EP3138639B1 - Method for manufacturing a metallic belt by means of endless rolling - Google Patents

Description

The invention relates to a method for producing a metallic strip by endless rolling, in which the strip is first cast in a casting plant and then continuously rolled in a rolling train with at least one roll stand to form the finished strip, with a conveyor line behind the last roll stand in the direction of travel of the strip for the strip is present, which extends up to a scissor driver and / or a reel driver, or where there is a conveyor line between two roll stands of the rolling train, a reel for winding the finished strip being arranged behind the shear driver and / or the reel driver, at least temporarily a nominal tension is maintained in the belt in the conveyor line.

A flatness measurement and control for hot strip behind a hot strip mill is known. In what is known as batch rolling (rolling of individual strips one behind the other), the unevenness is visually detected in the tensionless strip head area and usually eliminated with the help of the dynamic profile actuator of a work roll bend. When measuring center shafts, the work roll bending is reduced and increased with edge shafts. An optical flatness measuring device that is typically used here is disclosed in the DE 197 09 992 C1 .

In the so-called endless rolling - according to the generic method - a casting plant and a rolling train are connected to one another. Here, individual coils are produced by cutting the endless belt with scissors just before the reel. An endless casting and rolling process can take several hours. Since the strip is under tension between the rolling mill and the reel, an optical flatness measuring device usually does not show a usable result.

In order to ensure the strip quality over this long period of time, a known method is used to measure the flatness with a flatness measuring roller, by measuring the tensile stress distribution with a measuring roller and thus indirectly determining the flatness. Such a flatness measuring roller for the application of endless rolling is disclosed, for example, in US Pat DE 37 21 746 A1 . Other solutions are in the DE 198 43 899 C1 , in the EP 2 258 492 A1 , in the JP 6319 8809 A and in the US 7,963,136 B2 described. The WO 2006/042606 A1 discloses a method in which various basic possibilities for measuring the flatness of the strip are mentioned, but flatness measuring rollers adapted for hot use are also specifically used in the hot area. The WO 2006/042606 A1 discloses in particular a method for producing a metallic strip in which the following measuring cycle is run to determine the flatness of the strip: a) Reduction of the tensile stress in the belt located in the conveyor line from the nominal tensile stress to a reduced tensile stress value Carrying out step a): measuring the degree of flatness of the strip by means of an optical flatness measuring device; c) After performing step b): increasing the tensile stress in the belt located in the conveyor line from the reduced tensile stress value to the nominal tensile stress. A similar method is also disclosed in US 2002/080851 A1 . The flatness of the belt is also used in the DE 10 2007 053 523 A1 measured.

However, the flatness measuring roller is an expensive and maintenance-intensive measuring device. If a system is operated in batch and endless mode, an optical flatness measuring device is often also required.

In the case of endless rolling, however, this does not provide a useful result due to the facts presented above.

The invention is therefore based on the object of further developing a generic method in such a way that inexpensive flatness measurement and subsequent flatness control can also be carried out during continuous rolling with little effort.

1. a) Verminderung der Zugspannung in dem sich in der Förderstrecke befindlichen Band von der Nominal-Zugspannung auf einen verminderten Zugspannungs-Wert;
2. b) Nach der Durchführung von Schritt a): Messung des Planheitsgrades des Bandes mittels eines optischen Planheits-Messgeräts;
3. c) Nach der Durchführung von Schritt b): Erhöhung der Zugspannung in dem sich in der Förderstrecke befindliche Band von dem verminderten Zugspannungs-Wert auf die Nominal-Zugspannung,

wobei innerhalb des Messzyklus eine Durchführung der Planheitsverbesserung von parabolischen oder symmetrischen Planheitsanteilen durch Einsatz der Arbeitswalzenbiegung an mindestens einem Walzgerüst und/oder durch Einsatz einer Schwenkregelung und Verbesserung der asymmetrischen Planheitsanteile durch Veränderung der Anstellpositionen an mindestens einem Walzgerüst erfolgt,
wobei der Messzyklus periodisch während der Durchführung des Verfahrens alle 2 min bis 10 min wiederholt wird und
wobei die Durchführung der Schritte a) bis c) während eines Zeitraums zwischen 1 sec und 20 sec erfolgt.The solution to this problem by the invention is characterized in that the following measuring cycle is run at defined times to determine the flatness of the strip:

