A new or improved process for electro-plating the surface of aluminium or aluminium alloys

摘要

290,903. Gower, C. H. R., and O'Brien & Partners, Ltd., S. Oct. 25, 1927. Metals, pickling; copper, silver, nickel, zinc. and cadmium, depositing; preparing surfaces; treatment after electrolysis. - Aluminium or an aluminium alloy is prepared for plating by anodic treatment in a bath containing sulphuric acid or a substance giving rise to sulphuric acid at the anode. The following are suitable baths (a) sulphuric acid 1¢ pints, hydrochloric acid ¢ pint, water 12 pints (b) sulphuric acid 1 lb., hydrochloric acid lb., sodium sulphate 1 lb., water 1 gallon (c) sodium sulphate ¢ lb., ammonium chloride 6 oz., acetic acid 2 pints or sulphuric acid ¢ pint, water 1 gallon. The current density may be 40 amps. per sq. ft. at 4-5 volts. The article is introduced into the bath with the current on: the connections to one article should be arranged to give a uniform current distribution. The cathodes of lead or carbon. The treatment lasts from one to four minutes. Castings may be given a second anodic treatment for 30 seconds in a bath consisting of 1 gallon of a 6 per cent solution of brown potash and 2¢-3 oz. liquid ammonia. Articles of rolled aluminium or of the alloy known by the registered Trade Mark Duralumin may be given a second anodic treatment in a bath constituted as above with the addition of 5 oz, of nitric acid. The articles. after treatment should be washed and placed in the plating bath while wet. Prior to the anodic treatment the articles may be treated with a boiling solution of brown potash to remove grease and scoured with pumice powder or lime. The plating baths are preferably about 2‹ BÚ above the usual strength. A suitable copper bath contains copper sulphate 2“ lbs., potash alum 2 oz., sulphuric acid 5 fluid ounces, water 1 gallon. This is electrolyzed at 65-70‹ F. with a current density 16 amps. per sq. ft. at 2 volts. A suitable nickel bath contains nickel sulphate 1¥ lbs., citrate of soda 3 oz., water 1 gallon, together with sufficient nickel carbonate to render the solution neutral. This is electrolyzed at 120-140‹ F. at 5 volts reduced after a short time to 2 volts, the solution or the cathode being agitated. The nickel-plated article is washed and dried and baked for 10 minutes at 350‹ F. In the case of cadmium, zinc, and silver a voltage of 1¢ is sufficient.