an electrical furnace in which the thermal effect of an electric arc is used to smelt metals and other materials. The first industrial arc furnaces were built between 1898 and 1901 by P. Héroult in France and E. Stassano in Italy. The first arc furnace in Russia was built at the Obukhov Plant in St. Petersburg in 1910.

Arc furnaces are classified according to their method of heating as direct and indirect furnaces and furnaces with a submerged arc. In direct arc furnaces, electric arcs burn between electrodes and the body being heated (Figure l,a). In indirect arc furnaces the arc burns between electrodes at a certain distance from the materials being heated, and the heat from the arc is transmitted to them by radiation (Figure 1,b). In furnaces with a submerged arc, the arcs burn under a layer of solid charge that surrounds the electrodes (Figure 1,c). The charge is heated by the heat emitted in the arc and also by the Joule heat developed as the current passes through the charge.

Figure 1. Diagrams of arc furnaces: (a) direct, (b) indirect, (c) with submerged arc

Arc furnaces have come to be used extensively in metallurgy, mainly to smelt steel and, in somewhat different form, to smelt ferrous alloys and pig iron from ores, as well as in the chemical industry to produce calcium carbide, phosphorus, and other products. The electric power in an arc furnace is supplied from a transformer through copper bars and carbon or, more frequently, graphited electrodes, mostly of round cross section. Three-phase arc furnaces, in which the arcs burn between three electrodes and the material being processed, are the most widespread.

A modern electric steel-smelting arc furnace is a large, highly mechanized and automated unit (Figure 2), in which the time required for production operations between smeltings—the discharging of one smelting and loading for the next one—is reduced to a minimum, making possible the most efficient use of the furnace’s operation time.

The main element in the design of an arc furnace is the metal body in the form of a shell, usually of circular cross section. The shell is lined inside with highly refractory materials. The refractory lining of the removable roof of the furnace is ring-shaped. The roof is usually raised and moved aside in order to load the charge into the furnace. The walls

Figure 2. DSP-200 steel-smelting arc furnace, with a capacity of 200 tons: (1) graphited electrode 710 mm in diameter, (2) electrode holder, (3) roof, (4) water-cooled roof ring, (5) cylindrical shell, (6) water-cooled auxiliary door, (7) electromechanical mechanism for rotating furnace about vertical axis, (8) electromechanical mechanism for tilting furnace, (9) casting spout, (10) movable current lead from flexible water-cooled cables, (11) stem for vertical movement of stand-sleeve-electrode-holder-electrode system, (12) current lead from water-cooled copper tubes

of an arc furnace have one or two viewing ports and a taphole with a spout to pour the metal and slag into a ladle. The roof has openings for inserting electrodes equipped with water-cooled jackets (economizers). The arc furnace is mounted on a cradle so that it can be tilted toward a viewing port or taphole by an electrical or hydraulic drive mechanism. Modern arc furnaces have inductors for electromagnetic mixing of the molten batch.

Arc furnaces are built with various capacities (up to 250 tons) and with transformer capacities as high as 85,000 kilovolt-amperes.