EP0375095B1 - Method and device for controlling the strip width during the hot-rolling of strip - Google Patents

Abstract

The invention relates to a method and a device for controlling the strip width during the hot-rolling of strip on a multiple-stand finishing line of a rolling mill train in which the speeds of the working rolls of each stand are controlled as a function of the instantaneous operating state. Here, the strip widths are sensed directly after the last reduction per pass and/or before the penultimate reduction per pass and are compared with the desired width in a width controller. In the event of deviations, a strip-supply controller for the strip supply between the last stands is acted upon, which strip-supply controller, by adjusting the roll nips, corrects the strip supply and the tensile stress of the strip in such a way that the strip width changes. The method is optimized by additional control of the strip thickness according to the novel strip-supply principle as well as by dispensing with some loop lifters. <IMAGE>

Description

The invention relates to a method and a device for regulating the strip width in hot strip rolling according to the preambles of claims 1 and 9.

Hot strip rolling on modern continuous rolling mills, usually with five or more rolling stands in the finishing mill, is intended to set the finished geometry of the strip, which is predetermined within narrow tolerances, in addition to influencing the technological characteristics of the strip through controlled thermomechanical rolling.

Given the infeed cross section and known infeed speed of a strip and the desired outfeed cross section of the strip, its inevitable stretching during the rolling is compensated for by rolling speed increasing cascade-wise from stand to stand and thus increasing roll speed depending on the usually declining step reduction. As the dwell time increases, the strip cools down before and in the finished batch; therefore the base rolling speed and thus the heat dissipation is steadily increased due to increased deformation work in order to keep the metallurgically important final rolling temperature approximately constant (temperature-speed-up). These specifications for the speed ratios and the computed empty roll gap heights of the individual stands are specified by a target value calculator.

The belt speed and the roller circumferential speed are only the same in the flow sheath. The material experiences a lead and lag in the roll gap. In order to avoid problems arising as a result, rolling mills can be equipped with strip tension control by means of speed adjustment and / or loop lifters, which, in addition to a roll gap control and rolling force measurement and strip thickness measurement, enable control of the rolling mill (Iron and Steel Engineer, 9/84, pages 45-51) . This publication also describes in detail the functioning of a load-dependent control of the roll gap height (bearing play and stand expansion compensation) and the possibility of dispensing with loop lifters between the first stands of the finishing relay, the loop lifters being controlled by a minimum tension control due to known rolling forces and motor torques and the resulting change in speed Work rolls to be replaced.

Attempts have also already been made to achieve the greatest possible accuracy of the strip thickness by realizing a correction of the measured thickness tolerances for the roll gap heights of each stand resulting from the pass schedule by adjusting the load roll gap during rolling (DE-A-36 37 043) or the entire material flow through a rolling mill through a minimum tension control solely by means of speed correction of the work rolls and a thickness control on the first stand to influence (DE-A-27 21 973). A consideration of the fluctuations in bandwidth in the finished series has not been disclosed.

JP-A-63-068207 describes a method for width control of tandem rolling processes in which the width control does not take place before the last pass and there is no strip supply control. The looper is designed to be movable. This results in the need for complicated control technology. The measurement signal obtained must be compensated for by the angle and the acceleration.

From DE-A-22 49 366 (closest state of the art) a measuring and control system for prefabricated squadrons is known, with which primarily the tension in the band between the scaffolds is measured by loop lifters and the bandwidth behind the prefabricated squadron and by tension control the tension and so that the bandwidth should be corrected. The strip thickness should be neglected or optionally included as a factor in the tension calculation in order to keep the tension as constant as possible. If the tensile stress leads to a change in the sheet thickness, this should be corrected by speed and pressure control devices on the stands. An automatic load roll gap control or the selection of the stand tension control before the last stand is not disclosed; nor the type of voltage sensor.

It is therefore the object of the invention to propose a method and a device for regulating the bandwidth during hot rolling of strips in the finishing line of a rolling mill, which enable the bandwidth to be set precisely and quickly with relatively little effort for practical control optimization.

The object is achieved by claims 1 and 9. Advantageous embodiments of the invention are covered in the subclaims.

