EP0375094A2 - Method and device for the hot-rolling of strip - Google Patents

Abstract

The invention relates to a method and a device for controlling the hot-rolling of strip on a multiple-stand finishing line of a rolling mill train in which the speeds and the roll-nip heights of the working rolls of each stand are controlled as a function of the instantaneous operating state, in which arrangement, for the readjustment of the roll-nip height after the hot strip enters a stand, [lacuna] from a desired strip-thickness position is switched over to a strip-supply indicator, and to a rolling-force indicator when the strip leaves the preceding stand, the result of a previous thickness measurement being utilized for the first stand. The strip thickness - if need be while allowing for fluctuations in the strip width - can thereby be controlled very quickly and accurately. <IMAGE>

Description

The invention relates to a method and a device for regulating hot strip rolling according to the preambles of claims 1 and 14.

Hot strip rolling on modern continuous rolling mills, usually with five or more roll 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 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 decrease. 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 constantly increased due to increased deformation work in order to keep the metallurgically important final rolling temperature approximately constant (temperature-speed-up). A setpoint value calculator specifies these specifications for the speed ratios and the calculated empty roll gap heights of the individual stands.

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 that arise as a result, rolling mills can be equipped with strip tension control by adjusting the speed 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 for the roll gap heights of each stand resulting from the pass schedule a correction of the measured thickness tolerances by adjusting the load roll gap during rolling (DE-OS 36 37 043) or the whole To influence material flow through a rolling mill by means of a minimum tension control solely by means of speed correction of the work rolls and a thickness control on the first stand (DE-OS 27 21 973). A speed control loop is because of the big one Response time very slow due to the inertia of the rollers.

It is therefore the object of the invention to propose a method and a device for regulating the hot rolling of strips in the finishing line of a rolling mill, which enable a very precise adjustment of the strip thickness with relatively little effort for practical control optimization.

The object is achieved by claims 1 and 14. 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.

It is also taken into account that, at least to a first approximation, the spreading that occurs during rolling or constriction of the strip either remains constant or changes in a known manner, so that it can be used as a factor in a material flow calculation.

If you think of the rolling mill as a controlled system, to which the control loops for the target guide values of speed and idle roll gap or load roll gap are assigned, you get the rolling forces, the rolling moments, the loop lifter angles, the sliver thickness and the slowing speed as important output signals. The speeds of the rolls and the nip feeds are available as manipulated variables. The speeds influence the loop lifter angle and the material flow speed; the roll gap feed also influences the loop lifter angles, the material flow speed and the resulting strip thicknesses. In this controlled system, the variation in the resistance to deformation of the strip as a function of material type and temperature acts primarily as a disturbance variable. 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 cause strip geometry fluctuations.

Since there are enough manipulated variables available to influence the control system, there is primarily 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 delivery of the roll gap is best suited as a manipulated variable for a strip supply control and for correcting the strip thickness on the stands.

According to the invention, the usual guide setpoint for the position control loop "empty rolling 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, arithmetically 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. Different indicators are used as control variables for the individual band supply regulators, which act primarily independently of one another.

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 belt, the Roll gap are set on the first stand so that the mass flow, mathematically simplified as a product of thickness and speed, remains constant due to backflow of the material.

Since, according to the invention, the loop regulation between the front stands can be replaced by tension regulation of the belt, a relatively good flatness of the belt is achieved. 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 dispense with expensive swiveling loop lifters between the first stands and that the loop lifters in front of the last or more of the last stands can be designed as a simple, vertically movable deflection roller if the process concept according to the invention is used. 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.

When determining the strip tension between the stands, the method of radio transmission of strain gauge torque measurements can be used according to the invention. Compared to the torque determination from the current and voltage values of the roller drives, the strain gauge method directly records the torsional moments without loss the work roll shaft. 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 according to the invention. The aim is to achieve maximum deviations from the target strip thickness of less than 0.05 mm. For this purpose, the actual thickness value measured, for example, with a radiation measuring device - gamma emitter cesium 137 - is fed to a thickness controller, which can optionally generate two control signals correlating to the extent of the deviation from the target thickness.

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 (temperature speed-up) of the work rolls between two Scaffold groups of the finished batch locally the strip supply is increased or decreased with the effect that the strip supply controller intervenes and changes the strip thickness. 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.

An even more precise control of the strip thickness can be achieved if the change in bandwidth approximately calculated in the volume flow control or mass flow control is also largely compensated for by control technology. For this purpose, according to the invention, the bandwidth is regulated during the last stitch acceptance by measuring the bandwidth and comparing the measured values in a width controller with nominal values for the bandwidth. As soon as setpoint deviations arise, a new strip tension is calculated from this according to the predefined calculation scheme, which must lead to a change in the strip width before the last stitch acceptance. For this purpose, the width controller sends a signal to the strip supply controller of the last stand, which in turn generates the change in tension by adjusting the roll gap. With this quick control, local fluctuations in width, which u. a. correct from skid marks (rail shadows when heating slabs) without correcting the slower thickness control for 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 fluctuation in the bandwidth to be corrected.

