JP4948301B2 - Shape control method in cold rolling - Google Patents

Description

  The present invention relates to a method for optimizing rolling conditions so that the plate shape of a rolled metal strip matches a target shape.

In cold rolling, there is a method in which the shape of a rolled material is measured with a shape detector arranged on the delivery side of the rolling mill, and the control amount of shape control means such as roll bender and roll shift is corrected based on the measurement result. Generally adopted. However, the shape of the rolled material is often measured with a shape detector arranged at a position distant from the rolling mill, so that a detection delay occurs and control with high responsiveness may be difficult.
In order to control the shape with high-speed response, the rolling load is measured instead of the direct measurement of the plate shape on the premise that the fluctuation of the rolling load affects the shape change of the rolled material, and the rolling load is measured. Various methods for correcting the control amount of each shape control means based on the value have been proposed (see, for example, Patent Documents 1, 2, and 3).

In any method, the shape of the rolled shape is controlled based on the rolling shape prediction formula expressed as a function of the rolling load. In the rolling shape prediction formula, the rolling shape is evaluated only with one shape in the sheet width direction. Yes. Therefore, when the rolling load fluctuates greatly, it is difficult to obtain a good shape over the entire plate width.
In order to solve such a problem, the present inventors use a mathematical model that incorporates elongation difference at a plurality of locations along the sheet width direction, thereby controlling the shape control means in accordance with the rolling load variation. A method of correcting the amount and manufacturing a steel strip having a good shape over the entire plate width was developed and introduced in Patent Document 4.

Although this method is intended for shape control during rolling, the mathematical model can be applied as it is to preset control for initially setting shape control means at the start of rolling.
However, the method introduced in Patent Document 4 expresses the shape prediction formula by a function of the rolling load and the shape control means without considering the influence of the material crown. Therefore, in rolling with a four-high rolling mill or the like using a large diameter work roll, the bending deformation of the work roll is small, and the influence of the material crown becomes large. Prior to the shape control during rolling based on the shape measurement result by the shape detector in such rolling, when the shape control means is initially set by the mathematical model, a shape defect is likely to occur at the initial stage of rolling. In rolling with a rolling mill that does not have a shape detector, when the control amount of the shape control means is corrected according to the fluctuation of the rolling load, the influence of the material crown is taken into consideration from the start of rolling to the end of rolling. Therefore, a shape defect may occur over the entire length of the coil.

In addition, the method introduced in Patent Document 4 is based on the premise that the influence of the shape before rolling is small, and when the shape before rolling is good or the reduction ratio is large and the shape before rolling hardly remains. A good shape is obtained. However, when this method is applied under rolling conditions where the rolling reduction is small as in skin pass rolling, the shape before rolling may remain when the shape before rolling is not good, and a good shape may not be obtained.
For this reason, the present inventors perform preset control and shape control during rolling using a mathematical model that incorporates the effects of both the material crown and the shape before rolling, so that a better shape over the entire coil length than at the start of rolling. A method of manufacturing a steel strip having a thickness of 10 was developed and introduced in Patent Document 5.

The method introduced in Patent Document 5 is based on the premise that the shape control means has a wide specification range and can be controlled to the target shape over a wide range of rolling conditions. If the ability of the shape control means is sufficient, the shape is good. Is obtained. However, when the specification range of the shape control means is narrow, it is difficult to cope with a wide range of rolling conditions, and a good shape may not be obtained. In particular, when the rolling load is large and the ability of the shape control means is insufficient, a large ear extension shape is generated.
Therefore, the present inventors calculated a proper work roll crown amount using a mathematical model incorporating the effect of the work roll crown amount, and applied the work roll to start rolling corresponding to a wide range of rolling conditions. From time to time, a method for producing a steel strip having a good shape over the entire length of the coil was developed and proposed in Patent Document 6.

Japanese Patent Publication No.52-23873 JP 57-7309, JP-A-8-257612 Japanese Patent Laid-Open No. 11-267727 Japanese Patent Laid-Open No. 2005-177818 Japanese Patent Application No. 2006-021314

  Compared with the method introduced in Patent Document 5 by the method proposed in Patent Document 6, the range of rolling conditions that can be controlled to the target shape and obtain a good shape is expanded. However, when the rolling conditions are wide, such as when the elongation rate varies greatly in skin pass rolling and the rolling load changes greatly, the ability of the shape control means is insufficient, and it is not possible to cope with just the optimization of the work roll crown amount. There was a case.

