ROLLING WITH MINIMIZATION OF THE REDUCTION IN BENDING FORCE ON PIPELINE

Description

field of technology

[0001] The present invention is based on an operating method for a rolling stand for rolling a flat metal rolling stock, which has a rolling stock head, wherein the rolling stand comprises at least work rolls and backup rolls, wherein the work rolls are mounted in work roll chocks and a bending system which presses the work roll chocks apart acts on the work roll chocks, wherein the rolling stock head reaches the rolling stand at an actual penetration time, wherein a base setpoint is fed to a bending controller and the bending controller determines a resulting setpoint taking into account the base setpoint, wherein an actual value of the bending force is further fed to the bending controller, wherein the bending controller determines a base manipulated variable for the bending system based on the resulting setpoint and the actual value, so that when the bending system is controlled with the base manipulated variable, the actual value is brought as close as possible to the resulting setpoint, wherein the bending controller determines the resulting setpoint from a stabilization time which lies after the penetration time,with additional consideration of the actual rolling force occurring during rolling of the flat rolled stock.

[0002] The present invention further relates to a rolling unit for rolling a flat metal rolling stock, which has a rolling stock head, wherein the rolling unit comprises a rolling stand and a bending controller, wherein the rolling stand comprises at least work rolls and backup rolls mounted in work roll chocks, wherein the rolling stand comprises a bending system for pressing the work roll chocks apart, wherein the bending controller controls the bending system, wherein the rolling stand and the bending controller interact with one another during operation of the rolling unit in such a way that they carry out such an operating method. State of the art

[0003] Rolling mills for rolling flat stock are often designed as four-high stands (i.e., a rolling mill with work rolls and backup rolls) or as six-high stands (i.e., a rolling mill with work rolls, backup rolls, and intermediate rolls arranged between the work rolls and backup rolls). Metal strip is often rolled in them, and sometimes heavy plate.

[0004] Before rolling a particular rolling stock, a pass schedule calculation is performed. During the pass schedule calculation, setpoints are determined for the individual actuators of the roll stand, with which the actuators are to be operated during rolling of the respective rolling stock. The setpoints include at least the setting or the rolling force. They usually also include a setpoint – referred to as the base setpoint – for the bending force with which the work roll chocks, and thus also the work rolls, are to be pressed apart. The bending force can be used to influence the contour, profile, and flatness of the rolled stock.

[0005] Other actuators may also be present to influence contour, profile, and flatness, such as work roll shifting or local cooling. In stainless steel rolling mills, strip edge lubrication may also be used to influence the profile. However, these other actuators are not relevant within the scope of the present invention.

[0006] The pass schedule calculation is performed by a higher-level control system, commonly referred to as an L2 system in technical circles. The setpoints determined during the pass schedule calculation are passed from the control system to lower-level controllers, which implement real-time control during rolling of the rolled stock. The entire controller system is commonly referred to as an L1 system in technical circles. The setpoints are specified before the rolled stock reaches the roll gap between the work rolls of the rolling stand, i.e., before the first pass occurs.

[0007] For example, the setpoint for the bending force—the base setpoint—is specified by a bending controller. This setpoint is modified by various correction variables during the rolling of the flat rolled stock. One of the correction variables is an additional setpoint, which is determined as a function of the rolling force and—similar to an AGC—is intended to compensate for changes in roll bending that occur due to a change in the rolling force. However, this additional setpoint is only applied after the instabilities that arise during the initial pass have been corrected by the controllers of the L1 system.

[0008] The bending controller therefore determines a base control variable for the bending system based exclusively on the base setpoint and the actual bending force value during a tapping period that begins before the tapping time and ends after the tapping time. The controller controls the bending system according to the determined base control variable. The determination is carried out in such a way that the actual bending force value is always as close as possible to the base setpoint.

[0009] During piercing, the bending force (i.e., its actual value) drops. The bending controller attempts to compensate for this drop as quickly as possible. However, it takes several hundred milliseconds, sometimes up to 500 milliseconds, for complete compensation to occur.

[0010] The drop in bending force negatively influences the resulting contour and the associated profile as well as the flatness of the rolled stock. However, this can often be accepted. On the other hand, the drop in bending force leads to a brief unstable condition, the effects of which on the strip travel cannot always be predicted. In particular, it can happen that a hook forms in the rolled stock on the exit side of the roll stand. In some cases, the hook is so large that it hits the side guides on the exit side of the roll stand. This can damage the side guides and, in individual cases, even cause the rolling stock head to jam. In this case, the rolling stock head is no longer transported further, while the roll stand continues to push the rolling stock forward. This causes the rolling stock to bulge (so-called over-collapse).This leads at least to an unscheduled, prolonged interruption of the operation of the rolling stand, and sometimes even to considerable damage to the rolling stand or downstream equipment.

