Method and apparatus for stripping oxide layers from metal products

Abstract

The method includes the steps of determining an oxide layer removal energy density threshold from a portion of the product (3), comprising transmitting an analysis pulse of equal wavelength and pulse duration to a segment of the portion from an ablation laser (13) to form a ablated area, capturing an image of the segment, determining a dimension representative of the ablated area from the image, and evaluating the ablation energy density threshold from the dimension; and transmitting a ablation pulse to the portion, the energy density of the ablation pulse being higher than the ablation energy density threshold, the ablation laser (13) being controlled such that each point of the portion is exposed to an energy density higher than the ablation energy density threshold.

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for stripping the oxide layer covering the surface of a metal product, particularly steel, after exposure to an environment during which time, for example in a heat treatment furnace, is favorable for oxidation of some of the components. [Background technology]

[0002] In the remainder of this document, the preferred application of the invention is in the field of stainless steel strip and sheet of all classifications (austenitic, ferritic, austenitic ferritic, etc.), whether hot rolled or cold formed. However, this is not limiting and it should be understood that the invention may also be applied to other metals presenting similar technical problems to those encountered with stainless steel strip and sheet, in particular with the various types of carbon steels and special alloys, in particular ferrous alloys. It may also be applied to products other than strip and sheet, for example wire and welded and seamless tubes, with modifications to the described apparatus that will be obvious to the skilled person.

[0003] It is common for stainless steel sheet and strip to be in contact with an oxidizing environment, such as air, and undergo processes that lead to undesirable oxide layers forming on their surfaces at high temperatures. The composition of these oxides varies substantially according to the composition of the base material and the conditions under which they are formed. Most commonly, oxides of the elements Fe, Cr, Mn and Si predominate.

[0004] The treatments that lead to this formation are typically, but are not limited to, the reheating that the semi-finished product (ingots, slabs, blooms, billets) undergoes before hot rolling and the time in open air that it undergoes after hot rolling, and the various annealing processes at several hundred degrees that the strip or sheet undergoes before and / or during and / or after its cold rolling cycle, if this annealing is carried out in an environment that is not completely inert or reducing (the latter may be carried out in one or more stages, some of which may be separated by intermediate annealing processes). These undesirable oxides must of course be removed before the sheet or strip becomes a usable product or a semi-finished product ready to undergo the finishing forming operations that will make it a usable product. It is also often important to remove these oxides before the first cold rolling stage, to prevent them from becoming embedded in the surface of the semi-finished product during rolling and leading to a poor surface finish.

[0005] It should be understood that the undesirable oxide layer referred to here is not the thin Cr-oxide based layer (known as the "passive layer") that forms naturally in air and at room temperature on the surface of stainless steels to protect them from oxidation. The oxide layer that presents the problem and which we wish to remove is the one that forms during the time the strip spends in an oxidizing environment at high temperatures. Once this layer is removed, the surface of the stainless steel is exposed and the protective passive layer of Cr-oxide can form again quickly and naturally, making the stainless steel again in normal service conditions.

[0006] The use of mechanical descaling by shot blasting (projection of hard balls over the surface to be treated), which allows the majority of the oxide to be easily torn off or removed, for example, by brushing, and / or oxide breaking (passage of the strip between pairs of rollers working under bending, compression and traction), may not be sufficient to remove everything. Shot blasting also has the drawback of increasing the surface roughness, and subsequent operations on the sheet or strip may not allow correction if undesired.

[0007] Most commonly, the unwanted oxide layer is removed by a chemical or electrolytic stripping method, or a series of such stripping operations.

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

[0009] These peeling operations result in obtaining strips or sheets exhibiting surface finishes that usually fall into various standard categories. - Hot rolling, annealing and stripping, typically finishing 1D for products where chemical stripping is performed. Mechanical stripping (oxide breaking, shot blasting) is also commonly used upstream of chemical stripping. - Finishing 2B for products that have been annealed, stripped, typically electrolytic and chemical, and skin passing (a work-hardening rolling device that improves strip flatness and reduces roughness with a small reduction rate of the product thickness, usually around a few percent). - Finish 2D on cold rolled products that have been annealed and exfoliated but not skin passed. - Finish 2E on cold rolled products that have been annealed, shot blasted and peeled but not skin passed.

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

[0011] It consumes large amounts of acid with at most very limited possibilities to recover portions for later reuse.

[0012] The infrastructure required for the process, i.e. the continuous stripping bath and its accessories, is costly and cumbersome. It is not uncommon to find chemical stripping plants for conveyor belts up to 200 m long.

[0013] These units use hazardous products, especially hydrofluoric acid. Their liquid and solid pollutant emissions (sludge containing oxides that are mixed with the stripping liquid) must be stored and reprocessed according to strict regulations, a costly problem whose significance is only likely to increase in the future. The acid baths also transmit acid vapors, which, if heated, must be neutralized. Nitric acid is also a source of NOx emissions that must be captured and treated.

[0014] Electrolytic stripping methods are also used, performed while the strip or sheet is immersed in baths generally based on sodium sulfate, nitric acid or sulfuric acid, which also have to be reprocessed after use. Electrolytic stripping uses relatively large amounts of electrical energy and requires rather expensive equipment. Electrolytic stripping can be supplemented by chemical acid stripping, which is lighter than chemical stripping alone but presents the same drawbacks as described above. Electrolytic stripping also produces sludge that must be stored and reprocessed. Spent baths must be reprocessed. The sludge and bath reprocessing, although less expensive, less dangerous and less complicated than chemical stripping in acid baths, constitute further and crucial limitations to the use of the method.

[0015] Finally, the presence of hexavalent chromium in solution within the stripping liquid presents a significant health risk to humans and the environment, and its levels within the liquid and human exposure are measured and monitored.

[0016] Thus, at least in certain cases, the possibility of replacing chemical or electrolytic stripping of metal products with methods using lasers was studied. The classic book "Laser Cleaning" (Boris Luk'yanchuk, December 2002, ISBN: 978-981-02-4941-0) discusses such possibilities in particular for cleaning of works of art and architecture, and therefore relatively small fixed surfaces (especially chapter 2, "an overview of experimental research into the laser cleaning of contaminants from surfaces"). A laser beam is projected onto the surface to be cleaned and detaches the oxide layer.

[0017] In this way, the use of acids and / or sulfates is avoided and there is no need to rework polluting and harmful sludges and liquids. Only the removed oxides need to be collected, for example by suction, and it is possible to rework them, preferably by dry methods, in order to recover and recycle the contained metals. The safety of people and the workplace environment is better guaranteed. The entire laser surface cleaning operation also presents a better overall energy balance than with wet cleaning (chemical and / or electrolytic), as long as the electrical costs of the laser operation are not extremely high, especially with respect to those required for electrolytic stripping. The apparatus has clear advantages in terms of costs of civil engineering operations when assembling the apparatus and can be much smaller than the apparatus for stripping, which includes several successive baths. If pulsed lasers are used, it is possible to deliver high energy levels at high frequencies and with great autonomy in extremely short times, and the service life of these lasers can reach several years, especially without maintenance.

[0018] However, the use of existing techniques combined with CO2 or excimer lasers does not allow optimal results to be obtained on strips or sheets on industrial-scale lines due to the high operating costs due to the number of lasers used, given the heavy maintenance, the continuous operating mode with lasers or too long pulses, and the high speed of the current lines. Furthermore, the solutions offered assume a uniform surface condition due to the width and length of the strip (see EP0927595-A1), mostly due to a fixed line speed. On the same strip, the inertia of the machines, especially the furnaces, leads to a modification (of thickness and / or type) of the oxide layer if the speed of the line is changed for certain reasons. Even if it was previously considered that the nature and thickness of the oxide layer to be removed were known, these are subsequently changed, and the adaptation of the pulse frequency or energy only works if the oxide layer does not change (which is almost not the case). Finally, line speeds are now reaching about 100 to 150 m / min.

[0019] Document EP 3 631 049 A1 describes a method for stripping oxide layers, in which the composition and thickness of the oxide layer are determined by laser-induced plasma spectroscopy.

