Title of Invention	A METHOD FOR ROLLING A METAL STRIP
Abstract	This invention relates to a method and system for rolling a metal strip, in particular a steel strip, by means of a cold-rolling mill, which is followed by an annealing section and a cold-finishing part, the exit thickness or the intended thickness of the metal strip at the exit from the cold-rolling mill being determined as a function of the intended hardness and the intended thickness of the metal strip at the exit from the cold-finishing part.

Title of Invention

A METHOD FOR ROLLING A METAL STRIP

Abstract

This invention relates to a method and system for rolling a metal strip, in particular a steel strip, by means of a cold-rolling mill, which is followed by an annealing section and a cold-finishing part, the exit thickness or the intended thickness of the metal strip at the exit from the cold-rolling mill being determined as a function of the intended hardness and the intended thickness of the metal strip at the exit from the cold-finishing part.

Full Text	ADescription The invention relates to a method and equipment for rolling a metal strip by means of a cold-rolling mill, which is followed by an annealing section and a cold-finishing part. It has been shown that it is difficult to achieve the desired material hardness in the case of rolling mills of this type. Accordingly, it is the object of the invention to specify a method and equipment by means of which the desired material hardness may be achieved precisely. In the process, it is also desirable to achieve the desired value for the thickness of the metal strip at the exit from the cold-finishing part. According to the invention, the object is achieved by a method and equipment the features of fhe-invention according to -14. The exit thickness or the intended thickness of the metal strip at the exit from the cold-rolling mill is determined as a function of the intended hardness and of the intended thickness at the exit from the cold-finishing part. In thlk way, it is possible to achieve the desired intended hardness as the rolled strip runs out of the cold-finishing part. In this case, in a particularly advantageous refinement of the invention, the effect of the cold-finishing part, in particular the relationship between hardness of the metal strip and thickness reduction of the metal strip, as well as the effect of the annealing section, in particular on the material hardness, are taken into account. According to this particularly advantageous refinement of the invention, whilst taking into account the reduction in the material hardness in the annealing section and taking into account the relationship between the hardness of the metal strip and the thickness reduction of the metal strip in the cold-finishing part, the thickness of the rolled strip at the exit from the cold-roll ing mill is predefined in - 2 - such a way that, during the thickness reduction of the metal strip in the cold-finishing part to the desired intended thickness of the metal strip, the desired intended hardness is also established. It has been shown that the precision in reaching the desired intended hardness of the metal strip at the exit from the cold-finishing part may be improved considerably in this way. In an additionally advantageous refinement of the invention, the effect of the cold-finishing part, that is to say in particular the relationship between hardness of the metal strip and thickness reduction of the metal strip, is ascertained from the effect of the cold-rolling mill, that is to say in particular from the relationship between hardness of the metal strip and thickness reduction of the metal strip in the cold-rolling mill. The modelling of the relationship between thickness reduction of the metal strip and material hardness is carried out on the basis of the relationships between thickness reduction of the metal strip and material hardness at the roll stands of the cold-rolling mill or at some selected roll stands of the cold-rolling mill. In an alternative advantageous refinement for this purpose, the effect of the cold-finishing part, in particular the relationship between hardness of the metal strip and the thickness reduction of the metal strip, is determined in advance, in particular by means of tensile tests. In an additionally advantageous refinement, the ascertained effect of the cold-finishing part, in particular the ascertained relationship between hardness of the metal strip and thickness reduction of the metal strip, is corrected by comparing a measured value of the current hardness with the intended hardness of the metal strip at the exit from the cold-finishing part, with the effect of reducing the deviation between the intended hardness and the - 3 - measured value of the current hardness of the metal strip at the exit from the cold-finishing part. In an additionally advantageous refinement, the intended value for the thickness or the intended thickness of the metal strip at the exit from the cold-rolling mill, this value being ascertained from the effect of the cold-finishing part, in particular from the relationship between hardness of the metal strip and thickness reduction of the metal strip, is corrected by comparing the current hardness and the intended hardness of the metal strip at the exit from the cold-finishing part, with the effect of reducing the deviation between the intended hardness and the current hardness of the metal strip at the exit from the cold-finishing part. By means of these measures, relating to precise modelling