Device for electrolytically coating a metal wire turning in the form of a wet

Abstract

There is provided an apparatus for electrolytic coating of metal wires arranged in a web, also referred to as a "electroplating section". Compared with the electroplating part of the prior art, the equipment is provided with one or more ultrasonic transmitting box bodies which are suspended above the net, and when the equipment works, the stirred bottom plates of the box bodies are immersed in the electrolyte. The gap between the bottom of the ultrasonic emission box body and the metal wire mesh is accurately controlled. In a favorable embodiment, the bottom of the ultrasonic emission tank faces the irregular soluble anode. The ultrasound not only helps to improve the deposition of metal on the metal wire, but also promotes the dissolution of the soluble anode material.

Description

Technical Field

[0001] The invention relates to a device for coating a metal wire running in the form of a web. Such a device is used in an electroplating line for continuously electroplating a metal wire running through an electrolytic bath. Background Art

[0002] The process of electrolytically coating a metal wire by immersion in an electrolyte solution containing metal ions is well known. When the metal wire acts as a cathode, the positively charged coating metal ions in the electrolyte are attracted to the surface of the metal wire and deposited thereon after receiving one or more electrons from the surface of the metal wire. The metal wire is in contact with the negative pole of a current source external to the electrolyte solution, while the anode extracts electrons from the electrolyte to maintain the charge balance in the electrolyte. The aim of this process is to have the correct amount of coating metal deposited on the wire when it leaves the electrolytic bath compared to when it entered the electrolyte.

[0003] The rate at which the coating metal ions are deposited on the surface of the wire is proportional to the supplied electron current: the greater the supplied current, the faster the coating thickness increases. However, the mass transfer of the metal ions is limited by the double diffusion layer formed when the electric field is applied. When the current becomes too high, the mass transfer of the metal ions cannot keep pace with the supplied electron current. Parasitic reactions can therefore occur, such as the escape of hydrogen. These parasitic reactions have an adverse effect on the efficiency of the process expressed as the "cathode efficiency", which is the ratio of the number of atoms deposited to the number of electrons supplied, keeping in mind the valence state of the metal ions. Moreover, the quality of the coating is also adversely affected, because the coating becomes less dense, has foam and is no longer well attached to the wire substrate.

[0004] The cathode efficiency problem can be overcome by limiting the current density supplied to the wire surface. The current density is the total current supplied to the wire divided by the surface area of ​​the wire in contact with the electrolyte and is expressed in amperes per square decimeter. The current density at the surface can be limited by increasing the immersion length of the wire and / or reducing the speed of the line. However, neither solution is preferred:

[0005] Increasing the length of the line will incur additional costs for the line because the line becomes longer, requiring more space, additional baths, and equipment;

[0006] Reducing the line speed will obviously result in reduced output of the line.

[0007] It is known that throwing power, i.e. the amount of thickness that a coating grows per unit time, can be increased by agitation (disturbing the diffusion layer at the wire surface). A known method of agitating an electrolyte is to use an ultrasound source to shake and disturb the solution. Ultrasonic waves generate microbubbles at the wire surface by cavitation. These bubbles disrupt the diffusion layer between the substrate and the electrolyte, thereby improving the mass transfer of metal ions.

[0008] Electrolytic coating of static, non-moving objects in an electrolyte in an ultrasonic bath is known, see for example CN107313089A. Ultrasonic assisted deposition of electrolytic nickel coatings on thin metal wires is described in CN208667884U. In this context, a bath containing an electrolyte is ultrasonically agitated.

[0009] However, these embodiments cannot be extended 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 stirred uniformly. Such webs are used, for example, for the deposition of metals on wires, more particularly for the deposition of copper, zinc and other metals such as iron, cobalt, manganese, tin, nickel or their alloys. The steel wires are first electrolytically coated with copper and then with zinc, which subsequently diffuses into the copper, resulting in brass-coated steel wires. Such brass-coated steel wires are used as intermediate products in the manufacture of steel cords for tires, hoses, conveyor belts, transmission belts and many other applications.

[0010] Furthermore, because these facilities already exist, they cannot be simply updated without incurring significant costs. The inventors therefore sought solutions to these problems, as will be described below. Summary of the invention

[0011] The object of the present invention is to solve the problems of the prior art. The present invention provides a solution to improve the throwing power of new production lines for electrolytic coating of metal wires running in the form of a web. The present invention also provides a solution for upgrading existing production lines so that their throwing power can be improved at low cost. The present invention allows to increase the coating thickness without increasing the length of the production line and / or reducing the speed.

