Method for controlling a beam processing installation, associated system and installation

Abstract

A method for controlling a beam processing installation which comprises a rolling mill, and a cooling machine for water-cooling a steel beam downstream of the rolling mill, the method comprising: - s4: Computing a temperature TST predicted for the beam after it has traversed the cooling machine, computed taking into account an input temperature (Tin) of the steel beam before it enters the cooling machine, and taking into account one or more candidate cooling setpoints (vc*) for the cooling of the beam in the cooling machine, - the step s4 being executed iteratively to determine one or more cooling setpoints (vo*) such that the temperature TST computed in step s4 matches a target self-tempering temperature T*ST,j, - sc : controlling the beam processing installation based on said one or more cooling setpoints, or based on one or more corrected cooling setpoints (vj*) determined from the one or more setpoints.

Description

Method for controlling a beam processing installation, associated system and installation

[0001] The technical field is that of producing steel beams, for instance steel beams for buildings, bridges and other structures. It concerns more particularly the control of heat treatments applied to such beams during a production process.Technical background

[0002] For obtaining high performance steel beams (typically big beams called “jumbo” intended for instance for building skyscrapers), it is known, after the hot-rolling operations, to cool down the steel beam quickly using water jets, but in a well-controlled manner. Figure 1 schematically represents the evolution, with time t, of the temperature T at the surface of a steel beam, during such a water-cooling process. First (phase Ph1 in figure 1), the beam is cooled in air. Then it is water cooled quickly in a cooling machine (phase Ph2), and the temperature T drops significantly. And then, the beam ends its cooling in air (phase Ph3). During the water cooling, it is mainly the superficial part of the beam that is cooled down. And so, during the subsequent phase Ph3, the heat that remained in the bulk of the beam is gradually released and the surface temperature T thus temporarily increases after the beam has traversed the cooling machine (it becomes moderately high again) before finally decreasing (see figure 1).

[0003] This re-increase of the surface temperature, usually called « self-tempering », is useful from a metallurgic point of view if well controlled. In particular, it is useful to control the cooling of the beam in order to obtain a “self-tempering” temperature TST (which is the maximum over time t reached by the temperature T of the surface of the beam, after the beam has exited the cooling machine) that is close to a desired, target self-tempering temperature (well suited to optimize the final mechanical properties of the beam).

[0004] Controlling the self-tempering temperature obtained during such a cooling process is challenging due to the thermal inertia in this process (this temperature is reached once the fast-cooling process itself is finished) and due to the rather complex thermal evolution for the beam. In this context, it would thus be very useful to be able to predict accurately a value of the self-tempering temperature TST, or more generally to predict the thermal evolution of the beam during the cooling process. This would be useful too for a post-characterization of a beam, after its cooling (in order to estimate mechanical properties of the beam that has been produced, for instance).Summary

[0005] In this context, a method for controlling a beam processing installation, according to claim 1, is provided.

[0006] This method may comprise one or several additional features, defined in claims 1 to 12, considered alone or in combination.

[0007] The instant technology also concerns an electronic monitoring device according to claim 13, and a beam processing installation according to claim 14. The beam processing installation may further comprise a temperature sensor for measuring the input temperature, an additional temperature sensor for measuring the intermediate temperature, and an actuator or a low-level controller for controlling the speed with which the beam moves. The instant technology also concerns a computer program whose execution on a computer (possibly connected to relevant sensors, actuators or controller), makes the computer to execute the method for controlling presented above. The instant technology also concerns a non-transitory computer-readable medium storing such a computer program.Detailed description

[0008] The instant technology will now be described in more detail and illustrated by examples without introducing limitations, with reference to the appended figures.

[0009] Figure 1 schematically represents the evolution overt time t of a surface temperature of a steel beam, during a quench and self-tempering thermal treatment of the beam.

[0010] Figure 2 schematically represents a beam processing installation for applying a quench and self-tempering thermal treatment to a beam.

[0011] Figure 3 is a schematical perspective view of a part of an H-shape beam, to be processed in the beam processing installation of figure 2.

[0012] Figure 4 schematically represents flange and web water jets cooling the beam, in a cooling machine of the beam processing installation of figure 2.

[0013] Figure 5 schematically represents a longitudinal sampling of the beam into consecutive portions, for the sake of thermal computations and control.

[0014] Figure 6 schematically represents, as a block diagram, steps of a method for controlling the beam processing installation of figure 2.

[0015] Figure 7 schematically represents an initially homogeneous temperature field, and a temperature field at a subsequent instant, computed during an initialization step of the method of figure 6.

