DE3843730C2 - Method and device for regulating the strip width in hot strip rolling - Google Patents

Description

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

By hot strip rolling on modern continuous Rolling mills with mostly five or more rolling stands in the In addition to influencing the finished series technological characteristics of the belt by regulated thermomechanical rolling in tight tolerances predetermined finished geometry of the band set become.

Given the inlet cross-section and known Infeed speed of a belt as well as desired The cross-section of the tape becomes inevitable Stretching from stand to stand during rolling rolling speed rising in a cascade and thus increasing roller speed depending on the in the Usually degressively graded stitch acceptance compensated. With increasing dwell time, the belt cools before and in the Finished scale from; therefore the Basic rolling speed and thus the heat emission steadily increased due to increased deformation work, around the metallurgically important final rolling temperature to keep almost constant (temperature-speed-up). These specifications for the speed ratios and the calculated empty roll gap heights of the individual stands specifies a target value calculator.

The belt speed and the Roller peripheral speed are only in the  Flow sheath the same. The material experiences a preliminary and Lag in the nip. The problems that arise to avoid rolling mills with a Belt tension control through speed adjustment and / or Loop lifters can be equipped in addition to a Roll gap control and rolling force measurement as well Strip thickness measurement a control of the rolling mill enable (Iron and Steel Engineer, 9/84, page 45-51). In this release is also detailed the functioning of a load-dependent Regulation of the roll gap height (bearing play and Expansion compensation) and the possibility of No loop lifters between the first Scaffolding of the finished series, the Loop lifter due to a minimum tension control known rolling forces and engine torques and therefrom resulting change in speed of the work rolls replaced become.

An attempt has also been made to make the greatest possible Accuracy of strip thickness can be achieved by looking for roll gap heights resulting from the pass schedule A correction of the measured thickness tolerances by adjusting the load roll gap during rolling to realize (DE-OS 36 37 043) or the whole Material flow through a rolling mill through a Minimum train control solely by speed correction of the Work rolls and a thickness control on the first stand to influence (DE-OS 27 21 973). A consideration the fluctuations in bandwidth in the finished series not revealed.

From DE-OS 22 49 366 is a measuring and control system for Prefabricated squadrons known, primarily with the tension in the Band between the scaffolding by loop lifters and the Bandwidth measured behind and through the finishing line Speed control the tension and thus the  Strip thickness can be neglected or optional as Factor into the voltage calculation by the Keep tension as constant as possible. if the Tensile stress leads to a change in sheet thickness this through speed and pressure control devices to the Scaffolding to be corrected. A band supply regulation through Changing the nip height is not disclosed; just as little the type of voltage sensor.

It is therefore the object of the invention, a method and a device for regulating the bandwidth at Hot rolling of strips in the finished batch Propose rolling mill that is accurate and fast Setting the bandwidth allow at relative little effort for practical rule optimization.

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

The mass flows at the inlet and The finishing line is of the same size. In the well-known However, the continuity equation changes during the Procedure, the parameters width, thickness, Speed and weight of the tape. With the exception of The parameters can be weighted directly on the rolling mill measure up. The weights as a function of the rolling temperature and Material type is only used as an implicit statistical quantity detectable during rolling. The change in weight of approx. 0.1% during hot rolling is negligible.

The invention takes into account the knowledge that the Belt stock between the scaffolding must be regulated in order  stable operating condition during hot rolling to reach.

If you look at the rolling mill as a controlled system, the Control loops for the target guide speeds and Empty roll gap or load roll gap assigned are presented as important output signals the rolling forces, the rolling moments, the Loop lifter angle, the sliver thickness and the Outlet speed. The control variables are Speeds of the rolls and the roll gap infeeds Available. The speeds affect the Loop lifter angle and material flow rate; the roll gap feed also influences the Loop lifter angle, the material flow rate as well as the resulting strip thicknesses. Acts as a disturbance variable primarily the variation of the Strain of deformation of the tape as a function of Material type and temperature. This also includes so-called Skidmarks from the heating of the slab. Even irregularities when slitting or roughing of slabs and missing side upsetting units in the roughing mill leave bandwidth fluctuations arise.

In the simplest case, as is known per se, the existing loop control by speed correction of the Work rolls in front of or behind the sling in question used to increase or decrease the Band tension and thus the tape supply in the loop Correct bandwidth.