1. a) Reduction of the tensile stress in the belt located in the conveyor line from the nominal tensile stress to a reduced tensile stress value;
2. b) After performing step a): measuring the degree of flatness of the strip by means of an optical flatness measuring device;
3. c) After performing step b): increasing the tensile stress in the belt located in the conveyor line from the reduced tensile stress value to the nominal tensile stress,

The flatness improvement of parabolic or symmetrical flatness components is carried out within the measuring cycle by using the work roll bending on at least one roll stand and / or by using a swivel control and improving the asymmetrical flatness components by changing the setting positions on at least one roll stand,
wherein the measuring cycle is periodically repeated every 2 min to 10 min while the method is being carried out and
steps a) to c) being carried out for a period of between 1 second and 20 seconds.

It is preferably provided that the measuring cycle is repeated every 4 minutes to 6 minutes while the method is being carried out.

The measuring cycle can also be carried out before changing the rolling thickness of the strip.

Furthermore, the measuring cycle can be carried out after a change in the rolling thickness of the strip.

Furthermore, it can be provided that the measuring cycle takes place while a scissor cut is being carried out in the area of the reel.

Finally, it can also be provided that the measuring cycle is triggered by the operating personnel of the production plant for the production of the strip.

It can also be provided that the measurement period is minimized, taking process conditions and system limits into account.

The nominal tensile stress in the band is preferably kept between 10 N / mm ² and 50 N / mm ² , depending on the material strength of the band; however, it is preferably provided that the reduced tensile stress value is between 0 N / mm ² and 15 N / mm ² (especially: 0 N / mm ² to 9 N / mm ² ), particularly preferably between 0 N / mm ² and 5 N / mm ² . The nominal tensile stress in the strip is preferably reduced by 40% to 100% during the measuring cycle.

The belt tension in the conveyor line with the flatness measurement preferably remains unchanged during the flatness measurement cycle in the adjacent areas - that is, within the rolling train and / or between the shear or reel driver and / or reel.

Furthermore, a process and / or control model and / or a control can be used to trigger the measuring cycle, to determine the measuring length, to determine the nominal and reduced strip tensile stresses during the measuring cycle depending on the hot strip thickness and / or the strip material and / or the final rolling temperature and to monitor the process in compliance with the specified process limits. In this case, it is preferably provided that the specified process limits (process limits), maximum permissible flatness limit (edge waves, center waves, maximum recorded waves) and / or maximum permissible strip center deviation and / or maximum strip center deviation change, recorded by a measuring device, are observed and a change in strip tension level from this, in particular an increase in strip tension is caused during the flatness measuring cycle.

Between the measurement periods, the (highly dynamic) profile actuator can be brought as close as possible to the middle of its setting range, in particular by replacing the effect by means of CVC shifting or changing the thermal crown.

The use of an optical flatness measurement in the above-defined conveying path, provided according to the present invention, is an advantageous and inexpensive possibility for the precise and simple detection of the flatness state of the strip. In order to be able to detect the flatness of the strip during continuous rolling, the strip tension between the hot rolling train and the reel driver or shear driver is advantageously lowered in a metered manner for a certain measuring time.

The hot rolling train can be at least a single-stand rolling train or a multi-stand rolling train, as is the case, for example, in FIG EP 0 889 762 B1 is revealed. In the normal endless rolling process, the strip is under tension between the last active roll stand and the shear or reel driver to ensure stable rolling. After a certain rolling time, however, it is now provided according to the invention to reduce the strip tension for a predeterminable measurement period. The flatness measuring cycle with reduced tension can be run after a predefinable time or a special event, it can be run before a thickness change in the rolling train, it can be run after a thickness change in the rolling train or it can also be run while the Paper cut on the reel.

