FR2736364A1 - METAL BAND MASKING DEVICE SUITABLE FOR A RADIAL-TYPE ELECTRODEPOSITION CELL, FOR THE PREVENTION OF DENDRITES - Google Patents

Abstract

A device is claimed for masking the edges of a metal strip (B) suitable for use in a radial electroplating cell. The cell includes a roller support (1) for the metal strip (B), and soluble anodes (2) arranged facing the roller (1). The device comprises: (i) a mask (4) in the form of a narrow strip arranged over the length of each edge in the immediate proximity of the surface of the roller (1); (ii) a means (14) for anchoring the two ends of the mask (4); and (iii) a means (6) for fixing (ii). The mask (4) consists of an insulating, semi-rigid strip, esp. of a composite material with a polymer matrix, presenting, on its inner face turned towards the roller (1), on the one part of the inner side oriented towards the middle of the roller (1), a disconnection over the whole of its length and on the other part of the opposite outer side, some contacts in an anti-adherent material, regularly spaced and fixed on the inner face. Due to the fixing means (6), the mask (4) is applied against the surface of the roller (1) by the intermediary of the contacts, and positioned such that the edges may be engaged in the disconnection. The total thickness of the mask (4) is less than half the distance separating the anodes (2) from the roller (1). The width of the disconnection is at least 50% of the width of the edges to be masked. The anchoring means (14) comprises a roll (17), with its axis approximately parallel to that of the roller (1), presenting a slot over its whole length, and integral with the fixing means (6) and a fastening crossing the slot, integral with one end of the mask and incorporating a projecting tip embedded in the roll. Its thickness is greater than the width of the slot. The projecting tip is able to slide inside and over the length of the roll in order to modify the position of the mask (4) w.r.t. the edges of the metal strip.

Description

Metal strip edge masking device adapted to a cell

  radial type electrodeposition, for the prevention of dendrites. The invention relates to a device for preventing the appearance of dendrites on the edges of metal strips during a coating

  electrolytically continuous said strips in radial type cells.

  A radial-type cell includes a vessel that contains the electrodeposition bath, a partially immersed web support roll, submerged anodes arranged facing the substantially constant distance roller, means for circulating electrical current between said anodes and a band serving as a cathode, means for scrolling in the tank of the band supported by said roll and means for circulating said bath

  in the space between the anodes of the band.

  During the operation of the cell, the surface of the bath is in

  balance with the atmosphere and call the cell "open".

  The web support roll generally has an electrically insulating, generally rubberized coating; optionally, the surface of the central portion of the roll is conductive, when the roll serves to

  supplying electricity to the band which serves as a cathode.

  In continuous electroplating plants, it is known that the appearance of dendrites on the banks of the strips to be coated results from overcurrents.

  located along the said shores during the deposit.

  To limit these overcurrents, it is known to interpose an electrically insulating mask between the banks of the moving strip and the anodes: these are generally narrow strips of insulating material arranged along

from each shore.

  Now the realization of such a mask poses many problems in the case of radial cells, including including soluble anodes: - the two masks in the form of narrow strips must follow the shape

  of the roll that supports the band, which implies a shape in an arc.

  - the two masks of banks can not rest on the anodes which

  are soluble and must be interchangeable.

  - it is necessary that one can easily adjust the position of the masks of banks according to the format, that is to say of the width, the metal bands to

coated.

  Other problems are even more difficult to overcome, especially when the relative speed between the strip and the electrolysis bath is high, for example greater than 2 m / s: the two edge masks must be able to withstand in operation important hydrodynamic forces, created by scrolling the band

  and the circulation of the electrolysis bath between the roll and the anodes.

  Indeed, especially in the "open" cells, these hydrodynamic forces tend to move the masks in a direction transverse to the scrolling of the metal strip, so that they no longer protect the banks! - Conversely, if the position taken by the two masks during operation allows an effective masking of the banks, it should not lead to under-thickness deposits on the shore, or to bank deposits with a very high morphology. different from that of the deposit in the center of the band; - In case of accidental tearing of a mask during operation, it is necessary to avoid breaking the mask and to maintain

  run the electroplating plant.

  The aim of the invention is a bank masking device adapted to radial electrodeposition cells with soluble anodes and strong hydrodynamic stresses, corresponding in particular to relative velocities.

  between the strip to be coated and the electrolysis bath greater than 2 m / s.

  The subject of the invention is a device for masking metal strip edges adapted to a radial type electrodeposition cell, comprising a support roll for said metal strip and soluble anodes arranged facing said roll, said device comprising a shaped mask. narrow band disposed along each bank in the immediate vicinity of the surface of said roll, anchoring means at both ends of said mask and fastening means of said anchoring means, characterized in that said mask comprises a semi insulating strip -Rigid, in particular made of composite material with a polymer matrix, having, on its internal face facing said roll, on the one hand on the side facing the middle of said roll, a detachment along its entire length, on the other hand on the opposite side, studs in

  anti-adherent material, regularly spaced and fixed on said inner face.

  and characterized in that, thanks to the fixing means, said mask is applied against the surface of said roll by means of said pads and positioned so that said banks are engaged in said

recess.

