Method and device for stripping oxide layers from metal products

Abstract

The method comprises: determining an ablation energy density threshold value as a function of a section of the product (3), which in turn comprises: emitting an analysis pulse to a subsection of said section, the wavelength and the pulse duration of said analysis pulse being equal to the wavelength and the pulse duration of the ablation laser (13), so as to form an ablation zone; capturing an image of said subsection; determining a representative dimension of said ablation zone as a function of the image; and evaluating said ablation energy density threshold value as a function of the dimension; emitting an ablation pulse to said section, the energy density of said ablation pulse being higher than said ablation energy density threshold value, said ablation laser (13) being controlled in such a way that all points of said section are exposed to an energy density higher than said ablation energy density threshold value.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for removing an oxide layer covering the surface of a metal product (especially steel) after it has been exposed to an atmosphere that is oxidizing to some of its components during a heat treatment process in a furnace. Background Technology

[0002] In the following description, the preferred application of this invention is in the field of all types (austenitic, ferritic, austenitic-ferritic, etc.) of stainless steel strip and sheet (hot-rolled or cold-formed steel). However, it should be understood that this does not constitute any limitation, and the invention can also be applied to other metals that present similar technical problems with stainless steel strip and sheet, especially with various carbon steels and special alloys (particularly ferroalloys). With adaptations to the device that are obvious to those skilled in the art, the invention can also be applied to products other than strip and sheet, such as wire and welded and seamless pipes.

[0003] Stainless steel sheets and strips often require treatment that causes an unwanted oxide layer to form on their surface at high temperatures due to contact with oxidizing atmospheres such as air. The composition of this oxide layer varies significantly depending on the composition of the base metal and the formation conditions. In the most common cases, it is dominated by oxides of iron (Fe), chromium (Cr), manganese (Mn), and silicon (Si).

[0004] The aforementioned treatments that lead to oxide formation generally include, but are not limited to: reheating of semi-finished products (ingots, slabs, large billets, small billets) before hot rolling; the period of open exposure to air after hot rolling; and various annealing processes involving temperatures of several hundred degrees Celsius and in inert or insufficiently reducing atmospheres, before, during, and after a cold rolling cycle (divided into one or more stages, with intermediate annealing processes between some stages). Naturally, these undesirable oxides must be removed before the sheet or strip becomes a usable product or semi-finished product (which can undergo the final forming operation to make it usable). Furthermore, removing these oxides before the first cold rolling stage is often crucial to prevent them from embedding into the surface of the semi-finished product during rolling, resulting in poor surface finish.

[0005] It is important to understand that the "undesirable oxide layer" referred to here is not the thin chromium oxide-based layer (called the "passivation layer") that spontaneously forms on the stainless steel surface in air at room temperature, which protects the stainless steel from oxidation. The problematic oxide layer to be removed is the oxide layer that forms when the strip is exposed to a high-temperature oxidizing atmosphere. After removing this layer, the stainless steel surface will be exposed, and a protective chromium oxide passivation layer will quickly and spontaneously form again, allowing the steel to regain its "stainless" properties under normal use conditions.

[0006] Mechanical descaling, achieved through shot peening (throwing hard shot onto the surface to be treated) and / or oxide breaking operations (passing the strip between pairs of rollers to bend, compress, and pull it), can break up most oxides and make them easily removable, for example, by brushing, but may not be sufficient to completely remove oxides. Shot peening also has the disadvantage of increasing surface roughness, and when this disadvantage is intolerable to the process, subsequent operations on the sheet or strip may not be able to correct it.

[0007] In the most common cases, the unwanted oxide layer is removed by chemical or electrolytic stripping, or by performing such stripping operations sequentially.

[0008] Chemical stripping is carried out in one or more hydrofluoric acid, hydrochloric acid, sulfuric acid, or nitric acid baths. Electrolytic stripping is generally carried out in a sodium sulfate bath or an acid bath (nitric acid or sulfuric acid bath).

[0009] The surface finish of strips or sheets obtained through such stripping operations is typically classified into various standard categories: Surface finish 1D: Products that have undergone hot rolling, annealing and stripping. Stripping is generally chemical stripping, and mechanical stripping (oxide crushing, shot peening) is usually performed before chemical stripping. 2B surface finish: Products that have undergone annealing, stripping (usually electrolytic stripping and chemical stripping) and leveling (a work-hardening rolling process that improves the flatness and reduces the roughness of the strip, with a low product thickness reduction rate, usually a few percent). 2D finish: Cold-rolled products that have undergone annealing and stripping but have not been leveled; 2E finish: Cold-rolled products that have undergone annealing, shot peening, and stripping but have not been smoothed.

[0010] Chemical stripping is the most radical method for removing unwanted oxides, but it has many drawbacks.

[0011] This method consumes a large amount of acid, and there is at most a limited possibility that some of this acid can be recovered for later reuse.

[0012] The facilities required for this method, namely a series of stripping baths and their auxiliary equipment, are not only expensive but also cumbersome. In addition, chemical stripping plants often require conveyor belts up to 200 meters long.

[0013] Such facilities require the use of hazardous products, particularly hydrofluoric acid. Their polluting liquid and solid emissions (including sludge composed of stripping fluid and oxides) must be stored and reprocessed according to stringent regulations, which are only expected to become more stringent in the future, thus increasing costs. Furthermore, acid baths release acidic vapors when heated, which must be neutralized. Additionally, nitric acid is a source of NOx emissions that must be treated after collection.

[0014] In addition to electrolytic stripping, other methods involve immersing the strip or sheet in a stripping bath, typically based on sodium sulfate, nitric acid, or sulfuric acid, which also requires reprocessing after use. Electrolytic stripping requires very expensive equipment that consumes a relatively large amount of electricity. Electrolytic stripping can be supplemented with chemical acid stripping, which is less severe than chemical stripping alone, but suffers from the same drawbacks. Electrolytic stripping also produces slurry that must be stored and reprocessed, and the used stripping bath must also be reprocessed. Although the cost, hazards, and complexity of slurry and bath reprocessing in electrolytic stripping are lower than in chemical stripping using acid baths, these factors still significantly limit the application of this method.

[0015] Finally, the hexavalent chromium dissolved in the stripping solution poses a serious health risk to people and the environment, and its presence level in the liquid and human exposure must be measured and monitored.

[0016] Therefore, the inventors examined the possibility of using lasers, at least in some cases, to replace chemical or electrolytic stripping methods for metal products. This possibility is discussed in the classic work *Laser Cleaning* (Boris Luk'yanchuk, December 2002, ISBN: 978-981-02-4941-0), particularly in the cleaning of artworks and buildings (i.e., relatively small, fixed surfaces) (see especially Chapter 2: "An Overview of Experimental Studies in Laser Cleaning of Surface Contamination"). In this study, the oxide layer can be removed by projecting a laser beam onto the surface to be cleaned.

[0017] In this way, the use of acids and / or sulfates can be avoided, thus eliminating the need for further treatment of contaminated and harmful sludge and liquids; only the oxides removed, for example, need to be collected by suction. Furthermore, the collected oxides can preferably be reprocessed using dry methods to recover and regenerate their contained metals. This ensures the safety of personnel and the workshop environment. The power cost of laser operation is not particularly high, especially compared to the power cost required for electrolytic stripping, and the overall energy balance of laser surface cleaning is superior to that of wet methods (chemical and / or electrolytic methods). Laser cleaning devices can be much smaller than stripping devices that include a series of stripping baths, resulting in a significant advantage in terms of civil engineering costs during setup. When using pulsed lasers, high-frequency, high-level energy can be emitted autonomously in a very short time, and such lasers can have a lifespan of several years without any special maintenance.

