Cleaning plants for metal products

Abstract

A cleaning plant for hot rolled metal strip provided with a surface oxide layer, comprising unwinding means (1) for unwinding at least one coil of rolled strip and pickling means (3) for pickling said rolled strip, with measuring means (11) arranged between said unwinding means and said pickling means for measuring the thickness of said surface oxide layer and with gaseous hydrogen detection means (12) for detecting the presence of gaseous hydrogen in the fumes produced by said pickling means. A corresponding cleaning method is also claimed.

Description

[Technical Field]

[0001] The present invention relates to a cleaning plant and a cleaning method for oxidized metal products, in particular hot-rolled strip. [Background technology]

[0002] Conventional strip cleaning lines are intended to remove the surface oxide layer that forms on hot-rolled metal products. During the hot rolling process, the slabs, either formed by the continuous caster or introduced into the line from an external station by a reheating furnace known as hot charging, are rolled to reduce their thickness, defining a first strip with a thickness generally comprised between 0.8 and 12 mm.

[0003] Hot rolling is carried out at high temperatures, and after rolling, the strip is reeled up at temperatures ranging from 200°C to 750°C, depending on the chemical composition and the intended use of the final product. This means that some stretches of the metal product's surface are exposed to oxidizing agents such as air and water. It is impossible to process metal strip in an inert atmosphere, which causes oxidation of the surface layer of the product. This is a problem that must be solved in subsequent finishing processes, as the oxides formed can damage the surface quality of the product during cold rolling and / or painting, in addition to determining the weight loss of the finished material. This oxide layer generally consists of iron oxide in the part closest to the metal, i.e., the innermost part, and magnetite and hematite on the outside.

[0004] Furthermore, finishing processes are generally not performed immediately downstream of the hot rolling process. The hot-rolled strip is typically wound into coils of the desired weight or diameter (depending on the thickness of the strip exiting the rolling line) and cooled to ambient temperature in warehouses located near the hot rolling line. This can therefore cause further oxidation of the strip surface.

[0005] Since hot rolling and pickling may take place at different locations, the strip coil may be transported in very aggressive conditions in terms of corrosion attack, for example in the presence of salty air when transported by ship.

[0006] However, if this oxide layer, commonly known as scale or flakes, remains intact and adheres firmly to the metal strip, it performs a protective function for the metal strip. However, keeping the oxide layer intact is difficult due to both the action of atmospheric agents during transport and storage, and the inevitable breakdown of the scale itself.

[0007] Furthermore, moisture penetrates the cracks and reacts with the iron oxide layer closest to the metal surface, e.g., steel, forming iron hydroxide and ferric hydroxide, the increase in volume causing further exfoliation of the oxide layer and thus allowing attack of other parts of the metal.

[0008] The hot rolled strip has to be finished at a later stage on a finishing line according to production requirements.

[0009] The strip can remain in storage for even a few days before completion, allowing it enough time to cool down and reach ambient temperature, determining the formation of an oxide layer that can reach, for example, 5 to 20 μm per side of the strip. The oxide thickness is directly proportional to the nominal thickness of the strip, but also to the temperature of the strip during its winding.

[0010] Therefore, before the cold rolling process and subsequent coating (e.g., galvanizing or tinning, painting, etc.) of the product, the oxide coating must be cleaned from the material. Cleaning is particularly important because this oxide layer or scale can impair the surface quality of the finished product and make rolling difficult.

[0011] In current technology, strip is cleaned by specially laid out descaling and pickling lines, which usually precede cold rolling. An unwinding line for the previously hot-rolled strip is usually provided, followed by a device to destroy the scale so that subsequent processing can more easily remove it. The scale is cleaned from the product by a series of steps, including introducing the product into an acid bath (chemical pickling). The product can then be brushed and rinsed.

[0012] Current economic conditions and environmental needs are increasingly driving manufacturers to apply methods or techniques adapted to optimize process control while minimizing energy consumption, product consumption such as pickling, and processing waste intended as material yield and material quality yield.

[0013] However, it is currently not possible to precisely identify in advance the optimum process parameters for removing the correct amount of oxide with the minimum amount of acid.

[0014] Unfortunately, instead, more acid than necessary is very likely to be used, removing even some of the "good" product, i.e., some of the base metal of the strip, ensuring successful cleaning but at the expense of production efficiency. In fact, operators of pickling processes often prefer to produce slightly over-pickled strip to avoid quality rejects when under-pickled oxide residues not removed by the previous chemical attack are still present at the pickling means outlet.

[0015] Superpickled strips have, inter alia, the following drawbacks: -Decreased plant production capacity, - greater loss of yield due to the effects of chemical attack, - different surface quality (roughness) of one and the same strip, which may have a negative effect on the subsequent rolling and coating processes of the strip, -Increased use of consumables.

[0016] Conversely, an under-pickled strip may indicate that not enough acid was used or the duration of time in the treatment bath was sufficient. Therefore, the strip is not optimally cleaned and must be discarded / declassified or reprocessed.

