Method for producing a coated perforated steel strip

Abstract

The invention relates to a method for producing a metal-coated and perforated metal strip, wherein the metal strip and in particular sheet steel strip with a perforation or with a hole pattern is continuously electrolytically coated with one or more metals in an electrolytic coating device, wherein the current density during the coating of the sheet metal strip fulfils the following equation: current density < 58 + 110 / exp(1.3 ∗ x) measured in [A / dm²] where: x = D / a, where D is the largest in-circle diameter of the perforation in mm, a is the anode distance in mm; s is the sheet metal thickness in mm, where 0.4 ≤ s ≤ 2.5; x > 0.2 and wherein dendrite formation is avoided.

Description

[0001] Process for producing coated perforated steel strip

[0002] The invention relates to a method for producing coated perforated steel strip and the steel strip thus produced.

[0003] It is known to perforate steel strip before further processing, particularly with a hole pattern. The holes can be circular or take on any other shape, creating a hole pattern on the one hand or a grid on the other.

[0004] One application for such perforated steel strips is, for example, the cladding of noise barriers and the like. Since such noise barriers, as well as other outdoor applications, typically require protection from corrosion, steel sheets with an appropriate corrosion protection layer are often used for this purpose. The most commonly used corrosion protection layer is a zinc coating. Such zinc coatings are well-known and are applied either by electrolytic processes (ELO galvanizing) or via hot-dip galvanizing processes. ELO coatings are usually pure zinc coatings. In the hot-dip galvanizing process, alloys are typically used whose main element is zinc and which contain admixtures of aluminum, magnesium, or other elements.

[0005] When producing perforated sheets, strip-galvanized material is usually used, which is either electrolytically or hot-dip galvanized and then given the intended hole pattern by punching.

[0006] The disadvantage here is that, depending on the sheet thickness, little or no corrosion protection is provided on the punching surfaces. Furthermore, it is known to punch ungalvanized strip material, process it into blanks, and then galvanize the individual pieces. However, this has the disadvantage that small holes can become clogged. Furthermore, the sequence of punching, blank production, and piece galvanizing is expensive and complex.

[0007] Furthermore, it is conceivable to continuously coat such ungalvanized sheets with a hole pattern using the Sendzimir process, but such hot-dip galvanizing is fraught with major problems, since during hot-dip galvanizing, after passing through the zinc bath, stripping nozzles are usually used which use compressed air to strip off the adhering zinc to the desired thickness, which leads to turbulence in the area of ​​the holes and thus to uneven layer densities.

[0008] In the well-known Gravitel process, differences in layer thickness and dendrites at the edges of the holes are also to be expected because the current density becomes uneven due to the holes in the strip.

[0009] From DE19834759 Al a method is known for removing zinc dendrites, which form on the edges of a sheet metal strip during electrolytic galvanizing.

[0010] In “Dendritic zinc growth on the edges of flat steel strip during electro galvanizing,” LN Bengoa, S Bruno, HA Lazzarino, PR Serea, WA Eglia; International Congress of Science and Technology of Metallurgy and Materials, SAM CONAMET 2013; dendrite growth at the edges is also treated.

[0011] GB 1325933 Al describes a PVD coating process for metal meshes. In this process, a strip is guided horizontally through a PVD coating chamber. The walls of the coating chamber run close to the strip to minimize losses.

[0012] The coating material is only evaporated on the underside, but the strip should be homogeneous and evenly coated on both the top and bottom sides. This is only achievable, however, if the hole area / total area ratio is < 1 (in the projection perpendicular to the strip), i.e. the holes make up the majority. For this, a hole area / total area ratio of > 0.8 is required. It is also stated that electrochemical pre-cleaning before evaporation is sufficient. The coating layer thickness should be regulated by the strip speed or the strip temperature. Both methods have significant weaknesses. For higher layer thicknesses, the strip speed must be reduced, which also reduces productivity. If the strip temperature is changed, the layer formation (morphology) changes, and a higher strip temperature leads to higher vapor densities and leaks.

[0013] US Pat. No. 5,059,455 B discloses a process for hot-dip galvanizing perforated steel strip. In this process, a steel strip with a low perforation area, namely less than 23%, is subjected to a post-coating process. With this comparatively low perforation area, the strip can be coated under similar conditions to an unperforated steel strip. In a post-treatment step, the cut burr is re-rolled.

