EP3097992B1 - Method for pack rolling a metal strip - Google Patents

Description

The invention relates to a method for step rolling a metal strip according to the preamble of claim 1.

The step rolling is known as a method for the production of metal strips already in the field, also known as "flexible rolling". This method allows the production of metal strips which have different thicknesses over the length. For this purpose, the roll gap formed between a first work roll and a second work roll is selectively moved during the rolling process. Thus, different lengths or arbitrarily changing sections of the metal strip guided through the roll gap can be rolled with different strip thicknesses. As a result, over the metal band length distributed band sections with larger and band sections with a smaller band thickness arise. These different thickness band sections can also be connected to each other via differently configured gradients, that is, transitional sections.

With the step rolling method, rolled products having load and weight optimized cross-sectional shapes can be produced. It is usually designed as a band roll with a coiling device and a coil coiler on coil. It is also well known that strip rolls applied over the reel assist the rolling process and improve the flatness or straightness of the fabricated metal strip longitudinally in the rolling direction. From the EP 1 908 534 A1 is known a step rolling process, in which occurring mass flow changes and tape tension changes are compensated by drive controls of the reel drives and additional S-roller pairs to avoid disturbances of the winding process and to ensure a uniform coil tension or winding tension.

Of particular importance is that, unlike conventional strip rolling during step rolling during the rolling process due to the thickness changes the metal strip always great changes in rolling force occur. The desired band thickness change is indeed achieved, but has the consequence that significant changes in the roller and frame load and associated elastic deformations occur. This leads to undesirable changes in the nip and strip geometry, whereby the flatness of the rolled Bandes is negatively affected. Thus, changes in rolling force during the rolling process lead to elastic deformations of all rolls, such as roll flattening, roll deflection and embedding in the rolls. This results in a change in the band profile, which leads to flatness errors in the case of irregularities. So far, this impact is being tried, as in EP 1 074 317 B1 disclosed to reduce by a correction of the bending lines of the work rolls. Without such a correction would result in the described rolling process a characteristic of this load change unplanes metal strip profile.

There are ripples of the metal strip, such as edge waves or center waves, from, because the height change and related related change in length are not constant over the Walzgutbreite. This results in different thicknesses over the metal strip width, which lead to different lengths within the metal strip and thus cause the band errors mentioned.

In particular, the flatness of the metal strip is crucial for its proper further processing, since only with good or sufficient flatness homogeneous or the same conditions over the entire metal bandwidth.

In a conventional strip rolling process for the production of simple flat metal strips with constant thickness over their length, the flatness is monitored in addition to the strip thickness and controlled in case of deviations. A disadvantage of such a scheme is that a Ansprechund control time is required for this until such a regulation has addressed and the effect of a deviation is compensated by the effect of a correction.

Particularly in the step rolling, the problem of the response of the control and the required control time to the correction plays an important role. It is particularly disadvantageous that the control times are shortened, in particular with short transitions between the stages and at high belt speeds. This leads to geometrical limits of possible step bands, that is not all desired transitions from one strip thickness to another Tape thickness can be realized by rolling technology.

There may be a problem with the methods known in the art. Thus, the change of the roll adjustment in the step rolling always leads to a large change in the rolling force and a scheme for correcting resulting changes in the metal strip is due to the required response and control time unsuitable for the rapid change of strip thickness during step rolling.

According to the invention, this problem is solved by a method having the features of patent claim 1.