[0011] DE 10 2006 059 709 A1 discloses an operating method for a rolling stand for rolling flat metal stock. During a period of time during which a rolling stock head has not yet reached the rolling stand, the work rolls of the rolling stand are subjected to a bending force that is at least as great as the balancing force of the upper work roll and the upper backup roll (and, if applicable, additional rolls arranged between the upper work roll and the upper backup roll). From the moment the rolling stock head reaches the rolling stand, the bending force is determined according to the technological requirements of the rolling process. The resulting bending force can be greater or smaller than the minimum force and also greater or smaller than the balancing force.

[0012] JP S57 050 207 A discloses an operating method for a rolling stand for rolling flat metal stock. The method involves calculating in advance the time at which a rolling stock head reaches the rolling stand. From this point onward, a bending force is applied to the work rolls of the rolling stand by means of a bending system.

[0013] JP S59 061 512 A discloses an operating method for a rolling stand for rolling flat metal stock. A looper upstream of the rolling stand detects whether the rolling stock is subjected to tension on the inlet side of the rolling stand. This detects the initial pass and the final pass. During the initial pass, the bending forces acting on the work rolls of the rolling stand are adjusted such that the thickness of the rolling stock decreases toward its lateral edges. During the final pass, the bending forces are adjusted in a similar manner as soon as a drop in the load on the looper, and thus the discharge of the flat rolling stock from the upstream rolling stand, is detected.

[0014] From DE 43 31 261 A1, an operating method for a rolling stand for rolling a flat metal rolling stock is known, in which the work rolls can be subjected to positive and negative bending forces of different magnitudes by means of a bending system. Summary of the invention

[0015] The object of the present invention is to provide possibilities by means of which the unstable state can be avoided as far as possible.

[0016] The object is achieved by an operating method having the features of claim 1. Advantageous embodiments are the subject of dependent claims 2 to 7.

[0017] According to the invention, an operating method of the type mentioned at the outset is designed in that during a tapping period which begins before the actual tapping time and ends after the actual tapping time, an additional setpoint is fed to the bending controller in addition to the basic setpoint, so that the bending controller determines the resulting setpoint during the piercing period taking into account not only the basic setpoint but also the additional setpoint, and as a result the actual value of the bending force is greater than the basic setpoint immediately before the actual piercing time, and / or by switching an additional manipulated variable to the basic manipulated variable, a resulting manipulated variable is determined, which is fed to the bending system and the bending system is thereby controlled in such a way that the resulting manipulated variable is greater than the basic manipulated variable, and / or the basic manipulated variable and a minimum manipulated variable are fed to a selection element and the selection element feeds the maximum of the basic manipulated variable and the minimum manipulated variable to the bending system.

[0018] If the actual value of the bending force immediately before the piercing time is greater than the base setpoint, the bending force begins to drop at a higher level. This reduces the probability and extent of a hook forming. If the resulting manipulated variable is greater than 0, the hydraulic valve used to supply hydraulic fluid to the bending system is at least partially open at the piercing time. It therefore does not have to be opened at the piercing time. Piercing the rolled stock therefore leads to a smaller drop in the bending force. This also reduces the probability and extent of a hook forming. A resulting manipulated variable greater than 0 can be ensured by appropriately specifying the additional manipulated variable. For example, the additional manipulated variable can be set to 110% of the maximum possible value.Even if the bending controller determines the minimum possible value as the base control variable, the hydraulic valve is open to at least -100% +110% = 10%.

[0019] As an alternative to specifying the additional manipulated variable, the minimum manipulated variable can also be supplied directly. In this case, if the hydraulic valve is already opened by the base manipulated variable and the minimum manipulated variable is smaller than the base manipulated variable, the hydraulic valve remains open without changing its opening position. Regardless of the value of the base manipulated variable, the hydraulic valve is always opened at least as far as specified by the minimum manipulated variable. By selecting the appropriate minimum manipulated variable (i.e., greater than 0), it can be ensured in this case too that the hydraulic valve is at least partially open at the time of tapping.

[0020] It is possible for the additional setpoint and / or the additional manipulated variable and / or the minimum manipulated variable to be abruptly switched to their maximum value at the start of the tapping period. It is also possible for the additional setpoint and / or the additional manipulated variable and / or the minimum manipulated variable to be abruptly reduced to zero at the end of the tapping period. Preferably, however, the additional setpoint and / or the additional manipulated variable and / or the minimum manipulated variable are increased strictly monotonically from 0 to their maximum value with a finite gradient from the start of the tapping period and / or decreased strictly monotonically from their maximum value to zero with a finite gradient at the end of the tapping period.This results in smoother transitions, which place less strain on the bending controller, the hydraulic valve and the bending system in particular and also lead to a more stable transition, particularly when lowering the additional setpoint and / or the additional control variable and / or the minimum control variable to 0.

[0021] Options for raising and lowering with a finite gradient are generally known and familiar to those skilled in the art. For example, a ramp can be used, or a binary switching process can be smoothed using appropriate filtering.

[0022] Typically, an expected tapping time is determined by tracking the rolling stock. In this case, the start of the tapping period is preferably a predetermined time period before the expected tapping time.