[0014] EP 1479 474 B1 discloses a method for galvanizing a metallic flat material. First, holes are punched into the flat material, then the material is hot-dip galvanized and cut to length. Finally, after galvanizing, serrations are rolled onto the flat material.

[0015] The object of the invention is to provide a method for producing perforated metal strips, in particular steel strips, which enables corrosion protection even in the area of ​​the hole edges and can be carried out economically, ie with a comparatively high deposition rate.

[0016] The problem is solved by a method having the features of claim 1.

[0017] Advantageous further training is indicated in the dependent subclaims.

[0018] A further object of the invention is to provide a perforated metal strip, in particular a steel strip, which has corrosion protection even in the area of ​​the hole edges.

[0019] The problem is solved with a metal band having the features of claim 20.

[0020] Advantageous further training is indicated in the dependent subclaims.

[0021] The inventors recognized that a uniform distribution of the coating of zinc and, if necessary, other metals, especially the coating of the punched edges, is necessary. This should combine minimal deviations and a good surface finish with excellent coating quality.

[0022] This can be achieved using a process in which a perforated steel strip, including expanded metal or long blanks, is coated in a continuous electrolytic galvanizing process. The maximum current density is adjusted depending on the geometry of the hole pattern. This means that the current density is variably adjusted depending on the perforation pattern.

[0023] Typically, perforated sheets are not electrolytically galvanized because of a number of disadvantages.

[0024] On the one hand, in electrolytic galvanizing processes, the strip is pulled through a system with numerous deflection rollers and / or squeezing rollers, which requires a certain minimum strip tension. However, due to the reduced strip cross-section of perforated sheets, this is problematic, as the sheet can tear.

[0025] Furthermore, it is known that the edge effect on sheet metal causes dendrites to grow on the edges during coating, which must be removed from the longitudinal edges of the strip after ELO coating. The effort required to do this at the hole edges has so far prevented coating using the ELO process.

[0026] It was discovered that a conventional electrolytic coating process cannot be readily applied to sheets with perforated areas. It was found that coating a conventional perforated sheet with conventional equipment parameters either leads to the sheet tearing and / or damage to equipment components, such as current rollers.

[0027] For this reason, the operation of the system must be adapted to a perforated sheet in such a way that, on the one hand, the load-bearing capacity (= residual tensile strength) of the strip is taken into account and, on the other hand, the speed of the coating is throttled to a previously determined level in order to prevent damage to the system.

[0028] It has been found that speeds between 5 m / min and 120 m / min, especially between 10 m / min and 50 m / min, are well suited for this purpose.

[0029] Another aspect plays a role here. In electrolytic processes, the strip must also be dried after contact with the liquids. As expected, drying perforated strips is technically more complicated because a lot of liquid remains along the edges due to surface tension, and the edge length per square meter is much higher for a perforated strip. If a perforated strip is to be dried and a conventional system is used for this, good drying of the strip, and in particular the edges, is also possible on conventional systems at such belt speeds if non-opposing air knife nozzles and convection dryers are used, blowing perpendicularly or obliquely onto the strip. The air knife nozzles can preferably have an angle of 20° to 70° to the normal to the strip.

[0030] Preferably, the volume fraction of the hole pattern is at least 30%. This results in a volume fraction of the remaining sheet metal of less than 70%. This can be particularly advantageous for applications involving components for thermal regulation, such as thermal management for agricultural machinery, which still need to provide protection against external damage, as well as for applications in the field of sound insulation.

[0031] Here, the volume fraction of the perforation pattern can advantageously be more than 50% or even more than 70%. The volume fraction of the perforation pattern in % within the meaning of the invention is 100*(l - volume after perforation / volume before perforation).

[0032] It was recognized that the geometry of the hole pattern plays an essential role in setting the current density, which must be chosen to avoid dendrite formation

[0033] Surprisingly, the inventors discovered that the maximum current density that can be applied during coating depends essentially on the largest perforation (i.e., the largest inner diameter of the perforation) and less on the total punched volume. This means that, for example, a strip with a high volume fraction of the hole pattern with small perforations can be coated with a higher current density than a strip with a single, comparatively large perforation.

