EP1675694A1

EP1675694A1 - Method and control device for operating a mill train for metal strip

Info

Publication number: EP1675694A1
Application number: EP04790153A
Authority: EP
Inventors: Johannes Reinschke
Original assignee: Siemens AG
Current assignee: Primetals Technologies Germany GmbH
Priority date: 2003-10-06
Filing date: 2004-10-06
Publication date: 2006-07-05
Anticipated expiration: 2024-10-06
Also published as: CN1863612A; EP1675694B1; DE502004005723D1; JP2007507354A; ATE380607T1; CN100395044C; US20070006625A1; WO2005035156A1; DE10346274A1

Abstract

The invention relates to a method and a control device for operating a mill train for metal strip, which comprises at least one roll stand, the intrinsic flatness of the metal strip being determined at the discharge point of the mill train. In order to ensure in a reliable and sufficiently accurate manner that a required visible flatness of the rolled metal strip is kept within predefined limits, the bulging behavior of the metal strip is measured at the discharge point of the mill train and is translated into the intrinsic flatness of thermal strip by means of a bulging model. The visible flatness can thus be better regulated online along the entire mill train by using the bulging mode.

Description

description

Method and control device for operating a rolling mill for metal strip

The invention relates to a method according to the preamble of claim 1; one application is particularly suitable for operation in a hot rolling mill, e.g. in the finishing train, but is not limited to this.

Furthermore, the invention relates to a control device according to the preamble of patent claim 10.

From German Offenlegungsschrift DE 19851554 AI it is known to determine the profile and / or the flatness of a metal strip when it runs out of a rolling mill and to use it for presetting a rolling mill. The measured flatness is measured and fed to a neural network in the form of input parameters.

It is an object of the invention to operate a rolling mill for metal strip in such a way that a control is provided which ensures that the required visible flatness of the rolled metal strip is reliably maintained within specified barriers and with sufficient accuracy.

The object is achieved by a method of the type mentioned at the outset, the visible flatness and an intrinsic flatness of the metal strip being taken into account when controlling the roll stands using a dent model.

Due to the fact that both the visible flatness of the rolling mill and the intrinsic flatness can be taken into account according to the invention with the aid of the buckling model, extremely high requirements regarding the quality of the visible plan of the metal strip, although the visible flatness or waviness of the metal strip sometimes completely disappears when rolling under tension, that is, between the rolling stands, and is therefore practically not measurable within the rolling mill in many cases.

For the first time, the buckling model creates a clear connection between the intrinsic and visible flatness of the metal strip. This makes it possible for the first time not only to make a presetting based on flatness measurements, but to use the visible flatness for precise control or regulation of the rolling process in progress.

The visible flatness is advantageously determined in the form of a dent pattern. The dent pattern is easily comparable in terms of data technology and can be saved with relatively little effort.

The dent pattern is advantageously three-dimensional.

To determine the buckling pattern of the metal strip, it is advantageous to evaluate not only the relative length of individual tracks of the metal strip, but also at least one of the variables wavelength, amplitude and phase offset of the individual tracks. The buckling pattern can thus be recorded much more precisely.

A multitrack laser measuring device is advantageously used to determine the buckling pattern, which enables inexpensive detection of the buckling pattern with sufficient precision.

The visible flatness is advantageously measured topometrically. In this way, a flat detection of the strip surface structure and in particular the dent pattern is directly possible.

With the dent model, values for the visible flatness are advantageously converted into values for the intrinsic flatness or values for intrinsic flatness translated into values for visible flatness. In this way, intrinsic strip flatnesses calculated and visible strip flatnesses measured at the exit of a rolling mill can be adapted to one another or verified using a material flow model.

Advantageously, the flatness is translated online. This enables a particularly exact control or regulation of the strip flatness.

Advantageously, the flatness is translated with the help of an online-capable approximation function. In this way, on-line computing time can be saved when translating between visible and intrinsic flatness.