Due to the process, the mass flows at the inlet and outlet of the finished scale are the same. In the known continuity equation, however, the parameters of width, thickness, speed and weight of the strip change during the course of the method. With the exception of the weights, the parameters can be measured directly on the rolling mill. The weight as a function of the rolling temperature and the type of material can only be recorded as an implicit statistical variable during rolling. The change in weight of approx. 0.1% during hot rolling is negligible.

The invention takes into account the knowledge that the strip supply between the stands has to be regulated in order to achieve a stable operating state during hot rolling.

If you think of the rolling mill as a controlled system, to which the control loops for the nominal guide values of speed and idle roll gap or load roll gap are assigned, you get the rolling forces, the rolling moments, the loop lifting angles, the resulting strip thickness and the exit speed as important output signals. The speeds of the rolls and the nip feeds are available as control values. The speeds affect the loop lifter angles and the material flow speed; the roll gap feed also influences the loop lifter angle, the material flow speed and the resulting strip thickness. In this controlled system, the variation in the strength of the strip as a function of acts primarily as a disturbance variable Material type and temperature. This also includes so-called skidmarks (rail shadows) from slab heating. Irregularities in the slitting or roughing of slabs, as well as the lack of side upsetting units in the roughing mill, also result in bandwidth fluctuations.

In the simplest case, as is known per se, the existing loop control could be used by correcting the speed of the work rolls in front of or behind the loop in question, in order to correct the bandwidth by increasing or decreasing the tape tension and thus the tape supply in the loop.

Since there are enough manipulated variables available to influence the control system, there is no need to adjust the speed of the rollers. A change in roll nip height can occur much faster than a change in the roll speed, so that the feed of the roll gap is best suited as a control variable for a strip supply control for correcting the strip width on the stands.

The control signals for this belt supply control are generated by a width controller, which in turn receives signals from one or more bandwidth measurements, compares the measured values with the setpoints and, if there are deviations from the setpoint, applies a signal to the belt supply controller so that the strip tension is changed. The width measurement is carried out as close as possible behind the last frame, preferably with a Diode line camera, which register the strip edges as a contrast to a counter light source under the hot strip. The strip width is then regulated in such a way that the strip tension controller determines the strip tension before the last stitch, determined by the reaction force to a fixed deflection roller under the hot strip, and the change signal from the width regulator in such a way that the roll gap of the last stand is changed.

The result is that the hot strip is constricted or relieved and thus becomes wider. A change in the width also results in a change in the thickness, at least within limits, so that the final thickness of the strip is sensibly recorded and changes in thickness are corrected using a thickness control loop on the last stand. For this purpose, the thickness controller can apply a correction signal for the necessary roll gap height to the automatic load gap control device. Through this procedure, the tape supply is adjusted to the requirements in a controlled manner.

However, measuring the width only after the last stitch has disadvantages, since the delay means that part of the tape can no longer be corrected. Therefore, according to the invention, a width measurement is also installed in front of the penultimate frame, so that the bandwidth between the last two stitches can be controlled.

A width measurement at both points enables the result of the width correction based on the first measurement to be checked and corrected more precisely.

According to a further development of the invention, the width correction can also be carried out between the first two stitch decreases or the width correction can be divided between the two sections of the finishing scale mentioned, so that larger fluctuations in the width can be corrected without excessive undesired control strokes occurring.

However, an optimal width control cannot neglect the resulting changes in strip thickness. The simple method of thickness control described on the last stand allows only minor corrections, especially since the stitch reduction in the last stand should also make up the smallest amount. Therefore, it makes sense to check the strip tension over the entire finishing line and to supplement it with a constant strip supply control with high control speed.

For this purpose, the usual master setpoint for the position control loop "empty roll gap" after the strip has entered the first stand is replaced by actuating signals from the individual strip supply controllers. The strip supply controllers then control the mass flow, mathematically the volume flow, in the finishing line for the hot strip section with the exception of the strip end. Shortly before the end of the strip reaches a stand, the well-known automatic load gap control device replaces the strip supply control. With this switchover method, the current actual values of the strip thickness or the roll gap are taken over bumplessly as setpoints in order to prevent the control loops from settling again. For the individual primary independent band supply regulators use different indicators as control variables.

A setpoint deviation or the actual value for a specific strip supply of a section of the finished scale provides either the strip tension determination or the angle measurement of the loop lift deflection.