[0016] Figure 8 schematically represents an intermediate temperature of the beam, for the different portions of the beam, the intermediate temperature being measured just before the beam comes out of a rolling mill of the beam processing installation.Beam processing installation

[0017] Figure 2 schematically represents a beam processing installation 1 which comprises a hot rolling mill to shape a beam 2, a cooling machine 30 for water-cooling the beam once output by the rolling mill, and an electronic system 10 configured, inter-alia, for determining one or more cooling setpoints for the beam water-cooling. Here, the rolling mill comprises aroughing mill (not represented in figure 2), then an intermediate mill (also called main mill) which is a tandem mill 4, here, and then a finishing mill 3. The beam 2 is hot when processed in the rolling mill: its temperature is typically higher than 800°C, or even higher than 900 °C. In the beam processing installation 1, the beam is moved parallel to its axis, along the installation axis x, from the intermediate mill to the finishing mill and then to the cooling machine. The cooling machine 30 is arranged downstream of the rolling mill, along the path x followed by the beam 2 in the beam processing installation. More particularly, the cooling machine is arranged downstream of the last rolling stand of the rolling mill, that is, the cooling machine is arranged downstream of the finishing mill 3 here. There is no other rolling stand between the last stand of the rolling mill and the cooling machine 30.

[0018] The distance between a tandem mill output and the finishing mill input may, like here, be higher than the length of the beam 2 (in other words, the maximum length for the beams processed in the installation is equal or smaller than this distance, here). The cooling machine 30 is located immediately downstream of the finishing mill.

[0019] The beam processing installation 1 is equipped also with:a first temperature sensor 6 arranged to measure a surface temperature of the beam 2 at an upstream position Oe located upstream of the cooling machine 30. Here, the upstream position Oe is located upstream of the intermediary mill (that is, upstream of the tandem mill 4); this measured temperature is called the input temperature;a second temperature sensor 8 arranged to measure another surface temperature of the beam 2, at an intermediary position Os located between the upstream position Oe and the cooling machine; here, the intermediary position Os is located between the intermediary mill (here, the tandem mill 4) and finishing mill 3, and a third temperature sensor 9 arranged to measure another surface temperature of the beam 2 after the beam has traversed the cooling machine 30 (output temperature).

[0020] The temperature sensors may be pyrometers, or infrared cameras, for instance.

[0021] The beam 2 is a steel beam, or in other words a steel profile (or steel section). Its length may be from 10 to 200 meters at this stage of the manufacturing process (it may be subsequently cut to shorter lengths). The width of the beam (maximum transverse extension) would be from 10cm to 2m. In the detailed example presented here, the beam 2 is an H-beam (its section has an H shape), as represented in figure 3. Yet, the beam could have a different section shape. For instance, it may be an I-beam, a Z-beam, a T-beam, a II beam (that is forming a U-shape channel) or an L beam (that is, a steel angle).

[0022] The cooling machine may comprise one, two, or more successive cooling sections. Each cooling section is arranged for emitting water jets that strike some or all of the beam’sfaces. Here it comprises a first cooling section 31 and a second cooling 32, located one after the other along the installation axis x (figure 2). The cooling machine is arranged so that the jets belonging to one of the cooling sections can be controlled independently from the jets of the other(s) cooling section(s). At least one, here each cooling section is arranged for emitting both (figure 4):flange jets F J, for projecting water on one or more of flange faces of the beam, and - web jets WJ, for projecting water on one or both web faces of the beam.

[0023] The beam processing installation 1 comprises a low-level controller 13 for controlling actuators of the beam processing installation 1, in particular for controlling valves of the cooling machine 30, and for controlling the finishing mill 3, whose rolling speed fixes the speed at which the beam traverses the colling machine 30. The low-level controller 13 is also connected to sensors of the beam processing installation 1 (in particular one or more speed sensors and presence sensors for detecting the presence of the beam at different positions along the processing path). It may implement control loops such as PID loops. It receives the cooling setpoints from the higher-level electronic system 10. In particular, it receives from the electronic system 10 a speed setpoint, instructions specifying which of the above-mentioned jets are to be on and which are to be off, and one or more water flow setpoints for the jets that are to be on. The low-level controller 13 is configured to implement close to the actuators control, yet less elaborate control strategies than the electronic system 10 (for instance in the form of a proportional, integral, and possibly derivative control loop). The low-level controller 13 may take the form of a programmable logic controller (PLC) or other industrial-like computer or programmable circuit. It is operatively connected to the electronic system 10 and to the above-mentioned actuators and sensors (for instance through a local data bus).

[0024] Here, the electronic system 10 comprises a server 11 and a terminal 12. The terminal may be a human-machine interface (such as a display screen, possibly with an entering device like a keyboard and / or a pointing device like a mouse pad and / or buttons). The terminal may also be a standalone computer. Alternatively, the electronic system 10 may take the form of a stand-alone computer (including a human-machine interface), rather than a server with a distinct, possibly remote human-machine interface. Anyhow, the electronic system 10 comprises at least a progressor and a memory and can be programmed so as to execute elaborate tasks like numerical simulations. The electronic system 10 is operatively connected (through a local network, of through the internet, for instance) to an industrial database 14, itself connected to remote services 15 or users, such as production analytics services or supply chain tracking services.

[0025] The electronic system 10 (more precisely the server 11, here) is programmed to execute the method for controlling the beam cooling presented below.

