DE3011005A1 - Continuous electroplating of steel strip on one or both sides - using anode box with perforated base and strip cathode and electrolyte which is continuously recirculated - Google Patents

Abstract

An anode box has a perforated base so an electrolyte can flow through the holes onto the upper surface of a moving metal strip while a d.c. power supply creates a voltage between the box and the strip. The box can pref. be adjusted vertically to after the height of the box above the strip; and side baffle plates are pref. used to restrict the width of the descenting curtain of electrolyte. The plant is used esp. for the single-sided coating of steel strip with Zn, where the electrolyte flows over the two longitudinal edges of the strip into a collection tank so it can be recycled. Used in very high speed prodn. up to thirty anode boxes can be used in this simple and inexpensive plant.

Description

Galvanized steel is commonly used in applications

genes in which the life of the product without a protective coating with zinc would be unacceptably short. Until a relatively short time ago, people looked after to completely protect a product with a galvanized coating. One used either zinc-coated steel strips in the factory, or they are provided alternatively, made a finished product and then coated it with zinc. In each In this case, the product was completely or almost completely coated with zinc.

Relatively recently, applications were developed at for whom the galvanization of only one steel strip surface is desired, since the opposite surface should receive a smooth, decorative coating. Making them over a galvanized coating could be difficult. X \ utonobi 1 mudguards, AD double plates, body panels e.g.

are often galvanized on the inside surface to prevent them from attacking Inhibit corrosion by water trapped on the inside of the panels especially if this water contains significant amounts of road salt, and the outer surfaces are given a smooth coating for appearance and protection.

While there was a need for steel galvanized on one side, have been wasteful and inadequate and / or such in the past Used methods that required a very high capital investment.

One technique of one-sided coating is to coat the steel to immerse in a bath of molten zinc, taking one side in such a way has been treated so that their coating is prevented. It was, however difficult, Perform techniques to keep the zinc on one side of a strip. the Hot-dip galvanizing also changed the physical properties of the steel that electroplated and does not produce the uniformity Coating that can be achieved with electroplating technology.

A second known technique uses a relatively conventional one electrolytic strip electroplating line modified to the level to keep the plating solution level with only the bottom surface a steel strip to be galvanized comes into contact. This happened in the Hope that only this lower surface was electroplated. Unfortunately, a considerable one occurs Splash to 1 even when the plating solution level is monitored very closely will. Edge parts of the upper surface of the strip become due to this splash of the solution galvanized. With this technique, the edge parts coated above are cut away, and only a central portion of a strip creates a usable one-sided coated product. The cut sections are usually scrapped or used in applications where poor quality steel is required will; despite a possibly effective electroplating on the undersurface, the sprayed surface irregular and poorly galvanized and cannot be used for products that require quality strips.

Other techniques for one-sided electroplating were developed at which one surface is covered while the other is electroplated. It is for example, known to provide a strip of mild steel that runs over rollers which is partially immersed in an electroplating bath are and act to cover the surface with which they come into contact when the opposite surface is galvanized. Even if with this type of device an effective coating has been accomplished, account must be taken of the fact that the apparatus is complex and requires a very significant capital investment. the Required capital increases in that the galvanized coating for Self-propelled applications must be relatively difficult. In the case of one, this means effective route either a slow throughput or a relatively long and expensive route to develop the desired thick coating.

Most known electroplating systems use destructible electrodes. This means that the electrodes each have a fairly large piece of zinc for the Anodic dissolution include the zinc ions electroplated out onto the workpiece to replenish. When the zinc electrode is used up, the electrode / workpiece changes Distance and because of these and other variables it is difficult to get a very precise one and to achieve uniform plating thickness.

The Variables Involved in Destructible Electrode Plating led to the equipment and controls becoming expensive and complex. For example, intricate electrical controls have been developed that support the actual Query and change electroplating conditions in order to try to find a uniform To achieve electroplating with consuming electrodes.

The use of electrodes that do not deplete has been suggested. A non-consumable electrode consists of a senior Material which is held at a potential difference to the workpiece, so that Current flow between the electrode and the workpiece causes zinc ions to come out an electrically conductive electroplating solution that separates the space between the electrode and fills the workpiece to form an electroplated coating on the workpiece to be brought. When the ions on the workpiece are brought into the metallic state the solution will be adjacent to or near the workpiece depleted in zinc metal ions.

