PLATING METHOD FOR FORMING TWO LAYERS OF ZN AND AL

PURPOSE:To form two layers of Zn and Al having high adhesion on a cold rolled steel strip by plating by degreasing the steel strip, plating it with Zn in vacuum by vapor deposition and further plating it with Al in vacuum by thermal spraying. CONSTITUTION:A cold rolled steel strip 1 is introduced into an oxidizing furnace 3, degreased and introduced into a reducing furnace 4, where iron oxide on the surfaces of the steel strip 1 is reduced and the steel strip 1 is annealed. The steel strip 1 is cooled to 150-250 deg.C in a cooling furnace 5, passed through an atmospheric buffer chamber 6 and differential pressure chambers 7-10, and introduced into a vacuum deposition chamber 11, where the steel strip 1 is plated with Zn by the deposition of Zn vapor evaporated from a crucible 12. The steel strip 1 is then passed through a continuous duct 18 and a roll chamber 50 and introduced into a thermal spraying chamber 21, where Al is thermally sprayed in vacuum on a Zn layer formed on the steel strip 1 with thermal spraying guns 22, 23, 24.