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.

1 .- 21 . (canceled) 
     
     
         22 . A method for electrolytically coating a steel strip ( 2 ) with a coating based on zinc and/or a zinc alloy, comprising:
 feeding the steel strip ( 2 ) to a coating section ( 1 ) comprising at last one electrolytic cell ( 3 ) and successively electrolytically coating the steel strip ( 2 ) therein,   wherein the steel strip ( 2 ) is initially cathodically connected via at least one current roller ( 6 ) and is guided within the at least one electrolytic cell ( 3 ) at a defined distance parallel to at least one anode ( 5 ) arranged in the electrolytic cell ( 3 ),   wherein the at least one anode ( 5 ) is supplied with a modulated current and the coating takes place within the coating section ( 1 ) using a defined pulse pattern sequence ( 10 ), which is formed from at least one pulse pattern ( 11 ), wherein, in accordance with the pulse pattern sequence ( 10 ), the coating based on zinc and/or a zinc alloy is deposited and formed from an electrolyte ( 4 ) on the steel strip ( 2 ).   
     
     
         23 . The method according to  claim 22 ,
 wherein the modulated current is provided by at least one pulse rectifier ( 9 ), a negative pole of which is electrically connected to the at least one current roller ( 7 ) and a positive pole to the at least one anode ( 5 ).   
     
     
         24 . The method according to  claim 23 ,
 wherein the at least one pulse rectifier ( 9 ) is electrically connected to a central control unit ( 12 ) via which the coating is regulated.   
     
     
         25 . The method according to  claim 24 ,
 wherein the at least one pulse pattern ( 11 ) of the pulse pattern sequence ( 10 ) is transmitted from the central control unit ( 12 ) to the at least one pulse rectifier ( 9 ).   
     
     
         26 . The method according to  claim 22 ,
 wherein the at least one pulse pattern ( 11 ) of the pulse pattern sequence ( 10 ) comprises
 at least one cathodic pulse, 
 at least one anodic pulse, and/or 
 at least one pulse time-out, and 
   wherein the cathodic pulse and the anodic pulse are defined by a pulse duration.   
     
     
         27 . The method according to  claim 22 ,
 wherein the at least one anode ( 5 ) is formed as a plate anode, which is formed in one piece or from two or more partial anodes ( 16 ) formed in rod shape.   
     
     
         28 . The method according to  claim 22 ,
 wherein the steel strip ( 2 ) is guided within the at least one electrolytic cell ( 3 ) through at least two anode arrangements ( 13 ), each comprising two anodes ( 5 ) arranged parallel to one another.   
     
     
         29 . The method according to  claim 28 ,
 wherein each of the anodes ( 5 ) of each anode arrangement ( 13 ) is supplied with current via a separate pulse rectifier ( 9 ), such that each of the anodes ( 5 ) is electrically connected to a respective positive pole of each pulse rectifier ( 9 ) and a negative pole of each pulse rectifier ( 9 ) is electrically connected to the at least one current roller ( 6 ,  7 ).   
     
     
         30 . The method according to  claim 28 ,
 wherein the steel strip ( 2 ) is deflected between the at least two anode arrangements ( 13 ) via a deflection roller ( 8 ) arranged within the electrolytic cell ( 3 ,  5 ).   
     
     
         31 . The method according to  claim 22 ,
 wherein the steel strip ( 2 ) is guided within the coating section ( 1 ) through a plurality of at least two electrolytic cells ( 3 ) arranged one behind the other in a direction of strip travel (R).   
     
     
         32 . The method according to  claim 31 ,
 wherein the steel strip ( 2 ) is deflected between the at least two electrolytic cells ( 3 ) via at least one deflection roller formed as an intermediate current roller ( 14 ).   
     
     
         33 . The method according to  claim 22 ,
 wherein a hydrogen concentration is determined in the at least one electrolytic cell ( 3 ).   
     
     
         34 . The method according to  claim 22 ,
 wherein the steel strip ( 2 ) has a tensile strength R e ≥1000 MPa.   
     
     
         35 . The method according to  claim 22 ,
 wherein the at least one pulse pattern ( 11 ) of the pulse pattern sequence ( 10 ) in the at least one electrolytic cell ( 3 ) is selected with respect to its pulse type, its pulse shape, its pulse off-time, its pulse length along with its pulse number in such a way that the steel strip ( 2 ) is isolated from hydrogen adsorption.   
     
     
         36 . The method according to  claim 35 ,
 wherein the pulse length of at least one cathodic pulse and/or at least one anodic pulse amounts to 3 to 5 ms.   
     
     
         37 . The method according to  claim 35 ,
 wherein the pulse off-time between each two of a plurality of pulses amounts to 1.0 to 5.0 ms.   
     
     
         38 . The method according to  claim 35 ,
 wherein the pulse number between each of two types of pulses, a cathodic pulse and an anodic pulse, amounts to 1 to 50.   
     
     
         39 . The method according to  claim 35 ,
 wherein a ratio of pulse length to pulse time-out of the cathodic pulse amounts to 0.1 or 0.02.   
     
     
         40 . The method according to  claim 22 ,
 wherein the steel strip ( 2 ), after coating in the coating section ( 1 ), is fed to a post-treatment unit, in which the coated steel strip ( 2 ) is annealed.   
     
     
         41 . The method according to  claim 39 , wherein the annealing is performed at a temperature of ≤300° C. (PMT). 
     
     
         42 . A system for electrolytically coating a steel strip ( 2 ) with a coating based on zinc and/or a zinc alloy, comprising:
 optionally, a cleaning and/or an activation unit in which the steel strip ( 2 ) can be cleaned and/or activated;   a coating section ( 1 ) with
 at least one electrolytic cell ( 3 ), in which the steel strip ( 2 ) can be successively electrolytically coated, and 
 at least one current roller ( 6 ), via which the steel strip ( 2 ) can be cathodically switched, 
   wherein the at least one electrolytic cell ( 3 ) comprises at least one anode ( 5 ), which is arranged in such a way that the steel strip ( 2 ) that can be passed through the at least one electrolytic cell ( 3 ) can be passed through at a defined and parallel distance from the at least one anode ( 5 ),   wherein the system comprises at least one pulse rectifier ( 9 ), a negative pole of which is electrically connected to the at least one current roller ( 6 ) and a positive pole of which is electrically connected to the at least one anode ( 5 ), in such a way that the at least one anode ( 5 ) can be supplied with a modulated current,   wherein a coating process can be carried out within the coating section ( 1 ) using a defined pulse pattern sequence ( 10 ),   wherein the pulse pattern sequence ( 10 ) is formed from individual pulse patterns ( 11 ),   wherein in accordance with a pulse pattern sequence ( 10 ) a coating based on zinc and/or a zinc alloy can be deposited from an electrolyte ( 4 ) on the steel strip ( 2 ).