The regulation of the first scaffold differs from this. Here, the thickness and the speed of the incoming strip can be measured - assuming the permissible assumption that there is currently a constant strip width - a mass flow equivalent. When changing the thickness or speed of the strip, the roll gap can be adjusted on the first stand so that the mass flow, mathematically simplified as a product of the thickness and speed, remains constant due to the backflow of the material.

The loop control between the front stands can be replaced by a tension control of the belt. This results in a relatively good flatness of the belt. This enables the use of a thickness measuring system behind the first stand and thus the additional possibility of regulating the thickness of the hot strip on the first stand.

Experiments have surprisingly confirmed the assumption that one can do without expensive pivoting loop lifters between the first stands and the loop lifter before the last or more of the last stands as simple, vertically movable Can design deflection roller if you apply the process concept according to the invention. The effectiveness of the front loop lifter is anyway relatively low due to the belt stiffness, and the same effect can be achieved by a belt tension calculated from measured shaft torques of the work rolls and rolling forces by means of belt supply control of the following stand.

The method of radio transmission of strain gauge torque measurements can be used to determine the strip tension between the stands. Compared to the torque determination from the current and voltage values of the roller drives, the DMS method detects the torsional moments directly on the work roller shaft without loss. The results are then available without delay for the train calculation due to the radio transmission.

The selection of the most suitable indicators, which indicate a variation of the mass flow or band supply in front of the scaffolding, is made according to their most favorable properties with regard to the conditions: lowest investment costs, greatest control speed and best effect on the band geometry. It has proven to be advantageous to keep the sling lifter angle as constant as possible, because this prevents difficulties during adjustment that result from the non-angular force effect of the sling lifter on the belt.

If the strip thickness behind the finished scale is still outside the desired tolerances despite the strip supply regulation, a thickness regulation supplementing the strip supply regulation can be used. For this purpose, the actual thickness value measured with a radiation measuring device - gamma emitter cesium 137 - is fed to a thickness controller, which, if necessary, can generate two control signals correlating to the measure of the deviation from the target thickness. In the simplest control concept described at the beginning, the thickness controller then acts on the load roll gap control. However, since in this case the roll gap control variable is used for the strip supply control, another solution makes sense.

A change in thickness can be recorded as a trend in the thickness measuring device behind the finished scale and thus by changing the speed trend of the work rolls between two scaffolding groups of the finished scale, the strip supply can be increased or decreased locally with the effect that the strip supply regulator intervenes and the strip thickness changes. At the same time, a correction signal - delayed to adapt to the higher control speed of the roll gap control circuit - can be sent to the roll gap controller of the stand concerned, so that the strip supply actually does not change.

The width control by means of roll gap adjustment is included in this concept.

For this purpose, the width controller mentioned at the outset sends a signal to the belt supply controller of the last stand, which in turn then changes the tension by adjusting the Roll gap generated. With this fast dynamic control, the width fluctuations can be corrected without the slower thickness control providing speed compensation.
Otherwise the thickness controller must also receive a feedforward control.

For this regulation, the last stitch acceptance must be designed in such a way that it is greater in percentage than the bandwidth fluctuation to be corrected.

Fig. 1

die Kraftwirkung eines Schlingenhebers,

Fig. 2

eine erfindungsgemäße Regelung für eine Fertigstaffel als Blockschaltbild.

The invention will be explained in more detail with the aid of schematic drawings. Show it

Fig. 1

the force of a loop lifter,

Fig. 2

an inventive regulation for a prefabricated season as a block diagram.

The diagram in FIG. 1 shows the change in the specific tensile stress in the hot strip 10 over the angular position (looper angle) of a loop lifter (looper) at 4 to 10 bar fluid pressure (looper pressure) of the lifting cylinder of the loop lifter. Every change in the angle of the sling lifter causes tension fluctuations in the belt. With the tape supply control and the tape tension changes are significantly less than with the conventional loop control.

