Levitation of liquid sodium droplets
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INTRODUCTION
IN the last 10 years, there has been increasing interest in the application of electromagnetic technologies in the metals industry. Electromagnetic fields can be used to generate both thermal and mechanical energies within liquid metals. Electromagnetics is presently used in the metals industry to (1) heat the metal inductively fo/" temperature control and homogenization, (2) stir the liquid metal to allow quality improvements, (3) control the flow of the liquid metal (accelerating and braking), and (4) enable contactless processing of metal to produce high-purity alloys. The idea of casting metals and alloys without any physical contact has generated a lot of interest in the metals industry, especially in the production of metals/alloys that are highly reactive and have a very high melting point. Containerless casting can be achieved by levitating or pushing the liquid metal from the surface of the container. Electromagnetic levitation of liquid metals was first suggested by Muck,m and subsequent research is reviewed in detail by Peifer521 In 1952, Okress e t a/. [3,4] investigated both levitation and melting of solid bodies by induction. Mager,[5] using a dish-shaped meander coil, managed to support shallow pools of 140 g of aluminum, 200 g of copper, and 140 g of magnesium with 4 kW of power and at 10 kHz. Fogel e t al. f61 levitated 100 g of titanium and zirconium in a boat inductor. Stephan f71 reported levitation, with partial support, of sodium in mineral oil. He also reported some complete levitation but had very little control over the stability of the levitated metal. Sagardia fsl reported successful levitation of 1 kg of metal by using a set of three axisymmetric coils with different excitation current frequencies in each of the coils. The coils were arranged such that the tangential magnetic field had a finite value all over the surface of the metal. Currently, there are many theo-
S.S. ROY, formerly Graduate Student, Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, is Research Engineer with Homer Research Lab., Bethlehem Steel Corp., Bethlehem, PA 18016. A.W. CRAMB, Professor, Department of Materials Science and Engineering, and J.F. HOBURG, Professor, Department of Electrical and Computer Engineering, are with Carnegie Mellon University, Pittsburgh, PA 15213. B. LALLY, formerly Post Doctoral Fellow with the Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, is Staff Member with Los Alamos National Laboratories, Los Alamos, NM 87545. Manuscript submitted June 3, 1994. METALLURGICAL AND MATERIALSTRANSACTIONSB
retical and modeling programs studying the levitation process, but there still is a scarcity of experimental work. Some experimental work on levitation was reported by E1-Khaddah and Natarajant93 on aluminum and copper. The problems faced during the process of electromagnetically levitating liquid metal droplets inside a conical coil are the enormous power requirement and the restriction in the height
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