GB746772A - Improvements in or relating to processes for the electrolytic polishing of metals - Google Patents

Abstract

746,772. Electrolysis. EVER READY CO. (GREAT BRITAIN), Ltd., and TURNER, H. L. May 28, 1964 [June 30, 1953], No. 18146/53. Class 41. An electrolyte for anodic polishing of aluminium or aluminium-rich alloy comprises 70 to 80 per cent by weight ortho-phosphoric acid, up to 10 per cent by weight of organic reagents comprising 2 to 5 per cent by weight of diethylene glycol monoethyl ether or ethylene glycol monoethyl ether and 5 to 8 per cent by weight of diethylene glycol or ethylene glycol, and 20 to 10 per cent by weight of water. A preferred composition comprises 77 per cent ortho-phosphoric acid, 3 per cent diethylene glycol monoethyl ether, 7 per cent diethylene glycol and 13 per cent water. An aluminium salt, e.g. 1.5 per cent AlPO 4 may be added. In polishing a torch case, the case is cleared in a mild alkali and then immersed for 30 to 60 seconds in the composition which is heated to 60‹ to 100‹ C. The case is then connected as anode and D.C. at a voltage of 7 to 25 applied, a current density of 120 amps. per square foot of anode surface being preferred. The electrolyte is agitated, e.g. by air. The cathodes, which may be of lead or graphite, should have a greater surface area than the case, e.g. six times as great. The process continues for 2 to 20 minutes, when the case is removed and swilled in water. The thin aluminium oxide film is removed by a liquid composition, e.g. caustic soda, a mixture of chromic and phosphoric acids, a mixture of chromic and sulphuric acids, or solutions of the salts of these acids. After further swilling, the case is subjected to anodic oxidation, e.g. in sulphuric acid, to provide a protective film, which may be dyed and sealed in hot water. During the polishing process, the electrolyte is passed through a bed or column of cation exchange material, e.g. one containing sulphonic acid groups, to maintain the aluminium content of the electrolyte at the desired low level. Specification 704,953 is referred to.