Experiment and analysis of levitation-melting method of induction furnace

Abstract

This paper presents basic data on the effect of a high-frequency induction coil in the levitation-melting method.The buoyant force is measured with a digital balance under the constant 30 k W output, and the effect of the coil's position on the buoyancy is investigated experimentally. I n addition, the flux distribution In the actual coil, which has asymmetric shape, is calculated with the three-dimensional boundary element method. The rotating motion of a levitating metal caused by a n asymmetric flux distribution is discussed.In this paper, we show that controlling the movement of ingot may be a solution to the problem of uniform heating in this system. I. INTRODUC~~ONIn recent years, the melting technique has become very important in improving quality of metal and in developing a new material. In the conventional melting method, various kinds of crucibles suited to metal are usually adopted. However a reaction usually takes place between the molten metal and crucible.To solve the problem, a cold crucible method was proposed in Germany in 1950 [l]. This method is very useful in melting metal without contamination, because the molten metal is levitated by an electromagnetic force in space. The copper cold crucible is comprised of several segments, which are cooled internally with water. The metal crucible is placed in a high-frequency induction coil, and an ingot in the crucible is melted by induction heating. Because a repulsing magnetic force is induced between the molten metal and cold crucible, the position of the molten metal is stabilized. Since the cold crucible is one kind of flux concentrator, the effective magnetic flux density also increases in comparison to that without the crucible [2].However this method has some problems, and this equipment is not used generally yet. There are some difficulties in the levitation of molten metal in the liquid state, a restriction of the melting quantity (that is a limitation of the levitating quantity), and a problem in controlling the temperature 13-51. Our research has concentrated on the issue of the quantity of metal that can be levitated, and we have Manuscript received April 18, 1995.developed some improvements in the levitation-melting technique. While the principle of this method is clear, there are still many difficulties in a practical implementation of this technique. This paper presents basic data on effect of a high-frequency induction coil. Fig. 1 shows the shape of the cold crucible and the highfrequency inductioncoil. The copper cold crucible has eight segments, which are cooled internally with water. The sixturn exciting coil is double winding with copper tube. Fig. 2 shows the definition of parameters used in this measurement. The sample is a steel ball of diameter 43 mni, 2868 in weight. The metal was inserted into the crucible with a ceramic holder, and supported at the center of coil HI. The metal was levitated at upper part of HI after preheating 27 kW for 20 sec. suction 1/ Cooling water poker supply 'egmentr Cold crucible Fig. 1 Shape of the...

A method of noncontact suspension of rotating bodies using electromagnetic forces

“…This method has found application in containerless melting, where a conductor suspended in ac fields melts due to heating by eddy currents. [57][58][59][60][61][62][63][64][65][66] The advantage of noncontact suspension in this case is that the crucible material does not contaminate the melt. While, in this particular application, high losses are beneficial ͑they are needed to melt the conductor͒, in other applications the suspension, in contrast, has to be highly efficient.…”