WO2024068704A1

WO2024068704A1 - Apparatus for electrolytically coating metal wires running in a web

Info

Publication number: WO2024068704A1
Application number: PCT/EP2023/076654
Authority: WO
Inventors: Li PUHUA; Liang PEIQIN
Original assignee: Nv Bekaert Sa
Priority date: 2022-09-30
Filing date: 2023-09-27
Publication date: 2024-04-04

Abstract

An apparatus for electrolytically coating metal wires arranged in a web also called a 'plating section' is presented. Compared to prior art plating sections, the apparatus is provided with one or more ultrasound emission boxes that hang above the web, while the agitated bottom plate of the boxes is submerged in the electrolyte when the apparatus is operative. Provisions are made to accurately control the gap between the bottom of the ultrasound emission boxes and the wire web. In an advantageous embodiment the bottom of the ultrasound emission boxes faces an irregular, soluble anode. The ultrasound not only helps to improve the deposition of a metal on the wires, but at the same time promotes the dissolution of the soluble anode material.

Description

Apparatus for electrolytically coating metal wires running in a web Description

Technical Field

[0001 ] The invention relates to an apparatus for the coating of metal wires running in a web. Such apparatus is used in plating lines for continuous plating of metal wires running through an electrolytic bath.

Background Art

[0002] The process of electrolytically coating a metal wire by immersion in an electrolytic solution containing metal ions is well known. When the wire is held as cathode, the positively charged coating metal ions in the electrolyte are drawn to the surface of the metal wire and deposited thereon after having received one or more electrons from the metal wire surface. The metal wire is contacted with the negative pole of a current source outside the electrolytic solution, while an anode extracts electrons out of the electrolyte to keep charge balance in the electrolyte. The goal of such a process is to have deposited a precise amount of coating metal when the metal wire exits the electrolytic bath when compared to the entrance into the electrolyte.

[0003] The rate at which coating metal ions deposit on the surface of the metal wire is proportional to the electron current supplied: the more current is supplied the faster the coating thickness increases. However, the mass transport of metal ions is limited by the diffusion bi-layer that forms on the application of an electrical field. When the current becomes too high, the mass transport of the metal ions cannot keep pace with the electron current supplied. As a result parasitic reactions occur such as for example the effusion of hydrogen gas. These parasitic reactions have an adverse effect on the efficiency of the process expressed as ‘cathode efficiency’ that is the ratio of the number of atoms deposited over the number of electrons supplied, thereby keeping in mind the valence of the metal ion. Also the quality of the coatings is adversely affected as it becomes less dense, foamy and does no longer adhere well to the metal wire substrate. [0004] The cathode efficiency problem can be overcome by limiting the current density supplied to the metal wire surface. The current density is the total current supplied to the wire divided by the surface of the wire that is in contact with the electrolyte and is expressed in ampere per square decimetre. By either increasing the immersion length of the metal wire and/or reducing the speed of the line the current density at the surface can be limited. However, both solutions are not preferred:

- increasing the length of the line brings extra costs with it as the line gets longer, requiring more space, extra baths and equipment;

- decreasing the line speed obviously results in a reduced output of the line

[0005] It is know that by agitation, disturbing the diffusion layer at the surface of the wire the throwing power - that is the amount of thickness the coating grows per unit time - can be increased. A known way of agitating the electrolyte is to use ultrasonic sources to shake and disturb the solutions. The ultrasonic waves create microbubbles at the surface of the metal wire by cavitation. These bubbles break the diffusion layer between substrate and electrolyte and thereby improve the mass transport of metal ions.

[0006] The electrolytic coating of static, non-moving objects in an electrolyte in an ultrasonic bath is known, see e.g. CN107313089A. The ultrasonic assisted deposition of an electrolytic nickel coating on fine wires is described in CN208667884U. Here the bath containing the electrolyte is ultrasonically agitated.

