Apparatus and method for determining a lacquer coating thickness on electrical sheets

Abstract

The invention relates to an apparatus (10) and a method for determining a lacquer coating thickness of a strip (1) in a continuous process, in particular a process for producing or processing a metal strip or electrical sheet, in which, by means of a lacquering or coating device (20), a transparent or pigmented insulating or lacquer coating is applied to the strip (1), having at least one thickness sensor (2) arranged transversely to, preferably crossing, the conveying direction of the strip (1), the thickness sensor being connected in terms of signalling to a control unit (3) in order to determine the thickness of the lacquer coating on the strip (1), wherein at least one temperature sensor (4) for sensing a temperature of the strip (1) in a region T is provided, in the conveying direction of the strip (1), upstream of and / or at, preferably close to a measuring region D of the thickness sensor (2), and wherein the control unit (3) has a module (5) for temperature compensation of the measurement by the thickness sensor (2), to which the temperature sensor (4) is connected directly or indirectly in terms of signalling in order to correct a thickness value on the basis of the temperature measured by the temperature sensor (4).

Description

[0001] Device and method for determining a paint layer thickness on electrical steel sheets

[0002] The present invention relates to a device and a method for determining the thickness of a lacquer layer on a strip in a continuous process, in particular a production or processing process for a metal strip or electrical steel sheet, also referred to as electrical steel strip, in which a transparent or pigmented insulating or lacquer layer is applied to the strip by means of a lacquering or coating device. The lacquer layer thickness of such electrical steel strips or electrical steel sheets is conventionally determined using various methods and technologies in order to ensure the quality of the coating of such insulating layers or lacquer layers, which are, for example, in a range of 0.5 pm to 10 pm. The main function of such coatings with insulating lacquer is to insulate such electrical steel sheets or electrical steel strips in order to prevent electrical current flow and reduce eddy currents.In other areas, such metal strips are also coated for corrosion protection or to extend the service life of punching tools during further processing. The insulating or lacquer coatings are applied using various coating or lacquering devices in a generally continuous process with a continuous metal strip. At least one thickness sensor is provided to determine the lacquer layer thickness in the strip travel direction after coating and to detect or verify sufficient and uniform coating. Such thickness sensors are installed above and / or below the electrical sheet or strip after the coating device on appropriate system mounts.

[0003] In addition to infrared spectroscopy, the technology used to determine such paint layer thicknesses is beta backscattering, in which beta rays from a radioactive source are backscattered at the metal surface and, as they pass through the insulating layer, are attenuated depending on the layer thickness. Devices known as beta backscattering (isotope) measuring systems have the disadvantage that the availability of the necessary isotopes, such as krypton, strontium, or promethium, is increasingly reaching its limits. Beta transmission coating thickness measurement also has the disadvantage that, due to the radioactive isotopes, increased radiation protection is required for users and workers in the vicinity of such measuring devices. When beta transmission coating thickness measurements using radioactive rays, enclosures or screens are usually used to reduce the radiation hazard.However, the applicable radiation protection guidelines must be observed at all times. Since these emitters cannot be switched off, and the half-life of common isotopes such as promethium is approximately two to three years, at which point the emitted radiation is reduced by half, these sensors and emitters are no longer usable. Alternative radiation sources for such a backscattered radiation measuring device are either too weak or too strong, so there are no real alternatives to the isotope promethium, which is no longer available or will not be available for much longer.

[0004] Previously known devices for measuring paint layer thickness also have the disadvantage that measurements often become inaccurate due to disruptive factors in the production process, for example, when different surface roughnesses occur due to contamination or the rolling condition of the metal strip. Furthermore, the climatic conditions in the gap between the measuring system and the strip surfaces play a significant role. This means that temperature, air pressure, and humidity must be continuously measured and included in the evaluation. Excessive changes in the distance between the measuring system (typically 10 to 20 mm) and the metal strip of + / - 1 mm can lead to significant changes in the measured values. The measurement results with the existing paint layer thickness measuring devices are then incorrect and cannot provide a high-quality statement about the actual paint layer thickness.

[0005] Against this background, it is the object of the present invention to provide a device and a method for determining the paint layer thickness of such strips, in particular of electrical sheets or metal strips, in which an exact determination of the layer thickness and uniformity of the layer application on the metal strip is continuously made possible without being susceptible to interference.