[0026] This method is based on a numerical simulation of the temporal evolution of the temperature field within the beam. Executing this simulation iteratively enables to determine the cooling setpoint(s), here the speed setpoint, which is transmitted to the low-level controller 13 which then controls the actuator(s) of the installation 1 based on this setpoint(s). The cooling setpoint(s) is determined such that, for this setpoint, a predicted self-tempering temperature TST (predicted by the numerical simulation) matches a target self-tempering temperature T*ST,j, to be obtained. By matching it is meant being equal to, within 20°C, or even within 10°C or within 5°C. The numerical simulation is a finite differences computation. Regarding spatial variables (in addition to the temporal variable t), it may, like here, be a two-dimensional simulation, the two spatial dimensions corresponding to two coordinates along two transverse directions each perpendicular to the beam’s axis. It takes into account the beam dimensions and chemical composition. It takes also into account at least one temperature of the beam 2 measured before the beam 2 enters the cooling machine 30, here the input temperature Tm (the intermediate temperature is also taken into account, here, for adjusting the cooling setpoint just before the beam enters the cooling machine 30).

[0027] In terms of discretization, here, the beam is divided into a number n of consecutive longitudinal portions Pj, with i from 1 to n (figure 5), also called samples. The portion Pi is the head portion of the beam (located at its heading end, that is at the end of the beam that comes out of the finishing mill first). Pnis the tail portion (in other words end portion) of the beam, n may be from 3 to 100, or even from 3 to 50, and each sample may be from 0.2 to 5 meters long, or even from 1 to 4 meters long. For at least one longitudinal sample, in practice, a two-dimensional temperature field is computed, and its evolution over time t is computed, for a period encompassing at least the transit through the cooling machine 30 and a subsequent air-cooling. Here, this period spans at least: from the measurement of the input temperature, to a delivery of the beam at the end of the beam processing installation 1.

[0028] Determining the cooling setpoint(s) by iterative numerical simulations (which require significant computation time), while it is to be used for real-time, on-line control, is achieved thanks to specific arrangements that are presented below, with reference to figure 6.

[0029] Some general aspects of this method are presented first and the method is then presented in more details.In-advance determination of one or more cooling setpoints; general aspects

[0030] Remarkably, the method for controlling the beam processing installation comprises (figure 6):s1: acquiring the input temperature Tm of the steel beam 2, measured on a portion of beam, Pj, measured before said portion of the beam enters que cooling machine,s4: computing the temperature TST of said portion of the beam, which is a temperature predicted for the portion of beam after the portion of the beam has traversed the cooling machine 30, the temperature TST being computed taking into account the input temperature Tm measured and one or more candidate cooling setpoints to be employed for controlling the cooling of the beam in the cooling machine, the step s4 being executed iteratively to determine one or more cooling setpoints such that the temperature TST computed in step s4 is equal or substantially equal to a target self-tempering temperature T*ST,j, sc: controlling the beam processing installation 1 based on said one or more cooling setpoints, or based on one or more corrected cooling setpoints determined from the one or more setpoints.

[0031] In the exemplary embodiment described here in detail, the one or more setpoints, determined by executing repeatedly step s4, is a speed setpoint v0*, for the speed at which the beam 2 traverses the cooling machine 30. Still, in other embodiments, alternatively or in complement to the speed setpoint, one or more other cooling setpoints, like one or more water flow values for the water projected on the beam in the cooling machine, could be determined, by iterating step s4.

[0032] In the exemplary embodiment described here, the one or more candidate cooling setpoints is a candidate speed setpoint vc*, and the one or more corrected cooling setpoints is a corrected speed setpoint v*.

[0033] Regarding the temperature TST, predicted by numerical simulation in step s4, in this embodiment, it is the maximum over time reached by the temperature of the surface of the portion Pj of the beam, after this portion of the beam has exited the cooling machine (as illustrated in figure 1). Besides, the input temperature Tm of the portion Pj is measured directly, by the first temperature sensor 6, when the portion Pj passes at the upstream position Oe above mentioned. Still, in other embodiments, this measure could be a non-direct measurement, the input temperature Tinof the portion Pibeing then derived from another measurement, for instance derived from a temperature measurement carried out on another portion of the beam.

[0034] In this control method, the first execution of step s4 is launched immediately or almost immediately after the intput temperature Tinhas been measured (for instance within 1s or less). Anyhow, the first execution of step s4 is launched before the portion Pj of the beam enters the cooling machine, so that there is some time, for determining the speed setpoint v0* to be employed for controlling the speed at which beam (more sceptically at which the portion Pj) traverses the cooling machine, before this portion enters the cooling machine.

[0035] In this regard, as the input temperature Tm (which is employed for determining v0*) is measured at the upstream position Oe, which is located upstream (and even significantlyupstream) of the cooling machine, there is some time for achieving the determination of v0* before the portion of the beam considered enters the cooling machine.

[0036] In this respect, the upstream position Oe may be located, along the path x followed by the beam 2 and / or the computations achieved in step s4 may be parametrized, so that:a minimum transit time (or, alternatively, an average transit time) transit, between passing at the upstream position Oe and entering the cooling machine (or even between passing at position Oe and then entering the finishing mill), for the beam,is higher thana maximum computation time (or, alternatively, an average computation time) tcomput required for executing step s4 a given number of times (for instance 10 times) using the electronic system 10, multiplied by a safety coefficient which is for instance from 1 to 5.