[0017] Furthermore, the evolution of steel grades required to meet ever-increasing performance requirements, such as increased modulus and tensile strength and elongation at break, is complicating the chemical treatments performed on these categories of steel.

[0018] For example, the gradual but powerful drive to transition from hydrocarbon-based energy mobility to electric mobility is increasing the production of amorphous grain-oriented sheets characterized by a high presence of silicon in the alloy; unfortunately, silicon oxide is particularly difficult to remove in pickling baths.

[0019] This will have a major impact on future chemical pickling processes, which must be flexible and allow for rapid changes in reaction rates for the various different products being treated.

[0020] Therefore, a need is felt to provide an innovative cleaning plant for metal strips that is able to overcome the aforementioned drawbacks. Summary of the Invention

[0021] The object of the present invention is to provide a cleaning plant for metal strips, which detects a number of data useful to the operator and enables optimal, preferably automatic, adjustment of the operating parameters of the chemical pickling, making the chemical pickling highly accurate, cost-effective and ecologically sustainable.

[0022] A further object of the present invention is to provide a plant which detects and processes said multiple data in real time to automatically and instantly adjust the operating parameters of the pickling, thus achieving precise control of the chemical pickling process and thus further improving the pickling conditions compared to prior art solutions.

[0023] The automatic adjustment of the pickling parameters is achieved, for example, by software for simulating an oxide layer along the strip and controlling the pickling rate.

[0024] The solution of the present invention is very flexible and allows for rapid variation of reaction rates for different products being processed.

[0025] The present invention therefore achieves at least one of the above-mentioned objects by a cleaning plant for cleaning rolled metal strip provided with an oxide surface layer, said plant comprising, according to claim 1: - unwinding means for unwinding at least one coil of rolled strip; - chemical pickling means for pickling said rolled strip; measuring means for measuring the thickness of the surface oxide layer, the measuring means being arranged between the unwinding means and the chemical pickling means; Equipped with the measuring means comprises at least one laser source in cooperation with a fiber optic spectrometer defining a LIBS (Laser Induced Breakdown Spectroscopy) system adapted to analyze oxide composition in addition to thickness; gaseous hydrogen detection means for detecting the presence of gaseous hydrogen in fumes produced by said chemical pickling means; and A processing unit is provided which is adapted to process data from at least said measuring means and said gaseous hydrogen detection means and adapted to adjust operating parameters of said chemical pickling means and define optimum conditions for the pickling process.

[0026] A further aspect of the invention relates to a method for cleaning metal strips carried out by the aforementioned plant, the method comprising, according to claim 14, a) unwinding at least one coil of rolled strip by an unwinding means; b) measuring the thickness of the surface oxide layer of the rolled strip by a measuring means; c) pickling the rolled strip by chemical pickling means; Including, In step b), the measurement of the thickness of the oxide surface layer, together with the analysis of the oxide composition, is performed by at least one laser source associated with a fiber optic spectrometer defining a LIBS (Laser Induced Breakdown Spectroscopy) system, said fiber optic spectrometer measuring the presence of oxygen while a laser of said laser source penetrates the oxide surface layer placed on the strip and towards the non-oxidized base material, and if said spectrometer detects the absence of oxygen, the thickness of the oxide surface layer is equal to the depth drilled into said oxide layer by the laser source, In step c), gaseous hydrogen detection means provides for detection of gaseous hydrogen in fumes produced by the chemical pickling means; and A processing unit provides for processing data from both the measurement means and the gaseous hydrogen detection means and adjusting the operating parameters of the chemical pickling means accordingly.

[0027] Advantageously, the plant and method of the invention comprise: - Maximizing production capacity of chemical pickling means; -Improved material yield by minimizing acid attack on the oxide-free surface of the strip, -Improved product quality by eliminating over-pickled or under-pickled stretches of strip, -Optimization of energy and acid consumption This makes it possible.

[0028] Knowledge of the oxide layer thickness and O2 / Fe ratio through measurements, as well as the detection of gaseous hydrogen in the fumes emitted from the pickling bath, allows for greater flexibility and optimal estimation of pickling parameter adjustments. Optimization of process control determined by combined processing of data detected by at least one LIBS system and gaseous hydrogen detection means in the fumes advantageously allows for simultaneous minimization of energy consumption, product consumption such as pickling, and process waste intended as material yield and material quality yield.

[0029] The thickness of the oxide layer is measured by a technique known as LIBS (Laser-Induced Breakdown Spectroscopy), which uses a pulsed laser to achieve removal and vaporization of the oxide layer. The oxide phase change from a solid to a gaseous state creates a plasma, and the radiation emitted by the de-excitation of the excited species is read by a spectrometer, allowing the identification of the various elements present in the oxide layer. The thickness of the oxide layer can be determined by determining the number of pulses the laser has taken to reach the base material when the spectrum of the oxide layer is oxygen-free.

