U.S. patent application number 10/574723 was filed with the patent office on 2007-01-11 for method and control device for operating a mill train for metal strip.
Invention is credited to Johannes Reinschke.
Application Number | 20070006625 10/574723 |
Document ID | / |
Family ID | 34399272 |
Filed Date | 2007-01-11 |
United States Patent
Application |
20070006625 |
Kind Code |
A1 |
Reinschke; Johannes |
January 11, 2007 |
Method and control device for operating a mill train for metal
strip
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.
Inventors: |
Reinschke; Johannes;
(Nurnberg, DE) |
Correspondence
Address: |
SIEMENS CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
170 WOOD AVENUE SOUTH
ISELIN
NJ
08830
US
|
Family ID: |
34399272 |
Appl. No.: |
10/574723 |
Filed: |
October 6, 2004 |
PCT Filed: |
October 6, 2004 |
PCT NO: |
PCT/EP04/11171 |
371 Date: |
April 6, 2006 |
Current U.S.
Class: |
72/11.7 |
Current CPC
Class: |
B21B 37/28 20130101;
B21B 2001/225 20130101; B21B 38/02 20130101 |
Class at
Publication: |
072/011.7 |
International
Class: |
B21B 37/28 20060101
B21B037/28 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 6, 2003 |
DE |
103-46-274.0 |
Claims
1-14. (canceled)
15. A method for operating a metal strip mill train, comprising:
determining a desired flatness of the strip via a material flow
model; measuring an actual flatness of the metal strip near a
discharge point of the mill train; translating the measured metal
strip flatness into flatness values; controlling a roll stand of
the mill train via a bulge model that uses the desired and actual
flatness values as inputs to reduce the difference between the
actual flatness and the desired flatness of the metal strip.
16. The method as claimed in claim 15, wherein the actual flatness
of the metal strip is measured at the discharge point of the mill
train.
17. The method as claimed in claim 15, wherein the actual flatness
is determined as a bulge pattern.
18. The method as claimed in claim 17, wherein the bulge pattern is
three-dimensional.
19. The method as claimed in claim 18, wherein a relative length of
individual tracks of the metal strip is evaluated to determine the
bulge pattern along with a variable of the individual tracks
selected from the group consisting of: wavelength, amplitude and
phase offset.
20. The method as claimed in claim 19, wherein a laser measuring
device is used to determine the desired flatness of the metal
strip.
21. The method as claimed in claim 20, wherein the laser measuring
device is a multi-track laser measuring device.
22. The method as claimed in claim 20, wherein the actual flatness
of the metal strip is measured topometrically.
23. The method as claimed in claim 22, wherein the values for the
desired flatness are translated into values for the actual flatness
using the bulge model.
24. The method as claimed in claim 23, wherein the flatness values
are translated online.
25. The method as claimed in claim 24, wherein, the flatness values
are translated online via an approximation function.
26. The method as claimed in claim 25, wherein the metal strip
bulge pattern based on the strip flatness is determined via the
bulge model by applying an assumed temperature distribution in the
transverse direction of the metal strip.
27. The method as claimed in claim 26, wherein the actual flatness
of the metal strip is measured by a laser measuring device.
28. The method as claimed in claim 27, wherein the laser measuring
device is a multi-track laser measuring device.
29. The method as claimed in claim 27, wherein a flatness limit
value is predefined at points to control the mill train.
30. A metal strip mill train control device, comprising: a device
that measures an actual flatness of the metal strip; a regulating
unit coupled to a bulge model, the model using a device that
measures the actual flatness of the metal strip and a material flow
model to control a roll stand of the mill train to minimize the
difference between the actual flatness and the desired flatness of
the metal strip.
31. The control device as claimed in claim 30, wherein the actual
flatness measuring device is a laser measuring device.
32. The control device as claimed in claim 31, wherein the laser
measuring device is a multi-track laser measuring device.
33. The control device as claimed in claim 31, wherein the bulge
model is coupled to a topometric measuring system that determines a
bulge pattern of the metal strip.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2004/011171, filed Oct. 6, 2004 and claims
the benefit thereof. The International Application claims the
benefits of German Patent application No. 10346274.0 filed Oct. 6,
2003. All of the applications are incorporated by reference herein
in their entirety.
FIELD OF THE INVENTION
[0002] The invention relates to a method; one application is
particularly suitable for operation in a hot-rolling mill, e.g. in
the finishing train, but is not restricted to this.
[0003] The invention also relates to a control device.
