EP0875605B1 - Arrangement for the electrogalvanic metal coating of strips - Google Patents

Abstract

The arrangement is intended for electrogalvanic coating of strips (2) with a metal. Such strips run through an acid electrolyte enriched with the metal, in a direction parallel to at least one non-dissolvable anode from which a current flows to the strip connected as a cathode, and the metal from the electrolyte is deposited onto the strip surface. Each anode is divided into anode strips (5a, 5b) parallel to the direction of motion of the strip (2). These anode strips are insulated from one another, and are individually supplied with current.

Description

The invention relates to an arrangement for electrogalvanic metal coating of bands passing through a metal-enriched acidic electrolyte having at least one insoluble anode arranged parallel to the band from which the current flows to the band connected as a cathode, wherein metal from the electrolyte on the Surface of the tape is deposited, each anode is parallel to the direction of the tape divided into anode strips and each anode strip is individually powered.

Cold-rolled strip of normal carbon steel must be provided with a protective layer to prevent or at least greatly retard corrosion. The type of protective layer depends on the purpose and the economically justifiable effort.

The state of the art includes u. a. galvanizing. In galvanizing, the corrosion protection can be achieved by a metallic coating, which is applied by electrolysis.

Plants for applying one or both sides of such zinc layers in thicknesses of about 2.5 to 15 micrometers are known from the prior art. The anodes are arranged parallel to the tape in the smallest possible distance between 5 and 30 mm. The space between each anode and the belt is filled with a metal (zinc) enriched acidic electrolyte. During coating, the current flows from the anodes to the band connected as a cathode, on the surface of which the zinc is deposited.

With these conventional arrangements, there is a problem with both one and two-sided coating. The current density increases toward the edges of the band. As a result, an extremely high current density occurs at the strip edges, resulting in increased deposition of zinc. Therefore, in the edge region of the tape, the zinc layer is about 2 to 3 times thicker than the middle zinc layer.

Apart from the waste of metal and energy, this leads to problems in winding the belts and in subsequent processing. For this reason, the bands must be trimmed at the edges before winding very wide, which brings in addition to the considerable loss of material additional workload.

If the tape is to be coated on one side only with such an arrangement, further problems are added. If the anode of the strip side not to be coated is completely removed or replaced by a dummy anode (eg a plastic plate), not only edge teasing on the side to be coated, but also edge tedding occurs as a result of encompassing the current flow on the side not to be coated.

If the anode is merely switched off electrically on the side not to be coated, it is also possible for metal to be deposited on the side of the strip that is not to be coated. The reason for this is that of the opposite to the band wider anodes outside the band range current passes through the electrolyte to the switched-off anode and thus puts them under tension against the band.

To address these problems, so-called edge masks have already become known which, in the form of electrically insulating plates or foils, prevent the flow of current between the two anodes next to the strip.

The band edges comprise U-profiles arranged on the end faces of the electrically insulating plates. From the immersion depth of the strip edges in the U-profiles depends on the degree of Kantenaufzinkung. It is therefore necessary to always accurately track the U-Pofile the tape running. This requires a tape edge position measurement and complex edge mask drives with complicated measurement and control technology.

Another disadvantage of the edge masks is their susceptibility. For example, not smooth band edges or sudden width variations of the band can damage the edge masks. Expensive shutdowns and repairs are the result.

Finally, the edge masks require a minimum distance between the anodes to make them sufficiently stable.

Also, the edge masks do not solve the problem that the coating thickness across the width of the tape is a direct image of the cross profile of the tape. For example, if the tape has a transverse bow or other unevenness or imbalance between the anodes, this results in an uneven coating thickness. In order to avoid this undesired effect, the prior art coating processes are preceded by expensive draft-leveling equipment.

From CHEMICAL ABSTRACTS, vol.87, no.26, December 26, 1977, Columbus, Ohio, US; abstract 208626, TOYDA, TOSHIO ET AL: "Control of the thickness during electroplating of metal strip "XP 002060382 & JP 52 018 649 A (Nippon Steel Corp., JAPAN), a galvanic tinning plant for steel strip emerges, in which the anodes are divided longitudinally and individually supplied with power for controlling the layer thickness in the transverse direction of the steel strip.

Based on this prior art, the present invention seeks to provide an arrangement for electro-galvanic metal coating of the type mentioned above, the edge growths of the deposited metal safely prevented while avoiding the disadvantages of the arrangements with edge masks. In particular, a uniform metal coating should be ensured regardless of any Bandunplanheiten, a removal of the anode on a non-coated side superfluous and no moving parts in the anode area may be required.

In particular, this object is achieved in an arrangement of the type mentioned in that insulating materials arranged between the anode strips, the anode strips against each other and insulate that the insulating material protrude at least over the tape facing surface of each anode also in the electrolyte.

The arrangement according to the invention makes it possible, depending on the respective width of the strip to be coated, to supply only those anode strips with current which are located opposite the strip. For this purpose, the current band position can be determined with the existing tape position measuring system.