In the measuring cycle provided according to the invention, the complete flatness state is preferably recorded or measured over the strip width. For further processing, these signals are filtered and broken down into symmetrical and asymmetrical components. The asymmetrical components are preferably used for the automatic or (by the operator) manual pivoting of the adjustment of the last active rolling stand. The symmetrical or parabolic parts are in the form of center or edge waves for the Flatness control used on the run-out stand. More detailed information on the procedure for regulating flatness can be found below. The processing of the asymmetrical components or the control of the swivel control or adjustment takes place analogously in a manner known per se.

The speed of the strip tension change (increase or decrease) is measured in such a way that the flatness measuring and control loops can react and that the thickness control is not disturbed or the thickness tolerance itself is not adversely affected. The influence of the change in tensile stress on the belt width must also be taken into account and the width must be within the permissible range.

The mean minimum permissible strip tension level to be set between the last active finishing stand and the shears or the reel driver is preferably selected as a function of the hot strip thickness, the strip material and the final rolling temperature and is automatically taken into account by the process computer.

For the measurement period, a maximum permissible (positive) edge waviness and a (negative) center waviness and / or the maximum recorded unevenness over the width (i.e. also the asymmetrical components) are preferably taken into account, which are dependent on various process parameters. The use of highly dynamic profile actuators, such as. B. the work roll bending in order to correct the correspondingly measured unevenness in the measurement period in a manner known per se.

Fig. 1

(oben) schematisch den Verlauf einer Bandzugspannung in einem fertig gewalzten Band über der Zeit sowie (unten) den Verlauf der Bandplanheit über der Zeit und

Fig. 2

einen Ausschnitt aus einer Gieß-Walz-Anlage zur Herstellung eines metallischen Bandes, wobei der Bereich zwischen einem letzten aktiven Walzgerüst und einem Haspel sowie die Wirkungsweise eines Prozessmodells dargestellt ist.

An exemplary embodiment of the invention is shown in the drawing. Show it:

Fig. 1

(above) schematically the course of a strip tension in a finished rolled strip over time and (below) the course of the strip flatness over time and

Fig. 2

a section of a casting and rolling system for the production of a metallic strip, the area between a last active rolling stand and a reel and the mode of operation of a process model being shown.

The figures show schematically how a strip 1 is cast in an endless rolling process in a casting machine, not shown, and then rolled into the finished strip in a rolling train, also not shown. Only the last active roll stand 2 of the rolling train is shown. A scissor driver 3 and a reel driver 4 follow in the conveyor direction F behind the roll stand 2. In the conveyor direction F behind the reel driver 4, a reel 5 is arranged. Between the scissors driver 3 and the reel driver 4 there is a pair of scissors 7, with which the strip 1 can be cut through.

Behind the last roll stand 2 and the scissors driver 3 there is a conveyor line for the strip 1, in which the strip 1 is kept at least temporarily under a nominal tensile stress. A belt cooling system 8 can also be arranged in said conveyor section.

An optical flatness measuring device 6, with which the flatness of the strip 1 can be measured, is also arranged in the area of the conveyor line.

It is essential that a special measuring cycle is run at defined times, with which the flatness of the strip 1 is determined using the optical flatness measuring device 6.

During this measuring cycle, the tensile stress of the strip 1 is first reduced from the nominal tensile stress to a reduced tensile stress value.

The degree of flatness of the strip 1 is then measured by means of the optical flatness measuring device 6.

Once this has taken place, the tensile stress is increased again from the reduced tensile stress value to the nominal tensile stress.

