Method for operating a rolling stand

Abstract

The invention relates to a method and a computer program for operating a rolling stand, as well as to the corresponding rolling stand itself. The rolling stand has two work rolls that together span a roll gap for rolling a rolled product, in particular a metal strip. The work rolls are adjusted on the drive side and the operating side of the rolling stand, each with the aid of actuators 130, in particular in a position-controlled manner. To increase the productivity of the rolling stand, stabilize its operation, and improve the quality of the rolled stock produced in the event of impending or occurring changes or fluctuating situations during the operation of the rolling stand, the present invention proposes the following: When a change in the operation of the rolling stand is detected, a check is performed to determine whether at least one switching criterion is met. If the switching criterion is met, the system switches from normal operation to special operation. If the switching criterion is not met, the rolling stand continues to operate in normal operation.

Description

[0001] The invention relates to a method and a computer program for operating a rolling stand, as well as to the corresponding rolling stand itself. The rolling stand has two work rolls that together span a roll gap for rolling a rolled stock, in particular a metal strip. The rolling stand can be a hot rolling stand or a cold rolling stand, in particular a flat rolling stand. The work rolls are adjusted on the drive side and the operating side of the rolling stand using actuators, typically in the form of hydraulic adjusting cylinders, in particular with position control.

[0002] Such methods, computer programs and rolling stands are known in the state of the art.

[0003] For example, German patent application DE 10 2007 003 243 A1 discloses a control system for a rolling stand that includes both a force controller and a subordinate position controller. The force controller controls the force exerted on the rolling stock, while the position controller ensures the precise positioning of the rolls.

[0004] Another German patent application DE 10 2014 207 859 A1 discloses a method and a rolling system for cold rolling. The rolling system consists of upper and lower backup rolls and work rolls, which together form a roll gap. Intermediate rolls can optionally be arranged between the work and backup rolls.

[0005] US patent application US 2024 / 0 416 403 A1 describes a model-based predictive control (MPC) system for 4-Hi non-reversible cold rolling mills. The system uses sensor data and a multivariable model to control roll gap, rolling force, speed, and strip tension. A software processor processes sensor data, creates the model, and controls the rolling process.

[0006] When operating a roll stand of this type, situations can arise in which the operating points of the actuators have to be changed. Such situations include changing from an existing rolled product to a new one in continuous rolling mills, threading and unthreading situations in batch rolling mills, changes to the target thickness within the rolled product, and reversing passes in reversing rolling mills. The changes in rolling operation mentioned above and the resulting necessary changes to the operating points of the actuators for the work rolls are challenging situations for the operation of the roll stand because they sometimes involve drastic changes to at least one relevant process parameter such as strip tension, strip flatness, or strip thickness. At the same time, roll stand operators have ever-increasing demands for optimal yield from the roll stand, i.e. its throughput.Furthermore, ecologically and economically optimized rolling mill operation modes are required, as are greater stability during rolling operations, higher quality of the rolled stock, and improved efficiency, for example, through a reduction in off-gauge lengths. All of these requirements play a key role in the aforementioned change situations in rolling mill operation. In the current state of the art, rolling mills are usually operated with pure position control or pure force control of the actuators when one of these changes occurs.

[0007] If pure position control is used exclusively, stability-relevant disadvantages arise due to many possible changes or changing situations during operation of the rolling stand. Examples: - In the case of changing incoming strip thicknesses, e.g. when threading the rolled stock into the rolling stand, stability-relevant disturbances with regard to the tension, the thickness and / or the center position of the rolled stock as it passes through the rolling stand. These disturbances occur in particular when the thickness of the rolled stock on the incoming side changes in a position-controlled rolling stand, since in this case rolling takes place with a significantly changed rolling force and significantly changed take-off, which negatively affects the position of the rolled stock in the rolling stand and its flatness. Large changes / disturbances in the incoming strip thickness are common in cold rolling stands, for example, due to previous threading processes in stands of an upstream hot strip mill. Before running into a cold rolling stand, only the shortest possible lengths of the head and / or tail of the hot strip are usually cut off in order to reduce scrap. - Due to the position control, the rolling stand behaves comparatively stiffly or with little flexibility, which increases the risk of strip breaks if the rolling stock has a weld seam, for example, and thus passes through the rolling stand.

[0008] With pure position control, the setting accuracy for the hydraulic adjusting cylinders is lower than with pure rolling force control.

