Method for producing a coated perforated steel strip

Abstract

The invention relates to a method for producing perforated metal strips having a metallic coating, wherein metal strips and in particular steel sheet strips with a perforation or a hole pattern are fed to a coating device and are passed through the latter, in which the sheet metal strip is continuously PVD-coated with a vapor stream.

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 either pure zinc coatings applied using the electrolytic dipping process (ELO galvanizing) or hot-dip galvanizing (hot-dip galvanizing). In the hot-dip galvanizing process, alloys based on zinc are typically used, but with admixtures of aluminum, magnesium, or other elements.

[0005] In the production of corrosion-protected 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, there is little or no corrosion protection on the punching surfaces. It is also known to punch ungalvanized strip material, process it into blanks, and then galvanize it as a piece product. However, the disadvantage here is that perforations can become clogged beyond a defined minimum opening cross-section. 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. However, this hot-dip galvanizing process is fraught with significant problems, as it is only possible with relatively large hole diameters greater than 8 mm. Furthermore, after passing through the zinc bath, stripping nozzles are typically used during hot-dip galvanizing. These nozzles use compressed air to strip off the excess zinc to the desired layer thickness. In perforated strips, this treatment leads to turbulence in the area of ​​the holes, which results in uneven layer thickness and also impairs the opposing nozzles.

[0008] Similar disadvantages are to be expected with the well-known Gravitel process. The holes in the strip cause the current density and thus the layer thickness to become uneven, and dendrites form along the edges.

[0009] GB 1325933 Al describes a PVD coating process for metal mesh. In this process, a strip is guided horizontally through a PVD coating chamber. The walls of the coating chamber run very close to the strip to keep losses to a minimum. The coating material is only evaporated on the underside, but the strip should be coated homogeneously and equally 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 / recesses 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 vacuum coating is sufficient. The thickness of the coating should be regulated by the strip speed or the strip temperature. Both methods have significant weaknesses and limit the coating options.For higher layer thicknesses, the belt speed must be reduced, which also reduces the productivity of the process. When the belt temperature changes, the layer formation (morphology) changes, the layer adhesion deteriorates, and a higher belt temperature leads to further process-related problems.

[0010] DE 2526036 C2 discloses a PVD process for applying pyrolytic carbon to carbon structures.

[0011] The object of the invention is to provide a method for producing coated perforated steel strips, which in particular enables corrosion protection also in the area of ​​the hole edges and hole surfaces.

[0012] The problem is solved by a method having the features of claim 1.

[0013] Advantageous further developments are characterized in the dependent subclaims. The inventors have recognized that a uniform distribution of the coating, made of zinc or zinc alloys and optionally other metals, is necessary, particularly a coating of the punched edges and surfaces. This should combine minimal layer thickness deviations and a good surface finish with excellent layer quality.

[0014] The problem is solved with a process in which a perforated steel strip, including expanded metal or long blanks, is coated using a PVD process in a continuous flow PVD coating chamber. It was discovered that, using a plasma evaporator, the particle density in the PVD chamber can be adjusted by adapting the plasma parameters for coating the perforated strip. The particle flow is a function of the metal vapor density, and the quotient of (layer thickness at the punching surface) / (average layer thickness in the unpunched area) can be between 0.4 and 1.2.

[0015] According to the invention, it was found that a plasma evaporator enables a well-controllable evaporation rate and thus a high metal vapor density, whereby the particles have a high kinetic energy, so that this combination enables a uniform and efficient coating of the punching surfaces and punching edges in the continuous process.

[0016] It was found that both a horizontal strip run through a PVD chamber and a vertical strip run through a PVD chamber are possible.

[0017] With vertical strip travel, the process can be carried out in two stages, so that the strip is first guided in one direction, for example upwards, then deflected outside the coating chamber and finally guided downwards in order to achieve a symmetrical coating of both the punched and unpunched surfaces.

[0018] In addition, guide devices can be provided which, for example, regulate and direct the steam flow via baffles in order to avoid unfavorable layer thickness distributions.