In principle, the width control works if the bandwidth is measured after the last stitch decrease. However, the time delay in the control makes it seem more favorable to measure the bandwidth before the penultimate stitch acceptance or to use two measuring devices so that the width controller can already be controlled. The same method can also be used for width control by changing the tension of the belt between the first stands, provided that appropriate width measuring and control devices are used there.

• Fig. 1 die Kraftwirkung eines Schlingenhebers,
• Fig. 2 eine erfindungsgemäße Regelung für eine Fertigstaffel als Blockschaltbild.
• Fig. 3 eine erfindungsgemäße Regelung am ersten Gerüst einer Fertigstaffel als Blockschaltbild und
• Fig. 4 eine weitere erfindungsgemäße Regelung an den letzten Gerüsten einer Fertigstaffel als Blockschaltbild.

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

• 1 shows the force effect of a loop lifter,
• Fig. 2 shows a control according to the invention for a prefabricated season as a block diagram.
• Fig. 3 shows a control according to the invention on the first frame of a prefabricated scale as a block diagram and
• Fig. 4 shows another control according to the invention on the last scaffolding of 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 band supply control and the band tension changes are significantly less than with the conventional loop control.

Fig. 2 shows the conditions on the finishing line of a rolling mill for hot strip 10 with seven roll 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 are 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 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 setpoints for the roll speeds NL are predefined by a master setpoint calculator (not shown) and correspondingly during the rolling Desired pass schedule ramped and the desired temperature speed-up tends to increase. 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 obtains its actual value from the piece of belt entering the respective scaffolding 1 ... 7, 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 controller BVR thus regulates 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 regulator BVR is only a thickness regulator. 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 regulator 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 tape supply, the is available when the material deforms plastically. 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 strip 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. The strip tension computer ZB determines the strip tension or tensile force z 1 from the change and thus acts on the strip supply controller BVR on stand 2, which subsequently controls the load roll gap height s 2. The check is done thereby 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 by 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 and locked there. Force sensor 9 determines the tensile force z 6 and thus acts on the strip supply regulator BVR on stand 7. All strip supply regulators BVR ensure a constant strip supply between the stands by possibly changing the roll gap, with the result that the loop lifters 12 ... 15 only in narrow spaces Swing borders. 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 faults, 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, in which the entry thickness into the stand is divided by the extension factor by which the Band length increased. The width of the band 10 is negligible. The following applies to frameworks 1 to 7:
h 0. v 0 / v 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 variables 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 speed v 0 is at least ten times faster. Its effect is only delayed by the swinging in of the six consecutive band supply control loops. The exit thickness h E is most rapidly influenced 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, could you can also change the temperature speed-up for frameworks 1 to 6 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 can be regulated to a constant value by the belt supply controller of stand 1 at the entrance of the rolling mill, or, as shown in FIG. 2, the Product h Z x v1 can be kept constant by keeping v1 approximately constant by the speed controller and h Z by the belt supply controller of the first stand.

The measurement of the thickness values h 0 and h Z could therefore also be replaced according to FIG. 3 by measuring the current thickness h 0 with a thickness meter DO and the current entry speed v 0, without changing the control principle.

The tape supply controller BVR can of course only deliver their control signals delta s for the position controller PR as long as the tape supply indicators flow from the respective measuring sensors. When the end of the strip reaches a 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 f takes over the further regulation of the roll gap in a manner known per se. When switching from the strip supply controller BVR to the control device AGC, the current roll gap value is accepted without bumps. From the illustration 2 shows that the switchover from stand 2 to AGC takes place as soon as the belt 10 leaves the stand 1, because the belt supply controller BVR then no longer receives any tension values z 1. This applies analogously to frameworks 3 to 6, 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.

FIG. 4 shows the possibility of optimizing the course of the process by additionally providing the finished scale with a width regulation.

The width meter 11 records the bandwidth b 7 after the last stitch acceptance in the frame 7. The measured value is compared with the nominal width BE in the width controller BR. 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 stand 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 , which then detects an excessively large supply of strip 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 pre-controls the current bandwidth BR, so that width differences are true to location Loss of time can be corrected by settling the control loop.

Thus, the process sequence on the rolling mill can be optimally controlled 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 tolerances for the strip thickness h E to values of plus / minus 0.02 mm to the target thickness of 1.5 mm.