[0023] The predetermined early time period is, for example, dimensioned such that the additional setpoint and / or the additional manipulated variable and / or the minimum manipulated variable reach their maximum value at a time whose distance from the expected piercing time is at least as large as an error tolerance between the actual and the expected piercing time. The error tolerance can be readily estimated by a person skilled in the art based on the inaccuracies in the path tracking of the rolling stock head known to them. Typically, the predetermined time period is in the range between 0.5 s and 2.0 s, in particular between 0.8 s and 1.5 s, for example approximately 1.0 s.

[0024] It is possible for the end of the tapping period to be delayed by a predetermined amount of time after the expected tapping time. Preferably, however, the end of the tapping period is delayed by a predetermined amount of time after the actual tapping time. The actual tapping time can be easily detected, for example, due to an abrupt increase in the actual rolling force or the rolling torque actually applied by the work roll drives.

[0025] In both cases, the predetermined delayed time period is dimensioned such that the additional setpoint and / or the additional manipulated variable and / or the minimum manipulated variable maintain their maximum value until a point in time whose distance from the expected or actual piercing time is a predetermined value. From this point in time, the additional setpoint and / or the additional manipulated variable and / or the minimum manipulated variable can then be reduced to 0. The specified value – i.e., the time period during which the additional setpoint and / or the additional manipulated variable and / or the minimum manipulated variable are still maintained at their maximum value – is determined by the design and dimensioning of the bending system. The value is usually in the range between 0.1 s and 1.0 s, in particular between 0.2 s and 0.6 s, for example 0.3 s or 0.4 s.

[0026] Preferably, a maximum value of the additional setpoint and / or the additional manipulated variable and / or the minimum manipulated variable is determined before rolling the flat rolled stock depending on the properties of the rolled stock and / or depending on an expected rolling force. This allows the corresponding maximum value to be optimally matched to the specific rolling pass to be carried out. Alternatively or additionally, it is possible for the maximum value of the additional setpoint and / or the additional manipulated variable and / or the minimum manipulated variable to be determined such that the resulting manipulated variable assumes its maximum possible value immediately before the actual rolling start time. This procedure can be particularly useful for the front stands of a multi-stand finishing train or for a rolling stand for rolling heavy plate (plate mill).

[0027] Preferably, the additional setpoint and / or the additional manipulated variable and / or the minimum manipulated variable are determined in such a way that a drop in the actual value of the bending force at the actual piercing time, which would occur without the additional setpoint and / or the additional manipulated variable and / or the minimum manipulated variable, is compensated by at least 50%. Therefore, if the base setpoint has the value X and, without the additional setpoint and / or the additional manipulated variable and / or the minimum manipulated variable, a drop to the value Y would occur at the piercing, the additional setpoint and / or the additional manipulated variable and / or the minimum manipulated variable are preferably determined in such a way that the bending force drops to a maximum value of (X+Y) / 2, preferably even only to a value greater than (X+Y) / 2. It is particularly preferred if the bending force drops to a maximum of the base setpoint, i.e., to the value X.

[0028] The object is further achieved by a rolling unit having the features of claim 8. According to the invention, in a rolling unit of the type mentioned at the outset, the rolling stand and the bending controller interact with one another during operation of the rolling unit in such a way that they carry out an operating method according to the invention. Short description of the drawings

[0029] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of the embodiments, which are explained in more detail in conjunction with the drawings. Herein, in schematic representation: FIG 1a rolling stand from the side before rolling a rolling stock, FIG 2the rolling stock from FIG 1 from the side during the initial pass, i.e. at the beginning of rolling the rolled material, FIG 3 the rolling stand of FIG 1 from the side during rolling of the rolling stock, FIG 4 a part of the rolling stand of the FIG 1 bis 3 from the front, FIG 5 a part of a control structure for the rolling stand of the FIG 1 bis 4 , FIG 6 a time diagram for an operating procedure for the rolling stand of the FIG 1 bis 4 according to the prior art, FIG 7 a part of a control structure for the rolling stand of the FIG 1 bis 4 according to a first embodiment of the present invention, FIG 8 shows a time diagram for an operating method for the rolling stand of the FIG 1 bis 4 according to the first embodiment of the present invention, FIG 9 shows part of a control structure for the rolling stand of the FIG 1 bis 4 according to a second embodiment of the present invention, FIG 10 a time diagram for an operating method for the rolling stand of the FIG 1 bis 4 according to the second embodiment of the present invention and FIG 11 a part of a control structure for the rolling stand of the FIG 1 bis 4 according to a third embodiment of the present invention. Description of the embodiments

[0030] According to the FIG 1 bis 4 A rolling stand 1 comprises work rolls 2 and backup rolls 3. This represents the minimal configuration of the rolling stand 1 within the scope of the present invention. In addition, the rolling stand 1 could further comprise intermediate rolls. In this case, the intermediate rolls would be arranged between the work rolls 2 and the backup rolls 3. The work rolls 2 have, as shown in FIG 4 Bearing journals 4, with which the work rolls 2 are mounted in work roll chocks 5. Analogously, the backup rolls 3 have bearing journals 6, with which the backup rolls 3 are mounted in backup roll chocks 7.

