Method for the production of a metal strip coated with a coating of chromium and chromium oxide using an electrolyte solution with a trivalent chromium compound

A method for producing a metal strip coated with a coating containing chromium metal and chromium oxide and being electrolytically deposited from an electrolyte solution containing a trivalent chromium compound onto the metal strip by bringing the metal strip, which is connected as a cathode, into contact with the electrolyte solution, the method comprising:

• successively passing the metal strip at a predefined strip travel speed through a plurality of electrolysis tanks successively arranged in a strip travel direction,
• wherein the plurality of electrolysis tanks comprises a front group of electrolysis tanks including at least one front electrolysis tank;
• a middle group of electrolysis tanks including at least one middle electrolysis tank;
• and a rear group of electrolysis tanks including at least one rear electrolysis tank;
• wherein the front group of electrolysis tanks is at a first current density which is greater than 20 A/dm2;
• the middle group of electrolysis tanks, which follows the front group of electrolysis tanks in the strip travel direction, is at a second current density which is equal to or greater than the first current density;
• and the rear group of electrolysis tanks, which follows the middle group of electrolysis tanks in the strip travel direction, is at a third current density which is greater than the second current density;
• wherein in each electrolysis tank there is arranged at least one anode pair with two opposing anodes, wherein the metal strip is passed between and through the two opposing anodes of the at least one anode pair;
• and
• wherein the at least one anode pair of the at least one rear electrolysis tank has a shorter length than the at least one anode pairs of the at least one front electrolysis tank and the at least one middle electrolysis tank.

A method for producing a metal strip coated with a coating-containing chromium metal and chromium oxide and being electrolytically deposited from an electrolyte solution containing a trivalent chromium compound onto the metal strip by connecting the metal strip as a cathode and bringing the metal strip into electrolytic contact with the electrolyte solution, the method comprising:

• successively passing the metal strip at a predefined strip travel speed through a plurality of electrolysis tanks successively arranged in a strip travel direction one behind the other, the plurality of electrolysis tanks comprising a front group of electrolysis tanks, a middle group of electrolysis tanks following in the strip travel direction the front group of electrolysis tanks, and a rear group of electrolysis tanks following in the strip travel direction the middle group of electrolysis tanks,
• wherein the electrolysis tanks of the front group of electrolysis tanks are at a first current density, which is greater than 20 A/dm2 when the metal strip is in the front group of electrolysis tanks, the electrolysis tanks of the middle group of electrolysis tanks are at a second current density which is equal to or greater than the first current density when the metal strip is in the middle group of electrolysis tanks, and the electrolysis tanks of the rear group of electrolysis tanks are at a third current density which is greater than the second current density when the metal strip is in the rear group of electrolysis tanks.