster now in use commercially for aluminum casting are shown in Figure 1, where they are labeled as "Russian" or "Kaiser" to indicate their origins. The Russian type makes use of a "screen" (a band of conducting material, such as stainless steel) to control the EM field produced by the inductor. The Kaiser design dispenses with the screen, and the inductor cross section is shaped to produce the desired EM field. In addition to heat transport and solidification, two important phenomena occurring in EM casters are the EM support of the meniscus at the lip of the molten metal pool and the stirring of the metal by EM forces. The former EM effect is one reason for the success of EM casting; a physical mold is unnecessary, and surface imperfections produced by a mold are avoided. The latter effect may also be advantageous, because stirring can reduce segregation and alter cast structure. However, too vigorous a stirring is thought to be troublesome in that it occurs near the lip of the meniscus and may result in ripples leading to surface defects. Too vigorous a flow at the surface may also promote vaporization of alloy constituents or oxidation. The present paper reports on an investigation of meniscus support and electromagnetically driven flow in casters of the types shown in Figure 1. The investigation has made use of mathematical models, which physical modeling used to verify the mathematical models as well as provide insight into caster behavior. While there are many papers on electromagnetic castB.Q. LI, formerly Graduate Student, University of California, is with ALCOA Technical Center, Alcoa, PA 15069. J.W. EVANS, Professor, and D.P. COOK, Graduate Student, are with the Deparlanent of Materials Science and Mineral Engineering, University of California, Berkeley, CA 94720. Manuscript submitted February 7, 1990. METALLURGICAL TRANSACTIONS B
ers, those mentioned here are ones concerned with electromagnetic fields, meniscus support, and melt flow. Notable previous investigations of electromagnetic casting are those of Getselev and co-workers, I3-91 Layers, t~~ Lavers and Ahmed, t~lJ Viv~s and Ricou, t121Meyer et al. ,r~31 Sakane et al. ,Hal Shercliff,[15] and Breville et al. t~6j Particularly interesting is the work of Viv~s and Ricou, who constructed a physical model of an electromagnetic caster to determine the effect of various parameters, such as screen position, on electric fields, magnetic fields, and velocity within the melt (simulated by mercury). Measurements of velocity were also made on an actual caster at Pechiney Aluminum. Meyer et al. were able to mathematically model the laboratory results, as were Sakane et al., who also obtained a good match between the measurements at Pechiney and their mathematical model. Most of the previous investigations described in the previous paragraph have entailed a two-dimensional (2-D) treatment of the EM
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