Method and system for electrolytically coating a steel strip by means of pulse technology

Abstract

An electroplating method and a system for electrolytically coating a steel strip, in particular for the automotive sector, with a coating based on zinc and/or a zinc alloy utilizes pulse technology.

What is claimed is: 
     
         1 . A method for electrolytically coating a steel strip ( 2 ), comprising:
 feeding the steel strip ( 2 ) in a horizontal movement to a coating section ( 1 );   deflecting the steel strip ( 2 ), by a strip inlet current roller ( 6 ), from the horizontal movement to a downward vertical movement into an electrolytic cell ( 3 );   passing the steel strip ( 2 ), during the downward vertical movement, parallel to a first electrode ( 5 ) within the electrolytic cell ( 3 );   deflecting the steel strip ( 2 ) from the downward vertical movement to an upward vertical movement by a deflection roller ( 8 ) arranged within the electrolytic cell ( 3 );   passing the steel strip ( 2 ), during the upward vertical movement, parallel to a second electrode ( 5 ) within the electrolytic cell ( 3 );   deflecting the steel strip ( 2 ) from the upward vertical movement to the horizontal movement by a strip outlet current roller ( 7 );   applying current pulses from
 a first pulse rectifier ( 9 ) electrically connected to the strip inlet current roller ( 5 ) and to the first electrode ( 5 ) and 
 a second pulse rectifier ( 9 ) electrically connected to the strip outlet current roller ( 7 ) and to the second electrode ( 5 ); 
   depositing zinc or a zinc alloy contained in an electrolyte within the electrolytic cell ( 3 ) on the steel strip ( 2 ) by at least one cathodic pulse of the current pulses; and   oxidizing nascent hydrogen adsorbed on the steel strip ( 2 ) after the at least one cathodic pulse by at least one anodic pulse of the current pulses.   
     
     
         2 . A method for electrolytically coating a steel strip ( 2 ) with a zinc or zinc alloy based coating, comprising:
 feeding the steel strip ( 2 ) to a coating section ( 1 ) comprising an electrolytic cell ( 3 ) containing an electrolyte ( 4 ) comprising zinc or a zinc alloy;   connecting the steel strip ( 2 ) via a current roller ( 6 ) to a power supply, the current roller ( 6 ) being arranged outside the electrolytic cell ( 3 );   guiding the steel strip ( 2 ) in the electrolytic cell ( 3 ) at a defined distance parallel to an electrode ( 5 ), the electrode ( 5 ) being connected to the power supply;   electrolytically coating the steel strip ( 2 ) in the electrolytic cell ( 3 ) by applying a pulse sequence, including
 a cathodic pulse, during which the steel strip ( 2 ) is connected to a negative pole of the power supply and the electrode ( 5 ) is connected to a positive pole of the power supply; and 
 an anodic pulse during which the steel strip ( 2 ) is connected to the positive pole of the power supply and the electrode ( 5 ) is connected to the negative pole of the power supply. 
   
     
     
         3 . The method as in  claim 2 ,
 wherein, during the cathodic pulse, the coating is deposited on the steel strip by electroplating deposition, and   wherein the electroplating deposition is partially reversed during the anodic pulse.   
     
     
         4 . The method as in  claim 3 ,
 wherein an anodic current during the anodic pulse has a smaller magnitude than a cathodic current during the cathodic pulse.   
     
     
         5 . The method as in  claim 2 ,
 wherein the anodic pulse oxidizes nascent hydrogen adsorbed on the steel strip and removes the nascent hydrogen from the steel strip.   
     
     
         6 . The method according to  claim 2 ,
 wherein the current roller ( 6 ) is arranged upstream or downstream of the electrolytic cell ( 3 ) and deflects the steel strip ( 2 ) between a horizontal movement and a vertical movement.   
     
     
         7 . The method according to  claim 2 ,
 wherein the power supply includes a pulse rectifier ( 9 ), and   wherein the pulse rectifier ( 9 ) is electrically connected to a central control unit ( 12 ) via which the coating is regulated.   
     
     
         8 . The method according to  claim 7 ,
 wherein the pulse sequence ( 10 ) is transmitted from the central control unit ( 12 ) to the pulse rectifier ( 9 ).   
     
     
         9 . The method according to  claim 2 ,
 wherein the pulse sequence ( 10 ) comprises a pulse time-out between the cathodic pulse and the anodic pulse.   
     
     
         10 . The method according to  claim 2 ,
 wherein the electrode ( 5 ) is a single piece plate electrode.   
     
     
         11 . The method according to  claim 2 ,
 wherein the electrode ( 5 ) comprises two or more rod-shaped partial electrodes ( 16 ).   
     
     
         12 . The method according to  claim 2 ,
 wherein guiding the steel strip ( 2 ) in the electrolytic cell ( 3 ) at the defined distance parallel to the electrode ( 5 ) includes guiding the steel strip ( 2 ) within the electrolytic cell ( 3 ) through at least two electrode arrangements ( 13 ), each comprising two electrodes ( 5 ) arranged parallel to one another.   
     
     
         13 . The method according to  claim 12 ,
 wherein each of the two electrodes ( 5 ) of each electrode arrangement ( 13 ) is supplied with current via a separate pulse rectifier ( 9 ), such that each of the two electrodes ( 5 ) is electrically connected to a pole of each pulse rectifier ( 9 ) and an opposite pole of each pulse rectifier ( 9 ) is electrically connected to the current roller ( 6 ) or a further current roller ( 7 ).   
     
     
         14 . The method according to  claim 12 , further comprising
 deflecting the steel strip ( 2 ) between the at least two electrode arrangements ( 13 ) via a deflection roller ( 8 ) arranged within the electrolytic cell ( 3 ,  5 ).   
     
     
         15 . The method according to  claim 2 ,
 wherein guiding the steel strip ( 2 ) in the electrolytic cell ( 3 ) comprises guiding the steel strip ( 2 ) within the coating section ( 1 ) through a plurality of at least two electrolytic cells ( 3 ) arranged one behind another in a direction of strip travel (R).   
     
     
         16 . The method according to  claim 15 , further comprising
 deflecting the steel strip ( 2 ) between the at least two electrolytic cells ( 3 ) by at least one deflection roller formed as an intermediate current roller ( 14 ).   
     
     
         17 . The method according to  claim 2 , further comprising determining a hydrogen concentration in the electrolytic cell ( 3 ). 
     
     
         18 . The method according to  claim 2 ,
 wherein the steel strip ( 2 ) has a tensile strength R e ≥1000 MPa.   
     
     
         19 . The method according to  claim 2 ,
 wherein the cathodic pulse is part of a plurality of cathodic pulses in the pulse sequence, and   wherein the anodic pulse is part of a plurality of anodic pulses in the pulse sequence, and   wherein the pulse sequence includes fewer anodic pulses than cathodic pulses.   
     
     
         20 . The method according to  claim 2 , further comprising
 feeding the steel strip ( 2 ), after coating in the coating section ( 1 ), to a post-treatment unit; and   annealing the coated steel strip ( 2 ) at a temperature of ≤300° C. (PMT).