DE3843730A1 - Method and apparatus for controlling strip width during hot-strip rolling - Google Patents

Abstract

The invention relates to a method and an apparatus for controlling strip width during hot-strip rolling on a multi-stand finishing group of a rolling train. In the method, the speeds of rotation of the work rolls of each stand are controlled as a function of the instantaneous operating state. The strip widths are recorded directly after the last reduction and/or before the penultimate reduction and compared with the desired width in a width controller. In the event of differences, a strip supply controller for the strip supply between the last stands is acted upon and this corrects the strip supply and the strip tension in such a way, by correction of the rotational speed of all the work rollers or adjustment of the rolling gaps, that the strip width changes. The method is optimised by additional control of the strip thickness by the novel strip-supply principle and by dispensing with some of the loop lifters (Fig. 3). <IMAGE>

Description

The invention relates to a method and an apparatus for Regulating the range of hot strip rolling according to the generic terms of claims 1 and 11.

With hot strip rolling on modern continuous rolling mills usually five or more mill stands in the finishing line should next to the influence of the technological characteristics of the belt regulated thermomechanical rolling in tight tolerances predetermined finished geometry of the band can be set.

Given the inlet cross-section and known Infeed speed of a belt as well as the desired The cross-section of the tape is inevitably stretched during rolling through cascade-like from stand to stand increasing rolling speed and thus increasing roller speed in Dependence on the usually three-step stitch acceptance compensated. The belt cools before and in with increasing dwell time the pre-season on; therefore the base rolling speed and thus the heat output due to increased deformation work increased to the metallurgically important final rolling temperature to keep almost constant (temperature-speed-up). These guidelines for the speed ratios and the arithmetical A nominal master value calculator gives empty roll gap heights of the individual stands in front.  

The belt speed and the roller circumferential speed are but only the same in the flow sheath. The material experiences one Leading and lagging in the roll gap. The problems that arise can avoid rolling mills with a minimum tension control (DE-OS 25 41 071) by speed adjustment and / or loop lifter (DE-PS 33 14 466) with torque and position control for Belt tension correction to be equipped in addition to a Roll gap control and rolling force measurement as well as strip thickness measurement enable control of the rolling mill (Iron and Steel Engineer, 9/84, pages 45-51). In this publication is also details how a load-dependent control works the roll gap height (bearing play and stand expansion compensation) and the possibility of dispensing with loop lifters between the first scaffolding of the finished series, the Loop lifter through a minimum tension control based on known Rolling forces and engine torques and the resulting Speed change of the work rolls to be replaced.

Attempts have also been made to achieve the greatest possible accuracy the strip thickness by reaching for that from the pass schedule resultant roll gap heights of each stand a correction of the measured thickness tolerances by adjusting the load roll gap to realize during rolling (DE-OS 36 37 043) or entire material flow through a rolling mill through a Minimum draft control solely by speed correction of the Work rolls and a thickness control on the first stand too influence (DE-OS 27 21 973). Taking the So far, bandwidth fluctuations in the finished series have not been observed disclosed.

It is therefore an object of the invention, a method and a Device for regulating the strip width during hot rolling of strips to propose the one in the finishing line of a rolling mill precise setting of the bandwidth enable with relatively little Effort for practical rule optimization.

The object is achieved by claims 1 and 11 solved. Advantageous embodiments of the invention are in the Subclaims recorded.

The mass flows at the inlet and outlet of the Finished scale the same size. In the well-known continuity equation However, the parameters change during the course of the process Width, thickness, speed and weight of the tape. With the exception the parameters can be set directly on the rolling mill measure up. The weights as a function of the rolling temperature and type of material is only used as an implicit static quantity during rolling detected. The change in weight of approx. 0.1% during hot rolling is negligible.

The invention takes into account the finding that the tape supply between the scaffolding must be regulated to a stable To achieve the operating state during hot rolling.

If you look at the rolling mill as a controlled system, the control loops for the target guide values for speeds and empty roll gaps or load roll gaps are assigned, presents, receives the important output signals are the rolling forces Rolling moments, the loop lifter angles, the sliver thickness and the outlet speed. The speeds are the control values of the rolls and the nip feeds are available. The Speeds affect the loop lifter angle and the Material flow rate; influences the nip feed also the loop lifter angles, the material flow speed as well as the resulting strip thicknesses. The first to act as a disturbance variable  Line in this controlled system the variation of the Resistance to deformation of the tape as a function of the type of material and Temperature. This also includes so-called skidmarks (Rail shadow) from slab heating.