BACKGROUND OF THE INVENTION
[0004] It is known from the unexamined German application DE 198 51
554 A1 that the profile and/or flatness of a metal strip is
determined at the discharge point of a mill train and is used to
preset a mill train. The measured visible flatness is supplied here
to a neural network in the form of input parameters.
[0005] A flatness regulating system for metal strip is known from
DE 197 584 66 A1, with a method being employed to measure the
surface geometry of hot-rolled strip by generating lines on the
surface of the strip. The visible flatness measured in this manner
is supplied to a flatness regulator via a flatness analysis
system.
SUMMARY OF THE INVENTION
[0006] The object of the invention is to operate a mill train for
metal strip such that a control is provided to ensure that a
required visible flatness of the rolled metal strip is complied
with in a reliable and sufficiently accurate manner within
predefined limits.
[0007] The object is achieved by a method of the type mentioned
above, with values for the visible flatness being translated into
values for the intrinsic flatness using a bulge model to control
the roll stands and a material flow model being used to determine
the intrinsic flatness--looked at in the material flow
direction--before a physical point for measuring flatness.
[0008] The claimed possibility of taking into account both the
visible flatness of the mill train and the intrinsic flatness with
the aid of the bulge model means that extremely stringent
requirements can be complied with in respect of the quality of the
visible flatness of the metal strip, even though the visible
flatness or waviness of the metal strip sometimes completely
disappears during rolling under tension, i.e. between the roll
posts, and cannot therefore be measured in practice in many
instances within the mill train. By translating values for the
visible flatness into values for the intrinsic flatness or values
for the intrinsic flatness into values for the visible flatness,
intrinsic strip flatness values calculated using the material flow
model and visible strip flatness values measured at the discharge
point of a mill train can be brought into line with each other or
verified
[0009] The bulge model is used first to establish a unique
relationship between the intrinsic and visible flatness of the
metal strip. It is then possible for the first time not just to
carry out presettings on the basis of flatness measurements but
also to use the visible flatness for accurate control or regulation
of the ongoing rolling process.
[0010] The visible flatness is advantageously determined in the
form of a bulge pattern. The bulge pattern is easy to compare in
respect of data and can be stored with relatively little
outlay.
[0011] The bulge pattern is advantageously three-dimensional.
[0012] At least one of the variables wavelength, amplitude and
phase offset of the individual tracks is advantageously evaluated
in addition to the relative length of individual tracks of the
metal strip to determine the bulge pattern of the metal strip. The
bulge pattern can thus be identified much more accurately.
[0013] A multi-track laser measuring device is advantageously used
to determine the bulge pattern, allowing economical identification
of the bulge pattern with a sufficiently high level of
precision.
[0014] The visible flatness is advantageously measured
topometrically. This makes surface identification of the surface
structure of the strip and in particular of the bulge pattern
directly possible.
[0015] The flatness values are advantageously translated online.
This allows particularly precise control or regulation of the strip
flatness.
[0016] The flatness values are advantageously translated with the
aid of an on-line-capable approximation function. This can save
on-line computing time during the translation between visible and
intrinsic flatness.
[0017] The bulge pattern of the metal strip is advantageously
modeled using the bulge model by applying a fictitious temperature
distribution in the transverse direction of the metal strip based
on the intrinsic flatness of the metal strip. The thermal expansion
in the longitudinal direction of the strip, but not however in the
transverse direction, corresponding to this strip temperature
distribution corresponds to a length distribution that can be
assigned to the intrinsic flatness. Only one segment of limited
length must therefore be modeled and the model equations for
elastic plate deformations with major deflections can be worked out
with suitable edge conditions at the segment edges.
[0018] One or more flatness limit values are advantageously
predefined at freely selectable points within and/or after the mill
train in order to control the mill train. The flatness limit values
can relate to the intrinsic flatness and/or the visible flatness.
Because flatness limit values can be predefined everywhere within
or after the mill train, regulation accuracies for the rolling
process can be significantly increased.
[0019] The object is also achieved by a control device for
operating a mill train for metal strip with at least one roll
stand, with the control device for implementing a method described
above having at least one regulating unit coupled to a bulge model,
which is coupled to a device for measuring the visible flatness of
the metal strip and to a material flow model. Advantageous
embodiments of the control device are specified in the subclaims.