[0009] If only rolling force control is used, stability-related disadvantages also arise in certain change situations. Examples: - With pure rolling force control, no position swivel correction value can be transmitted to the control system for the actuators for adjusting the work rolls. This results in risky strip deviations in almost all roll change situations, which can neither be automatically corrected nor manually corrected. This often leads to the rolled stock or strip drifting sideways out of line, which increases the risk of damage to the rolling stand, especially to its rolls or housings. - In continuous rolling mills, rolling stock changes may occur, with a new rolling stock being welded to a previous rolling stock via a weld seam. In these cases, the rolling stock may exhibit a very soft spot immediately after the weld seam. A purely force-controlled rolling stand would produce a dangerous under-thickness, which is undesirable.

[0010] Based on this prior art, the invention is based on the object of developing a known method and computer program for operating a rolling stand as well as a known rolling stand itself in such a way that the productivity of the rolling stand is increased, the operation of the rolling stand is stabilized and the quality of the rolled stock produced is increased in the event of impending or occurring changes or changing situations during the operation of the rolling stand.

[0011] This object is achieved by the method claimed in claim 1. Accordingly, the method according to the invention is characterized by the following method steps: - Detection of an impending or occurring change in the operation of the rolling stand; - In response to the detected change: Check whether at least one switching criterion is met; and - if the switching criterion is met: switching from normal operation to a special operation of the rolling stand in the form of a subordinate position-controlled adjustment of the actuators with superimposed, force-controlled adjustment; or - if the switching criterion is not met: continued normal operation of the rolling stand in the form of a position-controlled adjustment of the actuators.

[0012] The terms “change situation” and “change in the operation of the rolling stand” are used synonymously.

[0013] The term “normal operation of the rolling stand” means a position-controlled adjustment of the working rolls of the rolling stand with the aid of the actuators.

[0014] The above definition applies to the term “special operation” of the rolling stand, i.e. it is a cascade control in the form of a subordinate position-controlled adjustment of the actuators for the work rolls with a superimposed force-controlled adjustment of the actuators.

[0015] The claimed cascade control advantageously enables an increase in the productivity and energy efficiency of the rolling stand and an improvement in the quality of the rolled goods rolled using the method claimed in the invention. This is true because the disadvantages described above for pure position control or pure force control can be avoided or at least reduced with the claimed cascade control. Compared to pure position control, the claimed cascade control offers the advantage that the rolling stand is less rigid and thus more compliant, reducing the risk of strip breakage when rolling goods with a weld seam pass through the rolling stand. Avoiding strip breakage enables a significant increase in the productivity of the rolling stand.

[0016] In particular, the tension of the rolled stock or its thickness can be adjusted significantly more stably if rolling is carried out according to the method according to the invention with the claimed cascade control for the adjustment of the work rolls of the rolling stand. This increases the stability of the rolling process.

[0017] The quality of the rolled stock is enhanced when applying the method according to the invention because the additional option of implementing a swivel control system on the subordinate operator and drive-side position control system prevents dangerous strip path changes during changeover situations, as would be the case with exclusive force control. The quality of the rolled stock is also enhanced by improving the setting accuracy of the positioning elements.

[0018] Examples of changes or changing situations detected according to the invention during operation of the rolling stand with their associated switching criteria for the switching provided according to the invention from normal operation to special operation and back are the subject of the dependent claims and are described further below.

[0019] This also applies to a more detailed description of the pure position control in normal operation and the cascade control in special operation.

[0020] According to the invention, the target setting force is increased or decreased based on plant-specific or technological limitations.

[0021] According to the invention, switching from normal operation to special operation or back preferably occurs in real time, so that the actual rolling operation is not disrupted or even interrupted. The switching is preferably also "smooth." At the time of switching, no change in the setpoint value that exceeds a certain threshold is transmitted to the actuator. Immediately after switching, the new setpoint, position or force via position, is approached, for example, in a ramp or S-ramp pattern.

[0022] As soon as a switching criterion according to the invention is no longer present or fulfilled, the method according to the invention provides for a switchover from the special operation back to the normal operation of the rolling stand.

[0023] A switching criterion and / or a direct switching command is specified by programs such as artificial intelligence or rule-based specifications, based on analyzed measurement data and / or based on analyzed data from rolled goods rolled in the past, which experienced changes during rolling during operation of the rolling stand. Measurement data refers to at least one of the following measurable variables: strip thickness, rolling force, strip tension, strip flatness, bending value, roll stand adjustment position, torque, speed of the rolled goods through the roll stand, strip profile transverse to the rolling direction, strip width, strip head position, strip foot position, rolling direction, etc., whereby the term "strip" is synonymous with rolled goods.

