JPH0699209A - Method for controlling crown and flatness of band plate - Google Patents

Abstract

(57) [Abstract] [Purpose] It is possible to prevent accuracy defects even when there are fluctuations in rolling conditions, and improve not only the crown of the strip but also the flatness of the strip. [Structure] When calculating and estimating the crown and flatness between rolling mills having the shape control function of the tandem rolling line by calculation, the shape change coefficient ε on the upstream side of the rolling stand is changed to a small value to set the crown. The route is obtained, and the actuator of each rolling stand is controlled according to this crown route.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tandem rolling mill equipped with a device such as a work roll bending device, a work roll shift device, a work roll pair cross device, a backup variable crown device, etc. TECHNICAL FIELD The present invention relates to a strip plate crown and flatness control method capable of producing a metal steel sheet having a predetermined crown and flatness by rolling.

[0002]

2. Description of the Related Art In order to accurately control a rolled sheet crown, it is necessary to estimate the rolled sheet crown with as high accuracy as possible before rolling. In order to estimate the strip crown after rolling with high accuracy, it is effective to make a theoretical analysis and then perform an operation based on the analysis results to make an estimation. Direction metal flow
There is a significant difference in analysis accuracy depending on how (lateral flow) is evaluated.

Conventionally, as a lateral flow analysis, 3
Dimensional analysis and approximate analysis have been performed. In addition to these, Kurizuhara et al. Substitute the lateral flow with the shape change coefficient ξ, and the geometric parameter γ (= D / D ₀ × D ^0.5 h ^1.5
/ B ² , where D: work roll diameter (mm), h: plate thickness (mm), B: plate width
(mm), D ₀ = 300 mm), an example of the arrangement is reported in “Plasticity and Working, 23” (1982-263, P1172).
FIG. 6 is a graph showing the relationship between the shape change coefficient ξ and the geometric parameter γ in this report. From the figure,
It can be seen that the shape change coefficient ξ increases as the geometrical parameter γ decreases.

However, an important point for theoretically analyzing the lateral flow is to know the shape change coefficient at each division position in the plate width direction. In this report, at each division position in the plate width direction. No reference is made to the shape change coefficient of. So with this method,
The strip crown after rolling cannot be estimated with high accuracy.

Further, instead of the method of theoretically obtaining the shape change coefficient at each division position in the plate width direction, as a more realistic method, the shape change coefficient is changed by changing the shape change coefficient only at the plate edge. Some express change. FIG. 7 is a graph showing the relationship between the distance x from the plate center and the plastic flow coefficient η (substituting the shape change coefficient),
This graph is

[0006]

[Equation 1]

It is obtained based on the above.

In the method shown in FIG. 7, the plastic flow coefficient η is set as a quadratic function of the distance x from the plate center, and the shape change coefficient is reduced from 100 mm from the plate end to 0 at the plate end.
It is what However, it is not clear from which plate width position the shape change coefficient that becomes 0 at the edge of the plate starts to decrease, so the shape change coefficient is reduced from the position 100 mm from the edge of the plate. There is no basis for this, and even with this method, the estimation accuracy of the strip crown after rolling is questionable.

Conventionally, various methods have been proposed for the purpose of accurately calculating the rolled plate crown. For example, in Japanese Patent Laid-Open No. 61-209708 or 61-209709, a learning control correction term is introduced in the estimation formula of the strip crown and strip flatness, and the correction is performed based on the actual values of the crown and flatness. A method of correcting and optimizing the amount and determining a preset value of the rolling condition of the next material set by calculation has been proposed. Hereinafter, the conventional estimation method will be described in detail by taking the method proposed by Japanese Patent Laid-Open No. 61-209709 as an example.