  The invention may also have one or more of the following features: - the total thickness of said mask is less than half the distance

  separating said anodes from said roll.

  - the width of said setback is at least 50% greater than the

width of said banks to be masked.

  said anchoring means comprise a cylinder of axis approximately parallel to said roller having a slot along its entire length and secured to the fastening means and a fastener passing through said slot, integral with one end of said mask and comprising a prominent tip embedded in said cylinder and of greater thickness than

said slot.

  - said tip is slidable inside and along said

  cylinder to change the position of the masks in relation to the banks.

  The invention will be better understood on reading the description which will

  follow, given by way of example, and with reference to the appended figures in which: - Figure 1 is a side view of a radial cell with a masking device of the banks according to the invention; - Figure 1 B is an enlarged representation of a portion referenced 1 B of Figure 1; - Figure 2 is a partial section along the axis 11-11 of Figure 1; FIG. 3 is a view from above of the means for fixing and anchoring the masks of the device according to the invention;

  - Figure 4 is a section along the axis IV-IV of Figure 3.

  With reference to FIG. 1, the radial type electroplating cell comprises a tank (not shown) which contains an electrodepositon bath, a band support roll partially immersed in the bath, and immersed soluble anodes 2 facing the roll 1 , means not shown for circulating an electric current between the anodes 2 and the metal strip B to be coated and serving as a cathode, scrolling means (not shown) in the tank of the band B supported by the roller 1 and means to circulate said bath in the space separating the anodes 2 of the band B. These means for circulating the bath comprise injection ramps 3 placed at the place where the band B scrolling in and out of the space

  separating the anodes 2 from the roll 1, a space that is generally called "gap".

  For the prevention of edge dendrites, the electrodeposition cell still includes a device for masking the banks of the current B-strip

scrolling.

  This masking device according to the invention comprises two identical masks 4 in the form of narrow strips each disposed facing a bank 10 of the moving band B and supported at each end 5 by means

  anchor 14 supported by fastening means 6.

  With reference to FIG. 2, the masks 4 consist mainly of a semi-rigid insulating strip 7, preferably of polymer matrix composite material; this composite material may for example be reinforced with

glass fibers.

  Each insulating strip 7 extends between the roll 1 and the anodes 2, on

  about half a circumference of the roll 1.

  According to the invention, along its inner face facing the roller 1, the insulating strip 7 comprises a recess 8 made on the side facing the middle of the roll 1 and supports, on the other side, regularly spaced studs 9 , as represented in FIG. 1B. Thanks to the fastening means 6, the two masks 4 are applied

  against the surface of the roll 1 by means of the studs 9.

  The contact or sliding surface of the studs 9 on the roll 1 is

  located in the immediate vicinity of the banks 10 of the band B scrolling.

  The pads 9 consist of platelets of non-adherent material, TEFLON type, fixed for example by gluing on the inner face of the strip

  insulating 7 outside the recess zone 8 (see Figure 1 B).

  The total thickness of the mask 4, ie the sum of that of the insulating strip 7 and the pads 9, is much smaller than that of the "gap" of the cell. For example, when the thickness of the gap is approximately 35 mm, the thickness

  total of mask 4 is about 8 mm.

  For a thickness of the mask of about 8 mm, there is for example an insulating strip thickness 7 of about 5 mm and a pad thickness 9 of 3

mm approx.

  Referring to Figure 1, the recess 8 extends over the entire

length of insulating tape 7.

  Referring to Figure 2, at the recess 8, the interval between the insulating strip 7 of the roll 1, corresponds to the depth of said

  recess in the strip 7 added to the thickness of the pads 9.

  This gap must be much greater than the thickness of the strip B. In contrast, the residual thickness of the insulating strip 7 at the step 8 must be sufficient to ensure the electrical masking function between the anodes 2 and the edges 10 of the strip B. This minimum thickness necessary to ensure the function of

  masking can be evaluated in a manner known per se.

  Thus, in the case of an insulating strip 7 of thickness 5 mm and pads 9 of thickness 3 mm, the depth of the recess 8 in the strip 7 is about 2 mm; The interval that separates the insulating strip 7 from the roll 1 is then about 5 mm and the residual thickness of the insulating strip 7 at the level of

  recess 8 is about 3 mm.

  The width of the recess 8 must be much greater than that of the banks 10, that is to say of the portion of band B on which it is sought to avoid

the dendrites.

  If this edge width 10 to be protected is approximately 15 mm, the width of the

  recess 8 is then about 30 mm.