[0030] Knowledge of the chemical reactions occurring in pickling baths, for example those where hydrochloric acid is predominantly used (especially for pickling low / medium carbon steel strip), has provided an interesting guide to assess the combination of chemical attacks on the unoxidized base material. The reactions occurring are as follows: 1) FeO + 2HCl → FeCl2 + H2O 2) Fe2O3 + 6HCl → 2FeCl3 + 3H2O 3)Fe3O4+8HCl→FeCl2+2FeCl3+4H2O 4) Fe + 2HCl → FeCl2 + H2 (gas)

[0031] Reactions 1) to 3) illustrate the effect of the presence of various types of oxides during the reaction, while reaction 4) shows that when acid reacts with iron without the presence of oxides, the resulting reaction involves the evolution of gaseous hydrogen. From this observation, it was decided to measure the amount of hydrogen present in the fumes and use this value as a parameter for assessing the extent of the pickling process, advantageously in combination with data on the oxide layer detected by the LIBS system.

[0032] In a first variant of the invention, the detection of residual oxides on the strip by a first optical detection means located at the inlet of the final chemical pickling tank is provided. This allows the operational parameters of the pickling in the final pickling tank to be modified, further minimizing waste due to quality issues. Indeed, the presence of clearly visible oxide residues on the strip surface allows the aforementioned software for optimizing pickling conditions to assess the level of under-pickling and prompt intervention regarding the pickling parameters of the final pickling tank, such as the movement speed and therefore the strip feed rate, and / or the level of turbulence in the acid solution present in the final tank.

[0033] In a second variant of the invention, a second optical detection means, located downstream of the pickling means, provides for the detection of strip surface characteristics such as surface roughness, reflectance, shading level, and / or emissivity. These characteristics are indicative of the level of over-pickling of the material. In fact, acid attack on an oxide-free surface not only changes its roughness, but also its crystalline structure due to the differential attack on the grain edges. This feedback allows pickling optimization software to modify the pickling operating parameters upstream of the pickling line, further minimizing waste due to quality issues.

[0034] In a third variant of the invention, detection of residual oxides on the strip by third optical detection means placed downstream of the pickling means is provided, this feedback also allowing the pickling optimization software to modify the pickling operating parameters upstream of the pickling line, thus further minimizing waste due to quality reasons.

[0035] In a fourth variant of the invention, acid and iron concentration analyzers are used to provide mass balances in the spent and regenerated acid solutions which are continuously transferred from and to the pickling means, respectively, thus allowing further improvement of pickling control.

[0036] Some or all of the features of the variants of the invention may be advantageously combined.

[0037] Generally, for super-pickling, the operating parameters of pickling can be modified as follows: -Increase process speed (increase production capacity) if plant conditions allow, -Reducing bath turbulence to slow down the reaction rate (reducing energy consumption), - Decreasing the bath temperature to slow down the reaction rate (reducing energy consumption), -Reduces acid concentration (reduced acid consumption).

[0038] In the case of under-pickling, the operating parameters of the pickling can instead be modified as follows: -Slowing down the process (reducing production capacity), -Increasing the turbulence of the bath to increase the reaction rate, -Increasing the bath temperature to increase the reaction rate, -Increases acid concentration.

[0039] The dependent claims describe preferred embodiments of the invention.

[0040] Further features and advantages of the present invention will become more apparent in the light of the detailed description of a preferred but not exclusive embodiment of a metal strip washing plant, given as a non-limiting example, with the aid of the accompanying drawings, in which: [Brief explanation of the drawings]

[0041] [Figure 1] 1 is a schematic diagram of an embodiment of a plant according to the invention; [Figure 2] 1 is a flow chart for an exemplary cleaning method according to the present invention. [Figure 3] 1 is a schematic diagram of a portion of a system of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0042] The figures show some examples of embodiments of cleaning plants for oxidized metal strips. In particular, the components shown in dashed lines in Figure 1 are optional and can be considered individually or together.

[0043] The plant according to the invention, in all its embodiments, comprises in turn: - unwinding means 1 for unwinding at least one coil of rolled strip having an oxide surface layer; measuring means 11 for measuring the thickness of the oxide surface layer; - chemical pickling means 3 for pickling the rolled strip; Equipped with.

[0044] In a first variant, the unwinding means 1 comprises a single rolled strip unwinding line, preferably a single unwinding reel.

[0045] In a second variant of the unwinding means 1, a double unwinding line for the rolled strip is provided, followed by cutting and welding machines to provide continuity to the unwound strip which is then pickled.

[0046] In particular, there may be provided at least two unwinding reels and a welding machine, preferably a laser welder, capable of creating joints between the strips unwound by the unwinding reels, thus defining a continuous strip, i.e. allowing for a continuous supply of metal strip downstream of the unwinding means. Optionally, there may be provided a tensioning device for adjusting the strip tension.

[0047] A possible storage system (not shown) is provided upstream and / or downstream of the chemical pickling means 3 .

[0048] Preferably, at least one scale breaking device 3 can be advantageously provided between the unwinding means 1 and the pickling means 5, said scale breaking device using, for example, a mechanical system for breaking down the oxide layer, making this oxide layer more removable by the subsequent chemical pickling means.

