Patent GB-769053-A (GB)
Title: Improvements in or relating to electric arc furnaces
IPC: F27D11/08
Filed: 1955-05-23
Abstract: 769,053. Arc melting furnaces. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. May 23, 1955 [May 26, 1954], No. 14780/55. Class 39(3) An arc furnace for melting material which is chemically active at its melting temperature such as titanium, zirconium, chromium, molybdenum and tungsten, or the carbides, oxides and other compounds of these metals comprises an air-tight enclosure 5 having in its lower portion a non-consuming oathodic melting pot 8 into which extends a vertically adjustable anode 21 from which an arc extends to the top of a melt accumulating in the pot, the length of the are being adjusted by vertical adjustment means; and a vacuum is maintained in the enclosure high enough to cause the arc to cover a large area of the anode and of the melt, means out of contact with the top of the melt such as a shield 41 or a magnetic field being provided to keep the arc from moving from the top of the melt to the side walls of the melting pot. The shield 41 is non-consuming and comprises a water-cooled annulus placed between the anode 21 and the side walls of the melting pot 8. The lower end of the shield extends below the lowest surface of the anode and is spaced closely above the top surface of the melt, said spacing being adjusted by raising the anode or by lowering the water-cooled bottom wall 12 of the melting pot. The bottom wall 12 is supported on a vertically-adjustable water cooled column 18 extending slidable through a removable bottom wall 14 of the enclosure and is connected by a wire 51 to the current supply to form the cathode. Additionally or alternatively to the shield, magnet means are placed outside the walls of the melting pot 8, which are of non- magnetizable material, for producing a magnetic field having flux-lines passing through the top surface of the melt, more especially between the lower end of the shield and the rim of the melt. The anode 21 in Fig. 1 comprises a water-cooled coil of copper tubing with its ends extending up through the roof of the enclosure, which is protected against radiant heat by a shield 56. A starting anode 27 passes centrally through the coil and has a horizontal extension 28 which is pivoted at 29 in insulated manner to the water-cooled enclosure wall. so that it mav be raised and lowered by a terminal lead 31 extending through the roof. A small starting electrode 54 of titanium is carried centrally on the base 12 of the melting pot, and after pouring in some powdered titanium from a hopper 35 with a vibrated base, the pusnbutton 53 closes a circuit to form an arc between the starting electrodes 27, 54, and the main arc .from the electrode 21 then starts. A vacuum of 5 m.m. or less of mercury is maintained in the enclosure by a vacuum pump 7. The level of titanium in the pot may be ascertained in known manner by measuring the wall temperature or the voltage of the arc-drop in the furnace The ingot 42 on the base 12 is finally removed through the bottom of furnace. Energy is supplied from a step-down deltastar transformer as shown. The annular electrode 21 may be replaced by three straight anodes internally water-cooled and extending symmetrically into the melting- pot from above. The anodes are directly energized from secondary terminals of the transformer 47, the cathode 12 being connected to the star-point of the secondary. A starting anode 77 is frictionally held on a protuberance on the inner surface of the shield 41 and may be energized from a battery, and this anode melts off. In Fig. 2 the anode 66 is water-cooled doublewalled and funnel-shaped and is vertically adjustable by a top supporting hook 83, together with a central hopper 65 and the arc shield 41, which is not water-cooled. The magnet comprises a magnetizable ring of channel cross section so that it terminates in upper and lower pole pieces which surround closely the walls of the melting pot with the upper pole above the surface of the melt and the lower pole is lower than this surface. The magnet is either permanent or is energized by a D.C. coil inside or around the vertical part of the magnet. The arc shield may also be of magnetizable material so that it also acts as an annular magnet. The main anode may alternatively comprise a large block of compressed titanium sponge, which owing to its size and its proximity to the water-cooled arc shield, is not melted or consumed to any material extent.