  The total width of the insulating strip 7 is at least equal to the sum of the width of the recess 8 and the width of the pads 9; for a width of

  recess 8 of 30 mm, it can be typically about 120 mm.

  The fastening means 6 which support the masks 4 by means of the anchoring means 14, furthermore provide the following functions: the adjustment of the tension of the masks 4 against the surface of the roll 1; the adjustment of the position of the masks 4 with respect to those of the banks

  the band B scrolling on the roll 1.

  To provide the voltage and position adjustment functions, the fastening means 6 comprise in a manner known in itself and

  as shown in Figures 3 and 4.

  lower transverse bars 12 and upper 11 integral with the frame of the cell; the bars 11, 12 are both approximately parallel to the axis of rotation of the cylinder 1; the top bar 11 is over

  close to the roll 1 than the lower bar 12.

  two extendable connecting rods 13 articulated at one end to the lower bar 11 and supporting at the other end the end 5 of the mask 4 by means of anchoring means 14; two extendable connecting rods 15 articulated at one end on the upper bar 11 and supporting at the other end each connecting rod 13 at a point

  articulation 16 located approximately in the middle of said connecting rod 13.

  The connecting rods 13 and 15 are extensible in the sense that their length can be adjusted; they consist for example of two nested tubes one

  in the other as shown in Figure 4.

  Thanks to the adjustment of the length of the connecting rods 13 and 15, it is thus possible to regulate

  the tension of the insulating strip 7 against the surface of the roll 1.

  The rods 13 and 15 are slidable respectively along the bars 12 and 11 in order to properly position the masks 4 in front of the banks 10 of the band B. It is possible to provide other fastening means without departing from the

present invention.

  The anchoring means 14 supported by the ends of two connecting rods 13 as shown in FIG. 3 provide a safety function, which allows the mask 4 to be released from its fastening means 6, in the event of an accident, by

  example in case of attachment of the band B scrolling on said mask.

  The anchoring means 14 comprise a cylinder 17 and a fastener 18.

  The cylinder 17 is integral with the ends of the two connecting rods 13 and kept approximately parallel to the bars 11, 12; according to the invention, the cylinder 17 is split along its entire length by a slot 19 oriented towards

  the entrance of the gap separating the anodes 2 of the roll 1.

  The fastener 18 passes through the slot 19 and has, at one end, clamping means for fixing the end 5 of the mask 4 and, at the other end, a

  prominent tip embedded in the cylinder 17.

  The thickness of the tip is greater than the slot 19 to not be able to

  pass through the said slot.

  Thus, the fastener 18 remains secured to the cylinder 17 under the normal conditions of biasing the mask 4 on the fastening means 6, which are

  defined by the normal operating conditions of the cell.

  The mechanical and geometrical characteristics of the cylinder 17 and the end piece are determined in a manner known per se on the one hand to prevent the opening of the slot under the normal conditions of loading the fastener 18 supporting the mask 4 when the cell is in operation, on the other hand to allow opening of the slot 19 sufficient to let the tip as soon as the solicitation of the fastener exceeds a predetermined threshold.

  The tip may be of square section as shown in Figure 4.

  According to an alternative embodiment, the anchoring means 14 may also have a function of adjusting the position of the masks 4 by

  compared to those of the banks 10 of the band B running on the roll 1.

  According to this variant, the cylinder 17 has a length much greater than the width of the mask 4; we can then slide the clip 18 inside

  of the cylinder 17 on a sufficient stroke to make said adjustment.

  It is also possible to mount on a threaded shaft the prominent tip of the fastener 18 to be able to accurately adjust the position of this fastener

  with respect to the ends of the cylinder 17.

  The operation of a radial cell equipped with a masking device according to the invention will now be described. The metal strip B to be coated is for example a 2 m steel strip

  about wide and 0.4 mm thick.

  For example, it is desired to carry out a zinc coating from

  of soluble zinc anodes and a chloride-based electrolysis bath.

  In the electrolytic deposition cell, by virtue of the fixing means 6, the position of the masks 4 facing the edges 10 of the metal strip B to be coated is adjusted, in particular by sliding the connecting rods 13 and 15 along the

fixed bars 11 and 12.

  More precisely, the position of the masks 4 is adjusted so that the banks 10 on each side of the band B are inserted into the

  step 8 masks 4, as shown in Figure 2.

  When the anchoring means 14 are made according to the variant presented above, which provides for the sliding of the fastener 18 in the cylinder 17, it is advantageous to use this device to adjust

  precisely the position of the masks.

  Between the extreme edge of the strip B and the inner edge of the recess 8, there is provided on each side a clearance sufficient to limit the risks.

  hooking of the band B on the masks 4 during scrolling.

  For a bandwidth of approximately 2m, this travel may be

The order of 10 mm on each side.