The advantages achieved by the invention result from the fact that the rolling force applied by the work rolls is kept constant during the rolling process. As a result, negative effects, such as rolling force-dependent errors, such as flatness errors, avoided in a simple manner. To achieve a constant rolling force, the further process parameters are to be adapted such that the rolling force does not change despite changing the roll gap, that is, it remains constant or approximately constant. Particularly suitable for this purpose is the control of a strip tension applied to the metal strip. Such a strip tension control should be so targeted that the rolling force applied by the work rolls to the metal strip is constant during the rolling process. With the targeted change of the belt tension can be achieved that the rolling force moves during the change of the roll gap at a constant level. During step rolling, it has been found that the disadvantages associated with a control, such as response time and control time, are unsuitable for satisfactorily producing short, defined transitions and small radii of arbitrarily recurring alternating profiles. For this reason, it is advantageous if the tape trains are set to predetermined values and controlled and also the adjustment between two predetermined values is also controlled. Such controlled Bandzuganpassung allows all rolling force-influencing effects, such as roller flattening, deflection, and band embedment and to ensure constant conditions for the rolling process. With a constant rolling force, the errors dependent on the rolling force change can be limited very simply and effectively, since the elastic deformations of the roll remain constant with a constant rolling force.

In one embodiment of the invention, it is provided that the constant rolling force changes only during the rolling process insofar as during the rolling process the elastic deformation of the work rolls, such as roll flattening, roll deflection and band embedding in the rolls, is constant or approximately constant. As a result, the errors dependent on the rolling force change can be limited very simply and effectively. For this purpose, the properties of the work rolls are taken into account when changing the rolling force such that during the rolling process no significant change in the elastic deformation takes place.

A particular embodiment of the invention provides that a forward web tension applied by the coiler device or a reverse web tension applied by the webbinding device is controlled during the rolling process. Furthermore, it is possible to control both the forward and reverse belt tension. The control of the belt tension is a suitable way to keep the rolling force constant, even if the rolling gap formed between the work rolls changes.

As a particularly advantageous embodiment, it was recognized that by a targeted Bandzugsteuerung, so a targeted change of Vorwärtsbandzugs or Rückwärtsbandzugs or a targeted change of both bands, and targeted control of the speed and pitch of the work rolls, preferably a change of all these parameters at the same time Geometry of transitions, in particular their slope and the radii of transition points, between the stepwise changed band thickness of the metal strip is affected. As a result, an expansion of the achievable by step rollers geometries is possible. In addition, caused by the change of geometries Rolling force changes and associated errors of the strip geometry, profile and flatness are reduced. This is of particular importance since step rolls in the transition points easily rolling force peaks arise, which adversely affect the stability of the rolling process. Particularly critical in this context, transition points have been identified which set between a negative slope formed by reduction of the roll gap and a subsequent flatter plane plane. At these transition points, the rolling force increases without further measures very strong, which leads to the problems already described.

A further embodiment of the invention provides that the roll gap is reduced in order to reduce the strip thickness, and the forward strip tension and the reverse strip tension are increased in order to obtain a constant rolling force. In particular, a reduction of the roll gap, without increasing this strip tension, regularly leads to an increase in the rolling force, as a result of which the problems already described for the rolling process occur. Particularly advantageous is the simultaneous control of the belt tension in the forward and backward direction, so both the belt tensioners of the decoiler and the coiler, during a reduction of the roll gap, by employment of the work rolls. With a targeted control of the belt tension, the change in the rolling force during the employment of the work rolls can be avoided or reduced.

It is also advantageous if, in order to increase the strip thickness, the roll gap is increased and the forward strip tension and the reverse strip tension are lowered in order to obtain a constant rolling force. With this control, the rolling force can be kept at a constant level.

As a particularly advantageous embodiment has been found that the pitch of the work rolls or the speed of the work rolls or both speed and pitch of the work rolls are controlled according to precalculated data. Also the speeds of the decoiler or the reeling device or the rotational speeds of both reeling devices are preferably to be controlled according to precalculated data. With these precalculated velocity data, suitable parameters can be targeted. The disadvantages of a control by the response and control time can be avoided. This makes it possible to optimally design the step rolling process and to avoid rolling force changes that would result from a change in the roll gap. With the precalculated velocity data, the parameters necessary for an optimal rolling process could be set and controlled. When calculating the speed data, the material properties and the desired geometry are taken into account.