[0012] According to a first aspect of the invention, an apparatus is described and explained. The apparatus is for electrolytic coating of metal wires running in the form of a web. In the context of the present application, a "web" is an arrangement of metal wires lying in one plane and parallel to each other. All the metal wires move in the same direction, parallel to each other, preferably at the same speed. This is referred to as "running in the form of a web". During operation, the metal wires will move continuously or step by step.

[0013] The apparatus comprises an overflow pan and a bath. In the context of the present application, "bath" refers to a physical container for holding, containing an electrolyte solution, rather than the electrolyte solution itself. The overflow pan is positioned within the contour of the bath. A pump is provided, which preferably continuously pumps the electrolyte solution from the bottom of the overflow pan into the overflow pan, so that the overflow pan continuously overflows and the overflow is collected in the bath. A wire mesh is arranged directly above the overflow pan so that the mesh, the wire, is always immersed in the electrolyte. The presence of the electrolyte liquid in the bath naturally defines the directions considered to be "below" and "above" relative to the gravitational field.

[0014] The apparatus is also provided with equipment, auxiliary equipment known to a person skilled in the art: a pump for circulating the electrolyte solution, a current source and contact rollers for feeding electrons to the wire mesh and extracting electrons from the anode immersed in the electrolyte solution, a level indicator, a temperature sensor and any other device that appears obvious to a person skilled in the art.

[0015] The device is characterized in that it includes one or more ultrasonic emission boxes located above the net. Each of the ultrasonic emission boxes has the shape of a box or a cuboid, and its height is less than its width or width. The bottom of the box is used for contact and must be able to physically contact the electrolyte when the device is working. The physical contact between the bottom of the ultrasonic emission box and the electrolyte must be complete, and at the same time, above the surface of the bottom of one or more boxes, the distance between the net and the bottom of the ultrasonic emission box must be constant.

[0016] If the bottom of one of the boxes is not in full contact with the electrolyte during operation, the coating on the wire will not be uniform in the transverse direction of the web. This must be avoided at all costs.

[0017] Preferably, the boxes are identical in shape and configuration. Preferably, a single box covers the entire width of the net. If a single box does not cover the entire width of the net, a pair of boxes can be installed side by side, or four boxes can be installed in a quartered arrangement. It is also possible to install six or eight boxes in a 3×2 or 2×3, 2×4 or 4×2 arrangement. The requirement is that the box must be able to cover the entire width of the net.

[0018] In order to accurately control the distance between the wire mesh and the bottom of the box, the box is mounted in a frame that keeps the bottoms of all the boxes in the same bottom plane. A gap adjustment system is provided that allows the distance between the bottom of the box and the wire mesh to be accurately adjusted. This gap adjustment system can be based on calibrated support blocks, on which the uprights attached to the frame are supported. The calibrated support blocks are firmly connected to the floor where the equipment is installed. The uprights can be made adjustable and fixed in place when the frame and the wire mesh have been properly contoured.

[0019] Preferably, the gap between the mesh and the bottom of the box can be adjusted between 5 mm and 40 mm. A small gap will enhance the transmission of ultrasonic energy from the ultrasonic transmitting box to the electrolyte near the wire mesh, but it may be difficult to maintain constant. For too large a distance, the ultrasonic energy is absorbed too much by the electrolyte.

[0020] The variation of the distance between the wire mesh and the bottom of the ultrasound transmitting box must be kept below 5 mm, preferably below 3 mm, and this is over the entire bottom area of ​​the ultrasound transmitting box. Too large a distance variation will produce an uneven coating of the wire mesh, which must be avoided.

[0021] In another embodiment, the overflow tray is filled with, includes, contains a soluble anode. The soluble anode is made of the metal to be deposited and dissolves into the electrolyte, while on the cathode side, the metal is deposited on the wire mesh. It is particularly preferred that the soluble anode has an irregular surface. The "irregular surface" is formed by a block of metal to be deposited. The block can be in the form of a ball, block, bulk, block or pellet of equal or different diameters. The block is randomly loaded in the overflow tray and is in electrical contact with the bottom plate connected to the positive pole of the current source. The size of the block is between 1 mm and 20 mm. "Size" here refers to the maximum distance between any two points on the surface of the block. The irregular surface of the soluble anode helps to prevent the formation of standing waves in the electrolyte. It also absorbs incoming sound waves, which enhance the dissolution of the soluble anode in the electrolyte, which is an unexpected advantage of the device.

[0022] Preferably, each of the one or more boxes comprises a sheet metal box and one or more ultrasonic emission sources. The one or more ultrasonic emission sources contact the bottom plate of the sheet metal box. The sheet metal allows good transmission of sound waves because it can be kept relatively thin. Preferably, there are 1 to 30 ultrasonic emission sources, depending on the area of ​​the bottom plate. Typically, one ultrasonic emission source is provided every 2 dm 2 Up to 6dm 2 There is one ultrasound source. One source may not generate enough ultrasound energy, but 30 transmitting sources increase the cost of the facility.