  The present invention has been devised to solve such problems, and by suppressing the change in rolling load that greatly affects the shape by controlling the front-rear tension, it compensates for the lack of capability of the shape control means, It aims at providing the control method which can manufacture the rolling material excellent in the shape accuracy with high productivity.

In order to achieve the object, the shape control method in the cold rolling according to the present invention has a rolling load, a control amount of the shape control means, a material crown amount, a work roll crown amount, and a plate width at a plurality of locations at different distances from the plate end. the growth rate difference before the rolling stock to the central portion as a variable, the mathematical model and the rolling load forward tension and backward tension to the variable representing the elongation difference after rolling with respect to the sheet width center for a plurality of locations at different distances from the plate end The mathematical model to represent is created in advance, the measured value of the material crown amount and the work roll crown amount and the elongation difference of the material before rolling are substituted into the mathematical model representing the elongation difference after rolling, and the elongation difference after rolling is The control amount of the shape control means and the rolling load are calculated so as to match the target value, and the calculated rolling load and the rolling load obtained from the mathematical model representing the rolling load match. Calculating a forward tension and backward tension to the control amount of the calculated shape control means, and setting the forward tension and backward tension.

  In addition, a mathematical model representing the amount of change in the rolling load is created in advance with the amount of change in the front tension and the rear tension as variables, and the control amount of the shape control means, the front tension and the rear tension are initialized by the above shape control method. After setting, the rolling load is continuously measured during rolling, and this measured value is substituted into the mathematical model representing the amount of change in the rolling load, and the front tension and the back tension are adjusted so that the rolling load matches the target value. When correcting, shape control during rolling is also possible.

  In the present invention, a change in rolling load that greatly affects the shape is suppressed by controlling the front-rear tension using a mathematical model that represents the rolling load with the front tension and the rear tension as variables. Therefore, the shortage of the shape control means is compensated for a wide range of rolling conditions, and a rolled material having a good shape can be obtained over the entire length of the coil from the start of rolling.

The present inventors have investigated and studied various cold rolling shape control methods that can obtain a good shape corresponding to a wide range of rolling conditions by suppressing changes in rolling load by controlling the front-rear tension. . As a result, paying attention to the fact that the rolling load has a substantially linear relationship with the front tension and the back tension, the rolling load is a variable and the appropriate rolling load is calculated by a mathematical model that represents the difference in elongation. It was found that the rolling load can be optimized by controlling the front / rear tension by using a mathematical model representing the rolling load as a variable, and a rolled material having a good shape can be produced.
Hereinafter, the shape control method of the present invention will be described for a four-high mill, but the present invention is naturally applicable to a multi-high mill having six or more stages.

In order to prevent not only simple shape defects such as ear elongation and medium elongation, but also complex elongation that is a complex combination of quarter elongation and various elongations, it is required to evaluate and control the rolling shape with multiple indices. The
Therefore, in the present invention, the rolling shape is evaluated by the difference between the elongation rate at a plurality of locations at different distances from the plate edge and the elongation rate at the center of the plate width. Specifically, the rolling shape is defined by the elongation difference ε _e and ε _q with respect to the plate width center of the plate end portion and the quarter portion. The elongation difference epsilon _e and epsilon _q el elongation of the plate edge _e, el _q elongation quota portions, when the growth rate of sheet width center and el _c, respectively formula (1) and (2) It is represented by
ε _e = el _e -el _c (1)
ε _q = el _q −el _c (2)

Similarly, the elongation difference ε _0e and ε _0q of the material before rolling is _defined as el _{0e for} the elongation of the plate end of the material before rolling, el _{0q for} the elongation of the quarter, and el _0c for the center of the _{sheet width} . Are represented by equations (3) and (4), respectively.
ε _0e = el _0e -el _0c (3)
ε _0q = el _0q -el _0c (4)
It should be noted that the measurement positions of the plate end portion and the quarter portion are determined empirically so as to appropriately represent the shape and obtain an accurate mathematical model.

