Use of Permanent Magnets in Electromagnetic Facilities for the Treatment of Aluminum Alloys
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NTRODUCTION
IN recent years, electromagnetic devices of different types have been widely used in the production and processing of aluminum alloys. Along with the traditional electric heating devices in furnaces and mixers, electromagnetic methods for liquid metal transportation, pouring, and stirring have been widely applied.[1–3] In most cases, the induction three-phase electromagnetic pumps that generate a traveling magnetic field in the melt zone are used for the above purposes. An alternating magnetic field induces electric currents in the molten metal. As shown in the literature,[4,5] the interaction of the alternating magnetic field and electric currents results in an electromagnetic force that drives the melt motion. Most of the power consumed by the three-phase induction pumps is spent on the creation of a required induction value of the magnetic field by a set of coils. Therefore, the application of permanent magnets in such devices is obvious.[6] In recent years, induction electromagnetic pumps with permanent magnets have been widely used in different applications. The traditional three-phase linear electromagnetic induction pumps have been described in numerous works. In contrast to those pumps, it is demonstrated that the traveling magnetic field in the TOMS BEINERTS, Researcher, and ANDRIS BOJAREVICˇS, IMANTS BUCENIEKS, YURI GELFGAT, and IMANTS KALDRE, Senior Researchers, are with the Institute of Physics, University of Latvia, Salaspils 2169, Latvia. Contact e-mail: imants. [email protected] Manuscript submitted August 28, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
induction pump could be generated by a system of permanent magnets with alternating polarity fixed on a rotating ferrous base cylinder.[7,8] The absence of specific windings to create a magnetic field is the main advantage of the permanent magnet pumps (PMPs), which ensures their higher efficiency and simpler design. So far electromagnetic pumps with permanent magnets were used only for low-temperature melts (up to T £ 773 K (500 C)) mainly in the specific applications in the research facilities and in liquid metal-cooled facilities mostly in nuclear research to cool very high heat flux from the hot zone. In these cases, the relatively thin walls of the pump channels allowed for minimizing the nonmagnetic gap (the distance between the magnetic pole surface and the liquid metal) to ensure the needed magnetic field strength in the pumps channel. For more possible applications in metallurgical technologies, the permanent magnet pumps were not effective due to the high temperature of the melts (‡973 K (700 C)) and due to the need to produce channels with rather thick walls (200 to 250 mm) from ceramic refractory materials. As a result, the nonmagnetic gap becomes very big, and hence, the magnetic field strength in the liquid metal zone becomes rather low, not providing sufficient efficiency of the pump. Nowadays new technologies for the production of permanent magnets and refractory materials have essentially improved the pumps’ properties. For example, the
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