Method for preheating a roller for rolling

Description

TECHNICAL FIELD

[0001] The field of the invention is that of metallurgy and more precisely that of rolling processes, preferably hot, of flat metal products made in particular from an aluminum alloy. STATE OF PRIOR ART

[0002] In metallurgy, a rolling process involves shaping a metal by plastic deformation to produce flat products (sheets, strips, bands, etc.), i.e. a product whose thickness is less than its width, which is also less than its length. The term metal strip will be used here to refer generally to a flat product.

[0003] To achieve this, a rolling mill usually comprises one or more successive rolling stands, each formed by a pair of counter-rotating rolls known as work rolls of the same diameter. The metal strip is deformed by compression as it passes between the work rolls. To limit the deformation of the work rolls, the rolling stand may comprise another pair of rolls known as support rolls, each arranged in contact with a work roll.

[0004] However, the rolled metal strip may have flatness defects, such as non-developable defects (e.g. long edges, long centers, etc.) and developable defects (e.g. bend, tile, and twist defects, etc.). These defects may arise from the deformation of the work rolls due to the high intensity of mechanical stresses, as well as from the heterogeneous thermal expansion of the work rolls along their longitudinal axis.

[0005] To limit the occurrence of these defects and obtain a rolled metal strip that has the desired profile and flatness, different solutions can be implemented. For example, the support rolls mentioned above can be used to reduce the bending of the work rolls. In addition, the work rolls can have a grinding crown, or grinding profile, i.e. a variation in diameter between the center of the roll and its ends, to achieve flatness of the metal strip, for example in slight long edges or long center, depending on the rolling stand considered. Furthermore, the rolling mill can include a thermal control device adapted to locally cool or heat the work rolls to modify the thermal expansion profile (thermal profile).

[0006] In this respect, document WO00 / 00307A1 describes a method for hot rolling a metal strip in a rolling mill comprising a thermal control device. In this example, the thermal control device makes it possible to modify the thermal expansion profile of the working rolls at the edge of the strip.

[0007] During rolling, the work rolls can expand due to the heat produced in the roll, and present a concave thermal expansion profile: the diameter profile of each work roll then presents an outward rounding (bulging), which leads to an increase in the thickness of the metal strip at its lateral edges. Note that, in this example, the work rolls do not present a grinding profile.

[0008] To limit this excess thickness at the edge of the strip, the thermal control device includes lateral inductors arranged opposite each working roll at the edge of the strip. Thus, the activation of the lateral inductors makes it possible to modify the thermal expansion profile and more precisely to increase the thermal expansion of the working rolls at the edge of the metal strip, thus reducing the local excess thickness of the latter.

[0009] Document FR2375920 describes another example of a rolling mill comprising a thermal control device with inductors. In this example, the inductors are regularly distributed along the longitudinal axis of the working rolls. The thermal control device also comprises a downstream roller for measuring the distribution of tensile mechanical stresses present in the rolled metal strip, as well as a downstream sensor for measuring the thickness distribution of the rolled metal strip. A feedback loop is provided to adapt the thermal power delivered by each inductor according to the measurement signals emitted by the downstream roller and the downstream sensor. However, this method leads to a loss of material since, on the one hand, the thermal profile of the working rolls may not be stabilized during the rolling of the metal strip, and on the other hand, any defects are detected after the metal strip has passed through the clearance.

[0010] It may also be useful to preheat the work rolls before carrying out the actual rolling operation. This makes it possible, in particular, to avoid the use of so-called starter metal strips, which are essentially intended to generate and stabilise the thermal expansion profile of the work rolls before the rolling operation, as these starter metal strips are generally not recycled and can therefore be scrapped.

[0011] In this respect, document WO2017 / 053343A1 describes a method for preheating working rolls. The thermal control device comprises nozzles for spraying a heating liquid (heating sprays) and nozzles for spraying a cooling liquid (cooling sprays), distributed along the longitudinal axis of the working rolls. The thermal control device further comprises multiple sensors for measuring the surface temperature of the working roll as well as the thermal expansion of the latter. The measured values can be compared to those calculated by a predefined thermal model, to then control the thermal power delivered by each of the heating and cooling sprays. However, this method requires the use of multiple sensors, including sensors for measuring the surface temperature of the working rolls.US 2017 / 080467 A1 describes a method for preheating at least one working roll of a rolling mill intended to roll a metal strip so that the working roll has a target thermal expansion profile determined along Ns longitudinal segments of the working roll, the rolling mill comprising a thermal control device comprising Ni spray nozzle inductors distributed along the longitudinal axis of the working roll opposite the Ns longitudinal segments, the method comprising determining the target thermal expansion profile at a calculation time, from i) predefined values of input parameters representative of the dimensions and mechanical and thermal properties of the metal strip to be rolled, and ii) a first predefined physical model expressing a relationship between the input parameters Pe and the target thermal expansion profile. STATEMENT OF THE INVENTION

[0012] The invention aims to remedy at least in part the drawbacks of the prior art, and more particularly to propose a method for preheating at least one of the working rolls of a rolling stand making it possible to expand the working roll according to a predefined target thermal expansion profile, quickly and efficiently, without it being necessary to use different types of measuring sensors.