of the relationship between hardness of the metal strip and thickness reduction of the metal strip, the desired intended hardness is achieved particularly well. If no measured values for the hardness of the metal strip at the exit from the cold-finishing part are available, then the current values are advantageously ascertained by means of inverse modelling, for ascertaining the current values for the model adaptation. The method according to the invention is particularly advantageously applied in achieving a constant material hardness over the entire length of the metal strip, as a result of which scrap is prevented to a great extent. In an advantageous refinement of the invention, the thickness of the metal strip is reduced by at least 10%, in particular by at least 20%, in the cold-finishing part. Furthermore, it is particularly advantageous to reduce the thickness of the metal strip by 20 to 40% in the cold-finishing part. Further advantages and inventive details emerge from the following description of exemplary - 4 - accompanying embodiments, using the/drawings and in conjunction with In detail: FIG 1 shows a rolling mill according to the invention FIG 2 shows the determination of a correction factor according to the invention FIG 3 shows a method for achieving a constant hardness over the length of the metal strip. FIG 1 shows a rolling mill for implementing the method according to the invention. A cold-rolling mill 2 having, by way of example, four roll stands 21, 22, 23, 24 is followed by an annealing section 3 and a cold-finishing part 4. A metal strip, which, for example, runs out of a hot-rolling mill 1, runs into the cold-rolling mill 2 in the exemplary embodiment according to FIG 1, and is further reduced. It is then annealed in the annealing section 3 and cold-finished in the cold-finishing part 4 and, according to the invention, has its thickness reduced. The relationships, illustrated in the functional blocks 5, 6 and 7, show the change in the material hardness in the cold-rolling mill 2, in the annealing section 3 and in the cold-finishing part 4. A metal strip with a thickness HEKTM and a hardness KF0 runs into the cold-rolling mill 2 and runs out of the cold-rolling mill 2 with the thickness HAKTM and the hardness KFKTM. Functional block 5 shows the physical relationship between material hardness KF and thickness reduction EPS of the metal strip. In this case, the thickness reduction EPS is defined as EPS = 1_ HE_ HA where HE is the entry thickness and HA is the exit thickness of the metal strip. In the annealing section 3, the material hardness KF decreases as a function of the thickness reduction of the metal strip in the cold-rolling mill, as functional block 6 shows. In the process, the material thickness remains unchanged, that is to say HAKTM = HEDCR. After passing through the annealing section 3, the metal strip has the material - 5 - hardness KF0. In the present exemplary embodiment, the cold-finishing part 4 has two roll stands 41 and 42. In an advantageous refinement of the invention, the rolled strip is essentially reduced by means of the first roll stand 41, By means of the second roll stand 42, the desired surface condition and flatness of the rolled strip are achieved. The rolled strip, which runs into the cold-finishing part 4 with the strip thickness HEDCR and material hardness KF0, runs out with the strip thickness HADCR and the material hardness KFDCR, as functional block 7 shows. According to the method of the invention, the pair of values HAKTM and KFKTM is set, in accordance with the relationships according to functional blocks 6 and 7, in such a way that the desired values for the exit thickness HADCR and the material hardness KFDCR are achieved by means of the thickness reduction in the cold-finishing part 4. If, for example, a rolled strip has the thickness HEKTM of 4 mm and the hardness KF0 of 300 N/mm2 at the entry to the cold-rolling mill, and if the desired thickness HADCR of the metal strip is 0.3 mm and the desired hardness KFDCR of the metal strip is 450 N/mm2, then for an exemplary configuration, the metal strip is to be rolled in the cold-rolling mill 3 in such a way that HAKTM = 0.5 mm and KFKTM = 600 N/mm . In the subsequent annealing section 3, the hardness of the metal strip is in turn reduced to the hardness KF0, that is to say 300 N/mm . As a result of the subsequent reduction of the metal strip in the cold-finishing part 4 from an entry thickness HEDCR of 0.5 mm to an exit thickness HADCR of°-3 mm,the hardness KFDCR of the metal strip at the exit from the cold-finishing part 4 is increased to the desired 450 N/mm2. The limits of the method according to the invention depend on the possible reduction in the cold-finishing part 4. If, for example, taking into account a material strength or hardness model (with MSO ~ KFO, MSI ~ KFI and KFE ~ MSE) - 6 - then, given the reduction variation in the_ cold-finishing part of 10 ... 