The present invention relates to the removal of the oxide layer which covers a metal product, particularly steel, after the latter has undergone exposure to an oxidizing atmosphere for some of its components, for example when staying in a heat treatment furnace.

In the following text, we take as a preferred example of application of the invention the field of stainless steel strips and sheets of all categories (austenitic, ferritic, austenitic-ferritic ...), fixed or scrolling rolled or thermoformed or cold. But it should be understood that this is absolutely not limiting, and the invention can be applied to other metals for which faced similar technical problems to those encountered on stainless steel coils and sheets, including various classes of carbon steels and special alloys, including ferrous. It may also apply to other products as tapes and sheets, for example of the son and the tubes with and without welding,

It is usual that the plates and stainless steel strips undergo treatments that lead to that a layer of undesirable oxides formed at high temperature on their surfaces in contact with an oxidizing atmosphere such as air. These oxides have a composition which varies considerably depending on the composition of the base metal and the conditions of their formation. Most usually, oxides of Fe, Cr, Mn and Si are preponderant.

Treatments that lead to this formation are, typically, not restrictively, the reheating that undergoes a semifinished product (ingot, slab, bloom, billet) before hot rolling and the stay in the open air after it performs hot rolling, and various annealed at several hundred degrees undergone by the band or the sheet before and / or during and / or after cold rolling cycle (the latter being performed in one or several stages, some of which may be separated by an intermediate annealing), if these annealing take place in an atmosphere which is not completely inert or reducing. These undesirable oxides must of course be eliminated, before the sheet or strip becomes a usable product or semi-finished product ready to undergo the ultimate shaping operations that will make it a usable product. It is also often important to remove these oxides before the first cold rolling step to prevent them are embedded in the surface of the semifinished product during rolling and result in a poor surface finish.

It should be understood that the layer of unwanted oxides referred to here is not the thin layer based on oxides of Cr (so-called "passive film") which forms spontaneously in air and at room temperature to Surface of stainless steels and protects them from oxidation. The oxide layer which is a problem, and that is to be eliminated, is that which forms during stays of the high temperature strip in an oxidizing atmosphere. Once removed layer, the surface of the stainless steel is exposed and the protective passive layer of Cr oxide may be formed again rapidly and spontaneously, making the new stainless steel under conditions of 'usual use.

The use of a mechanical descaling by blasting (spraying rigid balls on the surface to be treated) and / or a break-oxides (passage of the strip between pairs of rollers which make it work in bending, compression and tension) allows to crack and remove easily, for example by brushing, much oxides, but may be insufficient to remove all of it. Shot peening also has the disadvantage of increasing the surface roughness, that the operations later suffered by the sheet or the tape does not necessarily make it possible to correct when this is not desired.

Most typically, the undesired oxide layer is removed using a chemical or electrolytic etching process, or a succession of such stripping.

The pickling is carried out in one or more baths of hydrofluoric, hydrochloric, sulfuric or nitric acids. Electrolytic pickling is carried out typically in a sodium sulfate bath or an acid bath (nitric or sulfuric acids).

These stripping lead to the production of a strip or a sheet having a surface finish which is usually class in various categories forming the subject of standards:

- Finish D 1, for the products having undergone hot rolling, annealing and pickling, usually a chemical etching; a mechanical etching (oxide breeze, peening) is usually also used upstream of chemical pickling;

2B finish for products annealed, generally electrolytic and chemical pickling and skin-pass passage (skin-pass mill improves the flatness of the strip and reduce its roughness, with a low rate of reduction in the thickness of product which is of the order of several% in principle);

Finished 2D for cold-rolled annealed, pickled and no skin pass;

Finished 2E for cold-rolled annealed, shot peening, etching and no skin pass.

The chemical etching is the most radical method to remove unwanted oxides. But it has many disadvantages.

It consumes high amounts of acids, with, at most, very low possibility of recovering part for later use.

The necessary infrastructure for its implementation, namely the successive pickling baths and their annexes, are expensive and cumbersome. It is not unusual to meet chemical pickling plants scroll strips with a length of about 200 m.

These facilities use dangerous products, especially hydrofluoric acid. Their releases liquid and solid contaminants (sludge containing oxides mixed with the stripping liquid) must be stored and restated under strict regulations whose severity will only increase in the future, which is expensive. The acid baths, heated, also give off acid fumes that must be neutralized. Nitric acid is also a source releases NO x that must be captured and treated.

Are also used electrolytic pickling processes, carried out while the web or sheet is immersed in a bath typically based on sodium sulfate, or nitric or sulfuric acid, which must also be retired after use. The electrolytic pickling requires a fairly expensive equipment using a relatively large amount of electrical energy. It may be supplemented by a chemical acid pickling, lighter than when a single chemical etching is used, but which has the same type of disadvantages as those mentioned above. The electrolytic pickling product, too, sludge that must be stored and reprocessed. Worn bathroom need to be restated. The restatements sludge and bathrooms are less expensive, dangerous and complex than in the case of

Finally the presence of hexavalent chromium in solution in the pickling liquid is a strong risk to staff health and the environment: its contents in liquids and staff exposure are measured and monitored.

So opportunities were examined to replace, at least in some cases, chemical or electrolytic pickling metal produced by processes making use of a laser. The classic book "Laser Cleaning" (Boris Luk'yanchuk, December 2002, ISBN: 978-981 -0 -02 to 4941) suggests such possibilities, especially for cleaning of artworks and buildings (notably Chapter 2 "an overview of

Experimental research into the laser cleaning of contaminants from surfaces), so for fixed surfaces of relatively small sizes. The laser beam is projected onto the surface to be cleaned and causes the detachment of the oxide layer.