With the arrangement according to the invention, in particular, unplane tapes can advantageously also be coated by switching off the power supply of individual anode strips, which are closer to the strip surface than provided by the mean value of the distances.

As a result of the scattering effect of the adjacent anode strips, the tape is indeed further coated, but to a lesser extent. Weakened, this also applies to the next but one strip. As a result, switching off individual anode strips leads to a homogenization of the coating.

The insulating materials arranged between the anode strips, which protrude into the electrolyte at least beyond the surface of each anode facing the band, prevent a current transfer from a current-supplied anode strip to an unsupported anode strip. This has an advantageous effect, in particular in the band edge region, since the current flow is directed directly onto the strip surface and the usual high current density concentration is prevented in the state of the art. The individual anode strips are insulated from one another, for example, by insulating strips which project beyond the surface of the anodes formed by the anode strips in the direction of the electrolyte. The only a few millimeters into the electrolyte protruding insulating strip also prevent striking the tape.

If the anode strips are sufficiently narrow, the layer thickness can also be controlled by selecting the over or underfilling of the strip edges with the anode strips fed with current, for example dropping, uniformly or rising towards the strip edge.
The insulating strips projecting beyond the surface of each anode, with sufficiently narrow anode strips, protect the anode from tape stops, which can be caused by extremely unpleasant tapes or a decrease in the tension in the tape. The under current in conventional arrangements leading to high short-circuit currents and associated with severe damage to the anode surface band touches, be avoided in this embodiment of the invention therefore safe.

In order to counteract this risk even more effectively, the insulating strips are preferably made of wear-resistant and unbreakable material.

Another key advantage of the insulating strip projecting beyond the surface of each anode is that the electrolyte is guided parallel to or against the strip running direction. The uniform flow rate over the bandwidth results in a more uniform deposition of metal than in the known arrangements in which crossflows can occur, especially when the supply and / or removal of the flowing electrolyte into the anode area is not carefully performed.

In an advantageous embodiment of the invention, several anodes according to the invention are connected one behind the other in the running direction of the strip. Due to the individual control options of the anodes connected in series, the summation of the coating profile, which can be individually controlled with each individual anode, ensures an always uniform layer thickness.

The coating profile can be controlled particularly effectively by supplying current to the anode strips with the aid of a current regulator. The current regulator keeps the current level desired in each anode strip constant. Coulombic metal mass is directly proportional to the sum of currents according to Coulomb's law, so that the coating thickness can be precisely controlled (for example, one gram of zinc deposit requires 1.22 Ah).

Alternatively, the thickness of the coating can be controlled by having the anode strips of each anode over their length are divided several times and each anode strip part is preferably powered individually via a switch with power. For example, if the anode strip is divided 4-fold, each anode strip can be charged with 0%, 25%, 50%, 75%, and 100% current.

As a result, an adequately adequate layer structure is produced on the strip in the region of this part of the anode strip.

The invention is explained in more detail below with reference to schematic drawings and diagrams relating to the invention and to the prior art:

Figur 1:

Eine Anordnung zum elektrogalvanischen Beschichten von Bändern nach dem Stand der Technik ohne Kantenmasken,

Figur 2:

eine Anordnung zur elektrogalvanischen Beschichtung von Bändern nach dem Stand der Technik mit Kantenmasken,

Figur 3:

eine Darstellung der Schichtdicke bei unplanen Bändern am Beispiel eines Bandes mit Querbogen,

Figur 4:

ein Ausführungsbeispiel einer erfindungsgemäßen Anordnung zur elektrogalvanischen Metallbeschichtung,

Figur 5:

eine Darstellung zur Schichtdickensteuerung mit Hilfe einer erfindungsgemäßen Anordnung mit vier hintereinander geschalteten Anoden bei einseitiger Beschichtung sowie

Figur 6:

ein Diagramm zur Verdeutlichung des Schichtdickenausgleichs im Kantenbereich des Bandes.

Show it:

FIG. 1:

An arrangement for the electro-galvanic coating of strips according to the prior art without edge masks,

FIG. 2:

an arrangement for the electro-galvanic coating of strips according to the prior art with edge masks,

FIG. 3:

a representation of the layer thickness in unplaned tapes using the example of a strip with transverse bow,

FIG. 4:

An embodiment of an inventive arrangement for electro-galvanic metal coating,

FIG. 5:

a representation of the layer thickness control by means of an inventive arrangement with four successive anodes in one-sided coating and

FIG. 6:

a diagram illustrating the layer thickness compensation in the edge region of the tape.

FIG. 1 shows an arrangement for the electro-galvanic coating of a strip 2 running in an electrolyte 1. Parallel to the surfaces 2 a, 2 b of the strip 2, an upper and a lower anode 3 a, 3 b are arranged at a short distance. The width of the upper and lower anode 3a, 3b depends on the widest band to be coated. With a width of the band of, for example, 1850 mm, the anode width may be 2050 mm.