40%, a hardness variation of about 3 5% can be achieved. For this case, a variation in the entry thickness HDDCR from 0.33 to 0.5 mm in the cold-finishing part 4 is possible. This variation permits a change in the material strength KFDCR from 330 N/mm2 to 440 N/mm2. For the modelling, illustrated schematically, according to the functional blocks 5 and 7, a model comes particularly advantageously into consideration. Furthermore, it has proven to be advantageous to transfer the model for the relationship between material hardness KF and thickness reduction EPS for the cold-rolling mill to the cold-finishing part 4 as well. In this case, the relationship, ascertained for the cold-rolling mill, between hardness KF of the metal strip and thickness reduction EPS of the metal strip is particularly advantageously corrected by comparing the current hardness and the intended hardness at the exit of the metal strip from the cold-finishing part 4, with the effect of reducing the deviation between intended hardness and current hardness at the exit from the cold-finishing part 4. A correction of this type is shown by FIG 2. The setting of the material strength in the cold-finishing part can be carried out in accordance with the following automation stages: 1. Feed-forward control 8 as a result of calculating and rolling an exit thickness HADCR in the cold- rolling mill in accordance with the desired value for the hardness VKFDCR and the thickness HADCR of the metal strip after the cold-finishing part 4. 2. Feedback 9 as a result of ascertaining the achieved hardness KFDCR in the cold-finishing part - 7 - 4 and forming a correction value a for the thickness HAKTM of the metal strip at the exit from the cold-rolling mill 2 in accordance with the deviations from the desired value for KFDCR. 3. Ascertaining the material strength curve, that is to say the relationship between hardness KF of the metal strip and thickness reduction EPS, in the cold-rolling mill 2 over the length of the strip, and calculating and rolling the strip thickness HAKTM over the length of the strip in accordance with the ascertained material strength curve and the intended value for the hardness KFDCR of the metal strip. In detail, the exit thickness HAKTM of the metal strip is calculated in the feed-forward controller 8 in accordance with the desired hardness KFDCR of the metal strip. This is carried out as a function of the thickness of the metal strip HADCR at the exit from the cold-finishing part, the hardness KFDCR of the metal strip at the exit from the cold-finishing part, the thickness HEKTM of the metal strip at the entry to the cold-rolling mill, and of material properties MT of the rolled strip. The starting variables for the feedforward controller 8 are the thickness . HAKTM of the metal strip at the exit from the cold-rolling mill, and material parameters ME of 'the metal strip. These material parameters ME are essentially parameters which describe the hardness KFDCR of the metal strip. In the present example, they are the parameters KFO, KFI and KFE, which describe the relationship between hardness KFDCR Of the metal strip and thickness reduction of the metal strip. values tor tnickness-HADCR and hardness KFDCR of the metal strip, the feedback unit 9 ascertains a correction value a, with which the value for the thickness HAKTM of the metal strip at the exit from the cold-rolling mill is corrected. It has proven to be particularly advantageous to multiply the correction - 8 - parameter a and the desired thickness HAKTM of the metal strip at the exit from the cold-rolling mill. The correction parameter a is formed in such a way that the deviation between the current thickness HADCR of the metal strip at the exit from the cold-finishing part and the corresponding intended value is minimized. The more rapid cooling down of the outer and inner windings after the hot-rolling mill results in a higher strength of the ends of the strip. Even intermediate annealing after the cold-rolling mill is not able to eliminate this effect, as is shown by the curve 13 in FIG 3, in which the course of the hardness KF0 of the metal strip over the length BL of the metal strip is illustrated. In the case of deep-drawing material, in particular, it is generally necessary for these ends to be cut off following cold finishing, since the hardness KFDCR of the metal strip is intended to be constant over the length of the strip. In this case, the high proportion of scrap and the additional outlay lead to a high loading of the costs J Increases of up to 15% in material hardness occur; This increase in" material hardness decreases gradually over a strip length of about 50 m. Given an increase in material hardness of 15%, tne reduction EPSDCR in the cold-finishing part is reduced, according to the invention, by about 15%. This takes place particularly advantageously if the overall reduction EPSDCR is greater than 30%. In the case of the example cited above, a 15% change in the reduction means a change in the entry thickness of 50 jxm or 6%. The curves 13, 14, 15, 16 and 17 in FIG 3 illustrate the use of the method according to the invention for achieving a constant hardness KF over the length of the metal strip. At the exit from the cold-rolling mill, the metal strip has a hardness KF0 corresponding to curve 13. At the ends of the strip, that is to say in the regions 10 and 12, the metal strip has a greater hardness than in the middle region. The regions 10 and 12 may comprise, for example, a strip length of 50 m each. According to the invention, the cold-rolling mill is adjusted in such a way that the metal strip has a thickness corresponding to curve 14 at the exit from the cold-rolling mill. The course of the curve 14 is selected such that, given a thickness reduction EPSDCR in the cold-finishing part, as shown by curve 15, a constant course of the thickness HADCR and of the hardness KFDCR of the metal strip is established, according to the curves 16 and 17. We Claim: 10.. 