Claims (16)

1. A method for regulating the rolling of hot strip on a multi-stand finishing batch of a rolling mill, in which the roll gap height is measured, characterized in that for the readjustment of the roll gap height (s) after hot strip run-in into a stand, it is switched from a target strip thickness position to a strip supply indicator and to one Rolling force indicator is switched when the strip (10) runs out of the previous stand (1 ... 6), the result of a previous thickness measurement being used for the first stand (1). 2. The method according to claim 1, characterized in that the roll gap height (s) depending on the stand
- the desired target thickness before the hot strip (10) runs in,
- The current strip supply in front of a stand (1 ... 7) during the passage of the hot strip (10) through the finishing line and
- The current rolling force (f) is set as soon as the end of the hot strip (10) has left the previous stand (1 ... 6). 3. The method according to claim 1 or 2, characterized in that the tape supply in front of a frame is regulated by adjusting the roll gap height (s). 4. The method according to any one of claims 1 to 3, characterized in that for the strip supply control, the tensile stress (Z) in the hot strip is determined by measuring the rolling force (f) and the torque (m) on the drive shaft of the work roll. 5. The method according to any one of claims 1 to 4, characterized in that the deflection (a) of a loop lifter (12 ... 15) in front of the scaffold (3 ... 6) is measured for the tape supply control of a scaffold. 6. The method according to any one of claims 1 to 5, characterized in that the thickness (hE) of the hot strip (10) is measured behind the finished scale and the thickness is regulated in the event of deviations from the target value such that between two of the stands (1 .. .7) the strip supply is changed by changing the speeds (N1 ... N7) of all subsequent or previous work rolls. 7. The method according to claim 6, characterized in that signals for regulating the thickness of the hot strip (10) are used as time-delayed signals for adjusting the roll gap height (s) of the rear of the two stands. 8. The method according to any one of claims 1 to 7, characterized in that on the first frame (1) the indicators thickness (h0) and speed (v0) of Hot strip (10) in front or the thickness of the hot strip in front of (h0) and behind (hZ) the stand (1) is determined and then the roll gap height (s) is set. 9. The method according to any one of claims 1 to 8, characterized in that the reaction force (z6) of the hot strip (10) on a lockable deflection roller (16) is used as a strip supply indicator in front of the last stand (7). 10. The method according to any one of claims 1 to 9, characterized in that the bandwidth (b7) is additionally regulated. 11. The method according to claim 10, characterized in that
- the bandwidth is measured after (b7) the last stitch acceptance and / or before (b5) the penultimate stitch acceptance in the finished scale,
- The measurement results are fed to a width calculator (BR), which, if necessary, determines a setpoint deviation and uses this to calculate a value for a change in the strip tension between the last two stitch decreases and thus acts on the strip supply controller (BVR) of the last stand (7). 12. Use of a combination of different indicators for the determination of the current strip supply on the stands (1 ... 7) of a finishing line of a hot strip mill, where
- for the first scaffold (1) the speed (v0) and the strip thickness (h0) in front or the strip thickness (h0) in front of and behind (h7) the frame (1),
- for one or more subsequent stands (2) the torque (m) of the work roll shaft and the rolling force (f) in the previous stand (1) are measured,
- For at least the last scaffold (7), the tensile force in the belt (z6) in front of the scaffold (7) is determined by measuring the force on a lockable deflection roller (16),
- For the other scaffolding (3 ... 6) the deflection (a) of a loop lifter (12 ... 15) arranged in front of the scaffolding is determined,
for the stand-by-stand control of the strip supply by changing the roll gap height (s) and an additional control of the final thickness of the hot strip (10) by measuring the thickness (hE) of the hot strip behind the finishing relay and changing the strip supply at one point of the finishing relay by correcting the speeds in blocks ( N1 ... N7) of the preceding or following work rolls, if a deviation between the target and actual value of the final thickness (hE) of the hot strip (10) has been determined. 13. Application of the radio transmission of results in the direct torque measurement by means of strain gauges on the drive shafts of the work rolls of finishing train stands (1 ... 7) of a rolling mill for the instantaneous determination of the tensile stress (Z1) in the hot strip, preferably for Controlling the roll gap height during hot strip rolling. 14. Finished scale of a hot strip mill with measuring, control and regulating device for detecting and influencing the process parameters, preferably for applying the process according to one of claims 1 to 13, characterized by the combination of the following components:
- a strip supply controller (BVR) per stand (1 ... 7) influencing the roll gap height (s) and
- A thickness measuring device (DO, DZ) for the hot strip (10) in front of and / or behind the first stand (1) and a speed measuring device in front of the first stand and
- At least one height-adjustable deflection roller (16) in the position in front of the last frame (7),
- which are connected to the respective tape supply controller (BVR). 15. Finished scale according to claim 14, characterized by a measuring device (DE) for the final thickness (hE) of the hot strip (10) and connected to a speed controller (DNR) of one or more work rolls thickness controller (DR). 16. finished scale according to claim 14 or 15, characterized by a bandwidth measuring device (8, 11) behind the last frame (7) and / or before the penultimate frame (6) and a width controller (BR), which is connected to the belt supply controller (BVR) for the last stand (7).

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