[0019] In addition, an electrical potential difference in the range of 10 to 500 volts can be applied to the substrate, e.g., the metal strip, relative to the chamber wall via an external electrical circuit, allowing the local vapor flow to be influenced specifically in the area around the substrate to be coated. The total surface area of ​​the perforated sheet, the desired average layer thickness, and the vaporization enthalpies of the coating materials result in a plasma power proportional to the strip speed, which can be adjusted accordingly.

[0020] A hole pattern or perforation within the meaning of the invention can comprise a wide variety of patterns which are repeating similar to a repeat, as well as having unperforated areas lengthwise and / or transversely to the strip direction, which are provided, for example, for mechanical requirements (stability, rigidity) or for later processing operations (e.g. bending).

[0021] A correspondingly perforated metal strip can be produced in a separate plant and then delivered to the coating plant or alternatively can be produced inline continuously in a punching plant upstream of the coating plant.

[0022] The PVD coating according to the invention allows perforated steel strip to be coated very efficiently, providing corrosion protection for the punching surface. Another advantage is that the punching waste can be returned directly to the manufacturing plant for reuse, without the need to remove an existing coating prior to reuse.

[0023] In addition, coating materials are possible that are difficult or impossible to deposit using hot-dip galvanizing or electrolytic galvanizing, since the PVD process generally allows for a wider range of coating materials.

[0024] Furthermore, it was discovered that a wide range of possible layer thicknesses, for example, from 0.1 pm to approximately 20 pm, is possible while simultaneously achieving optimal coating of the punched edge. Furthermore, the layer thickness can be regulated across the strip width, allowing both sides of the strip to be vapor-deposited with different thicknesses and different materials. Depending on the system configuration, multilayer coatings are also possible.

[0025] The method according to the invention provides for applying a steam stream to both sides of a strip in order to coat it on both sides or applying a steam stream to one side in order to coat only one side.

[0026] The ratio of the hole area to the projected total area can be selected to be less than 0.7, in particular less than 0.6, and in particular less than 0.5, so that for a hexagonal hole pattern with a hole spacing of 7 mm and a hole radius of 2.5 mm, for example, the projection results in a hole area to total area ratio of 0.46. To achieve a uniform coating, the chamber walls or the evaporator must be at least ten times the thickness of the tape away from the tape, or alternatively, the hole area ratios specified above must be maintained.

[0027] According to the invention, a vacuum-based pretreatment by means of plasma is carried out before the coating in a vacuum, regardless of any chemical pre-cleaning of the substrate that may have been carried out beforehand.

[0028] According to the invention, the layer thickness is controlled by the plasma power of the evaporator, with both the strip speed and the strip temperature being kept as constant as possible. The plasma power can be adjusted within very short time intervals, particularly within seconds or even faster.

[0029] How quickly the coating thickness can be changed in the longitudinal direction of the strip is essentially limited by the length of the coating chamber and the strip speed. To coat the strip evenly on both sides, guide devices are used for a horizontal strip run with an evaporator located on the underside to evenly coat both sides, or symmetrically arranged evaporators are used for a vertical strip run.

[0030] The invention thus relates in particular to a method for producing metallically coated and perforated metal strips, wherein metal strips and in particular steel sheet strips with a perforation or with a hole pattern are fed to a coating device and passed through this, in which the sheet strip is continuously PVD-coated with a metal vapor stream.

[0031] One embodiment provides for the metal strip to have a sheet thickness of 0.3 mm to 2.5 mm. This is advantageous because, on the one hand, sufficient mechanical rigidity and stability can be ensured, and, on the other hand, a reliably uniform coating can be achieved at such thicknesses. From 2.5 mm, there is a risk of uneven coating in the walls and along the edges.

[0032] One embodiment provides for the strip to be coated with one or more layers, wherein the coating layers consist of one, several, or all of the group consisting of metals, oxides, carbides, nitrides, and carbonitrides. Advantageously, the desired layers can be produced using PVD depending on the desired area of ​​application or corrosion protection. One embodiment provides for both sides of the strip to be coated with the same or different coatings. This has the advantage that, for example, in outdoor applications, the weather-exposed side can be provided with a raised layer layer. Alternatively, for indoor applications or where adhesive or welded joints are desired, one side of the strip can be coated with easily weldable / adhesive layers.