[0020] This technique is unsatisfactory because damage to the metal under the oxide layer is required. In addition, determining the thickness and composition of the oxide layer does not make it possible to determine in a reliable manner which stripping parameters should be used to strip the oxide layer.

[0021] Document WO2018 / 096382 further describes a method and an apparatus for the laser delamination of metal articles.

[0022] According to the method, the emissivity of the oxidized surface of the metal product to be stripped is determined by transmitting a beam by a first laser onto this surface, intercepting the beams reflected by the oxidized surface and analyzing these reflected beams. The operating parameters of the stripping laser are then adapted as a function of the emissivity and are thus determined.

[0023] This method makes it possible to adapt the energy delivered by the ablation laser in order to effectively ablate the oxide layer present on the surface.

[0024] However, this method is not entirely satisfactory, since the emissivity does not always make it possible to determine the correct parameters for effective stripping of the oxide layer. [Prior art documents] [Patent documents]

[0025] [Patent Document 1] EP0927595-A1 [Patent Document 2] EP3631049A1 [Patent Document 3] WO2018 / 096382 [Patent Document 4] EP0509177-A2 [Patent Document 5] EP0695808-A1 [Non-patent literature]

[0026] [Non-Patent Document 1] "Laser Cleaning" (Boris Luk'yanchuk, December 2002, ISBN: 978-981-02-4941-0) Summary of the Invention [Problem to be solved by the invention]

[0027] One object of the present invention is therefore to propose a method and an apparatus for stripping flowing metal products, making it possible to obtain effective stripping on an industrial scale. [Means for solving the problem]

[0028] To this end, the present invention has as its object a method for stripping a flowing metal product exhibiting an oxide layer on its surface, said method using laser stripping by at least one stripping laser, said method comprising the following steps carried out successively on each section of a plurality of successive sections of the flowing product: - determining an oxide layer removal energy density threshold on a portion under consideration of said flowing metal product, said threshold corresponding to a minimum energy density required for removal of the oxide layer on said portion under consideration, transmitting an analysis laser pulse by a delivery system comprising a laser source, the analysis laser pulse being of equal wavelength and pulse duration to an ablation laser on the segment of the part under consideration to form an ablated area in the segment that is free of an oxide layer; capturing an image of a segment of the surface affected by said analytical laser pulse; determining a size representative of the peeled area from said image; Estimation of the oxide layer removal energy density threshold from information related to the representative dimensions and the energy profile of the analyzed laser pulses and - transmitting, by a delamination laser, a delamination laser pulse on the considered part for delamination, the energy density of the delamination pulse being higher than the determined oxide layer removal energy density threshold, The ablation laser is controlled by a control unit receiving the determined oxide layer ablation energy density threshold such that each point of the considered portion is exposed at least momentarily to an energy density higher than the oxide layer ablation energy density threshold.

[0029] According to other advantageous aspects of the invention, the method comprises one or more of the following characteristics, taken alone or in any technically possible combination, the characteristics being: - transmitting an analysis laser pulse forming in said segment a damaged area where the metal beneath the oxide layer has been damaged, the method further comprising the steps of determining from said image a dimension representative of the damaged area, and evaluating from information relating to the dimension representative of the damaged area and the energy profile of the analysis laser pulse a metal damage energy density threshold corresponding to an energy density above which degradation of the surface of the metal product beneath the oxide layer is observed, - the method further comprises transmitting the damage energy density threshold to the transmission system, whereby at a subsequent portion of the flowing metal product, the transmission system transmits an analysis laser pulse of an energy adapted such that at any point of the segment affected by the analysis laser pulse, the energy density is below the damage energy density threshold; - the information relating to the energy profile includes the shape of the energy profile and the energy or power of the analyzed laser pulse, - determining the oxide layer removal energy density threshold comprises determining a shape of the energy profile of the analysis laser pulse and / or determining the energy or power of the analysis laser pulse, - determining the oxide layer removal energy density threshold comprises determining a shape of an energy profile of the analysis laser pulses, the shape including deflecting a portion of each analysis laser pulse towards a beam analyzer and evaluating the shape of the energy profile by the beam analyzer; - determining the oxide layer removal energy density threshold comprises determining the energy and / or power of the analysis laser pulses, including diverting a portion of each analysis laser pulse towards a power meter and evaluating the energy and / or power of the analysis laser pulses by the power meter; - determining the oxide layer removal energy density threshold comprises determining the shape of the energy profile and / or the energy or power of an auxiliary laser pulse delivered by the delivery system, the auxiliary laser pulse being separate from the analysis laser pulse; - determining the shape and / or energy or power of the energy profile of the auxiliary laser pulse, delivering an auxiliary laser pulse through the delivery system; steering the auxiliary laser pulse towards a beam analyzer and / or towards a power meter by a mirror galvanometer scanning device; evaluating the shape of the energy profile of the auxiliary laser pulse by a beam analyzer and / or evaluating the energy and / or power of the auxiliary laser pulse by a power meter; The metal product is a strip, a bar, a sheet, a plate, a tube or a wire.

[0030] The invention also has as its object an apparatus for the laser stripping of a flowing metal product exhibiting an oxide layer on its surface by means of at least one stripping laser. The apparatus comprises: - a determining assembly configured to determine, for each of a plurality of successive portions of the flowing metal product, an energy density threshold for removal of the oxide layer corresponding to a minimum oxide layer removal energy density required for the portion under consideration, the determining assembly comprising: a delivery system including a laser source configured to deliver an analysis laser pulse of a wavelength and pulse duration equal to that of the ablation laser on the segment of the part under study to form an ablated area in the segment that is free of an oxide layer; an image acquisition system configured to acquire images of segments affected by the analytical laser pulses during the movement of the product; a processing system configured to determine a dimension representative of the ablated area from each image acquired by the image acquisition system and to evaluate an oxide layer removal energy density threshold from information related to said representative dimension and an energy profile of the analysis laser pulse, The apparatus further comprises: - comprising a laser ablation assembly comprising at least one ablation laser configured to deliver ablation laser pulses to each of a plurality of successive portions of the metal product flowing for ablation, and a control unit configured to receive an oxide layer ablation energy density threshold for the portion under consideration and to control the delivery by the ablation laser of laser pulses of energy above the oxide layer ablation energy density threshold such that each point of the portion under consideration is exposed at least momentarily to an energy density above the oxide layer ablation energy density threshold.

[0031] According to other advantageous aspects of the invention, the device comprises one or more of the following characteristics, taken alone or in any technically possible combination, which characteristics are: - the analysis laser pulse is capable of forming a damaged area in said segment where metal beneath an oxide layer has been damaged by the analysis laser pulse, and a processing system is configured to determine from said image a dimension representative of the damaged area, and to evaluate from information relating to the dimension representative of the damaged area and the energy profile of the analysis laser pulse a metal damage energy density threshold corresponding to an energy density above which degradation of the surface of the metal product beneath the oxide layer is observed; - the processing system is configured to transmit the damage energy density threshold to the transmission system, the transmission system being configured to adapt the energy of the analysis laser pulse as a function of the damage energy density threshold such that at any point in the affected segment of the next portion of the flowing product, the energy density is below the damage energy density threshold; - the information relating to the energy profile includes the shape of the energy profile and the energy or power of the analyzed laser pulse, - the laser ablation apparatus comprises a system for determining the shape of the energy profile of the analysis laser pulse and / or a system for determining the energy or power of the analysis laser pulse, a system for determining the shape of the energy profile of an analysis laser pulse, comprising a beam analyzer and an optical device, in particular a beam splitter, configured to deflect a portion of each analysis laser pulse towards the beam analyzer, the beam analyzer being configured to evaluate the shape of the energy profile from the deflected portion of the analysis laser pulse; - a system for determining the energy or power of an analysis laser pulse, comprising a power meter and an optical device, in particular a beam splitter configured to deflect a portion of each analysis laser pulse towards the power meter, the power meter being configured to evaluate the energy and / or power of the analysis laser pulse from the deflected portion of the analysis laser pulse; - the information related to the energy profile includes a shape and an energy or power of the energy profile of the analysis laser pulse, the laser ablation apparatus comprising a system for determining a shape and / or an energy or power of the energy profile of an auxiliary laser pulse delivered by the delivery system, the auxiliary laser pulse being separate from the analysis laser pulse; a group of laser sources and a group of ablation lasers distributed in the vicinity of said metal product for treating the entire surface of said metal product consisting of a strip, a bar, a tube, a sheet, a plate or a wire;

[0032] The invention also relates to a continuous processing line for metal products, which is equipped with a stripping device according to the invention.