[0007] However, these embodiments are not extendable to the electrolytic coating of very wide webs containing 40 to 120 wires running in parallel. The electrolytic bath becomes too wide and cannot be agitated uniformly Such webs are e.g. used for the deposition of metals on steel wire, more particular for the deposition of copper, zinc, and other metals like iron, cobalt, manganese, tin, nickel, or alloys thereof. Steel wires that are first electrolytically coated with copper, followed by electrolytic coating of zinc and subsequent diffusion of the zinc into the copper result in brass coated steel wires. Such brass coated steel wires are used as intermediate products in the manufacturing of steel cords for uses in tires, hoses, conveyor belts, transmission belts and many other applications.

[0008] Moreover, as these installations already exist, they cannot simply be renewed without endorsing a large cost. The inventor therefore sought a solution to these problems as will be described hereinafter.

Disclosure of Invention

[0009] The object of the invention is to resolve the problems of the current art. The invention provides a solution to have an increased throwing power on a new line for electrolytical ly coating metal wires running in a web. The invention also provides a solution to upgrade an existing line so that its throwing power can be increased at a low cost. The invention allows to increase coating thickness without increasing the line length and/or reducing speed.

[0010] According a first aspect of the invention an apparatus is described and explained. The apparatus is for electrolytical ly coating metal wires running in a web. In the context of this application a ‘web’ is an arrangement of wires that are in one plane and are parallel to one another. All the wires are moving in the same direction, parallel to one another, preferably at the same speed. That is what is meant with Tunning in a web’. During operation the wires are intended to be moving either continuous or stepwise.

[0011] The apparatus comprises an overflow tray and a bath. With ‘bath’ is in the context of this application meant a physical container for retaining, containing the electrolyte solution, not the electrolyte solution itself. Within the contours of the bath an overflow tray is positioned. A pump is provided that continuously pumps electrolyte solution into the overflow tray preferably from the bottom of the overflow tray so that the overflow tray continuously overflows, the overflow being caught in the bath. Just above the overflow tray the wire web is arranged such that the web, the metal wires are constantly immersed in the electrolyte. The presence of the electrolyte fluid in the bath naturally defines a ‘below’ and ‘above’ the directions being considered in relation to the gravity field. [0012] The apparatus is further provided with the equipment, the ancillaries as they are known to the skilled person: pumps for circulating the electrolyte solution, current sources and contact rollers for feeding electrons to the metal wire web and extracting electrons from the anode immersed in the electrolyte solution, level indicators, temperature sensors and any other devices that would be considered obvious to be present by the skilled person.

[0013] Characteristic about the apparatus is that it comprises one or more ultrasound emission box or boxes, that are placed above the web. Each of the ultrasound emission boxes has the shape of a box or cuboid, with a height less than its width or breath. The bottom of the boxes is intended to contact, must be able to be brought in physical contact with the electrolyte when the apparatus is working. Physical contact between the bottoms of the ultrasound emission boxes and the electrolyte must be complete and at the same time the distance between web and bottom of the ultrasound emission boxes must be constant over the surface of the one or more box bottoms.

[0014] If the bottom of one of the boxes is not in complete contact with the electrolyte during operation, the coating on the metal wires will not be uniform traverse the web. Such situation must be avoided at all cost.

[0015] Preferably the boxes are identical in shape and make. Preferably a single box covers the whole width of the web. If this would not be possible a pair of boxes can be mounted side by side, or four boxes are mounted in a quadrant arrangement. Six or eight boxes can also be mounted in a 3x2 or 2x3, 2x4, or 4x2 arrangement. The requirement is that the boxes must be able to cover the whole width of the web.

[0016] In order to precisely control the distance between the wire web and the bottom of the boxes, the boxes are mounted in a frame that keeps the bottoms of all boxes in the same bottom plane. A gap adjustment system is provided that allows to precisely adjust the distance between the bottom of the boxes and the wire web. Such gap adjustment system can be based on calibrated resting blocks on which studs attached to the frame rest. The calibrated resting blocks firmly connect with the floor on which the apparatus is mounted. The studs can be made adjustable and can be secured in position when the frame and wire web have been properly outlined.