[0013] For this purpose, the subject of the invention is a method for preheating at least one working cylinder of a rolling mill intended for rolling a metal strip so that the working cylinder has a target thermal expansion profile. Δd i c 1 ≤ i ≤ Ns determined along Ns longitudinal segments of the working cylinder, the rolling mill comprising a thermal control device comprising Ni inductors distributed along the longitudinal axis of the working cylinder opposite the Ns longitudinal segments, the method comprising the following phases: a / determination of the target thermal expansion profile Δd i c 1 ≤ i ≤ Ns , at a calculation time tk , from predefined values of input parameters Pe representative of the dimensions and mechanical and thermal properties of the metal strip to be rolled, and from a first predefined physical model M1 expressing a relationship between the input parameters Pe and the target thermal expansion profile Δd i c 1 ≤ i ≤ Ns ; b / determination of an effective average temperature profile T ¯ i eff t k 1 ≤ i ≤ Ns along Ns longitudinal segments of the working cylinder, from an effective thermal power profile P Q i eff t k − 1 1 ≤ i ≤ Ni generated by the Ni inductors and measured previously, and a second predefined physical model M2 expressing a relationship between the effective thermal power profile P Q i eff t k 1 ≤ i ≤ Ni and the effective mean temperature profile T ¯ i eff t k 1 ≤ i ≤ Ns ; c / determination of a target average temperature profile T ¯ i c t k 1 ≤ i ≤ Ns along the Ns longitudinal segments of the working cylinder, from the target thermal expansion profile Δd i c t k 1 ≤ i ≤ Ns determined and the effective average temperature profile T ¯ i eff t k 1 ≤ i ≤ Ns determined; d / determination of a deviation ΔT(tk ) between the target average temperature profile T ¯ i c t k 1 ≤ i ≤ Ns and the effective mean temperature profile T ¯ i eff t k 1 ≤ i ≤ Ns ; e / determination of a convergence criterion from the determined deviation ΔT(tk ), and stopping of the preheating when the convergence criterion is verified, and continuation of the phases of the preheating process when the convergence criterion is not verified; f / activation of the inductors comprising the following steps: determination of a target thermal power profile P Q i c t k 1 ≤ i ≤ Ni to be delivered by the Ni inductors from the determined deviation ΔT(tk ); activation of the inductors so that they deliver the target thermal power profile P Q i c t k 1 ≤ i ≤ Ni determined; measurement of an effective thermal power profile P Q i eff t k 1 ≤ i ≤ Ni actually delivered by the inductors; reiteration of steps b / to f / until the convergence criterion is verified, by incrementing the calculation time tk.

[0014] Some preferred but non-limiting aspects of this preheating method are as follows.

[0015] Target thermal expansion profiles Δd i c 1 ≤ i ≤ Ns , of effective average temperature T ¯ i eff t k 1 ≤ i ≤ Ns , and target average temperature T ¯ i c t k 1 ≤ i ≤ Ns can be determined for the longitudinal segments intended to be in contact with the metal strip to be rolled.

[0016] The step of determining the target thermal power profile P Q i c t k 1 ≤ i ≤ Ni may include the following steps: identification of the longitudinal segment, of index jmax, for which the deviation ΔT (jmax) (tk ) is maximum, and definition of the target thermal power P Q jmax c t k to a maximum value; determination of the target thermal power of the other longitudinal segments such that P Q j c t k = P Q jmax c t k × Δ T ¯ j t k / Δ T ¯ jmax t k .

[0017] An inductor of index j can only be activated when the ratio ΔT (j) (tk ) / ΔT (jmax) (tk ) is greater than or equal to a predefined RT threshold value, otherwise it remains inactive.

[0018] The thermal control device may comprise coolers distributed along the longitudinal axis of the working cylinder opposite the Ns longitudinal segments. The method may comprise a step of activating the coolers based on the difference ΔT(tk ) between the target average temperature profile T ¯ i c t k 1 ≤ i ≤ Ns and the effective mean temperature profile T ¯ i eff t k 1 ≤ i ≤ Ns .

[0019] The phase of determining the effective average temperature profile T ¯ i eff t k 1 ≤ i ≤ Ns can be carried out by numerical simulation, the working cylinder being discretized according to a 2D axisymmetric mesh.

[0020] The metal strip can be made of an aluminum alloy.

[0021] Another subject of the invention is a rolling method comprising the following steps a) preheating at least one working roll, preferably both working rolls, of a rolling mill intended to roll a metal strip according to the method according to the invention, b) rolling the metal strip with the at least one working roll thus preheated, preferably both working rolls. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the appended drawings in which: there Figure 1A is a schematic and partial view of a rolling stand of a rolling mill according to one embodiment, in section along the longitudinal axis of the rolling mill, illustrating the thermal control device; Figure 1Bis a schematic and partial view of a working cylinder of the rolling stand of the fig.1A , in section along the longitudinal axis of the working cylinder, illustrating the segmentation of the working cylinder into Ns longitudinal segments and the longitudinal distribution of the Ni inductors; the Figure 2A is a schematic and partial view of a working cylinder, in section along its longitudinal axis, highlighting an example of a thermal expansion profile; Figure 2B illustrates an example of a target thermal expansion profile of the working cylinder, as well as the parameters A, B, xx and u allowing it to be characterized; the figure 3 is a flowchart of a preheating process implemented by the rolling mill of the fig.1A according to one embodiment. DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0023] In the figures and in the remainder of the description, the same references represent identical or similar elements. In addition, the different elements are not shown to scale so as to enhance the clarity of the figures. Furthermore, the different embodiments and variants are not mutually exclusive and may be combined with each other. Unless otherwise indicated, the terms "substantially", "approximately", "of the order of" mean to within 10%, and preferably to within 5%. Furthermore, the terms "between ... and ..." and equivalent mean that the limits are included, unless otherwise indicated.

[0024] The invention relates to a method for preheating at least one working roll of a rolling stand, making it possible to thermally expand the working roll locally, according to a predetermined target profile, before the metal strip to be rolled is introduced into the grip. In the remainder of the description, the metal strip is made from aluminum, without the invention being limited to this type of material.

[0025] The target thermal expansion profile of preheating takes into account the characteristics of the metal strip to be rolled, and corresponds substantially to that generated during the actual rolling operation, by the heat input resulting mainly from the deformation of the metal strip in the roll. Also, at the end of the preheating operation, the work roll then has a thermal stability close to or substantially identical to what it will be during the rolling operation.

[0026] The target thermal expansion profile is predefined so that, during the rolling operation, the rolled metal strip has, at the exit of the grip, the desired thickness profile and flatness. As such, the flatness of a rolled metal strip is defined from an index IP corresponding to the ratio of the elongation of a material fiber to the average length L of the fibers, such as: IP = ΔL / L×10 5< .

[0027] In the remainder of the description, the profile of a physical quantity associated with the working cylinder is the variation (or distribution) of this physical quantity along the longitudinal axis of the cylinder. On the other hand, the profile of the metal strip is the variation (or distribution) of thickness in a cross-section along a transverse axis (width direction) of the metal strip.

[0028] There Figure 1Ais a schematic and partial view of a rolling mill 1 comprising several successive rolling stands 10, in section along the longitudinal axis of the rolling mill. Here only one rolling stand 10 is shown. The Figure 1B is a schematic and partial view of the rolling stand 10, in section along the longitudinal axis of the working cylinder.