Effective high-speed electroplating can only be achieved when maintaining the correct zinc ion concentration on the workpiece surface will. The problem of replenishing or maintaining zinc ions inhibited the implementation of previously known systems with non-consumable anode, which resulted in their not enjoying significant commercial success.

In the present invention, there has been an improved electroplating technique which is particularly suitable for galvanizing a steel strip. According to In the technique, an anode assembly is positioned relatively close to the workpiece. The assembly and workpiece are configured to provide a fluid flow path for the Set up electroplating fluid. The plating fluid is in a sufficient Quantity delivered to at least part of the flow path across the workpiece essentially at all times to keep it filled with flowing solution so that over the entire width of the workpiece is electroplated.

The solution flows from the fluid flow path into a sump for collection and is then fed to a zinc ion replenishment station. Once the zinc ions replenished the solution is recirculated through a filter and returned to the flow path returned.

The system of the invention has a number of distinct advantages on. A major advantage is that the fluid is only available through selected ones Sections flows, e.g.

over one workpiece side. There is another major benefit in that the relatively high flow rate results in good ion replenishment rates, which make it possible to use non-consumable anodes. This provides for systems with unused anodes characteristic advantages in electroplating and at the same time overcomes the disadvantages of these systems, which they had in the past Restrict use.

In a preferred embodiment of the invention, the anode is above of the strip and forms a non-detachable anode container for receiving the electroplating solution. The anode container has a galvanizing surface, which runs parallel to the workpiece surface, which has a galvanic coating should be provided.

The electroplating solution is pumped into the anode and can through openings pass through in the anode electroplating area. The solution occurs with the steel strip surface in contact and fills the gap between the anode and the strip. If the When the strip moves past the anode, electroplating takes place due to the current flow between the anode and the strip. The solution flows away from the edge of the strip and is collected in a collecting tank for later recirculation to the anode. At a location remote from the anode container, a source of zinc ions fills the ions used in the electroplating process.

In order to achieve a uniform electroplating, one criterion must be must be met, namely the maintenance of a uniform gap between the anode and the strip.

In the case of the anodic solution of a soluble anode, the electroplating current inconsistent due to changes in the physical anode configuration. The use of a non-soluble anode ensures that the gap width is constant remains and therefore the galvanization uniformity is maintained.

An essential feature of the invention is the control of the Current flow from the anode to the strip. To have a uniform coating thickness To ensure the strip width, covering plates are in the way of the solution flow introduced. These plates are electrically insulating and reduce the electroplating current at the strip edges, by two as tree growth and "edge structure" (edge buildup) to reduce known phenomena. There stripes with different widths If galvanized, these insulators or covers are moved to make a more uniform To achieve coating deposition.

An object of the invention is to provide a device and a Process for one-sided electroplating of a steel strip or the like. To be delivered. The insoluble anode ensures that the gap width between the anode and Stripe does not change over time. Electric inside or near the gap arranged insulators ensure uniform electroplating across the width of the strip.

The invention is illustrated below, for example, with reference to the drawing described; FIG. 1 shows an electroplating line in which the inventive Electroplating technique is used, Figure 2 is a partially sectioned perspective View of an electroplating anode cell according to the invention, FIG. 3 the schematic Representation of an uncovered electroplating cell arrangement, FIG. 4 the representation an electroplating cell with covers that guarantee a uniform thick galvanic coating are applied, and FIG. 5 one of the ones shown in FIG Station-like two-cell electroplating station.

Fig. 1 shows the scheme of an electroplating system according to the invention 10. The system is particularly suitable for applying a galvanic coating one side of a workpiece 11, for example a steel strip, is suitable.

The system 10 includes an anode cell shown at 20. The cell is arranged at a distance above the work piece and is for receiving a Electroplating solution formed. Only one anode cell is shown in the drawing; however, an industrial electroplating line can include 30 or more of these cells. The solution is obtained from a container 17 for the application material via two pumps 12 and a line 13 circulated or held. The solution occurs from the line into an anode cell 20 and leaves this in order to pass over the workpiece to flow.

The anode cells are above the workpiece while maintaining a a narrow gap between the workpiece and the anode cell. After this Leaving the anode cell, the electroplating solution fills this gap, then flows away from the workpiece and is collected in a garbage container 14. The captured Solution then goes to reaction station 15, through filter 16, and to the main reservoir returned to be pumped back into circulation to the anodes. In Fig. 1 the collecting container 14 is shown with the side wall broken away on one side, to show the solution draining off the workpiece.