[0033] The invention will be better understood from the following description, taken in conjunction with the accompanying drawings, in which: [Brief description of the drawings]

[0034] [Figure 1] 1 is a schematic diagram showing in profile a continuous line with a laser ablation device according to one embodiment of the present invention; [Diagram 2] FIG. 2 shows an example of a laser pulse energy profile 34. [Diagram 3]FIG. 2 is a diagram showing an example of a laser pulse energy profile 35. [Figure 4] FIG. 2 shows an example of a laser pulse energy profile 36. [Diagram 5] 3A-3C show examples of surface features obtained by transmitting laser pulses having the energy profile shown in FIG. 2. [Figure 6] FIG. 4 shows an example of a surface morphology obtained by transmitting a laser pulse having the energy profile shown in FIG. 3. [Figure 7] 5A-5C show examples of surface features obtained by transmitting laser pulses having the energy profile shown in FIG. 4. [Figure 8] 4 is a schematic diagram showing a part of a stripping device according to a second embodiment. [Figure 9] FIG. 9 is a diagram showing details of the peeling device in FIG. 8. [Figure 10] 13 is a schematic diagram showing a part of a peeling device according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The laser stripping device according to the invention, which is described in more detail and illustrated by way of example with reference to the treatment of a moving cold-rolled stainless steel strip that has just been cold-rolled and annealed on a continuous line, and which ensures at least a fundamental part of this stripping function, can also replace electrolytic and / or chemical stripping systems normally used in continuous lines of this type or be integrated in this continuous line upstream of them (examples of such continuous lines can be found, inter alia, in documents EP 0509177-A2 and EP 0695808-A1).

[0036] It will be appreciated that the laser delamination apparatus described herein may also be integrated into a continuous processing line including more or less equipment than described herein, or may be the subject of a separate apparatus dedicated to such delamination.

[0037] Also not shown is equipment that is typically present on such a line, which has no primary metallurgical role and is not in any case related to the laser stripping operation performed according to the invention. Notably, one may mention pinch rollers that initiate the strip in operation, and strip accumulators that act as "buffers" between some of the equipment, each of which may require different strip speeds.

[0038] The continuous line shown comprises an unwinding device 1 for a coil 2 of hot-rolled stainless steel strip 3, the thickness of which is typically a few tens or mm and a maximum width of 2 m. This strip 3, moving typically at a speed of up to 150 m / min, passes into a cold rolling mill 4, generally after being stripped by any chemical and / or mechanical means not shown, or by a laser with the means according to the invention as described, to reduce its thickness to a value typically of about 0.2 to 15 mm, in order to obtain a cold-rolled strip.

[0039] The cold-rolled strip 3 then passes into an annealing furnace 5, which is heated to a temperature of several hundred degrees, this temperature being adapted depending on the metallurgical purpose of the annealing. If this annealing is carried out (intentionally or accidentally) in the presence of non-negligible amounts of oxidizing gases, such as oxygen, it leads to the formation of an undesirable oxide layer on the surface of the strip 3, the composition, thickness and adhesion of which on the strip 3 depend, among other things, on the composition of the strip 3, the composition of the environment in the furnace 5, the temperature in the furnace 5 and the length of time the strip 3 is in the furnace 5. In view of the many parameters (in particular the composition of the strip 3, and the annealing conditions), which are not all easily controllable and which in every case can vary substantially depending on the exact treatment carried out, and in view of the manufacturing hazards, it is not possible to assign to this oxide layer precise systematic characteristics that would allow an easy standardization of the stripping conditions for the strip 3. This is also one of the disadvantages of the wet stripping method, especially the chemistry, where the composition of the bath cannot be easily adapted to what is actually necessary to obtain a satisfactory stripping of the strip 3 at the lowest cost.

[0040] According to the embodiment shown in FIG. 1, the laser stripping device is placed in line after the annealing furnace 5 .

[0041] The laser ablation apparatus includes an energy density threshold determining unit 10 and a laser ablation apparatus 12 .

[0042] The energy density threshold determination assembly 10 is intended to evaluate the effective energy density required to strip the oxide layer on the flowing strip. Indeed, it is possible to obtain a heterogeneous oxide layer over the length and / or width of the strip 3 to be stripped, either before or after spontaneous or involuntary changes in the upstream operating parameters of the line, for example deceleration or acceleration of the strip on the line, or heterogeneous contamination over the width of the strip 3 that has occurred in the furnace 5.

[0043] The energy density threshold determination assembly 10 determines an oxide removal energy density threshold S below which corresponds to the minimum energy density that is delivered by the laser stripping device 12 onto the metal product during the movement of the product to be stripped in order to strip the oxide layer present on the product surface. exp The energy density threshold determination assembly 10 is further intended to determine a minimum value or energy density threshold, referred to as a damage energy density threshold S above which degradation of the product surface, i.e., metal, beneath the oxide layer, is observed. end Preferably, the method is configured to determine a maximum laser energy density threshold, hereinafter referred to as the maximum laser energy density threshold.

[0044] The determination assembly 10 sequentially determines the oxide removal energy density threshold S on multiple portions of the product surface. exp and, if applicable, the damage energy density threshold S end The method is configured to determine:

[0045] The portions are for example transverse strips of a given length in the direction of movement of the product (also known as the longitudinal direction) and of a width equal to the product. Such a strip, when in the form of strip 3, is called an "elementary strip", in contrast to the product. The portions are then intended to be peeled off one after the other by the laser peeling device 12 as they pass in front of it.

[0046] As described below, the determination assembly 10 determines the oxide removal energy density threshold S on each segment of the portion. exp and, if applicable, the damage energy density threshold S end , the threshold value thus determined is therefore preferably considered as representative of the entire part under consideration.

[0047] For example, the portion may be a transverse element strip of a given length in the direction of movement of the product and a width equal to the product, and the determination assembly 10 may determine an oxide removal energy density threshold S on a segment of this element strip. exp and, if applicable, the damage energy density threshold S end and the threshold value thus determined is therefore considered as representative for the entire element strip.

[0048] The laser stripping device 12 is intended to transmit a laser beam onto the flowing product in order to strip the oxide layer as a function of an energy density threshold determined by the determination assembly 10 .

[0049] In particular, the laser stripping device 12 is intended to deliver a laser beam onto each portion of the flowing product to strip the oxide layer as a function of an energy density threshold determined by the determination assembly 10 for this portion.

[0050] The energy density threshold determination assembly 10 includes a laser pulse delivery system 20, an image acquisition system 22, a processing system 24, and a controller .

[0051] The laser pulse delivery system 20 is configured to deliver a beam of laser pulses onto the flowing product, the laser pulses having a wavelength and pulse duration equal to that of the laser used for ablation (e.g., a Nd:YAG laser having a wavelength of 1064 nm). These laser pulses are hereinafter also referred to as analytical laser pulses.

[0052] The laser pulse delivery system 20 includes at least one laser source 30 capable of delivering such analytical laser pulses. The laser source 30 is capable of delivering laser pulses of the same wavelength and pulse duration as the laser used for ablation.

[0053] The fact that the wavelength and pulse duration of the laser source 30 are the same as those of the peeling laser makes it possible to ensure that the absorption of light from the laser source 30 by the oxide covering the product is the same as for the peeling laser and that the settings of the peeling laser can therefore be directly based on the data obtained by the energy density threshold determination unit 10.