[0006] This object is achieved with a device for determining the lacquer layer thickness of a strip or electrical strip according to claim 1 and a method with the steps according to claim 12. Advantageous embodiments and further developments of the invention are the subject of the dependent claims.

[0007] According to the invention, a device is provided for determining a lacquer layer thickness of a strip in a continuous process, in particular a production or processing process of a metal strip or electrical steel sheet, in which a transparent or pigmented insulating or lacquer layer is applied to the strip by means of a lacquering or coating device, with at least one thickness sensor arranged transversely to the conveying direction of the strip, preferably traversing or alternatively stationary, which is signal-connected to a control unit for determining the thickness of the lacquer layer on the strip, wherein the device is characterized in that at least one temperature sensor for detecting a temperature of the strip in a region T in the conveying direction of the strip before and / or on,preferably close to a measuring range D of the thickness sensor and that the control unit has a module for temperature compensation of the measurement by the thickness sensor, to which the temperature sensor is connected directly or indirectly in terms of signal technology for correcting a thickness value on the basis of the measured temperature.

[0008] The thickness sensor of the device according to the invention is therefore at least one sensor with which the paint layer thickness can be detected. It can be a sensor based on laser-induced fluorescence technology, in which a laser, for example a solid-state laser, generates a luminous effect, known as fluorescence, on the surface of the metal strip through targeted local optical excitation, preferably in the ultraviolet spectral range, of molecules in the paint. The detection of the emitted fluorescence from the transparent or pigmented paint layers allows the paint layer thickness to be determined. Preferably, a pulsed laser light source is used, which enables time-resolved evaluation of the laser-induced fluorescence signals and thus offers additional advantages.Laser-induced fluorescence spectroscopy is performed with a thickness sensor preferably arranged traversing across the strip width, wherein, according to the invention, an additional measurement of the temperature of the metal strip is performed in a region in the strip travel direction upstream of the measuring region D. Alternatively, an IR sensor based on infrared absorption or based on ellipsometry, or a combination of these, can be used as the thickness sensor within the scope of the present invention.

[0009] With the IR sensor, a portion of the energy of the infrared radiation radiated onto the strip surface is absorbed by specific molecular groups in the paint and converted into thermal molecular vibrations. The resulting energy loss of the portion of radiation backscattered at the substrate surface of the metal strip below the paint layer can be measured by a detector as an intensity loss at specific wavelengths. According to the Lambert-Beer absorption law, the coating thickness of the paint can then be determined under defined conditions. Since the IR method with IR thickness sensors always requires backscattering of the measuring radiation from the respective substrate surface, the condition (roughness, texture) of the surface of the metal strip can have a disruptive influence on the coating thickness measurement, especially in the case of inhomogeneities or changing conditions.This has a minor influence on the LIF measurement, since the emission of the fluorescence to be detected is radiated isotropically in all spatial directions by individual, excited molecules of the resist above the substrate surface. Recording the intensity of a representative portion of this radiation is therefore not dependent on a backscattering process on the substrate surface.

[0010] Other methods, such as ellipsometry, which is based on recording the change in the polarization state of applied radiation upon reflection in the paint layer or the underlying substrate surface of the metal strip, are also, in principle, applicable within the scope of the present invention from a physical perspective. The thickness measurement using the thickness sensor is temperature-compensated in the device by a special control module, i.e., the measurement results from the thickness sensor measurement are adjusted based on the actual temperature of the electrical steel strip.