[0031] A rolling force F is applied to the backup roll chocks 7 and thus also to the backup rolls 3 during rolling of a rolled stock 8. The rolling force F is transferred via the backup rolls 3 to the work rolls 2. This is generally known to those skilled in the art. The rolled stock 8 itself consists of metal, for example steel or aluminum. It is a flat rolled stock, for example a strip or a heavy plate. It has a rolling stock head 9. The rolling stock head 9 is the area of ​​the rolling stock 8 that is rolled first in the rolling stand 1. Accordingly, in the FIG 1 bis 3 where x denotes a transport direction of the rolling stock 8.

[0032] The rolling stand 1 further comprises a bending system 10. The bending system 10 typically consists of at least two hydraulic cylinder units 11, 12, which act on the work roll chocks 5 on the drive side and the operator side, thereby pushing the work roll chocks 5 apart. The bending system 10 serves to adjust the contour, profile, and flatness of the rolled stock 8. In some cases, several hydraulic cylinder units 11, 12 act on each of the work roll chocks 5. In this case, correspondingly more hydraulic cylinder units 11, 12 are present.

[0033] The rolling stand 1 is designed according to FIG 5 controlled by a control structure. The control structure typically comprises a control device 13 and, in any case, a bending controller 14.

[0034] The control device 13 is a higher-level control device that acts as an L2 system, i.e., it determines the setpoints for subordinate controllers as part of a pass schedule calculation. FIG 5 In this regard, only a single controller is shown, namely a bending controller 14. In practice, of course, additional controllers are also present. However, within the scope of the present invention, only the bending controller 14 is relevant. Therefore, only the bending controller 14 is shown, and only the bending controller 14 will be explained below.

[0035] The pass schedule calculation is carried out for the rolling stock 8 before the rolling stock 8 is rolled in the rolling stand 1 (see FIG 1 ). Within the scope of the pass schedule calculation, the control device 13 determines setpoints for the adjustment of the rolling stand 1, if applicable, the roll displacement, and others. In particular, within the scope of the pass schedule calculation for rolling the rolled stock 8 in the rolling stand 1, the control device 13 determines a base setpoint FBB* of the bending force. The base setpoint FBB* can be a single, singular, time-constant value. Alternatively, separate base setpoints FBB* can be determined for different sections of the strip to be rolled. In this case, the base setpoint FBB* varies over time.

[0036] The base setpoint FBB* is sent to the bending controller 14 from a time t1 (see FIG 6 ). The time t1 is referred to below as the target time t1. At the target time t1, the rolling stock head 9 has not yet reached the rolling stand 1 (see FIG 1 ). The basic setpoint FBB* is generally supplied by the control device 13. In principle, however, the basic setpoint FBB* can also be supplied to the bending controller 14 by other means.

[0037] An actual value FB of the bending force is also fed to the bending controller 14. Methods for recording or determining the actual value FB are generally known to those skilled in the art. For example, to determine the bending force FB, the working pressures pP, pT in the working chambers of the hydraulic cylinder units 11, 12 can be mathematically linked in conjunction with the effective working surfaces.

[0038] The bending controller 14 controls the bending system 10. In particular, the bending controller 14 determines a base manipulated variable SB for the bending system 10 based on a resulting setpoint FB* and the actual value FB. The base manipulated variable SB is determined in such a way that the actual value FB is as close as possible to the resulting setpoint FB*, provided the bending system 10 is controlled with the base manipulated variable SB. The bending controller 14 determines the resulting setpoint FB* using at least the base manipulated value FBB*. Temporarily, the resulting setpoint FB* can be identical to the base manipulated value FBB*. However, at least temporarily, other variables are also included in the resulting setpoint FB*. This will become apparent later. Using the base manipulated variable SB, the bending controller 14 determines a resulting manipulated variable SR. Temporarily, the resulting manipulated variable SR can be identical to the base manipulated variable SB. During normal operation, i.e.During the stable rolling of the flat rolled stock 8, the bending controller 14 outputs the resulting manipulated variable SR to the bending system 10 and thereby controls the bending system 10.

[0039] The bending controller 14 determines, in particular, an opening state for hydraulic valves 15, 16 as the base control variable SB and also as the resulting control variable SR. These valves supply a high working pressure pP (pump pressure) and a low working pressure pT (tank pressure) to the working chambers of the hydraulic cylinder units 11, 12. The hydraulic valves 15, 16 are generally continuously adjustable valves, i.e., proportional valves or servo valves.

[0040] Based on the specification of the base setpoint FBB*, the bending controller 14 initially determines a relatively large base manipulated variable SB starting at the specification time t1, possibly even a maximum possible value MAX of the base manipulated variable SB (and thus also of the resulting manipulated variable SR). However, it reduces the base manipulated variable SB back to 0 or almost to zero as soon as the actual value FB of the bending force is adjusted as closely as possible to the base setpoint FBB*. In this context, it should also be noted that, within the scope of the present invention, positive values ​​of the base manipulated variable SB correspond to an increase in the bending force (up to a technically maximum possible value), while negative values ​​correspond to a decrease in the bending force.