The above-mentioned problem is also solved by a device which operates according to the method as described here and in the following and comprises means for carrying out the method. For this purpose, the device according to the invention comprises at least two work rolls which form a roll gap, a discharge reel device, a coiling device and adjusting and control means, by means of which the employment of the work rolls, the speed of the work rolls and the speed of the Ablaufhaspelvorrichtung and / or the Aufhaspelvorrichtung adjustable and / or are controllable.

Essential to the invention is summarized that when selectively changing the strip thickness of the forward and backward roll gap is controlled so that despite varying shape change, the rolling force remains constant. As a result, effects influencing the surface, such as roller flattening, deflection and band embedding, do not change or only insignificantly, so that flatness errors usually caused by this do not occur.

For this purpose, a closed process model is used, which describes the acting forces and kinematics in the roll gap, in particular under the action of the belt pulls, ie the outer longitudinal pulls. The rolling process, in particular the step rolling, is a three-dimensional forming process in which a coupled force system in the longitudinal and width direction acts in the roll nip. Through the interaction the forces are deformed the work rolls both in the radial direction and in the axial direction. These deformations occurring in particular in the axial direction result in different height changes in the width direction, which leads to flatness errors in the belt. By means of the process model, the rolling process is controlled in such a way that the forces acting on the roll gap are influenced with the help of targeted changes in the strip tension so that the elastic deformations of the rolls remain approximately constant due to constant rolling force and thus flatness errors due to uncontrolled roll deformation do not occur and a stable rolling process is achieved becomes. In the case of step rolling, it should also be noted that the process becomes multi-dimensional due to time-dependent variations in the strip thickness. Keeping the rolling forces constant by means of a controlled change in the strip tension must take these transient dependencies into account.

Figur 1a

schematische Darstellung einer erfindungsgemäßen Vorrichtung,

Figur 1b

schematische Darstellung einer erfindungsgemäßen Vorrichtung mit Stütz- und Arbeitswalzen,

Figur 2

Profilkontur bei Walzvorgang ohne erfindungsgemäße Anpassung,

Figur 3

Walzkraftverlauf bei Walzvorgang ohne erfindungsgemäße Anpassung über die Zeit,

Figur 4

erzeugter Bandzug der Ablaufhaspelvorrichtung ohne erfindungsgemäße Anpassung über die Zeit,

Figur 5

erzeugter Bandzug der Aufhaspelvorrichtung ohne erfindungsgemäße Anpassung über die Zeit,

Figur 6

Profilkontur bei Walzvorgang nach erfindungsgemäßer Anpassung,

Figur 7

Walzkraftverlauf bei Walzvorgang nach erfindungsgemäßer Anpassung über die Zeit,

Figur 8

angepasster Bandzug der Ablaufhaspelvorrichtung nach erfindungsgemäßer Anpassung über die Zeit,

Figur 9

angepasster Bandzug der Aufhaspelvorrichtung nach erfindungsgemäßer Anpassung über die Zeit.

Further features, details and advantages of the invention will become apparent from the following description and from the drawings. An embodiment of the invention is shown purely schematically in the drawings and will be described in more detail below. Corresponding objects or elements are provided in all figures with the same reference numerals. Show it:

FIG. 1a

schematic representation of a device according to the invention,

FIG. 1b

schematic representation of a device according to the invention with support and work rolls,

FIG. 2

Profile contour during rolling without adaptation according to the invention,

FIG. 3

Walzkraftverlauf during rolling without adaptation according to the invention over time,

FIG. 4

produced strip tension of the decoiler without adaptation according to the invention over time,

FIG. 5

produced strip tension of the coiler without adaptation according to the invention over time,

FIG. 6

Profile contour during rolling operation according to the invention adaptation,

FIG. 7

Walzkraftverlauf during rolling process according to the invention adaptation over time,

FIG. 8

adapted strip tension of the decoiler device according to the invention over time,

FIG. 9

adapted strip tension of the coiling device according to the invention over time.

