FR2682690A1 - GALVANOPLASTY PROCESS OF A METAL STRIP - Google Patents

Abstract

Process for electroplating a metal strip with zinc, of the type in which the strip passes through at least one electrolysis cell comprising a bath of ions to be deposited onto the strip and comprising electrically conductive rollers forming a cathode in contact with the said strip and at least one anode placed facing each roller. Each conductive roller-anode pair is supplied with electrical current. The deposition is performed by passing the strip between a first series of conductive roller-anode pairs supplied with current at an appropriate first intensity, then between a second series of conductive roller-anode pairs supplied with current at a second intensity of between 7.5 and 20 % of the first intensity.

Description

The present invention relates to a method of

  electroplating of a metal band.

  It applies in particular to training

  coating or deposition of zinc on a metal strip

  than. It is known to form a zinc coating on a metal strip by scrolling it at high speed in at least one electrolytic cell containing an ion bath to be deposited on said strip The electrolytic cell or cells comprise electric conductive rolls, cathode, in contact with the metal strip and at least one anode placed in

  look at each roll Each couple roll conductive

  the anode-generator is supplied with electric current.

  The coating metal contained in the bath

  is transported in the electrolyte by the elec-

  trolysis between the anodes and the band carried to a potential

  cathodic wire by electric conductor rollers.

  The conditions of formation of the zinc deposit depend in particular on the intensity of the current

  electrical power supplying couples roll driver-

  anode of the electrolytic cell (s).

  So far, all couples

  conductor-anode roller of or electrolytic cells

  is powered by an electric current whose inten-

  sity is generally the same for all couples, the

  higher possible, greater than 50 A / dm 2.

  However, it can be seen that at the end of the deposit, an increase in the roughness of the treated strip is obtained, which no longer meets the requirements of the customers, and in particular the bodybuilders for the external parts.

cars.

  The present invention is intended in particular to reduce the roughness of the strip, while forming an electrolytic deposition of metal on the surface of a strip

  whose adhesion and cohesion are of good quality.

  To this end, the subject of the present invention is a method for electroplating a metal strip, of the type in which the strip is passed through at least one electrolytic cell containing an ion bath to be deposited on the strip and comprising electrically conductive rolls forming a cathode, in contact with said strip and at least one anode placed opposite each roll, each pair of conductor-anode rolls being supplied with electric current, characterized in that the deposit is made by scrolling through the strip between a first series of conductor-anode roll couples supplied with current at a first appropriate intensity, and then between a second series of conductor-anode roll couples supplied with current at a second intensity of between 7.5 and 20% of the

first intensity.

  According to other features of the invention,

  tion: the second intensity is between 5 and 15 A / dm 2 and preferably equal to 10 A / dm 2, the second series corresponds to the last conductive-anode roller pair of the last electrolytic cell, the second series corresponds to the last two couples driveanode roll of the last

electrolytic cell.

  between the second series of conductive-anode roller couples, a coating is deposited on the metal strip, the thickness of which is between 0.05 and

  and 0.5 microns, preferably 0.2 microns.

  An example of implementation of the method according to

  the invention is described in more detail below.

  In this example, the electroplating process

  According to the invention, the invention is applied to the formation of zinc having a thickness of about 10 microns on a metal strip. This particular application of the method is

  commonly called electrozinguage.

  The metal strip travels at a speed of between 40 and 180 m / min in a bath of at least one electrolytic cell, containing zinc ions with

deposit on said strip.

  Typically, the electrolytic cell

  that includes electrically conductive, cathode-forming rolls in contact with the metal strip, and

  at least one anode placed opposite each roller.

  Each driver-anode roller pair is powered by

  electric current of appropriate intensity.

  The coating metal contained in the bath

  is transported in the electrolyte by the elec-

  trolysis between the anodes and the band carried to a potential

  cathodic wire by electric conductor rollers.

  The method according to the invention consists in carrying out the deposition by scrolling the strip between a first series of conductive anode roll couples supplied with current at a first appropriate intensity, generally greater than 50 A / dm 2, then

  between a second set of conductive roller couples

  anode supplied with current according to a second intensity

  between 7.5 and 20% of the first intensity.

  This second intensity is between 5

  and A / dm 2 and preferably 10 A / dm 2.

  Thus, during a first step of the process corresponding to the first series of conductive roller-anode rolls, a zinc deposit is made on the metal strip whose thickness is slightly less than the total thickness of the coating to be obtained, then during a second step corresponding to the second series of conductor-anode roller pairs, a very thin zinc deposition is carried out on the order of 0.05 to 0.5 microns, preferably 0.2 microns , to obtain the total thickness of the coating.

  The second series of conductive roller couples

  Anode-driver is the last or last pair of conductor-anode rolls of the last electrolytic cell. This reduction in the intensity of the supply current of the last two or two conductive roller-anode pairs of the last electrolytic cell makes it possible to significantly reduce the roughness of the treated strip and thus to avoid, subsequently, the decohesion of the coating eg zinc during

  a steaming operation intended, for example, to polymerize

  Rinse a layer of paint on the tape.

  Arithmetic roughness measurements were performed using a roughness meter on bare sheets, coated sheets without applying the method according to the invention and sheets coated according to the method described. It can be seen that for a bare sheet whose

  initial arithmetic roughness Ra is equal to 1.3

  crons, it is equal to 1.6 microns when the sheet is coated without applying the method according to the invention whereas it is only 1.4 microns when coated according to the process of the invention, total thickness of the

  coating being equal to 7.5 microns.

  Of course, the two successive steps of the method can be carried out in several cells

  electrolytic arranged in series.

Claims (4)

  A method of electroplating a metal strip, of the type in which the strip is scrolled in at least one electrolytic cell containing an ion bath to be deposited on the strip and comprising electrical conductive rollers, forming a cathode, in contact with said band and at least one anode placed opposite each roller, each pair conductor-anode roller being supplied with electric current, characterized in that the deposit is made by scrolling the strip between a first series of conductive-anode roller torque fed by current at a first appropriate intensity, then between a second series of conductive-anode roller torches supplied with current at a second intensity between 7.5 and 20% of the first intensity.   Process according to claim 1, characterized   in that the second intensity is between 15 A / dm 2 and preferably 10 A / dm 2.   3. Process according to claim 1, characterized   in that the second series corresponds to the last conductive-anode roller pair of the last electrolytic cell.   4. Process according to claim 1, characterized   rised in that the second set corresponds to the last two couples conductor-anode roll of the last electrolytic cell.   A method according to claim 1, characterized in that between the second set of conductive-anode roller pairs a coating is deposited on the metal strip, the thickness of which is between 0.05   and 0.5 microns, preferably 0.2 microns.