EP1074317A2 - Method for flexibly rolling a metal strip - Google Patents

Abstract

Flexible metal strip rolling, involving work roll bending line control during or immediately after each roll gap adjustment to obtain flat strip, is new. A flexible rolling process for metal strip comprises adjusting the roll gap during rolling to achieve different strip thicknesses along the strip length, the bending lines of the work rolls being controlled in dependence on the adjusted roll gap during or immediately after each roll gap adjustment in order to achieve strip flatness.

Description

The invention relates to a method for flexible rolling of a metal strip, wherein the metal strip during the rolling process by one between two work rolls formed roll gap and the roll gap targeted during the rolling process is moved to different strip thicknesses over the length of the metal strip to achieve.

Flexible rolling as a process for the production of flat metal strips with over their length defines different strip thicknesses is already known in practice. The flexible rolling is characterized in that during the rolling process Roll gap is moved specifically. Here are different lengths of tape rolled with different strip thicknesses over different pitches can be connected. The goal of flexible rolling is To produce rolled products with cross-sectional shapes optimized for load and weight. The process is usually designed as strip rolling from coil to coil. The strip tension applied over the reel supports the rolling process and significantly improves the straightness of the finished strip profile in the longitudinal direction, i.e. in Rolling direction.

When rolling in the context of the conventional strip rolling process are for deformation of the rolling stock located in the entry zone to the roll gap is considerable Forces required which lead to elastic deflection of the rollers. The deflection of the rollers mounted at both ends results in a bending line, which is usually parabolic and corresponds to the central axis of the roller. Since the deflection is a deviation from the uniform gap dimension or from corrective measures are required.

One measure, the deviation from the ideal gap - caused by the deflection of the rollers - to correct, consists in crowning the roller bales. Below the barrel-shaped or bulbous design of the roller bales is understood. With this type of correction it is possible to use only the work rolls, only the backup rolls or to bomb both the work rolls and the backup rolls. The crowning is supposed to be the deflection caused by the rolling forces and the dead weight of the rollers is caused so that the gap between the Rolling runs smoothly again, d. H. is constant over the length of the rollers. In As a rule, however, the correction of the bending line is not complete and applies because the Roll shape or the crowning is not changeable, only for a certain one Operating case.

Another possibility for correction consists in that one roll bale each Horizontal rotation around the center of its line of contact with the corresponding one The roller is placed at an angle to its axis. Because of this inclination the gap at the ends of the roll bale changes while it is in the middle remains unchanged. The inclination of the rollers allows the possibility of variation an approximate compensation of the deflection for almost all operating cases, but is the aforementioned parabolic grinding in terms of the achievable accuracy the roller bales equate.

It is also possible to apply forces to the journal of the rollers to generate a bending moment which counteracts the bending moments during rolling. This pretensioning of the rollers also allows the inclination an approximate compensation for almost all operating cases. The disadvantage is, however significantly increased bearing load. With regard to the achievable compensation preloading comparable to parabolic grinding.

Finally, there is another possibility to correct the work roll cooling, which is a thermal crowning.

It goes without saying that the previously mentioned correction options for achieving an ideal roll gap in rolling mills both individually and in combination can be used together.

In contrast to the conventional strip rolling process, it is special with flexible rolling problematic that during the rolling process due to the frequent Changes in thickness of the metal strip constantly large load fluctuations on the roll stand occur which, on the one hand, bring about the desired change in strip thickness, on the other hand, a significant change, especially for wider metal strips the roll load across the width. This will make the bend line of the work rolls, thus the geometrical formation of the roll gap and thus flatness is affected unless there is a correction to achieve uniformity Gap occurs. With flexible rolling, the nip is corresponding to the move the required belt profile without correction, this creates for this load change a characteristic unplanned band profile across the width. Because of this vagueness there is a risk of edge waves or band tears, as the related change in height and accordingly related change in length shape is not constant across the width. Because of this, there are different thicknesses across the Width and different lengths resulting from these tape errors.

