Method and device for determining the evenness of a metal strip

Abstract

The invention relates to a method for determining the evenness of a metal strip (1) and to a device (10) for carrying out the method.

Description

[0001] Method and device for determining the flatness of a metal strip

[0002] The invention relates to a method for determining the flatness of a metal strip, a corresponding device for carrying out the method and a use.

[0003] When flat-rolling metallic strip, strip flatness is a significant factor for further processing and subsequent final utilization. Strip flatness is an important quality characteristic and has a decisive influence on productivity and scrap yield in almost all production processes in the metalworking industry. Metallic strips with insufficient flatness can lead to significant production and quality disruptions in the production facilities downstream of the rolling process and during further processing. The flatness of a metallic strip is significantly influenced during the rolling process, where a flat strip is created by uniform elongation of the strip across the strip width.

[0004] During the rolling process, numerous parameters can have an undesirable, negative, but also controllable, influence on strip flatness. If thermal and / or mechanical influences cause uneven elongation of the metallic strip across the strip width, poor strip flatness results, which can manifest itself, among other things, in the form of waviness in the center or edge area of ​​the metallic strip.

[0005] During the cold and hot rolling of metal strip, undesirable unevenness can occur in the produced metal strip, which can extend, for example, in the running direction or longitudinal direction, as well as transversely to it. These unevennesses can lead to varying degrees of deflection of the metal strip perpendicular to the surface, which can disrupt flatness. Therefore, it is necessary to monitor the flatness of the produced strip during the rolling process and to positively influence the rolling process conditions in the event of deviations from flatness. To meet increasing quality demands, quality information systems are necessary that reliably support the detection of different flatness levels.

[0006] Various methods for measuring flatness are known from the state of the art. A wide range of optical 3D sensors is available for diffusely scattering, optically rough surfaces. One of the most widely used methods is based on the projection of strip patterns. The patterns are projected from one direction and observed from another with a camera, see, for example, EP 0 864 847 A2 and EP 1 418 400 A2. The known optical methods for determining strip flatness work with "diffuse" reflection. Metal strip surfaces thus exhibit non-directional, diffuse reflection or transmission of light in the visible spectrum.

[0007] The following documents are examples of further prior art: EP 2 910 893 Bl, EP 2 834 594 Bl and EP 3 487 642 Bl .

[0008] Due to high acquisition costs and insufficient sensitivity of the systems known from the prior art for assessing or determining strip flatness, the object of the invention is to optimize or improve the sensitivity and reliability of existing flatness measuring devices and also to simplify them considerably, which can significantly reduce the costs of acquiring these systems.

[0009] The object is achieved by a method for determining the flatness of a metal strip having the features of claim 1 and by a device for carrying out the method having the features of claim 7.

[0010] Further advantageous embodiments and developments will become apparent from the following description. One or more features from the claims, the description, and the figures may be combined with one or more features from further embodiments of the invention. One or more features from the independent claims may also be replaced by one or more features and combined with these. The proposed subject matter is to be understood only as a draft for formulating the invention, but without limiting it.

[0011] According to the first teaching, a method for determining the flatness of a metal strip is proposed. The method comprises the following steps: a) irradiating a section of a surface of the metal strip; b) detecting a reflection of the irradiated section; c) transforming the reflection into flatness information; d) repeating at least steps a) and b), wherein the metal strip is moved along its longitudinal extent so that, due to the movement, new sections of the surface of the metal strip are irradiated; e) concatenating the flatness information to determine the flatness of the metal strip at least over a partial length along its longitudinal extent, wherein the irradiation in step a) is carried out using at least one heat source (thermal) or a cold source.

[0012] The term "metal strip" encompasses metal strips made of any metallic material. The metal strip can preferably be a steel strip.