Based on the intrinsic flatness of the metal strip, its buckling pattern is advantageously modeled by means of the buckling model by applying a fictitious temperature distribution in the transverse direction of the metal strip. The thermal expansion corresponding to this strip temperature distribution in the longitudinal direction, but not in the transverse direction, corresponds to a length distribution that can be assigned to the intrinsic flatness. In this way, only a segment of limited length has to be modeled and the model equations of the elastic plate deformations with large deflections with suitable boundary conditions can be set up at the segment edges.

With the aid of a material flow model, an intrinsic flatness of the metal strip - viewed in the material flow direction - is advantageously determined in front of a physical measuring location of the flatness.

To control the rolling mill, one or more flatness limit values are advantageously specified at freely selectable points within and / or after the rolling mill. The flatness limit values can relate to the intrinsic flatness and / or the visible flatness. Because plan limit values can be specified anywhere within or after the rolling mill, control accuracies for the rolling process can be significantly increased.

The object is also achieved by a control device for operating a rolling train for metal strip with at least one roll stand, in particular according to the previously described method, the control device having at least one control unit which is coupled to a buckling model. Advantageous designs of the control device are specified in the subclaims. The advantages of the control device result analogously to those of the method.

Further advantages and details emerge from the following description of an exemplary embodiment in conjunction with the figures. Show:

1 shows a multi-stand rolling mill for rolling metal strip and a control device assigned to the rolling mill,

2a-2c examples of metal strips with flatness errors,

3 shows the subdivision of a metal strip into tracks,

4 shows a section of a multi-stand rolling mill with control device,

5 shows the geometry of a section of a metal strip,

According to FIG. 1, a rolling mill for rolling a metal strip 1 is controlled by a control computer 2. The metal strip 1 can be, for example, a steel strip, an aluminum strip or a non-ferrous metal strip, in particular a copper strip. The rolling mill has at least two roll stands 3. The roll stands 3 have at least work rolls 4 and - as indicated in FIG. 1 for one of the roll stands 3 - generally also support rolls 5. The roll stands 3 could also have more rolls, for example axially displaceable intermediate rolls.

The metal strip 1 runs through the rolling mill in its longitudinal direction x, the transverse direction y of the metal strip 1 being largely parallel to the axes of the work rolls 4.

The rolling train shown in FIG. 1 is designed as a finishing train for hot rolling steel strip. Although the present invention is particularly suitable for use in a multi-stand finishing train for hot rolling steel strip, it is not limited to this, in particular the rolling mill could also be designed as a cold rolling mill (tandem mill) and / or for rolling a non-ferrous metal ( For example, aluminum, copper or another non-ferrous metal).

The control device 2 has a control unit 11. This in turn has a module 10 for profile and flatness control, which is coupled to a material flow model 9. The control device 2 specifies scaffold controllers 6 setpoints for profile and flatness actuators (not shown in more detail). The scaffold controllers 6 then adjust the actuators in accordance with the specified target values.

The input variables supplied to the control device 2 include, for example, pass schedule data such as an entry thickness of the metal strip 1 and a rolling force and a pass reduction for each roll stand 3. The input variables generally also include a final thickness, a target profile value, a target thickness contour profile and a target flatness profile of the metal strip 1 at the outlet of the rolling mill. Usually the rolled metal strip 1 should be as flat as possible. Often, however, the metal strip 1 has flatness errors, as are shown schematically and by way of example in FIGS. 2a, 2b and 2c. Flatness errors of the metal strip 1 can be measured at a location x2, as indicated in FIG. 1, for example by means of a multi-track laser measuring device 13.

Figure 2a shows a central bulge of the metal strip 1. Figure 2b shows flatness errors at the edges of the metal strip 1. Figure 2c shows bulges of the metal strip 1, which occur repeatedly in the longitudinal direction x of the metal strip 1, in particular in two areas in the transverse direction y of the metal strip 1.

The buckling of the metal strip 1 is caused in particular by internal stresses in the metal strip 1. Internal stresses in the metal strip 1 are also referred to as intrinsic strip flatness ip.