Flatness is an essential requirement for a metal band. It is important to Ensure the same ratio from the center of the strip to the edge of the strip for further processing to be able to. If the tapes are not flat, undesirable effects can occur come while reeling. This manifests itself in friction stress peaks on the contact surfaces in the coiled reel either in the middle of the strip or at the edge of the strip depending on the belt profile. This can depend on the wrap angle and the occurring friction conditions to stick the coiled Lead strip, especially if an annealing treatment after rolling is carried out.

In the conventional strip rolling process for the production of flat metal strips Over its length of constant thickness, both the strip thickness and the Flatness is constantly set, monitored via complex control loops and when it occurs Deviations are regulated by appropriate actuators. A control device to regulate the roll deflection caused by rolling force in conventional Strip rolling process is known for example from DE 22 64 333 C3.

The problem is that there is a certain response time in the known control and requires a certain period of time for the regulation to respond and the Effect of a disturbance variable change through the effect of the regulation within the Measuring accuracy is corrected. This problem of the response of the scheme and The required control time plays a significant role, especially in flexible rolling Role, because sometimes very short tape sections with different thicknesses with some high rolling speeds have to be rolled, and the flatness ultimately should be guaranteed over the entire length of the flexibly rolled strip. This is extremely difficult, especially for wider metal strips.

The object of the present invention is to provide a method for flexible rolling a To provide metal strip in which a good flatness can be achieved can, even with relatively wide bands.

The previously derived and described task is the beginning of a method described type according to the invention essentially solved in that during each time the roll gap is adjusted or immediately afterwards the bending lines of the work rolls depending on the set nip to achieve flatness of the metal strip can be controlled. It is essential in the invention that Influencing the bending lines of the work rolls when setting the roll gap - at least initially - not via regulation, but via a controller, So a process in which one size - in the present case the bending lines of the work rolls - of a different size - in the present case the roll gap - in a predetermined, fixed relationship is influenced.

In the invention, the change in the bending line is compensated for due to the load changes in the case of a change in the roll gap by knowing the dependence of the bending line on the respective roll gaps. If, for example, the roll gap is adjusted from S ₁ to S ₂ for a specific rolling stock, this adjustment of the roll gap leads to a change in the deflection of the work rolls. This change in the bending line is known and forms the basis of the controlled compensation. The knowledge of the change in the bending line can follow from the given geometry, but can in particular be obtained empirically, namely by returning corresponding measurement variables during the rolling process.

As a result, the bending line is directly dependent on the respective roll gaps by application, d. H. Increase or decrease certain rebend forces adjusted to obtain a uniform gap dimension over the length of the roll gap. Through this controlling intervention on the rolling process when setting the Rolling gap can be targeted on the metal strip, before one possible subsequent regulation becomes effective at all, ultimately to a to provide its entire width of flat metal tape.

It is particularly advantageous if the flatness following the control and especially immediately after setting the roll gap via at least one Control loop is regulated. The invention therefore provides that first, d. H. when setting of the roll gap, only one control is carried out. External disturbances with exception the changing roll gap cannot be taken into account here. However, if the control intervention is completed, the regulation responds to the in Eliminate tape remaining flatness and thus achieve a flat metal tape.

During flexible rolling it is due to the given changes in thickness of the metal strip required several times to adjust the roll gap. thats why according to the invention further provided that shortly before or during the renewed Adjustment of the roll gap, the control of the flatness is interrupted and the bending lines the work rolls are controlled again depending on the new roll gap become. So there is a constant change between control and regulation depending on the predetermined change in thickness of the metal strip over its Length.