[0054] The laser source 30 is preferably mounted so as to be movable relative to the line, in particular in a direction parallel to the product surface and perpendicular to the direction of the product movement (i.e. movable through the product width). It is therefore possible to change the position of the product segment affected by the laser source during its movement across the product width. For this purpose, the laser pulse delivery system 20 is equipped, for example, with a scanning device capable of displacing the laser source laterally relative to the flowing product. Alternatively, the determination assembly 10 can also be entirely movable relative to the line, thereby changing the position of the product segment affected by the laser source during its movement across the product width.

[0055] For example, if each part being considered is an elemental strip of width equal to the product being peeled off, the scanning device can displace the laser source laterally relative to the flowing product so that the position of the segment of the product affected by the laser source changes over time across the width of the product (strip) 3.

[0056] The laser pulse delivery system 20 also includes an optical device 32 configured to focus the laser pulses delivered by the laser source 30 onto the surface of the flowing product.

[0057] The laser source 30 is configured to transmit an analytical laser pulse onto a segment of the considered portion of the surface of the flowing product, the energy density of which varies as a function of position on this segment. The energy density received at each point of the affected segment thus depends on the position of that point. The area of ​​the product surface affected by the analytical laser pulse is hereinafter referred to as the "spot".

[0058] For example, at certain points the energy density received may be too low to strip the oxide layer, and at other points the energy density may be sufficient to strip the oxide layer but insufficient to damage the metal underneath. In certain cases, the energy density received at a particular point may be sufficient to both strip the oxide layer and damage the metal underneath the oxide layer.

[0059] The energy density experienced at each point in the affected segment is characterized by the energy density profile, or more simply the energy profile, of the pulse.

[0060] The energy profile thus relates at each location, or multiple locations, within the plane of the product surface, to the energy density delivered at that location.

[0061] Figures 2, 3 and 4 respectively show three examples of energy profiles 34, 35, 36. In the three profiles shown, the abscissa axis X indicates the position along an axis contained in the plane of the product surface and the ordinal axis Y is the energy density experienced at that position. Each point on the energy profile is therefore associated with a given position, the energy density experienced at that position.

[0062] For example, the pulse presents an axis of symmetry Z parallel to the direction of pulse propagation (the pulse impact on the product is, for example, circular), and the energy profile relates the energy density to each distance relative to the center of the circle formed by the pulse impact (or the pulse center).

[0063] Energy profiles 34, 35 are examples of such profiles.

[0064] The energy profile 34 is circular in shape, ie, all points at the same distance from the pulse center receive the same energy density.

[0065] The energy profile 35 is rectangular in shape such that all points located on the sides of a square that has the center of the pulse as its center receive the same energy density.

[0066] According to another example, the impact of the pulse on the product is such that the energy density on the affected segment is constant along an axis Y perpendicular to the direction of pulse propagation, and the energy profile relates the energy density to each position along an axis X perpendicular to axis Y, and to the direction of pulse propagation.

[0067] Energy profile 36 is an example of such a profile. In this example, the energy density is an increasing linear function of position along axis X.

[0068] For example, as illustrated by profile 34, the energy profile is preferably Gaussian, ie, the energy density received in a plane perpendicular to the direction of pulse propagation follows a Gaussian distribution.

[0069] The energy profile of a Gaussian pulse can be expressed as: E(x)=E pic *exp(-x 2 / 2σ 2 ) E pic =E pulse / (2πσ 2 ) In the formula, E pic is the peak energy density of the Gaussian distribution. E pulse is the pulse energy, x is the distance to the center of the pulse, E(x) is the energy density received at distance x from the center of the pulse, σ is the standard deviation of the Gaussian distribution.

[0070] It is preferred that the energy density profile exhibits a low slope, i.e. the derivative of the energy density with respect to position is less than 1. In particular, for a Gaussian profile, σ>E pic *exp(-1 / 2).

[0071] Laser source 30 is preferably configured to deliver laser pulses with a known energy profile.

[0072] Alternatively, as described below, the energy profile of the laser pulse is not known a priori and the energy density threshold determination assembly 10 additionally includes a determination system for the energy profile of the pulse delivered by the laser source.

[0073] In all cases, the energy profile is characterized by its shape (as shown in Figures 2 to 4) and the power or energy of the pulses.

[0074] The image acquisition system 22 is configured to acquire, for each product portion under consideration, images of the segments affected by the laser pulses delivered by the delivery system 20 while the product is in motion.

[0075] The image acquisition system 22 comprises, for example, a camera 38, in particular a high resolution camera. During operation, the camera 38 is positioned in front of the product during its movement.

[0076] Controller 26 is configured to synchronize laser pulse delivery system 20 and image acquisition system 22. In particular, controller 26 is configured to control the delivery of laser pulses by delivery system 20 and the acquisition of images of areas affected by those pulses by image acquisition system 22.

[0077] The processing system 24 determines from each image acquired by the image acquisition system 22 an oxide removal energy density threshold S , which corresponds to the minimum energy density required to remove the oxide layer from the part under consideration. exp The method is configured to determine:

[0078] The processing system 24 further determines from each image acquired by the image acquisition system 22 a metal damage energy density threshold S , corresponding to the energy density above which degradation of the product surface is observed beneath the oxide layer. end Preferably, the device is configured to determine:

[0079] To this end, the processing system 24 is configured to receive each image acquired from the image acquisition system 22 .

[0080] The processing system 24 is further configured to receive information related to the energy profile of the laser pulses delivered by the laser pulse delivery system 20, and in particular by the laser source 30, onto the flowing product.

[0081] The processing system 24 includes, for example, an image analyzer 40 and a thresholding module 42 .

[0082] The image analyzer 40 is configured to determine at least one dimension of the spalled area, i.e., oxide-free, of the metal article surface by analysis of each captured image as transmitted by the image capture system 22 .

[0083] The image analyzer 40 is capable of determining information related to the ablated area, in particular the shape of this area, in particular at least one dimension representative of the contour of this area.

[0084] For example, for a pulse with a Gaussian energy density profile, the ablated region has a circular shape, and a dimension representative of this shape is, for example, the diameter, radius, circumference, or area of ​​the circular region.

[0085] According to another example, the exfoliated area is rectangular in shape and the dimensions representative of this shape are the length and / or width of the rectangular area.

[0086] The image analyzer 40 can communicate information related to the ablated regions to a thresholding module 42 .

[0087] The image analyzer 40 is additionally preferably configured to determine at least one dimension of the damaged area on the surface of the metal article, i.e., the area where the metal underlying the oxide layer is damaged.

[0088] The threshold determination module 42 can receive this information.

[0089] The threshold determination module 42 can further receive information related to the energy profile of the laser pulse that produced the ablated region of transmission, which generally includes the shape of the energy profile and the power or energy of the pulse.

[0090] In particular, the laser source is aligned with the segment of the product part under consideration at the moment t e The image of this segment is taken at the instant t e +Δt, and information related to the energy profile of the laser pulse is obtained at the instant t e represents a laser pulse delivered at

[0091] This information relating to the energy profile of the laser pulses is stored, for example, in a memory of the threshold determination module 42 .

[0092] The threshold determination module 42 determines an oxide removal energy density threshold S from the information related to the energy profile and the information related to the stripped area. exp It is possible to determine

[0093] The threshold determination module 42 further determines a metal damage energy density threshold S from the information related to the energy profile and the information related to the delaminated area. end Preferably, the method is configured to determine:

[0094] For this purpose, the threshold determination module 42 is capable of determining from the energy profile of the laser pulses which energy density led to ablation in order to obtain an ablated region.

[0095] For example, the threshold determination module 42 can determine from the energy profile what energy density is received on the contour of the stripped region, which then corresponds to a minimum energy density for stripping the oxide layer.

[0096] In particular, if the pulses delivered by the delivery system 20 are Gaussian pulses, the ablated region is circular with a diameter D and the oxide removal energy density threshold S exp is expressed in the following form: S exp =E pic *exp(-D 2 / 8σ2 )

[0097] By way of example, Figures 5 to 7 show segments of a product surface affected by pulses having profiles as shown in Figures 2 to 4, respectively.