[0049] The measuring means 11 for measuring the oxide layer thickness comprises, in particular consists of, at least one laser source cooperating with an optical fiber spectrometer defining a LIBS (Laser Induced Breakdown Spectroscopy) system also adapted to analyze the oxide composition and / or the concentration of oxide constituent elements. The term oxide composition refers to the chemical properties of the individual oxides or oxide mixtures. The term oxide constituent element concentration refers to the concentration of the individual ionic species that make up the individual oxides.

[0050] Advantageously, said fibre optic spectrometer is adapted to measure the presence of oxygen when a laser from a laser source penetrates the oxide layer present on the surface of the rolled strip towards the unoxidized base material.

[0051] The system uses a laser source for point ablation of the oxide layer. The laser source provides the energy necessary to bring the species belonging to the ablated oxide layer along its thickness into a plasma state. The de-excitation of the ions that make up the plasma allows, by use of a spectrometer, both the species present and their concentrations to be determined. The thickness of the oxide layer is advantageously detected upon the disappearance of the oxygen signal.

[0052] Thus, a fiber optic spectrometer can measure the presence of oxygen during point ablation of an oxide layer. If the spectrometer detects the absence of oxygen after time "t" of erosion, and thus during ablation, then the measurement of the depth of the eroded layer of material at time "t" corresponds to the thickness of the oxide surface layer.

[0053] In other words, the software calculates the erosion depth that would be equal to the thickness of the oxide surface layer at the disappearance of the oxygen peak, the time "t" of erosion and the erosion rate being known.

[0054] Spectroscopic measurements allow us to determine both the thickness and composition (e.g., O2 / Fe ratio) of the oxide layer. These data allow us to optimally define the operating parameters of the pickling process using optimization software to optimize the speed of the pickling process. A further advantage of using LIBS technology is that it is a minimally invasive, microdestructive technique in that the only damage caused is the ablation of material, forming cavities with dimensions depending on the focused laser spot.

[0055] In an advantageous variant, two or more measuring means 11, 11' are provided, arranged above and below the supply line of the rolled strip, to calculate the thickness of the oxide layer on both the top and bottom surfaces of the strip, as well as the difference between the edge and the center of the strip.

[0056] In particular, at least one measuring means 11 arranged above the supply line of the rolled strip 8 and at least one measuring means 11' arranged below the supply line of the rolled strip 8 are provided.

[0057] If more than one measuring means 11 and more than one measuring means 11' are provided, then at least four or more laser sources associated with respective fiber optic spectrometers are provided, defining four or more LIBS systems.

[0058] The measuring means 11 and therefore the LIBS system or LIBS system can be arranged fixedly or movably relative to the supply line of the rolled strip 8 .

[0059] The thickness of the oxide layer can be measured in several ways.

[0060] For example, measurements can be performed statically, with the strip flow into the cleaning plant temporarily interrupted (eg, while the strip is being welded) and resumed once the data has been acquired.

[0061] Alternatively, the measurement can be carried out continuously, for example by placing the measuring means 11 on a carriage adapted to move together with the metal strip.

[0062] Advantageously, in all embodiments of the plant of the invention, gaseous hydrogen detection means 12 are provided for detecting the presence of gaseous hydrogen in the fumes produced by said chemical pickling means 3 .

[0063] Such gaseous hydrogen detection means 12 may comprise or consist of detection equipment adapted to perform thermal conductivity measurements, for example, such gaseous hydrogen detection means 12 may comprise one, two or more thermal conductivity detectors.

[0064] In particular, a detection device can be used (Figure 3) comprising: two conduits 30, 31 through which the flow of fumes produced by the pickling tank 15 is divided and directed; a combustion chamber 32, such as a catalytic furnace, arranged along one of the two conduits, such as conduit 30, for ignition of combustion, so that hydrogen, if present, is combusted with the fume stream of the associated conduit 30; - Thermal conductivity detectors 33, 34 for detecting possible differences in thermal conductivity between the flows in the two conduits downstream of the combustion chamber 32.

[0065] If a difference in thermal conductivity is detected between the two conduit flows, this confirms the presence of gaseous hydrogen in the fumes and therefore over-pickling of the strip surface.

[0066] In the combustion chamber, the temperature of the fumes is generally below 80°C, so that a spark can be ignited to combust the gaseous hydrogen, which is the only component that reacts to the spark.

[0067] Therefore, a measurement of the gaseous hydrogen present in the fumes produced by the chemical pickling means is obtained by comparison of the two thermal conductivity signals emitted by the conductivity detector (in the hydrogen-free sample gas and in the reference gas), thus providing high measurement accuracy.

[0068] Preferably, the chemical pickling means 3 comprises two or more chemical pickling tanks containing an acidic solution arranged in series. The gaseous hydrogen detection means 12 may be positioned to detect the presence of gaseous hydrogen in the fumes produced by at least the last chemical pickling tank 15, preferably only the last tank 15 between said two or more chemical pickling tanks.