[0034] To avoid dendrite formation, the following relationship must be fulfilled depending on the hole pattern:

[0035] Current density < 58 + 110 / exp(l,3 * x) measured in [A / dm 2 ] where: x = D / a and largest inscribed diameter of the perforation D in mm,

[0036] Anode spacing a in mm is valid for x > 0.2. The metal strip or metal sheet strip has a metal sheet thickness s of 0.4 mm to 2.5 mm. This can be advantageous for mechanical stability and allows for an efficient coating process, even in the perforation walls.

[0037] To avoid dendrite formation, the largest inner diameter is the relevant influencing factor for the maximum average current density. Maximum average current density in the sense of the invention is the current intensity per cathode area which is set in order to electrolytically apply a coating to the steel strip.

[0038] The range of validity arises from the fact that x cannot be chosen arbitrarily small. Theoretically, a value for x of, for example, 0.1 is possible if D is very small and a is very large, e.g., with a maximum inner diameter of 1 mm and a 10 mm anode spacing. However, such a small hole pattern would be very difficult to coat and could potentially cause other difficulties. Therefore, according to the invention, the range of validity is restricted to x > 0.2. Preferably, the range of validity is restricted to x > 0.5.

[0039] The anode spacing a is the smallest distance between the anode surface and the sheet surface. The anode spacing is between 1 mm and 50 mm, preferably between 7 mm and 12 mm.

[0040] In order to make the coating more efficient and increase the speed of galvanizing, it may be advantageous to choose the current density using the following relationship:

[0041] Current density > 35 + 110 / exp(l,3 * x) in [A / dm 2 ].

[0042] This can be advantageous for the deposition rate and thus the possible strip speed through the galvanizing plant.

[0043] In order to make the coating process more efficient, it can be advantageous if the electrolyte has a zinc content of 50 to 150 g / L, preferably 110 to 130 g / L. In addition, sodium between 20 and 40 g / L, preferably 25 and 30 g / L, can be added as a conductive salt. This can be present as sulfate in sulfuric acid electrolyte at a pH of 1.2 to 1.9, preferably 1.4 to 1.6. The electrolyte temperature can be between 55 and 65°C, preferably between 56 and 59°C, and thus ensure a conductivity of 100 to 180 mS / cm, preferably 150 to 170 mS / cm, at room temperature. Perforated walls can be coated particularly advantageously if the perforations have an inscribed circle diameter of 0.4 to 50 mm, in particular 1 to 20 mm. This inscribed circle diameter can in particular correspond at least to the sheet thickness.

[0044] In the sense of the invention, the inscribed circle diameter corresponds to the inner diameter or is the circle diameter of the largest possible inscribed circle that could be drawn into the perforation. For circular perforations, this corresponds to the circle diameter; for perforations that have, for example, elliptical or rectangular shapes, this is the fictitious circle diameter of the largest possible inscribed circle that could be drawn into the perforation. Thus, the terms "inner diameter" and "inscribed circle diameter" are used synonymously.

[0045] A hole pattern within the meaning of the invention can comprise a wide variety of patterns, which can be repeating similarly to a repeat pattern, as well as having unperforated areas longitudinally and / or transversely to the tape direction, which are provided, for example, for mechanical requirements (stability, rigidity) or for subsequent processing operations (e.g., bending). Furthermore, it should be noted here that the terms "hole" and "perforation" are used interchangeably within the meaning of the invention.

[0046] The volume fraction of the hole pattern can in particular also be less than 70%, in particular less than 60% and in particular less than 50%, so that in the case of a hole pattern with round holes with a hole spacing of 7 mm and a hole radius of 2.5 mm in a hexagonal arrangement with a sheet thickness of 2 mm, for example, the volume fraction of the hole pattern is approximately 46%.

[0047] A suitably perforated metal strip can be produced in a separate plant and then delivered to the coating plant.

[0048] However, it is also advantageously possible to implement an inline process, particularly in the steelworks, whereby the metal strip is first continuously punched or perforated to create the desired hole pattern. The strip can then be fed to a pretreatment station for cleaning and / or pickling. In particular, the hole edges can also be treated, for example, by sandblasting. The strip can then enter the coating process, where it is subsequently continuously electroplated inline.