[0098] As shown in Figure 5, surface 46 results from delivering a pulse with energy profile 34. Contour 47 delimits an oxide-free, spalled region of the product. Surface 46 thus comprises non-spauled segments 48, and a circular spalled region delimited by contour 47. The spalled region comprises a central damaged region delimited by circular contour 49.

[0099] The delaminated area is defined by points on the surface 46 that have received sufficient energy density to delaminate the oxide layer. The contour 47 of the delaminated area is therefore defined by the oxide removal energy density threshold S exp It is formed by a point receiving an energy density equal to

[0100] As shown in Figure 5, the determination of the dimensions, in the presented example, the diameter D of the peeled area exp is therefore the minimum energy density required to remove oxide from the surface, the oxide removal energy density threshold S exp This enables the determination by comparison with the energy profile 34 (FIG. 2).

[0101] Further, the damaged area is formed by a point on the surface 46 that has received a sufficient energy density to damage the product below the oxide layer. end By determining the damage energy density threshold S end is for a metal, it can be determined by comparison with the energy profile 34.

[0102] In Fig. 6, surface 50 results from the delivery of a pulse with energy profile 35. A square-shaped contour 51 delimits the spalled area, which is free of oxide of the product. Surface 50 thus comprises a non-spabbed segment 52 and a spalled area. In this embodiment, the spalled area is square-shaped. The spalled area comprises a damaged area in its center, delimited by a square contour 53.

[0103] By delimiting the lateral length of the contour 51, and therefore by comparison with the energy profile 35, the oxide removal energy density threshold S exp Similarly, by determining the side length of the damaged region, it is possible to determine the metal damage energy density threshold S end It becomes possible to determine the following.

[0104] Finally, in Fig. 7, a surface 55 results from transmitting a pulse with energy profile 36. A rectangular shaped contour 56 delimits the oxide-free spalled region of the product. Surface 55 thus comprises non-spabbed segments 57 and spalled regions. In this embodiment, the spalled region is rectangular shaped. The spalled region comprises a central damaged region delimited by a rectangular contour 58.

[0105] The length of the contour 56 is delimited by the axis X to define the oxide removal energy density threshold S exp , can be determined by comparison with the energy profile 36. Similarly, by determining the length along axis X of the contour 58 of the damaged region, the metal damage energy density threshold S end It becomes possible to determine the following.

[0106] The threshold determination module 42 determines the oxide removal energy density threshold S exp , and, if applicable, the metal damage energy density threshold S end can be transmitted to the laser ablation device 12.

[0107] The processing system 24, and in particular the threshold determination module 42, also transmits to the delivery system 20 the oxide removal energy density threshold and the metal damage threshold S, if the latter is determined. end The delivery system 20 is then adapted to control the energy of the analysis laser pulse such that the delivery of the analysis laser pulse effectively leads to the ablation of a part of the affected segment without damaging the metal.

[0108] In particular, if no ablated area was generated by transmitting a previous analysis laser pulse (the ablation energy density threshold is not subsequently present), the transmission system 20 can receive this information from the processing system 24. The transmission system 20 can then control the transmission of an analysis laser pulse of higher energy than the analysis laser pulse transmitted the previous moment.

[0109] Conversely, if the transmission of a previous analysis laser pulse produced a damaged area, the transmission system 20 can receive a damage energy density threshold from the processing system 24. The transmission system 20 is then configured to control the transmission of an analysis laser pulse with a lower energy than the analysis laser pulse transmitted in the previous moment, in particular with an energy such that the energy density of the analysis laser pulse remains below the damage energy density threshold.

[0110] To obtain a reliable measurement, it is desirable that the strip 3 maintains a constant distance relative to the energy density threshold determination assembly 10, i.e. the strip 3 must not vibrate and must remain at a fixed height. This can be achieved by applying a sufficiently large tension to the strip 3 using an S-block or by placing a support roller 24 under the strip 3 to ensure a fixed height under the laser pulse delivery system 20.

[0111] For simplicity, Figure 1 shows the energy density threshold determination assembly 10 only on the top surface of the strip 3. But, of course, other lasers and associated sensors are also present on the bottom surface of the strip 3. Similarly, a support roller comparable to roller 24 can be placed in contact with the top surface of the strip 3 to ensure that the strip 3 maintains a fixed distance relative to the laser inspecting its bottom surface.

[0112] The laser ablation apparatus includes an array of ablation lasers 13 .

[0113] The ablation laser 13 is, for example, a pulsed Nd:YAG 1064 nm laser.

[0114] These ablation lasers 13 are intended to ablate the oxide layer present on the product surface.

[0115] Each ablation laser 13 is configured to deliver pulses of ablation beam 14 onto the surface of the flowing product, each pulse covering an area of ​​the product surface known as a spot.

[0116] The laser stripping device 12 further comprises a threshold value S t for controlling the stripping laser 13 . exp , and, if applicable, the metal damage energy density threshold S end The laser includes a control unit configured to determine operating parameters of the laser as a function of

[0117] In particular, the control unit 15 determines for each point of the considered portion of the product surface an oxide removal energy density threshold S exp The ablation laser 13 is configured to be controlled so as to be exposed to the higher energy density for at least a moment.

[0118] For this purpose, the control unit 15 determines whether the spot of the pulses delivered by the ablation laser 13 covers the entire part under consideration and whether each point of this part is within the oxide removal energy density threshold Sexp It is configured to monitor the peak energy density delivered by each ablation laser 13 and control the scanning of the part under consideration by the laser so as to be exposed to the higher energy density for at least a moment.

[0119] The peak energy density delivered by each ablation laser 13 is determined by the oxide removal energy density threshold S exp Higher, if necessary, the damage energy density threshold S end is selected to be less than.

[0120] To control such scanning, the control unit 15 comprises, for example, an optical and / or mechanical scanning system configured to laterally displace the spot of the beam 14 on the product surface, as well as an optical system that converts the spot into a line.

[0121] In a manner similar to the energy density threshold determination assembly 10, the strip 3 is maintained at a fixed height as it passes under the peeling laser 13, and it is desirable that a support roller 25 comparable to the previous support roller 24, or any other functionally equivalent device, can be used for this purpose.

[0122] Also, not shown, another laser 13, and possibly its associated support roller, is configured to operate at an oxide removal energy density threshold S exp , and, if applicable, the metal damage energy density threshold S end Based on this, the lower surface of the strip 3 is provided for peeling.

[0123] Each of the ablation lasers 13 may be positioned non-perpendicular to the metal sheet to minimize disturbance of the incident beam by oxide particles thrown up by the previous pulse delivered by the laser 13 itself or by other lasers 13 in the row.

[0124] According to one embodiment, each part is an elementary strip, and each elementary strip is treated several times by the ablation laser to ensure that successive pulses are not absorbed by particles and / or plasma from the previous pulse. In this case, the first substep of ablation of the horizontal line is performed over a distance D equal to N times the distance between the pulses required to obtain a uniform coverage. inter Then the line is split into pulses separated by a distance D inter The iterative process is then repeated N times, taking care to only shift the position of the start of the line between each substep.

[0125] The number of peeling lasers 13 required to treat the entire surface of the strip 3 is minimized by the fact that each peeling laser 13 is equipped with a high speed scanning system, either optical or mechanical, or a combination of both, for lateral displacement of the beam spots 14 to juxtapose the spots to form a continuous line covering the entire width of the strip 3, preferably with zero or minimal spot overlap to avoid the risk of delivering an excessive amount of energy in the spot overlap area. Alternatively, the laser peeling apparatus 12 includes a long distance focusing device, which allows covering the entire width of the strip 3 with a limited number of peeling lasers 13.

[0126] The use of laser ablation as performed according to the present invention provides great versatility to the ablation apparatus, especially since the ablation parameters can be easily adjusted during processing if they are found to be less than optimal during operation, for example when it may be possible to change the spot surface of each ablation laser 13 rather than a conventional beam focus adjustment system.