[0033] One embodiment provides for the strip to be coated with one, several, or all of the group consisting of zinc, magnesium, manganese, copper, chromium, aluminum, titanium, silicon, or alloys containing these elements or alloys of these elements as the main components. Main component within the meaning of the patent means that the element comprises the largest proportion of the coating alloy, preferably > 50%.

[0034] One embodiment provides for the layer thickness of the PVD coating to be 20 nm to 100 pm, preferably 100 nm to 50 pm, per strip side surface. This is advantageous because even thick coatings can be deposited that meet the high corrosion protection requirements, particularly in the construction sector. Another advantage is that comparatively very thin coatings can be deposited, thus achieving excellent adhesion without loss of hardness, distortion, or changes in the microstructure of the base material.

[0035] One embodiment provides for the coating thickness ratio of the strip side surface to the perforation walls to be between 0.4 and 1.2, preferably between 0.6 and 0.9. The advantage here is that such a ratio is absolutely sufficient for good corrosion protection, since the corrosive attack begins at the edges and does not occur first in the center of the wall. Therefore, the inventors recognized that a layer thickness ratio of approximately 0.4 can already provide sufficient protection.

[0036] One embodiment provides that the particle flow in the coating chamber is directed onto the belt using guide devices.

[0037] One embodiment provides that the guide devices are mechanical guide plates or electromagnetic guide devices.

[0038] One embodiment provides for the coating thickness to be measured and the guide devices to be controlled to achieve a desired coating thickness and layer thickness distribution. One embodiment provides for the distance between the walls of the coating chamber and the sheet to be set to correspond to 10 to 10,000 times, in particular 100 to 2,500 times, the sheet thickness. The advantage here is that the comparatively large distance allows for the vapor flow to be evened out, allowing the coating to be deposited as homogeneously as possible.

[0039] One embodiment provides for the distance between the guide devices and the sheet to be set to 0.005 to 1 times, in particular to 0.01 to 0.7 times, the sheet width. The sheet width can be between 500 mm and 2000 mm. The advantage here is that the comparatively large distance from the guide devices ensures that the steam flow hits the strip in a homogenized manner.

[0040] One embodiment provides that the metal strip is continuously punched or perforated to produce the desired hole pattern and is then continuously PVD coated inline.

[0041] It is advantageously possible to implement an inline process, particularly in the steel mill, 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 line, where it is subsequently continuously PVD coated inline.

[0042] 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.

[0043] One embodiment provides for the strip to be guided horizontally and / or vertically through the coating chamber. One embodiment provides for the process to be carried out as a multi-stage process with vertical strip travel, in which the strip is moved at least twice, namely at least once upwards and at least once downwards. This has the advantage that both sides of the strip can be exposed to comparable coating conditions, thus achieving comparable and reproducible coating properties on both sides.

[0044] The invention is explained by way of example with reference to a drawing. It shows:

[0045] Fig. 1: A schematic hole pattern;

[0046] Fig. 2: Possible designs of hole patterns;

[0047] Fig. 3: Highly schematic view of a coating chamber;

[0048] Figure 1 shows a hexagonal hole pattern. For example, for hole spacing a=7 mm, hole radius r=2.5 mm, and sheet thickness 0.9 mm, the ratio of coated area F including hole walls to area F o a sample without holes approx. 70%, because the following applies: 0.704

[0049] 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.

[0050] Figure 1 shows a typical schematic hole pattern. The hole structure is honeycomb-shaped with a hole spacing a=7 mm, a hole radius r=5 mm, and a sheet thickness s=0.9 mm.

[0051] Such a perforated sheet is fed into a PVD system with a corresponding coating chamber. The coating chamber is designed with locks so that the strip can be fed in and out without negatively changing the pressure conditions inside the coating chamber.

[0052] The perforated strip is coated by controlling the particle density in the coating chamber using defined plasma parameters. The particle flow is a function of the metal vapor density, whereby, for example, the average coating thickness (surface of the punched area) is - - - - - - = 0.6 to 0.9 average coating thickness (surface of the unpunched area).

[0053] The plasma vaporizer delivers a high vapor density with high kinetic energy and can be easily controlled. The combination of these two enables efficient continuous coating of punched surfaces.

[0054] With vertical strip travel, the process can be carried out as a two-stage process (upward-moving and downward-moving strip) in order to achieve a symmetrical coating of the entire strip surface including punching surfaces, whereby this also depends on the design of the evaporator.

