GB979583A - Refining metals - Google Patents

Abstract

<PICT:0979583/C6-C7/1> <PICT:0979583/C6-C7/2> In a process for refining metals and alloys, e.g. to remove gases and other inclusions, a consumable electrode of the metal to be treated is immersed in molten slag of higher melting point than the metal, and the metal is gradually melted by the slag and joins a mass of the same molten metal under the slag, the molten metal forming the second electrode, and the electric current flowing to it from the consumable electrode heats the slag. The mass of molten metal is then cooled, and the slag of lower co-efficient of expansion than metal forms a separated sheath around the latter, and also forms a clearance with the wall of the vessel. In examples tool and other alloy steels, magnet steels, non-ferrous metals and alloys may be treated, and the slags used include mixtures containing CaO, Al2O3. CaF2, MgO, TiO2, and B2O3. The end of an electrode 7, Fig. 3, dips into molten slag 1 below which is a pool of molten metal 4 acting as the lower electrode, and resting on solidified metal, which is insulated from the vessel by solidified slag sheath 3 spaced by shrinkage gaps 5, 51. The vessel 2 is provided with a cooling jacket formed by an outer wall of non-magnetic steel and an inner wall of copper. The slag has a melting point 50-70 DEG C. above that of the metal electrode. Either D.C. or A.C. power may be applied including 3-phase current supplied to three electrodes arranged in line or in a ring. Multiples of three electrode rings may be used and more even heating is achieved by rotating the molten steel, by imposing a magnetic field from a surrounding electrically energized helix. In an alternative arrangement, Fig. 8, the metal electrode consists of a tube of the metal 71 surrounding a rod of the metal 7, a voltage of 15-30 V. being maintained between the tubular electrode and the melt 4, and 60-80 V. between the rod element and the melt 4. The tube 71 may be replaced by a helical coil, and may also be of a different metal of higher melting point than the rod thus forming an alloy. The density of the metal 71 may be greater than the rod 7, when two slag layers are used, the slag 11 being less dense than rod 7, and slag 1 is intermediate in density between the two metals, so that molten metal from rod 7 floats on slag 1 within the tubular electrode which melts into the metal pool forming an alloy at 4. An inert gas may be introduced into the free space.