[0041] At a time t2, the rolling stock head 9 reaches the rolling stand 1 (see FIG 2 ). The time t2 is referred to below as the actual piercing time t2. The actual piercing time t2 can be easily detected, for example by detecting a significant increase in the rolling force F or a rolling torque of a drive of the work rolls 2. During the piercing, the bending force FB drops significantly. Drops of 50% and more are quite possible. Within a relatively short time, the bending controller 14 opens the hydraulic valves 15, 16 by specifying a corresponding base manipulated variable SB and thereby resets the bending force to its resulting setpoint FB*. The time required to restore the bending force is usually well under 1 s, for example approximately 500 ms.

[0042] After the actual piercing time t2, the rolling of the rolling stock 8 takes place (see FIG 3 ). Immediately after the penetration time t2, however, a comparatively unstable state of roll stand 1 arises, which is corrected by the various controllers assigned to roll stand 1 (including the bending controller 14). At a stabilization time t3, a stable state is reached again. The time interval between the stabilization time t3 and the penetration time t2 is determined by the design and dimensioning of the roll stand. It is generally in the range of 1 s or less, for example, 500 ms or even less.

[0043] Starting at stabilization time t3, a correction value δFB* is determined using a determination unit 17. The correction value δFB* is applied to the base setpoint FBB*. Starting at stabilization time t3, the resulting setpoint FB* is thus the sum of the base setpoint FBB* and the correction value δFB*. The correction value δFB* is determined in the determination unit 17 as a function of the (actual) rolling force F. The determination unit 17 thus implements a so-called DPC (= "bending AGC").

[0044] If necessary, additional correction variables can be fed to the bending controller 14 starting at stabilization time t3, for example, from a flatness control or a profile feedback control. Correction based on thermal influences is also possible. However, at least the compensation of rolling force-related influences is provided.

[0045] At a time t4, a rolling stock foot 18 (see FIG 1 bis 3 ) of the rolled stock 8 from the rolling stand 1. Analogous to the actual penetration time t2, the actual tapping time t4 can also be easily detected, in particular by detecting a significant drop in the rolling force F or a rolling torque of a drive of the work rolls 2. The time t4 is referred to below as the tapping time. As a rule, the switching of the correction value δFB* to the base setpoint FBB* is frozen shortly before the tapping time t4, i.e. the last determined correction value δFB* is retained. However, this is of secondary importance within the scope of the present invention.

[0046] The procedure of the prior art explained above is essentially retained, but modified and supplemented according to the invention. A possible modification and supplementation is described below in connection with the FIG 7 and 8explained in more detail, a further possible modification and addition in connection with the FIG 9 and 10 and yet another modification and addition in connection with FIG 11 .

[0047] Within the framework of the design according to the FIG 7 and 8 During a piercing period, an additional setpoint FBZ* is supplied to the bending controller 14 in addition to the base setpoint FBB*. The additional setpoint FBZ* can be supplied to the bending controller 14 by the control device 13. However, it can also be specified in another way, for example, by an operator (not shown).

[0048] The penetrating period begins at a start time t5 and ends at an end time t6. The start time t5 is before the actual penetrating time t2. The end time t6 is after the actual penetrating time t2. It is usually before the stabilization time t3. It can also coincide with the stabilization time t3. At least as a rule, however, the end time t6 should not be after the stabilization time t3. This is because, from the stabilization time t3 onwards, the purpose of the control systems of roll stand 1 is no longer to ensure a stable start to rolling. Rather, the purpose of the control systems of roll stand 1 is to roll the rolling stock 8 to its target properties, in particular to its target thickness and its target profile or its target contour. Specifying the additional setpoint FBZ* beyond the stabilization time t3 would be disadvantageous in this regard.

[0049] The additional setpoint FBZ* is applied to the base setpoint FBB*. Feeding the additional setpoint FBZ* to the bending controller 14 causes the bending controller 14 to determine the sum of the base setpoint FBB* and the additional setpoint FBZ* as the resulting setpoint FB*. The base manipulated variable SB is thus determined in such a way that the actual value FB of the bending force approximates this sum as closely as possible. Due to the modified setpoint (FBB*+FBZ* instead of FBB*), the actual value FB of the bending force immediately before the piercing time t2 is greater than the base setpoint FBB*.

[0050] Within the framework of the design according to the FIG 9 and 10During the tapping period, an additional manipulated variable SZ is added to the base manipulated variable SB. The sum of the base manipulated variable SB and the additional manipulated variable SZ is thus supplied to the hydraulic valves 15, 16 as the resulting manipulated variable SR. As a result, the resulting manipulated variable SR immediately before the actual tapping time t2 is greater than the base manipulated variable SB. The additional manipulated variable SZ can be supplied to the bending controller 14 by the control device 13. However, it can also be specified in another way, for example, by an operator (not shown).