[0037] For instance, if the minimum transit time observed transit is 30 seconds (given the position of the first temperature sensor), then, the computations achieved in step s4 may be parametrized (in terms of mesh finesse and temporal sampling, for instance) so that 10 executions of step s4 using the electronic system 10 requires a maximum time of 15s (safety coefficient of 2).

[0038] The measurement of the input temperature Tm of the portion Pj, and the consecutive (immediate) triggering of the first execution of step s4, may also be carried out at an instant, during the processing of the beam, such that the delay between:this instant, andthe entering of the portion Pj in the finishing mill, or alternatively, the entering of the portion Pj in the cooling machine, or alternatively the passage of the portion Pj at the intermediary position Os,is above a given duration threshold, for instance above 10, 20 or even 30s.

[0039] As above mentioned, in this embodiment, the input temperature Tm is measured before the beam comes out of the tandem mill 4. Thanks to that arrangement, there is a substantial time lapse for determining the speed setpoint v0*, before the beam enters the finishing mill, and then the cooling machine. More particularly, here, the input temperature Tm of the portion Pj of the beam is measured before this portion starts the last rolling pass in the tandem mill 4 (and so, the time lapse available for determining v0*, or a corrected version thereof is at least: the time taken for two tandem passes, plus transit from the tandem mill to the finishing mill). In practice, Tm may be measured, like here, before the last rolling pass in the tandem mill, and just after the last-but-one rolling pass in the tandem mill.

[0040] The portion here denoted Pj is the portion of the beam on which the input temperature Tm is measured. Pj may, like here, be located on a heading part of the beam, for instance on the first fourth of the beam (that is between the head of the beam and a position that is at 1 / 4 from the head of the beam, I being the length of beam). Pj may more particularly be a portion of the beam located a distance comprised between 1 / 20 and 1 / 4 pf the heading end of the beam. Pj is may be the fourth longitudinal sample (j=4), among the longitudinal samples Pj of the beam. Still, it is noted that the discretization of the beam into n longitudinal samples plays no significant role during the steps s1 to s5 described below, and more generally during the simulations made to determine values for the one or more cooling setpoints, here the speed setpoint v0*. Regarding the on-line control of the installation, this discretization plays a role when repeating steps s6, s7 and sc for the different, successive portions Pj of the beam (with i from 1 to n), to determine adjusted speed setpoints v* (adjusted respectively for these successive portions Pj).

[0041] Starting the determination of the speed setpoint in advance, as above explained, is beneficial in terms of available computation time for determining the setpoints. Yet, it requires to compute not only the evolution of the temperature during the water-cooling step, but also during the transfer of the beam, and possibly during rolling passes (with thermal exchanges with the working rolls, and heating caused possibly by friction and plastic strain), which makes the computation more complex.

[0042] Besides, the accuracy of the prediction for the self-tempering temperature TST may be reduced due to the fact that the thermal evolution is computed for an evolution period longer than just the cooling operation.

[0043] In the method for controlling the beam processing installation, a corrected speed setpoint vj* may be determined by:acquiring an intermediate temperature Tint,j, measured on the portion Pjof the beam considered (or, possibly, on another of the portions Pi) when this portion (or, possibly, said other portion Pi) of the beam passes at the intermediary position Os(in practice, measured by the second temperature sensor 8),computing the corrected speed setpoint vj* (or, possibly, vi*), based at least on the speed setpoint v0*, on the intermediate temperature Tint,j(or, possibly, Tint,i), and on a predicted intermediate temperature Tint,calc, predicted for the portion Pjof the beam when it passes at the intermediary position.

[0044] The predicted intermediate temperature Tint,calcis computed for instance in the course of one of the executions of step s4, during which the thermal evolution of the portion Pjiscomputed (in practice, during the last execution of step s4, or during an execution achieved for a value of the speed of the beam that equals v0*).

[0045] Using the measured intermediate temperature Tintj, and its predicted counterpart Tint, caic allows for readjusting the speed setpoint, should the predicted temperature Tint, caic departs from the measured one Tintj. In particular, if Tint, caic equals Tintj, the speed setpoint may be left uncorrected, while if Tint, caic departs from Tintj, the speed setpoint is corrected, with a correction all the higher than Tint, caic differs from Tintj.

[0046] This re-adjustment technique allows for overcoming the partial limitation mentioned above, relative to a possible reduction of the accuracy for the prediction of the temperature TST due to the in-advance triggering of the computation of the thermal evolution of the beam (i.e.: computation triggered while the beam is still substantially upstream of the cooling machine) and due to the fact that the actual value of the time for transferring the beam from the tandem mill to the entrance of the cooling machine may differs from the value of this transfer time employed for computing (predicting) the thermal evolution of the beam.

[0047] Here, the intermediary position Os, for this re-adjustment temperature measurement, is located between the intermediary mill 4, and the finishing mill 3.