During the metal coating, current flows from the anodes 3a, 3b to the band 2 connected as a cathode. The zinc from the electrolytes 1 is deposited on the surfaces 2a, 2b.

In order to prevent the growth of zinc on the edges 2c, 2d of the strip 2, the prior art has proposed the arrangement of so-called edge masks 4, as shown in FIG. They consist of insulating plates 4a, 4b and the band edges 2c, 2d comprehensive U-profiles 4c, 4d.

From the immersion depth t of the band edges 2c, 2d, the degree of zincing depends. A drive for the edge mask 4, not shown in FIG. 2, guides the U-profiles 4c, 4d exactly to the course of the band edges 2c, 2d. This is associated with a high measurement and control effort.

Both the arrangement according to FIG. 1 and FIG. 2 have the disadvantage that the coating thickness over the width of the strip is a direct image of the transverse profile of the strip 2.

FIG. 3 illustrates this relationship using the example of an arcuate cross-section of the band 2, which is guided between an upper and a lower anode 3a, 3b.

The arrangement according to the invention in FIG. 4 consists of individual anode strips 5a, 5b, which are arranged both above and below the band 2 in the exemplary embodiment shown. The individual anode strips 5a, 5b are insulated from one another by insulating strips 6a, 6b which protrude in the direction of the electrolyte 1 over the surface of the anodes formed by the strips 5a, 5b.

The anode strips 5a, 5b each form a lower and an upper box-shaped anode, which at the same time form the flow channel for the electrolyte 1 with lateral closures, not shown in FIG.

By at least one of the lateral terminations of the flow channel for the electrolyte 1 is detachably formed, the entire arrangement can be replaced by lateral displacement with little time for repair and / or maintenance. Special coating cells are dispensable in such an embodiment.

In the exemplary embodiment, each individual anode strip 5a, 5b is connected via its own switch 8a, 8b to a central rectifier 7a, 7b which supplies it with current.

In FIG. 4 it can be seen that only those switches 8a, 8b are closed, to which anode strips 5a, 5b are assigned, which are located opposite the surface 2a, 2b of the strip 2.

Instead of the central rectifiers 7a, 7b, it is also possible to assign a separate rectifier to each individual anode strip, which is connected to the anode strip either via a switch or a current regulator.

The only a few millimeters into the electrolyte 1 projecting insulating strips 6a, 6b prevent a striking of the tape. 2

The representation in FIG. 5 assumes that four anodes designed according to the invention (FIG. 4) are arranged one behind the other in the direction of strip travel. In the embodiment, only a coating on the surface 2a of the belt 2 takes place. The anode strips 5b of the lower anode are all turned off.

In the left half of the picture, the wiring of the individual anode strips 5a can be seen; in the diagram to the right next to it, over the width of the band 2 on the surface 2a forming strength of the zinc layer.

The equalization by the summation of the applied layer thicknesses by the successive anodes can be clearly seen.

Finally, FIG. 6 shows a smoothing of the zinc layer in the edge region when passing through only two anodes connected in series with different wiring of the anode strips 5a, 5b in the edge region of the strip 2.

Claims (8)

1. An arrangement for the electrogalvanic metal coating of strips that pass through an acidic electrolyte enriched with metal, with at least one insoluble anode that is arranged parallel to the strip and from which the current flows to the strip that acts as the cathode, wherein metal from the electrolyte is deposited on the surface of the strip, and wherein each anode is divided into anode strips parallel to the moving direction of the strip and each anode strip is individually supplied with a current,
   characterized in

   - that insulating materials arranged between the anode strips (5a, 5b) insulate the anode strips relative to one another, and in

   - that the insulating materials protrude into the electrolyte (1) at least beyond the surface of each anode that faces the strip.
2. The arrangement for the electrogalvanic metal coating of strips according to Claim 1,
   characterized in
   that the anode is wider than any strip (2) to be coated in the arrangement.
3. The arrangement for the electrogalvanic metal coating of strips according to Claim 1 or 2,
   characterized in
   that the insulating materials are realized in the form of wear-resistant and fracture-proof strips (6a, 6b).
4. The arrangement for the electrogalvanic metal coating of strips according to one of Claims 1-3,
   characterized in
   that the anode strips (5a, 5b) have a width between 5-40 mm.
5. The arrangement for the electrogalvanic metal coating of strips according to one of Claims 1-4,
   characterized in
   that several anodes are connected in series in the moving direction of the strip (2).
6. The arrangement for the electrogalvanic metal coating of strips according to one of Claims 1-5,
   characterized in
   that each anode strip (5a, 5b) is individually supplied with a current by means of a switch (8a, 8b).
7. The arrangement for the electrogalvanic metal coating of strips according to one of Claims 1-5,
   characterized in
   that each anode strip (5a, 5b) is individually supplied with a current by means of a current regulator.
8. The arrangement for the electrogalvanic metal coating of strips according to one of Claims 1-7,
   characterized in
   that the anode strips (5a, 5b) of each anode are divided several times over their length and each anode strip section preferably is individually supplied with a current by means of a switch.

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