[0018] However, the combination of existing technologies with CO2 lasers or excimer lasers fails to achieve optimal results for strips or sheets on industrial-scale production lines. This is because existing production lines operate at high speeds, resulting in heavy maintenance, continuous laser operation, excessively long pulses, and high operating costs due to the use of multiple lasers. Furthermore, such solutions assume a uniform surface condition based on the strip's width and length (see EP0927595A1) and often assume a fixed production line speed. For the same strip, if the production line speed changes for specific reasons, machine inertia, especially the inertia of the production furnace, will cause changes in the oxide layer (thickness or type). Although the characteristics and thickness of the oxide layer to be removed were previously considered known, these parameters have now changed, and adaptability of pulse frequency or energy only works if the oxide layer remains constant (which is generally not the case). Ultimately, existing production line speeds are set at around 100-150 m / min.

[0019] EP3631049A1 describes a method for removing oxide layers, in which the composition and thickness of the oxide layer are determined by laser-induced plasma spectroscopy.

[0020] This technique requires damaging the metal beneath the oxide layer, thus failing to meet the requirements. Furthermore, determining the thickness and composition of the oxide layer does not reliably determine the removal parameters that should be used for oxide layer removal.

[0021] In addition, WO2018 / 096382 describes a laser stripping method and apparatus for metal products.

[0022] According to this method, the emissivity of the oxide surface of the metal product to be stripped is determined as follows: a first laser beam is emitted towards the surface; the beam reflected from the oxide surface is intercepted; and the reflected beam is analyzed. Subsequently, the operating parameters of the stripping laser are adjusted to be a function of the determined emissivity.

[0023] This method can effectively remove the oxide layer on the surface by adjusting the energy of the stripping laser.

[0024] However, since the correct parameters for effectively removing the oxide layer cannot always be determined based on the emissivity, this method does not fully meet the requirements. Summary of the Invention

[0025] Therefore, one object of the present invention is to provide a method and apparatus for stripping moving metal products, which can achieve effective stripping on an industrial scale.

[0026] Therefore, as an object of the present invention, a method for removing an oxide layer from a moving metal product is provided. This method uses at least one removal laser for laser removal and includes sequentially performing the following steps on each of a plurality of consecutive segments of the moving product: - Determine the oxide layer removal energy density threshold for a target segment of the moving metal product, the oxide layer removal energy density threshold corresponding to the minimum energy density required to remove the oxide layer on the target segment, including: An analytical laser pulse is emitted by an emission system including a laser source onto a segment of the target region to form a stripping region lacking the oxide layer within the segment. The wavelength and pulse duration of the analytical laser pulse are equal to the wavelength and pulse duration of the stripping laser. Capture images of segments of the surface under the action of the analytical laser pulse; Based on the image, determine the representative size of the stripped area; Based on the representative size and information related to the energy distribution of the analytical laser pulse, the oxide layer removal energy density threshold is evaluated; The stripping laser emits stripping laser pulses onto the target section to strip it, wherein the energy density of the stripping pulses is higher than the determined oxide layer removal energy density threshold. The stripping laser is controlled by a control unit that receives a determined oxide removal energy density threshold in such a way that each point of the target segment is exposed to an energy density higher than the oxide removal energy density threshold at at least one moment.

[0027] According to other advantageous aspects of the invention, the method includes one of the following features, or includes multiple of the following features, either individually or in any technically feasible combination: The emission of the analytical laser pulse forms a damaged region of metal beneath the oxide layer within the segment, and the method further includes: determining a representative size of the damaged region based on the image; and evaluating a metal damage energy density threshold based on the representative size of the damaged region and information related to the energy distribution of the analytical laser pulse, the metal damage energy density threshold corresponding to an energy density beyond which degradation of the surface of the metal product beneath the oxide layer is observed; The method further includes: sending the damage energy density threshold to the emitting system, wherein, in the next segment of the moving metal product, the energy of the analytical laser pulse emitted by the emitting system is adjusted such that the energy density at any point in the segment under the action of the analytical laser pulse is lower than the damage energy density threshold; The information associated with the energy distribution includes: the shape of the energy distribution and the energy or power of the analytical laser pulse; The step of determining the oxide layer removal energy density threshold includes: determining the energy distribution shape of the analytical laser pulse; and / or determining the energy or power of the analytical laser pulse; The step of determining the oxide layer removal energy density threshold includes: determining the energy distribution shape of the analytical laser pulses, which in turn includes: deflecting a portion of each analytical laser pulse toward a beam analyzer; and evaluating the shape of the energy distribution by the beam analyzer; The step of determining the oxide layer removal energy density threshold includes determining the energy and / or power of the analytical laser pulse, which in turn includes: deflecting a portion of each analytical laser pulse toward a power meter; and evaluating the energy and / or power of the analytical laser pulse by the power meter; The step of determining the oxide layer removal energy density threshold includes: determining the energy distribution shape and / or the energy or power of the auxiliary laser pulse emitted by the emission system, wherein the auxiliary laser pulse is different from the analytical laser pulse; Determining the energy distribution shape and / or the energy or power of the auxiliary laser pulse includes: The auxiliary laser pulse is emitted by the emission system; The auxiliary laser pulse is guided toward the beam analyzer and / or the power meter by a galvanometer scanning device; The energy distribution shape of the auxiliary laser pulse is evaluated by the beam analyzer, and / or the energy and / or power of the auxiliary laser pulse is evaluated by the power meter; The metal products are strips, bars, sheets, plates, pipes, or wires.

[0028] As an object of the present invention, an apparatus is also provided for laser stripping of a moving metal product having an oxide layer on its surface using at least one stripping laser, comprising: - A determining component for determining an oxide layer removal energy density threshold for each of a plurality of successive segments of the moving metal product, the oxide layer removal energy density threshold corresponding to the minimum energy density required to remove the oxide layer on the target segment, the determining component comprising: The system includes a laser source that emits analytical laser pulses onto segments of the target region to form stripping areas lacking the oxide layer within those segments, wherein the wavelength and pulse duration of the analytical laser pulses are equal to the wavelength and pulse duration of the stripping laser. An image acquisition system is used to acquire segmented images of the product under the action of the analytical laser pulse during the product's movement; The processing system is used to determine the representative size of the stripping area based on each image acquired by the image acquisition system, and to evaluate the oxide layer removal energy density threshold based on the representative size and information related to the energy distribution of the analytical laser pulse. - A laser stripping assembly including at least one stripping laser for emitting stripping laser pulses onto each of the plurality of successive segments of the moving metal product for stripping; and a control unit for receiving the oxide layer removal energy density threshold of the segment and controlling the stripping laser to emit laser pulses with energy higher than the oxide layer removal energy density threshold, such that each point of the target segment is exposed to an energy density higher than the oxide layer removal energy density threshold at at least one moment.

[0029] According to other advantageous aspects of the invention, the device includes one of the following features, or includes multiple of the following features, either individually or in any technically feasible combination: The analytical laser pulse is capable of forming a damaged area within the segment where the metal beneath the oxide layer has been damaged by the analytical laser pulse. The processing system is used to determine a representative size of the damaged area based on the image, and to evaluate a metal damage energy density threshold based on the representative size of the damaged area and information related to the energy distribution of the analytical laser pulse. This metal damage energy density threshold corresponds to an energy density beyond which surface degradation of the metal product beneath the oxide layer is observed. The processing system is used to send the injury energy density threshold to the transmitting system, and the transmitting system is used to adjust the energy of the analytical laser pulse according to the injury energy density threshold so that the energy density at each point in the affected segment of the next segment of the moving product is lower than the injury energy density threshold. The information associated with the energy distribution includes the shape of the energy distribution and the energy or power of the analyzed laser pulse; The laser stripping device includes a system for determining the energy distribution shape of the analytical laser pulse and / or a system for determining the energy or power of the analytical laser pulse; The system for determining the energy distribution shape of the analytical laser pulse includes a beam analyzer and an optical device, particularly a beam splitter, for deflecting a portion of each analytical laser pulse toward the beam analyzer, the beam analyzer being used to evaluate the energy distribution shape based on the deflected portion of the analytical laser pulse; The system for determining the energy or power of the analytical laser pulse includes a power meter and an optical device, particularly a beam splitter, for deflecting a portion of each analytical laser pulse toward the power meter, the power meter being used to evaluate the energy and / or power of the analytical laser pulse based on the deflected portion of the analytical laser pulse; The information associated with the energy distribution includes the shape of the energy distribution and the energy or power of the analytical laser pulse. The laser stripping apparatus includes a system for determining the shape of the energy distribution and / or the energy or power of an auxiliary laser pulse emitted by the emission system, the auxiliary laser pulse being different from the analytical laser pulse. To treat the entire surface of the metal product, which is composed of strip, bar, tube, sheet, plate or wire, the apparatus includes a set of laser sources distributed near the metal product and a set of stripping lasers.