[0127] In the vicinity of the ablation laser 13, means (not shown) are provided for removing and preferably collecting the oxides detached from the surface of the strip 3, for example by suction or brushing towards a container, as well as any fumes that may be generated during the process (by evaporation of metal particles, oxides or organic substances). In this way, a maximum amount of such oxides can be easily recovered to prevent them from dispersing and polluting in the atmospheric environment and to allow a maximum portion to be reworked with a view to recovering the metal contained. In addition, this operation makes it possible to remove any oxides that may only be incompletely detached from the surface of the strip 3 by the laser 13 (especially on the upper surface of the strip 3, where gravity cannot help to detach the oxides). Finally, the suction of these dusts and vapors makes it possible to avoid damage to the optical system of the laser, which may be collected, heating or even breaking them.

[0128] Alternatively, the strip 3 is circulated vertically to prevent oxides removed from the surface of the strip 3 by the laser 13 from being redeposited on the surface of the strip 3 or on the determination assembly 10, in particular on the optical components of the determination assembly 10.

[0129] After passing under the peeling laser 13, the strip 3 is thus essentially completely peeled off. This is checked by suitable means, for example by an optical peeling quality control device such as a camera 16, or a set of such optical devices 16, which inspects the surface of the strip 3 over its entire width and determines which areas of the strip 3 may not have been peeled off in a satisfactory manner. Colour differences on the surface of the strip 3 can serve as a criterion for this determination. One advantage of said suction or brushing device or equivalent is that it is also possible to remove from the top surface any pieces of oxide that may have remained on (in particular) the top surface of the strip 3, without them being erroneously considered by the camera 16 as still being present and therefore requiring further peeling to be removed.

[0130] If the results provided by the optical device 16 are not satisfactory, further peeling may be performed on the incompletely peeled parts of the strip 3 or, to be on the safe side, on the entire strip 3 .

[0131] In addition, the line may comprise sections of wet chemical and / or electrolytic stripping tanks which may be filled at least temporarily after the laser stripping section in order to eliminate any defects that may be found. If the strip 3 has been successfully stripped, these tanks remain empty.

[0132] Another solution consists in deflecting the strip 3 into the stripping bath by means of vertically displaceable plunge rollers arranged in such a way that they can act on the upper surface of the strip 3. In normal operation, these rollers are in a position that allows the flowing strip 3 to be outside the stripping bath in the vicinity in which they are arranged. When it becomes apparent that a chemical and / or electrolytic stripping of the strip 3 is locally necessary, at least one of these plunge rollers is pressed onto the upper surface of the strip 3 and lowered so as to temporarily pass the segment of the strip 3 to be treated through the corresponding stripping bath used.

[0133] A method for stripping a flowing metal product exhibiting an oxide layer on its surface according to one embodiment will now be described and carried out by the apparatus described with reference to FIG.

[0134] In the example described, the peeling method is carried out after the passage of the product through the annealing furnace 5 .

[0135] Thus, by way of example, it should be considered that each part under consideration is an elementary strip having a width equal to the product to be peeled off.

[0136] For each part of the product under consideration, the method includes the steps of determining an oxide layer removal energy density threshold, and then stripping as a function of the removal energy density threshold so determined.

[0137] For each portion, the step of determining the oxide layer removal energy density threshold includes transmitting an analysis laser pulse of equal wavelength and pulse duration to the ablation laser 13 onto the segment of the portion under consideration to form a stripped region within the segment that is free of the oxide layer.

[0138] The analytical laser pulse is delivered by the delivery system 20, in particular by a laser source 30, and is focused by an optical device 32 onto the segment of interest.

[0139] The delivery of the analysis laser pulse is controlled by a controller 26, which controls the instant at which the pulse is delivered.

[0140] In addition, the energy of the analysis laser pulse is preferably controlled by the delivery system 20 such that the delivery of the analysis laser pulse effectively leads to ablation of a portion of the affected segment without damaging the metal.

[0141] The energy of the analysis laser pulse is selected as a function of information received by the transmission system 20, for example from the processing system 24 (in particular the threshold determination module 42), after the transmission of the analysis laser pulse at the previous instant.

[0142] In particular, if the transmission of a previous analysis laser pulse did not produce an ablated region (the ablation energy density threshold is not subsequently present), the transmission system 20 receives this information from the processing system 24. The processing system 20 then transmits an analysis laser pulse of higher energy than the analysis laser pulse transmitted in the previous moment.

[0143] Conversely, if the transmission of the previous analysis laser pulse produced a damaged area (as the damage energy density threshold is subsequently determined by the processing system 24), the transmission system 20 receives the damage energy density threshold from the processing system 24. The transmission system 20 then generates a transmission of an analysis laser pulse of lower energy than the analysis laser pulse transmitted in the previous moment, in particular of such energy that the energy density of the analysis laser pulse remains below the damage energy density threshold.

[0144] The product segments then pass in front of an image capture system 22 as they move.

[0145] The step of determining the ablation energy density threshold then involves capturing, by the acquisition system 22, an image of the segment of the surface affected by the analysis laser pulse.

[0146] From this image, the oxide removal energy density threshold S exp The signal is transmitted to a processing system 24 which determines

[0147] The processing system 24 also calculates from the image a metal damage energy density threshold S end It is preferable to determine

[0148] Oxide removal energy density threshold S exp Determining the area of ​​the ablated region includes determining the size of the ablated region from the image, which size is determined, for example, by the image analyzer 40.

[0149] Oxide removal energy density threshold S exp Determining then includes determining an oxide layer removal energy density threshold from the dimensions of the stripped area.

[0150] The oxide layer removal energy density threshold is determined by threshold determination module 42 from information relating to, for example, the dimensions of the ablated region and the energy profile of the analysis laser pulse whose transmission through the ablated region produced the ablated region.

[0151] Metal Damage Energy Density Threshold S end Determining the size of the damaged area on the affected segment includes determining from the image the size of the damaged area on the affected segment, which size is determined, for example, by the image analyzer 40.

[0152] Metal Damage Energy Density Threshold S end Determining then includes estimating a metal damage energy density threshold from the dimension so determined.

[0153] Metal Damage Energy Density Threshold S end is evaluated by the threshold determination module 42 from information relating to, for example, the dimensions of the damaged area and the energy profile of the analysis laser pulse whose transmission through the damaged area produced.

[0154] Removal Energy Density Threshold S exp and the damage energy density threshold S end is preferably transmitted to the transmission system 20 in order to make it possible to control the power of the analysis laser pulses transmitted at these later moments so that the transmission of these analysis laser pulses effectively leads to the ablation of part of the affected segment without damaging the metal.

[0155] The further moving product portion under consideration then passes in front of the laser stripping device 12 and is subjected to a stripping step.

[0156] During the ablation step, the laser 13 delivers a laser pulse onto the considered part for ablation, the energy density of the pulse being higher than a predefined ablation energy density threshold.

[0157] In particular, the control unit 15 determines an oxide removal energy density threshold S for the part under consideration. exp , and, if applicable, the damage energy density threshold S end , each point of the considered part is subjected to the oxide removal energy density threshold S expThe laser 13 is controlled to provide at least a momentary exposure to the higher energy density.

[0158] For this purpose, the control unit 15 determines whether the spot of the pulses delivered by the laser 13 covers the entire part under consideration and whether each point of this part is within the oxide removal energy density threshold S exp The peak energy density delivered by each laser 13 is monitored and the lasers are controlled to scan the part under consideration so as to be exposed at least momentarily to the higher energy density threshold.

[0159] The peak energy density delivered by each laser 13 is equal to the oxide removal energy density threshold S exp Higher, if applicable, the damage energy density threshold S end is selected to be lower.

[0160] After stripping, the detached oxide is removed and preferably collected, for example by suction or brushing towards a container.

[0161] The part under consideration is essentially completely delaminated after passing under the laser 13. As described above, the condition of the part is checked with the aid of an optical delamination quality control device, such as a camera 16, which inspects the surface of the part over its entire width and determines which areas of this part may not have been delaminated in a satisfactory manner.