[0029] Here and for the remainder of the description, a direct three-dimensional orthogonal reference frame XYZ is defined, where the X axis is oriented along the rolling direction and corresponds to the longitudinal axis of the rolling mill 1 and the metal strip 2 being rolled, the Y axis corresponds to the longitudinal axis of the cylinders, and the Z axis is oriented along the height of the rolling stand 10. The terms 'upstream' and 'downstream' are defined with reference to the longitudinal axis of the rolling mill 1, i.e. here to the X axis.

[0030] In this example, the rolling mill 1 may comprise several successive rolling stands 10 for rolling the same metal strip 2. It also comprises a thermal control device 20 adapted to control the thermal expansion profile of at least one of the working rolls 11 by means of a plurality of inductors 21 and possibly coolers 22.

[0031] Each rolling stand 10 is here of the 'quarto' type and comprises here a pair of working rolls 11 (lower and upper rolls), and a pair of support rolls 12 (lower and upper). Of course, other configurations are possible, such as 'sexto' or 'Sendzimir' type stands, among others. Each working roll 11 of the rolling stands 10 can be equipped with inductors 21 and possibly coolers 22 of the thermal control device 20. The rolling mill 1 can however comprise, upstream of the rolling stands 10, at least one reversible stand not equipped with inductors of the thermal control device.

[0032] The working cylinders 11 are equipped here with inductors 21 and coolers 22. They each have a diameter d ref at room temperature, when not in operation, which is here constant along the longitudinal axis Y: d ref (y) = d 0 . This diameter may, as a variant, not be constant and may have a rectification profile: d ref (y) = d 0 + Δd rec (y) mentioned above.

[0033] The thermal control device 20 comprises a plurality of inductors 21 and possibly a plurality of coolers 22, connected to a processing unit 23. It makes it possible to generate, within the framework of the preheating of the working cylinder 11 considered, and therefore before the rolling operation, a thermal expansion profile for the working cylinder 11 considered which is substantially equal to a predetermined target profile.

[0034] For this, it is considered that the working cylinder 11 is discretized over its entire length, along the longitudinal axis Y, into Ns successive longitudinal segments 11s, preferably of the same dimension. For example, the working cylinder 11 can be discretized into several longitudinal segments 11s of width equal to approximately 20 mm along the Y axis.

[0035] The thermal control device 20 comprises Ni inductors 21, with here Ni≤Ns. They are distributed along the longitudinal axis Y opposite the Ns successive longitudinal segments, here at a rate of 1 inductor for several successive longitudinal segments 11s. Not all the longitudinal segments 11s necessarily comprise inductors 21, in particular the longitudinal segments 11s located at the edge of the working cylinder 11 and which are not intended to form the grip (no contact with the metal strip 2). The inductors 21 can be placed upstream and / or downstream of the working cylinder 11. In this example, Ni inductors are located upstream and Ni inductors are located downstream of the working cylinder 11.

[0036] The inductors 21 are adapted to transmit thermal energy into the longitudinal segments 11s of the working cylinder 11. This involves electromagnetic induction heating, in the sense that each inductor 21 generates a magnetic field which induces an alternating electric current in the longitudinal segment(s) 11s opposite which it is arranged. The electromagnetic power received by the longitudinal segments 11s is converted by the Joule effect into heat power, which thus leads to an increase in the average temperature of the longitudinal segments 11s concerned.

[0037] The inductors 21 are activated and deliver thermal power in response to a control signal from the control unit 23 which defines a target value of the thermal power. However, it appears that the inductors 21 may not actually deliver the target value of the thermal power. Also, they each comprise a sensor (not shown) adapted to provide the processing unit 23 with a measurement of the thermal power actually delivered.

[0038] The thermal control device 10 may also comprise coolers 22, distributed along the working cylinder 11. Each cooler 22 may be a nozzle for spraying a coolant. These coolers 22 thus make it possible to reduce the average temperature of the longitudinal segments 11s of the working cylinder. They may be more or less numerous than the inductors 21. In addition, the longitudinal arrangement of the coolers 22 may not coincide with that of the inductors 21.

[0039] The processing unit 23 is adapted to carry out calculations at different successive calculation times tk, and to control the inductors 21 and where appropriate the coolers 22 so that the effective average temperature profile of the longitudinal segments 11s (and therefore the effective thermal expansion profile) is substantially equal to the target average temperature profile (and therefore to a target thermal expansion profile).

[0040] The processing unit 23 comprises a programmable processor capable of executing instructions recorded in an information recording medium. It further comprises a memory containing the instructions necessary for implementing the preheating method. It is also adapted to store the information calculated at each calculation instant tk. It also implements two predefined physical models M1 and M2.

[0041] The first predefined physical model M1 expresses a relationship between, on the one hand, input parameters Pe representative of dimensions and mechanical and thermal properties of the metal strip 2 to be rolled, and on the other hand, a target thermal expansion profile of the working cylinder defined at the level of the Ns longitudinal segments 11s.

[0042] The predefined physical model M1 can be a database (abacus) obtained previously, for example experimentally and / or numerically. Thus, to obtain the desired properties of the metal strip 2 (thickness profile, flatness, etc.) at the output of the footprint, the predefined physical model M1 establishes a relationship between the target thermal expansion profile necessary to obtain these properties of the metal strip 2, and the input parameters Pe.

[0043] The input parameters Pe relate in particular to the mechanical characteristics of the metal strip 2 to be rolled such as the type of aluminum alloy, the thermal characteristics such as the temperature of the metal strip 2 at the inlet of the rolling stand 10 and the desired coiling temperature, the dimensions of the metal strip 2 to be rolled such as its width W, the initial thickness H and the outlet thickness h. Other characteristics can be taken into account. These input parameters Pe make it possible to estimate the rolling force and therefore the heat produced in the roll during the rolling of the metal strip 2, as well as the bending of the working rolls under the mechanical force, these thermal and mechanical expansions being intended to be compensated by the preheating method according to the invention.