FIG. 3 shows the division of a metal strip 1 into fictitious tracks Sl to Sn or into measurement tracks Sl ^λ to Sm ^λ . If the metal strip 1 were cut into narrow longitudinal strips or into tracks S1 to Sn, one could measure an uneven strip length distribution (the intrinsic strip length distribution), which is the cause of the internal stresses in the metal strip 1. The multi-track laser measuring device 13 detects the relative

Length of the metal strip 1 per measurement track Sl ^x to Sm and preferably also determines quantities such as the wavelength, amplitude and / or the phase offset of the individual tracks Sl to Sm. It is crucial that the corresponding intrinsic or measured relative lengths do not match for corresponding fictitious tracks Sl to Sn and measurement tracks Sl to Sm.

As can also be seen from FIG. 4, when hot rolling metal strip 1, a distinction is made between intrinsic strip flatness ip and visible strip flatness vp. The intrinsic band flatness ip denotes, as stated above, the Band length distribution over the tracks Sl to Sn. The visible flatness vp results from the buckling behavior of the strip, which depends, among other things, on sizes such as the strip thickness, the strip width, the modulus of elasticity of the metal strip 1 and the total tension under which the metal strip 1 is located.

According to FIG. 4, the visible flatness vp is measured at a location x2 at the outlet of the rolling mill, in particular a finishing train, and fed to a buckling model 12. The measurement of the visible flatness vp takes place according to the invention in such a way that not only is the visible strip length distribution over the strip width in the transverse direction y the output variable of a measuring device, but the three-dimensional buckling pattern of the strip can be reconstructed from the measuring device output variables. In a multi-track laser measurement system, not only the (relative) length of the individual measurement tracks Sl ^Λ to Sm ^λ , but also the wavelength and phase offset for each track Sl ^λ to Sm are output by the measuring device. In a topometric measurement of the visible flatness vp, the surface structure of the metal strip 1 is recorded over a large area and in three dimensions over large areas of the metal strip 1. A topometric band flatness measurement is preferably based on a strip projection method. Stripe patterns are projected onto the surface of the metal strip 1 and continuously recorded with the aid of a matrix camera.

The intrinsic flatness ip is preferably calculated at a location xl between or after the roll stands 3, in particular between and / or after the roll stands 3 of a finishing train. The calculation is preferably carried out using a material flow model 9 (see FIG. 1), which is preferably part of a control unit 11. At a location x2 at the outlet of the rolling mill where the visible flatness vp is measured, the intrinsic flatness ip calculated by the material flow model 9 can be compared with the measured visible flatness vp with the aid of the buckling model 12. In particular with a cold rolling mill would be fundamental it is also possible to measure the intrinsic flatness ip on the metal strip 1.

The bulge model 12 creates a clear connection between intrinsic flatness ip and visible flatness vp, insofar as this is possible. For example, in the case of a very thick metal strip 1 with moderate intrinsic flatness, the intrinsic flatness ip cannot be inferred from the buckling behavior, since such a metal strip 1 generally does not bulge.

The different flatnesses (ip or vp) are preferably determined in the following order:

1. The visible flatness vp, which corresponds to the buckling behavior of the metal strip 1, is usually measured after a last rolling stand 3, for example at the outlet of a finishing train.

2. The intrinsic flatness ip of the metal strip 1 at the measurement site of the visible flatness vp (cf. step 1) is determined by means of the dent model 12.

3. The intrinsic flatness ip between the roll stands 3, that is to say for example within the finishing train, is determined by means of the material flow model 9. In this way, the intrinsic flatness - seen in the direction of material flow - can be determined in front of the physical measuring location of the flatness, here the intrinsic flatness.

The relationship between an intrinsic flatness ip between the roll stands 3 and an intrinsic flatness ip after the last of the roll stands 3 is established via the material flow model 9. Input variables such as the strip thickness contours of the metal strip 1 and flatness profiles or flatnesses before and after passing through a roll stand 3 can be fed to the material flow model 9. The Mate The radial flow model 9 determines the intrinsic flatness profile of the metal strip 1 after passing through the roll stand 3 and a rolling force profile in the transverse direction y of the metal strip 1 and leads it to a roll deformation model (not shown in more detail). The roll deformation model, which is not shown in detail, is preferably part of a control unit 11. The roll deformation model determines roll deformations and feeds them to a target value determiner, not shown, which, on the basis of the determined roller deformations and a contour-side contour profile of the metal strip 1, sets the target values for the profile and flatness actuators in determined each individual roll stand 3.