[0162] The steps of determining an oxide layer removal energy density threshold and stripping as a function of the removal energy density threshold are performed sequentially for each portion of the flowing product.

[0163] From one portion to the next, the laser source 30 is preferably displaced relative to the production line, in particular in directions parallel to the plane of product movement and perpendicular to the direction of movement (i.e., through the product width), so that the position of the segment of the product affected by the laser source 30 perpendicular to the direction of product movement changes from one portion to the next.

[0164] For example, in a strip 3 of width L (in a direction y parallel to the surface and transverse to the direction of movement), a first portion is affected by the laser source 30 on the segment with coordinate y=y0, a second portion is affected by the laser source 30 on the segment with coordinate y=y0+Δy, etc.

[0165] According to one embodiment, at least certain information ng on the energy profile of the pulse delivered by the laser source 30, in particular its shape or its power or energy, is not known a priori.

[0166] If the shape of the energy profile is not known, the energy density threshold determination assembly 10 may, for example, include a system for determining this shape.

[0167] The determination system is configured to analyze the laser pulses delivered by the delivery system 20 and determine the shape of the energy profile. Such a determination system is particularly useful when the shape of the pulsed beam delivered by the delivery system 20 is not stable over time.

[0168] The determination system shown by way of example in FIG. 8 comprises an optical device 62 , for example a beam splitter, configured to deflect a portion of each analysis laser pulse transmitted by the transmission system 20 towards a beam analyzer 64 .

[0169] The determination system further comprises a beam analyzer 64 configured to determine a shape of the pulse energy profile from a portion of the deflected pulse and communicate this shape to the threshold determination module 42 .

[0170] The beam analyzer 64 comprises a sensor held at a predetermined distance from the optical device 62, this distance being equal to the distance between the optical device 62 and the surface of the flowing product.

[0171] For this purpose, the beam analyzer 64 and the optical device 62 are, for example, mounted fixed relative to each other and to the product in a direction perpendicular to the product surface, but movably relative to the direction of movement of the strip 3. For example, as shown in Fig. 9, the beam analyzer 64 and the optical device 62 are fixedly mounted on a rolling system 67 above the product 3 surface. The rolling system is movable (by rolling) parallel to the product in the direction x of product movement.

[0172] Thus, a constant distance is maintained between the beam analyzer 64 and the optical device 62 on the one hand, and between the optical device 62 and the surface of the product 3 on the other hand.

[0173] Furthermore, the threshold determination module 42 is configured to modify the received energy profile to take into account the fact that this profile is obtained with a portion of a pulsed beam.

[0174] According to this embodiment, the method includes determining the shape of the profile.

[0175] The step of determining the shape of the profile involves, for example, deflecting a portion of the laser pulse transmitted by the delivery system 20, in particular by a beam splitter, towards a beam analyzer 64 and evaluating the shape of the energy profile by the beam analyzer 64.

[0176] The shape of the energy profile thus determined is then communicated to a threshold determination module 42 .

[0177] According to this embodiment, the pulse whose energy profile is determined is the same as the analysis laser pulse, i.e. the one that impacts the product surface in creating the ablated area.

[0178] The energy density threshold determination assembly 10 also preferably includes a device for determining the energy of each pulse transmitted by the laser source 30. Indeed, even if the average pulse energy is known, variations in this energy are possible, and knowledge of the energy of each pulse transmitted by the laser source 30 onto the product surface then allows a more accurate determination of the energy density threshold. Such a pulse energy determination device may, for example, include a calibrated photodiode positioned on one side of the laser beam.

[0179] According to another embodiment, the shape of the energy profile of the pulses delivered by the delivery system 20 is known but the energy or power of the pulses is not known, and the energy density threshold determination assembly 10 further includes a system for determining the energy or power of the pulses delivered by the delivery system 20.

[0180] Such determination systems are generally intended to periodically determine the power (or energy) of the delivered pulses for recalibration purposes, whereas energy determination devices as described above are generally intended to determine the energy of each pulse in real time.

[0181] This energy determination system differs essentially from the one shown as an example in FIG. 9 in that the beam analyzer 64 is replaced by a power meter.

[0182] This embodiment further does not require the power meter to be held at a distance from the optical device equal to the distance between the optical device and the surface of the flowing product.

[0183] According to this embodiment, the method includes determining the energy or power of the pulse.

[0184] The step of determining the energy or power of the pulse may, for example, include deflecting a portion of the laser pulse transmitted by the transmission system 20, in particular by a beam splitter, towards a power meter and evaluating the energy and / or power of the pulse by the power meter.

[0185] The pulse energy and / or power thus determined is then communicated to a threshold determination module 42 .

[0186] According to this embodiment, the pulse whose energy or power is determined is also the same that impacts the product surface, producing the ablated area.

[0187] According to another embodiment, shown by way of example in FIG. 10, the energy profile and / or power is determined based on a pulse delivered before or after the pulse that affects the product surface in generating the peeled region, hereinafter referred to as an auxiliary pulse.

[0188] According to this embodiment, the determination system comprises an optical device 68 configured to guide the pulsed beam delivered by the delivery system 20 selectively towards a beam analyzer and / or a power meter or towards the product surface. The determination system further comprises a beam analyzer 70 and / or a power meter 72 configured to determine the shape and / or energy of the energy profile of the beam.

[0189] The optical device 68 includes, for example, a galvanometer mirror scanner 74 , a mirror 76 , and preferably a beam splitter 78 .

[0190] A galvanometer mirror scanning device 74 (shown in two positions in FIG. 10) is configured to selectively deflect the entire beam delivered by the delivery system 20 either towards the product surface or towards a mirror 76 .

[0191] Mirror 76 is configured to reflect the beam thus deflected towards beam splitter 78 .

[0192] The beam splitter 78 is intended to separate the pulsed beam into two sub-beams, one part of which is directed towards the beam analyzer 70 and the other part towards the power meter 72 .

[0193] If the shape of the energy profile is known, the beam analyzer 70 and beam splitter 78 can be omitted.

[0194] Conversely, if the pulse energy is known, the power meter 72 and beam splitter 78 can be omitted.

[0195] According to this embodiment, the method includes transmitting auxiliary pulses by the delivery system 20 and directing these pulses towards a beam analyzer 70 and / or towards a power meter 72 .

[0196] If it is desired to determine the shape and energy or power of the energy profile, the auxiliary pulses are directed both towards the beam analyzer 70 and / or towards the power meter 72, particularly by the beam splitter 78.

[0197] The auxiliary pulses are directed towards the beam analyzer 70 and / or towards a power meter 72 by a galvanometer mirror scanning device 74 .

[0198] The method then includes evaluating the shape of the energy profile of the auxiliary pulse by a beam analyzer 70 and / or evaluating the energy or power of the pulse by a power meter 72 .

[0199] The shape, energy and / or power thus determined are then communicated to a threshold determination module 42 .

[0200] Once the auxiliary pulse is transmitted, the galvanometer mirror scanner 74 directs subsequent pulses towards the product 3 surface.

[0201] The method and the device according to the invention therefore make it possible to obtain an efficient stripping of metal products on an industrial scale, in particular thanks to the precise determination of the parameters making it possible to efficiently strip the oxide layer.