For control purposes, predetermined ones are determined depending on the different roll gaps Applied bending forces on the work rolls and / or the support rolls, around a work roll bend or a support and work roll bend to achieve. Corresponding to this, to correct an unplannedness of the Metal strip adapted to the respective load case back bending forces on the work rolls and / or back-up rolls applied to also a work roll bend and / or to achieve support and work roll bending. The aforementioned Control or regulation can preferably be carried out with the work and / or Implement backup roll bending because here - the travel speed of the roll gap accordingly - quick changes can be realized, which is especially the case with flexible Rolling with sometimes very short strip sections is important. Would be conceivable but also other ways of influencing flatness, e.g. B. by moving of intermediate rolls in the six-high mill stand, thanks to hydraulically supported Rolling or by cross-rolling. However, the goal is in any case, a plan, to produce flexibly rolled strip and at the same time the ability to reel it To improve or optimize metal strips.

So that the control responds as quickly as possible after the control, which, as has already been stated, especially in the case of flexible rolling, it is considerably more It is important to measure the flatness optically becomes. The optical measurement of the flatness can be done directly behind the work rolls realize in a simple way. The flatness of the metal strip preferably over the entire width of the metal strip behind the roll gap for each Length increment measured.

It is particularly preferred in connection with the optical measurement that Measurement of flatness across the entire width of the metal strip laser thickness measuring stations are provided and that the laser thickness measurement via triangulation he follows. Laser thickness measurement across the entire width of the metal strip enables a simple way to optimize the bending line of the work rolls online. The laser thickness measurement via triangulation enables through the small measuring spot and the high measuring frequencies of 1 kHz and more even with short band sections about 50 mm long to determine the cross profile.

It is understood that it is fundamentally possible to use measuring means other than optical ones to determine an unevenness remaining in the band after the control use. For example, a stressometer roll can be used.

For the rest, it is advantageous not only to regulate the flatness of the metal strip, but also also the strip thickness of the metal strip in the longitudinal direction. This can be in the control loop be integrated to bend the work rolls.

Fig. 1

eine schematische Darstellung eines Teils eines Walzgerüstes ohne Gegenbiegung,

Fig. 2

eine Ansicht des Walzgerüstes aus Fig. 1 mit Gegenbiegung und

Fig. 3

die Darstellung eines Regelkreises.

In the following, the invention will be explained again with the aid of a drawing showing only one exemplary embodiment. It shows

Fig. 1

1 shows a schematic representation of a part of a roll stand without counter-bending,

Fig. 2

a view of the rolling stand from FIG. 1 with counter-bending and

Fig. 3

the representation of a control loop.

1 and 2, part of a roll stand 1 is on the one hand without counter-bending (Fig. 1) and on the other hand with counter-bending (Fig. 2). In detail are shown a cylindrical work roll 2 with roll balls 3 and journals 4, 5, the are stored in bearings 6, 7. There is one above the work roll 2 Back-up roll 8 with a cylindrical back-up roll barrel 9 and bearing journal 10, 11, which are stored in bearings 12, 13. In the illustrated work roll 2 and Backing roll 8 is the upper rolls of the roll stand 1. Not shown are the two lower corresponding rolls, namely a lower work roll and a lower backup roller. Located between the two work rolls the roll gap S.

It is understood that the invention applies to both a four-high mill stand and a duo mill stand can be used and that instead of cylindrical work rolls 2 and back-up rolls 8 are also used in principle, cambered rolls can be.

1 shows an application in the rolling of a metal strip (not shown), a rolling force F _{W being} exerted on the work roll 2. The rolling force F _W causes an elastic deflection of the work roll 2, so that the bending line B of the work roll 2 results. The rolling force F _W leads not only to a deflection of the work roll 2, but also to a deflection of the support roll 8, which is not shown in detail.

2 shows the state of the rollers 2, 8 with counter-bending. In contrast to the state shown in FIG. 1, the roll gap S has a constant, uniform gap dimension, that is to say an at least substantially constant constant distance between the two facing surfaces of the work rolls. In the state shown in Fig. 2, the work roll 2 is not bent. The rolling force F _W counteracted by the backing roll 8 applied bending forces F _B.