[0030] The present invention also relates to a continuous processing line for metal products including the stripping device of the present invention. Attached Figure Description

[0031] A better understanding of the invention can be achieved by referring to the accompanying drawings and the following text. In the drawings: Figure 1 A schematic outline of a continuous production line including a laser stripping apparatus according to an embodiment of the present invention; Figures 2 to 4 Three examples of laser pulse energy distribution are shown: 34, 35, and 36. Figures 5 to 7 The figures shown are respectively having Figures 2 to 4 Three examples of surface features generated after laser pulse emission with the shown energy distribution; Figure 8 This is a partial schematic diagram of the stripping device according to the second embodiment; Figure 9 for Figure 8 Detailed view of the stripping device; Figure 10 This is a partial schematic diagram of the stripping device according to the third embodiment. Detailed Implementation

[0032] The laser stripping apparatus of the present invention will be described and illustrated below through an example of processing cold-rolled stainless steel strip that is in motion and has just undergone cold rolling and annealing on a continuous production line. The laser stripping apparatus of the present invention at least ensures a substantial portion of this stripping function and is also incorporated into the continuous production line, replacing, or located upstream of, the electrolytic and / or chemical stripping systems commonly used in such continuous production lines (see, for example, EP0509177A2 and EP0695808A1).

[0033] Needless to say, the laser stripping apparatus described herein can also be incorporated into a continuous processing line with more or fewer devices than those described herein, or it can be a standalone device specifically designed for this stripping operation.

[0034] Furthermore, the figure does not show equipment commonly found in such production lines that does not play a major metallurgical role and is not involved in the laser stripping operation performed according to the present invention under any circumstances. Such equipment, in particular, includes pinch rollers that initiate the movement of the strip and strip storage containers that serve as "buffers" between sections of equipment requiring different strip speeds.

[0035] The continuous production line shown includes an uncoiling device 1 for uncoiling the steel strip coil 2 of hot-rolled stainless steel strip 3. The thickness of the hot-rolled stainless steel strip 3 is generally a few tenths or millimeters of one millimeter, and the width is within 2 meters. The strip 3 typically moves at a speed of less than 150 meters per minute and generally enters the cold rolling mill 4 after undergoing any chemical and / or mechanical stripping treatment (not shown) or even laser stripping treatment by the apparatus of the present invention described below. The cold rolling mill 4 typically reduces the thickness of the strip 3 to a value on the order of 0.2 to 15 millimeters to obtain cold-rolled strip.

[0036] The cold-rolled strip 3 then enters an annealing furnace 5 and is heated to several hundred degrees Celsius within the furnace, a temperature that varies depending on the metallurgical purpose of the annealing process. When this annealing process is carried out (intentionally or unintentionally) in the presence of a non-negligible amount of oxidizing gases such as oxygen, it will result in the formation of an undesirable oxide layer on the surface of the strip 3. The composition, thickness, and adhesion of this oxide layer to the strip 3 depend particularly on the composition of the strip 3, the composition of the atmosphere within the annealing furnace 5, the temperature within the annealing furnace 5, and the length of time the strip 3 remains within the annealing furnace 5. Since not all of these numerous parameters are easily controlled, and such parameters can vary significantly under any circumstances depending on the precision processing performed (especially the composition of the strip 3 and the annealing conditions), and given potential production risks, it is not easy to standardize the strip 3 removal conditions by setting precise system characteristics for this oxide layer. This situation is also one of the drawbacks of wet stripping (especially chemical stripping) – the composition of the stripping bath cannot be easily adjusted to achieve the desired stripping effect at the lowest cost in practice.

[0037] according to Figure 1 In the embodiment shown, the laser stripping device is located downstream of the annealing furnace 5 in the production line.

[0038] The laser stripping device includes an energy density threshold determination unit 10 and a laser stripping device 12.

[0039] The energy density threshold determination component 10 is used to assess the effective energy density required to remove the oxide layer on a moving strip. In reality, due to intentional or unintentional changes in upstream operating parameters of the production line, such as deceleration or acceleration of the strip on the production line, or even before or after such heterogeneous contamination in the annealing furnace 5 along the width direction of the strip 3, a heterogeneous oxide layer to be removed along the length and / or width direction of the strip 3 may be generated.

[0040] Energy density threshold determination component 10 is used to determine, during the movement of the metal product to be stripped, a minimum energy density or threshold corresponding to the minimum energy density required to be emitted onto the product by the laser stripping device 12 to remove the oxide layer on the product surface, hereinafter referred to as oxide removal energy density threshold S. exp Preferably, the energy density threshold determining component 10 is further used to determine the maximum laser energy density threshold, hereinafter referred to as the damaging energy density threshold S. end When this threshold is exceeded, the product surface (i.e., the metal beneath the oxide layer) will deteriorate.

[0041] Component 10 is used to successively determine the oxide removal energy density threshold S for multiple sections of the product surface. expFurthermore, where applicable, its injury-causing energy density threshold S is also determined. end .

[0042] A segment is, for example, a horizontal strip of a given length along the product movement direction (also called the longitudinal direction), with a width equal to the product width. In contrast to a product in strip form 3, such a horizontal strip is called a "unit strip." Each segment is then used to be sequentially stripped by the laser stripping device 12 as it passes in front of the device.

[0043] Preferably, as described below, the determining component 10 is used to determine the oxide removal energy density threshold S. exp And, where applicable, determine the oxide removal energy density threshold S for a segment of each section. exp The determined threshold is then used as the representative value for the entire corresponding segment.

[0044] For example, a segment is a unit horizontal bar of a given length along the product movement direction, with a width equal to the product width. Component 10 is used to determine the oxide removal energy density threshold S. exp And, where applicable, determine the oxide removal energy density threshold S for a segment of the unit strip. exp The determined threshold is then used as the representative value for the entire unit bar.

[0045] The laser stripping device 12 is used to emit a laser beam onto a moving product to remove the oxide layer, based on the energy density threshold determined by the determining component 10.

[0046] The laser stripping device 12 is specifically used to emit a laser beam onto each segment of the moving product, based on the energy density threshold determined by the determining component 10, to remove the oxide layer.

[0047] The energy density threshold determination component 10 includes a laser pulse emission system 20, an image acquisition system 22, a processing system 24, and a controller 26.

[0048] The laser pulse emission system 20 is used to emit a laser pulse beam with a wavelength and pulse duration equal to that of the laser used for stripping (such as an Nd:YAG laser with a wavelength of 1064 nm) onto a moving product. This type of laser pulse is referred to as an analytical laser pulse.

[0049] The laser pulse emission system 20 includes at least one laser source 30 capable of emitting such analytical laser pulses. The laser source 30 is capable of emitting laser pulses with the same wavelength and pulse duration as the laser used for stripping.

[0050] By making the wavelength and pulse duration of the laser source 30 the same as those of the stripping laser, it can be ensured that the oxide covering the product absorbs the same amount of light from the laser source 30 as it absorbs from the stripping laser, thereby ensuring that the setting conditions of the stripping laser can be directly based on the data obtained by the energy density threshold determination unit 10.