Factors affecting the shape of the rolled material include the rolled material size, material, lubrication state, front / rear tension, rolling load, control amount of the shape control means, material crown amount, pre-rolling shape, work roll crown amount, and the like. Among these, regarding the rolled material dimensions, if the table is divided for each plate thickness and width, the influence of the change in the rolled material size in the section on the shape can be reduced. The material, lubrication state, and front / rear tension affect the shape of the rolled material, but most of the effect is caused by changes in roll deflection through the rolling load.
Therefore, the main factors affecting the shape change can be referred to as rolling load, control amount of shape control means, material crown amount, pre-rolling shape, and work roll crown amount. Therefore, the quantitative effects of the rolling load, the control amount of the shape control means, the material crown amount, the shape before rolling and the work roll crown amount on the rolling shape were examined.
The change in rolling load appears as a change in roll deflection and changes the shape of the rolled material. The relationship between the rolling load and the amount of roll deflection is almost linear since it is intended for deformation in the elastic region. Therefore, the elongation differences ε _e and ε _q expressed by the equations (1) and (2) are also linearly related to the rolling load P as shown in FIG.

The work roll bender also changes the rolling shape by changing the roll deflection in the same manner as the rolling load. As shown in FIG. 2, the linear relationship between the work roll bender force B and the elongation differences ε _e and ε _q is also obtained. It is in.
The amount of material crown was defined as the thickness difference between the plate edge and the center of the plate width. As shown in FIG. 3, the material crown amount Cr and the elongation differences ε _e and ε _q are also in a linear relationship.
As shown in FIGS. 4 and 5, the elongation differences ε _0e and ε _{0q of the} material before rolling and the elongation differences ε _e and ε _q after rolling are also in a linear relationship.
The amount of work roll crown was defined by the difference in diameter between the end of the work roll and the center of the work roll. As shown in FIG. 6, there is also a linear relationship between the work roll crown amount Wr and the elongation differences ε _e and ε _q .

From the above relationship between the factors _{mutually, a e, b e, c} e, d e, e e, f e, a q, b q, c q, d q, e q, the f _q as influence coefficients, wherein The rolling shape prediction formula can be expressed by (5) to (6).
ε _e = a _e · P + b _e · B + c _e + d _e · Cr + e _e · ε _0e + f _e · Wr (5)
ε _q = a _q · P + b _q · B + c _q + d _q · Cr + e _q · ε _0q + f _q · Wr (6)
Influence coefficients a _e , b _e , c _e , d _e , e _e , f _e , a _q , b _q , c _q , d _q , e _q , f _q are production types such as plate width, plate thickness, and material It is a constant determined by the above equation, and is obtained from an experiment or a simulation using an analysis model in which an elastic deformation analysis of a roll and a plastic deformation analysis of a material are coupled. Each influence coefficient is set in a table for each section such as plate width, plate thickness, and material, or expressed as a function of plate width, plate thickness, material, and the like.

In addition, in a typical 6-high rolling mill having a work roll diameter of about 400 mm, a general 20-high rolling mill having a work roll diameter of 100 mm or less, and the like, the work roll is likely to be greatly deformed. Although large, the influence on the shape of the material crown tends to be small. In this case, in Equations (5) and (6), the material crown amount Cr can be set to zero and the influence term of the material crown amount can be ignored.
In addition, when the shape before rolling is good or the rolling reduction is large and the shape before rolling does not remain, the influence on the shape before rolling is small. In this case, in Equations (5) and (6), it is possible to ignore the influence terms of the shape before rolling by _setting the elongation difference ε _0e and ε _0q of the material before rolling to zero.

Next, the quantitative effect of front / rear tension on rolling load was investigated. As shown in FIG. 7, any of the front and rear tensions acts in the direction of reducing the rolling load, and the rolling load P, the front tension T _f, and the rear tension T _b are in a substantially linear relationship. Incidentally, the direction of the rear tension T _b is the slope of the straight line is large in relation to the rolling load, of the front tension T _f is output than the center of the roll bite position of the neutral point the speed of the rolled material and the roll to match This is because the rear tension has a greater influence on the rolling load than the front tension because it is closer to the side.

Therefore, the rolling load prediction formula can be expressed by Expression (7) using x _p , y _p , and z _p as influence coefficients.
_{P = x p · T f +} y p · T b + z p (7)
The influence coefficients x _p , y _p , and z _p are constants determined by the production type such as the sheet width, sheet thickness, and material, and are an analysis model that combines experiments or elastic deformation analysis of the roll and plastic deformation analysis of the material. It is obtained from the simulation by each. Each influence coefficient is set in a table for each section such as plate width, plate thickness, and material, or expressed as a function of plate width, plate thickness, material, and the like.