[0051] When designing according to FIG 9 The basic control variable SB and the additional control variable SZ are added on the output side of the bending controller 14. In the design according to FIG 11 On the output side of the bending controller 14, the base manipulated variable SB and a minimum manipulated variable SM are fed to a selector 19. The selector 19 selects the larger of the manipulated variables SB and SM supplied to it and feeds the selected manipulated variable to the bending system 10 as the resulting manipulated variable SR. With this configuration, it is not necessary to specify the additional setpoint FBZ*, since the bending controller 14 can cause the resulting manipulated variable SR to be greater than the minimum manipulated variable SM. However, the bending controller 14 cannot cause the resulting manipulated variable SR to be smaller than the minimum manipulated variable SM. The minimum manipulated variable thus defines a minimum control state of the bending system 10.

[0052] As a rule, it is sufficient to either follow the procedure according to the FIG 7 and 8 or the procedure according to the FIG 9 and 10to take. In principle, however, it is also possible to combine the two procedures. For example, the additional control variable SZ can be applied primarily so that the actual value FB of the bending force is increased. In this case, the additional setpoint FBZ* can be adjusted accordingly at the same time, so that the bending controller 14 does not counteract the increase in the bending force due to the deviation of the actual value FB of the bending force from the basic setpoint FBB*. However, even without adjusting the additional setpoint FBZ*, it is possible to ensure that the resulting control variable SR is necessarily positive. For this, it is only necessary to select a sufficiently large additional control variable SZ. The design according to FIG 11 As a rule, does not have to be associated with any of the FIG 7 bis 10 be combined.

[0053] In particular from the FIG 8 and 10 , in individual cases also the FIG 7 and 9, various advantageous embodiments of the present invention can also be recognized. The same applies to the design of FIG 11 These embodiments are not required for the implementation of the basic principle of the present invention, but offer additional advantages. The embodiments are explained in more detail below. They can be implemented independently of one another, but can also be combined with one another if required. Furthermore, the embodiments are described below without exception in conjunction with FIG 8 and partly FIG 7 explained, i.e., for the case where the additional setpoint FBZ* is specified. However, the advantageous embodiments can also be implemented in a completely analogous manner if the additional manipulated variable SZ or the minimum manipulated variable SM are specified.

[0054] One possible configuration concerns the manner in which the additional setpoint FBZ* is specified from the initial time t5. In particular, the additional setpoint FBZ* is preferably increased from the initial time t5 in a strictly monotonous manner and with a finite gradient from 0 to a maximum value FBZ0*. The period during which this increase occurs can, in particular, be in the range of several hundred milliseconds. The increase should be completed before the actual tapping time t2. Appropriate procedures for gradual increases are generally known to experts.

[0055] Another possible configuration concerns the manner in which the additional setpoint FBZ* is reduced after the actual tapping time t2. In particular, the additional setpoint FBZ* is preferably reduced strictly monotonically and with a finite gradient from its maximum value FBZ0* to 0. The period during which this reduction occurs can, in particular, also be in the range of several hundred milliseconds. Corresponding procedures for gradual reduction are generally known to experts. However, the value 0 must be reached no later than the stabilization time t3.

[0056] Another possible embodiment concerns the determination of the starting time t5. In particular, an expected penetration time t7 can be determined within the framework of a path tracking of the rolling stock head 9 (the implementation of path tracking is generally known to those skilled in the art). Consequently, it is easily possible to determine the starting time t5 such that it precedes the expected penetration time t7 by a predetermined early time period T1.

[0057] The actual tapping time t2 can be before or after the expected tapping time t7. However, the temporal deviation is at most as large as a previously known error tolerance δt. The actual tapping time t2 therefore lies in the interval [t7-δt;t7+δt].

[0058] The predetermined early time period T1 can, in particular, be dimensioned such that the additional setpoint FBZ* has definitely already reached its maximum value FBZ0* by the actual tapping time t2. This configuration makes it possible, in particular, to ensure that the actual value FB of the bending force is also already adjusted as closely as possible to the sum of the base setpoint FBB* and the additional setpoint FBZ*. Alternatively, the predetermined early time period t1 can also be dimensioned such that the additional setpoint FBZ* has definitely not yet reached its maximum value FBZ0* by the actual tapping time t2. This configuration makes it possible, in particular, to ensure that the resulting manipulated variable SR has a positive value at the actual tapping time t2. Typically, the predetermined time period T1 is in the range between 0.5 s and 2.0 s, in particular between 0.8 s and 1.5 s, for example approximately 1.0 s.

[0059] A special method for determining the early time period T1 can also be combined with a special method for determining the additional setpoint FBZ* (or its maximum value FBZ0*). In particular, the early time period T1 can be determined such that at the actual tapping time t2, "the bending force FB is already as close as possible to the sum of the base setpoint FBB* and the additional setpoint FBZ*." At the same time, however, the additional setpoint FBZ* (or its maximum value FBZ0*) can be determined such that the actual bending force value FB cannot even reach the sum of the base setpoint FBB* and the additional setpoint FBZ* (for this reason, the above formulation was placed in quotation marks).This procedure results in the resulting manipulated variable SR being forced to a positive value - often even to the maximum value MAX - and remaining there because the actually desired result (FB = FBB* + FBZ*) cannot be achieved.

