GB676198A - Process for coating metallic objects with other metals - Google Patents

Abstract

676,198. Coating with metals; modifying metallic surfaces; annealing. ALFERIEFF, M. Dec. 1, 1947 [July 31, 1946], No. 31653/47. Classes 72 and 82(ii) Metallic bodies are coated with aluminium, zinc, lead, cadmium, tin or an aluminium alloy, by heating the body to a temperature from 35-180‹F lower than the annealing temperature of the body in a reducing atmosphere, then expelling occluded active gases by heating the body at the annealing temperature whilst subjecting the entire surface to the continuous flow of a practically inert atmosphere, and whilst protected by the inert atmosphere passing the body into a molten metal coating bath. The reducing atmosphere may be of hydrogen containing not more than 30 per cent of water vapour and the inert atmosphere may consist predominantly of nitrogen but may contain just sufficient hydrogen to counterbalance the effect of air penetration. As shown in Fig. 1, a degreased steel strip 1 passes through a furnace 4 having two heating chambers 5, 6, the former of which may be heated to 1470-1670‹F and the latter to 1510-1710‹F, the reducing atmosphere being passed into the chamber 5 at 9 and leaving at 10 and the inert atmosphere being circulated by a pump through the chamber 6 and an extension thereof forming a cooling chamber 11 and through a regenerating apparatus 15. The strip is cooled in the chamber 11 to 1100- 1280‹F and passes into a pure aluminium bath 12 maintained at a temperature not exceeding 1290‹F. Before the strip has cooled below 300‹F and preferably immediately after solidification of the coating, it may be lightly rolled at 16 or, during cooling or after passing through the rolls 16, it may pass through muffles 17 to permit gradual cooling to 700-400‹F over a period of 2-5 minutes whereafter it may be lightly rolled at 19. In a modification, Fig. 2, a nitrogen atmosphere containing 20 per cent of hydrogen is introduced at 20 into the cooling chamber 11 the end of which is immersed in a molten lead bath 21, the aluminium coating bath 22 floating above the lead bath in the container 23: to accelerate cooling, a water jacket is provided around the chamber 11. Pure nitrogen is fed into the heating chamber 6 at 25. After passing through the cooling bath and before cooling, the strip is heated in the furnace 26 to 1290-1830‹F for a few seconds until a blackish lustreless coating is obtained. In a further modification, Fig. 3, the aluminium coating bath 29 floats in the bell mouth 28 of the chamber 11 on a lead bath 27 through which the coated strip passes: in this form, the formation of a pure aluminium layer is prevented, the coating consisting exclusively of ironaluminium alloys.