Also irregularities when slitting or roughing slabs as well as missing side upsetting units in the roughing mill cause fluctuations in bandwidth.

In the simplest case, according to the invention, the existing one Loop regulation by speed correction of the work rolls or used behind the sling in question by increasing or lowering the tape tension and thus the tape supply in the Loop the bandwidth to correct. The control signals for this Belt supply control is generated by a width controller, the in turn with signals from one or more Bandwidth measurements are applied, the measured values with the Comparing target values and, if necessary, deviations from Setpoint applies a signal to the tape supply controller, see above that the tape tension is changed.

The width measurement is made as close as possible to the last one Scaffolding, preferably with a diode line camera, the Band edges as a contrast to a counter light source under the Record hot strip.

The bandwidth is then regulated in such a way that from Belt supply controller determines the belt tension before the last stitch through the reaction force on a fixed adjustable pulley under the hot strip, as well as the change signal from the width controller implemented such that the speeds of the previous stands be changed.

The result is that the hot strip is constricted or relieved and so it gets wider. A change in width has at least in Limits also result in a change in thickness so that sensibly the final thickness of the tape is detected and Thickness changes via a thickness control loop on the last stand  be corrected. The thickness controller can do this automatically Load roll gap control device with a correction signal for the Apply the necessary roll gap height. By doing this the tape supply is adjusted to the requirements in a controlled manner.

A width measurement only after the last stitch has disadvantages, because part of the tape is no longer corrected by the delay can be. A width measurement can therefore also be carried out according to the invention be installed in front of the penultimate scaffolding so that the bandwidth can be controlled between the last two stitches.

A width measurement at both points would be ideal to get the result check the width correction based on the first measurement and to be able to regulate more precisely.

According to the invention, the width correction can also be between the two first stitch decreases or the width adjustment can be made divided the two sections of the finished series be so that larger fluctuations in the width are corrected can occur without too large undesirable control strokes.

Because there are enough manipulated variables to influence the control system Are available, but can also be primarily on one Speed adjustment of the rollers can be dispensed with. A Roll gap height changes can be done much faster than one Change the roller speed, so that the delivery of the Roll gap as a manipulated variable for a strip supply control Correction of the bandwidth on the scaffolding is best suited.

An optimal width control can, however, result Do not neglect the change in tape thickness. The beginning described simple method of thickness control on the last stand only allows minor corrections, especially in the last scaffolding Stitch acceptance should absolutely make up the smallest amount. Therefore it makes sense to close the belt tension over the entire finishing line  control and through a constant tape supply control with high Supplement 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 by scaffolding by control signals from the individual strip supply controllers replaced. The tape supply controllers then control the Mass flow, arithmetically the volume flow, in the finished scale for the hot strip section with the exception of the strip end. Just before that When the end of the belt reaches a stand, the well-known automatic triggers Load roll gap control device the strip supply control again from. With this switchover method, the current actual values the strip thickness or the roll gap as setpoints taken over in order for the control loops to settle again avoid. For the individual primarily independently acting band supply controllers are different indicators than Controlled variable used.  

A setpoint deviation or the actual value for one certain tape supply of a section of the finished series either the tape tension determination or the angle measurement of the Loop lifter deflection.

The regulation of the first scaffold differs from this. Here can change the thickness and speed of the incoming belt - under the permissible assumption that there is currently a constant Bandwidth is available - i.e. a mass flow equivalent measured will. When changing the thickness or speed of the belt the roll gap can be adjusted on the first stand so that the Mass flow, mathematically simplified as a product of thickness and The speed at which the material backs up remains constant.

The loop regulation between the front scaffolding can be done by a tension control of the belt will be replaced. This way you reach a relatively good flatness of the volume. This enables use a thickness measuring system behind the first scaffolding and thus the additional possibility of regulating the thickness of the hot strip on the first Framework.

Experiments have surprisingly confirmed the assumption that one on expensive swiveling sling lifters between the first Can completely dispense with scaffolding and the sl last or more of the last scaffolding as a simple, vertical movable deflection roller can design if you can uses process design according to the invention.

The effectiveness of the front loop lifter is anyway due to that Band stiffness is relatively low, and can have the same effect a from measured shaft torques of the work rolls and rolling forces strip tension calculated by means of the strip supply control of the following Scaffolding can be achieved.  

When determining the belt tension between the stands according to the method of radio transmission from Strain gauge torque measurements are used. Opposite the Torque determination from the current and voltage values of the The DMS method records roller drives without loss Torsional moments directly on the work roll shaft. The results are then available for the radio transmission without delay Train calculation available.