1. A method for rolling a metal strip, comprising the steps of: - arranging a cold-rolling mill (2) upstream from an annealing section (3) and a cold finishing part (4); - determining harness (KFQCR) and "thickness (HADCR) set point values of the metal strip at an outflow from the cold-finishing part (4); and - determining a setpoint (HAKTM) of the metal strip at an outflow form the cold-rolling mill (4) as a function of the setpoint values for the hardness and thickness setpoint values (KFDCR, HADCR) of the metal strip at the outflow from the cold-finishing part (4). 2. The method as claimed in claim 1, wherein the metal strip is a steel strip. 3. The method as claimed in claim 1, comprising the steps of: -providing a rolling model (7) of the cold-finishing part (4), the setpoint thickness (HAKTM) of the metal strip being determined as a function of an effect of the cold-finishing part (4) using the rolling model (7). 4. The method as claimed in Claim 1 or 3, wherein the relationship between hardness (KF) of the metal strip and the thickness reduction (EPS) of the metal strip is modeled by means of the rolling model (7) of the cold-finishing part (4). 5. The method as claimed in claim 1 comprising the steps of: - providing a model (6) of the annealing section (3), the set point thickness (HAKTM) of the metal strip at the outflow, from the cold-rolling mill (2) being determined as a function of an effect of the annealing section (3) using the model(6) of the annealing section (3). 6..htethod according to. claim 3, 4 or 5, wherein the effect of the cold-finishing part (4), in particular the relationship between hardness ( KF) of the metal strip and the thickness reduction (EPS) of the metal stripMs determined form the effect of the cold-rolling mill (2), in particular from the relationship between hardness 11. (KF) of the metal strip and the thickness reduction (EPS) of the metal strip at the roll stands ( 21, 22,23, 24) or a selection of roll stands ( 21, 22, 23, 24) of the cold-rolling mill (2). 7. Method as claimed in claim 3,4, or 5, wherein the effect of the cold-finishing part (4), in particular the relationship between hardness (KF) of the metal strip and the thickness reduction (EPS) of the metal strip, is determined in advance, in particular by means of tensile tests. 8. Method as claimed in claim 3, 4, 5,6 or 7, wherein the ascertained effect of the cold-finishing part (4), in particular the ascertained relationship between hardness (KF) of the metal strip and thickness reduction ( EPS) of the metal strip, is corrected by comparing a measured value of the current hardness ( KFDCR) with the intended hardness of the metal strip at the exit from the cold-finishing part (4), with the effect of reducing the deviation between the intended hardness and the measured value of the current hardness (KFDCR) of the metal strip at the exit from the cold-finishing part (4). 9. The method as claimed in claims 3, 4, 5, 6, 7 or 8, wherein the intended value for the thickness (HAKTM) or the intended thickness of the metal strip at the exit form the cold-rolling mill (2) ascertained from the effect of the cold-finishing part (4), in particular ascertained from the relationship between hardness (KF) of the metal strip and thickness reduction, (EPS) of the metal strip, is corrected by comparing the current hardness (KFDCR) and the intended hardness of the metal strip at the exit from the cold-finishing part (4) by reducing a deviation between the intended hardness and the current hardness ( KFDCR) of the metal strip at the exit form the cold-finishing part (4). 10. The method as claimed in claim 1, wherein the metal strip has a length, and wherein the hardness (KFDCR) of the metal strip at the outflow form the cold-finishing part (4) is kept constant over the length (BL) of the metal strip. 11. The method as claimed in claim 1, wherein the cold-finishing part (4) comprises at least two roll stands (41, 42) the method comprising: 12. - reducing the thickness of the metal strip using at least one of the roll stands; and adjusting flatness and influencing a surface of the metal strip using at least another of the roll stands. 12. The method as claimed in claim 11, wherein the atleast one (41) of the roll stands is a first one of the roll stands, and the at least another (42) of the roll stands is a second one of the roll stands. 13. The method as claimed one of the preceding claims, wherein the thickness of the metal strip is reduced by at least 10%, in particular by at least 20%, in the cold- finishing part (4). 14. The method as claimed in claim 13, wherein the thickness of the metal strip is reduced by 20 to 40% in the cold-finishing part (4). 15. A system for rolling a metal strip carrying out the method as claimed in claims 1 to 14, comprising: - an annealing section (3) and a cold finishing part (4)' - a cold -rolling mill (2) arranged upstream from the annealing section (3) and the cold finishing part (4); characterized in that a computing device (8, 9) determining a set point thickness ( HAKTM) of the metal strip at the outflow from the rolling mill (2) as a function of a set point hardness ( KFDCR) and a setpoint thickness ( HADCR) at an outflow form the cold-finishing part (4). This invention relates to a method and system for rolling a metal strip, in particular a steel strip, by means of a cold-rolling mill, which is followed by an annealing section and a cold-finishing part, the exit thickness or the intended thickness of the metal strip at the exit from the cold-rolling mill being determined as a function of the intended hardness and the intended thickness of the metal strip at the exit from the cold-finishing part.