[0024] The position-controlled adjustment and / or the subordinate position-controlled adjustment with the superimposed force-controlled adjustment is carried out separately and individually for the actuators on the drive side and for the actuators on the operating side of the rolling stand. Therefore, for normal operation according to the invention, separate position control loops must be provided for the drive side and the operating side of the rolling stand. Similarly, two separate and individually controllable cascade controls must be provided for the actuators on the drive side and the operating side of the rolling stand.

[0025] The above-mentioned object of the invention is achieved not only by the claimed method but also by a computer program product according to claim 17 and by a rolling stand according to claim 18. The advantages of these solutions correspond to the advantages mentioned above with reference to the claimed method.

[0026] Two figures are attached to the description, where Fig. 1 a pure position control (normal operation); and Fig. 2 illustrates a cascade control (special operation).

[0027] The invention is described in detail below with reference to the figures in the form of exemplary embodiments.

[0028] The invention relates to a rolling stand with two work rolls that together span a roll gap for rolling a rolled stock. The work rolls are adjusted on the drive side and on the operating side of the rolling stand using actuators 130. The actuators 130 are preferably hydraulic adjusting cylinders.

[0029] The actuators are part of a control device 100 with which the rolling stand and in particular its work rolls in normal operation, in the form of a position control 100-I, see Fig. 1, or in a special operation in the form of a cascade control 100-I, 100-II, see Fig. 2, can be operated. The figures apply equally to the drive side and the operating side of the rolling stand.

[0030] Within the scope of the position-controlled adjustment 100-I during normal operation and / or during the subordinate position-controlled adjustment 100-I during special operation, Fig. 1 the actual position Ist-Pos of the work rolls on the drive and operating side of the rolling stand is determined with the aid of a position determination device 150-1 and regulated to a desired position Soll-Pos that is individually specified for each of the two sides. This is achieved by suitable variation of the adjustment of the actuators 130 in accordance with a position control deviation e-Pos between the actual and the desired position, which is determined by a position comparison device 110-I. The adjustment of the actuators 130 is carried out by an actuating signal S, which is generated by a position controller 120-I in accordance with the position control deviation e-Pos. The reference symbol 140-I designates the part of the controlled system relevant for the positioning of the actuators or the work rolls, i.e. the rolling stand.

[0031] Within the framework of the superimposed force-controlled employment 100-II during the special operation, according to Fig.2 the actual setting force Ist-F is determined with the aid of a force determination device 150-II and controlled to a target setting force Soll-F by suitable additional variation of the setting of the actuators 130 in accordance with a force control deviation eF between the actual and the target setting force determined by a force comparison device 110-II. This setting of the actuators 130 in accordance with the force control deviation represents an additional value which, within the framework of the cascade control 100, is generated by a force controller 120-II as its output signal F and is superimposed on the setting of the actuators 130 in accordance with the position control deviation e-Pos. The reference symbol 140-II designates the part of the controlled system relevant for the force adjustment, i.e. the rolling stand.

[0032] The position control 100-I and the force control 100-II or their combination in the form of cascade control can all be integrated in the control device 100, preferably including the switching input.

[0033] As already mentioned in the general part of the description, the position and / or force control for the drive side and the operating side of the rolling stand are carried out separately.

[0034] A switching device (not shown in the figures) serves to switch the control device 100 from normal operation to special operation and back in response to the presence or fulfillment of a switching criterion. The control device and the associated switching device are at least partially designed as a computer with an internal memory into which a computer program product is loaded, which depicts the inventive method described below.

[0035] The method according to the invention for operating the rolling stand comprises the following steps: - position-controlled setting of the work rolls by means of the actuators 130 for rolling the rolled material as normal operation of the rolling stand; - Detection of an impending or occurring change in the operation of the rolling stand; - In response to the detected change: Check whether at least one switching criterion is met, and - if the switching criterion is met: switching from normal operation to a special operation in the form of a subordinate position-controlled adjustment 100-I of the actuators 130 with superimposed force-controlled adjustment 100-II; or - if the switching criterion is not met: Continue normal operation.

[0036] According to a first exemplary embodiment, the detected change during operation of the rolling stand is a rolling stock change from a previous rolling stock to a new rolling stock. In this case, the test step checks, as a switching criterion, whether the new rolling stock has different dimensions and / or different properties than the previous rolling stock. The dimensions and / or properties between the rolling stocks are considered different if they fall below or exceed specified threshold values.