[0011] In the thickness sensors according to the invention, which are based on laser-induced fluorescence as one example, the energy of the laser is generated by optically exciting molecules in the paint layers or coating media. Thermal effects such as molecular motion, collisions, chemical effects, etc. can influence the measurable total intensity of the reflected or re-radiated fluorescence at a specific wavelength within a specified wavelength range of a coating. Investigations by the inventors have shown that the intensity of the fluorescence measured with the thickness sensor according to the device according to the invention decreases with increasing temperature of the strip or electrical strip. The changes in the fluorescence intensity due to the temperature of the strip depend on the coating material or type of paint used.Using stored data from calibration measurements or known material values, this decrease in fluorescence can be corrected accordingly when using the raw data from the thickness sensor with the device according to the invention by adjusting the final thickness values. These values ​​and corresponding calculation models are stored in the control unit according to the invention or the control module for temperature compensation. Temperature compensation can be achieved by calibrating a system once at the beginning of the device's use. Furthermore, when processing different paint types or coating materials, different values ​​from a database or by inputting them into the control unit can be used accordingly in order to achieve the inventive advantages of correct paint layer thickness determination across a wide range of applications.Temperature measurement with one or more temperature sensors at the measuring area or, alternatively, at, preferably close to, the measuring area D has the advantage and effect according to the invention of preventing any falsifications of the thickness measurement due to the sometimes very different and even high temperatures of such metal strips during processing. Even with significantly different strip temperatures of the metal strip, an exact measurement of the paint layer thickness can be performed in the specified range of, for example, 0.5 pm to 10 pm, without incorrect measurement values ​​arising, for example, due to the measurement technology of laser-induced fluorescence spectroscopy.

[0012] A temperature measurement can therefore be located at a measuring point or area either upstream of the thickness measuring area in the belt's conveying direction, or alternatively, overlapping it in or near the thickness measuring area. In the latter case, mutual interference between the two must be excluded.

[0013] Possible forms of temperature sensors used in connection with the present invention include, in particular, non-contact temperature detectors based on heat flow measurement ("convective heat flow" sensors). These temperature sensors have a very high accuracy in the range of + / - 0.1°C, thus enabling the high accuracy of measuring the strip temperature required for compensating the fluorescence signals in the thickness sensor to be achieved directly and without contact. Heat flow-based temperature sensors have the advantage of not requiring interference-prone optics. However, they must be mounted relatively close to the surface of the strip, for example, at a distance of 3 mm to 10 mm, in order to provide the precise temperature values ​​required for the inventive device for determining the thickness of paint layers.Other types of temperature sensors are also possible within the scope of the present invention: Thermal imaging cameras or radiation-based infrared sensors (pyrometers) can also be used. An important aspect of radiation-based temperature measurement with pyrometers has emerged as the shielding of the light path against radiation from the environment. Depending on the optics in front of the pyrometer, the distance of the system to the strip surface changes in order to ensure a specific measuring spot size. By selecting an appropriate optics, it is therefore possible to produce mechanical shielding up to distances of 40 mm from the strip surface (corresponds to the distance of the LIF sensor to the strip surface) with little space requirement. This minimizes the disruptive influence of ambient radiation on the measurement of the strip temperature via the thermal radiation emitted from the strip surface.Because of their compact design, pyrometers have the advantage of being mounted in close proximity to the measurement position of the coating thickness measurement being used, temperature measurement is possible in the same area or even directly in the area of ​​the thickness measurement spot; provided that the temperature and coating thickness measurement methods do not interfere with each other. This local temperature measurement also makes it possible to measure and record the temperatures of individual calibration samples as additional parameters during the calibration of the coating thickness measurement systems in the laboratory using the same pyrometer types and in the same configuration, as will be done later in the plant.This means that it is no longer necessary to measure the actual, absolute temperature of the tape, but rather to ensure a fixed relationship between the values ​​measured during calibration and the temperature values ​​measured inline with the pyrometer.

[0014] This would also allow paint-specific influences of radiation-based temperature measurement due to changing emissivity to be specifically considered from the outset, for example, by using two different pyrometer types or a short-term sequential measurement at different emissivity levels. This would then also enable precise and targeted compensation of the thickness measurement values ​​based on the respective influence of the strip temperature. Furthermore, local measurement with the pyrometers enables the recording of the temperatures of both strip surfaces, top and bottom separately, as well as possible gradients in the temperature distribution across the strip during a traversing measurement. The pyrometers can also be optionally combined with heat flow temperature sensors.The temperature sensors should only be contactless to avoid direct contact with the belt during the production process and the risk of damage or disruption to the temperature sensors as well as the belt surface.

[0015] The temperature sensor according to the invention is arranged in an area in the strip travel direction upstream of the measuring area of ​​the thickness sensor, so that the strip temperature can be determined in advance for the accuracy of the thickness measurement and taken into account in the evaluation through temperature compensation. The temperature sensor can also be provided in the measuring area D of the thickness sensor close to the thickness sensor itself, as long as a correct determination of the strip temperature of the metal strip can be achieved. Detecting only the ambient temperature is not meaningful or sufficient for correcting and compensating the measured value when determining the paint layer thickness using the laser-induced fluorescence method or other thickness measurement methods, but should also be recorded as an additional process parameter according to an optional embodiment within the scope of the present invention.

