Note: Descriptions are shown in the official language in which they were submitted.
CA 02620000 2008-02-21
METHOD FOR THICKNESS REGULATION DURING A
HOT-ROLLING PROCESS
The invention concerns a method for automatic gage
control during rolling, especially hot rolling, with at least
one rolling stand, where factors that are considered include
the present mean position of the adjustment cylinders of the
rolling stand and their total rolling force.
DE 20 20 402 discloses a method for calculating the gage
Gl of a thin, hard workpiece after a reducing pass through a
reducing mill train with opposing rolling surfaces and a
measuring instrument for measuring the roll separating forces,
which are produced during the passage of the workpiece through
the opposing rolling surfaces during a reducing operation, in
which
(a) a signal that is a measure of the gage G5 is
generated, which is determined by the point of intersection of
an appropriate mill stretch curve and an appropriate workpiece
deformation curve for the reducing operation,
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(b) a signal that is a measure of a gage G3 is generated,
which is determined by the point of intersection of the
measured force curve and the mill stretch curve,
(c) a signal that is a measure of a range of uncertainty
is generated, which is determined by the difference between
signals representing the gages G5 and G3,
(d) a signal that is a measure of a calculated stretch
error is generated by varying the signal that represents the
range of uncertainty as a function of the draft predicted for
the reducing pass, of the mill stretch predicted for the
reducing pass, and of the relative probability of error in
predicting both draft and mill stretch, and
(e) a signal that is a measure of the calculated gage G1
is generated by adding the signal that represents the gage G3
to the calculated stretch error.
DE 26 57 455 Al describes a method for compensating roll
deformation in rolling stands with prestressing that can be
automatically controlled, in which the strip thickness is
automatically controlled by hydraulic actuators, and in which
the contact force (Fa), which is the sum of the rolling force
and the automatically controllable prestressing force
according to the following equation:
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Fa = ( Fao + (Fr - Fro) ) * Ca/ (Ci + ca)
is varied by hydraulic prestressing cylinders in such a way
that, to the base set value (Fao) of the contact force, a
supplementary set value is added, which is formed from the
difference between the actual value (Fr) of the prestressing
force and the initial value (Fro) of the prestressing force and
is evaluated with the ratio (ca/(ci + Ca)) of the spring
stiffness (Ca) of the outer part of the stand to the sum of the
spring stiffness (ci) of the inner part of the stand and the
spring stiffness (ca) of the outer part of the stand.
DE 16 02 195 Al discloses a method for calculating the
gage of thin, hard workpieces, in which
-- a signal that is a measure of the gage G5 is
generated, which is determined by the point of intersection of
an appropriate mill stretch curve and an appropriate workpiece
deformation curve for the reducing operation,
-- a signal that is a measure of a gage G3 is generated,
which is determined by the point of intersection of the
measured force curve and the mill stretch curve,
-- a signal that is a measure of a range of uncertainty
is generated, which is determined by the difference between
signals representing the gages G5 and G3,
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-- a signal that is a measure of a calculated stretch
error is generated by varying the signal that represents the
range of uncertainty as a function of the mill stretch
predicted for the reducing pass and of the relative
probability of error in predicting both draft and mill
stretch, and
-- a signal that is a measure of the calculated gage Gl
is generated by adding the signal that represents the gage G3
to the calculated stretch error.
Until now, the so-called gage meter principle for
determining the present strip gage has been used for automatic
gage control during hot strip rolling. To this end, the
measured SDS, SOS of the adjustment cylinders is corrected by
the calculated mill stretch g (see also Figure 1). The mill
stretch g is calculated with the use of the measured rolling
force FDS, Fos and a mill stretch curve 1/MG. The strip gage
determined in this way is then compared with the gage set
value and automatically controlled. Besides the measurements
of position and rolling force, an exact mill model is needed
for this method.
In the rolling of hard materials and thin strip, small
inaccuracies in the mill model lead to relatively large errors
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in the strip gage and sometimes instability of the automatic
gage control system.
Therefore, the objective of the invention is to improve a
method of the type described above in such a way that the
disadvantages specified above are avoided.
In accordance with the invention, this objective is
achieved by minimizing the mill stretch component. This is
accomplished by carrying out at least one additional position
measurement by detecting position signals in the immediate
vicinity of the roll gap of the rolling stands. In this
connection, especially the position signals between the work
rolls and/or the backup rolls and/or the work roll chocks
and/or the backup roll chocks are to be considered/detected.