Fig. 2 shows the situation on the finishing line of a rolling mill for hot strip 10 with seven rolling stands 1 ... 7, four swiveling loop lifters 12 ... 15 and a vertically adjustable and lockable deflection roller 16 with force measuring device 9. The drives, measuring devices and actuators are not all shown for the sake of clarity. Each scaffold has a belt supply controller BVR and an additional thickness controller DR is installed on the last scaffold. According to the prior art, each stand also has a position controller PR and an automatic load roll gap control AGC, which receives the roll gap h currently calculated from the roll force f and the displayed position s of the rolls from a roll gap computer HR.

In the following functional description, large letters should indicate setpoints and small letters actual values.

All of the setpoints for the roll speeds NL are predefined by a master setpoint calculator (not shown) and, during the rolling, tend to be ramped in accordance with the desired pass schedule and the desired temperature speed-up. Speed controllers DNR ensure that the speeds comply with their current setpoints N 1 ... N 7.

The setpoints of the roll gap heights SL are also specified by the master setpoint computer before the start of the roll. They have to be readjusted continuously during rolling in order to adapt to the material flow or strip supply. The necessary supply signals delta S are provided by the belt supply controller BVR. Each belt supply controller BVR gets its actual value from that in the respective scaffold 1 ... 7 incoming piece of tape, while its setpoint SL is constant. The physical quantity used as the actual value is in all cases a measure of the supply of strip volume (mass supply) in front of the stand and after the previous stand. The belt supply controllers BVR thus regulate a constant belt supply between stands 1 ... 7.

In the first stand, the nominal thickness H Z, not shown, is used as the target value and the current thickness h Z as the actual value. Strictly speaking, this band supply controller BVR is only a thickness controller. It can be controlled by the thickness h 0.

On stands 3 to 6, loop lifter angles a12 ... a15 serve as the actual value for the belt supply controller BVR. Each angle is a measure of the tape length in stock.

With stands 2 and 7, the tensile force z 1 or z 6 in the incoming strip section is used as the actual value for the respective strip supply controller BVR. The tensile force indicates the supply of tape that is available when the material plastically deforms. With a low pulling force the stock is larger than with a large pulling force. The methods for determining the tensile forces z 1 and z 6 are very different for the stands 2 and 7. The tensile force z 1 in front of the stand 2 is determined from the measured values of the rolling force f and the torque m of the work roll shaft in the stand 1 before and after the run-in of the belt 10 in the scaffold 2 calculated in the belt tension calculator ZB.

The torque m is determined by strain gauges, not shown, and transmitted by radio to the belt tension computer ZB.

In order to determine the tensile force z 6 in front of the frame 7, a deflection roller 16 equipped with a force sensor 9 is used. For this purpose, it is hydraulically moved vertically into its target position immediately after tapping the scaffold 7 and blocked there.

The procedure for finishing a hot strip is regulated as follows:
After the strip 10 has entered the stand 1, the thicknesses h 0 and h Z are determined using the thickness gauges DO, DZ and the torque m and the rolling force f or the quotient m / f. The thickness is sent to the BVR, which takes over the further regulation on scaffold 1. After the belt 10 has entered the stand 2, the measured values m and f and their quotient change. From the change, the strip tension or tensile force z 1 is determined in the strip tension computer ZB and the strip supply controller BVR is thus applied to stand 2, which subsequently controls the load roll gap height s 2. The control is carried out via the position controller PR. After the stand 3 has been tapped, the loop lifter 12 is moved into the desired position; a setpoint deviation of a 12 leads to a change in the load roll gap height s 3 on the stand 3 through the BVR strip supply controller. The same procedure applies to the stands 4, 5, 6. After tapping the Scaffolding 7, the deflection roller 16 is moved into the desired position, as before, and locked there. Force sensor 9 determines the tensile force z 6 and thus acts on the belt supply controller BVR on the scaffold 7. All belt supply regulators BVR provide a constant strip supply between the stands by possibly changing the roll gaps, with the result that the loop lifters 12 ... 15 vibrate only within narrow limits. As a result, with "correct" presetting of the strip thickness HZ, very small deviations to be corrected are achieved, which are then corrected by the very fast roll gap adjustment.