[0055] The coating chamber may be equipped with guide devices to direct, distribute, and control the particle flow. These can be either baffles or electromagnetic guide devices. These regulate the local vapor flow.

[0056] Appropriate measurements can be taken on the coated sheets emerging from the vapor deposition chamber and fed back to the control devices so that they achieve a desired coating thickness or layer thickness distribution.

[0057] By applying an electrical potential difference to the substrate relative to the chamber wall, it is also possible to influence the local vapor flow, especially in the area around the substrate to be coated.

[0058] A comparatively simple control of the evaporator or evaporator capacity is achieved by calculating the latent heat of condensation for a specific amount of material. Since the total surface area of ​​the perforated sheet, the belt speed, and the desired average layer thickness are known as input parameters, the latent heat of condensation can be easily determined from the latent heat of condensation.

[0059] The process according to the invention enables efficient coating of perforated steel strip. For example, a zinc coating with uniform corrosion protection of the punching surface can be achieved. As a further advantage, the resulting uncoated punching waste can be directly recycled during the production of the perforated steel strip and reused for steel production without further processing in the plant.

[0060] In addition, depending on the selected coating material, a very wide range of possible coating thicknesses can be achieved, ranging from 0.1 pm to approximately 20 pm. The guide devices, in particular, allow the coating thickness to be regulated across the strip width. Furthermore, it is possible to vapor-deposit both sides of the strip with different materials. Furthermore, the coating process also allows for multilayer coatings of different coating materials without great effort.

Claims

Claims 1. Method for producing perforated metal strips with a metallic coating, wherein metal strips and in particular steel sheet strips with a perforation or hole pattern are fed to and passed through a coating device in which the sheet strip is continuously PVD-coated with a steam stream.

2. Method according to claim 1, characterized in that the strip has a metal sheet thickness of 0.3 mm to 2.5 mm.

3. Method according to claim 1 or 2, characterized in that the strip is coated with one or more layers, wherein the layers of the coating consist of one, several or all of the group consisting of metals, oxides, carbides, nitrides, carbonitrides.

4. Method according to one of the preceding claims, characterized in that both sides of the strip are coated with the same or different coating materials and / or layer thicknesses.

5. Method according to one of the preceding claims, characterized in that the strip is coated with one, several or all of the group consisting of zinc, magnesium, manganese, copper, chromium, aluminium, titanium, silicon or alloys with or made of these elements as main constituents.

6. Method according to one of the preceding claims, characterized in that the layer thickness of the PVD coating is 20 nm to 100 pm, preferably 100 nm to 50 pm, per strip side surface.

7. Method according to one of the preceding claims, characterized in that the layer thickness ratio of the coating of the strip side surface to the walls of the perforations is between 0.4 and 1.2, preferably 0.6 and 0.

9.

8. Method according to one of the preceding claims, characterized in that the particle flow in the coating chamber is directed onto the belt by means of guiding devices.

9. Method according to one of the preceding claims, characterized in that the guiding devices are mechanical guide plates or electromagnetic guiding devices.

10. Method according to one of the preceding claims, characterized in that the coating thickness is measured and the guide devices are controlled in such a way that a desired coating thickness and layer thickness distribution is achieved.

11. Method according to one of the preceding claims, characterized in that the distance between the walls of the coating chamber and the sheet metal is adjusted to correspond to 10 to 10,000 times, in particular 100 to 2,500 times, the thickness of the sheet metal.

12. Method according to one of the preceding claims, characterized in that the distance between the guide devices and the sheet metal is set to 0.005 to 1 times, in particular 0.01 to 0.75 times, the width of the sheet metal strip.

13. 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 subsequently continuously PVD-coated inline.

14. Method according to one of the preceding claims, characterized in that the belt is guided horizontally and / or vertically through the coating chamber.

15. Method according to claim 14, characterized in that, in the case of vertical belt travel, the process is carried out as a multi-stage process in which the belt is passed at least twice, namely at least once upwards and at least once downwards.

16. Perforated strip with metallic coating, characterized in that the layer thickness ratio of the coating of the strip side surface to the walls of the perforations is between 0.4 and 1.2, preferably 0.6 and 0.9.

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