The FIG. 1a schematically shows a device according to the invention. In the illustrated embodiment, the metal strip 4 is guided over the entire width 8 in the longitudinal direction 7 by a roll gap 3 formed by an upper work roll 1 and a lower work roll 2. Here, the metal strip 4 is unwound from the Ablaufhaspelvorrichtung 5 and wound after the rolling process, which takes place between the work rolls 1, 2, of the coiler 6. As a result, the metal strip 4 moves in the longitudinal direction 7 through the nip 3 and is processed on the entire bandwidth 8 of the work rolls 1, 2. With a change of the roll gap 3 between the work rolls 1, 2, the strip thickness of the metal strip 4 is changed stepwise in the longitudinal direction 7 during the rolling process and thus a profile contour 11 (FIG. FIG. 2 and 6 ) reached. The profile contour 11 ( FIG. 2 and 6 ) adjusts itself to the entire bandwidth 8 by preferably controlling the setting speed and the speed of the work rolls 1, 2, the speed of the decoiler 5 and the coiler 6 according to precalculated speed data by means of a controller 9 and adjusting means (not shown).

In FIG. 1b schematically is a one-armed 4-Walzen-Reversiergerüst from Walzenachsenrichtung shown. The work rolls 1, 2 are supported by two support rollers 23. The dashed arrows represent forces, speeds and torques and are intended to illustrate the rolling process.

The drawings according to the FIG. 2 and FIG. 6 show by way of example the profile contour 11 of a metal strip 4 (FIG. FIG. 1a ) with a length L after a rolling process as a diagram, the diagram ranging from 0 L to 1.12 L. "L" here represents a freely selectable value for the profile length produced. The profile height h plotted in the diagram is taken from the center of the metal strip 4 (FIG. FIG. 1a ) measured in the height direction, which is why the metal strip 4 ( FIG. 1a ) has twice the metal strip thickness after the rolling process. In the examples considered below, a metal strip 4 ( FIG. 1a ) with an inlet thickness of Ho, where "Ho" is any value for the inlet thickness and is preferably between 1.2 mm and 5 mm. During this rolling process, the strip thickness is reduced to a profile height h of 0.425 H ₀ , that is to say a metal strip thickness of 0.85 Ho, in which case a further stepwise setting of the work rolls 1, 2 (FIG. FIG. 1a ) and the material band 4 ( FIG. 1a ) is reduced in sections to a profile height h of 0.2875 Ho, ie a metal strip thickness of 0.575 Ho. Between the planar sections, level 16, level 18, level 20, of the metal strip profile 11 there are transitions having a pitch, reference numerals 17 and 19. In the FIG. 2 and FIG. 6 illustrated profile contour 11 has between the planar sections, level 16, level 18, level 20 and the gradients 17, 19, the transition points 12, 13, 14 and 15, which are used for further explanation. In FIG. 2 it can be seen that the achievable by employment of the roller profile contour 11 in particular at the transition point 13 of the profile contour 11 according to FIG. 6 deviates to the extent that the achievable radius in the transition point 13 is significantly smaller or in FIG. 2 hardly recognizable.

Out FIG. 3 is the rolling force curve 21 over a time interval T of in FIG. 2 Rolling process shown as a diagram. The rolling force W begins with where kN, where "where" is a value adjusting for the rolling force, and increases after the transition point 12 during the employment of the work rolls 1, 2 (FIG 1a). Its maximum reaches the rolling force W at the transition point 13 with 2.32 W ₀ kN. Subsequently, the rolling force W during the flat portion, level 18, between the transition points 13 and 14 is constant at 2.0 Wo kN before moving to the transition point 14, due to the renewed employment of the work rolls 1, 2 ( FIG. 1a ) decreases again and after the transition point 15 again reaches a value of Where kN.