[0049] The inline process offers several advantages. First, the punching waste is generated before coating. The uncoated punching waste can be directly reused as steel scrap in the steel mill. Furthermore, transport routes are short. Another advantage of the inline process is that the resulting surfaces are less aged. This eliminates the need to remove corrosion products from the uncoated metal sheet during storage and / or transport. Furthermore, the pretreatment of slightly oxidized or non-corroded surfaces can be carried out comparatively more efficiently.

[0050] With the invention, a layer thickness ratio of 0.9 can be achieved. This is achieved by setting the ratio of inscribed circle diameter D to sheet thickness s to greater than 6.

[0051] A layer thickness ratio is the minimum layer thickness in the area of ​​the hole wall (s w) to the average layer thickness in the area outside the holes (see above).

[0052] This is advantageous in cases of increased corrosion requirements or a comparatively low layer thickness, since 90% of the layer thickness can also be ensured in the area of ​​the perforated wall.

[0053] However, it has also been shown that even with a thinner layer thickness in the center of the hole wall, corrosion does not occur earlier, since the corrosive attack begins at the edges and does not occur first in the center of the wall. In thin sheets and relatively large holes, the minimum layer thickness at the hole walls can even be greater than the average layer thickness in the area outside the holes due to the peak effect of the edges.

[0054] The layer thickness of the metallic coating can be easily adjusted to thicknesses ranging from 2.5 pm to 50 pm, particularly from 4 pm to 20 pm per strip side surface, allowing even relatively thick coatings to be deposited. This is particularly advantageous in construction applications, where high levels of corrosion protection are often required.

[0055] With the invention, an ideal coating of the hole edges is achieved with an adapted operating mode and in particular with a tensile force limitation on the one hand or with a corresponding throttling of the strip speed on the other hand, so that comprehensive corrosion protection of a perforated sheet is achieved, which is also made possible in an economical process.

[0056] Surprisingly, dendrite formation does not occur despite the comparatively high current density. It has proven advantageous to limit the tensile force on the strip according to the residual cross-section such that, where the strip is flat, the maximum tensile stress does not exceed 70%, preferably 50%, of the strip's yield strength.

[0057] Advantageously, the strip is coated using a galvanic system consisting of 2 to 50 coating cells. This means that a system with just two coating cells is already sufficiently capable of ensuring the coating of perforated sheets according to the invention. However, by increasing the number of coating cells, the current density can be reduced at the same strip speed. This advantageously allows for thicker coatings, as already mentioned above, or higher strip speeds to be realized without defects.

[0058] The invention thus relates to a method for producing metallically coated and perforated metal strip, wherein the metal strip, in particular a steel sheet strip, is continuously electrolytically coated with one or more metals in an electrolytic coating device with a periodic hole pattern comprising at least two perforations, characterized in that the current density during the coating of the metal sheet strip satisfies the following relationship:

[0059] Current density < 58 + 110 / exp(l,3 * x) measured in [A / dm 2 ]where x = D / a , where

[0060] D is the largest inscribed diameter of the perforation in mm, a is the anode distance in mm; s is the metal sheet thickness in mm, where

[0061] 0.4 < s < 2.5; x > 0.2, while avoiding dendrite formation. The advantage here is that, on the one hand, the minimum thickness of 0.4 mm ensures sufficient mechanical rigidity and stability, and, on the other hand, a reliably uniform coating can be achieved at such thicknesses. From 2.5 mm, uneven coating of the walls and undesirable edge effects are possible.

[0062] A further development provides that the largest inscribed circle diameter D is set larger than the metal sheet thickness s, so that D > s. This can enable a robust punching process and provide the perforations to be produced easily and reliably.

[0063] A further development provides that the speed of the metal strip is adjusted by the coating device between 5 m / min and 120 m / min, in particular between 10 m / min and 50 m / min.

[0064] The advantage here is that such belt speeds allow good drying of the belt and especially of the edges even on conventional systems, whereby offset air knife nozzles and convection dryers are common.

[0065] A further development provides for the anode spacing (a) in the coating device to be set between 1 mm and 50 mm, preferably between 7 mm and 12 mm. It is advantageous that the anode spacing is at a certain distance from the strip; at a spacing of less than 1 mm, there is a risk of the strip touching the anode, which can cause damage. At a spacing of more than 50 mm, the energy loss due to the electrolyte resistance becomes too high.