The advantages of the control device are similar to those of the
method.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Further advantages and details will emerge from the
description which follows of an exemplary embodiment in conjunction
with the figures, in which:
[0021] FIG. 1 shows a multi-stand mill train for rolling metal
strip and a control device assigned to the mill train,
[0022] FIGS. 2a-2c show examples of metal strip with flatness
errors,
[0023] FIG. 3 shows the division of a metal strip into tracks,
[0024] FIG. 4 shows a section of a multi-stand mill train with a
control device,
[0025] FIG. 5 shows the geometry of a section of a metal strip.
DETAILED DESCRIPTION OF THE INVENTION
[0026] According to FIG. 1 a mill train for rolling a metal strip 1
is controlled by a control processor 2. The metal strip 1 can for
example be a steel strip, an aluminum strip or a non-ferrous metal
strip, in particular a copper strip. The mill train has at least
two roll stands 3.
[0027] The roll stands 3 have at least working rolls 4 and--as
shown in FIG. 1 for one of the roll stands 3--generally also
back-up rolls 5. The roll stands 3 could have even more rolls, for
example intermediate rolls that can be displaced axially.
[0028] The metal strip 1 passes through the mill train in its
longitudinal direction x, with the transverse direction y of the
metal strip being largely parallel to the axes of the working rolls
4.
[0029] The mill train shown in FIG. 1 is configured as a finishing
train for hot-rolling steel strip. The present invention is
particularly suitable for use with a multi-stand finishing train
for hot-rolling steel strip but is not restricted to this. The mill
train could in particular also be configured as a cold-rolling mill
train (tandem train) and/or for rolling a non-ferrous metal (e.g.
aluminum, copper or another non-ferrous metal).
[0030] The control device 2 has a regulating 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 predefines target
values for profile and flatness control elements (not shown here)
to the stand regulators 6. The stand regulators 6 then adjust the
control elements according to the predefined target values.
[0031] The input variables supplied to the control device 2 include
for example pass schedule data such as the input thickness of the
metal strip 1 and a roll force and draft reduction per pass for
each roll stand 3. The input variables generally also include an
end thickness, a target profile value, a target thickness contour
and a target flatness pattern of the metal strip 1 at the discharge
point of the mill train. The rolled metal strip 1 should generally
be as flat as possible.
[0032] However the metal strip 1 often has flatness errors, as
shown by way of an example and schematically in FIGS. 2a, 2b and
2c. Flatness errors of the metal strip 1 can be measured at one
point x2, as shown in FIG. 1, for example using a multi-track laser
measuring device 13.
[0033] FIG. 2a shows a centric bulge in the metal strip 1. FIG. 2b
shows flatness errors at the edges of the metal strip 1. FIG. 2c
shows bulges in the metal strip 1, which occur repeatedly in the
longitudinal direction x of the metal strip 1 and in two areas in
particular in the transverse direction y of the metal strip 1.
[0034] The bulges in the metal strip 1 are caused in particular by
internal stresses in the metal strip 1. Internal stresses in the
metal strip are also referred to as intrinsic strip flatness
ip.
[0035] FIG. 3 shows the division of a metal strip 1 into fictitious
tracks S1 to Sn or into measuring tracks S1' to Sm'. If the metal
strip 1 were to be cut up into narrow longitudinal strips or into
tracks S1 to Sn, it would be possible to 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 captures the relative
length of the metal strip 1 for each measuring track S1' to Sm' and
preferably also determines variables such as wavelength, amplitude
and/or the phase offset of the individual tracks S1' to Sm'. It is
important that the associated intrinsic or measured relative
lengths do not correspond for corresponding fictitious tracks S1 to
Sn and measuring tracks S1' to Sm'.
[0036] As shown in FIG. 4, a distinction is made between intrinsic
strip flatness ip and visible strip flatness vp when hot-rolling
metal strip 1. The intrinsic strip flatness ip refers, as mentioned
above, to the strip length distribution over the tracks S1 to Sn.
The visible flatness vp results from the bulge behavior of the
strip, which is for example a function of variables such as strip
thickness, strip width, the elasticity module of the metal strip 1
and the overall tension to which the metal strip 1 is
subjected.
