UBC Theses and Dissertations
Heat flow in consumable electrode remelted ingots Ballantyne, Alexander Stewart
A computer model based upon the alternating direction implicit finite difference method has been developed for the prediction of the thermal field in cylindrical consumable electrode remelted ingots. The model simulates both the solidification and ingot growth processes, and incorporates temperature-dependent thermophysical properties and boundary conditions. An accompanying model has also been developed for the slag in the electroslag remelting process. In order to obtain data for the confirmation of model results, heat flow measurements have been performed on a laboratory ESR machine. Comparisons have been made between model predictions and experimental results for both laboratory and industrial machines. These comparisons have generally involved the predicted and measured pool profiles since this is the easiest experimental result to obtain. On this basis, the model is about 90% accurate for most remelting situations. The one notable exception is vacuum arc remelted ingots produced at high melt rates. It is postulated that the high direct currents associated with these operations result in considerable pool movement. This increases the effective thermal conductivity in the liquid pool and thereby increases the actual pool depth to values substantially greater than the predicted depth. Several examples have been given to illustrate the application of the model as a design tool. Possible methods of maintaining base temperatures to prevent thermal cracking have been considered. Important factors affecting local solidification times have been examined and attempts have been made to predict the resulting structure as revealed by the secondary dendrite arm spacing. The model has been used to show how different melting cycles may be compared in order to arrive at the optimum balance between melting rate and length of hot top cycle. And, finally, attempts have been made to predict the combination of maximum permissible melt rate and ingot size in order to produce an ingot of acceptable quality.
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