The strip crown estimation formula and strip flatness estimation formula in a tandem rolling line equipped with N rolling mills having a shape control function are as follows. I is the number of stands (total number of stands N), and Ch _i is the i-th The strip crown on the stand exit side, ε _i is the i-th strip flatness on the stand exit side, and C _i is i
Constant term (function based on rolling conditions) in the strip crown estimation formula of the th stand, εc _i is a constant term in the strip flatness estimation formula of the i-th stand, Q _i is the shape control operation amount at the i-th stand, h _i is the strip thickness of the i-th stand output side,
C _Ri is a work roll initial crown of the i-th stand, x _i is a coefficient for converting the work roll initial crown of the i-th stand to a plate width equivalent amount, a _i is a crown genetic coefficient, and b _i is a strip plate entry side influence coefficient of the flatness of the output-side crown, the influence coefficient of the d _i to the plate crown shape control operation amount, xi] _i changes in the shape factor, the inlet side flatness of the outgoing side flatness of the f _i strip , Where e _i is the coefficient of influence of the work roll initial crown on the strip crown,

[0011]

## EQU00002 ## Strip crown: Ch _i = C _i + a _i Ch _i-1 + b _i ε _i-1 + d _i Q _i + e _i x _i C _Ri

[0012]

[Number 3] strip flatness: given by _{ε i = ξ i (Ch i} / h i -Ch i-1 / h i-1) + f i ε i-1 + εc i ······.

The crown of the strip rolled in the tandem rolling mill is measured by a crown meter installed downstream from the rolling mill, and based on the error between the target value and the actual value of the strip crown, for example, The target value correction amount Ch _LRN is determined by such calculation. That is, Ch _LRN (-
1) The previous target value correction amount, Ch _f target strip crown, C _h a band plate crown actual measured value, the K a learning gain

[0014]

## EQU4 ## The target value correction amount Ch _LRN is calculated by: Ch _LRN = KCh _LRN (-1) + (1-k) (Ch _f -C _h ) ... Then, the target plate crown of the next coil is added to the above target value correction amount Ch _LRN, and the upper and lower limit values of the strip plate flatness and the strip plate flatness and the operation amount upper and lower limit values are satisfied as an intermediate stand as Ch _f + Ch _LRN. , A combination of manipulated variables Q _i that achieves the target strip crown is determined.

In the method proposed in Japanese Patent Laid-Open No. 61-209709, in order to correct the fluctuation of the rolling conditions and the error of the strip flatness when the formula itself has an error,
Using the measured values of both strip flatness and strip crown, the target function G

[0016]

[Equation 5]

However, Ch: actual measured value of strip crown, ε:
Shape flatness actual measurement value, Ch _i ^* , Ch _N ^* : Strip plate flatness by a predetermined mathematical model, w _i , w _N , W: Estimate the strip plate crown at the intermediate stand so that the weighting coefficient becomes the minimum. ,
From this, the learning control correction amount is obtained as a roll crown, and the preset value for the shape control of the next coil is determined based on this learning control correction amount.

Thus, according to the method proposed by JP-A-61-209709 or 61-209708,
Since the shape change coefficient is set according to the rolled material, accuracy defects can be prevented even when there are fluctuations in rolling conditions, not only the strip crown but also the strip flatness can be improved, and the strip width can be changed. It is said that it can easily cope with

[0019]

However, as a result of further studies by the present inventors, the method proposed by JP-A-61-209708 or 61-209709 also provides (a) flatness. It is indispensable for highly accurate estimation that the actual results are highly accurate and that (b) the rolling material conditions (deformation resistance, dimensions, etc.) are constant.
It has been found that in a normal rolling line, these conditions often change, so that the estimation accuracy of the strip crown is reduced.

The object of the present invention is to prevent the accuracy from being deteriorated even when there is a change in rolling conditions, and to improve not only the accuracy of the band crown but also the accuracy of the band flatness. And to provide a flatness control method.

[0021]

Means for Solving the Problems The inventors of the present invention have made various studies in order to solve the above-mentioned problems, and have a problem of the above-mentioned conventional technique of how to make the shape change coefficient closer to the actual value of each rolled material. However, even if the shape change coefficient cannot be accurately identified and is set as a value that is slightly deviated from the exact solution, and as a result, it affects the flatness, By setting the shape change coefficient to a small value on the upstream stand and drawing out the crown control capability largely on the front stage side, the target value of the crown and flatness can be achieved by sufficiently satisfying the requirement of the constant crown ratio in the downstream stand. The present invention has been completed as a result of further studies, after finding that a steel sheet having a desired crown and flatness can be finally manufactured without causing a serious problem in rollability.