[0069] In a variant of the plant according to the invention, first optical detection means 13 are provided at the inlet of the final chemical pickling tank 15 to detect residual oxides on the surface of the strip. Such first detection means 13, for example, comprise at least one system for video analysis of the strip, which may include one or more cameras, possibly together with a corresponding lighting system. If oxide residues are visible on the surface of the strip, the operating parameters of the pickling in the final pickling tank 15 can be corrected by the aforementioned software, thus further minimizing quality defects due to insufficient pickling in a surprisingly optimal manner. In particular, one or more cameras are provided to analyze three different areas of the strip surface: the operator edge, the motor edge, and the center.

[0070] This video analysis system makes it possible, for example, to compare the color or brightness of the strip with a chromatic scale, preloaded in the memory of the processing unit 10, which indicates different degrees of cleaning of the product. By using a digital camera with a high pixel density, it is possible, for example, to define for each square meter of strip the ratio of the defective area to the pickled area, the minimum and maximum size of the defective area and its position on the strip (top / bottom, center / edge, head / tail or coil body, i.e. the part of the strip between the head and the tail).

[0071] Optionally, a second optical detection means 14 can be provided downstream of the chemical pickling means 3 to detect characteristics such as surface roughness and / or reflectance and / or shade level and / or emissivity of at least one surface of the strip. Such second optical detection means 14 may comprise, for example, an optical sensor adapted to detect residual surface effects on the surface, signs of over-pickling. This feedback also makes it possible to modify the operating parameters of the upstream pickling, thus minimizing quality deviations.

[0072] For example, such a sensor is a pyrometer that measures the emissivity of a pickled surface, which describes the ability of a surface to absorb heat and then transfer such energy by radiating in the infrared range.

[0073] The action of the acid on the metal surface of the strip modifies the surface roughness and consequently the emissivity, which is an index defining the possible effects of under- or over-pickling of the strip surface.

[0074] A third optical detection means 9, also arranged downstream of the chemical pickling means 3, can also be provided to detect residual oxides on the strip surface. This feedback also makes it possible to modify the operating parameters of the upstream pickling, thus minimizing quality deviations due to possible under-pickling. The third optical detection means 9 can comprise a video analysis system similar to the first optical detection means 13.

[0075] The order in which the second optical detection means 14 and the third optical detection means 9 are arranged downstream of the chemical pickling means 3 is irrelevant.

[0076] Preferably, rinsing means for rinsing the pickled strip are arranged between the chemical pickling means 3 and the second and / or third optical detection means 14,9.

[0077] In all embodiments of the plant of the invention it is possible to provide: regeneration means 17 for regenerating the discharged acid solution coming from the chemical pickling means 3 to obtain a regenerated acid solution; at least one pipe 18 for transporting the discharged acid solution from the chemical pickling means 3 to the regeneration means 17, a first flow meter 4, preferably arranged along the pipe 18, for measuring the flow rate of said discharged acid solution directed to the regeneration means 17; a first analyzer 6, preferably arranged along the pipe 18, for analyzing the acid and iron concentrations in the discharged acid solution; at least one pipe 19 for transporting the regenerated acid solution from the regeneration means 17 to the chemical pickling means 3, a second flow meter 5, preferably arranged along the pipe 19, for measuring the flow rate of the regenerated acid solution directed to the chemical pickling means 3; - A second analyzer 7, preferably placed along the pipe 19, for analyzing the concentration of acid and residual iron in the regenerated acid solution.

[0078] The regeneration means 17 comprise, for example, a chemical reactor in which iron in the form of oxide is separated from the discharged acid solution by a thermohydrolysis reaction and then concentrated and returned for pickling. In the reactor, the discharged acid solution (high in iron content) is heated in an oxidizing atmosphere which determines the evaporation of the solution, on the one hand recovering the free acid and, on the other hand, removing the iron as oxide.

[0079] This setup makes it possible to obtain a mass balance of the chemical reactions required to completely remove the oxide layer, using acid and iron concentration analyzers in the discharged and regenerated acid solutions, which are continuously transferred respectively from and to the chemical pickling means 3. In fact, these analyzers allow a further improvement of the pickling control, since they make it possible to calculate the amount of scale already removed, knowing the amount of initial oxide removed from the uncoiled strip, by well-known statistical models based on several processes.

[0080] Advantageously, a processing unit 10 is provided which is configured to process measurement data from at least the measuring means 11, possibly further the measuring means 11' and the gaseous hydrogen detection means 12 and to adjust the operating parameters of the chemical pickling means 3 accordingly.

[0081] Preferably, the processing unit 10 also includes: first optical detection means 13 for adjusting the operating parameters of the pickling of the last pickling tank, if applicable; possibly a second optical detection means 14 and / or a third detection means 9 for further adjusting the operating parameters of the chemical pickling means 3; If a regeneration means 17 is provided, the processing unit 10 can also process data from the first flow meter 4, the first analyzer 6, the second flow meter 5 and the second analyzer 7 to adjust the operating parameters of the chemical pickling means 3 accordingly.