[0037] According to a second embodiment, the detected change during operation of the rolling stand is a change in the pass size, particularly during reversing rolling, a drop in the inlet-side tension of the rolling stock, a change in the distance of the head of the rolling stock from the roll gap, and / or a change in the inlet-side speed of the rolling stock. In this case, the test step checks whether the respective change lies below or above a predetermined threshold value as a switching criterion.

[0038] According to a third embodiment, the detected change during operation of the rolling stand is a thickness change in the rolled stock detected at the inlet of the rolling stand. In this case, the switching criterion in the test step checks whether the ratio of the detected thickness change to a change in the vertical position adjustment of the adjusting cylinders of the work rolls in the rolling stand required in response to this change is below or above a predetermined threshold value.

[0039] According to a fourth embodiment, the detected change during operation of the rolling stand is a change in the speed of the work roll, a change in the roll gap size, and / or a change in the rolling force. In this case, the test step checks whether the respective change is below or above a predetermined threshold value as a switching criterion.

[0040] According to a fifth embodiment, the detected change during operation of the rolling stand is a target thickness change in the rolled stock initiated at the exit of the rolling stand. In this case, the test step checks, as a switching criterion, whether the ratio of the detected or initiated thickness change to a change in the vertical position adjustment of the adjusting cylinders of the work rolls in the rolling stand required in response to this change is below or above a predetermined threshold value.

[0041] In all five examples, the test step is followed by the following steps: - If the switching criterion is not met, normal operation is maintained; or - If the switching criterion is met, the control system is switched to special operation using the switching device.

[0042] As soon as the switching criterion is no longer met, the system switches back from special operation to normal operation.

[0043] At least during special operation, tension control for the rolling stock to be rolled can be implemented, preferably automatically, at the entry point of the rolling stand. Within the framework of this tension control, a tension control deviation is determined as the difference between a target tension and a determined actual tension of the rolling stock. Depending on the tension control deviation, or if the tension control deviation exceeds a specified tension threshold, a tension-based additional force value is generated, which is added to the specified target setting force during the superimposed force-controlled setting.

[0044] At least during the special operation, a preferably automatic swivel control can be carried out, in which the target positions for the adjusting cylinders for the work rolls in the rolling stand on its operating side and its drive side are specified individually, in particular deviating from one another, within the framework of the position-controlled adjustment during normal operation or within the framework of the subordinate, position-controlled adjustment during the special operation. List of reference symbols 100 control device 100-I position control 100-II superimposed force control 110-I Position comparison device 110-II force comparison device 120-I Position Controller 120-II force regulator 130 Actuator 140-I Part of the controlled system relevant for positioning the actuators 140-II the part of the control system relevant for force adjustment 150-I Position detection device 150-II force determination device eF force control deviation e-Pos position control deviation F Output signal of the force controller Actual F Actual force Actual Pos Actual value of the position S Control signal, output signal of the position controller Target F Target force Target Pos Target value for the position