[0016] The temperature sensor can be a single sensor, signal-coupled to the control module to compensate for the thickness sensor's measurement results. Multiple temperature sensors and / or multiple thickness sensors can also be provided, eliminating the need for a traversing arrangement of thickness sensors.

[0017] The device according to the invention offers significant advantages over the prior art of such devices for measuring paint layer thickness: The influences of interference factors from the production process are greatly reduced, particularly in laser-induced fluorescence but also in other thickness measurement methods, especially with regard to surface roughness.

[0018] According to an advantageous embodiment of the invention, the temperature sensor or the at least one temperature sensor of the device is a sensor that is stationary and positioned on the strip without contact. The sensor does not have to be arranged traversing across the strip width, but can be provided stationary at one location, for example, a central region of the metal strip. Alternatively, the temperature sensor can also be arranged together with the thickness sensor on a holder traversing - i.e., transversely to the strip travel direction. However, the stationary mounting of the temperature sensor has the advantage that comparatively little effort is required to construct the device in this regard. The connection to the control unit and the control module for the temperature signal transmission for temperature compensation can be made via a wireless or a wired signal line.The thickness values ​​recorded by the thickness sensor are then coupled to the temperature in the control unit and the control module, linking them to the temperature so that temperature compensation can be performed directly and continuously during the electrical steel processing process. This ensures consistently high-quality paint layer thickness determination with a comparatively simple design of the device.

[0019] According to a further advantageous embodiment of the invention, the at least one temperature sensor is arranged in a measuring area T in the belt conveying direction upstream of and close to the measuring area D of the thickness sensor at a distance of 1 cm to 200 cm, in particular 10 cm to 200 cm, from the measuring area D. Thus, the temperature of the metal strip is determined in an area relatively close to the measuring area D of the thickness sensor but at a certain distance from it. This prevents mutual interference between the measurement of the thickness sensor and the temperature measurement. Using the information on the actual temperature of the strip, the measurement of the thickness sensor can then be corrected accordingly in the control module of the control unit.The raw data from, for example, the fluorescence measurement with the thickness gauge is corrected using information regarding the strip temperature. This means that, depending on the temperature level, the results of the fluorescence measurement with the thickness sensor are adjusted in the control unit based on stored data. This measure allows even more precise thickness measurement results to be achieved with the device according to the invention.

[0020] The thickness sensor in the case of fluorescence measurement comprises, for example, a solid-state laser which emits laser beams at a high frequency and preferably at a slightly oblique angle (e.g., 60°) directed at the metal strip, which excites the paint or coating on the metal strip to glow due to the material composition. The reflected luminous values ​​are recorded by the thickness sensor, and this luminous effect is used in the control unit to precisely determine the layer thickness of the paint. The correction using the current temperature of the strip according to the invention makes it possible to provide a correct statement about the paint layer thickness with the device even when the temperatures of the electrical steel strip vary greatly. The control unit stores, for example, data regarding the influence of temperature on the fluorescence effect of the thickness sensor depending on the coating material or the type of paint.Thus, compensation for correcting the thickness value can also be carried out in the pm range - usually 0.5 to 10 pm - with the device according to the invention in a wide range of applications of such strip coatings.

[0021] According to a further advantageous embodiment of the invention, at least one temperature sensor is integrated into the thickness sensor or integrated into a holder of the thickness sensor. The device can thus be realized in an even more compact and smaller design. Attaching the temperature sensor does not require a separate holder if the temperature sensor is integrated into the holder of the thickness sensor or in the area of ​​the thickness sensor itself, close to it. Integration also has the advantage that the temperature measurement is carried out directly corresponding to the measuring point or measuring range of the thickness sensor. The temperature measurement thus represents a very precise, current recording of the temperature of the metal strip at the respective measuring point of the sensor for thickness determination.The influence of the temperature of the metal strip on the fluorescence effect used with the device according to the invention is thus very small after compensation with the control unit. It is essential for the inventive solution that the temperature sensor is arranged close to the thickness sensor, or that the measuring range of the temperature sensor is close to that of the thickness sensor or even directly overlaps with it. Overlapping is only not advisable if mutual influence of the measuring systems would lead to possible interference with the measurement results. With the inventive solution, interference effects due to increased temperature on the metal strip can be compensated with little additional equipment.It is also possible to measure the thickness of the paint layers or coatings on the electrical steel strips over a relatively large range using laser-induced fluorescence technology or other alternative measuring methods, without the need for complex additional measures or complex measuring equipment.