In calculating the rolling load P and the work roll bender force B such that the elongation difference ε _e , ε _q approaches the target values ε _e ⁰ , ε _q ⁰ , the evaluation function J shown in equation (8) is the minimum. The rolling load P and the work roll bender force B are calculated as follows.
_{J = w e (ε e -ε} e 0) 2 + w q (ε q -ε q 0) 2 (8)
In the equation, w _e and w _q indicate weighting factors.
Then, the front tension T _f and the rear tension T _b are calculated so that the calculated rolling load P and the rolling load obtained from the equation (7) coincide, and the calculated work roll bender force B, front tension T _f and rear tension are calculated. setting the T _b.

When the calculated work roll bender force B exceeds the upper and lower limit values of the specification range, the work roll bender force B is set to the upper and lower limit values so that the evaluation function J shown in Expression (8) is minimized. The rolling load P is calculated. Then, the front tension T _f and the rear tension T _b are calculated and set so that the calculated rolling load P and the rolling load obtained from the equation (7) match.
Further, when the calculated rolling load P exceeds the upper and lower limit values determined from the specification range of the front tension and the rear tension, the front tension T _f and the rear tension T _b are set to the upper and lower limit values, and are expressed by Expression (8). The work roll bender force B is calculated and set so that the evaluation function J is minimized.

In a rolling mill equipped with a shape detector, after the work roll bender force B is initially set by the method according to the present invention, shape control is performed during rolling based on the shape measurement result of the rolled material obtained by the shape detector. it can. In a rolling mill not equipped with a shape detector, a rolling load is continuously measured during rolling, and this measured value P _m is a mathematical expression that represents the amount of change in the rolling load expressed by equation (9) instead of equation (7). Substituting into the model, the front tension T _f and the rear tension T _b are corrected by ΔT _f and ΔT _b , respectively, so that the rolling load matches the target value P.
P = P _m + x _p · ΔT _f + y _p · ΔT _b (9)

In the above description, the rolling shape is defined by the elongation difference ε _e and ε _q with respect to the center of the plate width at the two points of the plate end portion and the quarter portion, and the work roll bender force B, the front tension T _f and the rear tension T _b are determined. Set or correct. However, the present invention is not limited thereto, and the rolling shape can be similarly controlled when the rolling shape is defined by using the elongation difference with respect to the center of the plate width at three or more points along the plate width direction.

The shape control means to be used is not limited to the work roll bender, and also when using an intermediate roll bender or an intermediate roll shift which is a shape control means of a six-high rolling mill, the rolling shape prediction formulas are expressed by the equations (5), ( It is expressed in the same line format as 6), and an intermediate roll bender, an intermediate roll shift, etc. can be set or corrected. For example, when controlling with a work roll bender and an intermediate roll bender, the rolling shape prediction formulas (10) and (11) are used, and the elongation differences ε _e and ε _q are the target values ε _e ⁰ and ε _q ⁰ , respectively. The work roll bender force B and the intermediate roll bender force I are calculated and set so that
ε _e = a _e · P + b _e · B + c _e + d _e · Cr + e _e · ε _0e + f _e · Wr + g _e · I (10)
ε _q = a _q · P + b _q · B + c _q + d _q · Cr + e _q · ε _0q + f _q · Wr + g _q · I (11)
Here, I is an intermediate roll bender force, and g _e and g _q are influence coefficients.

An example in which the present invention is applied to cold rolling using the four-high rolling mill shown in FIG. 8 will be described. The four-high rolling mill 1 includes a work roll bender 2 as shape control means. The rolling condition is input to the host computer 3 in advance. In the process computer 4, the influence coefficient calculated in advance for each section of the sheet width, sheet thickness and material, the measured value of the material crown Cr, the measured elongation difference ε _0e and ε _0q of the material before rolling, and the work roll crown amount Wr are obtained. The rolling load P and the work roll bender force B are calculated based on the equations (5), (6), and (8).
Then, the front tension T _f and the rear tension T _b are calculated so that the calculated rolling load P and the rolling load obtained from the equation (7) coincide, and the calculated work roll bender force B, front tension T _f and rear tension are calculated. the T _b is initialized.

