GB118357A - Improvements in or relating to Electric Furnaces. - Google Patents

Abstract

118,357. Wade, H., (Booth-Hall Co.). Sept. 27, 1917. Electrode furnaces.-One or more hearth electrodes, situated directly beneath the main electrodes, are replaced at starting by an auxiliary upper electrode, until the hearth has been heated to conductivity. Alternating current is preferred. In a single-phase furnace, one terminal of the supply transformer may be connected to the main upper electrode, and the other terminal to the adjustable auxiliary electrode and hearth electrode. In the two-phase furnace shown, two main upper electrodes C<1>, C<2> and two hearth electrodes B<1>, B<2> are connected so that the phase currents cross in the charge. The auxiliary electrode D<1> is connected permanently to one hearth electrode B<2> and at starting is also connected, say through a switch H', with the other hearth electrode. A three-phase furnace may have three main upper electrodes and one hearth electrode which, with the auxiliary electrode, is connected to the neutral point of one or more supply transformers. Auxiliary electrodes are preferably adjusted by hand, and main electrodes automatically by an electric motor, through rack-and-pinion and worm gear in each case. Arcs are preferably struck, at starting, from the main electrodes only, the auxiliary electrode being maintained in contact with the scrap-metal &c. charge; afterwards the auxiliary electrode is raised so as to become inoperative. A hearth electrode may consist of a mass of carbon filling or enclosing an iron or steel grid having a water-cooled projecting terminal.