[0044] The target thermal expansion profile corresponds to the distribution along the longitudinal axis Y of the local variation Δd th (y) in diameter of the working roll 11 due to a temperature variation ΔT between two successive calculation times tk. It is therefore a variation in diameter relative to the reference profile d ref (y), whether or not it includes the grinding component Δd rec (y). The target thermal expansion profile is independent of the calculation time tk, and is determined at the start of the preheating process (it can however be adjusted according to the thermal state of the preceding rolling mills (e.g. roughing stand). It is noted Δd th c y when the profile is defined along the continuous abscissa y along the longitudinal axis Y, and is noted Δd th i c 1 ≤ i ≤ Ns or more simply Δd th c (vector of Ns values) when defined along the Ns longitudinal segments 11s.

[0045] In this respect, the Figure 2Aillustrates a schematic and partial view, in section along the longitudinal axis Y, of a working cylinder 11 having a thermal expansion profile Δd th (y). The thermal expansion profile Δd th c y corresponds to the deviation from the reference profile d ref (y). In this example, the reference profile d ref (y) is constant (no rectification component). Of course, the thermal expansion profile Δd th c y is not to scale to favor clarity of the figure.

[0046] There Figure 2Billustrates an example of a target thermal expansion profile Δd th (y) of a working cylinder 11 determined by the predefined physical model M1, highlighting the parameters making it possible to characterize such a profile, the values of these parameters being stored in the predefined physical model M1. These parameters are denoted here A, B, u and xx. In this example, A is equal to 0.2mm, B is equal to 0.18mm, xx to 500mm, u to 400mm, for a set of predefined input parameters Pe, including a width W of the metal strip 2 to be rolled equal to 2000mm.

[0047] The target thermal expansion profile Δd th (y) is here a parabola over a distance W / 2-xx from the center of the working cylinder 11 along the longitudinal axis Y (more precisely from the center of the cylinder table 11), with an amplitude A at the center, and an amplitude B at the abscissa xx. Then, between the position xx and the end of the cylinder table, the profile has a decrease given by a function erf. The parameter u makes it possible to calculate the abscissa W / 2-xx+u from the center of the cylinder table for which the profile is B / 2. Of course, these parameters are given for illustrative purposes and other parameters can be used to characterize the target thermal expansion profile.

[0048] The predefined physical model M1 therefore includes the values of the parameters A, B, xx and u, which depend on the input parameters Pe. These values can also correspond to a standardized profile for a reference ratio W to H (width of the metal strip 2 over the input thickness H), for example here for W=1800mm and H=18mm. This standardization for a reference ratio W / H is useful when the input thickness depends in particular on the limits of the rolling stand. These values can be given for the rolling stand 10 considered, in particular for the first rolling stand 10 as well as for the following rolling stands 10 (for example, by means of an adaptation by homothety). Indeed, the preheating process can consist of heating the different rolling stands 10 of the rolling mill before the actual rolling operation.

[0049] Furthermore, when the rolling mill 1 comprises a reversible stand upstream of the rolling stands 10, the predefined physical model M1 may in particular provide for an update of the values of the parameters A, B, xx and u as a function of the amplitude of the thermal expansion profile of the working rolls 11 of the reversible stand. Thus, by way of example, the value of this amplitude is known and is subtracted from the value of the parameter A. The reversible stand is an upstream stand which is not thermally controlled by the thermal control device 20, in the sense that it does not comprise inductors 21. On the other hand, it comprises coolers 22 here.

[0050] Finally, as indicated later, when the target thermal expansion profile has been determined, the processing unit 23 performs its discretization according to the Ns longitudinal segments 11s.

[0051] The predefined physical model M2 expresses, for each calculation instant tk , a relationship between a measured profile of effective thermal power P Q i eff t k 1 ≤ i ≤ N and an effective mean temperature profile T ¯ i eff t k 1 ≤ i ≤ N of the working cylinder 11. Subsequently, we use the vector notation for these profiles: P Q eff t k And T eff< (tk ), where the vectors have Ni and Ns values respectively.

[0052] The effective thermal power profile P Q eff t k corresponds to the measurements made by the sensors of the Ni inductors 21 at the calculation instant tk and transmitted to the processing unit 23. From these measurements, the predefined physical model M2 determines the average thermal energy received by the longitudinal segments 11s considered between the two consecutive calculation instants. The predefined physical model M2 can be a database (abacus) obtained previously, for example experimentally and / or numerically.

[0053] The effective mean temperature profile T eff< (tk ) corresponds to the average temperature of the Ns longitudinal segments 11s at the calculation time tk , and depends in particular on the average thermal energy received from the inductors 21 (and where appropriate the average thermal energy lost due to the coolers 22), and therefore on the measured profile of effective thermal power P Q eff t k . This is an average temperature of the longitudinal segments 11s of the working cylinder 11, and not just the average temperature of the surface of the cylinder 11 in the longitudinal segments 11s. The average temperature is therefore constant at any point in the volume of each longitudinal segment 11s considered.

[0054] The effective mean temperature profile T eff<(tk ) is here determined by means of numerical simulation software by solving the predefined physical model M2 where the working cylinder 11 is discretized into an axisymmetric mesh, where the meshes are formed along the longitudinal axis Y of the Ns longitudinal segments 11s. It may preferably be a 1D axisymmetric mesh where each mesh corresponds to a longitudinal segment, or even a 2D axisymmetric mesh, i.e. along the longitudinal axis Y (longitudinal segments) and along a radial axis. The predefined physical model M2 is a physical model which performs a balance of the incoming and outgoing heat flows, and takes into account the thermal diffusion along the longitudinal axis Y.Thus, depending on the average thermal energy received by each longitudinal segment 11s (inductors 21) and the average thermal energy lost (coolers), input parameters which make it possible to estimate a mechanical force and therefore a thermal energy produced in the grip during the rolling operation, the predefined physical model M2 (e.g. 2D axisymmetric model) is solved by numerical simulation, for example in finite differences, and makes it possible to determine the effective average temperature profile. T eff< (tk ) of the Ns longitudinal segments.

[0055] There figure 3illustrates a flowchart of a method for preheating a working roll 11 of a rolling mill 1 according to one embodiment. Of course, the method can concern the two working rolls 11 of the rolling stand considered, as well as all the rolling stands of the rolling mill 1. The method is implemented before the actual rolling operation of the metal strip 2, and stops when the rolling operation begins. Preheating can, however, be activated again when the convergence criterion mentioned below is no longer verified.