[0066] A further development provides for the metal strip to be coated with one, several, or all elements from the group of zinc, tin, manganese, chromium, copper, nickel, iron, or an alloy comprising at least two elements from the group. Zinc is particularly advantageous in this case, as it can provide comparatively high corrosion protection at a low cost.

[0067] A further development provides for the coating composition to be adjusted so that it contains more than 90 mass percent, in particular more than 95 mass percent, zinc. A further development provides for the coating to be applied with a layer thickness of 2.5 μm to 50 μm, preferably 4 μm to 20 μm, per strip side surface. This is advantageous because even thick coatings can be deposited that meet the high corrosion protection requirements, even in the construction sector.

[0068] A further development provides that the layer thickness of the inner wall of at least one perforation (Sw) and the layer thickness of the surface in the area outside the perforation (s0) are adjusted in such a way that s w > 0.9 s0, where D / s > 6 is chosen.

[0069] The advantage here is that a high deposition rate in the wall can be ensured by selecting the inscribed diameter of the perforation in relation to the sheet thickness, i.e. with a ratio of D / s > 6. This means that, for example, with a layer thickness s o With an average thickness of 10 pm outside the holes, at least 9 pm can be ensured as the minimum value of the coating thickness Sw in the hole wall. This can ensure particularly high corrosion protection and high uniformity across the entire strip.

[0070] A further development provides for the metal strip to be coated with a galvanic system consisting of 2 to 50 coating cells.

[0071] The advantage here is that by increasing the number of coating cells, the current density can be reduced, which means that thicker layers or higher belt speeds can be achieved without errors.

[0072] A further development proposes that the perforation reduces the volume of the metal strip by at least 70%. This has the advantage that even comparatively high punching volumes can be processed while still being reliably coated. This can also be advantageous for applications in thermal management or noise protection, as the greatest possible permeability of the steel sheet can be advantageous in these cases.

[0073] A further development proposes that the remaining volume fraction of the metal strip be more than 20%. This is advantageous because it ensures mechanical stability.

[0074] A further development provides that the current density satisfies the following relationship: Current density > 35 + 110 / exp(l,3 * x) , measured in [A / dm 2 ].

[0075] This can be advantageous for the deposition rate and thus the possible maximum strip speed through the galvanizing plant.

[0076] A further development provides that the largest inscribed diameter of the perforation D is set such that it is between 0.4 mm and 50 mm, in particular 1 mm and 20 mm, and particularly preferably 2.5 mm and 15 mm. This has the advantage that, if the minimum hole size is exceeded, a sufficient amount of coating can be present in the hole walls, yet dendrite formation cannot occur at the edges. Choosing an excessively large hole size can negatively impact mechanical stability.

[0077] A further development provides that either rolled cold-rolled strip or annealed cold-rolled strip or pickled hot-rolled strip is used as the metal strip and is cleaned before coating.

[0078] A further development provides for the metal strip to be pretreated with alkali and / or blasted.

[0079] A further development provides for the metal strip to be post-treated after coating. In particular, the post-treatment can include the steps of oiling, passivation, and / or phosphating in any combination.

[0080] The advantage here is that the perforation allows comparatively more oil, such as prelube, to be applied to the non-perforated areas during a lubrication step, for example, by spraying. This means that these areas, which will later be beveled, can contain more oil, which can facilitate this post-processing.

[0081] The phosphating step is particularly advantageous because it takes place up to a certain layer thickness and the process stops automatically when this height is reached, so this step can be particularly advantageous for perforated belts.

[0082] A further development provides that the post-treatment includes the steps of oiling and / or passivating and / or phosphating in any combination.

[0083] This also makes it possible to combine post-treatment steps. For example, combining phosphating and passivation, or phosphating and oiling, is particularly beneficial with regard to paint adhesion and corrosion protection. A further development involves continuously punching or perforating the metal strip to create the desired hole pattern, followed by continuous inline electroplating. The advantage here is that the punching waste is generated before the coating process and can be recycled directly in the steel mill.