[0017] Preferably the gap between the web and the bottom of the boxes can be adjusted between 5 to 40 mm. A small gap will increase the transmittal of ultrasonic energy from the ultrasound emission boxes to the electrolyte in the vicinity of the wire web but may be difficult to keep constant. With a too large distance the ultrasonic energy is absorbed to much by the electrolyte.

[0018] The variation of the distance between the wire web and the bottom or bottoms of the ultrasound emission boxes must be kept lower than 5 mm, preferably lower than 3 mm and this over the complete bottom area of the ultrasound emission boxes. A too large variation in distance leads to an uneven coating of the wire web that must be avoided.

[0019] In a further embodiment the overflow tray is filled with, comprises, contains a soluble anode. A soluble anode is made of the metal to be deposited and dissolves into the electrolyte while at the cathode side the metal is deposited on the wire web. Particularly preferred is if this soluble anode has an irregular surface. An ‘irregular surface’ is formed by pieces of the metal to be deposited. The pieces can be in the form of balls of equal or variant diameters, nuggets, chunks, clumps, or globules. The pieces are randomly packed in the overflow tray and make electrical contact with a bottom plate connected to the positive pole of a current source. The pieces have a size of between 1 mm and 20 mm. With ‘size’ is here meant the maximum distance between any two points of the surface of the piece. The irregular surface of the soluble anode helps to prevent the formation of standing waves in the electrolyte. It also absorbs the incoming sound waves that enhance the dissolution of the soluble anode in the electrolyte, which is an unexpected advantage of the apparatus.

[0020] Preferably, each one of the one or more boxes comprises a metal sheet box and one or more ultrasound emission sources. The one or more ultrasound emission sources contact the bottom plate of the metal sheet box. The metal sheet allows for a good transmission of the sound waves as it can remain relatively thin. Preferably between one and thirty ultrasound emission sources are present, depending on the area of the bottom plate. Typically one ultrasound source is present per 2 to 6 dm². One source may not generate enough ultrasound energy while thirty emission sources increase the cost of the installation.

[0021 ] Typically the ultrasound sources are piezoelectric transducers that transform an electrical waveform into mechanical vibration. Such transducers are well known in the art.

[0022] The bath and overflow tray is made of electrically insulating material such as polymer plate. Typical polymers used are polyethylene, polypropylene, polycarbonate, or the like. The polymer absorbs the sound waves generated.

[0023] As the one or more boxes are made of metal and are in contact with the electrolyte they are prone to metal deposition in case stray currents would reach the metal boxes. Therefore the metal boxes are preferably electrically insulated by using an insulating gap adjustment system. Alternatively or additionally the boxes can be coated with a non-conductive coating or paint such as a Teflon based coating or an enamel coating.

[0024] As these boxes tend to be heavy and the wire web needs to be reached for threading the web, a lift system is needed to lift the one or more boxes out of the electrolyte. Care must be exercised that the lift system does not allow stray currents to reach the metal boxes that is the lift system must electrically insulate the metal boxes from the electrical environment. Lifting can be done by means of electrical, pneumatic or mechanical means.

[0025] The current state of the art is that the rim of an overflow tray has straight edges. This makes it very easy to thread the installation with wire. However, this has the disadvantage that the overflow level is limited by the pump flow rate. This limits the height of the electrolyte level above the wire web which on its turn makes it more difficult to keep the bottom of the boxes in the electrolyte in a controlled way.

[0026] In order to increase the electrolyte level above the wire web in a preferred embodiment an electrolyte restraining device such as a comb is introduced on the overflow tray edge. The wire passes in between the teeth of the comb and due to the comb the electrolyte level rises higher and it is easier to immerse the bottom of the boxes in the electrolyte.