Because there are enough manipulated variables to influence the Control system are available, but can also be primary no speed adjustment of the rollers become. Changing the roll gap height can be significant happen faster than changing the roller speed,  so that the delivery of the roll gap as a manipulated variable for a band supply control to correct the band width best suited to the scaffolding.

The control signals for this tape supply control are from generated a width controller, which in turn with signals affected by one or more bandwidth measurements is compared, the measured values with the target values and if necessary, deviations from the nominal value Tape supply controller is supplied with a signal so that the tape tension is changed.

The width measurement is made as close as possible behind the last scaffolding, preferably with one Diode line scan camera that contrasts the band edges a counter light source under the hot strip. The bandwidth is then regulated in such a way that from Strap supply controller the strap tension before the last stitch, determined by the reaction force to a adjustable deflection roller under the hot strip, as well the change signal from the width controller implemented 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 or narrower. A change in Width also has a change in, at least within limits Thickness, so that the final thickness of the Band is detected and changes in thickness over a Thickness control loop on the last stand can be adjusted. The thickness controller can do this automatically Load roll gap control device with one Correction signal for the necessary roll gap height act upon. By doing this, the Tape supply controls adjusted to the requirements.

A width measurement only after the last stitch has Disadvantages, because of the delay part of the tape can no longer be corrected. Therefore  according to the invention also a width measurement before penultimate scaffold to be installed so that the Bandwidth between the last two stitches can be piloted.

A width measurement at both points would be ideal in order to achieve this Result of the width correction based on the first measurement control and regulate more precisely.

According to the invention, the width correction can also be between the first two stitch approvals or Latitude correction can be applied to the two sections mentioned of the finished series, so that larger ones Fluctuations in the width can be corrected without that too large undesirable control strokes occur.

An optimal width control can, however resulting changes in tape thickness to neglect. The simple described at the beginning Method of thickness control on the last scaffold only leaves minor corrections, especially in the last scaffolding Absolutely the smallest amount should. Therefore, it makes sense to pull the tape all over Finished batch control and through a constant Belt supply control with high control speed too complete.

To do this, the usual master setpoint for the Position control loop "empty roll gap" after running in Band in the first scaffold by means of control signals of the individual tape supply controller replaced. The Belt 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. Shortly before the end of the belt reaches a scaffold, releases the familiar one automatic load roll gap control device Band supply regulation again. With this  Switching procedures are based on the current actual values of the Strip thickness or the roll gap as smooth Setpoints are accepted to ensure that the To avoid control loops. Primarily for the individual independent band supply controller different indicators used as a control variable.

A setpoint deviation or the actual value for a certain tape supply of a section of the The finished batch delivers either the tape tension determination or the angle measurement of the loop lifter deflection.

The regulation of the first differs from this Scaffolding. Here the thickness and speed of the incoming tape - under the permissible assumption that there is currently a constant bandwidth - i.e. one Mass flow equivalent are measured. When changing the The thickness or speed of the strip can be the roll gap be set on the first scaffold so that the Mass flow, mathematically simplified as a product Thickness and speed, through backflow of the material remains constant.

The loop regulation between the front scaffolding can be replaced by a tension control of the belt. Thereby a relatively good flatness of the belt is achieved. This enables the use of a thickness measuring system behind the first scaffolding and thus the additional possibility of Thickness control of the hot strip on the first stand.

It has surprisingly been accepted in experiments confirms that one goes for expensive swiveling loop lifters between the first scaffolding and the Loop lifters before the last or more of the last Scaffolding as a simple, vertically movable deflection roller can design if one of the invention Process conception applies.  

The effectiveness of the front loop lifters is anyway due to the tape stiffness relatively low, and the same Effect can be measured by a measured from the wave moments Work rolls and rolling forces calculated strip tension using Belt supply control of the following scaffold reached become.

When determining the belt tension between the According to the invention, the scaffolding method Radio transmission of strain gauge torque measurements applied become. Compared to the moment determination from the electricity and The DMS method records the tension values of the roller drives the torsional moments directly on the Work roll shaft. The results are then available through the Radio transmission without delay for train calculation to disposal.

Choosing the most suitable indicators, the one Variation of the mass flow or band supply Show in front of a scaffold, is after each most favorable properties in terms of conditions hit: lowest investment, biggest Control speed and best effect on the Band geometry. It has proven to be advantageous that Keep loop lifter angle as constant as possible because thereby difficulties that do not arise from the force of the loop lifter proportional to the angle the tape result in the adjustment being prevented become.