[0023] Typically, the ultrasound source is a piezoelectric transducer that converts an electrical waveform into mechanical vibrations. Such transducers are well known in the art.

[0024] The bath and overflow pan are made of electrically insulating material, such as polymer sheets. Typical polymers used are polyethylene, polypropylene, polycarbonate, etc. The polymer absorbs the generated sound waves.

[0025] When one or more of the tanks are made of metal and in contact with the electrolyte, they are susceptible to metal deposition in the event that stray currents reach the metal tanks. Therefore, the metal tanks are preferably electrically insulated by using an insulating gap adjustment system. Alternatively or additionally, the tanks may be coated with a non-conductive coating or paint, such as a Teflon-based coating or an enamel coating.

[0026] Because these tanks are often heavy and require access to a wire mesh to pass through, a lifting system is required to lift one or more tanks out of the electrolyte. Care must be taken that the lifting system does not allow stray currents to reach the metal tanks, i.e., the lifting system must electrically isolate the metal tanks from the electrical environment. Lifting can be accomplished by electrical, pneumatic or mechanical means.

[0027] The state of the art is that the rim of the overflow pan has a straight edge. This makes it very easy to pass the wire through the facility. However, this has the disadvantage that the overflow level is limited by the flow rate of the pump. This limits the height of the electrolyte level above the wire mesh, which in turn makes it more difficult to keep the bottom of the tank in electrolyte in a controlled manner.

[0028] In a preferred embodiment, in order to increase the electrolyte level above the wire mesh, an electrolyte restriction device, such as a comb, is introduced on the edge of the overflow pan. The wire is inserted 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 tank in the electrolyte.

[0029] Alternatively, the frame holding the one or more tanks may be provided with electrolyte confinement means, such as brushes made of a polymer.

[0030] In a preferred embodiment, the transducers in one box are arranged in an irregular grid. An "irregular" grid is a grid that is not in accordance with any of the 17 possible wallpaper arrangements. A symmetrical arrangement is not preferred because it would produce a preferred deposition area if the base plate is excited in a resonant mode. The body of the transducer can be fixed to a solid frame, while the actuator is connected to a flexible base plate.

[0031] In another preferred embodiment, the ultrasonic emission source is driven by alternating current. The alternating current is characterized by its amplitude, frequency and phase angle. The alternating current can be a square wave, a sine wave or any other wave, as long as it is a harmonic. In a preferred embodiment, the phase angle of the alternating current at the entrance of the ultrasonic emission source is different for all sources in a box. This can be achieved by increasing the length of the feed line between the ultrasonic emission sources or by adding a delay line between the AC power supply and the ultrasonic transmitter. The advantage of this embodiment is that it breaks the symmetry and prevents the formation of a preferred coating area.

[0032] According to a second aspect of the invention, a steel wire production line for coating steel wire mesh is claimed. The production line comprises at least one electrolytic plating section. In this section, one or more of the above-mentioned devices are present. The steel wire production line may be a newly installed production line. Alternatively, it may be an upgraded production line, which is an existing production line, in which one of the electrolytic plating sections is replaced by one or more of the above-mentioned devices.

[0033] Production lines of particular interest are those in which copper or zinc, manganese, cobalt, iron or nickel are deposited on metal wires, such as steel wires. Furthermore, the production line may comprise different sections in which at least one of the devices described is present. In particular, the throwing power of electroplating with copper can be greatly improved.

[0034] According to a third aspect of the invention, a method for upgrading an existing steel wire electroplating line for coating a traveling steel wire mesh is claimed. The method comprises the step of introducing one of the aforementioned apparatuses as one of the electroplating sections. Alternatively, an existing electroplating section having an electrolyte bath and an overflow pan may be provided with an ultrasonic transmitting box as described. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A side view perpendicular to the wire direction of a first embodiment of a device according to the invention is depicted in the plane of the wire.

[0036] Figure 2 A second embodiment of the device according to the invention is shown in a top view.

[0037] In the following, the hundreds digit refers to the digit of the drawing. The ones and tens digits refer to specific features of the device, wherein the same numerals in the drawings refer to the same parts. DETAILED DESCRIPTION

[0038] exist Figure 1 , a portion of an electroplating line 100 is shown in a cross-sectional plane oriented parallel to the wires of the mesh and perpendicular to the wire mesh. The wires 124 travel in a single plane. A pump 106 circulates electrolyte out of the bath 102 into an overflow pan 120. A current source 130 provides current between the soluble anodes 108 and the wires through lines 128. The soluble anodes 108 receive their current through a grid 110 that carries the soluble anodes.