[0051] Preferably, the laser source 30 is mounted in a manner that allows it to move relative to the production line, particularly in a direction parallel to the product surface and orthogonal to the product movement direction (i.e., along the width direction of the product). This allows the position of product segments under the action of the moving laser source to be changed along the product width direction. For this purpose, the laser pulse emission system 20 includes, for example, a scanning device capable of moving the laser source laterally relative to the product movement direction. Alternatively, the assembly 10 is designed to move entirely relative to the production line, thus also allowing the position of product segments under the action of the moving laser source to be changed along the product width direction.

[0052] For example, if each target segment is a unit strip with a width equal to the width of the product to be stripped, the scanning device can move the laser source in a transverse direction relative to the product movement direction, so that the position of the product segment under the action of the laser source changes with time along the width direction of the product (strip).

[0053] The laser pulse emission system 20 also includes an optical device 32 for focusing the laser pulses emitted by the laser source 30 onto the moving surface of the product.

[0054] Laser source 30 is used to emit analytical laser pulses onto a segment of a target area on a moving product surface. The energy density of the laser pulse varies depending on the position on that segment. Thus, the energy density received at each point on the segment under laser irradiation will depend on the position of that point. Hereinafter, the product surface area under the analytical laser pulse will be referred to as the "irradiation spot".

[0055] For example, at some points, the received energy density may be too low to remove the oxide layer, while at other points, the energy density may be sufficient to remove the oxide layer without damaging the underlying metal. In some cases, the energy density received at certain points may be sufficient to remove the oxide layer while damaging the underlying metal.

[0056] The energy density received at each point in the segment under laser irradiation is characterized by the energy density distribution of the pulse (referred to as "energy distribution").

[0057] It can be seen that at each or multiple locations on the surface of the product, the energy distribution is related to the energy density emitted at that location.

[0058] Figure 2 , Figure 3 and Figure 4 Examples 34, 35, and 36 show three energy distributions. In these three distributions, the horizontal axis X represents the position along the axis contained in the plane of the product surface, and the vertical axis Y represents the energy density received at that position. Therefore, each point on the energy distribution is associated with a given position and the energy density received at that position.

[0059] For example, the pulse has a symmetry axis Z parallel to the direction of pulse propagation (the range of action of the pulse on the product is, for example, circular), and the energy distribution associates the energy density with each distance relative to the center of the circle formed by the range of action of the pulse (also called the pulse center).

[0060] Energy distributions 34 and 35 are two examples of this type of distribution.

[0061] The energy distribution 34 is circular, meaning that all points at the same distance from the pulse center receive the same energy density.

[0062] The energy distribution 35 is square in shape, so that all points on the sides of the square centered on the pulse center receive the same energy density.

[0063] According to another example, the range of the pulse on the product is such that the energy density on the segment under laser irradiation is constant along the Y-axis orthogonal to the pulse propagation direction, and the energy distribution relates the energy density to every point on the X-axis orthogonal to the Y-axis and the pulse propagation direction.

[0064] Energy distribution 36 is an example of this type of distribution. In this example, the energy density increases linearly with position on the X-axis.

[0065] Preferably, for example as shown in distribution 34, the energy distribution is a Gaussian distribution. That is, the energy density received in a plane orthogonal to the pulse propagation direction conforms to a Gaussian distribution.

[0066] The energy distribution of a Gaussian pulse can be represented as follows: E(x) = E pic *exp(-x 2 / 2σ 2 ) E pic =E pulse / (2πσ 2 ) in: E pic The peak energy density is a Gaussian distribution; E pulse For pulse energy; x is the distance from the center of the pulse; E(x) is the energy density received at a distance x from the center of the pulse; σ is the standard deviation of the Gaussian distribution.

[0067] Preferably, the energy density distribution has a small slope, meaning the derivative of the energy density with respect to location is less than 1. In the case of a Gaussian distribution, this is especially true if σ > E. pic *exp(-1 / 2).

[0068] Preferably, the laser source 30 is used to emit laser pulses with a known energy distribution.

[0069] As an alternative, as described below, since the energy distribution of the laser pulse is unknown in advance, the energy density threshold determination component 10 further includes a determination system for determining the energy distribution of the pulse emitted by the laser source.

[0070] In any case, the energy distribution is determined by its shape (such as...) Figures 2 to 4 (as shown) and pulse power or energy characterization.

[0071] The image acquisition system 22 is used to acquire images of each target segment of the product under the action of the laser pulse emitted by the emission system 20 during the product movement process.

[0072] The image acquisition system 22 includes, for example, a camera 38, particularly a high-resolution camera. During operation, the camera 38 is positioned in front of the product, which is in a moving state.

[0073] The controller 26 is used to synchronize the laser pulse emitting system 20 with the image acquisition system 22. Specifically, the controller 26 controls the emitting system 20 to emit laser pulses and controls the image acquisition system 22 to acquire images of the areas affected by these pulses.

[0074] Processing system 24 is used to determine, based on each image acquired by image acquisition system 22, an oxide removal energy density threshold S corresponding to the minimum energy density required to remove the oxide layer from the target segment. exp .

[0075] Preferably, the processing system 24 is further configured to determine, based on each image acquired by the image acquisition system 22, the metal-induced damage energy density threshold S corresponding to the maximum energy density that will not cause degradation of the product surface below the oxide layer. end .

[0076] For this purpose, the processing system 24 is used to receive each image acquired by the image acquisition system 22.

[0077] The processing system 24 is also used to receive information related to the energy distribution of laser pulses emitted by the laser pulse emitting system 20, especially the laser source 30, onto the moving product.

[0078] The processing system 24 includes, for example, an image analyzer 40 and a threshold determination module 42.

[0079] Image analyzer 40 is used to determine at least one dimension of the area to be removed from the surface of the metal product, i.e. the absence of oxides, by analyzing each emitted image acquired by image acquisition system 22.

[0080] The image analyzer 40 is able to determine information related to the stripped area, especially information related to at least one dimension representing the shape of the area, and especially information related to the outline of the area.

[0081] For example, in the case of a pulse with a Gaussian energy density distribution, the stripping region has a circular shape, and the dimensions representing this shape are, for example, the diameter, radius, circumference, or area of ​​the circular region.

[0082] According to another example, the shape of the stripped area is rectangular, meaning that the dimensions of the shape are the length and / or width of the rectangular area.

[0083] The image analyzer 40 can transmit information related to the stripping area to the threshold determination module 42.

[0084] Preferably, the image analyzer 40 is also used to determine at least one dimension of the damaged area on the surface of the metal product (i.e., the area of ​​metal damaged beneath the oxide layer).

[0085] The threshold determination module 42 is able to receive this information.

[0086] The threshold determination module 42 can also receive information related to the energy distribution of the laser pulse that forms the stripping region. This information generally includes the shape of the energy distribution and the power or energy of the pulse.

[0087] Specifically, when the laser source is at time t e A pulse is emitted to a segment of the target area of ​​the product, and the image of that segment is at time t. e When +Δt is collected, the information related to the laser pulse energy distribution represents time t. e The emitted laser pulse.

[0088] This information related to the laser pulse energy distribution is stored, for example, in the memory of the threshold determination module 42.

[0089] The threshold determination module 42 can determine the oxide removal energy density threshold S based on information related to energy distribution and information related to the stripping area. exp .

[0090] Preferably, the threshold determination module 42 is further configured to determine the metal-induced damage energy density threshold S based on information related to energy distribution and information related to the stripping area. end .

[0091] For this purpose, the threshold determination module 42 can determine the energy density required to obtain the stripped area by stripping process based on the energy distribution of the laser pulse.

[0092] For example, the threshold determination module 42 can determine the energy density received on the outline of the stripping region based on the energy distribution, and this energy density corresponds to the minimum energy density required for oxide layer stripping.

[0093] Specifically, when the pulse emitted by the emission system 20 is a Gaussian pulse and the stripping region is a circular region with a diameter D, the oxide removal energy density threshold S exp It can be represented in the following form: S exp = E pic *exp(-D 2 / 8s 2 ) For example, Figures 5 to 7 The figures shown are respectively in the state of having Figures 2 to 4 The product surface is segmented under the distributed pulse action shown.

