DC arc photography and modelling

Direct-current arc furnaces operate with a graphite cathode positioned above a molten slag and metal bath contained inside a furnace vessel. The plasma arc, consisting of ionised particles at extremely high temperatures, forms a conducting path between the graphite cathode and the molten bath. The power provided by the arc can be controlled by adjusting the arc length and the current. The high-intensity plasma arc emanates from a relatively small attachment area on the graphite electrode, and extends down to the surface of the molten bath. Photographs of the arc are presented and compared to models of the shape of the arc. These models provide a description of how the arc voltage varies as a function of arc length and current, for a given set of conditions in the furnace. The arc attachment zone, where the arc impinges on the molten slag surface, is highly turbulent and operates at a very high temperature. This promotes very rapid melting, fast reaction kinetics, and effective mixing. The impingement of the arc causes a crater-like depression in the surface of the slag. This has a significant effect on the distribution of current in the molten slag, and the voltage drop across the slag. The shape and size of this depression has been photographed, and the resulting information used in a model of the depression.