A Review of Permanent Magnet Stirring During Metal Solidification
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WITH the growing demand for high quality ferrous and non-ferrous metals, the production of defect-free products becomes increasingly important. It is well-established that electromagnetic stirring (EMS) is one of the most useful methods for generating uniform temperature and concentration fields as well as refining the cast structure.[1–5] While EMS methods with three-phase alternating current (AC) magnetic field inductors have been known for many years, they consume high levels of electrical power and require intense water cooling of the inductor coils. As an alternative approach, permanent magnet stirring (PMS) has been developed, using a pair or multiple alternating polarity NdFeB permanent magnets in an axial symmetric array which, during rotation,
JIE ZENG is with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, 100083 Beijing, China and also with the Department of Materials Science & Engineering, University of Toronto, Toronto, ON, M5S 3E4, Canada. Contact e-mail: [email protected] WEIQING CHEN is with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing. YINDONG YANG and ALEXANDER MCLEAN are with the Department of Materials Science & Engineering, University of Toronto. Manuscript submitted February 20, 2017.
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produce a rotating magnetic field within the molten metal.[6–8] In comparison with EMS methods, a movable permanent magnet system provides advantages that include lower power consumption, simpler design aspects and higher magnetic density. During recent years, a number of laboratory studies have focused on the effect of PMS on the stirring of low-melting alloys and pure metals.[9,10] Some results show that the cylindrical permanent magnet system can achieve up to 10 times higher energy efficiency compared to AC inductors and have the potential for a wide-range of industrial applications.[10] Compared with the relatively large number of PMS laboratory studies as well as numerous reports on the industrial application of EMS, relatively few papers have reported the use of rotating permanent magnets within energy-intensive industries, such as the steelmaking sector. In 1982, Kawami et al.[11] and Hagiwara et al.[12] developed an in-mold stirrer using a rotating magnetic field that was created by mechanical rotation of a permanent magnet. It was found that the rotating magnetic field improved the surface and internal quality of continuously cast billets and was effective in decreasing pinholes, center porosity, and carbon segregation as well as increasing the equiaxed crystal zone. Almost 35 years later, a final solidification stage permanent magnet stirrer that was developed for the continuous casting of high carbon steel billets, achieved similar encouraging results.[13] However, despite the significant advantages
of PMS, the technology has not yet received wide industrial application perhaps because several issues related to the principle, design, and operating advantages have not b
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