[0094] like Figure 5 As shown, surface 46 is obtained after emitting a pulse with energy distribution 34. Contour 47 is the stripped area of ​​missing oxide on the product. Therefore, surface 46 includes an unstripped portion 48 and a circular stripped area defined by contour 47. This stripped area includes a central damaged area defined by circular contour 49.

[0095] The stripping region is formed by points on surface 46 that receive sufficient energy density to strip the oxide layer. Therefore, the contour 47 of the stripping region is formed by the energy density received relative to the oxide removal energy density threshold S. exp Points with equal energy density are formed.

[0096] Thus, as Figure 5 As shown, the size of the stripping area is determined (in the example in the figure, it is the diameter D). exp After that, by comparing with the energy distribution 34, the oxide removal energy density threshold S, which is the minimum energy density required to remove oxides from the surface, can be determined. exp ( Figure 2 ).

[0097] Furthermore, the damaged area is formed by points on surface 46 that receive sufficient energy density to damage the product beneath the oxide layer. The diameter D of the contour 49 defining the damaged area...end Then, by comparing it with the energy distribution 34, the metal-induced injury energy density threshold S can be determined. end .

[0098] exist Figure 6 In this process, after emitting a pulse with an energy distribution 35, a surface 50 is obtained. A square outline 51 defines an oxide-free stripping area of ​​the product. Therefore, surface 50 includes an unstripped portion 52 and a stripped area. In this embodiment, the stripped area is square in shape. The stripped area includes a damaged area enclosed by a square outline 53 at its center.

[0099] Thus, after determining the side length of profile 51, the oxide removal energy density threshold S can be determined by comparing it with the energy distribution 35. exp Similarly, after determining the side length of the damaged area, the metal-induced damage energy density threshold S can be determined. end .

[0100] Finally, Figure 7 In the process, after emitting a pulse with an energy distribution 36, a surface 55 is obtained. A rectangular outline 56 delineates the oxide-free stripping area of ​​the product. Therefore, the surface 55 includes an unstripped portion 57 and a stripped area. In this embodiment, the stripped area is rectangular in shape. The stripped area includes a central damaged area delineated by the rectangular outline 58.

[0101] After determining the length of profile 56 along the X-axis, the oxide removal energy density threshold Sexp can be determined by comparing it with the energy distribution 36. Similarly, after determining the length of the damaged region along the X-axis, the metal-induced damage energy density threshold S can be determined. end .

[0102] The threshold determination module 42 can send the oxide removal energy density threshold S determined in the manner described above to the laser stripping device 12. exp And, where applicable, also send the metal-induced injury energy density threshold S. end .

[0103] Preferably, the processing system 24, particularly the threshold determination module 42, is also adapted to send an oxide removal energy density threshold and a metal damage threshold (Send, if these values ​​have been determined) to the emission system 20. The emission system 20 is adjusted to control the energy of the analytical laser pulse so that, after the analytical laser pulse is emitted, a portion of the segment under laser irradiation can be effectively stripped away without causing metal damage.

[0104] Specifically, if the previously emitted analytical laser pulse failed to create a stripped area (meaning it failed to reach the removal energy density threshold), the emitting system 20 can receive this information from the processing system 24. The emitting system 20 can then control the energy of the emitted analytical laser pulse to be higher than the energy of the analytical laser pulse emitted at the previous moment.

[0105] Conversely, if the previously emitted analytical laser pulse caused damage to the region, the emitting system 20 can receive the damage energy density threshold from the processing system 24. The emitting system 20 then controls the energy of the emitted analytical laser pulse to be lower than that of the analytical laser pulse emitted at the previous moment, specifically keeping the energy density of the analytical laser pulse below the damage energy density threshold.

[0106] For reliable measurements, the strip 3 must maintain a constant distance from the energy density threshold determining component 10; that is, the strip 3 must not vibrate and must be kept at a fixed height. This can be achieved by applying a sufficiently large tension to the strip 3 with an S-shaped pressure block, or by placing a support roller 23 under the strip 3 to ensure it is at a fixed height below the laser pulse emission system 20.

[0107] For the sake of simplicity, Figure 1 The illustration shows a scenario where the energy density threshold determination component 10 is positioned only on the upper surface of the strip 3. However, naturally, other lasers and associated sensors are also positioned on the lower surface of the strip 3. Similarly, a support roller, similar to the support roller 23, can be positioned on the upper surface of the strip 3 to contact it, ensuring that the strip 3 remains at a fixed distance relative to the laser that inspects its lower surface.

[0108] The laser stripping device includes an array of stripping lasers 13.

[0109] The stripping laser 13 is, for example, an Nd:YAG 1064nm pulsed laser.

[0110] This type of stripping laser 13 is used to remove the oxide layer on the surface of a product.

[0111] Each stripping laser 13 is used to emit a pulse of beam 14 onto the moving product surface for stripping. Each pulse covers an area of ​​the product surface, which is called the action spot.

[0112] The laser stripping device 12 further includes a control unit 15 for controlling the stripping laser 13, particularly for determining the oxide removal energy density threshold S. exp (Where applicable, there is also the metal-induced injury energy density threshold S) end The operating parameters of laser 13.

[0113] Control unit 15 is specifically configured to ensure that each point within a target segment on the product surface is exposed at least at one moment to an energy density S greater than the oxide removal energy density threshold determined for that segment. exp A method for controlling the stripping laser at higher energy densities 13.

[0114] For this purpose, the control unit 15 monitors the peak energy density emitted by each stripping laser 13 and controls these lasers to scan the target segment so that the pulses emitted by the stripping laser 13 cover the entire target segment, and so that every point in the segment is exposed to the oxide removal energy density threshold S at least at one moment. exp At higher energy densities.

[0115] The peak energy density emitted by each stripping laser 13 is selected to be higher than the oxide removal energy density threshold S. exp Furthermore, as needed, below the injury energy density threshold S end .

[0116] To achieve control over such scanning, the control unit 15 includes, for example, an optical and / or mechanical scanning system for laterally moving the spot of the beam 14 on the surface of the product or an optical system for converting the spot of the beam into a line of action.

[0117] Similar to the energy density threshold determining component 10, the strip 3 must remain at a fixed height as it passes under the stripping laser 13, and this can be achieved by a support roller 25 similar to the aforementioned support roller 23 or any other device with equivalent function.

[0118] In addition, other lasers 13 (not shown) and their possibly associated support rollers are provided to adjust the oxide removal energy density threshold S. exp And, where applicable, also based on the metal-induced injury energy density threshold S end The lower surface of strip 3 is stripped.

[0119] Each stripping laser 13 may be configured not to be perpendicular to the metal plate in order to minimize the interference of oxide particles sputtered by pulses previously emitted by the laser 13 itself or other lasers 13 in the same row on the incident beam.

[0120] According to one embodiment, each segment is a unit strip, and each unit strip is processed multiple times by a stripping laser to prevent subsequent pulses from being absorbed by particles and / or plasma generated by previously emitted pulses due to continuous pulse emission. In this case, the segments are spaced apart by a distance D. interThis involves performing the first horizontal line stripping sub-step with pulses N times the inter-pulse distance required to achieve uniform coverage, and then repeating this horizontal line stripping process N times, offsetting the starting position of the horizontal line by a distance D between each sub-step. inter .

[0121] By equipping each stripping laser 13 with a high-speed scanning system, the number of stripping lasers 13 required to process the entire surface of the strip 3 can be minimized. This high-speed scanning system, which is an optical or mechanical system, or both, enables the beam spot 14 to move laterally so that the spots are arranged side-by-side in a continuous line covering the entire width of the strip 3. Preferably, there is no overlap between the spots, or only a very small amount of overlap, to prevent the risk of transferring excessive energy to the overlapping areas. Alternatively, the laser stripping device 12 includes a long-distance focusing device, which enables the coverage of the entire width of the strip 3 with a limited number of stripping lasers 13.