[0084] A further development provides for the use of a steel strip with the following composition (all data in mass%):

[0085] Carbon up to 0.70, preferably 0.002 to 0.30;

[0086] Silicon up to 1.9, preferably up to 1.5;

[0087] Manganese up to 3.0, preferably 0.04 to 2.5;

[0088] Chromium up to 1.5, preferably up to 0.9;

[0089] Molybdenum up to 2.0, preferably up to 0.1;

[0090] Nickel up to 2.0, preferably up to 0.15;

[0091] Titanium up to 0.2 preferably up to 0.12

[0092] Vanadium up to 0.2, preferably up to 0.02;

[0093] Tungsten up to 0.2, preferably up to 0.02;

[0094] Aluminum up to 2.0, preferably 0.20 to 0.70;

[0095] Boron up to 0.01, preferably up to 0.005;

[0096] Sulphur up to 0.1, preferably up to 0.04;

[0097] Phosphorus up to 0.3, preferably up to 0.1;

[0098] Nitrogen up to 0.02, preferably up to 0.01;

[0099] Rest iron and smelting-related impurities.

[0100] It is advantageous that the steel material is a comparatively low-alloy steel material, which on the one hand can have good punchability and on the other hand can have sufficient galvanization properties.

[0101] A further aspect of the invention relates to a metal strip, in particular produced according to the above-mentioned method, characterized in that the metal strip is an electrolytically coated steel strip and has a periodic hole pattern comprising at least two perforations, wherein the layer thickness of the electrolytic coating on the inner wall of at least one perforation (Sw) and the layer thickness of the electrolytic coating on the surface in the area outside the perforation (s0) satisfy the following ratio: Sw > 0.9 s0, where D / s > 6. A further development provides that the metal strip or the steel strip has the following composition:

[0102] Carbon up to 0.70, preferably 0.002 to 0.30;

[0103] Silicon up to 1.9, preferably up to 1.5;

[0104] Manganese up to 3.0, preferably 0.04 to 2.5;

[0105] Chromium up to 1.5, preferably up to 0.9;

[0106] Molybdenum up to 2.0, preferably up to 0.1;

[0107] Nickel up to 2.0, preferably up to 0.15;

[0108] Titanium up to 0.2 preferably up to 0.12

[0109] Vanadium up to 0.2, preferably up to 0.02;

[0110] Tungsten up to 0.2, preferably up to 0.02;

[0111] Aluminum up to 2.0, preferably 0.20 to 0.70;

[0112] Boron up to 0.01, preferably up to 0.005;

[0113] Sulphur up to 0.1, preferably up to 0.04;

[0114] Phosphorus up to 0.3, preferably up to 0.1;

[0115] Nitrogen up to 0.02, preferably up to 0.01;

[0116] Rest iron and smelting-related impurities.

[0117] The invention is explained by way of example with reference to a drawing. It shows:

[0118] Figure 1: A schematic hole pattern;

[0119] Figure 2: Micrographs of a hole edge including the surrounding material in the coated state;

[0120] Figure 3: The representation according to Figure 2 in enlarged form;

[0121] Figure 4: A table with test results;

[0122] Figure 5: A metal strip coated according to the invention wound into a coil;

[0123] Figure 6: A close-up view of an exemplary coated according to the invention

[0124] Hole pattern; Figure 7: A representation of the hole pattern from Figure 6 in the production line;

[0125] Figure 8: A close-up view of an exemplary hole pattern coated according to the invention;

[0126] Figure 9: Four exemplary hole patterns with and without dendrites;

[0127] Figure 10: A diagram showing the maximum current density;

[0128] Figure 11: An example representation for determining the inscribed circle diameter;

[0129] Figure 1 shows a highly schematic representation of an exemplary hole pattern, in this case a hexagonal hole structure with hole spacing a=7 mm, hole radius r=2.5 mm; the sheet thickness s is 0.9 mm. The total coated area F including the hole walls is approximately 70% compared to the area Fo of a sample without holes, because:

[0130] The smallest cross-section of the punched sheet in relation to the cross-section of the unpunched sheet is (a-2r) / a, i.e. 2 / 7.

[0131] In Figures 2 and 3, the micrographs shown show the coating of the surface and the hole edges of the above-mentioned band with the hole pattern mentioned.

[0132] As you can see, the coating is very even with no defects and no strong differences in thickness.

[0133] Figure 4 shows a table with 9 tests with different hole patterns as well as different largest inscribed circle diameters D from 4 to 90 mm and different selected distance anode to sheet a.

[0134] The ratio x was calculated in each case, and the maximum current density was determined. The actual current density used is shown next to it. The zinc coating was then qualitatively assessed and examined for dendrite formation.