[0039] As an example of particular interest, the soluble anode may be bulk copper and the electrolyte may be copper pyrophosphate.

[0040] The electroplating part (i.e. the device in the sense of the present invention) is also equipped with a metal box 112. At the bottom of the box are piezoelectric ultrasonic transmitters 122. The outside of the box is coated with a non-conductive coating or even a non-stick coating, for example a coating based on Teflon (R). This is to avoid that the bottom of the metal box is coated with metal. These transmitters 122 are fed by a line 126 connected to an AC source 125, which generates the required waveform.

[0041] The box is held in a frame having sides 114 and 114'. The frame sides 114, 114' are supported on adjustable posts 116, 116'. When the device needs to be opened, the box 112 is lifted by a toothed belt 118 driven by a matching pulley balanced by a counterweight (not shown). When the box 112 is lowered, the frame sides 114, 114' are supported on the posts 116, 116' in a controlled and accurate manner, thereby ensuring a small but constant gap "Δ" between the bottom of the box 112 and the wire mesh 124. The distance between the wire mesh and the bottom of the box is set to 20 mm.

[0042] In order to increase the level of the electrolyte, an electrolyte restriction device 104 is provided, which is a thin brush with non-conductive bristles. When the device is working, a 40kHz AC signal is provided to the ultrasonic transmitter 122 through line 126. Each box can provide a total power of 1.5kW. While maintaining very good coating quality, the deposition current of the device can be 50% to 90% higher than the conventional current.

[0043] exist Figure 2 A second embodiment 200 is shown in FIG. Figure 2 A top view is drawn in FIG. There are two ultrasonic transmitting boxes 212 and 212'. The box includes an ultrasonic transmitting source 222 fed by a cable 226. Note that the ultrasonic transmitting sources are arranged in an irregular pattern to avoid the formation of standing waves in the bottom metal plate of the ultrasonic transmitting boxes 212, 212'. In addition, the line 226 has a different length for each transmitter in order to change the phase angle of the AC current when it reaches the ultrasonic source.

[0044] The boxes 212 and 212' are held in a frame 214. The frame is provided with a protrusion 232 having an adjustment nut 234, and the protrusion 232 is supported on a solid reference block. The frame is also provided with an electrolyte limiting device 204 for raising the liquid level of the electrolyte so that the bottom of the ultrasonic transmitting boxes 212, 212' is safely immersed in the electrolyte.

Claims

1. An apparatus for electrolytically coating a metal wire in the form of a mesh, the apparatus comprising a bath for containing an electrolyte and an overflow pan for keeping the metal wire immersed in the electrolyte, wherein: The device further comprises one or more ultrasonic emission boxes, which are placed above the net. When the device is working, the bottom plate of the box contacts the electrolyte.

2. The device according to claim 1, wherein: The one or more boxes are held in a frame, the apparatus further comprising a gap adjustment system for adjusting the distance between the base plate and the mesh within a range from 5 mm up to 40 mm.

3. The device according to claim 1 or 2, wherein: The overflow pan also includes a soluble anode having an irregular surface.

4. The device according to any one of claims 1 to 3, wherein: The one or more boxes include a sheet metal box and an ultrasonic emission source, the ultrasonic emission source contacting a bottom plate of the sheet metal box.

5. The device according to any one of claims 1 to 5, wherein: The bath and the overflow tray are made of polymer sheets.

6. The device according to any one of claims 1 to 6, wherein: The one or more tanks are electrically insulated from the electrolyte.

7. The device according to claim 6, wherein: The one or more boxes are coated with an insulating layer.

8. The apparatus according to any one of claims 1 to 7, wherein: The device is further provided with a lifting system, which is used to lift the one or more tanks out of the electrolyte, and the lifting system is electrically insulated from the one or more tanks.

9. The device according to claim 8, wherein: The frame is provided with an electrolyte confinement device.

10. The device according to any one of claims 1 to 9, wherein: The ultrasound emission sources are positioned in an irregular grid.

11. The apparatus according to any one of claims 1 to 10, wherein: The ultrasonic transmitting source is driven by an alternating current, wherein the phase angle of the alternating current when reaching the ultrasonic transmitting source is different for all sources in a box.

12. A steel wire production line for coating steel meshes, said production line comprising an electrolytic plating section, wherein one or more devices according to any one of claims 1 to 11 are present in said electrolytic plating section.

13. The steel wire production line according to claim 14, wherein: Electrolytic plating of steel mesh utilizes one or more of copper, zinc, manganese, cobalt, iron, nickel, etc.

14. A method for upgrading an existing steel wire electroplating production line for coating a traveling steel wire mesh, the production line comprising one or more electrolytic plating sections, wherein one or more devices according to any one of claims 1 to 11 are introduced into any of the one or more electrolytic plating sections.

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