[0013] Irradiation of a section of a surface of the metal strip is carried out, for example, using at least one heating element whose temperature differs from the ambient temperature and the temperature of the metal strip or the surface temperature, in particular by at least 20 K, preferably by at least 30 K, and more preferably by at least 50 K higher. A heating wire is preferably used as the heating element, which is arranged above or below the section to be irradiated for thermal irradiation, in particular with respect to the plane (metal strip plane) of the movably guided metal strip. Thus, as the metal strip moves past, a section of the surface of the metal strip can be (thermally) irradiated on its top or bottom. The heat source is reflected in the metal surface. As a result, the thermal reflection on the surface of the metal strip brought about by the heat source is recorded.This means that, for example, data from a momentary state is available.

[0014] Alternatively, it is also possible, for example, to use a cooling element, in particular to thermally inspect hot surfaces, wherein the temperature of the cooling element or the cold source differs from the temperature of the metal strip or the surface temperature, in particular by at least 20 K, preferably by at least 30 K, and more preferably by at least 50 K lower. The operating principle is similar to that described above. The cold source is reflected in the metal surface. As a result, the thermal reflection induced by the cold source on the surface of the metal strip is recorded.

[0015] Thermal reflection can be recorded, for example, using a thermal imaging camera. This captures the heat radiation generated by the use of a heat source, which is reflected from the surface of the metal strip. A thermal imaging camera, sometimes also referred to as a thermography, thermal, or infrared camera, is an imaging device that receives infrared radiation. The use of a thermal imaging camera has the particular advantage of being able to capture two-dimensional thermal radiation. Furthermore, a thermal imaging camera offers the advantage of being able to provide the two-dimensional thermal radiation in real time, if desired. The spatial resolution of the measurement data depends in particular on the type and positioning of the thermal imaging camera in relation to the moving metal strip.

[0016] Transforming the reflection(s) into flatness information can be achieved, for example, using data processing software or programs. In other words, the data of the instantaneous state recorded by the thermal imaging camera is further processed to provide flatness information. Such programs / software are commercially available.

[0017] By stringing together the flatness information, a continuous flatness profile over the length of a metal strip can be visualized and / or documented. The advantage of a continuous flatness profile is that the available data can be used to determine the flatness over at least a partial length along the longitudinal extent of the metal strip, preferably along the entire length of the metal strip.

[0018] A key advantage of detecting thermal reflection is that it allows for continuous, non-contact, and real-time monitoring of the metal strip's surface. Another advantage is that it enables, for example, continuous monitoring of the irradiated section of the metal strip as it moves through.

[0019] The method according to the invention enables a preferred full-surface and continuous detection of the flatness of the surface of the metal strip in a manufacturing process in the metalworking industry to be automated.

[0020] The method according to the invention does not work with diffuse reflection, but with the much more sensitive specular reflection, which, in contrast to diffuse reflection, does not evaluate the surface itself, but rather the mirror image of the heating element or the cooling element.

[0021] A further advantage of the described method is that thermal imaging cameras are standard in current production facilities, which ensures comparatively low procurement and use, while also ensuring that the necessary equipment and expertise are already available in many cases. In one embodiment of the method, for example, it can be provided that the thermal reflection is detected in a wavelength range between 3 micrometers and 14 micrometers, in particular in a wavelength range between 7 micrometers and 14 micrometers.The comparatively long-wave spectral range between 7 pm and 20 pm offers the particular advantage that many metals exhibit very low emissivity in this wavelength range, thus maximizing thermal radiation or thermal reflection from the irradiated section. This results in particularly good visibility of the thermal reflection detected with the described methods, which leads to reliably analyzable results even under unfavorable measurement conditions.

[0022] Many commercially available thermal imaging cameras cover a wavelength range from 7 micrometers to 14 micrometers, so the acquisition costs of such systems are moderate.

[0023] In one embodiment, it can advantageously be provided that the irradiated section encompasses the entire width of the metal strip. This ensures that new sections are successively irradiated as the metal strip moves, thus allowing a partial length up to the entire surface of the metal strip to be captured.