This way, we avoid to use acids and / or sulfates, and there are no adjustments sludge and pollutants and hazardous liquids to perform. One only has to collect the oxides detached, for example by suction, and one has the possibility to reprocess, preferably dry, to recover their metal content and value. The safety of personnel and the workshop environment is better assured. All of the cleaning operation of the laser surface also has a better overall energy balance that wet (chemical and / or electrolytic), especially as the laser operation of the electricity cost is not very high, particularly in relation to what is necessary for an electrolytic pickling. The Installation can be much more compact than a pickling plant comprising several successive baths, where clear benefits on the cost of civil engineering operations during the construction of the facility. If using fiber lasers drawn, it is possible to send high amounts of energy in a very short time at a high frequency and with long battery life, and the life of these lasers can be several years without maintenance.

However, the use of already existing technologies, coupled with lasers C0 2, Excimer or Nd: YAG, does not allow to obtain optimum results from strips or sheets scroll industrial size, due to heavy maintenance, an operating mode of continuous lasers or landing nets too long and a too high operating cost due to the number of lasers used, given the high frame rate of current lines. Furthermore the solutions are solutions assuming a uniform surface state according to the width and length of the web (see EP 0927595-A1) and, usually, a fixed frame rate. On the same tape, if the tape speed should change for a specific reason, the inertia of the machinery, and primarily that of the furnace, leads to a change (in thickness and / or in kind) of the oxide layer. Although the nature and the thickness of the oxide layer removing were previously considered as known, they are then modified and an adaptation of the frequency or pulsed energy in function of the speed functions only if the oxide layer does not change (which is not the case in general). Finally line speeds reach about 100-150 m / min now. If the tape is desired to be etched 2 m wide moving at this speed, current scanners scanning the surface are limited by the speed of their motor, much less than the speed which would be necessary to avoid a scan over a very short distance involving an array of hundreds of lasers in the width of the sheet. For example, a Nd: YAG 1064 nm, 1 mJ, having a spot measuring 0.120 mm on a side,

The object of the invention is to provide a metal products pickling plant, in particular in strip-shaped scroll from coil hot-rolled sheet or cold bars, son, or tubes with or seamless, to exploit the best opportunities laser etching of these metal products on an industrial scale. This facility should be as versatile as possible for treating products in steels of various compositions, various oxidation states of various sizes and thicknesses (for strip and sheet), the products can be scrolled in the installation laser etching at various speeds.

To this end, the invention relates to an etching method of a metal product in scroll having on its surface an oxide layer, said etching process using a laser, characterized in that:

- at least one first laser wavelength equal to that of lasers used for etching, or preferably a group of such first lasers, each send a ray that is reflected on the oxidized surface of the product to be pickled, said reflected rays by the oxidized surface being intercepted by sensors that send information that they collect in a processing unit;

- a processing unit calculates the radius of the absorption by the product surface, based on information collected by the sensors, deduces the emissivity of the oxidized surface of the metal product in the direction of said reflected rays, and correlates this with emissivity reference information pre-recorded in said processing unit;

- at least a second laser, or preferably a group of such second lasers, each send pulsed with a radius on the product surface to be etched, said spots of said landing nets rays covering the entire surface to be etched through an optical scanning and / or mechanical laterally moving the spots of the rays on the product surface, or an optical system transforming spots in lines, said one or more second lasers being controlled by a control unit receiving the information provided by the processing unit for determining the operating parameters to impose said second lasers to obtain the

stripping the product surface, by comparison with experimental results prerecorded in the control unit;

- and means of inspection of the etched surface of the product verify the effectiveness of the stripping by detecting the possible persistence of non-etched areas or poorly pickled.

Fluence spot draws each of said at least one second laser may be between 1 and 20 J / cm 2 .

Among the pre-recorded information in the processing unit may include the product composition and roughness, measured or estimated, of its surface.

After stripping and prior to the inspection of the surface can be carried to a discharge oxides stripped from the product surface, such as by suction and / or by brushing.

After inspection of the product surface, we can proceed to an additional stripping of the product, at least in areas whose inspection showed that their pickling by the one or more second lasers has been insufficient.

Said additional etching can be performed by at least one third laser or a group of such third lasers, according to information provided by said inspection means of the surface.

Can be checked by inspection of the second means, such as optical means, the performance of said additional pickling.

The product, after further stripping and optionally detecting imperfect areas etched by the second means of inspection, can be sent in at least one pickling bath, chemically or electrolytically.

Said additional etching may also be performed by means of at least one pickling bath, chemically or electrolytically.

Said metal moving product can be a strip or a sheet, and is etched on the both sides of said strip or sheet.

The invention also relates to a laser etching system of a metallic moving product, characterized in that it comprises:

- at least one first laser wavelength equal to that of lasers used for etching, or preferably a group of such first lasers, each sending a ray which is reflected on the oxidized surface of the product to be pickled, and sensors that intercept the rays reflected by said oxidized surface and send the information they collect in a processing unit;

- a processing unit which calculates absorption radius by the product surface, based on information collected by the sensors, and deduce the emissivity of the oxidized surface of the metal product, and correlates this information with emissivity of reference prerecorded in said processing unit;

- at least a second laser, or preferably a group of such second lasers, which each send a radius on the product surface to be etched, the spots of said beams being capable of covering the entire surface to be etched through optical scanning systems and / or mechanical laterally moving the spots of the rays on the product surface, or an optical system transforming spots in lines, and a control unit controlling said one or more second lasers and receiving information provided by the processing unit for determining the operating parameters to impose said second lasers for stripping the product surface, by comparison with experimental results prerecorded in the control unit,and controlling said second lasers by imposing said operating parameters;

- and means of inspection of the etched surface of the product verify the effectiveness of the stripping by detecting the possible persistence of non-etched areas or poorly pickled.

