Patent GB-762130-A (GB)
Title: An improved liquid bath furnace and methods for continuous heat treatment of articles of manufacture
IPC: C21D1/44
Filed: 1954-03-12
Abstract: 762,130. Annealing. BOSTROEM, T. March 12, 1954 [March 13, 1953], No. 7224/54. Class 72 [Also in Group XII] The heat treatment of elongated metallic bodies, particularly light alloy strip, bar, wire, tube &c. by flotation on a bath of molten material, is carried out in apparatus comprising an assembly of superposed hot baths 1-7, an insulating hood 10 seated on gas-tight seals 9 on a base 8, feed and discharge rollers 14 and 18 respectively for strip 12, and driven rollers 15 feeding the strip from one bath to the next lower bath. The topmost bath 1 is a preheating bath in which fluid at a temperature equal to, or slightly higher than, the critical temperature of the metal, is fed from a tank 52 by nozzles 53 over, and in countercurrent to, the strip 12. In the remaining baths, the fluid material, e.g. lead, is fed concurrently with the strip from the exit end of one bath into the feed end of the next lower bath by an overflow connection (Fig. 5, not shown). Baffles 20 of downwardly decreasing size on the hood 10 and baffles 19 of downwardly increasing size on the baths 1-7 divide the apparatus into chambers defining a zigzag path for an atmosphere gas supplied over the first soaking bath 2 and taken off over the last soaking bath 7. Each bath may be formed internally with baffles deflecting the molten material forwardly and centrally below the strip 12 (Figs. 10-13, not shown). Fig. 9 (not shown) discloses a system for circulating and reheating the bath fluid, a separate heater being provided for the overheated fluid supplied to the preheating bath. In the event of a complete or partial interruption of the strip movement, the temperature of the fluid circulated to the preheating bath is lowered by diluting it with cooler fluid under control of a valve actuated in accordance with the voltage generated by a motor connected with the rollers 15. The fluid in the baths, as described in Specification 620,138, is preferably a molten metal, neutral to and of a higher specific gravity than, the treated metal strip &c. For light alloys having an aluminium or magnesium base, lead may be used. The atmosphere gas may comprise a mixture of reducing and inert gases containing substantial quantities of hydrogen, carbon monoxide and nitrogen, with smaller quantities of carbon dioxide and watervapour, but no oxygen. A modification, Fig. 3, has superposed baths 1-3 anchored by links 99 to fixed supports 100 at alternate ends only, and the top and bottom of the side walls of the baths are formed with grooves 102 engaging bearings or rollers 103. The rollers 15, 16 are journalled at 104 in the side walls of the baths, and on one side are in disengagable connection with driving shafts 107 driven from a common motor 111 through shafts and worm gearing 113. A synchronized drive through worm gearing 118 and a shaft 117 actuates the exit rollers 18, a similar drive being, provided for the feed rollers 14. In a further modification, Fig. 8, the baths 1-5 are supported as in the previous modification, but the strip in the preheating chamber 1 is heated by a gas continually circulated by a fan 90 in a circuit 84 incorporating deflectors 88 and 89 to divert the gas respectively from and to the surface of the strip. The circuit 84 is divided into branches 93 and 94 provided with heating elements 95 and cooling elements 96 respectively and also with valves 98 controlling the passage of the gas therethrough.