Apparatus and method for selective coating of metal parts

Abstract

An apparatus and method for simultaneously anodizing the heads of several aluminum pistons includes a plating tank having an array of apertures extending through one of its side walls, one aperture for each piston; and means for securing the head of each piston in its respective aperture. A seal disposed in each aperture ensures that the aperture is sealed upon the securing of the piston therein, with only the piston's head being placed in fluid communication with the interior of the plating tank. An acid electrolyte is directed into the plating tank through electrically-conductive sparging nozzles positioned therein opposite the heads of the pistons, thereby forming an electrolytic cell with the pistons as anodes and the sparging nozzles as cathodes. A power supply simultaneously applies a current to the cell, i.e., across the electrolyte via the pistons and sparger nozzles, to effect electrolytic coating of each piston's head. After the desired coating is achieved, the current is removed and the electrolyte drained from the tank. Rinse water is then directed into the tank through the same sparging nozzles to rinse any remaining electrolyte from the pistons. After the rinse water is drained, hot water is directed into the tank through the sparging nozzles to seal the coating. After a final draining of the tank, the coated pistons are removed from the apertures.