[0060] Another possible configuration concerns the determination of the end time t6 – subject to the condition that the end time t6 does not occur after the stabilization time t3. As already mentioned, the actual tapping time t2 can be easily recorded or determined based on recorded measured values. Consequently, it is easily possible to determine the end time t6 such that it occurs a predetermined time interval T2 after the actual tapping time t2.

[0061] Preferably, the predetermined late time period T2 is dimensioned such that the additional setpoint FBZ* maintains its maximum value FBZ0* up to a point in time whose distance from the actual tapping time t2 has a predetermined value. This value can in particular be in the range between 0.1 s and 1.0 s. For example, it can be between 0.2 s and 0.6 s. A value between 0.3 s and 0.4 s is particularly preferred. After this last-mentioned point in time, the additional setpoint FBZ* is then reduced - possibly abruptly, preferably gradually - from its maximum value FBZ0* to 0. Reaching the value 0 corresponds to the end time t6. Since the time period during which the additional setpoint FBZ* is reduced is also known, the end time t6 can be easily determined starting from the actual tapping time t2.

[0062] Alternatively, it is possible to determine the predetermined late time period T2 based on the expected tapping time t7. In this case, the determination is not based on the actual tapping time t2, but rather on the expected tapping time t7.

[0063] A further possible embodiment concerns the manner in which the additional setpoint FBZ* (or its maximum value FBZ0*) is determined—for example, by the control device 13. In particular, properties of the rolling stock 8 can be utilized. On the one hand, the properties are actual values ​​or expected values ​​of the rolling stock 8 that the rolling stock 8 has or is presumed to have before rolling in the rolling stand 1. Examples of such values ​​are the width, the thickness, the temperature and the chemical composition, and possibly also the pretreatment of the rolling stock 8. On the other hand, the properties are target values ​​that the rolling stock 8 should have after rolling in the rolling stand 1. Examples of such values ​​are the width and the thickness of the rolling stock 8.Furthermore, mechanical properties of the rolling stand 1 are known, for example the modulus of elasticity of the stand frame, the diameters of the work rolls 2, the diameters of the backup rolls 3, and others. Finally, as part of the pass schedule calculation, expected values ​​for operating parameters of the rolling stand 1 for rolling the rolled stock 8 are determined - for example by the control device 13 - in particular an expected value FE for the rolling force F. Preferably, the additional setpoint FBZ* or its maximum value FBZ0* is determined as a function of the properties of the rolled stock 8 and / or the expected value FE of the rolling force F. If necessary, the mechanical properties of the rolling stand 1 can also be taken into account. The concrete determination can be made, for example, using a formula or a table. The formula or the table can, for example, be stored in the control device 13.

[0064] Another possible embodiment also concerns the manner in which the additional setpoint FBZ* or its maximum value FBZ0* is determined. In particular, the additional setpoint FBZ* can be determined such that the resulting manipulated variable SR assumes its maximum possible value immediately before the actual tapping time t2. This determination of the additional setpoint FBZ* results in the hydraulic valves 15, 16 being fully open at the actual tapping time t2, and thus the total working pressure pP of the hydraulic system (including accumulators) stabilizes the tapping. This procedure can be particularly useful in a heavy plate mill and in the front rolling stands of a multi-stand finishing mill (for a metal strip). However, an application of this procedure to the rear rolling stands of a multi-stand finishing mill is also possible in principle.

[0065] A final possible configuration also concerns the manner in which the additional setpoint FBZ* or its maximum value FBZ0* is determined. In particular, the additional setpoint FBZ* can be determined in such a way that a drop in the actual value FB of the bending force at the actual piercing time t2, which would occur without the additional setpoint FBZ* being supplied to the bending controller 14, is compensated by at least 50%.

[0066] In many cases, it will be sufficient if the hydraulic valves 15, 16 are not fully open, but only slightly open. Particularly for such cases, configurations are useful in which the minimum control variable SM is specified and the minimum control variable SM has a relatively low value, for example, a value between 8% and 20% of the maximum possible control of the hydraulic valves 15, 16. However, specifying a larger minimum control variable SM for other cases should not be ruled out.

[0067] The present invention offers many advantages. In particular, the initial piercing process is significantly stabilized. Furthermore, the period of time elapsed from the piercing time t2 until the actual value FB of the bending force returns to the base target value FBB* is shortened. Finally, the threading process and the rolling process as such are stabilized. Although the invention has been illustrated and described in detail using the preferred embodiment, the invention is not limited by the disclosed examples, and other variants may be derived therefrom by those skilled in the art without departing from the scope of the invention as defined by the claims. List of reference symbols

[0068] 1Roll stand 2Work rolls 3Back-up rolls 4, 6Bearing journals 5Work roll chocks 7Back-up roll chocks 8Rolling stock 9Rolling stock head 10Bending system 11, 12Hydraulic cylinder units 13Control device 14Bending controller 15, 16Hydraulic valves 17Determination unit 18Rolling stock foot 19Selection element FRolling force FEExpected value FB*Resulting setpoint FBB*Basic setpoint FBZ*Additional setpoint FBZ0*Maximum value FBInsual value of the bending force MAXMaximum possible value pP, pTWorking pressures SBBasic manipulated variable SMMinimal manipulated variable SRResulting manipulated variable SZAdditional manipulated variable t1 to t7Times T1, T2Time spans xTransport direction δFB*Correction value δtFault tolerance