Full Text

ADescription
The invention relates to a method and equipment for rolling a metal strip by means of a cold-rolling mill, which is followed by an annealing section and a cold-finishing part. It has been shown that it is difficult to achieve the desired material hardness in the case of rolling mills of this type.
Accordingly, it is the object of the invention to specify a method and equipment by means of which the desired material hardness may be achieved precisely. In the process, it is also desirable to achieve the desired value for the thickness of the metal strip at the exit from the cold-finishing part.
According to the invention, the object is
achieved by a method and equipment
the features of fhe-invention according to -14. The exit thickness or the
intended thickness of the metal strip at the exit from the cold-rolling mill is determined as a function of the intended hardness and of the intended thickness at the exit from the cold-finishing part. In thlk way, it is possible to achieve the desired intended hardness as the rolled strip runs out of the cold-finishing part. In this case, in a particularly advantageous refinement of the invention, the effect of the cold-finishing part, in particular the relationship between hardness of the metal strip and thickness reduction of the metal strip, as well as the effect of the annealing section, in particular on the material hardness, are taken into account. According to this particularly advantageous refinement of the invention, whilst taking into account the reduction in the material hardness in the annealing section and taking into account the relationship between the hardness of the metal strip and the thickness reduction of the metal strip in the cold-finishing part, the thickness of the rolled strip at the exit from the cold-roll ing mill is predefined in

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such a way that, during the thickness reduction of the metal strip in the cold-finishing part to the desired intended thickness of the metal strip, the desired intended hardness is also established. It has been shown that the precision in reaching the desired intended hardness of the metal strip at the exit from the cold-finishing part may be improved considerably in this way.
In an additionally advantageous refinement of the invention, the effect of the cold-finishing part, that is to say in particular the relationship between hardness of the metal strip and thickness reduction of the metal strip, is ascertained from the effect of the cold-rolling mill, that is to say in particular from the relationship between hardness of the metal strip and thickness reduction of the metal strip in the cold-rolling mill. The modelling of the relationship between thickness reduction of the metal strip and material hardness is carried out on the basis of the relationships between thickness reduction of the metal strip and material hardness at the roll stands of the cold-rolling mill or at some selected roll stands of the cold-rolling mill.
In an alternative advantageous refinement for this purpose, the effect of the cold-finishing part, in particular the relationship between hardness of the metal strip and the thickness reduction of the metal strip, is determined in advance, in particular by means of tensile tests.
In an additionally advantageous refinement, the ascertained effect of the cold-finishing part, in particular the ascertained relationship between hardness of the metal strip and thickness reduction of the metal strip, is corrected by comparing a measured value of the current hardness with the intended hardness of the metal strip at the exit from the cold-finishing part, with the effect of reducing the deviation between the intended hardness and the

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measured value of the current hardness of the metal strip at the exit from the cold-finishing part.
In an additionally advantageous refinement, the intended value for the thickness or the intended thickness of the metal strip at the exit from the cold-rolling mill, this value being ascertained from the effect of the cold-finishing part, in particular from the relationship between hardness of the metal strip and thickness reduction of the metal strip, is corrected by comparing the current hardness and the intended hardness of the metal strip at the exit from the cold-finishing part, with the effect of reducing the deviation between the intended hardness and the current hardness of the metal strip at the exit from the cold-finishing part.
By means of these measures, relating to precise modelling of the relationship between hardness of the metal strip and thickness reduction of the metal strip, the desired intended hardness is achieved particularly well. If no measured values for the hardness of the metal strip at the exit from the cold-finishing part are available, then the current values are advantageously ascertained by means of inverse
modelling, for
ascertaining the current values for the model adaptation.
The method according to the invention is particularly advantageously applied in achieving a constant material hardness over the entire length of the metal strip, as a result of which scrap is prevented to a great extent.
In an advantageous refinement of the invention, the thickness of the metal strip is reduced by at least 10%, in particular by at least 20%, in the cold-finishing part. Furthermore, it is particularly advantageous to reduce the thickness of the metal strip by 20 to 40% in the cold-finishing part.
Further advantages and inventive details emerge from the following description of exemplary