[0082] Regarding the metal strip cleaning method of the present invention that can be carried out by the above-mentioned plant, said method comprises the following steps: a) unwinding at least one coil of rolled strip by unwinding means 1; b) measuring the thickness of the surface oxide layer of the rolled strip by means of measuring means 11, 11'; c) pickling the rolled strip by said chemical pickling means 3;

[0083] In step b), the thickness of the oxide surface layer, together with an analysis of the oxide composition, is measured by at least one laser source associated with a respective fiber optic spectrometer defining a Laser Induced Breakdown Spectroscopy (LIBS) system.

[0084] Advantageously, during step c), said gaseous hydrogen detection means 12 provides for the detection of gaseous hydrogen in the fumes produced by the chemical pickling means 3, preferably in the fumes produced by the last pickling tank 15, i.e. the pickling tank distal from the unwinding means 1.

[0085] The combined processing of the data coming from the measuring means 11 and the gaseous hydrogen detection means 12 by the processing unit 10 and the resulting adjustment of the operating parameters of the chemical pickling means 3 surprisingly makes it possible to optimize the pickling process.

[0086] FIG. 2 shows an example of a flow chart of a part of a cleaning method according to the present invention.

[0087] Advantageously, the processing unit 10 uses software, preferably installed in said processing unit 10, comprising a pickling adjustment model, or more simply a pickling model 20, configured to adjust one or more of the following pickling parameters: - the process speed, i.e. the strip feed speed at which the strip moves through the pickling bath, the concentration of the acid in the acid solution of the pickling tank, e.g. hydrochloric acid; - the temperature of the acid solution in the pickling tank, -Turbulence level of acid solution.

[0088] The pickling model 20 then generates process settings and applies these to the strip entering the pickling bath.

[0089] The pickling model 20 interacts with an oxide layer simulation model 21 , or more simply an oxide layer model or scale model 21 , which is preferably included in said processing unit 10 .

[0090] The oxide layer simulation model 21 generates simulation data of the oxide surface layer along the strip, in particular along the entire extension of the strip.

[0091] The pickling adjustment model 20 adjusts pickling parameters including the strip feed rate in the chemical pickling means 3 and / or the turbulence level of the acid solution present in said chemical pickling means 3, and preferably said pickling parameters further including the acid concentration in the acid solution and / or the temperature of said acid solution.

[0092] The simulation data is sent to the pickling adjustment model 20.

[0093] To generate the simulation data, the oxide layer simulation model 21 receives both first input data 22 relating to the strip as wound on the coil and second input data 23 consisting of data detected by the measurement means 11, 11' during operation of the plant.

[0094] The first input data 22 includes at least the strip thickness, strip width, metal grade, and strip coiling temperature, while the second input data 23 includes the thickness of the oxide surface layer and the oxide composition, preferably also the concentrations of the oxide constituent elements.

[0095] Simulation data for the oxide surface layer along the strip are obtained by comparing the first input data 22 and the second input data 23 with a database containing data for sets of strips with different thicknesses, widths, metal materials and wound at different winding temperatures.

[0096] More specifically, the scale model 21 receives first input data 22, such as initial data of the strip when wound into a coil, the first input data being: -strip thickness, -strip width, -steel grade, - strip winding temperature, - Possible manufacturing data Includes:

[0097] The scale model 21 also receives second input data 23 consisting of data detected by the measuring means 11, 11' during operation of the plant of the invention, namely the thickness of the oxide surface layer, the oxide composition and the concentrations of the oxide constituent elements, in particular the presence of oxygen.

[0098] Using both the first input data 22 and the second input data 23, the scale model 21 generates a simulation of the amount of oxide present throughout the strip stretch by comparison with a database, for example including stored oxide measurements relating to sets of strips preferably of different thicknesses, widths, materials and wound at different winding temperatures.

[0099] Preferably, the oxide surface layer simulation data includes at least one of the following data: -thickness (micrometers), - weight of oxide to be removed (grams / m 2 ), -estimation of the average oxide composition, - Pickling coefficient of the strip.

[0100] As is known, the pickling coefficient is defined as a factor Kd, whose value is less than or equal to 1 but greater than 0.5. This value is used as a multiplication factor to define the strip feed speed or pickling speed. The maximum speed occurs for Kd=1. For strips that are difficult to pickle, Kd=0.5.

[0101] This information is sent to the pickling model 20 to define pickling parameters, such as those listed above, preferably customized to the head, center, and tail of the strip being processed. The pickling model 20 then generates process settings.

[0102] At least one control loop is provided to improve control of the pickling process. For each control loop, one or more values ​​provided by the pickling model 20 are compared with respective values ​​measured or analyzed by corresponding instrumentation installed along the plant. If the difference between the measured value and the value provided by the pickling model 20 does not exceed a threshold (error: no), the model estimate is considered adequate and no feedback is generated. Conversely, if the difference between the measured value and the value provided by the pickling model 20 exceeds a threshold (error: yes), feedback is generated requesting the pickling model 20 to generate a value offset to improve process control.