By using the dent model 12, the material flow model 9 and the profile and flatness control implemented in module 10 (see in each case FIG. 1) can be adapted to the measurement data of the visible flatness vp. Lower and upper bounds can be specified for the visible flatness vp or for the corresponding visible band unevenness, which can be translated into barriers for the intrinsic flatness ip or intrinsic flatness with the aid of the buckling model 12. The bulge model 12 calculates the buckling pattern of the metal strip 1 from the intrinsic flatness. The visible flatness can in turn be determined from the calculated buckling pattern. Inverse modeling is used for the reverse conclusion.

The dent model 12 is preferably based on the theory of elastic plate deformations. The intrinsic flatness ip is modeled by applying a fictitious strip temperature distribution over the strip width, that is to say in the transverse direction y, which leads to thermal expansion in the longitudinal direction x of the metal strip 1, to be precise equal to the length distribution belonging to the intrinsic flatness ip. Now consider a band segment as shown in FIG. 5 with length a, width b and thickness h. In the drawing, the longitudinal direction x, transverse direction y and a perpendicular z. Only a band segment with a length a of half or a whole base buckling length is modeled, with periodic boundary conditions at the head and foot ends of the band segment. The boundary conditions at the strip edges are the free edges. The model equations are partial differential equations as well as the associated boundary conditions, which can be solved, for example, using the finite difference method or the finite element method.

Depending on the computing time of the solution algorithm, the dent model 12 can be used directly online. Alternatively, an online-capable approximation function can be generated using an offline model, which is then used online for the buckling model 12.

In order to better understand the mode of operation of the dent model 12, one must first recognize that, for example, when hot-rolling a metal strip 1, the measured deflections of the metal strip 1, which are attributable to the buckling of the metal strip 1, generally have a significantly larger order of magnitude than that Strip thickness h. Typically, however, their magnitude is significantly smaller than both the typical wavelength of the buckling behavior and the bandwidth b. While the classic, linear theory of plate deformation only applies if the deflections are less than or equal to approximately 1/5 of the strip thickness h, a non-linear description of the plate warps must be used in the present case. In addition to the quantities shown in FIG. 5, which describe the metal strip 1, the elastic modulus, or elastic modulus for short, is also used, with a constant elastic modulus generally being assumed. The non-linear buckling behavior can now be described as follows: (I) 2- V ⁴ w (x, y) = - + L (w (x, y), Φ (x, y)) hh

D. Here, forces acting in the strip plane are expressed in the form of a potential Φ, which is also commonly referred to as Airy's stress function, w denotes the vertical displacement of the metal strip 1 during p describes the pressure distribution acting from the outside, which acts in the perpendicular z. D is defined by the following equation:

Eh ³ (II) D: = - 12 (1-v ² ) Here E stands for the modulus of elasticity and \> stands for the transverse contraction number of the metal strip 1.

The following also applies to the term L (w, Φ) from equation (I):

_{/ -rττv τ} , _Λ , d ² wd ² Φ d ² wd ² Φ d ² wd ² Φ (III) L (w, Φ): = ———-____- 2- dx ² dy ² dy ² dx ² dxdy dxdy If you make assumptions regarding thermally caused internal stresses ( ^Λλ stresses ") and strains (""strains"), you get:

(IV) 1 ₇ <d ² T (x, y) d ² T (x, y) d ² wd ² w 1, _t ,,

T denotes the temperature in the metal strip 1 and κ _x or κ _y the coefficient of thermal expansion in the longitudinal or transverse direction (x or y).

Equations (I) and (IV) form a system of two coupled, non-linear, partial differential equations. If suitable boundary conditions are used, such as free margins or periodic boundary conditions Head and foot ends of a band segment, equations (I) and (IV) can be solved numerically in an iterative manner.

