The Role of Side Arcing in the Global Energy Partition during Vacuum Arc Remelting of INCONEL 718

The energy flows during vacuum arc remelting (VAR) of a 20-in.-diameter ingot of INCONEL 718 have been investigated experimentally, numerically, and theoretically, and the results are compared and discussed. The temperatures at a number of points on the outer surface of a VAR crucible were measured during a melt. A forward heat-flow model was constructed and the (initially unknown) interior heat flux distribution refined iteratively until the predicted crucible temperatures matched the measurements. The model included radial and vertical heat flow within the crucible and the development of a heated cooling water layer near the outer surface of the crucible. Significantly, it is shown that the temperature difference between the crucible outer surface and the bulk cooling water was not a linear function of the heat flux at the crucible inner surface. It is shown that results from the literature of plasma physics can be used to place bounds upon the partition of energy during VAR. These bounds are combined with the numerically-inferred power distribution within the crucible to estimate the position of the ingot top during the experiment and, hence, the overall energy partition. Side-arcing from the electrode to the crucible is shown to be predicted to transfer more energy to the crucible than has previously been expected. Time variation in the measured crucible outer surface temperature was also investigated as a means to estimate the ingot top position, and the results are compared with those from numerical modeling and plasma physics arguments. It is shown that the two methods are in fairly good agreement, but that they are in contrast with some aspects of results reported previously.