Here, the gist of the present invention is that when a steel sheet having a predetermined crown and flatness is manufactured by tandem rolling a strip using a rolling mill having a shape control function, The target values of the crown and flatness of the strip between rolling stands are (i) changing the shape change coefficient and (ii) setting the crown change amount of each rolling stand based on the changed shape change coefficient. With the method of controlling the actuator of each rolling stand according to the calculated target value by estimating the amount of change in the crown value on the exit side of the final stand, the method of controlling the crown and flatness of the strip. is there.

That is, in the conventional method, the shape change coefficient ξ _i is calculated as being constant, but it is not possible to flexibly and accurately cope with the change in rolling conditions.
Therefore, in the present invention, when the target value of the crown and flatness of the strip in each conventional rolling stand is calculated, in the upstream stand, the shape change coefficient is easily modified, for example, by slightly changing the shape change coefficient. And the crown and flatness of the strip at each rolling stand are controlled accordingly.

[0024]

The operation of the present invention will be described in detail below. In the present invention, when calculating and estimating the crown and flatness between each rolling mill having a shape control function, which is installed in the tandem rolling line, the shape change coefficient is fixed as a constant value as in the conventional case. Instead, the rolling path on the upstream side is slightly changed and set to obtain the crown path, and the actuator of each rolling stand is controlled according to the crown path.

Therefore, according to the present invention, the crown and flatness of the finally obtained strip can be accurately controlled to predetermined values without accurately obtaining the shape change coefficient. Next, the logic for determining the crown and flatness in the present invention will be described in detail with reference to (1) to (6).

(1) With the rough bar crown value (calculated value or measured value is good) as the initial value, the shape control function (actuator) is set to the neutral position in all continuous finishing rolling stands (the neutral point within the control capability range). The crown path in the case of is calculated for each rolling stand.

(2) When the actuator of each rolling stand is changed within the range from the maximum capacity to the minimum capacity, how much the crown amount changes from the crown path obtained in (2). In particular,

[0028]

ΔC _i = α _Hi ΔC _i-1 + α _Bi ΔP _Bi + α _Vi ΔP _Vi + α _Ci Δδ _i ... C _i : Plate crown value of i-th stand P _Bi : Vendor value of i-th stand P _Vi : VC value of the i-th stand δ _i : Work roll shift value of the i-th stand α _Hi : Influence coefficient due to the inlet side crown change amount α _Bi : Influence coefficient due to the inlet side bender change amount α _Vi : Inlet side VC pressure change amount Influence coefficient α _Ci : Calculated by the influence coefficient due to the change amount of work roll shift on the input side. That is, the so-called facility capacity limit is calculated.

(3) Next, it is assumed that the rough bar is flat, and the crown path change allowance is calculated when the crown is changed to the flatness constraint limit value in each rolling stand. In particular,

[0030]

[Equation 7]

Δλ _i : Elongation strain deviation on the exit side of the i-th stand η _i : Coefficient of shape change H _i : Plate thickness of the i-th stand That is, the so-called flatness limit is calculated.

(4) Here, in each rolling stand,
(2) and (3) are simultaneously established. The area can be limited, ie the area of the crown path can be limited. (5) Check whether the target crown on the exit side of the final finishing stand satisfies (4).

(6) Using the target crown obtained in (5) as an initial value, the crown is traced back to the upstream rolling stand at a constant ratio, the target crown in each rolling stand is determined, and the target crown in each rolling stand is achieved. Determine the actuator settings for each rolling stand.