Said inspection means of the etched surface of the product may be optical means.

The installation may comprise means for removing the stripped oxides of the product surface, such as by suction and / or by brushing.

It may include means of implementation of a supplementary stripping placed downstream of said means of inspection of the etched surface of the product.

Said means for performing an additional pickling comprise at least one third laser or a group of such third lasers, operating according to the information provided by said inspection means of the surface.

The means of implementation of an additional etching may comprise at least one pickling bath, chemical or electrolytic.

The laser etching system can be disposed on a continuous processing line also comprising a furnace placed before it.

Said continuous line may include a rolling installation of the metal product.

To treat both faces of said metal product, which consists of a strip or a sheet of scrolling, the installation may comprise on either side of said product, at least a first laser, at least a second laser, and means inspection of each surface of said product.

To treat the entire surface of said metal product consisting of a bar, a tube or a wire, the installation may comprise, distributed in the vicinity of the periphery of said metal product, a first group of lasers, a group of second lasers and inspection means the entire surface of said product.

As will be understood, the invention is to provide a laser etching of a metal product in any format using a multi-purpose facility, providing multiple stripping efficiency and control instruments for optimizing the -ci while performing stripping treatment itself.

The invention will be better understood on reading the description which follows, given with reference to the accompanying figure which shows schematically a profile example of plant according to the invention laser etching of a metal strip, with possible manufacturing variation.

The laser pickling plants to be described in detail and illustrated with examples will be in reference to the treatment of stainless steel cold rolled strip scrolling, just undergone cold rolling and annealing on a continuous line and the laser pickling installation according to the invention, which ensures at least the bulk of the stripping function is also integrated on this line continues, replacing the electrolytic pickling plants and / or chemical customarily used on such continuous line (you can find examples of such continuous lines particularly in EP 0509177 A2 and EP-0695808-A1).

It goes without saying that the laser pickling installation according to the invention to be described can also be incorporated into a continuous processing line having more or fewer devices than what will be described, or be a separate facility specifically dedicated to stripping.

Also, it does not show the devices usually present on such lines have no major role metallurgical and, in any case, do not intervene as such in driving the realized laser etching according to the invention . pinch rollers that may be mentioned for the running of the strip, and strip accumulators which act as "buffers" among some of the equipment that may require each a running speed of the different band.

The solid line shown comprises a first unwinding installation 1 a coil 2 a 3 stainless steel hot-rolled strip whose thickness is typically of the order of a few mm and the width of which can range typically up to 2 m. This band 3 is set scrolling speeds typically up to 150 m / min, and generally after having been etched by chemical means any

and / or not shown mechanical, or even by laser with means according to the invention such as one will be described, it passes through a cold rolling mill 4, which reduces its thickness to a value which is typically of the order of 0.2 to 15 mm to obtain a cold rolled strip

The strip cold rolled 3 then passes through an annealing furnace 5, where it is heated to a temperature of several hundred ° C, which is a function of metallurgical objectives of the annealing. If annealing is carried out (deliberately or accidentally) in the presence of a significant amount of an oxidizing gas such as oxygen, it leads to the formation of a layer of unwanted oxides on the surface of the strip 3, whose composition, thickness and adhesion of the strip 3 depend mainly on the composition of the strip 3, the composition of the atmosphere of the furnace 5, the temperature in the oven 5, residence time of the band 3 in the oven 5. given these numerous parameters that are not easily controlled and all that, anyway,

According to the invention, after the annealing furnace 5, is arranged on the line, and on each side of the strip 3, a first row of lasers 6 of a wavelength equal to that of lasers to be used for the etching (e.g., Nd: YAG wavelength of 1064 nm) whose radii of the spots 7 of the band 3 can ideally cover the entire width of the web 3 which overlap as little as possible. The location of these spots may vary optionally by means of a scanning system similar surface that will be described for lasers 13 providing pickling, so that the spots of the first laser 6 cover all or a large part of the surface of the web without an excessive number of first lasers 6 is necessary. This first row of lasers 6 is associated with a series of sensors 8 on which are returned radiation 9 from the reflection of the rays 7 on the oxidized surface of the web 3. The first laser 6 must be placed with an angle of incidence known to recover, using the sensors 8, reports that the proper angle of reflection. Comparing, by a processing unit 10 suitable signal and programmed in a conventional manner, the intensities of radiation 9 received by each of the sensors 8 with reference intensities at said angle of reflection, prerecorded in said processing means 10, for bare strip, or oxidized in a standardized way, which have the same composition and the same roughness than the web 3 processed. This determines the spectral emissivity,

The purpose of the first lasers 6 is to determine the effective energy required for the stripping in the strip width and in the length in the moving web. Indeed it is possible, due to deliberate or sustained variations, process parameters upstream of the line, for example slowdowns, the tape acceleration on the line, or a heterogeneous pollution on the width of the strip 3 which has occurred in the furnace 5 or before thereof, to obtain a mixed oxide layer on the length and / or width of the strip 3 to be etched. The first lasers 6 and 8 corresponding sensors can quantify heterogeneity.

The fact that the wavelength of the first laser 6 is the same as the pickling lasers ensures that the radii of the absorptions of the first lasers 6 of oxides covering the band 3 will be the same as for lasers pickling and stripping laser adjustments will be based directly on data obtained by the first laser sensors 6 and 8.

For reliable measurement of the absorption of the first lasers 6, the band 3 must maintain a constant distance from the first laser sensors 6 and 8, that is to say that the band 3 does not oscillate and must remain fixed height. This can be done by applying a sufficiently high traction to the strip 3 by means of S blocks or by placing a supporting roller 24 in the band 3 ensuring the fixity of its height the first lasers 6.