[0048] More generally, the intermediary position Os is located between the upstream position Osand the cooling machine 30, more particularly between the upstream position Osand the last rolling strand of the rolling mill (that is between the upstream position Os and the finishing mill 3, here). The intermediary position Os is for instance at a distance, from the input of the cooling machine, which is from 3 to 20 m.In-advance determination of one or more cooling setpoints: detailed arrangements

[0049] As represented in figure 6, the control method comprises here, before the repetitive executions of step s4:- a step s’2 of computing an initial temperature field for the portion Pj, across a section of the beam, this temperature field being such that the surface temperature of the beam equals the measured input temperature Tm (figure 7)- a step s2 of determining cooling regimes, undergone by different faces of the beam, when water-cooled in the cooling machine 30.

[0050] Step s’2

[0051] In step s2’, a numerical simulation of a temporal evolution of a temperature field within a section of the beam is achieved, starting from a virtual initial state for which the temperature within the section is uniform (figure 7, left part), this initial temperature To being above 1000°C, or even above 1100°C, for instance equal to 1200 °C. the temporal evolution of the temperature field is then computed, by finite differences (for a 2-dimensionnal discrete representation of the section of the beam), for heat exchanges by air and radiation cooling atthe surface of the beam. Figure 8 shows the gradual decrease of the surface temperature Tsurfof the beam during this (virtual) cooling.

[0052] The temperature field, at the time step for which the computed surface temperature Tsurf equals the measured input temperature Tm (figure 7, centre and right diagrams), is selected, and is the starting point (the initial state) for the computation of the temporal evolution of the temperature within the portion Pj achieved in step s4 (that is for predicting the temporal evolution of the temperature of the portion Pj after this portion has passes the upstream position Oe).

[0053] This procedure enables to start the computation of step s4 from a temperature field that is realistic and in adequation with the measured input temperature Tm, while a temperature measurement is available only for a surface temperature (not for bulk temperatures, within the beam section).

[0054] step s2

[0055] Different cooling configurations can be employed, in the cooling machine, as the respective jets of the two cooling sections can be controlled independently, and as the flange jets and web jets can also be controlled independently. For instance, in a given cooling configuration, the flange(s) of the beam could be water-cooled by jets while the web is not, the web being thus cooled by air (and radiation), or possibly by remaining, run-off water (but not by direct water impingement). In an other configuration, the web only could be water cooled, not the flange(s). Or, the flange(s) could be water cooled in the first and second cooling sections 31, 32, while the web is water-cooled only in the second cooling section.

[0056] In step s2, for different flange and web faces of the beam, a cooling regime for the face considered is determined based on cooling configuration data which specify jets of the cooling machine are to be on and which of said jets are to be off, during the cooling of the beam 2 in the cooling machine.

[0057] Being able to use multiple different cooling configurations is very useful. Indeed, some geometrical imperfections of the beam output by the rolling mill, such as squareness defects, flatness defects or evenness defects can be corrected using dedicated cooling configurations (for which not all the jets are on). Besides, the fact that the jets of the second cooling section 32 are controllable independently from those of the first cooling section 31 gives more flexibility, regarding the choice of the thermal route followed by the beam (e.g.: progressive cooling, or more abrupt cooling), and thus more flexibility in terms of final mechanical properties for the beam.

[0058] Here, the cooling configuration data is predetermined (prior to the method described here), and remain unchanged during the execution of the method for controlling the cooling of the beam.

[0059] Repetitive executions of step s4

[0060] Step s’2 and s2 may be executed in advance, before measuring the input temperature Tm of the portion Pj of the beam (in step s1).

[0061] Immediately after step s1, a first execution of step s4 is achieved.

[0062] During step s4, the temporal evolution of the thermal field within the portion Pj, is computed, from the instant Tm is measured to a final, delivery of the beam after its cooling in the cooling machine. The maximum, reached over time t, by the surface temperature of the portion Pj, which is TST, is thus computed. This temporal evolution is computed for a speed, at which the portion Pj traverses the cooling machine 30, which equals a candidate speed setpoint vc*. The speed at which the beam traverses the cooling machine is a key parameter of the cooling process. Indeed, the longer the beam stays in the cooling machine, the higher the temperature decrease (for a given water flow). It is the control parameter employed here for controlling the cooling process, so as to obtain a desired self-tempering temperature for the beam portion Pj.

[0063] The cooling configuration and the water flow values influence also directly the strength of the cooling. Here, the cooling configuration and the water flow values remain unchanged, during the different executions of step s4. In other words, in this embodiment, only the candidate speed setpoint is modified from one execution of step s4 to the other, until the predicted TST temperature matches a target self-tempering temperature T*ST,j, for the portion Pj, which is tested in step s5.

[0064] Once a candidate speed point, for which TST matches T*ST,j, has been found, the speed setpoint v0* is set to equal this candidate speed point and the repetitions of step s4 stop. The repetitions of step s4 also stop if the total number of executions of step s4 reaches a maximum number of repetition allowed (equal to 10, here). In this case, the speed setpoint v0* equals the candidate speed setpoint for which the difference between TST matches T*ST,jwas the smallest.

