process for anodic treatment of aluminium or aluminium alloys in the middle oxydischer coatings production

摘要

447,420. Electrolytic sur ace treatment of aluminium and its alloys. GOWER, C. H. R., and BOWEN, E. WINDSOR-, Thames Factory, Rainville Road, Hammersmith, London. Nov. 17, 1934, No. 33156. [Class 41] The articles are subjected to anodic treatment in a bath containing acetic acid and a relatively small proportion of phosphoric and sulphuric acids with or without boric acid, the bath being maintained in motion ; the metal is thereby cleaned and provided with a thin and even film of oxide which may then be thickened by further anodic treatment in usual baths. Suitable proportions are 10-15 per cent by volume of acetic acid, 2-2¢ per cent of phosphoric acid and 2¢-3 per cent of sulphuric acid together with ¢-1 oz. per gallon of boric acid. With current density 3-4 amps. per sq. ft. and temperature 80-90‹ F. the treatment is completed in 1-5 minutes. A coating sufficient for protective purposes may be obtained by extended treatment in the same bath or by further anodic treatment in a chromic acid, oxalic acid or other bath. Specifications 395,390, 396,743, 412,193, and 447,421 are referred to,