A suitable one is used at the start of the electroplating process Zinc electroplating solution with a pH above 4.5, preferably in the range 1.5-2.5, and at a temperature above room temperature, preferably about 600C. These Solution is prepared and made up with technically pure zinc sulfate salts and cleaned with carbon powder and zinc dust. The zinc sulfate salts dissociate and deliver Zinc ions for the coating.

The workpiece and the anode cell are kept at different electrical potentials by an electrical energy source such as that supplied by a direct current rectifier. Because of this difference in energy, electroplating takes place on the workpiece, which can be traced back to the flow of electrons from the anode to the workpiece. The galvanization reaction follows the well-known equation The electrons required to complete this reaction flow through the anode, which must therefore contain a metallic or a suitable conductive material. In one embodiment of the invention, the anode is made of a lead-silver alloy material. A corrosion-resistant material suitable for anode formation contains 1/2% silver and 99 1/2% lead.

The direct current is controlled by a control module whose Control output of the belt speed and the width of the steel strip proportional is. Details of this rectifier current control are in the US patent application with serial number 8594 of 2.2.79 disclosed.

When the galvanic coating is deposited on the workpiece, it decreases the zinc ion concentration. To maintain the ion concentration, will the container 17 at Mr reaction station 15 is constantly filled with zinc ions. That Filling with ions is preferably carried out by adding metallic zinc and Zinc oxide penetrates into the electroplating solution contained in the reaction station. As zinc ions are used for electroplating, sulfuric acid is generated at the anode. This acid is used to make the solution of metallic zinc and zinc oxide to support the production of zinc sulphate, which is responsible for the formation of zinc ions the electroplating process dissociates.

Drive rollers 19 cause the relative longitudinal movement between the Anode cells 20 and the workpiece 11. The current density on the workpiece, the desired Coating thickness and the number of anodes determine the speed with which these Drive rollers drive the workpiece.

The width of the gap between the cell 20 and the workpiece 11 is adjustable. The setting is made using a guide roller 22, which is provided on both sides of the cell 20. because the guide rollers are relative be moved up or down to the anode, the gap between the workpiece and the anode either smaller or larger.

2 shows a preferred embodiment of the anode cell 20.

It is a rectangular container with a bottom surface 23 that has a number of 6.4 mm (1/4 ") diameter openings 24. These serve to enable the electroplating solution in the anode to be applied to the workpiece 11 to flow. In addition to the electroplating surface, the anode container includes four wall surfaces 25 which form the container. An upper part 26 is on with bolts of the anode along a flange 27 which extends along the periphery of the anode container extends. The anode is fastened to a frame 36 by means of bolts. This frame holds the anode above the workpiece. The upper part is made of non-conductive Material such as methacrylic resin (Lucite) and helps create a contact rail 28 to be held in place.

The contact rail 28 provides a suitable means of attachment the anode to a source of electrical direct current potential for maintenance of the current flow for the electroplating reaction.

As shown, line 13 enters the anode canister from above a. Once inside the anode, the lead can turn into a "T" or other suitable fittings (30) branching off the electroplating solution is directed to both sides of the anode container.

You can adjust the pressure delivered by the pump 12 to the To change fluid flow through the anode. A higher one Pressure leads to a faster flow of the fluid through the openings and ensures that the gap between the workpiece and the anode is filled during the electroplating process remain. The flow required to create a full volume of electrolyte in the gap maintain depends on the cross-sectional area of the overflow from the gap to the collecting container. This area is: the length of the anode times the distance between the anode and workpiece. A baffle plate 42 arranged at both ends of the anode can the Reduce the overflow at the outlet and inlet ends (Fig. 2). The baffle plate extends along the width of the anode and comes into direct contact with the workpiece, to drive the solution from both sides of the workpiece into the collecting container. For the In the event that the solution seeps past the baffle plate, a pair of rubber pinch rollers prevent it 43, 44 (Fig. 1) that solution flows past the collecting container.

Tests show that the necessary to maintain a completely filled Gap required flow rate is roughly proportional to the overflow area. if the gap width is halved while the anode length is kept constant, so one can also Halve the solution flow rate needed to fill the gap.

Fig. 2 illustrates the guide rollers 22 which the workpiece relatively position to the anode cell. By releasing a pair of links on both sides of the rollers 22, the vertical positioning of the guide roller zen can be set. This setting defines the gap between the workpiece and the anode. By changing the anode / workpiece distance, the user can empirically ensure that the gap is completely filled with solution and so on achieve maximum electroplating current flow.