[0056] Generally speaking, the preheating process includes a preliminary phase 10 of determining the target thermal expansion profile Δ dc< of the working cylinder, then followed by several phases carried out at each calculation instant tk, namely a phase 20 of determination of the effective average temperature profile T eff<(tk ) of the working cylinder, a phase 30 of determining the target average temperature profile T c< (tk ) of the working cylinder, then, based on a deviation between the two average temperature profiles T eff< (tk ) and T c< (tk) determined, of an activation phase or not of the inductors on the basis of a target thermal power profile P Q eff t k having been determined.

[0057] As indicated previously, the working cylinder 11 is discretized into Ns longitudinal segments 11s, and the thermal control device 20 comprises Ni inductors 21 distributed along the longitudinal axis Y, with here Ns ≥ Ni. In this example, for the sake of clarity, the coolers 22 that the thermal control device 20 may comprise are not taken into account.

[0058] Phase 10: Determination of a target thermal expansion profile Δd th i c 1 ≤ i ≤ Ns of the working cylinder 11. We subsequently use vector notation Δd th c .

[0059] In a step 11, input parameters Pe are defined, representative of the mechanical characteristics of the metal strip 2 to be rolled, such as the type of aluminum alloy, thermal characteristics such as the temperature of the metal strip at the inlet of the rolling stand and the desired winding temperature, and the dimensions of the metal strip 2 to be rolled, such as its width W, the initial thickness H and the outlet thickness h.

[0060] In a step 12, the processing unit 23 then determines the target thermal expansion profile Δd th c from the defined input parameters Pe and by means of the predefined physical model M1 implemented in the memory of the processing unit 23.

[0061] In step 13, the target thermal expansion profile is discretized Δd th c y on the Ns longitudinal segments 11s, to obtain the profile Δd th i c 1 ≤ i ≤ Ns (note Δd th c ).

[0062] Note that the thermal expansion profile Δd th c , as well as the target average temperature profiles T c< (tk) and effective T eff< (tk ) can only be defined for the longitudinal segments 11s intended to be in contact with the metal strip 2, that is to say here for the longitudinal segments 11s with index ranging from iwi to iwf.

[0063] The following phases 20 to 60 are performed iteratively at different successive instants, the time being discretized at a predefined calculation frequency, for example every 45 seconds. Thus, each iteration of rank k is associated with a calculation instant tk also called the current instant.

[0064] Phase 20: Determination of an effective mean temperature profile T ¯ i eff t k 1 ≤ i ≤ Ns (and noted T eff< (tk )) of the Ns longitudinal segments 11s of the working cylinder 11.

[0065] In step 21, the effective average temperature profile is determined T eff< (tk ) of the working cylinder 11. As previously stated, this is the average temperature of each longitudinal segment 11s of the working cylinder 11 (constant temperature on the surface and in the volume of the longitudinal segment), and not just the surface temperature. This average temperature is responsible for the (average) thermal expansion of the longitudinal segment 11s considered.

[0066] This profile is determined from an effective thermal power profile P Q i eff t k − 1 1 ≤ i ≤ Ni (and noted in a vector manner P Q eff t k delivered by the inductors 21 and previously measured by the sensors of the inductors 21 at the calculation instant t k-1, and by means of the second predefined physical model M2 expressing a relationship between the effective thermal power profile P Q eff t k and the effective mean temperature profile T eff<(tk ). At the first calculation instant tk=1 , the inductors 21 not having yet delivered thermal power, the effective temperature profile T eff< (tk=1) can be equal to the ambient temperature, or even can be equal to a predefined temperature (uniform or not) corresponding to the thermal state of the working rolls following, for example, previous rolling operations.

[0067] Phase 30: Determination of a target average temperature profile T ¯ i c t k 1 ≤ i ≤ Ns (and noted T c< (tk )) of the Ns longitudinal segments 11s of the working cylinder 11.

[0068] In step 31, the target average temperature profile is determined T c< (tk ) of the Ns longitudinal segments 11s of the working cylinder 11, from the effective average temperature profile T eff< (tk ) and the target thermal expansion profile Δd th c To do this, we take as a reference a longitudinal segment 11, here with index iwi, where one of the lateral edges of the metal strip 2 is located. Then, we calculate the target average temperature from the following relationship: ∀ j = iwi , iwf T ¯ j c t k = T ¯ iwi eff t k + Δd j c − Δd iwi c / α × d ref j , where d ref (j) is the reference diameter at index j, and where α is the average thermal expansion coefficient of the working cylinder 11. Of course, other calculations are possible.

[0069] Phase 40: determination of a gap ΔT(tk ) between the target average temperature profile T c< (tk ) and the effective average temperature profile T eff< (tk ).

[0070] In a step 41, a maximum deviation ΔT (jmax) (tk ) is determined here between the target average temperature profile T c< (tk ) and the effective mean temperature profile T eff< (tk ). To do this, we identify the longitudinal segment 11s with index jmax located between iwi and iwf for which the temperature difference is maximum: Δ T ¯ jmax t k = max j = iwi , iwf T ¯ j c t k − T ¯ j eff t k The objective here is to identify the inductor 21 closest to this longitudinal segment of index jmax whose target thermal power will be brought to a maximum value. Phase 50: convergence criterion

[0071] In a step 50, a convergence criterion is determined in which a deviation Ec(tk ) representative of the deviation ΔT(tk ) between the target average temperature profile and the target average temperature profile is compared to a predefined threshold value ε T c< (tk ) and the effective mean temperature profile T eff< (tk ). This deviation Ec(tk ) is therefore also representative of the deviation between the target thermal expansion profile Δ dc< (tk ) and the effective thermal expansion profile Δ d eff< (tk ).

[0072] The deviation Ec(tk ) can be defined in different ways. It can be the local maximum value ΔT (jmax) (tk ) between the target mean temperature profile T c<(tk ) and the effective mean temperature profile T eff< (tk ). It can also be a point-by-point comparison between the target mean temperature profile T c < (tk ) and the actual mean temperature profile T eff< (tk ), for example an average or a possibly weighted sum of the difference in absolute value between these two profiles. It can also be an activation duration of the inductor 21 associated with the longitudinal segment of index jmax, that is to say the one for which the temperature difference ΔT (jmax) (tk ) is maximum.