In the illustrated embodiment, the bending line B runs that of the central axis corresponds to the work roll 2, parallel to the outside of the work roll 2 cambered roll barrel 3, this is not the case. In this case one is over the length of the work roll constant roll gap as opposed to the illustration 2, the work roll bent, although the delimiting the roll gap Line or surface of the work roll runs horizontally.

The method according to the invention for flexible rolling of a metal strip is running now so that the roll gap S is deliberately moved during the rolling process, to achieve a predetermined change in thickness of the metal strip over its length. It is essential here first that during the setting of the roll gap S or immediately afterwards the bending lines B of the work rolls 2 as a function of the set one Roll gap to be controlled to achieve flatness of the metal strip. This is due to the knowledge of the bending line dependency of the different ones Rolling gaps possible. This is due to the different nips caused deviation from the ideal gap compensated.

Following the control intervention described above when adjusting the The flatness S is controlled by the flatness via the control loop shown in FIG. 3. As a result, there is an unevenness remaining in the strip after the controlling intervention corrected. If the roll gap S is adjusted again later, the control becomes interrupted and controlled again in the manner previously explained.

For control purposes, depending on the various roll gaps, predetermined rebending forces F _{B are} applied to the support rolls 8 in order to achieve a work and support roll bending. With the same goal, rebending forces F _{B are} applied to the work rolls 2 to compensate for the flatness.

For control purposes, a measured value acquisition is first carried out using appropriate measuring means. Both the longitudinal and the transverse profile are measured. The longitudinal profile or cross profile detection is then carried out, the control deviation between the actual value and the target value of the respective control variable being determined. The respective correction values are then fed to a control loop. In the case of longitudinal profile detection, the change Δh in the thickness of the metal strip is corrected to the predetermined target value in accordance with the predetermined target value. A corresponding change ΔS of the roll gap is required for this. Finally, the back bending forces F _B to be applied to the respective work rolls 2 depend on the change in the roll gap S.

Claims (10)

A method for flexible rolling of a metal strip, the metal strip being passed through a roll gap formed between two work rolls during the rolling process and the roll gap being specifically moved during the rolling process in order to achieve different strip thicknesses over the length of the metal strip, characterized in that during each adjustment of the Roll gap or immediately thereafter the bending lines of the work rolls are controlled in dependence on the set roll gap in order to achieve flatness of the metal strip. A method according to claim 1, characterized in that the flatness afterwards to the control and especially immediately after the setting of the roll gap is regulated via at least one control loop. Method according to claim 2, characterized in that shortly before or during the adjustment of the flatness is interrupted when the roll gap is readjusted and the bending lines of the work rolls as a function of the renewed roll gap adjustment can be controlled again for the new rolling case to achieve flatness. Method according to one of claims 1 to 3, characterized in that for Control depending on the different nips predetermined Rebending forces are applied to the work and / or back-up rolls to a To achieve work roll bending or a support and work roll bending. Method according to one of claims 2 to 4, characterized in that for Correcting an uneveness of the metal strip adapted to the respective load case Back bending forces are applied to the work and / or back-up rolls, around a work roll deflection and / or support and work roll deflection achieve. Method according to one of claims 2 to 5, characterized in that the Non-contact flatness measurement, e.g. B. optically. Method according to one of claims 2 to 6, characterized in that the Flatness of the metal strip over the entire width of the metal strip behind the Roll gap is measured for each length increment. A method according to claim 6 or 7, characterized in that for measuring the Flatness laser thickness measuring stations distributed over the entire width of the metal strip are provided and that the laser thickness measurement is carried out via triangulation. Method according to one of claims 2 to 5, characterized in that the Touching flatness measurement, e.g. B. is done via a stressometer role. Method according to one of claims 1 to 9, characterized in that the Strip thickness of the metal strip is regulated in the longitudinal direction.

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