[0065] The cooling configuration, and the water flow values, taken into account in step s4, are for instance preset prior to the executions of step s4:based on flatness and / or squareness corrections to be applied to the beam,and / or based on one or more metallurgical criteria, relative to the heat treatment applied to the beam during its quenching and self-tempering in the cooling machine 30.

[0066] When executing step s4, to compute the temporal evolution of the temperature field within the portion Pj, the powers (for instance in Watts per square meter), corresponding to the heat exchanges at the surface of the beam, are computed for the different phases of the beam processing. For a transfer from one position to another, in air, a cooling power corresponding to air cooling and radiation cooling is computed. When rolled in the tandem mill 3 or in the finishing mil, specific thermal models for that rolling operation are employed, for the heatexchanges. And when in the cooling machine, for each surface of the beam, the cooling power is computed depending on the cooling regime undergone by the face considered (for instance: direct water cooling, or air cooling, or run-off water cooling), and, when applicable, depending the water flow values for the relevant waterjets.

[0067] When computing the temporal evolution of the temperature field within the portion Pj, the fact that phase transformations (like austenite to ferrite, to bainite or to martensite transformations) may occur in the steel during its cooling is also taken into account.

[0068] From the results of the executions of step s4, two sensitivity coefficients KT and KCT are also determined. KT and KCT reflect, respectively, how much the temperature TST is modified when the temperature of the beam portion at the intermediary position Os varies, and how much the temperature TST varies when a transit time tc, taken for traversing the cooling machine, varies. KCT is thus computed according to the following formula:„ _ ^(TsT^tcKCT~—& Twhere Δ(TST)tcis a variation of the TST temperature caused by a variation Δtcof the transit time tc, while the intermediate temperature Tint,calc(as computed when executing step s4) is unchanged.

[0069] KCT can be computed directly from the results of the executions of step s4. Indeed, these executions correspond all to a same value of Tjnt.caic, but correspond to different values of the transit time tc, as they are executed for different values of the speed v at which the beam portion traverses the cooling machine. Indeed, the transit time tcequals L / v where L is the length of the cooling machine (length to be travelled to traverse the cooling machine, which is for instance from 3 to 15 m). Still, KCT may also be computed thanks to an additional numerical simulation of the thermal evolution of the beam achieved for a modified value of tc.

[0070] The sensitivity coefficient KT is computed according to the following formula:_ ^(TsT^TintKt~ ~hT int.calcwhere Δ(TST)Tintis a variation of the TST temperature corresponding to variation ΔTint,calcof the intermediate temperature Tint,calc, while the transit time tcis unchanged.

[0071] For computing of the coefficient KT, an additional computation of the thermal evolution of the temperature field for the portion Pj,, may be required, this additional computation being achieved for a higher value of the time for transferring the beam from the tandem mill to the finishing mill, in order to obtain a value of the calculated intermediate temperature Tjnt.caic different than the one obtained for previous numerical simulations of the thermal evolution of the beam.

[0072] Here, KT and KCT are both positive (computed taking absolute values of the variations of the quantities considered).

[0073] Adjustment of the speed setpoint

[0074] The speed setpoint v0*, and the sensitivity coefficients KT and KCT are determined, as above explained, while the portion Pj of the beam travels, in the beam processing installation, from the upstream position Oe to the intermediary position Os.

[0075] Then, when the portion Pj passes at the intermediary position Os, its intermediate temperature Tint,jis measured by the temperature sensor 8, in step s6, and the corrected speed setpoint vj* is then computed, in step s7, by correcting the speed setpoint v0* depending on Tint,jand Tint,calc.

[0076] Then, in step sc, the electronic system 10 sends the corrected speed setpoint v* to the low-level controller 13, which controls then the speed of rotation of the rolls of the finishing mill 4 so that the speed at which the beam travels through the cooling machine matches the corrected speed setpoint Vj* when sample Pj traverses the cooling machine.

[0077] In step s7, the corrected speed setpoint v* is computed according to the formula below:=IXrC^intj—Tint.caic) +vjvoACTwith ΔT*ST,j= T*ST,j- T*ST,j,corran optional correction of the target self-tempering temperature T*ST,j.

[0078] The target self-tempering temperature T*ST,jfor the portion Pj of the beam may, like here, be equal to a global target self-tempering temperature T*STfor the beam 2.

[0079] The global target self-tempering temperature T*ST may be entered by an operator using the terminal 12. It may be computed in advance (either by the electronic system 10, or by another electronic device) using a metallurgical model, and based on: initial properties of the beam (chemical composition of the steel, and possibly one or more dimensions), target properties for the beam after its processing in the installation 1 (eg: mechanical properties and / or microstructural properties).

[0080] When the target self-tempering temperature is uniform over the beam’s length, like here, individual target self-tempering temperatures for the different beam portions Pi, i=1,...,n are equal to each other, and equal to the global target self-tempering temperature T*ST: T*ST,i= T*STfor i from 1 to n.