[0073] The convergence criterion is considered to be verified when the deviation Ec(tk ) is less than or equal to the threshold value ε, in which case the preheating of the working roll(s) is considered to be complete (step 70). Information can then be given to the user of the rolling mill 1, for example the deviation Ec(tk ) in question, or information on the remaining heating time (ratio between the temperature deviation and the thermal power injected). On the other hand, the convergence criterion is considered not to be verified when the deviation Ec(tk ) is greater than the threshold value ε, in which case the preheating process continues with phase 60. Note that phase 50 is carried out here between phases 40 and 60, but it can obviously be carried out at other times in the process, for example after phase 60. In the case where the convergence criterion is not verified, we continue with phase 60.

[0074] Phase 60: Determination of a target thermal power profile P Q i c t k 1 ≤ i ≤ Ni (and noted P Q c t k ) and activation of the inductors accordingly.

[0075] In a step 61, the target thermal power profile is determined. P Q c t k to be delivered by the inductors 21. It is therefore possible to provide for activating only the inductors 21 intended to be opposite the metal strip during the rolling operation, i.e. those located opposite the longitudinal segments 11s with indices between iwi and iwf. For this, the target thermal power of the inductor 21 with index jmax is defined at 100% of the maximum thermal power PQ,max. The target thermal power is then defined P Q j eff t k to be delivered by the other inductors 21 of index j as being equal to the maximum thermal power PQ,max modulated by the ratio ΔT (j) (tk ) / ΔT (jmax) (tk ). To take into account lateral thermal diffusion, an activation threshold can be taken into account: thus, when the ratio ΔT (jmax) (tk ) / ΔT (jmax) (tk ) is lower than a predefined threshold RT, the inductor 21 of index j considered is not activated. We thus obtain the target thermal power profile P Q c t k inductors 21.

[0076] During a step 62, a control signal is transmitted by the processing unit 23 to the inductors 21 so that they deliver a target thermal power P Q c t k . Depending on the target thermal power value P Q j c t k , the inductors 21 activate or not and deliver (or attempt to deliver) the determined target thermal power. Equivalently, a control signal can be transmitted to the coolers 22 when the local effective average temperature is higher than the local target average temperature, so as to reduce the corresponding deviation.

[0077] During a step 63, each sensor of the inductors 21 measures the thermal power P Q j eff t k actually delivered, here simultaneously with their operation, and transmits the measured value to the processing unit 23. These values thus form an effective thermal power profile P Q eff t k .

[0078] When the convergence criterion has not been verified, we then repeat phases 20 to 50, and we increment the calculation time tk.

[0079] On the other hand, when it has been checked, this phase 60 may not have been carried out, and the information is given to the operator of rolling mill 1 that the effective average temperature profile T eff< (tk ) converged to the target mean temperature profile T c< (tk ), and therefore that the effective thermal expansion profile Δd th eff t k converged to the target thermal expansion profile Δd th c t k The rolling operation of the metal strip 2 can therefore begin and the inductors 21 can be deactivated, immediately (or not), to the extent that the heat produced by the rolling of the metal strip 2 in the grip will cause a thermal expansion of the working cylinder 21 corresponding to the target profile target thermal expansion Δd th c .

[0080] It appears that the preheating method according to the invention makes it possible to preheat the working roll(s) 11 simply and efficiently before the actual rolling of the metal strip 2 is carried out. Indeed, the use of inductors 21 and a predefined physical model M2 receiving the measurements of the effective thermal power of the inductors 21 make it possible to quickly and precisely modify the effective average temperature profile so that it tends towards the target average temperature profile.

[0081] Indeed, the inductors 21 modify the average surface and volume temperature of the longitudinal segments 11s, and not only the surface temperature like the spray nozzles of a heating liquid, which makes it possible to use a simplified predefined physical model M2, for example a 2D axisymmetric type model, which directly determines the average temperature of the longitudinal segments of the working cylinder without going through the measurement of the surface temperature. On the other hand, in the prior art where spray nozzles of a heating liquid are provided, the physical model needs to be more complex and must determine the average temperature from the measurement of the surface temperature (hence the user of dedicated sensors).In addition, the injected thermal power is transmitted directly into the longitudinal segments of the working cylinder, without an exchange coefficient, since there is heating by the Joule effect of the induced eddy currents. On the contrary, with a heating liquid (water for example), energy efficiency is impacted by the exchange coefficient, and the maximum heating is limited by the boiling temperature of the liquid.

[0082] Particular embodiments have just been described. Different variants and modifications are possible within the scope of the invention. Thus, as mentioned previously, the thermal control device may comprise coolers distributed along the longitudinal axis Y of the working cylinder, and the processing unit may transmit a control signal to the coolers on the basis of the difference Δ T (tk ) between the target mean temperature profile T c<(tk ) and the effective mean temperature profile T eff< (tk ).

[0083] In a preferred embodiment, the metal strip comprises an aluminum alloy, preferably the aluminum alloy is an alloy selected, according to the designation of the aluminum association, from the alloy AA2014, AA2017, AA2024, AA2027, AA2046, AA2050, AA2056, AA2060, AA2074, AA2098, AA2139, AA2195, AA2198, AA2214, AA2219, AA2519, AA2524, AA2618, AA2654, AA3003, AA3004, AA3005, AA3103, AA3104, AA3105, AA5005, AA5049, AA5050, AA5052, AA5083, AA5086, AA5088, AA5150, AA5154, AA5182, AA5186, AA5200, AA5251, AA5252, AA5254, AA5383, AA5454, AA5456, AA5657, AA5754, AA6016, AA6056, AA6060, AA6061, AA6063, AA6082, AA6156, AA6182, AA6909, AA7010, AA7011, AA7017, AA7019, AA7020, AA7021, AA7022, AA7039, AA7040, AA7049, AA7050, AA7056, AA7072, AA7075, AA7079, AA7099, AA7122, AA7150, AA7175, AA7178, AA7449, AA7450 or AA7475.

