The interaction of a DC transferred arc with a melting metal: Experimental measurements and mathematical description
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I.
INTRODUCTION
T H E R E are numerous systems in materials processing operations which involve the interaction between a plasma jet and an initially solid metal block or ingot, which will then progressively melt as a result. Arc welding, the operation of electric arc furnaces, and plasma melting may be cited as typical examples. T,2 The plasma melting of metals and alloys is an important subset of these problems, because this technology is capable of producing rather pure melts of high quality. The quantitative representation of these systems requires that the modeling of the plasma system proper be coupled (through appropriate boundary conditions) to the heat transfer problem associated with the melting process. While melting problems have been extensively studied, in connection with welding applications, the modeling of electroslag remelting, and vacuum arc remelting systems, and useful work has also been done on the modeling of both transferred and nontransferred plasmas, 3"4'5 the representation of a situation where these two phenomena are coupled has not yet been reported in a comprehensive manner. It is' readily appreciated that the plasma portion of the system and the heat transfer processes occurring in the melting billet are connected through the boundary conditions which describe the heat flux falling on the exposed surface of the metal phase. While the heat flux impinging on a metal block due toa DC plasma arc has been measured by several investigators, 6'7'8 all this prior work entailed the use of water-cooled copper anodes so that these results may not be fully applicable to situations where the anode consists of a liquid metal. The work to be described in this paper was undertaken in order to carry out the experimental measurement of the heat transfer rate from a plasma jet to a metal block, under conditions such that partial melting occurs, and then to compare these measurements with predictions based on the G. BACKER, formerly a Research Assistant at Massachusetts Institute of Technology, is a Project Engineer with the General Motors Corporation, Warren, M148090-9040. J. SZEKELY is a Professor in the Department of Materials Science and Engineering at Massachusetts Institute of Technology, Cambridge, MA 02139. Manuscript submitted August 2, 1985.
METALLURGICAL TRANSACTIONS B
transport equations written down for both the plasma and the metal phases. A critical comparison of the measurements and the predictions will provide an assessment of the appropriateness of the currently employed modeling approaches and at the same time should provide helpful directions regarding future work that is desirable in this area.
H. APPARATUS AND EXPERIMENTAL PROCEDURE The objective of the experimental program was to measure the rate of heat transfer from a DC transferred arc plasma to an initially solid metal block which was allowed to melt partially as a result. The heat transfer from the plasma jet to the block was followed by monitoring the transient temperature profiles within the metal anode. This technique
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