Should the tape thickness behind the finished relay despite Band supply control still outside of the desired one Tolerances are, according to the invention one Belt supply control additional thickness control used become. To do this, use a radiometer - Gamma emitter cesium 137 - measured actual thickness fed to a thickness controller, possibly two  Control signals correlating to the degree of deviation from the target thickness can produce. In the initially described The thickness controller then acts on the simplest control concept the load roll gap control. Since in this case the control value for the roll gap for the strip supply control another solution is useful here.

A change in thickness can be seen as a trend in the thickness gauge behind the finished scale, and thus can by Change in the speed trend of the work rolls between two scaffolding groups of the prefabricated scale locally the Tape supply can be increased or decreased with the effect that the tape supply regulator intervenes and the tape thickness changes. At the same time, a correction signal - delayed to adapt to the higher one Control speed of the roll gap control circuit - to the Roll gap controller of the affected stand are directed, so that the tape supply does not actually change.

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

The width controller mentioned at the beginning gives a signal to the tape supply controller of the last stand, which then again the change in tension by adjusting the Roll gap and not - as with the simplest concept - of the speeds of the work rolls. With this the fast dynamic control can Correct latitude fluctuations without the slower Thickness control via speed adjustment for compensation worries. Otherwise the thickness regulator must also be a Receiving disturbance variables.

The last stitch acceptance must be so for this regulation be designed so that it is larger than the percentage bandwidth fluctuation to be corrected.

The invention is to be described in more detail with the aid of schematic drawings are explained. Show it:

Fig. 1, the force effect of a looper,

Fig. 2 shows a control according to the invention 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. In the case of the sliver supply control, the sliver tension changes are significantly less than with the conventional sling 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 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 from a roll gap computer HR the roll gap h currently calculated from the rolling force f and the displayed position s of the rolls.

The following functional description is intended to be large Letters target values and small letters actual values mark.  

All setpoints for the roller speeds NL are from a master setpoint calculator, not shown predetermined and during the rolling according to the desired pass schedule ramped and the desired Temperature-speed-up tends to increase. Speed controllers DNR ensure that the speeds are their current setpoints N1. . . Comply with N7.

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 framework, the nominal, not shown, becomes Thickness H Z as setpoint and the current thickness hZ as Actual value used. This is strictly speaking Belt supply controller BVR is just a thickness controller. He can be controlled by the thickness h0.

Loop stands a12 are used for stands 3 to 6 . . . a15 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 z1 or z6 in the incoming belt section is used as the actual value for the respective belt 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 z1 and z6 are very different for stands 2 and 7 . The tensile force z1 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 not shown Strain gauges determined and sent to the radio Transfer belt tension calculator ZB.

In order to determine the tensile force z6 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 process sequence for finish rolling a hot strip is regulated as follows:

After the strip 10 has entered the stand 1 , the thicknesses h0 and hZ are determined using the thickness gauges D0, DZ and the torque in and the rolling force f and 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 in the belt tension or pulling force is determined z1 and thus the ribbon supply controller BVR applied to structure 2 in Bandzugrechner For example, the controls below the load nip height s2. 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 a12 leads to a change in the load roll gap height s3 by the belt supply controller BVR on stand 3 . The same procedure applies to frameworks 4 , 5 , 6 . After the scaffold 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 z6 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, due to interference, for example resulting from temperature or thickness differences of the Supporting strip, the desired thickness tolerances behind the Finished scale will be exceeded. This is done by a final thickness measurement determined. For correction the tape supply regulation is supplemented by a regulation the exit thickness hE. The mode of action of Thickness control using the thickness controller DR is off based on 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 :

h0v0 / v7 = hE.

Here h0 is the entry thickness and hE the exit thicknesses, v0 the entry speed in stand 1 and v7 the exit speed from stand 7 .

The quotient v0 / v7 is the reciprocal extension factor. In order to influence the exit thickness hE, the quantities h0, v0 and v7 are suitable according to the equation. In this control loop, however, these three variables act on the exit thickness hE at different speeds. The equation only describes the steady state of equilibrium; the dynamic behavior is different. The entry thickness h0 has the slowest effect on the exit thickness hE. The running time of the belt 10 through all the stands has a delaying effect here. The influence of velocity v0 is at least ten times faster. Their effect is only delayed by the swinging in of the six consecutive band supply control loops. The exit thickness hE is most quickly influenced by the speed v7, because only the last strip supply control loop has to settle here. Speed v7 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 v7, which is added positively or negatively to the speed specified by the computer via the roll speed N7. Instead, you could also change the temperature speed-up for frameworks 1 to 6 by the value delta v7.