[0103] The flow chart of FIG. 2 relates to an exemplary variant of the plant of the invention, which in addition to the measuring means 11: regeneration means 17 with associated first flow meter 4, first analyzer 6, second flow meter 5 and second analyzer 7; gaseous hydrogen detection means 12, first optical detection means 13, second optical detection means 14, third optical detection means 9 is provided, with the following control loops cascaded on top of each other: a first control loop for optionally adjusting the mass balance of the chemical pickling reaction, using values ​​of the discharged acid solution flow rate, the acid and iron concentration in the discharged acid solution, the regenerated acid solution flow rate, and the acid and residual iron concentration in the regenerated acid solution, detected by the first flow meter 4, the first analyzer 6, the second flow meter 5, and the second analyzer 7, respectively; a second control loop for possibly reducing / eliminating over-pickling, indicated by the possible presence of gaseous hydrogen in the fumes of at least the last pickling tank, said presence being detected by gaseous hydrogen detection means 12; a third control loop for possibly reducing / eliminating under-pickling indicated by the presence of residual oxides on the surface of the strip entering the last pickling bath, said presence being detected by the first optical detection means 13; a fourth control loop for possibly reducing / eliminating under-pickling indicated by the presence of residual oxides on the surface of the strip at the outlet of the last pickling bath, said presence being detected by third optical detection means 9; a fifth control loop for potentially reducing / eliminating over-pickling using the surface roughness and / or reflectance and / or grey level and / or emissivity values ​​of at least one surface of the strip detected by the second optical detection means 14;

[0104] The aforementioned second control loop generates a feedback when a difference between the gaseous hydrogen value in the fumes detected by the gaseous hydrogen detection means 12 and the gaseous hydrogen value in the fumes provided by the pickling adjustment model 20 exceeds a predetermined threshold, and the feedback requests the pickling adjustment model 20 to adjust at least one pickling parameter so that the difference does not exceed the threshold. The first control loop, the third control loop, the fourth control loop, and the fifth control loop may be optional, individually or all together.

Claims

1. 1. A cleaning plant for cleaning rolled metal strip provided with an oxide surface layer, comprising: - unwinding means (1) for unwinding at least one coil of rolled strip; - chemical pickling means (3) for pickling said rolled strip; - measuring means (11) for measuring the thickness of the oxide surface layer, arranged between the unwinding means (1) and the chemical pickling means (3); Equipped with said measuring means (11) comprising at least one laser source cooperating with a fiber optic spectrometer defining a Laser Induced Breakdown Spectroscopy (LIBS) system also adapted to analyze oxide composition, a gaseous hydrogen detection means (12) for detecting the presence of gaseous hydrogen in the fumes produced by the chemical pickling means (3); a processing unit (10) configured to process data from at least the measuring means (11) and the gaseous hydrogen detection means (12) and to adjust operating parameters of the chemical pickling means (3) accordingly; The processing unit (10) an oxide layer simulation model (21) configured to generate simulation data of the oxide surface layer along the strip by receiving first input data (22) relating to the coiled strip and second input data (23) consisting of data detected by the measuring means (11) during operation of the plant; a pickling adjustment model (20) configured to adjust pickling parameters including a feed rate of the strip steel in the chemical pickling means (3) and / or a turbulence level of the acid solution present in the chemical pickling means (3), the pickling parameters further including an acid concentration of the acid solution and / or a temperature of the acid solution; the simulation data is transmitted to the pickling adjustment model (20); a pickling adjustment model (20) configured to generate a feedback signal requesting the pickling adjustment model (20) to adjust at least one of the pickling parameters so that the difference does not exceed a threshold value when the difference between the gaseous hydrogen value in the fumes detected by the gaseous hydrogen detection means (12) and the gaseous hydrogen value in the fumes provided by the pickling adjustment model (20) exceeds a threshold value.

2. 2. The cleaning plant of claim 1, wherein the chemical pickling means comprises two or more chemical pickling tanks, and the gaseous hydrogen detection means (12) is positioned to detect the presence of gaseous hydrogen in the fumes produced by at least the last chemical pickling tank (15).

3. 3. A cleaning plant according to claim 1 or 2, wherein the gaseous hydrogen detection means (12) either comprises or consists of a detection instrument adapted to perform thermal conductivity measurements.

4. 3. A cleaning plant according to claim 2, wherein first optical detection means (13) are provided for detecting residual oxides on the surface of the strip, said first optical detection means (13) being arranged at the inlet of the final chemical pickling bath (15).

5. 5. A cleaning plant according to claim 4, wherein further optical detection means (9, 14) for detecting the level of cleanliness of the strip are provided and are arranged downstream of the chemical pickling means (3).

6. 6. A washing plant according to claim 5, wherein the further optical detection means comprises second optical detection means (14) for detecting the surface roughness and / or reflectance and / or grey level and / or emissivity of at least one surface of the strip.

7. 7. A cleaning plant according to claim 6, wherein the further optical detection means further comprise third optical detection means (9) for detecting residual oxides on the surface of the strip.

