Patent GB-809444-A (GB)
Title: Improvements in or relating to the vacuum melting of high-melting metals and alloys by means of an electric arc
IPC: F27B5/04
Filed: 1955-02-22
Abstract: 809,444. Arc-melting furnaces. HERAEUS G. m. b. H., W. C. Feb. 22, 1955 [Feb. 22, 1854], No. 5284/55: Class 39(3) In melting a highly reactive metal e.g. zirconium or tantalum or their alloys under reduced pressure by an arc between an electrode 9 of the metal to be melted and an ingot 13 formed by the metal molten from the electrode, the electrode 9 is progressively formed as a rod from short pre-formed lengths of the material or from the material in powder form, and progressively fed to the arcing chambers at the rate at which it is consumed: and the electrode is degasified immediately before the arcing chamber by passage through chambers 10a, 10b, 10c and 11 where it is subjected to successively lower reduced gas pressures. Thus the metal in powder or granules is fed from a hopper 4, which is under atmospheric or reduced pressure and may be heated, through a measuring device 7 and a tube 8 to pass under a tamper 3 reciprocated by a motor 2 with a pressure of 2-10 tons per square cm. The consolidated rod electrode 9 is thus forced down the tube 10 and passes through the chambers 10a, 1Ob 10c in which a partial vacuum is maintained low by prevacuum pumps 24, and vacuum pumps 26. The lowest pressure is maintained in the lowest compartment 10c, which is connected to two vacuum pumps 26. An inert gas e.g. argon may be fed to one compartment 10b from a cylinder 23 through a pressurereducing and pressure-indicating valve 23b and a flow velocity indicator 23c. A vacuum of down to 10-<SP>4</SP> mm. Hg may be maintained by a diffsion pump 27 in the high vacuum chamber 11, which may carry waiter-cooling pipes 20. The arc-melting chamber has water-cooled walls. The ingot 13 formed from material molten from the electrode tip is supported by a lowering device 14 forming a counter-electrode, to which current is supplied by a cable 22c. The support 14 is water-cooled and may be lowered by gearing 15 driven by a motor 16. Current is supplied to the electrode 9 by a cable 22a near the tamper, the heat developed by current passing through the electrode aiding its degasification. When an alloy ingot is required, the electrode is formed by metering desired quantities of the metals concerned from separate hoppers 4 to the tamper 3. The compression may be carried out in an inert gas and the material may be heated during compression. The tampering speed, the arc current and voltage and the melting- off speed are matched to ensure that the rate of melting and of forming the electrode are equal by use of the arc voltage. In a modification (Fig. 2, not shown) the electrode materials are formed into short rods, which are fed in turn through guides on to the top of the descending electrode and are welded thereto by passage of current through the joint from opposed electrodes in a chamber in which a reduced gas pressure, preferably of argon at 5 mm. is maintained. The electrode is fed down by rollers applied thereto in the vacuum chamber 11, current being supplied to the electrode through these rollers. Direct current of 2000-8000 amps is used at 10-45 volts. The electrode in the chamber 11 may be additionally heated by passing current through it or by high frequency. Degasified powdered or granulated metal is fed by a conveyer to the arc chamber to start or aid ingot formation. Specification 809,443 [Group XXVI] is referred to.