[0081] In this embodiment, the target self-tempering temperatureis corrected (meaning that ΔT*ST,jis not null) if the measured, intermediate temperature Tint,jof the portion Pj is below the so-called Ar3 temperature (that is below the temperature for an austenite to ferrite phase transformation during a temperature decrease). In this case, the correction ΔT*ST,jis set to a positive value (in other words, T*ST,j,corris below T*ST,j), the correction increasing for instance with the difference Ar3 - Tint,j. This reduction of the self-tempering temperature allowsfor compensating for a strength reduction caused by ferrite formation below the Ar3 temperature. Conversely, if the intermediate temperature Trntj is above Ar3,is null, here.

[0082] The correction applied in step s7 thus allows to adjust the speed setpoint:based on the actual, measured intermediate temperature Tintj, compared to the intermediate temperature Tint,calcthat was computed in advance by numerical simulation, to somehow re-align the temperature predictions,and also based on a local adjustment of the target self-tempering temperature, for the beam portion considered, in view of the actual, measured intermediate temperature Tint,jfor that portion.

[0083] As represented in figure 6, the adjustment procedure above described is executed repeatedly for the different beam portions Pj, i=1,...,n. Steps s6, s7 and scare executed repeatedly, successively for the different beam portions Pi, with i from 1 to n, as they pass, one after each other, at the intermediary position Os.

[0084] Namely, for the portion Pi(with i from 1 to n), the temperature Tint,iof that portion is measured by the second temperature sensor 8 when the portion Pipasses at the intermediary position Os.

[0085] Then, a locally adjusted speed set point v* is computed for that portion according to the formula below:“7=“7 T — [Kr(Tinti — Tint caic^ + AT$Y JvtvoKCTwith ΔT*ST,i= T*ST,i- T*ST,i,corran optional correction of a target self-tempering temperaturehere, ΔT*ST,i=T*ST,i,corr, and this correction is computed for each portion Piin the same manner as above explained for the portion Pj.

[0086] Adjusting speed setpoints individually, for each portion of the beam, based on the temperature measured for that portion just before the finishing mill and subsequent cooling, is highly beneficial, as the temperature along the beam is not uniform, at this point of the beam processing. Figure 8 illustrates this non-homogeneity of the temperature along the beam, just before it enters the finishing mill. In the case of figure 8, n=32.

[0087] It is noted that the adjustment of the speed setpoint is executed n times, for all the successive portions of the beam. Conversely, the determination of the uncorrected, initial speed setpoint v0* is achieved for one portion of the beam only, namely for the portion Pj. This overall arrangement allows for controlling the cooling conditions in an optimal way for each portion, as temperature variations along the beam are taken into account, while executing the highly demanding computation of v0* just once (or possible twice, or a few times, but not n times). This is beneficial, as the time available for computing v0* is limited (by the transfer time between Oeand Os, in the process), and would often not be sufficient for computing directely,by iterative numerical simulations, one speed set point for each portion (each longitudinal sample) of the beam.

[0088] In this embodiment, the portion Pj for which the input temperature Tin is measured, and for which the iterative simulations are executed is, is P4(that is the fourth portion, when starting from the beam head), the beam being divided into 32 portions (n=32).

[0089] Determining the speed setpoint v0* for a portion that is, like here, located in a first, heading zone of the beam is beneficial. Indeed, it allows to have more time for computing v0*, as this computation time is limited by the time lapse between measuring the input temperature for the portion Pj considered, and having the head portion of the beam, Pi, entering the finishing mill. Besides, having the portion Pj that is not completely at the head of the beam (that is not Pi) is beneficial, as it allows avoiding boundaries effects (computation simulation being possibly less accurate for the head portion Pi than for P4, for instance).Exemplary test results

[0090] Figure 9 represents values of a difference AT between the actual self-tempering temperature, reached in practice after the cooling machine, and the desired, target selftempering temperature T*ST,i,corr. These results are obtained when controlling the beam processing installation according to the above-described method. In figure 9, each group of point, that is each column, corresponds to one beam, the different points of the group corresponding to the different portions of the beam. For each beam, a box plot is also represented, to show the spread of the distribution quartiles. Figure 9 represents test results for 20 different beams. Figure 9 illustrates that the instant control method allows for an accurate control of the self-tempering temperature reached during the thermal treatment of the beams.

Claims

CLAIMS1. A method for controlling a beam processing installation (1) which comprises a rolling mill, and a cooling machine (30) arranged downstream of the rolling mill, along a path (x) followed by a beam (2) in the beam processing installation, the beam being water-cooled when the beam traverses the cooling machine, the method comprising:s1: acquiring an input temperature (Tm) of a steel beam (2), measured on a portion (Pj) of beam before said portion of the beam enters the cooling machine,s4: Computing a temperature TST of said portion of the beam, which is a temperature predicted for the portion of beam after the portion of the beam has traversed the cooling machine (30), the temperature TST being computed taking into account the input temperature (Tm) and one or more candidate cooling setpoints (vc*) for the cooling of the beam in the cooling machinethe step s4 being executed iteratively to determine one or more cooling setpoints (v0*) such that the temperature TST computed in step s4 matches a target self-tempering temperature T*ST,j,sc: controlling the beam processing installation (1) based on said one or more cooling setpoints (v0*), or based on one or more corrected cooling setpoints (v*) determined from the one or more setpoints (v0*).