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accompanying embodiments, using the/drawings and in conjunction with
In detail:
FIG 1 shows a rolling mill according to the invention FIG 2 shows the determination of a correction factor
according to the invention FIG 3 shows a method for achieving a constant
hardness over the length of the metal strip.
FIG 1 shows a rolling mill for implementing the method according to the invention. A cold-rolling mill 2 having, by way of example, four roll stands 21, 22, 23, 24 is followed by an annealing section 3 and a cold-finishing part 4. A metal strip, which, for example, runs out of a hot-rolling mill 1, runs into the cold-rolling mill 2 in the exemplary embodiment according to FIG 1, and is further reduced. It is then annealed in the annealing section 3 and cold-finished in the cold-finishing part 4 and, according to the invention, has its thickness reduced. The relationships, illustrated in the functional blocks 5, 6 and 7, show the change in the material hardness in the cold-rolling mill 2, in the annealing section 3 and in the cold-finishing part 4. A metal strip with a thickness HEKTM and a hardness KF0 runs into the cold-rolling mill 2 and runs out of the cold-rolling mill 2 with the thickness HAKTM and the hardness KFKTM. Functional block 5 shows the physical relationship between material hardness KF and thickness reduction EPS of the metal strip. In this case, the thickness reduction EPS is defined as
EPS = 1_ HE_ HA
where HE is the entry thickness and HA is the exit thickness of the metal strip. In the annealing section 3, the material hardness KF decreases as a function of the thickness reduction of the metal strip in the cold-rolling mill, as functional block 6 shows. In the process, the material thickness remains unchanged, that is to say HAKTM = HEDCR. After passing through the annealing section 3, the metal strip has the material

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hardness KF0. In the present exemplary embodiment, the
cold-finishing part 4 has two roll stands 41 and 42. In
an advantageous refinement of the invention, the rolled
strip is essentially reduced by means of the first roll
stand 41, By means of the second roll stand 42, the
desired surface condition and flatness of the rolled
strip are achieved. The rolled strip, which runs into
the cold-finishing part 4 with the strip thickness HEDCR
and material hardness KF0, runs out with the strip
thickness HADCR and the material hardness KFDCR, as
functional block 7 shows. According to the method of
the invention, the pair of values HAKTM and KFKTM is set,
in accordance with the relationships according to
functional blocks 6 and 7, in such a way that the
desired values for the exit thickness HADCR and the
material hardness KFDCR are achieved by means of the
thickness reduction in the cold-finishing part 4. If,
for example, a rolled strip has the thickness HEKTM of
4 mm and the hardness KF0 of 300 N/mm2 at the entry to
the cold-rolling mill, and if the desired thickness
HADCR of the metal strip is 0.3 mm and the desired
hardness KFDCR of the metal strip is 450 N/mm2, then for
an exemplary configuration, the metal strip is to be
rolled in the cold-rolling mill 3 in such a way that
HAKTM = 0.5 mm and KFKTM = 600 N/mm . In the subsequent
annealing section 3, the hardness of the metal strip is
in turn reduced to the hardness KF0, that is to say
300 N/mm . As a result of the subsequent reduction of
the metal strip in the cold-finishing part 4 from an
entry thickness HEDCR of 0.5 mm to an exit thickness
HADCR of°-3 mm,the hardness KFDCR of the metal strip at
the exit from the cold-finishing part 4 is increased to
the desired 450 N/mm2. The limits of the method
according to the invention depend on the possible
reduction in the cold-finishing part 4. If, for
example, taking into account a material strength or
hardness model (with MSO ~ KFO,
MSI ~ KFI and KFE ~ MSE)

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then, given the reduction variation in the_ cold-finishing part of 10 ... 40%, a hardness variation of about 3 5% can be achieved. For this case, a variation in the entry thickness HDDCR from 0.33 to 0.5 mm in the cold-finishing part 4 is possible. This variation permits a change in the material strength KFDCR from 330 N/mm2 to 440 N/mm2.
For the modelling, illustrated schematically, according to the functional blocks 5 and 7, a model comes particularly advantageously into consideration. Furthermore, it has proven to be advantageous to transfer the model for the relationship between material hardness KF and thickness reduction EPS for the cold-rolling mill to the cold-finishing part 4 as well. In this case, the relationship, ascertained for the cold-rolling mill, between hardness KF of the metal strip and thickness reduction EPS of the metal strip is particularly advantageously corrected by comparing the current hardness and the intended hardness at the exit of the metal strip from the cold-finishing part 4, with the effect of reducing the deviation between intended hardness and current hardness at the exit from the cold-finishing part 4. A correction of this type is shown by FIG 2. The setting of the material strength in the cold-finishing part can be carried out in accordance with the following automation stages:
1. Feed-forward control 8 as a result of calculating
and rolling an exit thickness HADCR in the cold-
rolling mill in accordance with the desired value
for the hardness VKFDCR and the thickness HADCR of
the metal strip after the cold-finishing part 4.
2. Feedback 9 as a result of ascertaining the
achieved hardness KFDCR in the cold-finishing part