Claims

1. Operating method for a roll stand (1) for rolling a flat rolling stock (8) made of metal, which has a head of the rolling stock (9), - wherein the roll stand (1) has at least working rollers (2) and support rollers (3), - wherein the working rollers (2) are mounted in working roller chocks (5) and a bending system (10) that presses the working roller chocks (5) apart acts on the working roller chocks (5), - wherein the head of the rolling stock (9) reaches the roll stand (1) at an actual entry time (t2), - wherein a base setpoint (FBB*) is supplied to a bending feedback controller (14) and the bending feedback controller (14) determines a resultant setpoint (FB*) taking into account the base setpoint (FBB*), - wherein the bending feedback controller (14) furthermore is supplied an actual value (FB) of the bending force, - wherein the bending feedback controller (14) by means of the resultant setpoint (FB*) and the actual value (FB) determines a basic manipulated variable (SB) for the bending system (10), so that when the bending system (10) is controlled with the basic manipulated variable (SB), the actual value (FB) is approximated as closely as possible to the resultant setpoint (FB*), - wherein the bending feedback controller (14) determines the resultant setpoint (FB*) as from a stabilization time (t3), which is after the entry time (t2), also taking into account an actual rolling force (F) occurring during the rolling of the flat rolling stock (8), characterized in that during an entry period which begins before the actual entry time (t2) and ends after the actual entry time (t2), - the bending feedback controller (14) is supplied with an additional setpoint (FBZ*) in addition to the base setpoint (FBB*), so that the bending feedback controller (14) during the entry period determines the resultant setpoint (FB*) taking into account not only the base setpoint (FBB*) but also the additional setpoint (FBZ*), and as a result the actual value (FB) of the bending force is greater than the base setpoint (FBB*) immediately before the actual entry time (t2), and / or - by applying an additional manipulated variable (SZ) to the basic manipulated variable (SB), a resultant manipulated variable (SR) is determined, which is supplied to the bending system (10) and the bending system (10) is thereby controlled in such a manner that the resultant manipulated variable (SR) is greater than the basic manipulated variable (SB), and / or - a selection member (19) is supplied the basic manipulated variable (SB) and a minimum manipulated variable (SM), and the selection member (19) supplies the maximum of basic manipulated variable (SB) and minimum manipulated variable (SM) to the bending system (10).

2. Operating method according to Claim 1, characterized in that the additional setpoint (FBZ*) and / or the additional manipulated variable (SZ) and / or the minimum manipulated variable (SM) are raised strictly monotonically from 0 to a maximum value (FBZ0*) from the beginning (t5) of the entry period with a finite gradient and / or are reduced strictly monotonically from their maximum value (FBZ0*) to zero at the end (t6) of the entry period with a finite gradient.

3. Operating method according to Claim 1 or 2, characterized in that an expected entry time (t7) is determined by means of path tracking for the rolling stock (8), and in that the beginning (t5) of the entry period is before the expected entry time (t7) by a predetermined early time span (T1).

4. Operating method according to Claim 1, 2 or 3, characterized in that the end (t6) of the entry period is after the actual entry time (t2) by a predetermined late time span (T2).

5. Operating method according to one of the preceding claims, characterized in that before the rolling stock (8) is rolled in the roll stand (1), a maximum value of the additional setpoint (FBZ*) and / or the additional manipulated variable (SZ) and / or the minimum manipulated variable (SM) are determined as a function of properties of the rolling stock (8) and / or as a function of an expected rolling force (FE).

6. Operating method according to one of the preceding claims, characterized in that the maximum value of the additional setpoint (FBZ*) and / or the additional manipulated variable (SZ) and / or the minimum manipulated variable (SM) is determined in such a manner that the resultant manipulated variable (SR) assumes its maximum possible value (MAX) at the actual entry time (t2).

7. Operating method according to one of the preceding claims, characterized in that the additional setpoint (FBZ*) and / or the additional manipulated variable (SZ) and / or the minimum manipulated variable (SM) are determined in such a manner that a drop in the actual value (FB) of the bending force at the actual entry time (t2), which would be adjusted without the additional setpoint (FBZ*) and / or the additional manipulated variable (SZ) and / or the minimum manipulated variable (SM), is compensated for by at least 50%.

8. Rolling unit for rolling a flat rolling stock (8) made of metal, which has a head of the rolling stock (9), - wherein the rolling unit has a roll stand (1) and a bending feedback controller (14), - wherein the roll stand (1) has working rollers (2), mounted at least in working roller chocks (5), and support rollers (3), - wherein the roll stand (1) has a bending system (10) that presses the working roller chocks (5) apart, - wherein the bending feedback controller (14) actuates the bending system (10), characterized in that the roll stand (1) and the bending feedback controller (14) during the operation of the rolling unit interact with one another in such a manner that they carry out an operating method according to one of the above claims.