GB453803A - Process and apparatus for coating metallic objects with layers of other metals - Google Patents

Abstract

453,803. Coating with metals. SEDZIMIR, (known as SENDZIMIR), T., Katowice, Poland. Sept. 23, 1935, No. 26366. [Class 82 (ii)] [See also Group XII] A metal article to be coated by hot dipping is treated to produce a very thin surface film of an oxygen compound of the metal, the film is reduced to metal by subjecting the article to a high temperature, e.g. an annealing temperature, under reducing conditions, and the article is then partially cooled, e.g. to a temperature of 50-150‹ C. above the temperature of the molten metal bath, under non- oxidizing conditions immediately prior to its introduction into the bath. The reduction of the film may be effected by heating the article in a reducing atmosphere or by passing it through a bath of, for example, molten lead. In the form shown in Fig. 1, the strip 10 is passed through an oxidizing furnace 1 and then through a gas seal 14 into a reducing furnace 2, the furnaces being heated, for example, by electrical means 33. The furnace 2 communicates by means of an adjustable door 36 with a cooling chamber 38 which may be provided with adjustable heat insulation 57 and is sealed by a bell 40 dipping into the coating bath 41 and to which reducing gas is supplied through a pipe 19. The coating bath which may be made of metal or refractory material is provided with electrical heating means 33, but in operation the whole or a part of the heat necessary to maintain the metal in the molten state may be obtained from the strip, which is only partially cooled in the chamber 38. In the form shown in Fig. 2, the oxidation is effected by passing the strip through a bath 26, which may contain water, or water mixed with acids, alkalis, or cleaning agents, passing the strip through a chamber 28 in which the atmosphere is kept moist by sprays 27, and then drying the strip by passing it between heaters 13. The coated metal may be removed from the coating bath into a hood 60, sealed at one end by the coating bath 41 and at the other by a bath 16 of water or oil. The hood is filled with non-oxidizing gas by a pipe 19 and the coated metal is cooled by water sprays 61 playing on the surface of the hood. After leaving the hood the strip may be passed through a drier 13<1>. In another form, the strip, after passing through an oxidizing furnace, is passed into a bath of molten lead, which is heated at one end to anneal the strip and reduce the film of oxide. In the remainder of the lead bath the strip is partially cooled, the bath being covered with heat insulating means, and is passed into the coating bath through a layer of granular or powdered material, e.g. charcoal, which prevents access of air. In the form shown in Fig. 4, the strip passes first through a moistening bath 26 in a container 25 to which is connected one lead 30 from a generator 29 and then through a chamber 68<1> in which the oxide film is formed into a chamber 68 supplied with reducing gas. It then passes into a bath 45 of molten lead in which is immersed an electrode 32 connected to the other lead 31 from the generator. The current passes along the strip between the ends of the two leads and anneals the strip in the chambers 68<1> and 68, forming the oxide in the chamber 68<1> and reducing it to metal in the chamber 68. In the bath 45 the strip is partially cooled and passes up through a coating bath 41<1> floating on the lead bath. Fig. 5 shows an apparatus for coating simultaneously a plurality of strips, the strips being passed separately through the oxidizing and reducing furnaces and then combined between rolls 70 in the cooling chamber 38, passed together round rolls 71, 72 and 73 and into the coating bath in which they are separated by rolls 58, 75 in the bath and rolls 74 above the bath. In another form, Fig. 9, the annealing and reducing chamber may be vertical, the strips being brought together into the furnace through sealing rolls 14 and separated in the furnace, recombined on a roll 71 at the entrance of the cooling chamber 39 and again separated by rolls in and above the coating bath. Fig. 11 shows an apparatus for coating strips on one side only, the combined strips being separated in pairs on rolls 58, 581 and 58<11> in the coating bath, recombined on rolls 59, 591 and 5911 above the bath and, if desired, given a second coating in a similar manner in a second bath 41<1>. If one of the strips is to be coated on both sides it may .be separated on a roll 109 and re-immersed in the bath. If desired in anv form of the apparatus, the cooling chamber may extend over the coating bath and form a hood in which the coated metal can cool in a non-oxidizing atmosphere, and a plurality of coating baths, for example, a series of baths containing metals of progressively decreasing melting points, e.g. copper, brass, aluminium, and zinc, may be used. Figs. 7 and 8 show devices which may be placed in the cooling chamber to remove all traces of oxidizing gases. In Fig. 7 a bath of readily oxidizable metal 78 is used in which a drum 47 revolves bringing a film of the metal into contact with the atmosphere, any oxides formed being removed by a scraper 55. In Fig. 8 gas from the cooling chamber is withdrawn by a pump 50 and bubbled through a bath of oxidizable metal 78 containing baffles 53 and then through condenser tubes 54 back into the chamber.