GB966664A - Coating process - Google Patents

Abstract

A process of coating a metal article with a layer of a metal coating material comprises feeding the article continuously through an evacuated chamber, depositing a thin layer of the coating material by condensation from the vapour, forming an alloy layer of the metal of the article and the deposited layer of coating material, and then depositing a further layer of coating material by condensation from the vapour on to the thus formed alloy layer. The coating material may be zinc or aluminium and the article may be strip steel, and the process may be incorporated in a process for making strip steel, e.g. after annealing and cleaning apparatus. The article may be coated on one or both sides thereof and it may be moving at a speed of 2000 feet per minute; it may be non-ferrous and may be heated before or after it enters the chamber. The article is preferably cleaned and degreased before entering the chamber, and the latter has roller inlet and outlet seals. In an example a steel substrate is heated to about 157 DEG C. and zinc coating material was vaporized and superheated to a temperature above 450 DEG C., the zinc forming a coating of less than 0.001 inch thick; the coating may be only several microinches thick. The substrate is then heated to a temperature of about 460 DEG C. or slightly above to form a layer of zinc steel alloy. The substrate is subsequently cooled to below the vaporizing temperature of the zinc, i.e. 343-405 DEG C. over a pressure range of 0.01-0.1 mm. of mercury, and a further coating of zinc is deposited by condensation on the alloy layer. The coating of zinc may be from 1 microinch to 0.001 inch thick.