[0135] It can be seen that no dendrite formation occurred at a current density below the current density limit. However, at a current density that was too high (as in experiments 3, 4, and 6), strong dendrite growth was clearly visible. This can also be clearly seen in Figure 9, bottom left and bottom right.

[0136] The table clearly shows that the absolute value of the current density is not the only decisive factor, but rather depends on the ratio D / a. For example, the current density used in Experiment 3 was 79 A / dm 2 and led to dendrites, in experiment 5 it was 80 A / dm 2 i.e. a higher value, which in itself is more likely to lead to dendrites, but this was not a problem due to the selected hole pattern and anode spacing.

[0137] Figures 5 to 7 show example hole patterns from or in production. Figure 6 shows a hole pattern Qg 10-15; this means a square row with a side length of 10 mm for the square holes and a distance of 15 mm from hole center to hole center, resulting in a web width of 5 mm between the holes. "Row" means that in this example, these holes are arranged in a line and not offset. The sheet thickness s was 2 mm. The inscribed circle diameter D is therefore also 10 mm.

[0138] Figure 6 shows another example hole pattern. A 1.5 mm thick sheet was used here. It shows circular holes with a 5 mm diameter, arranged offset. The hole pattern is an Rv 5-8, i.e., 5 mm hole diameter with 8 mm hole spacing. The web width is therefore 3 mm. In this example, the holes are round and arranged offset in a hexagonal pattern. For this example, this means D = 5 mm, s = 1.5 mm.

[0139] The strip is galvanized and post-treated, in this case phosphated.

[0140] Figure 7 shows an image of the perforated strip in the electrolytic coating line with the same pattern as in Figure 6.

[0141] This makes it possible to effectively coat even perforated belts.

[0142] Figure 8 shows an edge coated according to the invention in a perforation directly at the punched edge of the perforation. It shows the steel sheet (1), an electrolytically deposited zinc layer (2) on top of it, and on top of that a lacquer layer (3), which was optionally applied after the galvanizing step.

[0143] The punch burr on the steel strip is clearly visible; this is almost unavoidable during production. The invention advantageously demonstrates that the zinc layer adheres particularly well to the punch burr, meaning that this particularly exposed area is galvanized with a comparatively thick layer of zinc. This is even more evident if the steel strip is subsequently painted in an optional process step, since this layer adheres comparatively thinly to this edge, which would therefore represent a weak point.

[0144] Figure 10 shows the formula for determining the maximum average current density across the selected hole pattern. Applying a current density below the curve can prevent dendrite formation.

[0145] Figure 11 shows an example of how the inscribed circle diameter is determined. It is the diameter of the largest circle that lies entirely within the punched area. For the example perforation pattern shown in Figure 11, which in this case represents a type of offset double hole, the largest inscribed circle diameter is determined by inscribing the largest possible circle into the pattern. In Figure 11, this corresponds to one of the two hole diameters of the double hole, thus resulting in D for the entire perforation.

Claims

Claims 1. A method for producing metallically coated and perforated metal strip, wherein the metal strip, in particular a steel sheet strip, is continuously electrolytically coated with one or more metals in an electrolytic coating device with a periodic hole pattern comprising at least two perforations, characterized in that the current density during the coating of the metal sheet strip satisfies the following relationship: Current density < 58 + 110 / exp(l,3 * x) measured in [A / dm 2 ]where x = D / a , where D is the largest inscribed diameter of the perforation in mm, a is the anode distance in mm; s is the metal sheet thickness in mm, where 0.4 < s < 2.5; x > 0.2 and avoiding dendrite formation.

2. Method according to claim 1, characterized in that the largest inscribed circle diameter D is set larger than the metal sheet thickness s, so that D > s.

3. Method according to claim 1 or 2, characterized in that the speed of the metal strip is adjusted by the coating device between 5 m / min and 120 m / min, in particular between 10 m / min and 50 m / min.

4. Method according to one of the preceding claims, characterized in that the anode distance (a) in the coating device is set between 1 mm and 50 mm, preferably between 7 mm and 12 mm.

5. Method according to one of the preceding claims, characterized in that the metal strip is coated with one element, several or all elements from the group of zinc, tin, manganese, chromium, copper, nickel, iron or an alloy comprising at least two elements from the group.