The advantage of the method of the invention is that the
position measurement contains a smaller mill stretch
component. Thus, only the roll flattening and the roll
bending are to be considered. Other components, such as the
expansion of the columns and the crossheads, do not have to be
considered. Specifically in the measurement of the separation
of the work roll chocks, the suspension of the Morgoil
bearings, the bending of the backup rolls, and backup roll
eccentricities do not have to be taken into consideration. As
CA 02620000 2008-02-21
shown in Figure 2, the prior-art method for automatic gage
control is still used in its entirety and is improved or
expanded by the features described above.
The method of the invention results in a more exact
determination of the strip gage in the case of hard materials
and, especially in the case of thin strip rolling, improves
the dynamic behavior of the automatic gage control system.
In a further development of the invention, the signals
that are obtained can also be used for automatic position
control and/or for automatic swivel control and/or for
calculation of the strip gage and thus for automatic control
of the strip gage.
A specific embodiment of the invention is described in
greater detail below with reference to the accompanying
schematic drawings.
-- Figure 1 shows a flowchart for automatic gage control
in accordance with the prior art.
-- Figure 2 shows a flowchart for automatic gage control
in accordance with the invention.
Figure 1 shows a flowchart of prior-art automatic gage
control during rolling, especially hot rolling. A rolling
stand consisting, for example, of a pair of work rolls AW and
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a pair of backup rolls SW has an operating side OS and a drive
side DS. A strip B is positioned between the pair of work
rolls AW. In the previously known method for automatic gage
control, the cylinder position of the operating side Sos and
the cylinder position of the drive side SDs are determined, and
the present mean cylinder position SACT is determined. In
addition, the total rolling force FACT is determined by
determining the rolling force on the operating side Fos and the
rolling force on the drive side FDS. The mill stretch g is
calculated with the use of the total rolling force FACT and a
mill stretch curve 1/MG. The present strip gage hACT is
determined by measurement of the present mean cylinder
position SACT and the calculated mill stretch g. The present
strip gage hACT is compared with the strip gage set value hREF
and used for automatic gage control. The automatic gage
controller outputs the position set value for the automatic
cylinder position control system.
In accordance with the invention, the prior-art automatic
control system is improved as shown in the flowchart in Figure
2. To this end, for example, the separation of the work roll
chocks on the operating side SROs and on the drive side SRDS is
measured, and then the mean separation of the work roll chocks
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SR is determined. The value for the present mean cylinder
position SACT, which continues to be determined, as in the
prior art, is directly compared with the cylinder position set
value SREF -
The values of the rolling force on the operating side Fos
and the rolling force on the drive side FDs also continue to be
determined and lead to the total rolling force FACT. These are
combined, in accordance with the invention, with a mill
modulus MR with respect to the work roll chocks, and then the
mill stretch gR with respect to the work roll chocks is
determined.
In accordance with the invention, the mill modulus MR
depends on the selected position measurement. The position
signals of the position measurement that are to be taken into
consideration for the method, with at least one position
signal being required, are determined between the work rolls
AW and/or the backup rolls SW and/or the work roll chocks
and/or the backup roll chocks. The mill stretch to be taken
into consideration in the method of the invention is to be
coordinated with the given site of the position signal that is
obtained.
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= ~ '
The separation on the operating side SROs and the
separation on the drive side SRDS lead to the mean separation
of the work roll chocks SR, for example. The present strip
gage hACT is determined from the separation of the work roll
chocks SR and the mill stretch with respect to the work roll
chocks gR and is then compared with the strip gage set value
hREF and automatically controlled.
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List of Reference Symbols
AW work roll
SW backup roll
W rolling stand
B strip
DS drive side
OS operating side
FACT total rolling force
Fos rolling force on the operating side
FDS rolling force on the drive side
SACT present mean cylinder position
SoS cylinder position on the operating side
SDS cylinder position on the drive side
SREF cylinder position set value
hACT present strip gage
hREF strip gage set value
SR mean separation of the work roll chocks
SROS separation on the operating side
SRDS separation on the drive side
gR mill stretch with respect to the work roll chocks
MR mill model with respect to the work roll chocks
g mill stretch
MG mill modulus