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4 and forming a correction value a for the thickness HAKTM of the metal strip at the exit from the cold-rolling mill 2 in accordance with the deviations from the desired value for KFDCR. 3. Ascertaining the material strength curve, that is to say the relationship between hardness KF of the metal strip and thickness reduction EPS, in the cold-rolling mill 2 over the length of the strip, and calculating and rolling the strip thickness HAKTM over the length of the strip in accordance with the ascertained material strength curve and the intended value for the hardness KFDCR of the metal strip.
In detail, the exit thickness HAKTM of the metal strip is calculated in the feed-forward controller 8 in accordance with the desired hardness KFDCR of the metal strip. This is carried out as a function of the thickness of the metal strip HADCR at the exit from the cold-finishing part, the hardness KFDCR of the metal strip at the exit from the cold-finishing part, the thickness HEKTM of the metal strip at the entry to the cold-rolling mill, and of material properties MT of the rolled strip. The starting variables for the feedforward controller 8 are the thickness . HAKTM of the metal strip at the exit from the cold-rolling mill, and material parameters ME of 'the metal strip. These material parameters ME are essentially parameters which describe the hardness KFDCR of the metal strip. In the present example, they are the parameters KFO, KFI and KFE, which describe the relationship between hardness KFDCR Of the metal strip and thickness reduction of the
metal strip.
values tor tnickness-HADCR and hardness KFDCR of the metal strip, the feedback unit 9 ascertains a correction value a, with which the value for the thickness HAKTM of the metal strip at the exit from the cold-rolling mill is corrected. It has proven to be particularly advantageous to multiply the correction

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parameter a and the desired thickness HAKTM of the metal strip at the exit from the cold-rolling mill. The correction parameter a is formed in such a way that the deviation between the current thickness HADCR of the metal strip at the exit from the cold-finishing part and the corresponding intended value is minimized.
The more rapid cooling down of the outer and inner windings after the hot-rolling mill results in a higher strength of the ends of the strip. Even intermediate annealing after the cold-rolling mill is not able to eliminate this effect, as is shown by the curve 13 in FIG 3, in which the course of the hardness KF0 of the metal strip over the length BL of the metal strip is illustrated. In the case of deep-drawing material, in particular, it is generally necessary for these ends to be cut off following cold finishing, since the hardness KFDCR of the metal strip is intended to be constant over the length of the strip. In this case, the high proportion of scrap and the additional outlay lead to a high loading of the costs J Increases of up to 15% in material hardness occur; This increase in" material hardness decreases gradually over a strip length of about 50 m. Given an increase in material hardness of 15%, tne reduction EPSDCR in the cold-finishing part is reduced, according to the invention, by about 15%. This takes place particularly advantageously if the overall reduction EPSDCR is greater than 30%. In the case of the example cited above, a 15% change in the reduction means a change in the entry thickness of 50 jxm or 6%.
The curves 13, 14, 15, 16 and 17 in FIG 3 illustrate the use of the method according to the invention for achieving a constant hardness KF over the length of the metal strip. At the exit from the cold-rolling mill, the metal strip has a hardness KF0 corresponding to curve 13. At the ends of the strip, that is to say in the regions 10 and 12, the metal strip has a greater hardness than in the middle region. The regions 10 and 12 may comprise, for example, a

strip length of 50 m each. According to the invention, the cold-rolling mill is adjusted in such a way that the metal strip has a thickness corresponding to curve 14 at the exit from the cold-rolling mill. The course of the curve 14 is selected such that, given a thickness reduction EPSDCR in the cold-finishing part, as shown by curve 15, a constant course of the thickness HADCR and of the hardness KFDCR of the metal strip is established, according to the curves 16 and 17.

We Claim: 10..
1. A method for rolling a metal strip, comprising the steps of:
- arranging a cold-rolling mill (2) upstream from an annealing section (3)
and a cold finishing part (4);
- determining harness (KFQCR) and "thickness (HADCR) set point values of
the metal strip at an outflow from the cold-finishing part (4); and
- determining a setpoint (HAKTM) of the metal strip at an outflow form the
cold-rolling mill (4) as a function of the setpoint values for the hardness
and thickness setpoint values (KFDCR, HADCR) of the metal strip at the
outflow from the cold-finishing part (4).

2. The method as claimed in claim 1, wherein the metal strip is a steel strip.
3. The method as claimed in claim 1, comprising the steps of:
-providing a rolling model (7) of the cold-finishing part (4), the setpoint thickness (HAKTM) of the metal strip being determined as a function of an effect of the cold-finishing part (4) using the rolling model (7).
4. The method as claimed in Claim 1 or 3, wherein the relationship between
hardness (KF) of the metal strip and the thickness reduction (EPS) of the metal
strip is modeled by means of the rolling model (7) of the cold-finishing part (4).
5. The method as claimed in claim 1 comprising the steps of:
- providing a model (6) of the annealing section (3), the set point thickness
(HAKTM) of the metal strip at the outflow, from the cold-rolling mill (2)
being determined as a function of an effect of the annealing section (3)
using the model(6) of the annealing section (3).
6..htethod according to. claim 3, 4 or 5, wherein the effect of the cold-finishing part (4), in particular the relationship between hardness ( KF) of the metal strip and the thickness reduction (EPS) of the metal stripMs determined form the effect of the cold-rolling mill (2), in particular from the relationship between hardness

