Electrolytic process for producing oxide coatings on aluminum and aluminum alloys

Claim 1

A PROCESS FOR COATING ALUMINUM AND ALUMINUM ALLOY METAL ARTICLES WITH A HARD AND TOUGH COATING OF OXIDE OF ALUMINUM, WHICH COMPRISES PASSING AN ELECTRIC CURRENT THROUGH AN ELECTROYLTIC CELL CONTAINING AN ELECTROLYTE. MAINTAINED AT A REDUCED TEMPERATURE WITH SAID ARTICLE FORMING THE ANODE, SAID ELECTROLYTE COMPRISING A WATER SOLUTION OF AN ELECTRO-ANODIZING ACID, ESTABLISHING THE VOLTAGE APPLIED ACROSS SAID CELL AT A VALUE IN A RANGE OPERATVIE TO PRODUCE A MEASURABLE COATING OF OXIDE OF ALUMINUM ON THE ARTICLE WITHOUT BURNING, ESTABLISHING SAID APPLIED VOLTAGE AT SUCCESSIVELY HIGHER VALUES BY VOLTAGE INCREMENTS, EACH SAID VOLTAGE INCREMENT BEING CHOSEN TO REESTABLISH APPROXIMATELY THE CURRENT INITIALLY OBTAINED AT THE FIRST-MENTIONED VOLTAGE AND MAINTAINING THE VOLTAGE AT EACH SAID ESTABLISHED VALUE UNTIL SAID CURRENT DECREASES BY A MATERIAL PERCENTAGE.