For simplicity, Figure 1 only shows the first lasers 6, their sensors 8 and their associated support rollers 24 on the top side of the band 3. But, of course, other lasers and their associated sensors are also present on the lower surface of the strip 3. Similarly, a comparable support roller to roller 24 may be placed in contact with the upper surface of the strip 3 to ensure that the strip 3 maintains a fixed distance lasers inspecting its lower surface.

As the effective roughness of the strip 3 is difficult to measure in the case where the tape 3 is scrolling, one can take the assumption that this roughness is the same as that of the surfaces of the working rolls 1 1, 12 of the cold rolling mill 4, which is known in principle that these cylinders 1 January 12 are regularly checked and, if necessary, corrected for, precisely, they do not require the surfaces of the web 3 during rolling roughness which would be excessive or out of control. It will often be sufficient to evaluate this roughness on one of the work rolls 1 January 12 as normally their roughness evolves similarly when using them, but you can also choose not to assume a priori the equal roughness of the rolls 1 1 12 and evaluate them both separately. Under the hot rolling roughness can also be controlled by comparison with measurements made previously outside the pickling line on these products or similar products.

Note that if the product to be processed is different from a web 3 unwound scroll from a coil 2, (e.g. if it is a sheet metal already cut and rolled), and if possible to evaluate the effective roughness before entering the annealing furnace 5, then we can establish the measure of emissivity oxidized product to be treated on this effective roughness.

Then, the strip 3 passes in front of a second row of lasers 13 (for example, pulsed Nd: YAG 1064 nm) each sending a beam 14 on the surface of the strip 3.

These lasers 13 of the second row are those actually charged stripping itself. They occupy positions in the transverse direction of the strip 3 that make each of them is, optimally, substantially facing one of the lasers 6 of the first row. They are controlled by a control unit 15 which determines what should be their various operating parameters based on:

The results of emissivity measurements of the web surface 3 provided by the first laser 6, the sensors 8 and the processing unit 10 of the information they provide and are transmitted to the unit 15 for controlling the lasers 13 of the second row;

And experimental results prerecorded in the control unit 15 that can learn, from calibrations performed previously on samples of reference composition, roughness and emissivity identical or similar to those of the band 3 to be treated, what would the most appropriate parameters for the operation of each of pickling lasers 13, in particular according to the emissivity measured in the region of band 3 that it can reach, to achieve satisfactory pickling the strip. Of course, the processing unit 10 and the control unit 15 can be grouped into a single apparatus able to perform by itself all the functions of the two units 10, 15.

In the same way as for the lasers 6 and sensor 8, the band 3 is to maintain a fixed height during the passage under the lasers 13, and a support roller 25 similar to the previous support roller 24, or any other functionally equivalent device, can be used for this purpose.

Also, other lasers 13 not shown, and possible associated backing roll are provided for etching the lower surface of the strip 3, on the basis of information provided by unrepresented 6 lasers inspecting said lower surface.

The lasers 13 may be each placed not perpendicular to the sheet in order to minimize disturbance of the incident beam by the oxide particles projected in previous landing nets emitted by the laser 13 itself or other lasers 13 of the row.

The number of lasers 13 required for processing of the entire surface of the strip 3 is minimized in that each laser 13 has an ultra-fast scanning system, optical or mechanical or a combination of both principles, providing lateral movement of the spot of the beam 14 so as to juxtapose the spots to form a continuous line covering the entire width of the band 3, preferably with no or minimal recovery spots to avoid the risk of sending amounts excessive energy in the spots overlap zones.

An operating parameter that must also be considered is the scrolling speed of the web 3, which will determine the frequency of landing nets and / or the scanning speed of the laser 13. The higher the frame rate, the higher the frequency and / or the scanning speed pulsed must be high, so that it is ensured that a given portion of the width of the surface of the strip 3 is processed by the laser 13 is concerned adequately and substantially identical to the other portions. Regardless of the scrolling speed, each strip portion in the width must be processed and must have received the required energy density and is given by the control unit 15. This energy density will depend on the number of landing nets , energy by draws, frequency pulsed,

Using a laser etching performed according to the invention provides the pickling plant versatility, especially as the stripping parameters can be easily adjusted during treatment if it is found during the operation they are not optimal. This is the case, for example, the surface of each spot of the second laser 13, a conventional system for adjusting the focusing of the beam, can change.

One possible simplification of the invention is that instead of having a row of first laser 6 which correspond an equal number of second laser 13, it uses a smaller number of first lasers 6, or even a single first laser 6, assuming that the oxidation of the surface of the strip 3 is identical in a wide area surrounding a first given laser 6 or over the entire width of the strip 3 if there is only one laser 6 . is then made to operate groups of second lasers 13, or all of the second laser 13 when there is a first laser 6, with the same parameters.

In the vicinity of the second laser 13, there are means (not shown) for discharging and preferably collect, for example by suction or brushing in the direction of a container, the oxides which were detached from the surface of the strip 3 so that the fumes can be generated during the treatment (the spraying of metal particles, oxides or organic materials). This way, we give the possibility to easily recover a maximum amount of these oxides, so they do not disperse in the ambient atmosphere in the pollutant, and to give the opportunity to restate most to recover the metals they contain. In addition, this operation allows to get rid of oxides which have been just that imperfectly detached from the surface of the web 3 by the lasers 13 (particularly on the upper surface of the strip 3, where one can not rely on gravity to help the detachment of the oxides). Finally the suction of the dust and fumes prevents damage of the optical systems of laser on which they can agglomerate, causing their overheating or their breakages.