[0024] The section for irradiating or detecting the thermal reflection can be arranged in a rolling mill, preferably in a cold rolling mill, a surface finishing plant, or an inspection plant. The section and the detection can thus be arranged in the direction of travel of the metal strip as it enters and / or exits the rolling mill.

[0025] A further embodiment of the method advantageously provides that steps a) to c) and e) are carried out continuously in-situ.

[0026] A second teaching of the invention provides a device for carrying out the method for determining the flatness of a metal strip, comprising: - at least one heat source or cold source for irradiating a portion of a surface of the metal strip; - at least one thermal imaging camera for detecting a thermal reflection of the irradiated portion; - means for transforming the thermal reflection into flatness information; and - means for storing and / or displaying the flatness information obtained by concatenating the flatness information in order to determine the flatness of the metal strip at least over a partial length along its longitudinal extent.

[0027] To avoid repetition, reference is made to the procedural details.

[0028] With the device according to the invention, in addition to the flatness of the metal strip, additional strip irregularities, such as edge and center waves across the width of the metal strip, but also compliance with the specified pass line, fluctuations in the position of the metal bath, possible skew, one-sided hanging strip side and small geometric surface anomalies in a manufacturing process in the metalworking industry can be checked or evaluated.

[0029] A further, independent teaching of the invention provides for the use of the aforementioned device according to the invention or the method according to the invention for determining the flatness of a metal strip in a surface finishing system. The surface finishing system can be designed as a hot-dip coating system. Alternatively, the surface finishing system can be designed as an electrolytic coating system. The aforementioned systems are state of the art and are used to apply a metallic layer to the surface of the metal strip. As a further alternative, the surface finishing system can be designed as a strip coating system, which is also state of the art and usually involves applying one or more organic layers to the surface of the metal strip.

[0030] A further, independent teaching of the invention provides for the use of the aforementioned device according to the invention or the method according to the invention for determining the flatness of a metal strip in a rolling mill. The rolling mill can preferably be a conventional cold rolling mill.

[0031] In the following, specific embodiments of the invention are explained in more detail with reference to the figures. The figures and the accompanying description of the resulting features are not to be interpreted as limiting the respective embodiments, but serve to illustrate exemplary embodiments of the invention. Furthermore, the respective features can be used with each other and with features of the above description for a possible further development and improvement of the invention, especially in additional embodiments not shown.

[0032] The figures show:

[0033] Fig. 1: a schematic perspective view of an embodiment of a device according to the invention;

[0034] Fig. 2: a snapshot of a thermal imaging camera;

[0035] Fig. 3: a representation of a sequence of flatness information in a first display and

[0036] Fig. 4: a representation of a sequence of flatness information in a second display.

[0037] Figure 1 shows an embodiment of a device (10) according to the invention. The device (10) comprises at least one heat source (2), for example in the form of a heating element, preferably in the form of a heating wire, which is arranged such that, when a metal strip (1) is guided along, a section of a surface of the metal strip (1), preferably an entire width of the surface of the metal strip (1), can be irradiated. Furthermore, the device (1) comprises at least one thermal imaging camera (3), which is arranged such that it can capture the thermal reflection of the section irradiated by the heat source (2) as the metal strip (1) is guided along. Alternatively, a cold source can also be used, for example if hot surfaces are to be inspected.

[0038] The device (10) according to the invention can be used within existing systems for processing metal strips, such as in rolling mills and / or surface finishing systems or inspection systems, in order to be able to determine or assess the flatness of the metal strip (1) sensitively and reliably.

[0039] Figure 2 shows a snapshot of the thermal imaging camera (3). It is clearly visible that the thermal imaging camera (3) images the longitudinal edges of the metal strip (1) being moved through the device (10). This also captures the two irradiated sections extending across the entire width of the metal strip (1). These sections are visible as thermal reflections, with the irradiated sections being visible as brighter areas in the image due to the irradiation of the heat sources (2). The thermal imaging camera (3) is, for example, from Dias Infrared GmbH and has the identification number PYROVIEW 640L.