2. A method according to claim 1 wherein, in step s1, the input temperature (Tm) of the beam is measured on said portion of the beam before said portion exits the rolling mill.

3. A method according to claim 1 or 2, wherein the beam processing installation (1) is controlled based on the one or more corrected cooling setpoints (v*) in step sc, wherein the input temperature (Tm) is measured on said portion (Pj) of the beam when said portion passes at an upstream position (Oe) located upstream of the cooling machine, and wherein the method further comprises:acquiring an intermediate temperature (Tintj), measured on said portion (Pj) of the beam or on another part of the beam (Pj), when said portion or said other part of the beam passes at an intermediary position (Os), located between said upstream position (Oe) and the cooling machine (30),Determining the one or more corrected cooling setpoints (Vj*) based at least on the one or more setpoints (v0*) and on the intermediate temperature (Tintj).

4. A method according to claim 3, wherein the rolling mill comprises a main mill (4) and a subsequent finishing mill (3) which is the last rolling stand traversed by the beam (2) before coming out of the rolling mill, and wherein the intermediary position (Os) for the measurement of the intermediate temperature (Tintj) is located between the main mill (4) and the finishing mill (3), while the input temperature (Tin) of said portion (Pj) is measured before a last rolling pass of said the portion in the main mill (4).

5. A method according to claim 3 or 4, wherein:- the one or more cooling setpoints comprise a speed setpoint v0* for a speed (v) at which the beam traverses the cooling machine,- the method comprising computing two sensitivity coefficients KT and KCT reflecting, respectively, how much the temperature TST is modified when the temperature of the beam at the intermediary position (Tintj) varies, and how much the temperature TST varies when the speed (v) of the beam varies, or when a transit time taken for traversing the cooling machine with said speed (v) varies,- the method comprising computing a corrected speed setpoint vj* based on at least on: the speed setpoint v0*, the two sensitivity coefficients KTand KCT, the intermediate temperature (Tint,j) and a predicted intermediate temperature (Tint,calc) for said portion (Pj) of the beam when said portion of the beam passes at the intermediary position.

6. A method according to claim 5, wherein the predicted intermediate temperature (Tmt, caic) is computed in the course of one of the executions of step s4.

7. A method according to claim 5 or 6, wherein the coefficient KCT reflects how much the temperature TST varies when the transit time taken for traversing the cooling machine varies, the corrected speed setpoint v* being computed according to the following formula:L / v*j= L / v*o+ (1 / KCT)[KT(Tint,j− Tint,calc) +vjvoKCTwhere:- L is a length to be travelled to traverse the cooling machine (30),- Tintj is the intermediate temperature,- Tint, caic is the predicted intermediate temperature and- AT*ST,jis an optional correction of the target self-tempering temperature T*ST,j.

8. A method according to anyone of claim 7, wherein AT*ST,jis computed depending on the measured, intermediate temperature Tintj, AT*ST,jbeing equal tozero if the intermediate temperature Tintj is above a transition temperature Ar3 for an on-cooling austenite to ferrite transformation, and having a non-zero value if Trntj is below Ar3.

9. A method according to anyone of claims 3 to 8, wherein the method comprises: for each of different successive parts of the beam Pj with i from 1 to n, one of which being said portion (Pj) of the beam:- measuring a temperature Tint of the part Pj considered when the part Pj passes at said intermediary position (Os),- computing one or more locally-adjusted cooling setpoints (v*) for the part Pj of the beam, based at least on:- said one or more cooling setpoints (v0*),- and the temperature Tintj,- controlling the beam processing installation (1) so as to cool the part Pj, in the cooling machine, according to the one or more locally-adjusted cooling setpoints (v*) computed for the part Pj.

10. A method according to claims 9 and 7, or according to claims 9 and 8, wherein, for each of the successive parts of the beam Pj, with i from 1 to n, the locally-adjusted cooling setpoints computed for the part Pj of the beam comprise a locally-adjusted speed setpoint v* which is computed according to the following formula:L / v*i= L / v*o+ (1 / KCT)[KT(Tint,i- Tint,calc) +vlvoKCTwhere ΔT*ST,iis an optional correction of a target self-tempering temperaturefor the part Pj of the beam.

11. A method according to anyone of the preceding claims, wherein the temperature TST determined in step s4 is the maximum over time reached by the temperature of the surface of said portion of the beam after said portion of the beam has exited the cooling machine.

12. A method according to anyone of the preceding claims, wherein said portion (Pj) of the beam is located within a heading, first fourth of the beam (2), a distance between said portion and a head of the beam being optionally higher than l / 20 where l is the length of the beam.

13. An electronic system comprising at least a processor and a memory, configured for executing the method according to anyone of the preceding claims.

14. A beam cooling installation comprising:- the electronic system of the preceding claim, andthe cooling machine for water-cooling the beam.(it may comprise also the temperature sensor, the additional temperature sensor, an actuator or a low-level controller for controlling the speed with which the beam moves)15. A computer program comprising instructions whose execution on a computer makes the computer to execute the method according to anyone of claims 1 to 12.

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