Method for coating a moving steel strip with a metal or metal alloy coating

Abstract

A method for coating a moving steel strip with a metal or metal alloy coating, wherein the steel strip runs through a bath of molten metal or metal alloy to coat the steel strip, and the coated steel strip is wiped to control the thickness of the coating using foils or sheets. The bath of molten metal has a volume at most 10,000 times the volume V of the coating on the steel strip per second, volume V in m3 being given by the formula V=2×d×w×s, wherein d=the thickness of the coating in meters, w=the width of the strip in meters, and s=the velocity of the strip in meters per second.

1 . Method for coating a moving steel strip with a metal or metal alloy coating, comprising running the steel strip through a bath of molten metal or metal alloy to coat the steel strip, and wiping the coated steel strip to control the thickness of the coating using foils or sheets, wherein the bath of molten metal has a volume at most 10,000 times the volume V of the coating on the steel strip per second, volume V in m3 being given by the formula V=2×d×w×s, wherein
 d=the thickness of the coating in meters 
 w=the width of the strip in meters 
 s=the velocity of the strip in meters per second. 
 
     
     
         2 . Method according to  claim 1 , wherein the bath of molten metal has a volume at most 2000 times the volume V of the coating on the steel strip per second. 
     
     
         3 . Method according to  claim 1 , wherein the bath of molten metal has a volume such that metallic dross particles formed in the bath of molten metal or metal alloy on average are smaller than the thickness of the metal or metal alloy coating on the steel strip after wiping. 
     
     
         4 . Method according to  claim 1 , wherein the wiping of the molten metal or metal alloy is performed using foils or sheets which are pressed towards the moving steel strip, wherein the moving of the steel strip causes a hydrodynamic lifting force by the coating which is in equilibrium with the pressure exerted on the foils or sheets. 
     
     
         5 . Method according to claim, wherein the bath of molten metal or metal alloy is positioned under the foils or sheets. 
     
     
         6 . Method according to  claim 1 , wherein the bath of molten metal or metal alloy is in fluid connection with the metal or metal alloy layers between the steel strip and the foils or sheets. 
     
     
         7 . Method according to  claim 1 , wherein a replenishing bath with metal or metal alloy is used to refill the bath of molten metal or metal alloy. 
     
     
         8 . Method according to  claim 1 , wherein electromagnetic induction is used to retain the molten metal or metal alloy in a container for the bath of molten metal or metal alloy. 
     
     
         9 . Method according to  claim 1 , wherein the metal or metal alloy in the bath is protected from oxygen in surrounding air. 
     
     
         10 . Method according to  claim 1 , wherein the foils or sheets are pressed towards the strip to control the thickness of the metal or metal alloy coating. 
     
     
         11 . Method according to  claim 1 , wherein the steel strip is annealed before entering the bath of metal or metal alloy. 
     
     
         12 . Method according to  claim 1 , wherein the steel strip is heated to a predetermined temperature before entering the bath of metal or metal alloy. 
     
     
         13 . Method according to  claim 1 , wherein the temperature of the bath of metal or metal alloy is higher than the temperature of the steel strip when entering the bath. 
     
     
         14 . Method according to  claim 1 , wherein the metal or metal alloy coated steel strip is cooled after leaving the bath of metal or metal alloy. 
     
     
         15 . Method according to  claim 1 , wherein the steel strip has a width of 0.75 to 2.25 meters. 
     
     
         16 . Method according to  claim 1 , wherein the steel strip has a velocity of 2 to 10 m/s. 
     
     
         17 . Method according to  claim 1 , wherein the metal or metal alloy coating has a thickness of 1 to 30 m on each side of the steel strip. 
     
     
         18 . Method according to  claim 1 , wherein the metal is zinc or aluminum or tin or an alloy of one of these metals. 
     
     
         19 . Method according to  claim 1 , wherein the bath of molten metal has a volume at most 500 times the volume of the coating on the steel strip per second. 
     
     
         20 . Method according to  claim 1 , wherein the bath of molten metal has a volume at most 100 times the volume of the coating on the steel strip per second. 
     
     
         21 . Method according to  claim 1 , wherein the bath of molten metal or metal alloy is positioned under the foils or sheets, and the steel strip is moved vertical or under an angle of at most 45 degrees with the vertical first through the bath of molten metal or metal alloy and then in between the foils or sheets. 
     
     
         22 . Method according to  claim 1 , wherein a shielding gas is used to protect the molten metal or metal alloy in the bath from outside air. 
     
     
         23 . Method according to  claim 1 , wherein the temperature of the bath of metal or metal alloy is higher than the temperature of the steel strip when entering the bath, wherein the temperature of the bath is 0-30° C. higher than the temperature of the steel strip. 
     
     
         24 . Method according to  claim 1 , wherein the temperature of the bath of metal or metal alloy is higher than the temperature of the steel strip when entering the bath, wherein the temperature of the bath is 10-20° C. higher than the temperature of the steel strip.