[0022] According to a further advantageous embodiment of the invention, a plurality of temperature sensors are provided distributed across the width of the strip. With multiple temperature sensors, different temperatures in different areas of the metal strip can also be taken into account when compensating for the paint layer thickness measurement. For example, two or four stationary temperature sensors can be arranged, evenly distributed across the width, to measure the temperature of the metal strip across its entire width.The values ​​recorded by the temperature sensors are passed on as signals to the control unit, in which the compensation of the measurement of the thickness sensor is carried out by using the stored values ​​of the fluorescence with the respective laser sensors or similar sensors of the thickness sensor and, based on this, the adjustment and compensation of the raw data of the measured values ​​of the thickness sensor is carried out by increasing or reducing the thickness values.

[0023] The present invention also relates to a method for determining a lacquer layer thickness of a strip in a continuous process according to the features of claim 12. The method according to the invention is particularly intended for implementation with a system or device according to the features of claims 1 to 11, wherein alternative devices are also included in the patent application when using the method steps according to the invention.

[0024] According to the invention, a method for determining a lacquer layer thickness of a strip in a continuous process, in particular a production or processing process of a metal strip or electrical sheet, in which a transparent or pigmented insulating or lacquer layer is applied to the strip by means of a lacquering or coating device, with at least one thickness sensor arranged transversely to the conveying direction of the strip, which is signal-connected to a control unit for determining the thickness of the lacquer layer on the strip, wherein the method is characterized:

[0025] Detecting a temperature of the strip in a region T in the conveying direction of the strip in front of a measuring region D of the thickness sensor with at least one temperature sensor;

[0026] Transmitting the measured temperature to the control unit and / or a temperature compensation module;

[0027] Temperature compensation of the measurement by the thickness sensor with a module in the control unit, to which the temperature sensor is connected directly or indirectly by signal for correcting a thickness value based on the temperature measured by the temperature sensor.

[0028] According to an advantageous aspect of the invention, the thickness measurement is carried out on the basis of laser-induced fluorescence technology (LIF).

[0029] According to an advantageous embodiment of the method according to the invention, the temperature is measured by a convective heat flow sensor or by a pyrometer.

[0030] Further advantageous refinements, developments, aspects, and advantages of the invention will be explained in more detail below with reference to some embodiments of the device according to the invention in conjunction with the accompanying drawings. The drawings show: Fig. 1 a schematic view of an embodiment of a device according to the invention for layer thickness measurement with temperature detection in the strip travel direction in front of the thickness sensors; and Fig. 2 a diagram illustrating the temperature influence on fluorescence signals of a thickness sensor of a device according to the invention.

[0031] Fig. 1 shows a schematic view of a first exemplary embodiment of an apparatus 10 according to the invention for measuring the layer thickness of a coating or paint layer on strips 1, with temperature detection in the strip travel direction upstream of the thickness sensor(s) 2, as can also be used to carry out the method according to the invention. In this exemplary embodiment of Fig. 1, the apparatus 10 comprises a thickness sensor 2 arranged above and below the strip 1 or electrical strip, which in this first example is based on laser-induced fluorescence technology. Here, a laser beam is emitted at a relatively high frequency, usually slightly obliquely, onto the surface of the strip 1, and the emitted fluorescent light is detected in the thickness sensor 2 and forwarded to a control unit 3.The actual thickness of the coating on the strip 1, which can be, for example, an insulating layer or lacquer layer on an electrical strip 1 or metal strip, is then determined in the control unit 3. Alternatively, an infrared sensor, an ellipsometry-based sensor, or a combination thereof can be used for the thickness measurement within the scope of the present invention.