[0122] By performing laser stripping according to the present invention, the stripping device can achieve greater versatility, particularly because when it is found during operation that the stripping parameters are not optimal, these parameters can be easily adjusted during the process. This adjustment can be achieved, for example, through the working spot of each stripping laser 13, rather than through a conventional beam focusing adjustment system.

[0123] Near the stripper laser 13, a device (not shown) is provided to remove (and preferably collect) oxides detached from the surface of the strip 3, as well as any dust mist (formed by the vaporization of metal particles, oxides, or organic matter) that may be generated during processing, by suction or brushing towards the container. In this way, such oxides can be easily and maximally recovered to prevent them from spreading and contaminating the surrounding atmosphere, and their reprocessing can be maximized to recover the metals they contain. Furthermore, this operation allows for the further removal of any oxides that failed to ideally detach from the surface of the strip 3 by the laser 13 (especially oxides on the upper surface of the strip 3 that cannot be detached by gravity). Finally, the dust and vapor can accumulate on the laser optical system, causing it to heat up or even crack. Removing such dust and vapor by suction prevents such damage to the laser optical system.

[0124] As an alternative, the strip 3 can be vertically circulated to prevent oxides that have detached from the surface of the strip 3 under the action of the laser 13 from being re-deposited on the surface of the strip 3 or on the defined component 10 (especially the optical elements of the defined component 10).

[0125] Thus, after passing under the stripping laser 13, the strip 3 is, in principle, completely stripped. The stripping quality can be checked using a suitable device, such as an optical stripping quality control device like a camera, or a group of such optical devices 16. This device inspects the surface of the strip 3 across its entire width and determines which areas of the strip 3 may have substandard stripping quality. Color differences on the surface of the strip 3 can serve as a basis for this judgment. One advantage of the aforementioned suction or brushing device or equivalent is that it prevents any detached oxide patches remaining on the surface of the strip 3 (especially the upper surface) from being mistakenly identified by the camera as detached oxide, thus requiring further stripping processing to remove them.

[0126] If the optical device 16 determines that the strip 3 is not satisfactory, further stripping can be performed on the strip 3 that is not satisfactory, or further stripping can be performed on the entire strip 3 on the side that meets the requirements.

[0127] In addition, the production line may include a chemical and / or electrolytic wet stripping station downstream of the laser stripping station, the stripping tank being at least temporarily filled with liquid to eliminate any defects found. Such a stripping bath may remain empty once strip 3 has been successfully stripped.

[0128] Another approach involves deflecting the strip 3 into a stripping bath via a vertically movable pressure roller, wherein the pressure roller is configured to act on the upper surface of the strip 3. This roller is located near the stripping bath and, during normal operation, is positioned to keep the moving strip 3 outside the stripping bath. When it is obvious that localized chemical and / or electrolytic stripping of the strip 3 is required, at least one of these pressure rollers moves downwards to press against the upper surface of the strip 3, causing the portion of the strip 3 to be treated to temporarily pass through the corresponding stripping bath to be used.

[0129] The following describes a method for removing an oxide layer from the surface of a moving metal product according to one embodiment, the method comprising combining... Figure 1 The described device performs the operation.

[0130] In the described example, the stripping method is performed after the product passes through annealing furnace 5.

[0131] Therefore, for example, each target segment should be considered as a unit strip with a width equal to the width of the product to be peeled off.

[0132] For each target segment of the product, the method includes the steps of determining an oxide layer removal energy density threshold and subsequently stripping it based on the determined removal energy density threshold.

[0133] For each segment, the step of determining the oxide layer removal energy density threshold includes: emitting an analytical laser pulse with a wavelength and pulse duration equal to that of the stripping laser 13 on a segment of the target segment to form an oxide-free stripping region within that segment.

[0134] The analysis laser pulse is emitted by the emission system 20, particularly by the laser source 30, and focused onto the target segment by the optical device 32.

[0135] The emission of the laser pulses is controlled by controller 26. Controller 26 controls the timing of pulse emission.

[0136] Furthermore, the energy of the analytical laser pulse is preferably controlled by the emission system 20 in such a way that the emission of the analytical laser pulse effectively removes a portion of the segment under laser action without damaging the metal.

[0137] The energy of the analyzed laser pulse is selected, for example, to vary with the information received by the transmitting system 20 from the processing system 24 (especially the threshold determination module 42) after the laser pulse was emitted at the previous moment.

[0138] Specifically, if the previously emitted analytical laser pulse failed to create a stripped area (meaning it failed to reach the removal energy density threshold), the emitting system 20 receives this information from the processing system 24. The emitting system 20 then emits an analytical laser pulse with a higher energy than the analytical laser pulse emitted at the previous moment.

[0139] Conversely, if the previously emitted analytical laser pulse creates a damaged area (the damaging energy density threshold has been determined by the processing system 24), the emitting system 20 receives that damaging energy density threshold from the processing system 24. The emitting system 20 then generates and emits analytical laser pulses with lower energy than the analytical laser pulse emitted at the previous moment, specifically maintaining the energy density below the damaging energy density threshold.

[0140] The product segment, which is in motion, then passes in front of the image acquisition system 22.

[0141] The step of determining the removal energy density threshold then includes the acquisition system 22 capturing images of the segmented surface under the action of the analytical laser pulse.

[0142] The image is sent to the processing system 24, which then determines the oxide removal energy density threshold S based on the image. exp .

[0143] Preferably, the processing system 24 further determines a metal-induced injury energy density threshold S based on the image. end .

[0144] Determine the oxide removal energy density threshold Sexp This includes determining the size of the area to be removed based on the image. This size is determined, for example, by the image analyzer 40.

[0145] Determine the oxide removal energy density threshold S exp This then includes determining the oxide layer removal energy density threshold based on the size of the stripping area.

[0146] The oxide layer removal energy density threshold is determined, for example, by the threshold determination module 42 based on the size of the stripping area and information related to the energy distribution of the analytical laser pulse that generates the stripping area.

[0147] Determine the metal-induced injury energy density threshold S end This includes determining the size of the damaged area of ​​the segment under laser irradiation based on the image. This size is determined, for example, by the image analyzer 40.

[0148] Determine the metal-induced injury energy density threshold S end This then includes: assessing the metal-induced injury energy density threshold based on the determined dimensions.

[0149] Metal-induced injury energy density threshold S end For example, the threshold determination module 42 evaluates the damage based on the size of the damaged area and information related to the energy distribution of the analytical laser pulse that generated the damaged area.

[0150] Preferably, the energy density threshold S is removed. exp and the injury energy density threshold S end The signal is sent to the transmitting system 20 to control the power of the analytical laser pulses emitted at subsequent times, so that such analytical laser pulses emitted at subsequent times can effectively strip away a portion of the segment under their action without damaging the metal.

[0151] Subsequently, the target section of the product, which is still in motion, passes in front of the laser stripping device 12 and undergoes the stripping process there.

[0152] During the stripping process, laser 13 emits laser pulses onto the target segment to strip it, and the energy density of the pulses is higher than the determined removal energy density threshold.

[0153] Specifically, the control unit 15 receives the oxide removal energy density threshold S determined for the target section. exp And, where applicable, also receive the injury energy density threshold S. end Moreover, this ensures that every point within the target segment is exposed to the oxide removal energy density threshold S at least at one moment. exp Controlling the laser at higher energy densities 13.

[0154] For this purpose, the control unit 15 monitors the peak energy density emitted by each laser 13 and controls these lasers to scan the target segment so that the pulses emitted by the laser 13 cover the entire target segment, and so that every point in the segment is exposed to the oxide removal energy density threshold S at least at one moment. exp At higher energy density thresholds.

[0155] The peak energy density emitted by each laser 13 is selected to be higher than the oxide removal energy density threshold S. exp And, where applicable, below the injury energy density threshold S end .

