Study of meniscus behavior and surface properties during casting in a high-frequency magnetic field
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I.
INTRODUCTION
SURFACE quality of continuously cast metals can be improved by imposing a continuous high-frequency magnetic field from the outside of a mold. Regarding this improvement of the surface quality, various mechanisms have been discussed, tt-51 So far, the author and colleaguest6,71 have proposed new concepts of "soft contacting solidification" and "slow cooling solidification" tightly related to the mechanism of improving surface quality. The former concept is based on the reduction of the hydrostatic pressure between melt and a mold due to magnetic pressure, and the latter concept is based on the reduction of cooling rate through both an intermittent contact between melt and a mold caused by a magnetic pressure and joule heating. As we can imagine, since the two concepts are tightly related to meniscus behavior, it is important to study the effect of a magnetic field on the meniscus motion. In this study, in order to confirm the proposed concepts, model experiments were conducted by use of molten gallium and molten tin. The investigation consisted of two parts. (1) The first one is the direct visualization of the meniscus behavior, in which molten gallium is adopted as a simulator of molten steel, and the evaluation of the surface quality of cast metal under the continuous high-frequency magnetic field, in which molten tin is used again as a simulator. (2) The second part is to introduce a newly developed intermittent highfrequency magnetic field and to investigate the relationship between the meniscus behavior and the surface TINGJU LI, Graduate Student, KENSUKE SASSA, Assistant Professor, and SHIGEO ASAI, Professor, are with the Department of Materials Processing Engineering, Nagoya University, Nagoya 464-01, Japan. SH1NJI NAGAYA, formerly Undergraduate Student, Department of Materials Processing Engineering, Nagoya University, is Member, Mitsubishi Electric Co., Nagoya, Japan. Manuscript submitted May 3, 1994. METALLURGICALAND MATERIALSTRANSACTIONSB
quality of tin billets by use of the new magnetic field. The functions of the new magnetic field are discussed. II.
EXPERIMENTAL APPARATUS AND PROCEDURES
A. Direct Observation of Meniscus Behavior The experimental apparatus is shown in Figure 1. In order to allow the direct observation of the meniscus behavior, a glass ring was inserted into a graphite mold so as to adjust the inner diameter of the glass ring to that of the mold. An optical fiberscope camera linked to video equipment was set at the vicinity of the ring. The meniscus behavior of a molten gallium (melting point 301.8 K) was continuously recorded under the imposition of the high-frequency magnetic field from the outside of the mold. The surface wave motion of the molten gallium was measured by a laser level sensor, and the spectrum of the wave motion was obtained by use of a Fast Fourier Transform (FFT) analyzer.
B. Continuous Casting of Molten Tin Molten tin was continuously cast by imposing the high-frequency magnetic field from the outside of the graphite mold from which the glass
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