[0032] Such a coating or lacquer layer is generally transparent or pigmented so that it is translucent and has a thickness in a range of generally 0.5 μm to 10 μm. Such lacquer layers or insulating layers are applied in particular to strips as so-called electrical strips in order to provide corrosion protection or to achieve electrical insulation. The device 10 according to the invention has, in addition to the thickness sensors 2 or at least one thickness sensor 2 and the control unit 1, at least one temperature sensor 4, which in this exemplary embodiment is arranged in front of the thickness sensor 2 below the strip 1 in the strip travel direction (cf. direction of the arrow of the strip 1 in Fig. 1). The strip 1 is coated with the insulating layer or lacquer layer in an upstream coating device 20, for example via a roll coater 6, and the lacquer is then dried in a drying unit 9.After this coating process in the coating device 20, the actual layer thickness applied to the strip 1 must be checked and verified to ensure the quality of the electrical or metallic strip 1. With the device 10 according to the invention, the raw data of the measured values ​​of the thickness sensors 2 are compensated or corrected in the control unit 3 via a specific temperature compensation module 5. The temperature measured values ​​of the temperature sensor 4, which non-contactingly measures the actual temperature of the strip 1 at the point before the measuring area D in a temperature measuring area T, are entered into the temperature compensation module 5. The raw data of the thickness measured values ​​from the measurement of the thickness sensors 2 are then compensated using the temperature values ​​in the control unit 3 and corrected accordingly in order to determine correct values ​​for the actual thickness of the coating of the metal strip 1.

[0033] In this exemplary embodiment according to Fig. 1, the temperature sensor 4 is arranged below the metal strip 1 in the area T in front of the measuring area of ​​the thickness sensor D and close to a guide roller below the strip 1. This ensures that the temperature sensor 4 is arranged sufficiently close to the strip 1 for precise temperature measurement and cannot be damaged. The temperature sensor 4 can be provided with an automatic, mechanical displacement device via an additional distance sensor. This ensures that it is always kept at the correct distance from the strip surface, even in the event of strip fluctuations. When passing through a weld seam between two strips, the temperature sensor can also be moved to a greater distance from the strip to avoid damage.Preferably, the temperature sensor 4 is a non-contact sensor that performs a non-contact temperature measurement using the so-called "convective heat flow detector." Alternatively or additionally, thermal imaging cameras or non-contact radiation-based temperature measuring devices, so-called pyrometers, can also be provided.

[0034] The temperature sensor 4 can be mounted stationary in front of the thickness sensors 2 on a separate holder, which is attached as close as possible to the strip. Alternatively, the temperature sensor 4 can be integrated into a holder of the thickness sensors 2 and perform the temperature measurement for the inventive compensation of the fluorescence values ​​or other measured thickness values ​​in the control unit 3 and the corresponding compensation module 5 near the measuring range D of the thickness sensors 2. The compensation of the measured values ​​from the measurement of the thickness sensors 2, which are sent to the control unit 3 as raw data via signal technology, is carried out to adjust the fluorescence values ​​of material-specific properties of such coatings, which generally decrease with increasing temperature. At a nominal temperature of, for example, 25°C, the nominal fluorescence value measured with the thickness sensors 2 is generally a correct value (see Fig. 2).However, with increasing temperature, depending on the type of material or type of coating (paint type), this value decreases and then usually has to be corrected upwards in the range up to 40%.

[0035] The relationship between the decreasing fluorescence of the raw data and the correction values ​​depending on the temperature of the strip 1 is illustrated in Fig. 2, which is shown for different paint types 1, 2, 3 and 4. The corresponding values ​​are stored in the control unit 3 and the temperature compensation module 5 of the control unit 3 either in a database or are determined and adjusted accordingly when the device 10 is set up or separately under laboratory conditions. Calibration for the specific application of the device 10 is also possible. By compensating with the actual temperature present on the strip 1 and thus in the coating on the strip 1, the most precise values ​​possible for the thickness of the coating can be determined using the device 10 according to the invention.The control unit 3 with the temperature compensation module 5 is adapted and configured, either in software or hardware, to perform such temperature compensation during the layer thickness measurement of the device 10 with the thickness sensors 2. For this purpose, the correlations between the strip temperature and the thickness values, for example, fluorescence thickness values, of such layer thickness measurements with the thickness sensors 2, as illustrated in Fig. 2, are stored in a database or as input values ​​of the control unit 3. A procedure in a program module of such a temperature compensation module 5 according to the invention can be as follows, using the example of fluorescence thickness measurement:

[0036] The temperature correction of the fluorescence data is carried out in the control unit 3 of the measuring system in the temperature compensation module 5, for example, in the following steps:

[0037] Step 1 :

[0038] Simultaneous detection of the fluorescence at a surface position by the thickness sensors 2 and the strip temperature by the sensors 4 as close as possible to the fluorescence measurement with a suitable temperature sensor 4 typically at 10 ms intervals

[0039] Step 2:

[0040] Selection of the temperature compensation function from a database in the control unit 3 with paint-specific parameters (current paint type as a specification from the process data), which are stored in an associated database / file during system calibration.

[0041] Typical function: 2nd degree polynomial (3 parameters) or linear function (2 parameters)

[0042] Step 3:

[0043] Calculate a correction factor in module 5 of control unit 3 from the selected temperature compensation function with the associated paint-specific parameters for the currently measured strip temperature values. Step 4:

[0044] Application of the determined correction factor to the currently measured fluorescence value and calculation of the corrected fluorescence intensity for the thickness measurement of the device 10.

[0045] Step 5:

[0046] Calculation of the current coating or layer thickness value from the corrected fluorescence value using the paint-specific calibration function stored in the system database.

[0047] Step 6:

[0048] Output or further calculation (e.g. averaging) of the current coating or layer thickness value to a display unit of the device 10 or process control unit.

[0049] The measured values ​​of the layer thicknesses with the device 10 are usually the existing coating thicknesses in g / m 2or a layer thickness calculated from it in pm. However, determining the layer thickness in pm requires that the exact density values ​​of the respective paint layer on the dried paint belt 1 are known or are calculated accordingly in control unit 3 or module 5 from known formulas or historical values. For this purpose, a gravimetric method for thickness determination according to DIN ISO EN 3233-2 is used, for example.

[0050] According to a further advantageous embodiment of the invention, a backscattering measuring unit 7 is provided, which measures the backscattering from the strip surface of the strip 1. Furthermore, a backscattering compensation module 8 is integrated in the control unit 3 and is signal-coupled to the backscattering measuring unit 7. In this way, in addition to temperature compensation, the invention also advantageously allows for correction or compensation of the backscattering influence on such lacquer layers of electrical steel strips or other strips 1. Such an optional embodiment of the invention with backscattering compensation is particularly advantageous in applications such as the coating of electrical steel sheets with insulating lacquers, because in this case the steel strips are used in the cold rolling mill without further surface finishing.The roughness and quality of the surface of such strips 1 or steel surfaces is therefore generally not always very good and can fluctuate, which can then influence the thickness measurement values. These influences can also be compensated for according to the invention by measurements with a backscatter sensor, thus enabling a relatively precise and accurate detection of the actual layer thickness of such strips 1. This optional configuration is schematically shown in Fig. 1 with the dashed control signal line.

[0051] According to a further alternative embodiment of the invention, feedback from the thickness measurement in the device 10 can be provided to the coating device 20, as also illustrated by a dashed line in Fig. 1. This allows the coating process to be directly influenced via the coating elements or roll coaters 6 of the coating device 20 if there are deviations from a target value of the thickness of the insulating layer or coating of the strips 1.

[0052] List of reference symbols

[0053] 1 tape or electrical tape

[0054] 2 Thickness sensor 3 Control unit

[0055] 4 Temperature sensor

[0056] 5 Temperature compensation module

[0057] 6 coating elements or roll coaters

[0058] 7 Backscatter measurement unit 8 Backscatter compensation module

[0059] 9 Drying unit

[0060] 10 Device for determining paint layer thickness

[0061] 20 Coating and drying equipment

[0062] D Measuring range thickness sensor

[0063] T measuring range temperature sensor

Claims

Claims 1. A device (10) for determining a lacquer layer thickness of a strip (1) in a continuous process, in particular a production or processing process for a metal strip or electrical steel sheet, in which a transparent or pigmented insulating or lacquer layer is applied to the strip (1) by means of a lacquering or coating device (20), with at least one thickness sensor (2) arranged transversely to the conveying direction of the strip (1), preferably traversing, which is signal-connected to a control unit (3) for determining the thickness of the lacquer layer on the strip (1), characterized in that at least one temperature sensor (4) for detecting a temperature of the strip (1) in a region T in the conveying direction of the strip (1) is provided before and / or on, preferably close to, a measuring region D of the thickness sensor (2), and in that the control unit (3) has a module (5) for temperature compensation of the measurement by the thickness sensor (2),with which the temperature sensor (4) is connected directly or indirectly for the purpose of correcting a thickness value on the basis of the temperature measured by the temperature sensor (4).