After passing under the second laser 13, the band 3 is, in principle, completely pickled. It is checked by suitable means, for example with an optical device for controlling the quality of the etching such as a camera 16 or a set of such optical devices 16, which examines (s) the surface the strip 3 over the whole of its width and determines (nt) which areas of the web 3 would possibly not pickled satisfactorily. Differences in color on the surface of the strip 3 may be the basis for this determination. A benefit of the suction device or brushing or equivalent which just mentioned is that it prevents pieces of

If the results provided by the optical device 16 are not satisfactory, then one can proceed to a complementary etching on portions of the pickled strip imperfectly or, for safety reasons, the entire band.

Thus, in the variant of the invention shown in Figure 1, there is downstream of the or the quality of the etching control devices and vacuum cleaners / possible brushes a plurality of third lasers 17 comparable to the second laser 13, which send each a radius 18 on the areas of the surface of the strip 3 which has been detected through the camera 16 or a functionally equivalent device, that they were imperfectly etched by the second laser 13. These third lasers 17 may be identical, in their distribution over the width of the band 3, to the second lasers 13 and also possess a maintained height of the band system (e.g. a roller). One can also predict fewer,

One can also provide optical systems on third lasers 17 to laterally move their beams without physical movement of the laser 17. It is thus possible to minimize the number of third lasers 17 that should be used for complete stripping of the strip 3, in particular if experience showed that completion of stripping was always useful in a limited number of areas.

Optimally, another device for recovering oxides by suction, brushing or the like can also be present in the vicinity of the third lasers 17.

Optimally, the quality of the etching control means such as a camera 19 similar to the aforementioned camera 16 can detect the possible presence of persistent imperfectly etched areas.

If the pickling of the strip 3 is satisfactory after passing under the second lasers 13 or under the third lasers 17, if any, the strip 3 can continue its processing, for example by undergoing a passage in a skin-pass then being wound to obtain a tape reel cold-rolled and annealed, which can be marketed or to undergo other treatments such as coating.

If the pickling of the strip 3 is still considered unsatisfactory after its passage under the second lasers 13 and then under the third lasers 17, when present, may be considered various alternatives within the scope of the invention.

If pickling defects are relatively light, can continue processing the band 3, but with the expectation that its surface quality will not be that expected, and it will likely take the downgrade, that is ie the sale to the customer at a lower price than initially planned, or a client that will surface quality requirements less stringent than the client who commissioned the band 3.

If the defects of the strip 3 are frankly unacceptable at this point, it must discard the portion of the strip 3 which contains the, or then again turns the whole of the band 3 in the laser stripping section, analogously to which is usual in the prior art when no longer chemical or electrolytic pickling means downstream of the last inspection.

But an alternative may be provided on the line, after the laser stripping section, a stripping section bins wet chemical and / or electrolytic, which could be filled at least temporarily, to remove the defects. If the band 3 would be stripped correctly, these baths remain empty. This alternative solution is shown symbolically in Figure 1, wherein the strip 3 can follow a path 20 which directs it towards an electrolytic pickling bath 21 and then to a chemical etching bath 22. This configuration is, of course, that a non-limiting example, and the pickling section "backup" can be designed differently, for example by not making use of only one of these two types of baths 21, 22.

Another solution is to achieve the deflection of the strip 3 or in the pickling baths 21, 22 by means of divers rollers vertically movable and arranged to be able to act on the upper surface of the strip 3. In normal operation, these rollers are in a position such that they leave the running web 3 outside the pickling bath 21, 22 in the vicinity of which they are arranged. When it is a chemical etching and / or electroplating of the strip 3 is locally required, at least one of these rollers divers lowers so as to press the upper surface of the strip 3 and to temporarily enter the portion of the strip 3 to be treated or in the pickling baths 21, 22 corresponding one wants to use.

Alternatively, one may provide that there is no third lasers 17, and the tape 3 can be oriented, if necessary, by a path 23 to the wet stripping section 21, 22 previously described, after inspection by the control means 16 after the laser etching performed by the second laser 13. it is also possible to have systematically used this wet stripping section 21, 22 in order to be fully assured that the band 3 will be in a surface condition satisfactory everywhere.

The settings of the electrolytic pickling section 21, if any, can be optimally adjusted for the results of the inspection by the monitoring means 16, 19. It may, however, consider increasing band 3 systematically at least in the electrolytic pickling bath 21. When inspecting the belt 3 or by the cameras 16, 19 shows that the use of this bath is not useful for a portion of the given band, it can make the bath electrolytic pickling 21 simply by cutting idle its power supply.

A final inspection of the surface of the strip 3 on leaving the wet stripping section 21, 22 can be performed to check the quality of the final result.

Of course, the illustrated solution consisting in call, optionally or automatically, to a wet etching by means of section 21, 22 to correct possible defects of pickling by the lasers 13, 17 is, at first sight, to reduce the financial interest and ecological this variant of the invention compared to an installation that would be limited to the use of one or more laser stripping for cleaning of the web 3.

However, be aware that one of the effects of the laser etching, even if it does not always necessarily allow alone, to completely remove the layer of unwanted oxides on the tape 3, is at least , modify the remaining portion of this oxide layer to make it more homogeneous and thus more easily décapable wet. The stripping or wet which are then made by the baths 21, 22 to eliminate the residual oxides may use less aggressive baths and / or smaller volumes if the entire pickling must be performed wet. It should also consider the fact that by stripping any additional wet can avoid downgrade or put off the metal which does have not been fully processed by the laser pickling section, and therefore limit the financial impact of these imperfections. this wet stripping section can also design 21, 22 as a substitute entirely by laser stripping section where it must undergo a maintenance operation that prevents its use. In this way, the pickling line is usable even during this maintenance.

