Manufacturing method of metal strip coated with chromium and chromium oxide coating using electrolytic solution containing trivalent chromium compound and electrolytic system for carrying out the method

摘要

A method of producing a metal strip coated with a coating, said coating containing chromium metal and chromium oxide and being electrolytically deposited from an electrolyte solution that contains a trivalent chromium compound and at least one salt for increasing conductivity and at least one acid or one base for setting a desired pH value, onto the metal strip by bringing the metal strip into electrolytically effective contact with the electrolyte solution during an electrolysis time. The metal strip is successively passed at a predefined strip travel speed in a strip travel direction through a plurality of electrolysis tanks successively arranged in the strip travel direction. At least the first electrolysis tank, as viewed in the strip travel direction, or a front group of electrolysis tanks is filled with a first electrolyte solution and the last electrolysis tank, as viewed in the strip travel direction, or a rear group of electrolysis tanks is filled with a second electrolyte solution. The second electrolyte solution contains no additional components apart from the trivalent chromium compound as well as the at least one salt and the at least one acid or base and is especially free of organic complexing agents and free of buffering agents.