[0084] In one embodiment, the metal strip is a clad aluminum alloy. In one embodiment, the aluminum alloy is clad on at least one face, preferably two faces, with a 1000 series alloy depending on the aluminum combination, preferably the AA1050 alloy or with the AA7072 alloy. In a preferred embodiment, the central portion of the clad aluminum is the AA2024 or AA2524 alloy and the cladding is a 1000 series alloy, preferably AA1050. In another preferred embodiment, the central portion of the clad aluminum is the AA7075, AA7175 or AA7475 alloy and the cladding is the AA7072 alloy. Clad aluminum alloys are known as clad product in NF EN 12258-1.

[0085] In a preferred embodiment, the rolling of the metal strip is hot rolling. Preferably, the hot rolling is carried out with a rolling mill which is part of a plurality of hot rolling mills operating in tandem, preferably preceded by a reversible hot rolling mill.

[0086] In one embodiment, the temperature of the aluminum alloy, optionally clad, before its hot rolling is at least 350°C and at most 510°C or 490°C or 470°C or 450°C or 430°C or 410°C or 390°C or 370°C. In another embodiment, the temperature of the aluminum alloy, optionally clad, before its hot rolling is at least 370°C and at most 510°C or 490°C or 470°C or 450°C or 430°C or 410°C or 390°C. In another embodiment, the temperature of the aluminum alloy, optionally clad, before its hot rolling is at least 390°C and at most 510°C or 490°C or 470°C or 450°C or 430°C or 410°C. In another embodiment, the temperature of the aluminum alloy, optionally clad, before its hot rolling is at least 410°C and at most 510°C or 490°C or 470°C or 450°C or 430°C.In another embodiment, the temperature of the aluminum alloy, optionally clad, before its hot rolling is at least 430°C and at most 510°C or 490°C or 470°C or 450°C. In another embodiment, the temperature of the aluminum alloy, optionally clad, before its hot rolling is at least 450°C and at most 510°C or 490°C or 470°C. In another embodiment, the temperature of the aluminum alloy, optionally clad, before its hot rolling is at least 470°C and at most 510°C or 490°C. In another embodiment, the temperature of the aluminum alloy, optionally clad, before its hot rolling is at least 490°C and at most 510°C.

[0087] In one embodiment, the temperature of the aluminum alloy, optionally plated, after its hot rolling is at least 230°C and at most 370°C or 350°C or 330°C or 310°C or 290°C or 270°C or 250°C. In another embodiment, the temperature of the aluminum alloy, optionally plated, after its hot rolling is at least 250°C and at most 370°C or 350°C or 330°C or 310°C or 290°C or 270°C. In another embodiment, the temperature of the aluminum alloy, optionally clad, after its hot rolling is at least 270°C and at most 370°C or 350°C or 330°C or 310°C or 290°C. In another embodiment, the temperature of the aluminum alloy, optionally clad, after its hot rolling is at least 290°C and at most 370°C or 350°C or 330°C or 310°C.In another embodiment, the temperature of the aluminum alloy, optionally clad, after its hot rolling is at least 310°C and at most 370°C or 350°C or 330°C. In another embodiment, the temperature of the aluminum alloy, optionally clad, after its hot rolling is at least 330°C and at most 370°C or 350°C. In another embodiment, the temperature of the aluminum alloy, optionally clad, after its hot rolling is at least 350°C and at most 370°C.

[0088] In one embodiment, the surface temperature of the preheated work roll is at least 200°C and at most 320°C or 300°C or 280°C or 260°C or 240°C or 220°C. In another embodiment, the surface temperature of the rolls during hot rolling is at least 220°C and at most 320°C or 300°C or 280°C or 260°C or 240°C. In another embodiment, the surface temperature of the rolls during hot rolling is at least 240°C and at most 320°C or 300°C or 280°C or 260°C. In another embodiment, the temperature of the surface rolls during hot rolling is at least 260°C and at most 320°C or 300°C or 280°C. In another embodiment, the temperature of the surface rolls during hot rolling is at least 280°C and at most 320°C or 300°C.In another embodiment, the surface temperature of the rolls during hot rolling is at least 300°C and at most 320°C.

[0089] In another preferred embodiment, the rolling of the metal strip is cold rolling. Preferably, the cold rolling is carried out with a rolling mill which is part of a plurality of cold rolling mills operating in tandem.

[0090] In one embodiment, the surface temperature of the preheated work roll is at least 100°C and at most 200°C or 180°C or 160°C or 140°C or 120°C. In another embodiment, the surface temperature of the rolls during cold rolling is at least 120°C and at most 200°C or 180°C or 160°C or 140°C. In another embodiment, the surface temperature of the rolls during cold rolling is at least 140°C and at most 200°C or 180°C or 160°C. In another embodiment, the surface temperature of the rolls during cold rolling is at least 160°C and at most 200°C or 180°C. In another embodiment, the surface temperature of the rolls during cold rolling is at least 180°C and at most 200°C.

[0091] For example, the two working rolls, with a diameter of 700 mm, of a hot rolling mill were each equipped with 33 inductors of 80 mm depending on the length of said rolls. The working rolls were discretized into segments of 20 mm in length for the implementation of the preheating process according to the invention. The use of the roll preheating process made it possible to eliminate the use of starting metal strips to stabilize the thermal profile necessary for hot rolling aluminum alloys. This improvement concerns in particular the alloys AA5083, AA5086, AA5088, AA5182, AA5052, AA5754, AA2098, AA2198, AA2195, AA2024 and AA2524. This improvement also applies to clad aluminum alloys, with the core being AA2024 or AA2524 aluminum alloy and the cladding being AA1050.This improvement also applies to clad aluminum alloys whose core is AA7075 or AA7175 aluminum alloy and whose cladding is AA7072.