Next to each electroplating anode cell 20 are two cover plates 31 moving in and out of the plating solution stream will. These cover plates 31 are adjusted to control the flow of current to the workpiece edges to restrict and so two as edge buildup and tree growth avoid known phenomena. Consist in the preferred embodiment of the invention These masks are made of 1.9 mm thick stainless steel bursts with a 1.0 mm are coated with a thick layer of paint to ensure electrical insulation.

Tree growth and edge build-up can occur when it comes to the plating solution is allowed to flow unrestrictedly from the anode to the workpiece. Tree growth is illustrated schematically in FIG. 3. The so-called trees grow lengthways the workpiece edge and reduce the galvanic coating near the workpiece edge is a phenomenon in which macroscopic lumps appear along the edges of the workpiece and lead to a non-uniform galvanic coating.

By constantly exposing a portion of the current flow it is possible to turn off these phenomena. During the electroplating, the cover plates arranged so that their edges almost coincide with the edge of the workpiece (Fig. 4). When the covers are in this position, the trees will not step nor the lumps along the edge of the workpiece. Excessive deposition of the galvanic Coating on or near the edge of the strip is prevented as the current path is not continuous across the edge of the strip.

Figure 2 shows one technique for attaching the plating covers. A cover plate guide 33 is attached to the frame 36 and is therefore with respect to the anode cell. The covers 31 slide along a region 40 the guide parallel to the anode plating surface. The guide 33 is vertical Direction positioned so that the cover by sliding the cover 31 longitudinally this area 40 is the area of the current flow within the gap between the The anode and the strip. The positioning of the covers varies in Depending on the width of the material to be electroplated. If settings considered necessary due to the growth of trees or tubers, the user repositions the cover plate by sliding it along the guide 33 moves.

In this way, the user of the electroplating process keeps the Control over the position of the cover width and can adjust this positioning in Vary depending on the results obtained during the electroplating process.

Changes can be made in the structure in an advantageous manner In particular, the plating cells can be positioned in a vertical arrangement and the electroplating solution can be pumped onto a vertically arranged workpiece. The solution only makes contact with the workpiece and the anode for an instant and then flows away from the workpiece due to gravitational forces. You can Arrange the anode underneath the workpiece and the solution can flow into a gap between the workpiece and the anode and can be driven from either side drain off the anode.

During operation, the drive rollers move the workpiece on the anode cells over when the plating solution runs out of the Source 15 to the cells 20 and is pumped onto the workpiece.

The number of times to get the correct plating thickness required anode cells depends on the speed of the workpiece, the electroplating current density and the required thickness. The potential difference between the anode and the workpiece causes the electroplating reaction. A uniform current density is maintained, by ensuring that the gap remains filled. The solution flow is for different gap widths are monitored and adjusted to ensure the continuity of the flow to ensure.

5 shows an electroplating station 50 with two anodes. This station comprises a framework 52 for the assembly of two anode cells and a number of rollers. The rollers maintain the relative position of the strip and the anodes and additional electrical potential differences between the two.

in As in the case of / Fig. 2, each anode cell shown in Fig. 5 cell shown a non-soluble anode with a flange 27, which is around extends around the anode container. The anode container has a number of holes in the bottom (not shown in Fig. 5) which it the electroplating solution as it passes through allow the station to flow from the feed line 13 to the steel strip. The anode container rest according to Fig. 5 on a frame 56, which with an adjustable Section 58 of the framework 52 is connected. The support device 56 sets a right-angled Surface 59 with suitable internal dimensions for receiving the anode flange. Since the frame 52 and the support device 56 are fixedly arranged with respect to their surroundings the anode is likewise stationary.

At ROmen 52 s a pair of setting rollers 60 and two pairs (Xmmicailet rollers 62, 63 attached. The adjustment rollers 60 are used to strip the steel in one to keep a fixed distance from the anode when it passes the electroplating station. The adjustment rollers 62, 63 prevent the plating solution from traveling along the strip flows past the edges of the collecting tank, where it makes contact with the electrical contacts interferes with the strip. The upper squeegee roller 62 is on a bracket 64 rotatably mounted, which is attached to the frame 52. The carrier 64 is like this mounted to pivot about an axis 65 parallel to the surface of the strips can. This freedom of rotation allows the squeegee roller to streak to adapt with changing thickness and also irregularities in the strip.

A hold-down roller 66 and a contact roller 67 are in phantom shown. The contact roller is used to keep the strip moving as it passes the Keep the station at a constant electrical potential. The hold-down roller is used only as an aid to keep the strip past the electroplating station on its way.