[0037] According to FIG. 4 the visible flatness vp is measured at
one point x2 at the discharge point of the mill train, in
particular a finishing train, and supplied to a bulge model 12. The
visible flatness vp is measured according to the invention such
that not only is the visible strip length distribution over the
strip width in the transverse direction y an output variable of a
measuring device but the three-dimensional bulge pattern of the
strip can also be reconstructed from the measuring device output
variables. In the case of a multi-track laser measuring system
therefore not only the (relative) length of the individual
measuring tracks S1' to Sm' is output by the measuring device but
also wavelength and phase offset for each track S1' to Sm'. With a
topometric measurement of the visible flatness vp the surface
structure of the metal strip 1 is captured at the surface and
three-dimensionally over large areas of the metal strip 1. A
topometric strip flatness measurement is preferably based on a
strip projection method. Strip patterns are thereby projected onto
the surface of the metal strip 1 and continuously captured with the
aid of a matrix camera.
[0038] The intrinsic flatness ip is preferably calculated at a
point x1 between or after the roll stands 3, in particular between
and/or after the roll stands 3 of a finishing train. The
calculation is thereby preferably made using a material flow model
9 (see FIG. 1), which is preferably part of a regulating unit 1.
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 bulge model 12 at one point x2 at the discharge point of the
mill train, at which the visible flatness vp is measured. In the
case of a cold-rolling mill in particular it would essentially also
be possible to measure the intrinsic flatness ip on the metal strip
1.
[0039] The bulge model 12 allows a unique relationship to be
established between intrinsic flatness ip and visible flatness vp,
as far as possible. Thus for example with a very thick metal strip
1 with moderate intrinsic lack of flatness it is not possible to
conclude the intrinsic flatness ip from the bulge behavior, as such
a metal strip 1 generally does not bulge.
[0040] The various flatness values (ip and vp) are preferably
determined in the following sequence: [0041] 1. The visible
flatness vp, which generally corresponds to the bulge behavior of
the metal strip 1, is generally measured after a last roll stand 3,
for example at the discharge point of a finishing train. [0042] 2.
The bulge model 12 is used to determine the intrinsic flatness ip
of the metal strip 1 at the point for measuring the visible
flatness vp (see step 1). [0043] 3. The material flow model 9 is
used to determine the intrinsic flatness ip between the roll stands
3, for example within the finishing train. The intrinsic flatness
can therefore be determined before the physical point for measuring
flatness, in this instance intrinsic flatness, looked at in the
material flow direction.
[0044] 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 using the material flow model 9.
Input variables such as the strip thickness contours of the metal
strip 1 as well as flatness patterns or flatness values before and
after passage through a roll stand 3 can be supplied to the
material flow model 9. The material flow model 9 determines the
intrinsic flatness pattern of the metal strip 1 online after
passage through the roll stand 3 as well as a roll force pattern in
the transverse direction y of the metal strip 1 and supplies it to
a roll deformation model (not shown in more detail here). The roll
deformation model (not shown in more detail here) is preferably
part of a regulating unit 11. The roll deformation model determines
roll deformations and supplies them to a target value determination
unit (not shown in more detail here), which uses the determined
roll deformations and a contour pattern of the metal strip 1 on the
stand discharge side to determine the target values for the profile
and flatness control elements in each individual roll stand 3.
[0045] Use of the bulge model 12 allows the material flow model 9
and the profile and flatness control implemented in the module 10
(see FIG. 1 in each instance) to be adjusted based on the measured
data for visible flatness vp. Upper and lower limits can be
specified for the visible flatness vp or for the corresponding
visible lack of flatness of the strip and these limits can be
translated with the aid of the bulge model 12 into limits for the
intrinsic flatness ip or intrinsic lack of flatness. The bulge
model 12 uses the intrinsic lack of flatness to calculate the bulge
pattern of the metal strip 1. The calculated bulge pattern can be
used in turn to determine the visible lack of flatness. Inverse
modeling is used for the converse conclusion.
[0046] The bulge model 12 is preferably based on the theory of
elastic plate deformation. The intrinsic flatness ip is modeled by
applying a fictitious strip temperature distribution over the strip
width, i.e. in the transverse direction y, resulting in thermal
expansion in the longitudinal direction x of the metal strip 1 and
at the same time to the length distribution associated with the
intrinsic flatness ip.
[0047] Let us look now at a strip segment of length a, width b and
thickness h as shown in FIG. 5. The drawing also shows the
longitudinal direction x, transverse direction y and a
perpendicular z. Only a strip segment with a length a of a half or
whole basic bulge length and with periodic edge conditions at the
top and bottom ends of the strip segment is modeled. The edge
conditions at the sides of the strip are free edges. The model
equations are partial differential equations and the associated
edge conditions, which can be solved for example using finite
difference methods or finite element methods.
[0048] The bulge model 12 can be used directly online as a function
of the computing time of the solution algorithm. Alternatively an
offline model can be used to generate an online-capable
approximation function, which is then used online for the bulge
model 12.