8. - regeneration means (17) for regenerating the discharged acid solution coming from said chemical pickling means (3) and obtaining a regenerated acid solution; a first flow meter (4) for measuring the flow rate of the discharged acid solution directed towards the regeneration means (17); a first analyzer (6) for analyzing the acid and iron concentrations in the discharged acid solution; a second flow meter (5) for measuring the flow rate of the regenerated acid solution directed to the chemical pickling means (3); a second analyzer (7) for analyzing the concentration of acid and residual iron in said regenerated acid solution; is established, 2. The cleaning plant according to claim 1, wherein the processing unit (10) is also adapted to process data from at least the first flow meter (4), the first analyzer (6), the second flow meter (5), and the second analyzer (7) and to adjust the operating parameters of the chemical pickling means (3) accordingly.

9. 5. The cleaning plant according to claim 4, wherein the processing unit (10) is also adapted to process data from the first optical detection means (13) and to adjust the operating parameters of the chemical pickling means (3) accordingly.

10. 7. The cleaning plant according to claim 6, wherein the processing unit (10) is also adapted to process data from the first optical detection means (13) and the second optical detection means (14) and to adjust the operating parameters of the chemical pickling means (3) accordingly.

11. 8. The cleaning plant according to claim 7, wherein the processing unit (10) is also adapted to process data from the first optical detection means (13), the second optical detection means (14) and the third optical detection means (9) and to adjust the operating parameters of the chemical pickling means (3) accordingly.

12. - a regeneration means (17) for regenerating the acid solution discharged from said chemical pickling means (3) and obtaining a regenerated acid solution; a first flow meter (4) for measuring the flow rate of the discharged acid solution directed towards the regeneration means (17); a first analyzer (6) for analyzing the acid and iron concentrations in the discharged acid solution; a second flow meter (5) for measuring the flow rate of the regenerated acid solution directed to the chemical pickling means (3); a second analyzer (7) for analyzing the concentration of acid and residual iron in said regenerated acid solution; is established, 12. A cleaning plant according to claim 9, 10 or 11, wherein the processing unit (10) is also adapted to process data from at least the first flow meter (4), the first analyzer (6), the second flow meter (5) and the second analyzer (7) and to adjust the operating parameters of the chemical pickling means (3) accordingly.

13. 10. A method for cleaning metal strips carried out by a plant according to claim 1, comprising the steps of: a) unwinding at least one coil of rolled strip by said unwinding means (1); b) measuring the thickness of the oxide surface layer of the rolled strip by means of the measuring means (11); c) pickling the rolled strip by the chemical pickling means (3); Including, In step b), the measurement of the thickness of the oxide surface layer, together with the analysis of the oxide composition, is performed by at least one laser source associated with a fiber optic spectrometer defining a Laser Induced Breakdown Spectroscopy (LIBS) system, the fiber optic spectrometer measuring the presence of oxygen while a laser of the laser source penetrates the oxide surface layer present on the rolled strip towards the non-oxidized base material, and if the spectrometer detects the absence of oxygen, the thickness of the oxide surface layer is equal to the depth drilled into the rolled strip by the laser source, In step c), the gaseous hydrogen detection means (12) provides for the detection of gaseous hydrogen in the fumes produced by the chemical pickling means (3); and said processing unit (10) provides for the processing of data from both said measuring means (11) and said gaseous hydrogen detection means (12) and for the adjustment of said operating parameters of said chemical pickling means (3) accordingly; The processing unit (10) the oxide layer simulation model (21) configured to generate simulation data of the oxide surface layer along the strip by receiving first input data (22) relating to the coiled strip and second input data (23) consisting of data detected by the measuring means (11) during operation of the plant; a pickling adjustment model (20) configured to adjust the pickling parameters including the feed rate of the strip steel in the chemical pickling means (3) and / or the turbulence level of the acid solution present in the chemical pickling means (3), the pickling parameters further including the acid concentration of the acid solution and / or the temperature of the acid solution; the simulation data is transmitted to the pickling adjustment model (20); at least one control loop is provided, the at least one control loop being configured such that, when a difference between a gaseous hydrogen value in the fumes detected by the gaseous hydrogen detection means (12) and a gaseous hydrogen value in the fumes provided by the pickling adjustment model (20) exceeds a threshold, a feedback is generated requesting the pickling adjustment model (20) to adjust at least one of the pickling parameters so that the difference does not exceed the threshold.

14. 14. The cleaning method of claim 13, wherein the first input data (22) includes at least a strip thickness, a strip width, a metal material grade, and a strip coiling temperature, and the second input data (23) includes an oxide surface layer thickness and an oxide composition.

15. The simulation data of the oxide surface layer along the strip is obtained by comparing the first input data (22) and the second input data (23) with a database containing data relating to sets of strips of different thicknesses, widths, metal materials and wound at different winding temperatures, the simulation data comprising the following data: - thickness (micrometers), - weight of oxide to be removed (grams / m ２ ), - Estimation of the average oxide composition, - Pickling coefficient of strip 15. The cleaning method of claim 14, comprising at least one of:

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