Furthermore, the end use of a light pickling wet leads to a finished most assuredly like-for those whose customers are used only in the case of using a single laser etching. This can make the bands 3 and produced acceptable without reticence by customers as they are not convinced that a single laser etching, well executed, is sufficient to obtain strips with good surface qualities. Without use of pickling baths 21, 22, surface finish pickled strips 3 only laser would be new types of finishes that may be required to include in standards.

As said, the adaptations of the method, as it has been described and illustrated are apparent to those skilled in the art when one wants to treat different product running webs. A very similar system can process sheets or plates, previously cut from strips or otherwise obtained.

In the case of treatment of bars, son or tubes, various lasers and inspection means are arranged around the surface to be etched, and it is obvious that the term "row of lasers" that was used for the description of example 1 is also valid for this type of application, considering that the word "row" does not imply that the relevant lasers are located in the same plane parallel to the product to be stripped: they can be as arranged in a substantially parallel path to the product of the perimeter to be treated.

In some cases where the metal products to be treated are of very small width, it would remain in the spirit of the invention to use only one laser in each group of laser 8, 13, 17 that was mentioned. We can then choose to focus at least the second and third etching lasers 13, 17 so that their spots cover the entire surface continuously stripping, or keep small dimensions of the spots but to move these lasers so as to make it possible to treat the entire surface of the product using a single laser etching step. This would be particularly suitable, especially, the treatment of small diameters son. Of course, the laser movement speed will depend, inter alia,

In the case of treatment of welded tubes, can be advantageously particular emphasis on the laser etching at the weld bead, which is the most likely to have undergone a significant surface oxidation part, by choosing individual settings for the one or second laser 13 that treat.

Regarding the second and third lasers 13, 17 used for implementing the method according to the invention can be used include:

- Optical systems that generate for each laser 13, 17 a thin blade, several centimeters long; a scan is then not necessary and the frequency and energy pulsed as directed by the control unit 15 to obtain the required energy density as a function of the actual speed of the strip 3 is varied;

- Or polygon scanners that create a beam scanning motion 14, 18 from the lasers 13, 17, with scan speeds up beyond 200 m / s.

Can be used, for example, lasers 13, 17 Nd: YAG delivering pulsed 1 mJ or 100 mJ. The dimensions of the spots (spots pulsed on the tape) are determined by their potency. By cons by defocusing the landing nets or using optical systems, as is known, they can be diverging or converging more and thus change the sizes of the spots.

A laser 1 mJ has a power of 1000 W at a frequency of 1 MHz or 500 W at a frequency of 500 kHz and a stationary spot diameter of 1 14 μηι or a spot diameter higher and variable if used in for this purpose optical means or means for defocusing of the pulse. A 100 mJ laser has a power of 1000 W at a frequency of 10 kHz or 500 W at a frequency of 5 kHz, and an easily adjustable spot size by varying the focusing of the beam, which may be of the order of mm .

The laser 1 mJ therefore generally has a smaller laser spot than 100 mJ. This is explained by the fact that passing a quantity of high energy in a small draws would cause excessive heating of the fiber. The shape of the pulse is also different, the draws of the laser 1 mJ being tapered while that of 100 mJ laser is usually cylindrical (but defocusing can be used to make conical). Indeed, a high energy amount is obtained at the expense of beam quality, where the difference in shape and dimensions between the two described types of lasers.

Mechanisms that come into play in the laser etching process are numerous: vaporization of the oxide under the influence of heat, changes in the metal / oxide interface by the shock wave due to being drawn, and thermal expansion taking off oxide. The article "Preliminary study on the laser cleaning of stainless steels after-high temperature oxidation / Pandora Psyllaki Roland Oltra," Materials Science and Engineering A 282 (1 -2, pp: 145-152, April 2000 deals with this aspect. one can also add the oxide restructuring effect, which becomes homogeneous as a result of the laser and can be removed in a more easy and reliable way, either directly by the various lasers,

Among the reference information to be stored in the processing unit 10 include the spectral emissivity measurements in the direction to consider and total hemispherical emissivity as a function of the composition of the strip, its

temperature and its dimensions (thickness, width) and the orientation of the laser beam (for the directional emissivity).

Thus, for example, strips of 1500 mm wide and 0.78 mm thick austenitic stainless steel 304L and for strips of 1250 mm wide and 1, 46 mm thick austenitic stainless steel Mo 316L, data examples to be stored as references for oxidized bands in the processing unit 10 are given in table 1, these data having been determined experimentally.

Depending studied shades and different oxide thicknesses, the parameters of the laser, for example a pulsed Nd: YAG laser - 1 mJ, must permit removal of the oxide layers according to their nature. Oxides degradation thresholds for 120 ns landing nets are between 1 and 5 J / cm 2 . Distribution pulsed on the surface is suitable, but to have an ideal recovery in the example described, we chose almost no overlap between two drawn from the scanning direction, and a coverage of 75% between two drawn from the sense of travel of the strip 3 (an area of the band in which this recovery occurs is affected by spots of four landing nets). Under these conditions, the fluence draws must be applied, in general, between 1 and 20 J / cm2 for each spot (depending on the kinds and thicknesses of oxides to be removed). In this example, it is placed between 2 and 1 1 J / cm 2 . One can then remove a thickness of oxide on the surface, e.g., a stainless steel 316L or 304L, of the order of a few tenths of μηι several μηι.

La fluence par puise applicable dans le cas des éventuels troisièmes lasers 17 est typiquement du même ordre de grandeur (1 à 20 J/cm2) que pour les deuxièmes lasers 13. Elle pourra, dans les faits, souvent être inférieure comme, normalement, l'essentiel du décapage aura déjà été assuré par les deuxièmes lasers 13. Optimalement, cependant, il est préférable que les troisièmes lasers 17 puissent procurer la même fluence par puise que les deuxièmes lasers 13 pour qu'ils puissent, à eux seuls, assurer un décapage complet des portions de la surface du produit qu'un réglage imparfait des deuxièmes lasers 13 auraient laissées non décapées du fait d'un non-recouvrement des spots de deux puises successifs.