Nevertheless, the desired thickness tolerances behind the finished scale can be exceeded due to disturbances, for example as a result of temperature or thickness differences in the preliminary strip. This is determined by a final thickness measurement. For correction, the strip supply control is supplemented by a control of the exit thickness h E. The mode of operation of the thickness control with the aid of the thickness controller DR has been derived from the following consideration:

With each rolling process, the thickness h of the strip 10 emerging from the roll gap is obtained by dividing the entry thickness into the stand by the extension factor by which the strip length increases. The width of the band 10 is negligible. The following applies to frameworks 1 to 7: $$\text{h 0. v 0 / <figure-callout id="7" label="v" filenames="imgf0001.png" state="{{state}}">v</figure-callout> 7 = h E.}$$

Here, h 0 is the entry thickness and h E the exit thicknesses, v 0 the entry speed in stand 1 and v 7 the exit speed from stand 7. The quotient v 0 / v 7 is the reciprocal extension factor. In order to influence the exit thickness h E, the quantities h 0, v 0 and v 7 are suitable according to the equation. However, these three variables act on the exit thickness h E at different speeds in this control loop. The equation only describes the steady state equilibrium; the dynamic behavior is different. The entry thickness h 0 has the slowest effect on the exit thickness h E. The running time of the belt 10 through all the stands has a delaying effect here. The influence of the speed v 0 is at least ten times faster. Its effect is only delayed by the swinging in of the six successive band supply control loops. The exit thickness h E is influenced most quickly by the speed v 7, because only the last strip supply control loop has to settle here. The speed v 7 is therefore best suited as an actuator for a thickness control circuit. In the control concept of the rolling mill according to FIG. 2, the thickness controller DR supplies a correction signal delta v 7, which is added positively or negatively to the speed specified by the computer via the roll speed N 7 . Instead, the temperature speed-up for frameworks 1 to 6 could be changed by the value delta v 7.

Large control strokes of the thickness controller DR are undesirable because they mean load redistribution among the stands. In order to relieve the thickness controller DR work, either the product calculated from the measured values h 0 and v 0 at the entrance to the rolling mill can be regulated to a constant value by the strip supply controller of stand 1, or, as in FIG. 2, shown, the product h Z x v1 are kept constant by keeping v1 approximately constant by the speed controller of the first stand.

The measurement of the thickness values h 0 and h Z could therefore also be replaced by the measurement of the current thickness h 0 with a thickness gauge DO and the current run-in speed v 0 without changing the control principle.

The belt supply controller BVR can of course only supply their control signals delta s for the position controller PR as long as the belt supply indicators flow from the respective measuring sensors. When the end of the strip reaches a measuring sensor, the corresponding BVR strip supply controller must be deactivated. Then, according to the invention, the load roll gap control AGC acted upon by the rolling force takes over the further regulation of the roll gap in a manner known per se. When switching from the BVR strip supply controller to the AGC control device, the current roll gap value is accepted without bumps. From the illustration in FIG. 2 it follows that the switchover from stand 2 to AGC takes place as soon as the strip 10 leaves the stand 1, because the strip supply controller BVR then no longer receives any tension values z 1. For scaffolds 3 to 6 this applies analogously, since the loop lifters have to be deactivated; correspondingly, no true force effect can be measured for the scaffold 7 on the deflection roller 16.

The process sequence for a new belt 10 begins again as described.

With a finished scale controlled in this way, optimal width corrections of the strip can be carried out during rolling.

The width meter 11 measures the bandwidth b 7 after the last stitch acceptance in the frame 7. In the width controller BR, the measured value is compared with the target width BE. In the event of a deviation, the width controller BR calculates a control signal delta Z and thus acts on the belt supply controller BVR of the scaffold 7. If the bandwidth b 7 is too large, the signal delta Z will result in a tension value being applied to the controller BVR with the tension tension z 6 , who then detects an excessively large strip supply and opens the roll gap on stand 7 by the value delta S, with the result that the tensile stress in the strip is increased and the strip width is reduced. The control effect is faster if, as shown, a further width meter 8 in front of the scaffold 6 precontrols the current bandwidth BR, so that width differences can be corrected locally without loss of time by swinging in the control loop.

The process sequence on the rolling mill can thus be optimally regulated and the effort for loop lifters, measuring devices and control systems is kept within limits. Tests with this control system have shown an improvement in the strip width tolerance of 20 mm and the tolerances for the strip thickness h E to values of plus / minus 0.04 mm to the target thickness of 1.5 mm.

