Frank J. Zanner

Metal transfer during vacuum consumable arc remelting

An investigation was conducted to determine how metal is transferred during vacuum consumable arc remelting. The transfer mode was found to be dependent on arc length for the electrode sizes (0.10 to 0.20 m diam) and electrical parameters studied (1.9 to 3 kA and 25 V). At short arc lengths ≤0.03 m, metal transfer was found to occur when liquid metal spikes hanging from the cathode form a low resistance bridge (drop short) by touching the anode and then subsequently rupture. The formation and rupture of these molten metal bridges was confirmed with electrical resistance measurements. During the bridge lifetime (0.0003 to 0.020 s) the arc was extinguished and all of the electrical power was directed through the molten bridge. At long arc lengths (>0.1 m) the spikes separate before touching the anode. Experimental observations concerning the coalescence of molten material at the cathode tip were made and they were found to be in agreement with theories on liquid instabilities. A review of pertinent literature concerning vacuum arcs was conducted and this along with general information on vacuum consumable arc re-melting are included as background information.

Vacuum consumable arc remelting electrode gap control strategies based on drop short properties

An investigation was conducted to determine the influence of electrode gap on the properties of drop shorts during vacuum consumable arc remelting. The goal of this work was to yield an electrode gap control strategy based on easily measured electrical parameters. For a particular alloy, at one current level and low pressure (<4 X 10-3 Torr), this goal was achieved, in that drop short period was found to be highly correlated with electrode gap. However, this model was found to be constrained by statistics which require counting 100 drop shorts in order to obtain a valid measurement. Other control strategies involving anode spikes, drop short resistance, and energy/resistance ratios were also evaluated and these properties showed poor correlation with electrode gap.

Optical diagnostics for metallurgical processes

Many industrially important metallurgical processes are accompanied by the emission of light, the analysis of which often supplies useful information concerning the current state of the process while also providing insight into the details of specific process mechanisms. Optical diagnostic techniques are finding an increasingly wide range of application throughout the metallurgical community. This paper discusses the application of emission spectroscopy and imaging techniques to the analysis of such diverse processes as vacuum arc remelting, laser welding, and arc welding. A discussion of these techniques is presented, addressing such subjects as instrumentation, data analysis, the kind of information available and its potential impact on the selection of process parameters. Special attention is given to discussing the difficulties encountered in applying these diagnostic technologies to /open quotes/real life/close quotes/ processes in non-laboratory environments. 44 refs., 6 figs.