Les bandes de 304L ont été élaborées comme suit : laminage à chaud jusqu'à une épaisseur de 3 mm, recuit puis décapage chimique sur une première ligne de recuit, puis laminage à froid sur un laminoir de type Sendzimir (20 cylindres) jusqu'à une épaisseur de 0,78 mm en un seul trait, recuit sur une deuxième ligne à une température allant jusqu'à 1 120°C pendant 1 minute et 6 secondes avec une vitesse de défilement de 77 m/min, conduisant à une couche d'oxydes d'épaisseur 250 nm environ.

Les bandes de 316L ont été élaborées comme suit : laminage à chaud jusqu'à une épaisseur de 3 mm, recuit puis décapage chimique sur une première ligne de recuit, puis laminage à froid sur un laminoir quarto à émulsion jusqu'à une épaisseur de 1 ,46 mm, recuit sur une deuxième ligne à une température allant jusqu'à 1 150°C pendant 1 minute et 16 secondes avec une vitesse de défilement de 67 m/min, conduisant à une couche d'oxydes d'épaisseur 250 nm environ.

Tableau 1 : Emissivités directionnelles mesurées expérimentalement pour deux types de bandes oxydées

Les lasers peuvent aussi être utilisés à l'aide d'un système optique transformant le puise en ligne, ou à l'aide d'un scanner polygone.

Dans le cas où l'on utilise un système optique transformant le puise en ligne, si on utilise un laser 100 mJ avec une aire de spot de 1 ,4 x 1 ,4 mm soit 1 ,96 mm2, sur une bande défilant normalement à 100 m/min, pour avoir un laser opérant sur une ligne de 15 cm, cette aire de spot nécessite une largeur de spot de 0,013 mm, soit 13 μηι. Si la bande défile à 100 m/min, elle parcourt 13 μηι en 0,0078 ms. Pour que le spot recouvre toute la surface visée, il faut donc un puise tous les 0,0078 ms, ce qui correspond à 128 kHz pour une puissance totale des lasers de 12,8 kW. 12 lasers sont donc nécessaires à cet effet pour une bande de 1500 mm de large.

Si on désire que chaque laser opère sur une ligne de 10 cm, la largeur de spot doit être de 20 μηι selon le même calcul que précédemment. Toujours pour une vitesse nominale de la bande de 100 m/min, il faut une fréquence de 85 kHz correspondant à une puissance totale de 8,5 kW. 13 ou 14 lasers sont donc nécessaires pour une bande de 1500 mm de large. Il en faudrait 20 pour une bande de 2000 mm de large.

Dans le cas où l'on utilise un scanner polygone, il faut reprendre le calcul effectué précédemment en calculant la vitesse nécessaire de balayage pour avoir au moins toute la surface traitée dans le sens de défilement et dans la largeur de la bande. Si l'on prend un puise de 1 ,4 mm de côté, sur une bande défilant normalement à 100m/min, pour avoir un laser opérant sur 15 cm, le scanner polygone doit être capable de parcourir deux fois cette distance quand la bande se sera déplacée de 1 ,4mm, soit à une vitesse de 360 m/s. La fréquence du laser doit être capable de fournir une rangée de puises juxtaposés dans la direction du scan, soit un peu moins de 260 puises aller, soit environ 600kHz.

Dans ces conditions, il a été possible d'obtenir un très bon décapage des oxydes de 304L comme de 316L, ne nécessitant pas de décapage chimique ou électrochimique ultérieur.

Les paramètres à prendre en compte pour le pilotage des deuxièmes et troisièmes lasers 13, 17, et devant tenir compte de la nature du produit à traiter (composition, largeur) et de son histoire (paramètres du recuit au cours duquel l'essentiel de la couche d'oxydes à décaper s'est formée, rugosité imposée par les cylindres du laminoir à chaud ou à froid), en plus de l'émissivité que les premiers lasers 6 et les capteurs 8 associés ont permis de mesurer, sont notamment :

La vitesse de défilement de la bande ;

La puissance du laser ;

- La durée des puises ;

La fréquence des puises ;

La largeur de bande que chaque laser est appelée à traiter ;

La vitesse de déplacement (mécanique et/ou optique) des spots des lasers. L'émissivité mesurée est, de préférence, comparée avec la valeur standard théorique enregistrée dans l'unité de traitement 10 que la nature du produit et son histoire auraient a priori imposée. Si le résultat est franchement différent de celui escompté, montrant ainsi que la formation des oxydes ne s'est pas déroulée exactement comme attendu, alors on peut apporter un facteur correctif à un ou plusieurs des paramètres de fonctionnement des deuxièmes lasers 13 de façon à adapter ces paramètres aux conditions réelles rencontrées. La caméra 16, ou le dispositif équivalent, permet de s'assurer que le correctif aux réglages préenregistrés a été suffisamment efficace, et dans le cas contraire, de commander en conséquence les troisièmes lasers 17 ou de dévier directement le produit vers les bains de décapage 21 , 22. On peut ainsi limiter autant que possible le recours aux bains de décapage 21 , 22 en plus ou à la place des troisièmes lasers 17 pour corriger les imperfections de l'étape principale du décapage assurée par les deuxièmes lasers 13.

Si, pour simplifier la programmation de l'unité de traitement 10 et le processus de modélisation et d'apprentissage, on ne souhaite pas lui intégrer la possibilité d'apporter de tels facteurs correctifs, on peut, bien entendu, se contenter de se reposer entièrement sur la caméra 16, les troisièmes lasers 17 et/ou les bains de décapage 21 , 22 pour corriger les possibles imperfections du traitement par les deuxièmes lasers 13.