This procedure is exemplified in Figure 1 shown for a flatness control. In this figure it can be seen that a flatness measurement is started each time a measurement trigger cycle has elapsed (for example, 5 minutes). Here - as explained - the strip tension between the rolling train and the shear or reel driver is reduced at a predeterminable rate from the nominal tension level of preferably between 5 and 50 N / mm ² to a lower strip tension of preferably 0 to 10 N / mm ² . This low strip tension is specified for a specific time in order to enable flatness measurement and control for a specified period of time. The measurement period should be as short as possible. It is preferably between 1 second and less than or a maximum of 20 seconds. A minimum measurement period is aimed for. To end the measurement period, the tensile stress is increased again to the nominal tensile stress level at a rate that can also be specified.

The belt tension increase and the belt tension decrease can take place at different speeds. The level of tension between the reel driver and the reel preferably remains constant.

If the maximum positive or negative flatness limit or the asymmetrical or maximum flatness limit is reached, the drawdown is automatically interrupted, as shown in Figure 1 is exemplarily shown in the measurement period B (which is behind a measurement period A). In other cases, the train can be raised again a little. Since there is a lack of flatness, the flatness controller continues to change the work roll bending (not shown) accordingly. If the measured unevenness is released from its limit, the strip tension can be further reduced.

If it occurs in the intended measurement period (see, for example, measurement period A in Figure 1 ) a flat belt, the nominal tension level is preferably approached early again (see the solid line in Figure 1 , above) to minimize the active measurement period. In any case, at the latest at the end of measurement period A, the tensile stress in the strip is increased again to the nominal value (see dashed line in Figure 1 , above).

When the setting limit of the profile control element is reached (for example the work roll bending), the flatness in the corresponding direction can no longer be improved. Then the reduction of the train level is interrupted or the train level is raised again to the nominal train level in order to also minimize the active measurement period.

Between the measurement periods, it is provided that the highly dynamic profile control element (e.g. the work roll bending) is set as far away from its control limits as possible or placed in the middle of its setting range in order to be able to act optimally in both directions for the next measurement period. For this purpose, for example, the roll gap effect of the work roll bending is replaced by a slow change in the CVC shift (change in the work roll crown) or by changing the thermal crown shape by changing the water crown, water zone cooling or water level (= release circuit). In this conversion phase, the process model (PCFC model) uses cyclical calculations to record the conditions in the roll gap, controls this release circuit and thus ensures the quality of the strip contour, flatness and flatness of a higher order, etc.

To be on the safe side, the signal of the strip center deviation behind the finishing train is also monitored during the measurement period. This means that if the maximum permissible strip center deviation, recorded with a measuring device 10, is exceeded, in the positive or negative direction or if the permissible amount of strip center deviation, the tension level between the finishing train and the shear or reel driver is raised again to the nominal strip tension level.

The corresponding dependencies, processes, limits, minima and maxima for the values as well as the process parameters flatness, thickness, width, thickness deviation etc. are set, controlled and / or regulated by a process model. The most important components and influencing variables mentioned above are shown in accordance with Figure 2 can be seen where a process model 9 for controlling the strip tension for the purpose of flatness control and / or pivot control for the endless mode is shown schematically, the relevant influencing variables being indicated.

The above explanations relate to the flatness and swivel control and targeted change in the tension level between an active roll stand (namely the last active roll stand of the rolling train) and a driver. In general, however, this procedure can also be used between two finishing stands within the hot strip mill. For this purpose, an optical flatness measuring device would be installed between the stands.

Alternatively, the flatness between the stands is recorded visually by the operators, who manually control the work roll bending and the amount of swiveling of the thickness adjustment after the operator has been informed of the reduction in tension (manual operation would generally also be possible behind the finishing train).

The flatness measurement is preferably arranged as close as possible behind the rolling train. However, when using the method described above, it is also possible to arrange the flatness measurement behind the rolling train and / or in front of the shear driver - ie behind the cooling section - and thereby to carry out a flatness control or flatness check.

List of reference symbols:

1

tape

2

Roll stand

3

Scissor driver

4th

Reel driver

5

reel

6th

optical flatness measuring device

7th

scissors

8th

Belt cooling

9

Process model / rule model

10

Measuring device for recording the strip center deviation

F.

