Simulation of the Electric Signal During the Formation and Departure of Droplets in the Electroslag Remelting Process
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ELECTROSLAG remelting (ESR) is a metallurgical process which combines and couples many phenomena such as magnetohydrodynamics (MHD), heat and mass transfer, and electrochemistry. Due to the use of opaque materials and high temperatures, experimental observation of the process is very difficult. Many fundamental aspects of this process are still unclear and subject of controversy. The process is monitored and controlled mainly through the electric signal measured during melting. It is known that the droplet formation and departure generate a large part of the observed voltage fluctuation (known also as voltage or resistance swing). In addition, the development of heat and mass transfer at the slag/droplet interface is important for the final
A. KHARICHA, Senior Scientist, Group Leader, and M. WU, Professor, Group Leader, are with the Christian-Doppler Laboratory on Advanced Process Simulation of Solidification and Melting, Department of Metallurgy, Montanuniversitaet Leoben, 8700 Leoben, Austria, and also with the Chair for Simulation and Modelling of Metallurgical Processes, Department of Metallurgy, Montanuniversitaet Leoben, 8700 Leoben, Austria. Contact e-mail: abdellah.kharicha@ unileoben.ac.at A. LUDWIG, Full Professor, is with the Chair for Simulation and Modelling of Metallurgical Processes, Department of Metallurgy, Montanuniversitaet Leoben. E. KARIMI-SIBAKI, Ph.D. Student, is with the Christian-Doppler Laboratory on Advanced Process Simulation of Solidification and Melting, Department of Metallurgy, Montanuniversitaet Leoben. Manuscript submitted March 20, 2014. Article published online January 25, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
ingot quality, composition, and cleanliness. The heat transfer from the slag to the liquid pool is largely dominated by the droplets. In References 1, 2, transparent experimental models were presented in which single droplet departure during melting was observed. The slag was a transparent eutectic LiCl–KCl alloy which was used to remelt electrodes made of metals with low melting temperatures (Pb, Cu, Zn, Al). During melting, the voltage across the slag layer was monitored with an oscilloscope. Figures 1 and 2 represent the typical oscilloscope trace of the voltage during the formation and departure of aluminum droplets. This typical change in electric parameters (voltage or resistance) can then be used to detect the occurrence of a droplet departure in the conventional non-transparent slags. The typical droplet mass was estimated in References 3, 4 by combining the resulting dripping frequency with the melting rate. Systematic experiments to correlate the dripping frequency with process parameters using non-transparent slags are reported in Reference 4. With the same power input and up to slag height of about 300 mm, the frequency of droplet departure was found to increase with slag height. Almost no change was observed for slag height larger than 300 mm. Based on the droplet signature as the one measured in Figures 1 or 2, an invention (US Patent 6019811 (2
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