11.
(KF) of the metal strip and the thickness reduction (EPS) of the metal strip at the roll stands ( 21, 22,23, 24) or a selection of roll stands ( 21, 22, 23, 24) of the cold-rolling mill (2).
7. Method as claimed in claim 3,4, or 5, wherein the effect of the cold-finishing

part (4), in particular the relationship between hardness (KF) of the metal strip
and the thickness reduction (EPS) of the metal strip, is determined in advance, in
particular by means of tensile tests.
8. Method as claimed in claim 3, 4, 5,6 or 7, wherein the ascertained effect of the

cold-finishing part (4), in particular the ascertained relationship between hardness (KF) of the metal strip and thickness reduction ( EPS) of the metal strip, is corrected by comparing a measured value of the current hardness ( KFDCR) with the intended hardness of the metal strip at the exit from the cold-finishing part (4), with the effect of reducing the deviation between the intended hardness and the measured value of the current hardness (KFDCR) of the metal strip at the exit from the cold-finishing part (4).
9. The method as claimed in claims 3, 4, 5, 6, 7 or 8, wherein the intended value for
the thickness (HAKTM) or the intended thickness of the metal strip at the exit form
the cold-rolling mill (2) ascertained from the effect of the cold-finishing part (4),
in particular ascertained from the relationship between hardness (KF) of the
metal strip and thickness reduction, (EPS) of the metal strip, is corrected by
comparing the current hardness (KFDCR) and the intended hardness of the metal
strip at the exit from the cold-finishing part (4) by reducing a deviation between
the intended hardness and the current hardness ( KFDCR) of the metal strip at the
exit form the cold-finishing part (4).
10. The method as claimed in claim 1, wherein the metal strip has a length, and wherein
the hardness (KFDCR) of the metal strip at the outflow form the cold-finishing part
(4) is kept constant over the length (BL) of the metal strip.
11. The method as claimed in claim 1, wherein the cold-finishing part (4) comprises at
least two roll stands (41, 42) the method comprising:

12.
- reducing the thickness of the metal strip using at least one of the roll
stands; and adjusting flatness and influencing a surface of the metal strip
using at least another of the roll stands.
12. The method as claimed in claim 11, wherein the atleast one (41) of the roll stands is
a first one of the roll stands, and the at least another (42) of the roll stands is a
second one of the roll stands.
13. The method as claimed one of the preceding claims, wherein the thickness of the
metal strip is reduced by at least 10%, in particular by at least 20%, in the cold-
finishing part (4).
14. The method as claimed in claim 13, wherein the thickness of the metal strip is
reduced by 20 to 40% in the cold-finishing part (4).
15. A system for rolling a metal strip carrying out the method as claimed in claims 1
to 14, comprising:
- an annealing section (3) and a cold finishing part (4)'
- a cold -rolling mill (2) arranged upstream from the annealing section (3)
and the cold finishing part (4);
characterized in that a computing device (8, 9) determining a set point thickness ( HAKTM) of the metal strip at the outflow from the rolling mill (2) as a function of a set point hardness ( KFDCR) and a setpoint thickness ( HADCR) at an outflow form the cold-finishing part (4).
This invention relates to a method and system for rolling a metal strip, in particular a steel strip, by means of a cold-rolling mill, which is followed by an annealing section and a cold-finishing part, the exit thickness or the intended thickness of the metal strip at the exit from the cold-rolling mill being determined as a function of the intended hardness and the intended thickness of the metal strip at the exit from the cold-finishing part.

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Patent Number

209248

Indian Patent Application Number

01173/CAL/1998

PG Journal Number

34/2007

Publication Date

24-Aug-2007

Grant Date

23-Aug-2007

Date of Filing

06-Jul-1998

Name of Patentee

SIEMENS AKTIENGESELLSCHAFT

Applicant Address

WITTELSBACHERPLATZ 2, 80333 MUENCHEN, GERMANY

Inventors:

#	Inventor's Name	Inventor's Address
1	ECKHARD WILKE	FLURWEG 1, D-91080 MARLOFFSTEIN, GERMANY
2	ROLAND BRUSTLE	GROBWNBUCH 141, D-91077 NEUNKIRCHEN,

PCT International Classification Number

B 21 B 37/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	19729773.0	1997-07-11	Germany