[0027] Aternatively the frame that holds the one or more boxes can be provided with an electrolyte restraining device such as a brush made of polymer.

[0028] In a preferred embodiment the transducers in one box are arranged in a non-regular grid. A ‘non-regular’ grid is a grid that is not according any one of the 17 possible wallpaper arrangements. Symmetry is not preferred as it leads to preferred deposition areas if the bottom plate would be excited at resonant modes. Possibly the body of the transducers are fixed to a sturdy frame while the actuator connects to the flexible bottom plate.

[0029] In a further preferred embodiment, the ultrasound emission sources are driven by an alternating current. An alternating current is characterised by its amplitude, frequency and phase angle. The alternating current can be a square wave, or a sinusoidal wave or any other wave as long as it is harmonic. In a preferred embodiment, the phase angle of the alternating current at entry of the ultrasound emission sources is different for all sources in one box. This can be achieved by increasing the length of the feed lines between the ultrasound emission sources or by adding delay lines in between the alternating current source and the ultrasound emitters. The advantage of this embodiment is that it breaks symmetry and prevents the formation of preferred coating areas.

[0030] According a second aspect of the invention a steel wire line for coating a web of steel wires is claimed. The line comprises at least one electrolytic plating section. In that section, one or more of the above described apparatus is present. The steel wire line can be a newly installed line. Or it can be an upgraded line which is an existing line wherein one of the electrolytic plating sections is replaced with one or more of the described apparatus.

[0031 ] Particular lines of interest are lines wherein copper or zinc, manganese, cobalt, iron or nickel are deposited on the metal wire, for example steel wire. Also the line may comprise different sections wherein at least one of the apparatus described are present. In particular the throwing power of plating with copper can be greatly enhanced. [0032] According a third aspect of the invention a method to upgrade an existing steel wire plating line for coating a running web of steel wires is claimed. The method comprises the step of introducing one of the apparatus discussed previously as one of the plating sections. Alternatively, an existing plating section with electrolyte bath and overflow tray can be provided with ultrasound emission boxes as described.

Brief Description of Figures in the Drawings

[0033] Figure 1 describes a side view, in the plane of the wires, perpendicular to the wire direction of a first embodiment of the apparatus according the invention.

[0034] Figure 2 shows a top view of a second embodiment of the apparatus according the invention.

[0035] In what follows, the hundred digit refers to the number of the figure. The unit and ten’s number refer to particular features of the apparatus, wherein like numbers across figures refer to identical parts.

Mode(s) for Carrying Out the Invention

[0036] In Figure 1 a section of a plating line 100 is shown in a cross section plane oriented parallel to the wires of web and perpendicular the wire web. The wires 124 run in a single plane. The pump 106 circulates the electrolyte out of the bath 102 into the overflow tray 120. The electrical current source 130 provides current between soluble anodes 108 and the wire through line 128. The soluble anodes 108 receive their current through a grid 110 carrying the soluble anodes.

[0037] As an example of particular interest, the soluble anodes can be copper nuggets, and the electrolyte copper pyro phosphate.

[0038] The plating section, i.e. the apparatus in the meaning of the invention is further equipped with a metal box 112. At the bottom of the box, piezoelectric ultrasonic sound emitters 122 are present. The outer side of the box is coated with a non-conductive coating or even non-stick coating such as a Teflon(R) based coating. This to avoid that the bottom of the metal box would become coated with metal. These emitters 122 are fed by a line 126 that connects to an AC source 125 that generates the required wave pattern.

[0039] The box is held in a frame, with sides 114 and 114’. The frame sides 114, 114’ rest on adjustable studs 116, 116’. When the apparatus needs to be opened, the box 112 is lifted by toothed belts 118 driven by matching pulleys balanced by a counterweight (not shown). When the box 112 is lowered the frame sides 114, 114’ rest on the studs 116, 116’ in a controlled and precise way thereby ensuring a small but constant gap ‘A’ between the bottom of the box 112 and the wire web 124. The distance between the wire web and the box bottom is set to 20 mm.