Choosing the most suitable indicators that show a variation of the Show mass flow or tape supply in front of a scaffold according to their most favorable properties in terms of Conditions met: lowest investment, largest Control speed and the best effect on the belt geometry. As It has proven advantageous to use the loop lifter angle to keep it as constant as possible because this creates difficulties that arise from the non-angle-proportional force effect of the loop lifter the band result in the regulation being prevented.

Should the tape thickness behind the finished relay despite Belt supply control still outside the desired tolerances According to the invention, the tape supply control can supplementary thickness control can be used. To do this, use the a radiation measuring device - gamma emitter Ceasium 137 - measured actual thickness value fed to a thickness controller, the possibly two control signals correlating to the degree of Can produce deviation from the target thickness. In the beginning The thickness controller then works in the simplest control concept described on the load roll gap control. But in this case for Strip supply control the roll gap control variable is used here another solution makes sense.  

A change in thickness can be seen as a trend in the thickness gauge the finished scale and thus can be changed by changing the Speed trends of the work rolls between two groups of stands Finished scale locally the band supply can be increased or decreased with the effect that the tape supply controller 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 - to the roll gap controller of the affected Scaffolding are routed so that the tape supply actually does not change.

The width regulation is implemented in this concept Roll gap adjustment included.

For this purpose, the width controller mentioned at the beginning gives a signal to the Belt supply controller of the last scaffolding, which then in turn the Tension change by adjusting the roll gap and not - as with the simplest concept - the speeds of the work rolls generated. With this fast dynamic control, the Correct latitude fluctuations without the slower Thickness control via speed adjustment ensures compensation. Otherwise the thickness regulator must also be a Receiving disturbance variables.

The last acceptance test must be designed for this regulation that it is larger in percentage than the one to be corrected Bandwidth fluctuation.

The invention is to be explained in more detail with the aid of schematic drawings will. It shows

Fig. 1, the force effect of a looper,

Fig. 2 is a scheme according to the invention for a finishing group of a block diagram,

Fig. 3 shows a simple width control according to the invention on a finished scale 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 thus the changes in tape tension are significantly less than with the conventional loop control.

Fig. 2 shows the conditions at the finishing group of a rolling train for hot wide 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 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, capital letters should be used Mark 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 reach their current setpoints N 1 . . . Comply with 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 controller BVR thus regulates a constant belt supply between the stands 1 . . . 7 .

In the first stand, the nominal thickness HZ, 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 .

For scaffolding 3 to 6 , loop lifter angles a 12 are used . . . a 15 as actual values 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 stands 2 and 7 . The tensile force z 1 in front of the stand 2 is calculated 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 strip 10 has entered the stand 2 in the strip 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 like follows regulated:

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 control takes place via the position controller PR . After initial pass of the framework 3 of the looper is moved to desired position 12, a setpoint deviation of a 12 performs the strip supply regulator BVR to stand 3 to a change in the load roll nip height S3. The same procedure applies to frameworks 4, 5, 6 . After the framework 7 has been tapped, 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 scaffold 7 . All BVR strip supply controllers provide a constant strip supply between the stands by possibly changing the roll gaps, with the result that the loop lifters 12 . . . 15 only swing 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 faults, for example as a result of temperature or thickness differences in the preliminary strip. This is determined by a final thickness measurement. To correct this, the strip supply control is supplemented by a control of the outlet thickness h E. The operation of the thickness control with the aid of the thickness controller DR has been derived from the following consideration:

During 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 :

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 quantities h 0 , v 0 and v 7 are suitable according to the equation. In this control loop, however, these three variables act on the exit thickness h E at different speeds. The equation only describes the steady state of 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 velocity v 0 is at least ten times faster. Their effect is only delayed by the settling 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. Speed v 7 is therefore best suited as an actuator for a thickness control loop. 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 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 × v 1 can be kept constant by keeping v 1 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 meter DO and the current run-in 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. If 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 strip supply controller BVR to the control device AGC , 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 belt 10 leaves the stand 1 , because then the belt supply controller BVR no longer receives any tension values z 1 . This applies analogously to frameworks 3 to 6 , since the loop lifters have to be deactivated; for scaffold 7 , true deflection force can accordingly no longer be measured on deflection roller 16 .

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

With a prefabricated relay regulated in this way, optimal Adjust the width of the strip while it is rolling.

The width meter 11 measures 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 tensile stress value being applied to the BVR controller loaded with tensile stress z 6 , which will then determine an excessive strip supply and open the roll gap on stand 7 by the delta S value the consequence that the tension in the band is increased and the bandwidth 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 can be corrected locally without loss of time by swinging in 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 band width tolerance of 20 mm and the tolerances for the band thickness h E to values of plus / minus 0.04 mm to the target thickness of 1.5 mm.