Conveying direction

Claims (14)

1. Method of producing a metallic strip (1) by endless rolling, in which initially the strip is cast in a casting plant and this strip is subsequently continuously rolled to the finished strip in a roll train with at least one roll stand (2),
   wherein a conveying path, which extends up to a shears driver (3) and/or a coiler driver (4), for the strip (1) is present behind the last roll stand (2) in conveying direction (F) of the strip (1), wherein a coiler (5) for winding up the finished strip (1) is arranged behind the shears driver (3) and/or the coiler driver (4) or wherein a conveying path is present between two roll stands of the roll train, wherein a coiler (5) for winding up the finished strip (1) is arranged behind the roll train,
   wherein a nominal tensile stress is maintained in the strip (1) in the conveying path at least temporarily,
   wherein the following measuring cycle for determination of the planarity of the strip (1) is operated at defined points in time:

   a) reducing the tensile stress in the strip (1), which is present in the conveying path, from the nominal tensile stress to a reduced tensile stress value;

   b) after performance of step a): measuring the degree of planarity of the strip (1) by means of optical planarity measuring apparatus (6);

   c) after performance of step b): increasing the tensile stress in the strip (1), which is present in the conveying path, from the reduced tensile stress value to the nominal tensile stress,

   wherein within the measuring cycle a performance of the planarity improvement of parabolic or symmetrical planarity components by use of working roll bending at at least one roll stand and/or by use of pivot regulation and improvement of the asymmetrical planarity components by changing the adjustment positions at at least one roll stand is carried out,
   wherein the measuring cycle is periodically repeated every 2 minutes to 10 minutes during performance of the method and
   wherein performance of the steps a) to c) is carried out during a time period between 1 second and 20 seconds.
2. Method according to claim 1, characterised in that the measuring cycle is repeated every 4 minutes to 6 minutes during performance of the method.
3. Method according to claim 1, characterised in that the measuring cycle is performed before a change in the rolling thickness of the strip.
4. Method according to claim 1, characterised in that the measuring cycle is performed after a change in the rolling thickness of the strip.
5. Method according to claim 1, characterised in that the measuring cycle is carried out during performance of a shears cut in the region of the coiler (5).
6. Method according to claim 1, characterised in that the measuring cycle is triggered as occasion requires by the operator of the production plant for producing the strip.
7. Method according to any one of claims 1 to 6, characterised in that the measuring time period is minimised with consideration of process conditions and plant limitations.
8. Method according to any one of claims 1 to 7, characterised in that the nominal tensile stress in the strip (1) is kept between 10 N/mm² and 50 N/mm².
9. Method according to any one of claims 1 to 8, characterised in the reduced tensile stress value lies between 0 N/mm² and 15 N/mm², preferably between 0 N/mm² and 9 N/mm².
10. Method according to any one of claims 1 to 9, characterised in that the nominal tensile stress in the strip is reduced during the measuring cycle by 40% to 100%.
11. Method according to any one of claims 1 to 10, characterised in that the strip tensions in the regions adjacent to the conveying path with the planarity measurement remain unchanged during the planarity measuring cycle.
12. Method according to any one of claims 1 to 11, characterised in that a process model and/or regulation model (9) and/or a control is or are used in order to trigger the measuring cycle, to ascertain the measuring length, to set the nominal and reduced strip tensile stresses during the measuring cycle in dependence on the hot strip thickness and/or the strip material and/or the final rolling temperature and to monitor the process with observation of predetermined process limits.
13. Method according to claim 12, characterised in that the predetermined process limits of maximum permissible planarity limit and/or maximum permissible strip centre deviation and/or maximum strip centre deviation change, as detected by measuring apparatus (10), are observed and a strip tension level change, particularly a strip tension increase, during the planarity measuring cycle is undertaken on the basis thereof.
14. Method according to any one of claims 1 to 13, characterised in that between the measuring time periods the profile setting element is brought as close as possible to the middle of its setting range, in particular by removing the effect by means of CVC displacement or change of the thermal crown.

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