[0156] After stripping, the detached oxides are removed, for example by suction or brushing towards the container, and preferably collected.

[0157] After passing under laser 13, the target section is, in principle, completely removed. As described above, the condition of the section is inspected, for example, using an optical removal quality control device such as a camera. This device inspects the surface of the section across its entire width and determines which areas of the section may have unsatisfactory removal quality.

[0158] The steps of determining the oxide layer removal energy density threshold and the stripping process based on the removal energy density threshold are performed sequentially for each segment of the moving product.

[0159] Preferably, between adjacent sections, the laser source 30 is moved relative to the production line, particularly in a direction parallel to the product movement plane and orthogonal to its movement direction (i.e., along the product width direction), so that the position of the product segment orthogonal to the product movement direction and under the action of the laser source 30 changes between adjacent sections.

[0160] For example, for a strip 3 with a width L (along the Y direction, which is parallel to the surface and transverse to the direction of movement), the first segment with coordinates y=y0 is under the action of the laser source 30; the second segment with coordinates y=y0+Δy is under the action of the laser source 30; and so on.

[0161] According to one embodiment, at least some information related to the energy distribution of the pulses emitted by the laser source 30, particularly their shape, power, or energy, is unknown beforehand.

[0162] When the shape of the energy distribution is unknown, the energy density threshold determination component 10 includes, for example, a system for determining this shape.

[0163] This determination system is used to analyze the laser pulses emitted by the transmitting system 20 and determine the shape of the energy distribution. Such a system is particularly useful when the shape of the pulsed beam emitted by the transmitting system 20 does not remain stable over time.

[0164] Figure 8 The illustrated determination system includes an optical device 62, such as a beam splitter, for deflecting a portion of the analytical laser pulse emitted by the emission system 20 toward the beam analyzer 64.

[0165] The determination system also includes a beam analyzer 64 for determining the shape of the pulse energy distribution based on a portion of the deflected pulse and sending the shape to the threshold determination module 42.

[0166] The beam analyzer 64 includes a sensor held at a predetermined distance from the optical device 62, the predetermined distance being equal to the distance between the optical device 62 and the moving product surface.

[0167] For this purpose, the beam analyzer 64 and the optical device 62 are, for example, mounted relative to each other and fixed relative to the product in a direction orthogonal to the product surface, but movable relative to the direction of movement of the strip 3. For example, as Figure 9 As shown, the beam analyzer 64 and the optical device 62 are fixedly mounted on a rolling system 67 located on the surface of the product 3. This rolling system can translate (by rolling) relative to the product along the product movement direction X.

[0168] In this way, not only can a constant distance be maintained between the beam analyzer 64 and the optical device 62, but also a constant distance can be maintained between the optical device 62 and the surface of the product 3.

[0169] Furthermore, since the received energy distribution is obtained based on a partial pulse beam, the threshold determination module 42 is also used to correct the received energy distribution.

[0170] According to this embodiment, the method includes determining the shape of the above distribution.

[0171] Determining the shape of the above distribution includes, for example, deflecting a portion of the laser pulse emitted by the emission system 20, particularly through a beam splitter, toward the beam analyzer 64; and having the beam analyzer 64 assess the shape of the energy distribution.

[0172] The energy distribution shape determined in this way is then sent to the threshold determination module 42.

[0173] According to this embodiment, the pulse whose energy distribution needs to be determined is an analytical laser pulse, that is, a pulse that generates a stripping area by acting on the product surface.

[0174] Preferably, the energy density threshold determining component 10 further includes means for determining the energy of each pulse emitted by the laser source 30. In practice, even if the average pulse energy is known, this energy may fluctuate; therefore, by knowing the energy of each pulse emitted by the laser source 30 onto the product surface, the energy density threshold can be determined more accurately. Such pulse energy determining means includes, for example, a calibrated photodiode disposed on one side of the laser beam.

[0175] According to another embodiment, the energy distribution shape of the pulse emitted by the transmitting system 20 is known, but the energy or power of the pulse is unknown. In this case, the energy density threshold determining component 10 further includes a system for determining the energy or power of the pulse emitted by the transmitting system 20.

[0176] Such determination systems are typically used to periodically determine the power (or energy) of the emitted pulses for recalibration. In contrast, the energy determination devices described above are typically used to determine the energy of each pulse in real time.

[0177] This energy determination system and Figure 9 The main difference in the system shown in the example is that a power meter is used instead of a beam analyzer 64.

[0178] Furthermore, in this embodiment, it is not necessary to keep the power meter at a predetermined distance from the optical device, which is equal to the distance between the optical device and the moving product surface.

[0179] According to this embodiment, the method includes determining the energy or power of the pulse.

[0180] Determining the energy or power of a pulse includes, for example, deflecting a portion of the laser pulse emitted by the transmitting system 20, particularly through a beam splitter, toward a power meter; and evaluating the energy and / or power of the pulse by the power meter.

[0181] The pulse energy and / or power determined in this way are then sent to the threshold determination module 42.

[0182] According to this embodiment, the pulse whose energy or power is to be determined is also a pulse that generates a stripping area by acting on the surface of the product.

[0183] according to Figure 10 In another illustrative embodiment, the pulse used to determine the energy distribution and / or power is not a pulse that generates the stripping area by acting on the product surface, but a pulse emitted before or after it, hereinafter referred to as an auxiliary pulse.

[0184] According to this embodiment, the determination system includes an optical device 68 for selectively guiding a pulsed beam emitted by the emission system 20 to a beam analyzer and / or a power meter, or to a product surface. The determination system also includes a beam analyzer 70 and / or a power meter 72 for determining the shape of the energy distribution and / or the energy of the beam.

[0185] Optical device 68 includes, for example, a galvanometer scanner 74 and a reflector 76, and preferably includes a beam splitter 78.

[0186] Galvanometer scanning device 74 (in) Figure 10 (shown at two locations) is used to selectively deflect the entire beam emitted by the emission system 20 toward the product surface or toward the reflector 76.

[0187] The reflector 76 is used to reflect the beam deflected onto it in the manner described above toward the beam splitter 78.

[0188] Beam splitter 78 is used to split the pulsed beam into two sub-beams, one of which is directed toward beam analyzer 70 and the other toward power meter 72.

[0189] If the shape of the energy distribution is unknown, the beam analyzer 70 and beam splitter 78 can be omitted.

[0190] Conversely, if the pulse energy is known, the power meter 72 and the beam splitter 78 can be omitted.

[0191] According to this embodiment, the method includes: emitting auxiliary pulses by the transmitting system 20, such pulses being directed toward the beam analyzer 70 and / or toward the power meter 72.

[0192] When it is necessary to determine the shape of the energy distribution and the energy or power, the auxiliary pulse is directed toward the beam analyzer 70 and / or toward the power meter 72 via the beam splitter 78.

[0193] The auxiliary pulse passes through the galvanometer scanning device 74 toward the beam analyzer 70 and / or toward the power meter 72.

[0194] The method then includes: evaluating the shape of the energy distribution of the auxiliary pulse by a beam analyzer 70; and / or evaluating the energy or power of the pulse by a power meter 72.

[0195] The shape, energy, and / or power determined in the manner described above are then sent to the threshold determination module 42.

[0196] After the auxiliary pulse is emitted, the galvanometer scanner 74 directs the subsequent pulse toward the surface of the product 3.

[0197] Therefore, the method and apparatus of the present invention can achieve efficient removal of metal products on an industrial scale. Furthermore, thanks particularly to the precise determination of parameters, efficient removal of oxide layers is achieved.

[0198] Although the illustrated example uses a flat product such as strip, the present invention can also be applied to other types of products such as metal rods, pipes, or metal wires.