Claims

1. Process for preheating at least one work roll (11) of a rolling mill (1) intended to roll a metallic strip (2) so that the work roll (11) has a target thermal expansion profile Δd i c 1 ≤ i ≤ Ns determined along Ns longitudinal segments of the work roll, the rolling mill (1) including a thermal control device (20) including Ni induction coils (21) distributed along the longitudinal axis of the work roll (11) facing the Ns longitudinal segments (11s), the process including the following phases: a. determining (10) the target thermal expansion profile Δd i c 1 ≤ i ≤ Ns , at a calculation time tk, • based on predefined values of input parameters Pe representative of the dimensions and mechanical and thermal properties of the metallic strip to be rolled, • and a first predefined physical model M1 expressing a relationship between the input parameters Pe and the target thermal expansion profile Δd i c 1 ≤ i ≤ Ns ; b. determining (20) an effective mean temperature profile T ¯ i eff t k 1 ≤ i ≤ Ns along Ns longitudinal segments of the work roll, • based on an effective thermal power profile P Q i eff t k − 1 1 ≤ i ≤ Ni generated by the Ni induction coils and measured beforehand, • and a second predefined physical model M2 expressing a relationship between the effective thermal power profile P Q i eff t k 1 ≤ i ≤ Ni and the effective mean temperature profile T ¯ i eff t k 1 ≤ i ≤ Ns ; c. determining (30) a target mean temperature profile T ¯ i c t k 1 ≤ i ≤ Ns along the Ns longitudinal segments of the work roll, based on the target thermal expansion profile Δd i c t k 1 ≤ i ≤ Ns determined and the effective mean temperature profile T ¯ i eff t k 1 ≤ i ≤ Ns determined; d. determining (40) a deviation ΔT(tk) between the target mean temperature profile T ¯ i c t k 1 ≤ i ≤ Ns and the effective mean temperature profile T ¯ i eff t k 1 ≤ i ≤ Ns ; e. determining (50) a convergence criterion based on the deviation ΔT(tk) determined, and stopping the preheating (70) when the convergence criterion is satisfied, and continuing the phases of the preheating process when the convergence criterion is not satisfied; f. activating (60) of the induction coils including the following steps: • determining a target thermal power profile P Q i c t k 1 ≤ i ≤ Ni to be supplied by the Ni induction coils based on the deviation ΔT(tk) determined; • activating the induction coils such that they supply the target thermal power profile P Q i c t k 1 ≤ i ≤ Ni determined; • measuring an effective thermal power profile P Q i eff t k 1 ≤ i ≤ Ni actually supplied by the induction coils; g. repeating steps b / to f / until the convergence criterion is satisfied, by incrementing the calculation time tk.

2. Preheating process according to claim 1, wherein the target thermal expansion Δd i c 1 ≤ i ≤ Ns , effective mean temperature T ¯ i eff t k 1 ≤ i ≤ Ns , and target mean temperature T ¯ i c t k 1 ≤ i ≤ Ns profiles are determined for the longitudinal segments intended to be in contact with the metallic strip (2) to be rolled.

3. Preheating process according to claim 1 or 2, wherein the step of determining the target thermal power profile P Q i c t k 1 ≤ i ≤ Ni includes the following steps: • identifying the longitudinal segment, of index jmax, for which the deviation ΔT(jmax)(tk) is maximum, and defining the target thermal power P Q jmax c t k at a maximum value; • determining the target thermal power of the other longitudinal segments such that P Q j c t k = P Q jmax c t k × Δ T ¯ j t k / Δ T ¯ jmax t k .

4. Preheating process according to claim 3, wherein an induction coil (21) of index j is only activated when the ratio ΔT(j)(tk) / ΔT(jmax)(tk) is greater than or equal to a predefined threshold value RT, otherwise it remains inactive.

5. Preheating process according to any one of claims 1 to 4, wherein the thermal control device (20) includes coolers (23) distributed along the longitudinal axis of the work roll (11) facing the Ns longitudinal segments (11s), and including a step of activating the coolers (23) based on the deviation ΔT(tk) between the target mean temperature profile T ¯ i c t k 1 ≤ i ≤ Ns and the effective mean temperature profile T ¯ i eff t k 1 ≤ i ≤ Ns .

6. Preheating process according to any one of claims 1 to 5, wherein the phase of determining the effective mean temperature profile T ¯ i eff t k 1 ≤ i ≤ Ns is performed by digital simulation, the work roll (11) being discretized according to a 2D axisymmetric mesh.

7. Preheating process according to any one of claims 1 to 6, wherein the metallic strip (2) is produced from an aluminum alloy.

8. Rolling process including the following steps a. preheating at least one work roll, preferably two work rolls, of a mill intended to roll a metallic strip according to the process of one of claims 1 to 7, b. rolling the metallic strip with the thus preheated at least one work roll, preferably the two work rolls.

9. Rolling process according to claim 8, characterized in that the metallic strip comprises an aluminum alloy, preferably the aluminum alloy is an alloy chosen from AA2014, AA2017, AA2024, AA2027, AA2046, AA2050, AA2056, AA2060, AA2074, AA2098, AA2139, AA2195, AA2198, AA2214, AA2219, AA2519, AA2524, AA2618, AA2654, AA3003, AA3004, AA3005, AA3103, AA3104, AA3105, AA5005, AA5049, AA5050, AA5052, AA5083, AA5086, AA5088, AA5150, AA5154, AA5182, AA5186, AA5200, AA5251, AA5252, AA5254, AA5383, AA5454, AA5456, AA5657, AA5754, AA6016, AA6056, AA6060, AA6061, AA6063, AA6082, AA6156, AA6182, AA6909, AA7010, AA7011, AA7017, AA7019, AA7020, AA7021, AA7022, AA7039, AA7040, AA7049, AA7050, AA7056, AA7072, AA7075, AA7079, AA7099, AA7122, AA7150, AA7175, AA7178, AA7449, AA7450 or AA7475 alloy.

10. Rolling process according to claim 9 characterized in that the aluminum alloy is cladded on at least one side, preferably two sides with a 1000 Series alloy according to the Aluminum Association, preferably AA1050 alloy or with AA7072 alloy.

11. Rolling process according to one of claims 8 to 10 characterized in that the rolling of the metallic strip is a hot rolling.

12. Rolling process according to claim 11 characterized in that the temperature of the aluminum alloy, optionally cladded, prior to its hot rolling is at least 350°C and at most 510°C.

13. Rolling process according to claim 11 or 12 characterized in that the surface temperature of the preheated work roll is at least 200°C and art most 320°C.

14. Rolling process according to one of claims 8 to 10 characterized in that the rolling of the metallic strip is a cold rolling.

15. Rolling process according to claim 14 characterized in that the surface temperature of the preheated work roll is at least 100°C and at most 200°C.