[0040] The steps of irradiating the sections of the surface of the metal product (1) and detecting the reflection(s) of the irradiated sections are repeated, the metal strip (1) being moved in its longitudinal extent so that, as a result of the movement, new sections of the surface of the metal strip (1) are irradiated, the reflection(s) being transformed by suitable means (4), for example by means of a program or software, for example "Pyrosoft Professional" from Dias Infrared GmbH, preferably which converts the images generated by the thermal imaging camera (3) into further processable information, inter alia into flatness information or into several flatness information items.By means of a sequence of the flatness information(s), i.e. the evaluation of the continuous images of the thermal imaging camera (3), the flatness of the metal strip (1) can be determined at least over a partial length along its longitudinal extent, preferably over the entire length of the metal strip (1).

[0041] The alignment of the flatness information and thus the flatness of the metal strip (1) can preferably be determined in situ and preferably output graphically via suitable means (5) either two-dimensionally (see Figure 3) or three-dimensionally (see Figure 4), for example on monitors in a control center. The means (5) can thus be storage units and / or display units.

[0042] Figure 3 shows the flatness of a metal strip (1), which was determined as the metal strip (1) was guided along in the direction of the arrow, across its width and across its entire length. In the left third of the length of the metal strip (1), extreme center and edge waves can be seen, the middle third shows essentially good flatness, and slight center waves are present in the right third. Figure 4 shows the flatness of a metal strip (1), which was determined as the metal strip (1) was guided along in the direction of the arrow, across its width, here over a width of approximately 1225 mm, and across its entire length, here approximately 2000 m. Strip unevenness is more noticeable at the beginning and end of the strip, where so-called tack seams are used to connect leading and trailing strips to ensure continuous operation.This procedure is common practice in the metalworking industry.

Claims

Patent claims 1. A method for determining the flatness of a metal strip (1), the method comprising the following steps: a) irradiating a section of a surface of the metal strip (1); b) detecting a reflection of the irradiated section; c) transforming the reflection into flatness information; d) repeating at least steps a) and b), wherein the metal strip (1) is moved in its longitudinal extent such that, due to the movement during the repetition, new sections of the surface of the metal strip (1) are irradiated; e) stringing together the flatness information in order to determine the flatness of the metal strip (1) at least over a partial length along its longitudinal extent, characterized in that the irradiation in step a) is carried out by means of at least one heat source (2) or a cold source.

2. Method according to claim 1, wherein at least one heating element is arranged as heat source (2) above or below the section to be irradiated for irradiation.

3. Method according to claim 1 or 2, wherein the detection in step b) is carried out via a thermal imaging camera (3).

4. Method according to one of the preceding claims, wherein the detection in step b) is carried out in a wavelength range between 3 micrometers and 14 micrometers.

5. Method according to one of the preceding claims, wherein the irradiated section comprises an entire width extension of the metal strip (1).

6. A process according to any one of the preceding claims, wherein steps a) to c) and e) are carried out continuously in situ. Device (10) for carrying out the method for determining the flatness of a metal strip (1), comprising: at least one heat source (2) or cold source for irradiating a portion of a surface of the metal strip (1); at least one thermal imaging camera (3) for detecting a thermal reflection of the irradiated portion; Means (4) for transforming the thermal reflection into flatness information; and Means (5) for storing and / or displaying the flatness information obtained by stringing together the flatness information in order to determine the flatness of the metal strip (1) at least over a partial length along its longitudinal extent. Use of a device according to claim 7 or a method according to one of claims 1 to 6 in a surface finishing plant. Use of a device according to claim 7 or a method according to one of claims 1 to 6 in a rolling mill. Use of a device according to claim 7 or a method according to one of claims 1 to 6 in an inspection plant.

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