  Thanks to the extendable connecting rods 13 and 15, the tension of the

  masks 4 against the roller surface 1.

  Referring to Figures 1 B and 2, the mask 4 in the operating position is in contact with the surface of the roll 1 through the pads 9; while the band B scrolls, the roller 1 which rotates slides so

  on the pads 9, which are anti-adherent.

  The tension of the masks 4 must not be too high, to limit friction with the surface of the roll 1, however, it must be sufficient to properly hold the masks 4 in front of the banks 10 of the band B. In a manner known in the art. itself, zinc is deposited, in particular by scrolling the band B in the cell through the scrolling means, passing an electric current between the anode 2 and the band B serving cathode while circulating the bath electrolysis in the

  "gap", in particular thanks to the injection ramps 3.

  It may be necessary to refine the setting of the tension of the masks 4, which also depends on the running speed of the band and the bath circulation speed in the "gap". During the operation of the cell, the hydrodynamic forces acting on the masks 4 help to separate them from the roll 1 and to limit

  the friction of the masks 4 on the roll 1.

  According to the invention, it can be seen that despite high speeds of tape running and bath circulation in the "gap", the masks 4 remain firmly in place opposite the banks 10 of the band B, which makes it possible to avoid

the appearance of dendrites in banks.

  According to the invention, it is also noted that the banks on the banks do not offer under-thickness and have a morphology comparable to that of the

deposits in the center of the band.

  As an indication, the relative speed between the band and the bath is greater

at 2 m / s.

  Without prejudging a complete explanation of the phenomena involved, the Applicant attributes this surprising effect to the geometry of the masks 4, which, thanks in particular to the recess 8 and the intervals between the pads 9, allows a free flow of the electrolysis bath , even in directions

  different from the tape scrolling.

  As the circulation of the bath is little impeded by the masks 4, the hydrodynamic forces are no longer likely to move them out of the zone of the banks 10 of the band, thanks also to the rigidity of the insulating strips 7; the

  masks then retain their effectiveness.

  Conversely, the flexibility of the insulating strips 7 also contributes to the stability of the masks 4, since it is thanks to it that the masks 4 move slightly away from the roll 1 during operation, which further facilitates the circulation of the bath and limits the friction of the masks 4 on the

roll 1.

  Thus, since the insulating strips 7 are semi-rigid, in particular made of composite material with a polymer matrix, the masks 4 are both rigid enough to remain facing the banks 10 and sufficiently flexible to assume a stable position slightly spaced from the surface of the

roll 1.

  Another supposed effect of the free circulation of the bath between the masks 4 and the banks 10 of the band is to allow a deposit having approximately the same thickness and the same morphology as in the center of the band.

the band.

  According to the invention, thanks to the anchoring means 14 (FIG. 4), in the event of an accident, for example in the case of attachment of the band B while traveling on one of the masks 4, the mask 4 is disengaged from the fastening means 6: indeed, under the effect of the tension exerted on the mask 4 at the moment of attachment, the fastener 18 is disengaged from the cylinder 17 by spreading the slot 19

  to let through his prominent tip.

  Thanks to this security, there is no risk of breaking the mask 4, even in the event of a collision accident it is also possible to continue the coating of the strip after the unhooking of the mask, obviously without

  benefit from edge masking on the side where the mask is unhooked.

Claims (4)

  1.- strip masking device (10) of metal strip (B) adapted to a radial type electrodeposition cell, comprising a support roller (1) for said metal strip and soluble anodes (2) arranged facing said roller (1), said device comprising a narrow band-shaped mask (4) disposed along each bank (10) in close proximity to the surface of said roll (1), anchoring means (14) at both ends thereof mask and fixing means (6) of said anchoring means, characterized in that said mask (4) comprises a semi-rigid insulating strip (7), in particular made of composite material with a polymer matrix, having, on its inner face, to said roll (1), on the one side facing the middle of said roll (1), a recess (8) along its entire length, on the other hand on the opposite side, studs (9) made of adhering, regularly spaced and fixed on said inner face. and characterized in that, thanks to the fixing means (6), said mask (4) is applied against the surface of said roll (1) by means of said studs (9) and positioned so that said   edges (10) are engaged in said recess (8).   2.- Device according to claim 1 characterized in that the total thickness of said mask (4) is less than half the distance between   said anodes (2) of said roll (1).   3.- Device according to any one of the preceding claims   characterized in that the width of said indentation (8) is at least   50% greater than the width of said banks (10) to be masked.   4.- Device according to any one of the preceding claims   characterized in that said anchoring means (14) comprise a cylinder (17) of axis approximately parallel to said roller (1) having a slot (19) over its entire length and secured to the fastening means (6) and a fastener (18) passing through said slot (19), secured to one end (5) of said mask (4) and having a prominent tip embedded in said cylinder (17) and of greater thickness than said slot.