2. Device (10) according to claim 1, characterized in that at least one temperature sensor (4) is provided integrated on the thickness sensor (2) or a holder of the thickness sensor (2).

3. Device (10) according to claim 1 or 2, characterized in that the temperature sensor (4) is a sensor positioned stationary on the belt (1) without contact.

4. Device (10) according to one of the preceding claims, characterized in that at least one temperature sensor (4) is arranged in a measuring range T in the belt conveying direction close to or overlapping with the measuring range D of the thickness sensor (2) at a distance of 1 cm to 200 cm, in particular 10 cm to 50 cm, from the measuring range D.

5. Device (10) according to one of the preceding claims, characterized in that a plurality of temperature sensors (4) are provided distributed over a width direction of the strip (1).

6. Device (10) according to one of the preceding claims, characterized in that the temperature sensor (4) is a heat flow-based convective heat flow sensor or a pyrometer.

7. Device (10) according to one of the preceding claims, characterized in that the thickness sensor (2) is a thickness sensor (2) based on laser-induced fluorescence.

8. Device (10) according to one of the preceding claims, characterized in that a backscatter measuring unit (7) for measuring an actual backscatter from the surface of the strip (1) and a backscatter compensation module (8) are provided in the control unit (3) for correcting a thickness value of the thickness sensor (2).

9. Device (10) according to one of the preceding claims, characterized in that the temperature sensor (4) has a shield against ambient temperature influences and for focusing on a measuring point or area on the strip (1).

10. Device (10) for determining a lacquer layer thickness of a strip (1) in a continuous process, in particular a production or processing process of a metal strip or electrical sheet, in which a transparent or pigmented insulating or lacquer layer is applied to the strip (1) by means of a lacquering or coating device (20), with at least one thickness sensor (2) arranged transversely to the conveying direction of the strip (1), preferably traversing, which is based on laser-induced fluorescence technology and is connected by signal technology to a control unit (3) for determining the thickness of the lacquer layer on the strip (1), characterized in that at least one temperature sensor (4) for Detection of a temperature of the strip (1) in a region T in the conveying direction of the strip (1) in front of a measuring region D of the thickness sensor (2) is provided and that the control unit (3) has a module (5) for temperature compensation of the laser-induced fluorescence measurement by the thickness sensor (2), to which module the temperature sensor (4) is connected directly or indirectly in terms of signal technology for correcting a thickness value on the basis of the measured temperature.

11. Device (10) according to claim 10 in combination with one or more of the preceding claims 2 to 9.

12. Method for determining the lacquer layer thickness of a strip (1) in a continuous process, in particular a production or processing process of a metal strip or electrical sheet, with a device (10) according to one of claims 1 to 11, in which a transparent or pigmented insulating or lacquer layer is applied to the strip (1) by means of a lacquering or coating device (20), with at least one thickness sensor (2) arranged transversely to the conveying direction of the strip, which is signal-connected to a control unit (3) for determining the thickness of the lacquer layer on the strip (1), the method being characterized by: Detecting a temperature of the strip (1) in a region T in the conveying direction of the strip (1) in front of a measuring region D of the thickness sensor (2) with at least one temperature sensor (4); transmitting the measured temperature to the control unit (3) and / or a module (5) of the control unit (3); Temperature compensation of the measurement by the thickness sensor (2) with a module (5) in the control unit (3), to which the temperature sensor (4) is connected directly or indirectly in terms of signal technology for correcting a thickness value on the basis of the temperature measured with the temperature sensor (4).

13. The method according to claim 12, wherein the thickness measurement of the paint layer thickness is carried out by means of a laser-induced fluorescence measurement.

14. The method according to claim 12 or 13, wherein the temperature is measured by a connective heat flow sensor or by a pyrometer sensor.

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