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 h0 and v0 can be regulated to a constant value by the strip supply controller of stand 1 at the entrance of the rolling mill, or, as shown in FIG. 2, the product hZ can be controlled × v1 can be kept constant by keeping v1 approximately constant by the speed controller of the first stand.

The measurement of the thickness values h0 and hZ could therefore also by measuring the current thickness h0 with Thickness gauge D0 and the current infeed speed v0 can be replaced without changing the control principle.

The belt supply controller BVR can of course only deliver their control signals delta s for the position controller PR as long as the belt supply indicators flow from the respective measuring sensor. 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 then the strip supply regulator BVR no longer contains any tension values z1. For scaffolds 3 to 6 this applies analogously, since the loop lifters have to be deactivated; for scaffold 7 , true deflection force can no longer be measured accordingly 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 width corrections of the tape during the Carry out rolling.

The width meter 11 measures the bandwidth b7 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 b7 is too large, the signal delta Z will result in a tensile stress value being applied to the BVR controller with tensile stress z6, which then determines that the strip supply is too large and opens the roll gap on stand 7 by the value delta S with which As a result, 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.

The process sequence on the rolling mill is thus optimal adjustable and the effort for loop lifters, measuring devices and control systems are kept within limits. Try with this control system have an improvement in Bandwidth tolerance around 20 mm and the tolerances for the Strip thickness hE to values of plus / minus 0.04 mm Result in a target thickness of 1.5 mm.

Claims (10)

1.Procedure for continuously regulating the strip width when finishing hot strip on a multi-stand rolling mill, whereby the strip width is measured at least behind the finishing strip and the strip thickness behind the last stand, and changes in thickness are corrected using a thickness control loop on the last stand, characterized by the combination of the following process steps:

• - the bandwidth (b5, b7) 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 (Z) in the band ( 10 ) is calculated before the last stitch,
• - An indicator signal proportional to the tensile force (z6) is detected as the reaction force of the belt ( 10 ) on a positionable and lockable deflection roller ( 16 ),
• - With the indicator signal and the change signal, a strip supply controller (BVR) is applied, which changes the strip supply by changing the roll gap height (s) before the last stand ( 7 ).

2. The method according to claim 1, characterized in that that the bandwidth (b5, b7) before and at the same time behind the last two stitches. 3. The method according to any one of claims 1 or 2, characterized in that the band supply of all scaffolding ( 1 ... 7 ) is regulated. 4. The method according to claim 3, characterized in that for the adjustment of the roll gap height (s) after hot strip entry into a stand switched from the target strip thickness setting to a strip supply indicator and switched to a rolling force indicator when the strip ( 10 ) from the previous stand ( 1 6 ) expires. 5. The method according to any one of claims 1 to 4, 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 the speed of the work rolls. 6. The method according to any one of claims 1 to 5, characterized characterized that additionally the bandwidth between the first two stitches by adjusting the parameter roll gap or speed is regulated. 7. The method according to claims 1 to 6, characterized by the use of a combination of different indicators for the current strip stock on the stands of a finishing line of a hot strip mill, wherein

• - for the first stand ( 1 ) the speed (v0) and the strip thickness (h0) in front or the strip thickness (h0) in front of and behind (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 recorded,
• - For at least the last scaffold ( 7 ), the tensile force in the belt (z6) in front of the scaffold ( 7 ) is determined by force measurement using a 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,
• the thickness (h0, hz, hE) and width (b5, b7) of the hot strip ( 10 ) are determined by non-contact radiation measurement,

to regulate the strip width (b7) by adjusting the roll gap height (s) of a stand ( 2 or 7 ) of one or more work rolls. 8. The method according to claims 1 to 7, characterized by the use of 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 tension ( z1) in hot strip ( 10 ), preferably for controlling the strip width during hot rolling. 9. Finished season of a hot strip mill with measuring, control and regulating devices for detecting and influencing the process parameters for using the method according to one of claims 1 to 8, characterized by

• - at least one height-adjustable, non-oscillating deflection roller ( 16 ) in front of the last scaffold ( 7 ) and an associated dynamometer ( 9 ),
• - A with the measuring device ( 9 ) and a width controller (BR) connected strip supply controller (BVR), which acts on the roll gap height (s).