WE CLAIMS

1 .- A method for pickling a metal moving product having on its surface an oxide layer, said etching process using a laser, characterized in that:

- at least one first laser (6) of wavelength equal to that of lasers (13, 17) used for etching, or preferably a group of such first lasers (6) each send a radius (7) is reflected on the oxidized surface of the product to be pickled, said spokes (9) reflected by the oxidized surface being intercepted by sensors (8) sending the information that they collect in a processing unit (10);

- a processing unit (10) calculates the absorption of the beam (7) by the product surface, based on information collected by the sensors (8), deduces the emissivity of the oxidized surface of the metal product in the direction said reflected rays (9), and this correlates with emissivity reference information pre-recorded in said processing unit (10);

- at least one second laser (13), or preferably a group of such second lasers (13) each send a pulsed beam (14) on the product surface to the etching, the spots of said landing nets said spokes ( 14) covering the entire surface to be etched through a scanning optical and / or mechanical laterally moving the radii of spots (14) on the product surface, or an optical system transforming spots in lines, said one or more second lasers being controlled by a control unit (15) receiving the information provided by the processing unit (10) for determining the operating parameters to impose said second lasers (13) for stripping the product surface, by comparison with experimental results prerecorded in the control unit (15);

- and means of inspection of the etched surface of the product verify the effectiveness of the stripping by detecting the possible persistence of non-etched areas or poorly pickled.

2. Method according to claim 1, characterized in that the fluence of each spot draws said at least one second laser (13) is between 1 and 20 J / cm 2 .

3. A process according to claim 1 or 2, characterized in that, among the pre-recorded information in the processing unit (10) displaying the product composition and roughness, measured or estimated, of its surface.

4. - Method according to one of claims 1 to 3, characterized in that after stripping and prior to the inspection of the surface is carried out an evacuation of the oxides of the pickled product surface, such as by suction and / or brushing.

5. - Method according to one of claims 1 to 4, characterized in that, after the inspection of the product surface, it makes an additional stripping of the product, at least in areas whose inspection showed that their etching the one or more second lasers (13) has been insufficient.

6. - A method according to claim 5, characterized in that said complementary etching is executed by at least a third laser (17) or a group of such third lasers (17), according to information provided by said inspection means of the surface.

7. - Method according to claim 6, characterized in that checks by second means of inspection, such as optical means (19), the performance of said additional pickling.

8. A process according to claim 6 or 7, characterized in that the product, after the additional etching and optionally detecting imperfect areas etched by the second inspection means, is sent into at least one pickling bath, chemical ( 22) or electrolyte (21).

9. - A method according to claim 5, characterized in that said complementary etching is effected by means of at least one pickling bath, chemical (22) or electrolyte (21).

10. - Method according to one of claims 1 to 9, characterized in that said metal moving product is a strip or sheet, and in that the etched on both sides of said strip or sheet.

1 1 .- Pickling plant laser of a metal moving product, characterized in that it comprises:

- at least one first laser (6) of wavelength equal to that of lasers (13, 17) used for etching, or preferably a group of such first lasers (6), each sending a radius (7) is reflected on the oxidized surface of the product to be pickled, and sensors (8) which intercept the reflected rays (9) through said oxidized surface and send the information they collect in a processing unit (10);

- a processing unit (10) which calculates the absorption of the beam (7) by the surface of the product, from the information collected by sensors (8), and which deduces the emissivity of the oxidized surface of the metal product , and correlates this with emissivity reference information pre-recorded in said processing unit (10); - at least a second laser (13), or preferably a group of such second lasers (13), each of which sending a beam (14) on the product surface to the etching, the spots of said spokes (14) being capable of cover the entire surface to be etched by means of optical scanning systems and / or mechanical laterally moving the radii of spots (14) on the product surface, or an optical system transforming spots in lines,

- and means of inspection of the etched surface of the product verify the effectiveness of the stripping by detecting the possible persistence of non-etched areas or poorly pickled.

12.- laser Pickling plant according to claim 1 1, characterized in that said means of inspection of the etched surface of the product are optical means (16).

13. - laser Pickling plant according to claim 1 1 or 12, characterized in that it comprises means for discharging stripped oxides of the product surface, such as by suction and / or by brushing.

14. - laser Pickling apparatus according to one of claims 1 1 to 13, characterized in that it comprises means for performing an additional pickling placed downstream of said means of inspection of the etched surface of the product.

15.- laser Pickling plant according to claim 14, characterized in that said means for performing an additional pickling comprise at least a third laser (17) or a group of such third lasers (17) operating according to the information provided by said inspection means of the surface.

16. - laser Pickling plant according to claim 14 or 15, characterized in that said execution means of an additional etching comprises at least one pickling bath, chemical (22) or electrolyte (21).

17. - laser Pickling apparatus according to one of claims 1 to 16, characterized in that it is arranged on a continuous processing line also comprising a furnace (5) placed before said laser pickling plant.

18.- laser Pickling plant according to claim 17, characterized in that said continuous line comprises a rolling installation of the metal product.

19. - laser Pickling apparatus according to one of claims 1 1 to 18, characterized in that, for treating both faces of said metal product, which consists of a strip (3) or a sheet of scrolling, it comprises, on and the other said product, at least one first laser (6), at least one second laser (13) and means of inspection of each surface of said product.

20. - laser Pickling apparatus according to one of claims 1 1 to 18, characterized in that, to treat the entire surface of said metal product consisting of a bar, a tube or a wire, it comprises, distributed adjacent the periphery of said metal product, a group of first lasers (6), a group of second lasers (13), and means of inspection of the entire surface of said product.