Over the same considered time interval T show the FIGS. 4 and 5 the voltage curves of the band trains as a diagram. In FIG. 4 is the voltage curve 22 of the Rückwärtsbandzuges σ _{0 of} the decoiler device 5 FIG. 1a ), which remains constant at σ ₀ * MPa throughout the rolling process. The tension 22 of the forward belt tension σ _{1 of} the coiler 6 (FIG. FIG. 1a ) changes, however, during the time interval T considered. The tension of this tape tension increases, as from FIG. 5 shows, during the rolling process between the transition points 12 and 13 to a maximum of 1.23 σ ₁ * MPa, before the voltage drops to the transition point 14 again. σ ₀ * and σ ₁ * represent stress values ranging from 15% to 60% of the yield stress at the considered strip profile position.

The FIG. 6 shows by way of example the profile contour 11 metal strip 4 ( FIG. 1a ) after a rolling process. As already mentioned above, the strip thickness is reduced to a profile height h of 0.425 Ho, that is to say a metal strip thickness of 0.85 Ho, whereby subsequently a further stepwise adjustment of the work rolls 1, 2 (FIG. FIG. 1a ) and the material band 4 ( FIG. 1a ) is reduced in sections to a profile height h of 0.2875 H ₀ , ie a metal strip thickness of 0.575 Ho. Between the planar sections, level 16, level 18, level 20, of the metal strip profile 11 there are transitions having a pitch, reference numerals 17 and 19. In FIG. 6 It can be seen that by adjusting the rollers 1, 2 ( FIG. 1a ) achievable profile contour 11 in particular at the transition point 13 of the profile contour 11 according to FIG. 2 deviates in that the achievable radius in the transition point 13 is significantly greater and corresponds to the radius in the transition point 14. This profile contour 11 is only by a targeted adjustment of the belt tension, roller speed and pitch possible during the rolling process.

The end FIG. 7 apparent diagram shows the rolling force curve 21 over the time interval T of in FIG. 6 shown rolling process. The rolling force W begins with Where kN and rises after the transition point 12 during the employment of the work rolls 1, 2 ( FIG. 1a ) minimal. Your maximum reaches the rolling force W at the transition point 13 with just 1.14 Wo kN. Subsequently, the rolling force W is constant during the flat section, level 18, between the transition points 13 and 14 before moving to the transition point 14, due to the renewed employment of the work rolls 1, 2 (FIG. FIG. 1a ) decreases again and after the transition point 15 again reaches a value of W ₀ kN.

Over the same considered time interval T show the FIGS. 8 and 9 in diagrams the voltage curves of the band trains. In FIG. 8 is the voltage curve 22 of the Rückwärtsbandzuges σ _{0 of} the decoiler device 5 FIG. 1a ), which is adjusted during the rolling process. The strip tension is during the employment of the work rolls 1, 2 ( FIG. 1a ) between the transition points 12 and 13 adapted to a tensile stress of 6.7 σ ₀ * MPa. This tension is maintained for the rolling process up to the transition point 14, before the strip tension of the decoiler device 5 (FIG. FIG. 1a ) is reduced again. The tension 22 of the forward belt tension σ _{1 of} the coiler 6 (FIG. FIG. 1a ) also changes during the considered time interval T. Thus, the tension 22 of this strip tension increases during the rolling process between the transition points 12 and 13 to 8 σ ₁ * MPa, before the voltage drops 22 after the transition point 14 again.

The invention can be summarized as follows: an increase in the rolling force W ( FIG. 1a ) is effectively prevented by the deformation and stress state in the roll gap 3 ( FIG. 1a ) by the on the metal strip 4 ( FIG. 1a ) applied bandages σ ₀ , σ _{1 is} changed. Usually, by reducing the roll gap, the vertical stress increases, resulting in a higher rolling force W (FIG. FIG. 1a ). With the adaptation of the belt tension σ ₀ , σ ₁ is achieved, however, that to achieve flow conditions in the nip 3 ( FIG. 1a ) a lower resulting vertical stress is required.