In such a crown and flatness determining logic, according to the present invention, the crown path estimated by calculation can be easily modified by appropriately selecting the shape change coefficient ξ _i . The shape change coefficient ξ _i is determined in the calculation logic as a shape change coefficient that does not change the shape even if the crown is greatly changed, and the crown control capability is sufficiently extracted in the preceding stage of the tandem rolling mill. This is desirable from the viewpoint that rolling instability is small while the plate thickness is large.

As described above, according to the present invention, the shape change coefficient used in the estimation calculation of the crown and the flatness is made variable to change the crown path to obtain the optimum crown path, and the optimum crown path is obtained. Since the tandem rolling is performed based on the above, it is possible to prevent the accuracy from being degraded even when there is a change in the rolling conditions, and it is possible to improve the accuracy of not only the strip crown but also the strip flatness.

[0036]

Examples In the hot thin sheet rolling, in the production of a high-strength steel sheet (tensile strength ≧ 540 kN / mm ² ) in which it is relatively difficult to satisfy both the crown and the flatness, the crown of the strip according to the present invention and An example in which the flatness control method is applied will be shown.

The number of rolling stands was a seven-stand finishing mill, and the shape correcting function was work roll bending force, variable crown backup roll, and work roll shift with CVC roll).

The high-strength steel sheet has a tensile strength of 54
The thickness was 0 kN / cm ² or more, the plate thickness was 2.8 mm, and the plate width was 1082 mm. Since the present invention is characterized in that the shape change coefficient is changed as described above, two levels of shape change coefficient are selected for comparison also in this embodiment.

FIG. 1 shows the set value of the shape change coefficient (in FIG. 1, the plastic flow coefficient is used) in each rolling stand. Further, FIG. 2 is a graph showing a comparison of the crown paths for Case 1 and Case 2 in FIG.
(a) shows the case 1 and FIG. 2 (b) shows the case 2.

From FIG. 2, it can be seen that the crown path changes in each of Case 1 and Case 2. That is,
In Case 2, it can be seen that the crown was largely changed by performing the strong reduction in the upstream finishing rolling stand.

Further, FIGS. 3, 4 and 5 show set values of various actuators for achieving the crown path shown in FIG. 2, and the bending force and the VC are set in order from FIG. 3, respectively.
The pressure and shift amount are shown.

From FIGS. 3 and 5, it can be seen that the bending force and the CVC shift amount in Case 2 were set so as to be sufficiently utilized in the upstream rolling stand. Also,
It was also confirmed that the finish-side target crown and the flat target value can be secured by going through the crown path as shown in Case 2.

[0043]

As described above in detail, according to the present invention, it is possible to prevent the accuracy from being deteriorated even when the rolling conditions are changed, and it is possible to improve not only the accuracy of the strip crown but also the flatness of the strip. It was

[Brief description of drawings]

FIG. 1 is a graph showing an example of set values of a shape change coefficient (a plastic flow coefficient is used in FIG. 1) in each rolling stand in the present invention.

2A and 2B are graphs showing comparison of crown paths for case 1 and case 2 in FIG. 1, FIG. 2A showing case 1 and FIG. 2B showing case 2 respectively.

3 is a graph showing a set value of a bending force for achieving the crown path shown in FIG. 2 for each rolling stand.

FIG. 4 is a graph showing a set value of VC pressure for achieving the crown path shown in FIG. 2 for each rolling stand.

5 is a graph showing a set value of a shift amount for achieving the crown path shown in FIG. 2 for each rolling stand.

FIG. 6 is a graph showing a relationship between a shape change coefficient ξ and a geometrical parameter γ.

FIG. 7 is a graph showing the relationship between the distance x from the plate center and the plastic flow coefficient η (substituting the shape change coefficient).

Claims (1)

[Claims] 1. When manufacturing a steel sheet having a predetermined crown and flatness by performing tandem rolling on a strip using a rolling mill having a shape control function, the crown of the strip between each rolling stand and The flatness target value is changed by (i) changing the shape change coefficient, and (ii) setting the crown change amount of each rolling stand based on the changed shape change coefficient. A method for controlling the crown and flatness of a strip, which is calculated by estimating a value change amount and controls the actuator of each rolling stand according to the calculated target value.