[0040] In order to increase the level of the electrolyte an electrolyte restraining device 104 is provided that is a thin brush of non-conducting brush hair. When the apparatus is operative an AC signal of 40 kHz is supplied to the ultrasound emitters 122 through line 126. In total a power of 1 .5 kW can be supplied per box. The apparatus allowed to have a 50 to 90% higher deposition current compared to the conventional current, while maintaining a very good coating quality.

[0041] A second embodiment 200 is shown in Figure 2. There a top view is sketched. Two ultrasound emission boxes 212 and 212’ are present. The boxes comprise ultrasound emission sources 222 that are fed through line cables 226. Note that the ultrasound emission sources are arranged in a non-regular pattern to avoid standing wave formation in the bottom metal plate of the ultrasound emission boxes 212, 212’. Also the lines 226 have a different length for each emitter in order to change the phase angle of the AC current upon arrival at the ultrasound source.

[0042] The boxes 212 and 212’ are held in a frame 214. The frame is provided with protrusions 232 with an adjustment nut 234 that rests on a solid reference block. The frame is further provided with an electrolyte restraining device 204, for raising the electrolyte level so that the bottom of the ultrasound emission boxes 212, 212’ are securely submerged into the electrolyte.

Claims

1 . An apparatus for electrolytical ly coating metal wires in web, said apparatus comprising a bath and an overflow tray, said bath for containing the electrolyte, said overflow tray for keeping said metal wires immersed in the electrolyte, characterised in that said apparatus further comprises one or more ultrasound emission boxes, said boxes being placed above the web, the bottom plate of said boxes contacting the electrolyte when said apparatus is operative.

2. The apparatus according to claim 1 , wherein said one or more boxes are held in a frame, said apparatus further comprising a gap adjustment system, said gap adjustment system for adjusting the distance between said bottom plates and said web in a range from 5 up to 40 mm.

3. The apparatus of claim 1 or 2 wherein said overflow tray further comprises a soluble anode, said soluble anode having an irregular surface.

4. The apparatus according to claims 1 to 3 wherein said one or more boxes comprise a metal sheet box and ultrasound emission sources, said ultrasound emission sources contacting the bottom plate of said metal sheet box.

5. The apparatus according to any one of claims 1 to 5 wherein said bath and said overflow tray are made of polymer plate.

6. The apparatus according to any one of claims 1 to 6 wherein said one or more boxes are electrically insulated from the electrolyte.

7. The apparatus according to claim 6 wherein said one or more boxes are coated with an insulating layer.

8. The apparatus according to claim 1 to 7 wherein said apparatus being further provided with a lift system, said lift system for lifting said one or more boxes out of the electrolyte, said lift system being electrically insulated from said one or more boxes.

9. The apparatus according to claim 8 wherein said frame is provided with an electrolyte restraining device.

10. The apparatus according to any one of claims 1 to 9 wherein said ultrasound emission sources are positioned in a non-regular grid.

11 .The apparatus according to any one of claims 1 to 10 wherein said ultrasound emission sources are driven by an alternating current wherein the phase angle of said alternating current when reaching the ultrasound emission sources is different for all sources in one box. A steel wire line for coating a web of steel wires, said line comprising an electrolytic plating section, wherein in said electrolytic plating section one or more apparatus according the any one of the claims 1 to 11 is present. The steel wire line according to claim 14 wherein electrolytic plating of the wire web is with one or more out of the group comprising copper, zinc, manganese, cobalt, iron, nickel,... A method of upgrading an existing steel wire plating line for coating a running web of steel wires, said line comprising one or more electrolytic plating sections, wherein one or more apparatus according to any one of claims 1 to 11 in any one of the one or more electrolytic plating sections is introduced.