[0049] To understand the mode of operation of the bulge model 12
better, it first has to be acknowledged that when hot-rolling a
metal strip 1 for example, the measured deflections of the metal
strip 1, which are due to the bulging of the metal strip 1, are
generally significantly larger than the strip thickness h. They are
however typically significantly smaller than both the typical
wavelength of the bulge behavior and also the strip width b. While
the traditional, linear theory of plate deformation only applies
when the deflections are less than or equal to approximately 1/5 of
the strip thickness h, in the present instance a non-linear
description of the plate warp must be used. In addition to the
variables shown in FIG. 5, which describe the metal strip 1, the
elasticity module or e-module for short is also used, with a
constant e-module generally being assumed. The non-linear bulge
behavior can now be described as follows: D h .gradient. 4 .times.
w .function. ( x , y ) = p h + L .function. ( w .function. ( x , y
) , .PHI. .function. ( x , y ) ) ( I ) ##EQU1##
[0050] Forces operating in the plane of the strip are thereby
expressed in the form of a potential .PHI., also referred to
generally as Airy's stress function. w refers to the vertical
displacement of the metal strip 1 while p describes the pressure
distribution operating from outside, which acts in the
perpendicular z. D is defined by the equation below: D .times. : =
Eh 3 12 .times. ( 1 - v 2 ) ( II ) ##EQU2##
[0051] E thereby stands for the e-module and v stands for the
Poisson's ratio of the metal strip 1.
[0052] The following also applies for the term L(w,.PHI.) from
equation (I): L .function. ( w , .PHI. ) .times. : = .differential.
2 .times. w .differential. x 2 .times. .differential. 2 .times.
.PHI. .differential. y 2 - .differential. 2 .times. w
.differential. y 2 .times. .differential. 2 .times. .PHI.
.differential. x 2 - 2 .times. .differential. 2 .times. w
.differential. x .times. .differential. y .times. .differential. 2
.times. .PHI. .differential. x .times. .differential. y ( III )
##EQU3##
[0053] If assumptions are now made in respect of internal stresses
and strains due to thermal causes, the following results: 1 E
.gradient. 4 .times. .PHI. .function. ( x , y ) + K x .times.
.differential. 2 .times. T .function. ( x , y ) .differential. y 2
+ K y .times. .differential. 2 .times. T .function. ( x , y )
.differential. x 2 = ( .differential. 2 .times. w .differential. x
.times. .differential. y ) 2 - .differential. 2 .times. w
.differential. x 2 .times. .differential. 2 .times. w
.differential. y 2 = - 1 2 .times. L .function. ( w .function. ( x
, y ) , w .function. ( x , y ) ) ( IV ) ##EQU4##
[0054] T thereby refers to the temperature in the metal strip 1 and
K.sub.x or K.sub.y the coefficient of thermal expansion in the
longitudinal or transverse direction (x or y).
[0055] The equations (I) and (IV) form a system of two coupled,
non-linear, partial differential equations. If suitable edge
conditions are now inserted, for example free edges or periodical
edge conditions at the top and bottom ends of a strip segment, the
equations (I) and (IV) can be solved numerically in an iterative
manner.
[0056] The basic concept of the invention can be summarized as
follows:
[0057] The invention relates to a method and a control device for
operating a mill train for metal strip 1, having at least one roll
stand 3, with the intrinsic flatness ip of the metal strip 1 being
determined at the discharge point of the mill train. To ensure
compliance with a required visible flatness vp of the rolled metal
strip 1 within predefined limits in a reliable and sufficiently
accurate manner, it is proposed that the visible flatness vp or
bulge behavior of the metal strip 1 be determined or preferably be
measured at the discharge point of the mill train and be translated
into the intrinsic flatness ip of the metal strip 1 using a bulge
model 12. The visible flatness can thus be used online with the aid
of the bulge model 12 to control the roll stands of the mill train.
According to the invention the visible flatness vp can be better
regulated preferably online throughout the mill train with the aid
of the bulge model 12.
[0058] The bulge model 12 is online-capable and establishes a
unique relationship between the absolute intrinsic flatness ip of
the rolled metal strip 1 and the actual measured visual defects in
the metal strip 1, in other words the visible flatness vp. It is
possible for the first time to verify, adjust and coordinate a
material flow model 9 based on the intrinsic flatness or its
corresponding profile and flatness control in respect of the actual
measured values.
* * * * *