[0202] Although the examples given refer to flat products such as strips, the invention is also applicable to other types of products such as metal bars, tubes or metal wires. [Explanation of symbols]

[0203] 1 Unwinding device 2 Coil 3 Stainless Steel Strip 4. Cold rolling mill 5 Annealing furnace 10 Energy density threshold determination unit, energy density threshold determination assembly 12 Laser peeling device 13. Delamination laser 14 Beam, beam spot 15 Control Unit 20 Laser Pulse Delivery System 22 Image Acquisition System 24 Processing System 25 Support roller 26 Controller 30 Laser Source 32 Optical Devices 34 Energy Profile 35 Energy Profile 36 Energy Profile 38 Camera 40 Image analyzer 42 Threshold Judgment Module 46 Surface 47 Contour 48 Segments 49 Contour 50 surface 51 Contour 52 Segments 53 Contour 62 Optical Devices 64 Beam Analyzer 68 Optical Devices 70 Beam Analyzer 72 Power Meter 74 Galvanometer Mirror Scanner, Galvanometer Mirror Scanning Device 76 Mirror 78 Beam splitter

Claims

1. 1. A method for stripping a flowing metal product (3) exhibiting an oxide layer on its surface, said method using laser stripping with at least one stripping laser (13), the steps of: - determining the oxide layer removal energy density threshold on the portion under consideration of the flowing metal product (3), which corresponds to a minimum energy density required for removal of the oxide layer on the portion under consideration, transmitting an analysis laser pulse by a delivery system (20) comprising a laser source (30), the analysis laser pulse being of equal wavelength and pulse duration to the ablation laser (13) over the segment of the part under consideration to form an ablated area within the segment that is free of the oxide layer; capturing an image of the segment of the surface affected by the analytical laser pulse; determining from the image a dimension representative of the exfoliated area; Evaluating an oxide layer removal energy density threshold using information related to the representative dimensions and the energy profile of the analysis laser pulse. and - transmitting by the ablation laser (13) an ablation laser pulse on the portion under consideration for ablation, the energy density of the ablation pulse being higher than the determined oxide layer removal energy density threshold, The ablation laser (13) is controlled by a control unit (15) receiving the determined oxide layer ablation energy density threshold such that each point of the portion under consideration is exposed for at least a moment to an energy density higher than the oxide layer ablation energy density threshold.

2. 2. The method of claim 1, further comprising the steps of: transmitting an analysis laser pulse to form a damaged area in the segment where metal beneath the oxide layer is damaged; determining a dimension representative of the damaged area from the image; and evaluating, from the information related to the dimension representative of the damaged area and an energy profile of the analysis laser pulse, a metal damage energy density threshold corresponding to an energy density above which degradation of the surface of the metal product (3) beneath the oxide layer is observed.

3. 3. The method of claim 2, further comprising a step of transmitting the damage energy density threshold to the transmission system (20), characterized in that at a next portion of the flowing metal product (3), the transmission system (20) transmits an analysis laser pulse of adapted energy such that at any point of the segment affected by the analysis laser pulse, the energy density is lower than the damage energy density threshold.

4. The method of claim 1 , wherein the information related to the energy profile includes the shape of the energy profile and the energy or power of the analyzed laser pulse.

5. 5. The method of claim 4, wherein the step of determining the oxide layer removal energy density threshold comprises determining the shape of the energy profile of the analysis laser pulse and / or determining the energy or power of the analysis laser pulse.

6. 6. The method of claim 5, wherein the step of determining the oxide layer removal energy density threshold comprises determining the energy profile shape of the analysis laser pulses, the determining step comprising: deflecting a portion of each analysis laser pulse towards a beam analyzer (64) and evaluating the energy profile shape by the beam analyzer (64).

7. 7. The method of claim 5, wherein the step of determining the oxide layer removal energy density threshold comprises a step of determining the energy and / or power of the analysis laser pulses, the step including diverting a portion of each analysis laser pulse towards a power meter and evaluating the energy and / or power of the analysis laser pulses by the power meter.

8. 5. The method of claim 4, wherein the step of determining the oxide layer removal energy density threshold comprises a step of determining a shape of an energy profile and / or an energy or power of an auxiliary laser pulse delivered by the delivery system (20), the auxiliary laser pulse being separate from the analysis laser pulse.

9. 9. The method of claim 8, wherein the step of determining the shape of the energy profile and / or the energy or power of the auxiliary laser pulse comprises transmitting the auxiliary laser pulse by the transmission system (20), directing the auxiliary laser pulse by a galvanometer mirror scanning device (74) towards a beam analyzer (70) and / or towards a power meter (72), evaluating the shape of the energy profile of the auxiliary laser pulse by the beam analyzer (70), and / or evaluating the energy and / or power of the auxiliary laser pulse by the power meter (72).

10. 10. The method according to claim 1, wherein the metal product (3) is a strip, a bar, a sheet, a plate, a tube or a wire.

11. An apparatus for laser ablation of a flowing metal product (3) exhibiting an oxide layer on its surface by means of at least one ablation laser (13), comprising: - a determining assembly (10) configured to determine, for each of a plurality of successive portions of the flowing metal product (3), an oxide layer removal energy density threshold corresponding to a minimum energy density required to remove the oxide layer on the portion under consideration, said determining assembly (10) comprising: a delivery system (20) comprising a laser source (30) configured to deliver an analysis laser pulse of equal wavelength and pulse duration to the ablation laser (13) on the segment of the part under study to form an ablated area in the segment, free of the oxide layer; an image acquisition system (22) configured to acquire images of the segment affected by the analytical laser pulse while the product is flowing; a processing system (24) configured to determine a representative dimension of the ablated area from each image acquired by the image acquisition system (22) and to estimate the oxide layer removal energy density threshold from information related to the representative dimension and an energy profile of the analysis laser pulse, The apparatus further comprises: - a laser stripping device (12) comprising at least one stripping laser (13) configured to deliver stripping laser pulses to each of the plurality of successive portions of the flowing metal product for stripping, and a control unit (15) configured to receive the oxide layer removal energy density threshold for said portions and to control the delivery by the stripping laser (13) of laser pulses of energy above the oxide layer removal energy density threshold such that each point of the portion under consideration is exposed at least momentarily to an energy density above the oxide layer removal energy density threshold.

12. 12. The laser stripping apparatus of claim 11, wherein the analysis laser pulse forms a damaged area in the segment where metal beneath the oxide layer has been damaged by the analysis laser pulse, and the processing system (24) is configured to determine a dimension representative of the damaged area from the image and to evaluate, from the information relating to the dimension representative of the damaged area and the energy profile of the analysis laser pulse, a metal damage energy density threshold corresponding to an energy density above which degradation of the surface of the metal product (3) beneath the oxide layer is observed.

13. 13. The laser ablation apparatus of claim 12, characterized in that the processing system (24) is configured to transmit the damage energy density threshold to the transmission system (20), and the transmission system (20) is configured to adapt the energy of the analysis laser pulse as a function of the damage energy density threshold such that at any point of an affected segment of a next portion of the moving product, the energy density is lower than the damage energy density threshold.

14. 14. The laser ablation apparatus of claim 11, wherein the information related to the energy profile includes a shape of the energy profile and an energy or power of the analysis laser pulse, and the laser ablation apparatus is equipped with a system for determining the shape of the energy profile of the analysis laser pulse and / or a system for determining the energy or power of the analysis laser pulse.

15. 15. The laser ablation apparatus of claim 14, wherein the system for determining the shape of the energy profile of the analysis laser pulse comprises a beam analyzer (64) and an optical device (62), in particular a beam splitter configured to deflect a portion of each analysis laser pulse towards the beam analyzer (64), and the beam analyzer (64) is configured to evaluate the shape of the energy profile from the deflected portion of the analysis laser pulse.

16. 16. The laser ablation apparatus according to claim 14 or 15, wherein the system for determining the energy or power of the analysis laser pulse comprises a power meter and an optical device (62), in particular a beam splitter configured to deflect a portion of each analysis laser pulse towards the power meter, the power meter being configured to evaluate the energy and / or power of the analysis laser pulse from the deflected portion of the analysis laser pulse.

17. 14. The laser ablation apparatus of claim 11, wherein the information relating to the energy profile includes the shape and energy or power of the energy profile of the analysis laser pulse, and the laser ablation apparatus comprises a system for determining the shape and / or energy or power of the energy profile of an auxiliary laser pulse transmitted by the delivery system (20), the auxiliary laser pulse being separate from the analysis laser pulse.

18. 18. A stripping device according to any one of claims 11 to 17, characterised in that it comprises a group of laser sources (30) and a group of stripping lasers (13), distributed in the vicinity of the metal product (3) for treating the entire surface of the metal product consisting of a strip, a bar, a tube, a sheet, a plate or a wire.

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