Claims

[1] Method for operating a rolling stand with two work rolls which together span a roll gap for rolling a rolled product, and with actuators for adjusting the work rolls on the drive side and on the operating side of the rolling stand, the method comprising the following steps: - position-controlled adjustment of the work rolls by means of the actuators (130) for rolling the rolled stock as normal operation of the rolling stand; characterized by - Detection of an impending or occurring change in the operation of the rolling stand; - In response to the detected change: Check whether at least one switching criterion is met, and - if the switching criterion is met: switching from normal operation to a special operation in the form of a subordinate position-controlled adjustment of the actuators with superimposed force-controlled adjustment; or - if the switching criterion is not met: Continue normal operation. [2] Method according to claim 1, characterized by that within the framework of the position-controlled adjustment (100-I) during normal operation and / or during special operation, the actual position of the work rolls on the drive and / or operating side is adjusted to a desired position by suitable variation of the adjustment of the actuators (130) in accordance with a determined position control deviation (e-Pos) between the actual and the desired position (actual Pos, desired Pos). [3] Method according to one of the preceding claims, characterized by , that the detected change in the operation of the rolling stand is, for example, a change of rolling stock from a previous rolling stock to a new rolling stock; and that in the test step, as a switching criterion, it is checked whether the new rolling stock has different dimensions and / or different properties than the previous rolling stock; and that - if the switching criterion is not met - normal operation is maintained; or that - if the switching criterion is met - the system switches to special operation. [4] Method according to one of claims 1 to 2, characterized by , that the detected change in the operation of the rolling stand is a change in the pass size, in particular when rolling in the form of reversing rolling, a drop in the inlet-side tension of the rolling stock, a change in the distance of the head of the rolling stock to the roll gap and / or a change in the inlet-side speed of the rolling stock; and that in the test step, as a switching criterion, it is checked whether the respective change is below or above a predetermined threshold value; and that, if the switching criterion is not met, normal operation is maintained; or that - if the switching criterion is met - the system switches to special operation. [5] Method according to one of claims 1 to 2, characterized by , that the change detected during operation of the rolling stand is a change in the thickness of the rolled stock detected at the inlet of the rolling stand; and that in the test step, as a switching criterion, it is then checked whether the ratio of the detected thickness change to a change in the position adjustment of the adjusting cylinders of the work rolls in the rolling stand required as a reaction thereto is below or above a predetermined threshold value; and that - if the switching criterion is not met - normal operation is maintained; or that - if the switching criterion is met - the system switches to special operation. [6] Method according to one of claims 1 to 2, characterized by , that the change detected during operation of the rolling stand is a target thickness change in the rolled stock initiated at the exit of the rolling stand; and that in the test step, as a switching criterion, it is then checked whether the ratio of the detected thickness change to a change in the vertical position adjustment of the adjusting cylinders of the work rolls in the rolling stand required as a reaction thereto is below or above a predetermined threshold value; and that - if the switching criterion is not met - normal operation is maintained; or that - if the switching criterion is met - the system switches to special operation. [7] Method according to one of claims 1 to 2, characterized by , that the detected change in the operation of the rolling stand is a change in the speed of the work roll, a change in the roll gap size and / or a change in the rolling force, and that in the test step, as a switching criterion, it is checked whether the respective change is below or above a predetermined threshold value; and that - if the switching criterion is not met - normal operation is maintained; or that - if the switching criterion is met - the system switches to special operation. [8] Method according to one of the preceding claims, characterized by , that, within the framework of the superimposed force-controlled adjustment, the actual adjustment force is adjusted to a target adjustment force by appropriately varying the adjustment of the actuators in accordance with a determined force control deviation between the actual and the target adjustment force; and that this adjustment of the actuators according to the force control deviation represents an additional value which is superimposed on the adjustment of the actuators according to the position control deviation. [9] Method according to claim 8, characterized by , that at least during special operation, tension control of the rolling stock to be rolled is preferably automatic; that, within the framework of tension control, a tension control deviation is determined as the difference between a target tension and a determined actual tension of the rolling stock; and that according to the tension control deviation or if the tension control deviation exceeds a specified tension threshold value, a tension-based additional force value is generated, which is added to the specified target setting force in the superimposed force-controlled setting. [10] Method according to claim 8 or 9, characterized by that the target setting force is increased or decreased based on system limits or technological limitations. [11] Method according to one of the preceding claims, characterized by that - as soon as the switching criterion is no longer met - a switchover from the special operation back to normal operation takes place. [12] Method according to one of the preceding claims, characterized by that switching from normal operation to special operation or back takes place in real time. [13] Method according to one of the preceding claims, characterized bythat switching between normal operation and special operation is smooth in both directions. [14] Method according to one of the preceding claims, characterized by that at least during the special operation, a preferably automatic swivel control is carried out, in which the target positions for the adjusting cylinders for the work rolls in the rolling stand on its operating side and its drive side are specified individually, in particular deviating from one another, within the framework of the position-controlled adjustment. [15] Method according to one of the preceding claims, characterized by that the position-controlled adjustment and / or the subordinate position-controlled adjustment with the superimposed force-controlled adjustment is carried out separately and individually for the actuators on the drive side and for the actuators on the operating side of the rolling stand. [16] Method according to one of the preceding claims, characterized bythat the switching criterion and / or a direct switching command is specified by programs such as artificial intelligence or rule-based specifications, based on analyzed measurement data and / or based on analyzed data from rolled goods rolled in the past in which there were changes in the operation of the rolling stand during rolling. [17] A computer program product which can be loaded directly into the internal memory of a digital computer and which comprises software code sections which carry out the steps according to the preceding method claims when the computer program product is run on the computer. [18] Rolling stand with - two work rolls which together form a roll gap for rolling a rolled product; - actuators for adjusting the work rolls on the drive side and on the operating side of the rolling stand during normal operation; and - a control device with the actuators for carrying out normal operation; characterized by , that the control device is further configured to operate the rolling stand in a special mode as an alternative to normal operation; that a switching device is provided for switching the control device from normal operation to special operation and back in response to the presence or fulfillment of a switching criterion; and that the control device and the switching device are designed as or in a computer with an internal memory into which the computer program product according to claim 17 is loaded for running in the computer.

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