The line 13 shown in FIG. 5 branches into three inlets 68, which ensure that the solution completely fills the anode container. As in the embodiment shown in FIG. 2, each unit ends in a T-outlet piece for injecting the fluid into the container. As well as the fluid from the anode container holes has been ejected away, it flows towards the strip and then from the strip edges away for recirculation and replenishment in the sump when the electroplating process persists.

The invention thus relates to a method and a device for Electroplating one or both sides of a steel workpiece. One insoluble electroplating anode is positioned at a close distance from the workpiece, a uniform flow path of the electroplating solution between the anode and the Form workpiece. The solution is through the anode pumped to to come into contact with the workpiece for just a moment and put it in a collecting container to fall for recirculation. A potential difference between the anode and the That current causes the electrolyte solution to create a workpiece galvanic coating of the workpiece flows. The solution from the collection container becomes a reaction station for replenishing the zinc metal ions. The solution is then filtered back into a main storage tank and from there again to Electroplating anode pumped.

Claims (9)

Apparatus and method for applying a galvanic coating on one or both sides of a metallic strip Patent claims: 1. 1. Electroplating device for equipping a surface of an electroplating station workpiece moving past with a galvanic coating, g e k e n n z e i c h n e t by a) an anode container with an electroplating surface which is a A plurality of openings comprises, b) means for the supply of an electroplating solution to the anode, which allows the solution to flow through the openings onto the workpiece, and c) a source of energy to power the workpiece and the anode at different electrical levels Potentials for generating an electroplating current between the anode and the workpiece to keep. 2. Apparatus according to claim 1, characterized in that g e k e n n -z e i c h n e t that the anode is arranged above the workpiece and that the flow of the Solution through the openings to the gap the fluid allowed, with an upper level Surface of the workpiece to come into contact. 3. Apparatus according to claim 2, g e k e n n z e i c h n e t through a screen for restricting the electroplating current to a workpiece section. 4. Apparatus according to claim 1, g e k e n n z e i c h n e t through a device for adjusting the distance between the anode and the workpiece, to ensure that the plating solution fills the gap. 5. Method for equipping a surface of a workpiece with a galvanic coating, not marked by the following steps: a) that a potential difference between the surface and an electrical power source is created, b) that the space between the surface and the source is substantially is filled with sufficient electroplating solution to create a current flow path between the anode and the surface set up; and c) that the solution from the surface can drain. - 6. Process for galvanizing steel, g e -k e n n z e i c h n e t by the following steps: a) that a galvanizing anode and a workpiece made of steel can be placed in close proximity to each other in order to Establish fluid flow path between them, b) that a liquid Electroplating solution flows along the path in a volume sufficient to keep a establish electrical flow path from the anode to a surface of the workpiece, the electrical flow path being essentially entirely over the surface in at least one direction is formed, c) that an electrical potential difference is formed between the anode and the workpiece in such a way that a current flows that the zinc ions in the plating solution create a zinc coating on the workpiece form, d) that plating solution flowing away from the fluid path is collected, e) that the zinc ion concentration in the collected solution is replenished, and f) that the replenished solution flows along the fluid flow path. 7. Process for galvanizing a strip of steel, g e k e n n n z e i c h n e t, through the steps, a) that one with a galvanic Coating of steel strips to be provided is moved along a path, b) that a electrically conductive path in a space between the strip and one nearby The insoluble electrode arranged on the strip is set up by plating solution flows in between. c) that the flow of fluid from the space between the electrode and the strip is limited in part to allow such conductive flow across the Maintain the width of the strip, d) that simultaneously with the restriction allows the fluid to escape from the substantially unimpeded Space flows along a plating fluid escape path and that the fluid then flows into a collecting container is collected, e) that a voltage potential between the Electrode and strip is applied to keep zinc ions out of the way for the plating be applied to the strip, f) that the zinc ion content of the collected Solution is replenished, and g) that the replenished fluid through the Space between the electrode and the strip flows. characterized, 8. The method according to claim 7, / that edge portions of the strip to be covered to the equipment with a galvanic coating to limit along edge portions of the strip and thereby essentially one to achieve uniform thickness of the electroplating across the strip. 9. The method according to claim 7, characterized in that g e k e n n z e i c h -n e t, that the flow is limited in the longitudinal direction of the strip path and that the flow to the collecting tank takes place on the side of the walkway.