Claims (9)

1. Method of continuously regulating the strip width during the finish rolling of hot strip on a multiple-stand rolling train, wherein the strip width at least behind the finishing group and the strip thickness behind the final stand are measured, and variations in thickness are compensated-for via a thickness regulating circuit on the final stand, characterised by the combination of the following method steps:

   - the strip width (b5, b7) is continuously measured directly after the final pass and before the penultimate pass,

   - the measurement values are fed to a width regulator (BR) provided with anticipatory control, a deviation from the desired value is possibly ascertained there, and a correction signal for the tensile force (Z) in the strip (10) is calculated therefrom before the final pass,

   - an indicator signal (z6), which is proportional to the tensile force, is detected, and

   - the indicator signal and the correction signal impinge on a strip supply regulator (BVR), which adjusts the supply of strip before the final stand (7) by changing the roller nip height (s) of this stand.
2. Method according to claim 1, characterised in that the supply of strip to all of the stands (1...7) is regulated.
3. Method according to claim 2, characterised in that, for the adjustment of the roller nip height (s) after the hot strip has entered a stand, a changeover is effected from the desired strip thickness position to a strip supply indicator, and a changeover to a roller force indicator is effected when the strip (10) emerges from the preceding stand (1...6).
4. Method according to one of claims 1 to 3, characterized in that the final thickness (hE) of the hot strip (10) is additionally regulated by adjusting the parameters, roller nip or rotational speed, of the working rollers.
5. Method according to one of claims 1 to 4, characterized in that the strip width between the first two passes is additionally regulated according to the same principle.
6. Method according to one of claims 1 to 5, characterized in that the reaction force of the strip (10) to a positionable guide roller (16) is used as the indicator signal for the tensile force.
7. Method according to claims 1 to 6, characterised by the use of a combination of various indicators for the instantaneous supply of strip to the stands of a finishing group of a hot strip rolling mill, wherein

   - for the first stand (1), the speed (vO) as well as the strip thickness (hO) before or the strip thickness (hO) before and behind (hZ) the stand (1) are detected,

   - for one or more stands (2), the torque (m) of the working roller shaft and the rolling force (f) in the preceding stand (1) are detected,

   - for at least the final stand (7), the tensile force in the strip (z6) before the stand (7) is determined by measuring the force by means of a guide roller (16),

   - for the other stands (3...6), the deflection (a) of a loop lifter (12...15), which is disposed before the stand, is determined,

   - the thickness (hO, hZ, hE) and width (b5, b7) of the hot strip (10) are determined by contactless radiometry, for regulating the strip width (b7) by adjusting the roller nip height (s) of a stand (2 or 7) of one or more working rollers.
8. Method according to claims 1 to 7, characterised by the use of radio signals to transmit results when directly measuring torque by means of expansion measuring strips on the drive shafts of the working rollers of finishing group stands (1...7) of a rolling train for determining without any delay the tensile stress (z1) in the hot strip (10) for regulating the strip width during the hot-rolling process.
9. Finishing group of a hot strip rolling train having measuring, controlling and regulating means for determining and influencing the operational parameters, for use with the method according to one of claims 1 to 8, wherein

   a) a strip thickness measuring device (DE) is disposed behind the final stand,

   b) a thickness regulator (DR) is provided for compensating-for variations in thickness, and

   c) a strip width measuring device is disposed behind the final stand, characterised by

   d) at least one vertically adjustable, non-oscillatory guide roller (16) before the final stand (7) and a dynamometer (9), which is connected thereto, and

   e) a strip supply regulator (BVR), which is connected to the dynamometer (9) and a width regulator (BR) and acts on the roller nip height (s),
   wherein

   f) a strip width measuring device is disposed before the penultimate stand,

   g) the width regulator (BR) is so designed that deviations from the desired value for the strip width are ascertained and superimposed on the strip supply regulator (BVR) with correction signals for the strip tension before the final stand,

   h) the dynamometer supplies an indicator signal, which is proportional to the strip tension, to the strip supply regulator (BVR), and

   i) the strip supply regulator (BVR) acts on the roller nip height of the final stand, based on the signals from the strip width regulator (BR) and dynamometer, in order to correct the supply of strip, and hence the strip tension before the final stand, in such a manner that the strip width is adjusted to the desired value.

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