Claims

1. A method for removing an oxide layer from a moving metal product (3) on its surface, characterized in that, The method uses at least one stripping laser (13) to perform laser stripping, wherein the method includes sequentially performing the following steps on each of a plurality of consecutive segments preceding and following the moving product: - Determine the oxide layer removal energy density threshold of the target segment of the moving metal product (3), wherein the oxide layer removal energy density threshold corresponds to the minimum energy density required to remove the oxide layer on the target segment, including: An analytical laser pulse is emitted by an emission system (20) including a laser source (30) onto a segment of the target section to form a stripping region lacking the oxide layer within the segment, wherein the wavelength and pulse duration of the analytical laser pulse are equal to the wavelength and pulse duration of the stripping laser (13); Capture an image of the surface of the segment under the action of the analytical laser pulse; Based on the image, determine the representative size of the stripped area; Based on the representative size and information related to the energy distribution of the analytical laser pulse, the oxide layer removal energy density threshold is evaluated; - The stripping laser (13) emits a stripping laser pulse onto the target section for stripping, wherein the energy density of the stripping laser pulse is higher than the determined oxide layer removal energy density threshold. The stripping laser (13) is controlled by a control unit (15) that receives a determined oxide removal energy density threshold, such that each point of the target segment is exposed to an energy density higher than the oxide removal energy density threshold at at least one moment.

2. The peeling method according to claim 1, characterized in that, The emission of the analytical laser pulse forms a damaged area of ​​the metal located below the oxide layer within the segment, wherein the method further includes: determining a representative size of the damaged area based on the image; and evaluating a metal damage energy density threshold based on the representative size of the damaged area and information related to the energy distribution of the analytical laser pulse, wherein the metal damage energy density threshold corresponds to an energy density beyond which degradation of the surface of the metal product (3) below the oxide layer is observed.

3. The peeling method according to claim 2, characterized in that, Further includes: The damage energy density threshold is sent to the emitting system (20), wherein, in the next segment of the moving metal product (3), the energy of the analytical laser pulse emitted by the emitting system (20) is adjusted such that the energy density at any point in the segment under the action of the analytical laser pulse is lower than the damage energy density threshold.

4. The peeling method according to claim 1 or 2, characterized in that, The information associated with the energy distribution includes: the shape of the energy distribution and the energy or power of the analyzed laser pulse.

5. The stripping method according to claim 4, characterized in that, The step of determining the oxide layer removal energy density threshold includes: determining the energy distribution shape of the analytical laser pulse; and / or determining the energy or power of the analytical laser pulse.

6. The stripping method according to claim 5, characterized in that, Determining the energy distribution shape of the analytical laser pulse in the step of determining the oxide layer removal energy density threshold includes: deflecting a portion of each analytical laser pulse to a beam analyzer (64); and evaluating the energy distribution shape by the beam analyzer (64).

7. The stripping method according to claim 5, characterized in that, Determining the energy and / or power of the analytical laser pulse in the step of determining the oxide layer removal energy density threshold includes: deflecting a portion of each analytical laser pulse toward a power meter; and evaluating the energy and / or power of the analytical laser pulse by the power meter.

8. The peeling method according to claim 4, characterized in that, The step of determining the oxide layer removal energy density threshold includes: determining the energy distribution shape and / or the energy or power of the auxiliary laser pulse emitted by the emission system (20), wherein the auxiliary laser pulse is different from the analytical laser pulse.

9. The peeling method according to claim 8, characterized in that, Determining the energy distribution shape and / or the energy or power of the auxiliary laser pulse includes: The auxiliary laser pulse is emitted by the emission system (20); The auxiliary laser pulse is directed toward the beam analyzer (70) and / or toward the power meter (72) by means of the galvanometer scanning device (74). The energy distribution shape of the auxiliary laser pulse is evaluated by the beam analyzer (70), and / or the energy and / or power of the auxiliary laser pulse is evaluated by the power meter (72).

10. The stripping method according to claim 1 or 2, characterized in that, The metal product (3) is a strip, bar, sheet, plate, pipe or wire.

11. An apparatus for laser stripping of a moving metal product (3) having an oxide layer on its surface by means of at least one stripping laser (13), characterized in that, include: - A determining component (10) for determining an oxide layer removal energy density threshold for each of a plurality of successive segments of the moving metal product (3), the oxide layer removal energy density threshold corresponding to the minimum energy density required to remove the oxide layer on a target segment, wherein the determining component (10) includes: An emission system (20) having a laser source (30) is provided, wherein the emission system (20) is used to emit analytical laser pulses onto segments of the target segment to form stripping regions in the segments where the oxide layer is missing, wherein the wavelength and pulse duration of the analytical laser pulses are equal to the wavelength and pulse duration of the stripping laser (13); Image acquisition system (22) is used to acquire images of segments under the action of the analytical laser pulse during the movement of the product; The processing system (24) is used to determine the representative size of the stripping area based on each image acquired by the image acquisition system (22), and to evaluate the oxide layer removal energy density threshold based on the representative size and information related to the energy distribution of the analytical laser pulse. - A laser stripping device (12) including at least one stripping laser (13) for emitting stripping laser pulses onto each of the plurality of successive segments of the moving metal product for stripping; and a control unit (15) for receiving the oxide layer removal energy density threshold of the segment and controlling the stripping laser (13) to emit stripping laser pulses with energy higher than the oxide layer removal energy density threshold, such that each point of the target segment is exposed to an energy density higher than the oxide layer removal energy density threshold at at least one moment.

12. The laser stripping device according to claim 11, characterized in that, The analytical laser pulse is tuned to form a damaged area of ​​the metal located below the oxide layer within the segment, whereby the analytical laser pulse damages the metal. The processing system (24) is used to determine a representative size of the damaged area based on the image and to evaluate a metal damage energy density threshold based on the representative size of the damaged area and the information related to the energy distribution of the analytical laser pulse. The metal damage energy density threshold corresponds to an energy density beyond which degradation of the surface of the metal product (3) below the oxide layer is observed.

13. The laser stripping device according to claim 12, characterized in that, The processing system (24) is used to send the injury energy density threshold to the transmitting system (20), wherein the transmitting system (20) is used to adjust the energy of the analytical laser pulse according to the injury energy density threshold so that the energy density at each point in the affected segment of the next segment of the moving product is lower than the injury energy density threshold.

14. The laser stripping device according to claim 11 or 12, characterized in that, The information associated with the energy distribution includes the shape of the energy distribution and the energy or power of the analytical laser pulse, wherein the laser stripping apparatus includes a system for determining the shape of the energy distribution of the analytical laser pulse and / or a system for determining the energy or power of the analytical laser pulse.

15. The laser stripping device according to claim 14, characterized in that, The system for determining the energy distribution shape of the analytical laser pulse includes a beam analyzer (64) and an optical device (62) for deflecting a portion of each analytical laser pulse toward the beam analyzer (64), wherein the beam analyzer (64) is used to evaluate the energy distribution shape based on the deflected portion of the analytical laser pulse.

16. The laser stripping device according to claim 15, characterized in that, The optical device (62) is a beam splitter.

17. The laser stripping device according to claim 14, characterized in that, The system for determining the energy or power of the analytical laser pulse includes a power meter and an optical device (62) for deflecting a portion of each analytical laser pulse toward the power meter, wherein the power meter is used to evaluate the energy and / or power of the analytical laser pulse based on the deflected portion of the analytical laser pulse.

18. The laser stripping device according to claim 17, characterized in that, The optical device (62) is a beam splitter.

19. The stripping device according to claim 11 or 12, characterized in that, The information related to the energy distribution includes: the shape of the energy distribution and the energy or power of the analytical laser pulse, wherein the laser stripping device includes a system for determining the shape of the energy distribution and / or the energy or power of an auxiliary laser pulse emitted by the emission system (20), wherein the auxiliary laser pulse is different from the analytical laser pulse.

20. The stripping device according to claim 11 or 12, characterized in that, In order to process the entire surface of the metal product consisting of strip, bar, tube, sheet, plate or wire, the stripping device includes a set of laser sources (30) and a set of stripping lasers (13) distributed near the metal product (3).

Images