LOCAL ANODIC OXIDATION TREATMENT AND EQUIPMENT THEREFOR

PURPOSE:To stably form an excellent anodic oxide film by determining the heat transfer coefficient of a hollow body beforehand and adjusting the temp. of a fluid for cooling the outer surface of the hollow body so as to keep the temp. of the surface to be treated and of the electrolyte at almost same temp. at the time of subjecting the inner surface of the hollow body made of Al to anodic oxidation treatment. CONSTITUTION:The anodic oxide film is formed only on the inner surface of the hollow part 14 made of Al based metal by this local anodic oxidation treatment. In this treatment, the hollow body 14 is placed in the cooling tank 17 and cooled from the outside by using the cooling liquid 12 and then a current is allowed to pass through between the cathode 15 and the anode 14 while adjusting the temp. of the electrolyte 13 that flows into the cell from the cathode 15 and the temp. of the inner surface of the hollow body used as the anode 14 to appropriate same temp. to form the Al oxide film on the inner surface of the hollow body 14. At this time, the heat transfer coefficient of the hollow body 14 is determined beforehand by allowing a fluid that does not participate in the anodic oxidation to circulate through the inside of the hollow body 14 and measuring the temp. difference between the circulating fluid and the cooling liquid 12. Then each of the temp. of the electrolyte 13 and the cooling liquid 12 is adjusted appropriately by using a computer 3, o which the heat transfer coefficient determined above is inputted, so as to keep the temp. of the electrolyte 13 and of the inner surface of the hollow body 14 cooled with the cooling liquid 12 at almost same temp.. Thus the anodic oxide film having good quality is stably formed.