6. Method according to one of the preceding claims, characterized in that the coating composition is adjusted such that it comprises more than 90 mass percent, in particular more than 95 mass percent, of zinc.

7. Method according to one of the preceding claims, characterized in that the coating is applied with a layer thickness which is 2.5 pm to 50 pm, preferably 4 pm to 20 pm, per strip side surface.

8. Method according to one of the preceding claims, characterized in that the layer thickness of the inner wall of at least one perforation (s w ) and the layer thickness of the surface in the area outside the perforation (s0) are adjusted such that s w > 0.9 s0, where D / s > 6 is chosen.

9. Method according to one of the preceding claims, characterized in that the metal strip is coated with a galvanic system consisting of 2 to 50 coating cells.

10. Method according to one of the preceding claims, characterized in that the volume of the metal strip decreases by at least 70% due to the perforation.

11. Method according to claim 10, characterized in that the remaining volume fraction of the metal strip is more than 20%.

12. Method according to one of the preceding claims, characterized in that the current density satisfies the following relationship: Current density > 35 + 110 / exp(l,3 * x), measured in [A / dm 2 ].

13. Method according to one of the preceding claims, characterized in that the largest inscribed circle diameter of the perforation D is set such that it is between 0.4 mm and 50 mm, in particular 1 mm and 20 mm, particularly preferably 2.5 mm and 15 mm.

14. Method according to one of the preceding claims, characterized in that either rolled cold strip or annealed cold strip or pickled hot strip is used as the metal strip and is cleaned before coating.

15. Method according to one of the preceding claims, characterized in that during the pretreatment the metal strip is pretreated with alkali and / or blasted.

16. Method according to one of the preceding claims, characterized in that the metal strip is post-treated after coating.

17. The method according to claim 16, characterized in that the post-treatment comprises the steps of oiling and / or passivating and / or phosphating in any combination.

18. Method according to one of the preceding claims, characterized in that the metal strip is continuously punched or perforated to produce the desired hole pattern and is then continuously electrolytically coated inline.

19. Method according to one of the preceding claims, characterized in that the metal strip used is a steel strip with the following composition (all data in mass%): Carbon up to 0.70, preferably 0.002 to 0.30; Silicon up to 1.9, preferably up to 1.5; Manganese up to 3.0, preferably 0.04 to 2.5; Chromium up to 1.5, preferably up to 0.9; Molybdenum up to 2.0, preferably up to 0.1; Nickel up to 2.0, preferably up to 0.15; Titanium up to 0.2 preferably up to 0.12 Vanadium up to 0.2, preferably up to 0.02; Tungsten up to 0.2, preferably up to 0.02; Aluminum up to 2.0, preferably 0.20 to 0.70; Boron up to 0.01, preferably up to 0.005; Sulphur up to 0.1, preferably up to 0.04; Phosphorus up to 0.3, preferably up to 0.1; Nitrogen up to 0.02, preferably up to 0.01; Rest iron and smelting-related impurities.

20. Metal strip, in particular produced by a method according to one of claims 1-19, characterized in that the metal strip is an electrolytically coated steel strip and has a periodic hole pattern comprising at least two perforations, wherein the layer thickness of the electrolytic coating on the inner wall of at least one perforation (Sw) and the layer thickness of the electrolytic coating on the surface in the area outside the perforation (s0) satisfy the following ratio: s w > 0.9 s0, where D / s > 6.

21. Metal strip according to claim 20, characterized in that the metal strip is a steel strip and has the following composition: Carbon up to 0.70, preferably 0.002 to 0.30; Silicon up to 1.9, preferably up to 1.5; Manganese up to 3.0, preferably 0.04 to 2.5; Chromium up to 1.5, preferably up to 0.9; Molybdenum up to 2.0, preferably up to 0.1; Nickel up to 2.0, preferably up to 0.15; Titanium up to 0.2 preferably up to 0.12 Vanadium up to 0.2, preferably up to 0.02; Tungsten up to 0.2, preferably up to 0.02; Aluminum up to 2.0, preferably 0.20 to 0.70; Boron up to 0.01, preferably up to 0.005; Sulphur up to 0.1, preferably up to 0.04; Phosphorus up to 0.3, preferably up to 0.1; Nitrogen up to 0.02, preferably up to 0.01; Rest iron and smelting-related impurities.

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