The basic idea of the invention can be summarized as follows:

The invention relates to a method and a control device for operating a rolling mill for metal strip 1, which has at least one rolling stand 3, the intrinsic flatness ip of the metal strip 1 being determined at the outlet of the rolling mill. In order to ensure that the required visible flatness vp of the rolled metal strip 1 is reliably and with sufficient accuracy within predetermined barriers, it is proposed to determine the visible flatness vp or the buckling behavior of the metal strip 1 at the outlet of the rolling mill, or preferably to measure it and by means of to translate a dent model 12 into the intrinsic planning unit ip of the metal strip 1. The visible flatness can thus be used online with the aid of the dent model 12 to control the rolling stands of the rolling mill. In the entire rolling mill, the visible flatness vp according to the invention can preferably be better regulated online, with the aid of the buckling model 12.

The bulge model 12 is online-capable and establishes a one-to-one relationship between the absolute intrinsic flatness ip of the rolled metal strip 1 and the actually measured visual defects of the metal strip 1, that is to say the visible flatness vp. For the first time, the verification, adaptation and coordination of a material flow model 9 based on the intrinsic flatness or its corresponding profile and flatness control with respect to the actual measured values is made possible.

Claims

claims

1. A method for operating a rolling mill for metal strip (1), which has at least one rolling stand (3), wherein a visible flatness (vp) of the metal strip (1) at the outlet of the rolling mill is taken into account, characterized in that when controlling the Rolling stands, the visible flatness (vp) and an intrinsic flatness (ip) of the metal strip (1) are taken into account using a dent model (12).

2. The method according to claim 1, so that the visible flatness (vp) is determined in the form of a buckling pattern.

3. The method according to claim 2, d a d u r c h g e k e n n z e i c h n e t that the buckling pattern is three-dimensional.

4. The method according to claim 2 or 3, dadurchgekennzeic hn et that to determine the buckling pattern in addition to the relative length of individual tracks (Sl to Sn) of the metal strip (1) at least one of the sizes wavelength, amplitude and phase offset of the individual tracks (Sl to Sn ) is evaluated.

5. The method according to any one of the preceding claims, that a multi-track laser measuring device (13) is used to determine the intrinsic flatness (ip).

6. The method according to any one of claims 1 to 4, since you rchgek characterized that the visible flatness (VP) is measured topometrically.

7. The method as claimed in one of the preceding claims, that the values for the visible flatness (vp) are translated into values for the intrinsic flatness (ip) by means of the bulge model (12).

8. The method as claimed in one of the preceding claims, that the values for the intrinsic flatness (ip) are translated into values for the visible flatness (vp) by means of the bulge model (12).

9. The method according to claim 7 or 8, so that the translation of the flatness (ip or vp) takes place online.

10. The method according to any one of claims 7 to 9, so that the flatnesses (ip or vp) are translated with the aid of an online-compatible approximation function.

11. The method according to any one of the preceding claims, since you rchgekennzeic hn et that, based on the intrinsic flatness (ip) of the metal strip (1), its buckling pattern by means of the buckling model (12) by applying a fictitious temperature distribution in the transverse direction (y) of the metal strip ( 1) is determined.

12. The method as claimed in one of the preceding claims, that an intrinsic flatness (ip) is determined in front of a physical measuring location of the flatness by means of a material flow model (9).

13. The method according to any one of the preceding claims, characterized in that one or more flatness limit values are specified at freely selectable points for controlling the rolling mill.

14. Control device (2) for operating a rolling train for metal strip (1) with at least one roll stand (3), in particular according to a method according to one of the preceding patent claims, wherein the control device (2) has at least one control unit (11), since You rchgek characterized that the control unit (11) is coupled to a dent model (12).

15. Control device (2) according to claim 14, d adu r c h g e k e nn z e i c h n e t that the bulge model (12) is coupled to a device for measuring the visible flatness (vp) of the metal strip (1).

16. Control device (2) according to claim 14 or 15, so that the control device (2) has at least one material flow model (9).

17. Control device (2) according to one of the claims 14 to 16, d a d u r c h g e k e nn z e i c h n e t that the device for measuring the visible flatness (vp) is a multi-track laser measuring device (13).

18. Control device (2) according to one of the claims 14 to 17, so that the buckling model (12) for determining a buckling pattern of the metal strip (1) is coupled to at least one topometric measuring system.