Fig. 3 shows the integration of a width control loop analogous to Fig. 2 in a conventional finishing scale in which the belt supply controller BVR are designed as a speed-controlling loop controller. The reference numerals from FIG. 2 have been retained for the sake of clarity. Since the parameter roll speed N 5 , N 6 is used here for the width control, according to the invention the current thickness hE of the strip 10 must be regulated by applying the load roll gap control AGC , which then corrects the roll gap by delta S with the thickness controller DR .

Claims (15)

1.Procedure for the continuous finishing of hot strip on a multi-stand rolling mill, the strip thickness and the strip width being measured at least behind the finishing strip and the strip thickness being corrected if necessary by means of a thickness control overlaying an automatic load roll gap control, characterized by the combination of the following process steps:

• - the bandwidth (b 5 , b 7 ) is measured continuously immediately after the last stitch or before the penultimate stitch,
• the measured values are fed to a width controller (BR) , where a setpoint deviation is determined and a change signal for the tensile force ( ΔZ ) in the band ( 10 ) is calculated before the last stitch,
• an indicator signal (z 6 ) proportional to the tensile force is detected,
• - With the indicator signal and the change signal, a tape supply regulator (BVR) is applied, which changes the tape supply in front of the last scaffold ( 7 ).

2. The method according to claim 1, characterized in that the bandwidth (b 5 , b 7 ) is measured simultaneously before and after the last two stitches. 3. The method according to claim 1 or 2, characterized in that the strip supply is changed by changing the roll gap height (S) . 4. The method according to claim 1 or 2, characterized in that the tape supply is changed by changing the speeds (N 1 ... N 7 ) of one or more work rolls. 5. The method according to any one of claims 1 to 4, characterized in that the band supply of all scaffolding ( 1 ... 7 ) is regulated. 6. The method according to any one of claims 1 to 5, characterized in that in addition the final thickness (hE) of the hot strip ( 10 ) is regulated by adjusting the parameters of the roll gap or speed of the work roll, the actuating variable not used for the width control being adjusted. 7. The method according to any one of claims 1 to 6, characterized characterized in that in addition the bandwidth between the the first two stitches are regulated according to the same principle. 8. The method according to any one of claims 1 to 7, characterized in that the reaction force of the belt ( 10 ) on a positionable deflection roller ( 16 ) is used as an indicator signal for the tensile force. 9. Use of a combination of different indicators for the current strip stock on the stands of a finishing line of a hot strip mill, where

• - for the first stand ( 1 ) the speed (v 0 ) and the strip thickness (h 0 ) before or the strip thickness (h 0 ) before and after (hZ) the stand ( 1 ),
• - for one or more 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 (z 6 ) in front of the scaffold ( 7 ) is determined by force measurement on a deflection roller ( 16 ),
• - For one or more scaffolds ( 3 ... 6 ) the deflection (a) of a loop lifter ( 12 ... 15 ) arranged in front of the scaffold is determined,
• the thickness (h 0 , hZ, hE) and width (b 5 , b 7 ) of the hot strip ( 10 ) are determined by non-contact radiation measurement,

to regulate the strip width (b 7 ) by adjusting the roll gap height (s) of a stand ( 2 or 7 ) or the speeds (N 1 ... N 7 ) of one or more work rolls. 10. Use 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 (z 1 ) in the hot strip ( 10 ). 11. Finished scale of a hot strip mill with measuring, control and regulating devices for recording and influencing the process parameters, characterized by the combination of the following components:

• - a bandwidth measuring device ( 8, 11 ) behind the last scaffold ( 7 ) and / or in front of the penultimate scaffold ( 6 ),
• - a width controller (BR) connected to the width measuring devices,
• - A measuring device ( 9 ) for a strip tension indicator and
• - A with the indicator measuring device ( 9 ) and the width controller ( BR) connected tape supply controller (BVR) .

12. Finished relay according to claim 11, characterized by additional bandwidth meters in front of the first and / or behind the second stand and an associated width controller. 13. Finished scale according to claim 11 or 12, characterized by a strip supply controller (BVR) influencing the roll gap height ( s) per stand ( 1 ... 7 ). 14. Finished relay according to one of claims 11 to 13, characterized by at least one height-adjustable, non-oscillating deflection roller ( 16 ) in front of the last frame ( 7 ) and an associated dynamometer ( 9 ).