The control of the strip tension σ ₀ , σ ₁ via the change of the reel speeds, which must be taken into account for the targeted control of the strip tension σ ₀ , σ _1, the coil diameter, so that by changing the reel speeds a desired reel torque is achieved, the σ ₀ , σ ₁ , acts. With the control of the strip tension σ ₀ , σ ₁ , the flow condition in the roll gap 3 (FIG. FIG. 1a ) and achieved without the vertical stresses and thus the rolling force W ( FIG. 1a ) are significantly changed.

LIST OF REFERENCE NUMBERS

1

Upper work roll (upper roll)

2

Lower work roll (lower roll)

3

nip

4

metal band

5

Pay-off device

6

Aufhaspelvorrichtung

7

longitudinal direction

8th

bandwidth

9

control

10

Bandzugmessrolle

11

profile Silhouette

12

Übergangsstelle12

13

Übergangsstelle13

14

Übergangsstelle14

15

Übergangsstelle15

16

Ebene16

17

Steigung17

18

Level 18

19

Gradient 19

20

Level 20

21

Rolling force progression

22

voltage curve

23

backup rolls

W

Rolling force in kN

W ₀

Initial value for rolling force

H

Profile height in mm

H ₀

Inlet thickness of the metal strip

I

rolled profile length in mm

L

Value for entire profile length

t

Time in s

T

time interval

σ ₀

Backward band move in MPa

σ ₀ *

Initial value for reverse tape tension

σ ₁

Forward tape train in MPa

σ ₁ *

Initial value for forward tape tension

Claims (8)

1. Method for step rolling a metal strip (4), wherein the metal strip (4) is unwound from an uncoiler device (5) and is wound up by a coiler device (6), wherein during the rolling process, the metal strip (4) is guided through a roll gap (3), formed between two work rolls (1, 2), and the roll gap (3) is changed in a specific manner during the rolling process, wherein as a result, a strip thickness of the metal strip (4) is changed stepwise in the longitudinal direction (7) during the rolling process, characterised in that a strip tension, applied to the metal strip (4), is controlled in a specific manner so that the roll force (W), applied to the metal strip (4) by the work rolls (1, 2), is constant during the rolling process.
2. Method according to claim 1, characterised in that the constant roll force W changes during the rolling process only to the extent that the elastic deformation of the work rolls (1, 2) is constant or is approximately constant during the rolling process.
3. Method according to any one of the preceding claims, characterised in that a forwards strip tension o'₁, applied by the coiler device (6) and/or a backwards strip tension o'₀, applied by the uncoiler device (5) is controlled during the rolling process.
4. Method according to any one of the preceding claims, characterised in that the shape of transitions, in particular the gradient thereof and the radii of transition points (12, 13, 14, 15), between the strip thickness, which is changed in steps, of the metal strip (4) is influenced by a specific strip tension control and by a specific control of the speed and adjustment speed of the work rolls (1, 2),
5. Method according to any one of the preceding claims 3 to 4, characterised in that to reduce the strip thickness, the roll gap (3) is reduced and the forwards strip tension o'₁ and the backwards strip tension o'₀ are increased.
6. Method according to any one of the preceding claims 3 to 5, characterised in that to increase the strip thickness, the roll gap (3) is increased and the forwards strip tension o'₁ and the backwards strip tension o'₀ are reduced.
7. Method according to any one of the preceding claims, characterised in that the adjustment speed of the work rolls (1, 2) and/or the speed of the work rolls (1, 2), of the uncoiler device (5) and/or of the coiler device (6) are controlled according to precalculated speed data.
8. Device for implementing a method according to any one of the preceding claims, comprising at least two work rolls (1, 2) which form a roll gap (3), an uncoiler device (5), a coiler device (6) and adjusting means and control means (9) which can adjust and/or control the adjustment of the work rolls (1, 2), the speed of the work rolls (1, 2) and the speed of the uncoiler device (5) and/or of the coiler device (6).

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