The four-high rolling mill 1 is not provided with a shape detector, and the rolling load is continuously measured by the load meter 6 during rolling, and the measurement result is input to the host computer 3. Then, this measured value P _m is substituted into the equation (9), and the front tension T _f and the rear tension T _b are corrected by ΔT _f and ΔT _b , respectively, so that the rolling load coincides with the target value P.
In this rolling mill, skin pass rolling is performed in the range of 0.6% to 3.2% elongation. When rolling with the same crown roll, when the elongation is as small as 0.6%, the rolling load is small, so that the medium elongation is When the elongation rate is as large as 3.2%, the rolling load becomes large and the ear elongation tends to occur. Therefore, shape control was performed by the method of the present invention when the elongation was 0.6% (Example 1) and when the elongation was 3.2% (Example 2), and the shape after rolling was measured with an off-line shape measuring instrument. .

Example 1;
A hot-rolled steel strip in the form of an ear with a sheet width of 1020 mm, a sheet thickness of 1.0 mm, a material crown amount of 18 μm, and a steepness of 0.5% is fed into the four-high rolling mill 1 and is fed by a work roll 5 having a diameter of 600 mm and a crown amount of 45 μm. Skin pass rolling was performed at an elongation of 0.6%. Note that the target values ε _e ⁰ and ε _q ⁰ of the elongation difference ε _e and ε _q are both 0. For comparison, shape control was performed by the method introduced in Patent Document 6.
As shown in FIG. 9, the steel strip whose shape was controlled by the method of the present invention had a steepness within 0.5% over the entire length of the coil from the start of rolling, and was rolled into a good shape. On the other hand, the work roll crown is optimized, but in the conventional method in which the change in rolling load that greatly affects the shape is not suppressed by controlling the front-rear tension, the rolling load is too small. The steepness was about 0.7% over the entire length.

Example 2;
A hot rolled steel strip with an edge extension shape with a plate width of 1020 mm, a plate thickness of 1.0 mm, a material crown amount of 15 μm, and a steepness of 0.5% is fed into the four-high rolling mill 1 and is fed by a work roll 5 having a diameter of 600 mm and a crown amount of 45 μm. The skin pass was rolled at an elongation of 3.2%. Note that the target values ε _e ⁰ and ε _q ⁰ of the elongation difference ε _e and ε _q are both 0. For comparison, shape control was performed by the method introduced in Patent Document 6.
As shown in FIG. 10, the steel strip whose shape was controlled by the method of the present invention had a steepness within 0.5% over the entire length of the coil from the start of rolling, and was rolled into a good shape. On the other hand, the work roll crown is optimized, but in the conventional method in which the change in rolling load that greatly affects the shape is not suppressed by controlling the front-rear tension, the rolling load is too large. Ear elongation with a steepness of about 0.7% occurred over the entire length.

Graph showing the effect of rolling load on elongation difference Graph showing the effect of work roll bender force on the difference in elongation A graph showing the effect of the amount of material crown on the difference in elongation Graph _{showing the} effect of elongation difference ε _{0e of the} material before rolling on elongation difference ε _{e Graph showing the effect} of elongation difference ε _0q on the elongation difference ε _q of the material before rolling Graph showing the effect of work roll crown amount on elongation difference Graph showing the effect of forward and backward tension on rolling load Schematic diagram of the four-high rolling mill and control system used in the examples The graph which shows the steepness of the steel strip rolled in Example 1 The graph which shows the steepness of the steel strip rolled in Example 2

Explanation of symbols

1: Four-high rolling mill 2: Work roll bender 3: Higher computer 4: Process computer 5: Work roll 6: Load cell

Claims (2)

Rolling load, control the amount of shape control means, material crown amount, the elongation difference before the rolling stock for the plate width central portion in a plurality of locations at different distances from the work roll crown value and plate end a variable, the distance from the plate end A mathematical model that represents the difference in elongation after rolling with respect to the center of the sheet width and a mathematical model that represents the rolling load with the front tension and the rear tension as variables are created in advance, and the amount of material crown, the amount of work roll crown, and before rolling. substituting the measured value of the growth rate difference between the material to a mathematical model that represents the elongation difference after the rolling, and calculates the control amount and the rolling load of the shape control means such elongation difference after rolling coincides with the target value In addition, the front tension and the rear tension are calculated so that the calculated rolling load and the rolling load obtained from the mathematical model representing the rolling load coincide with each other, and the calculated shape control means is controlled. The shape control method in cold rolling and sets the forward tension and backward tension. A mathematical model that represents the amount of change in rolling load with the amount of change in front tension and rear tension as variables is created in advance, and the rolling load, control amount of shape control means, material crown amount, work roll crown amount, and plate end Mathematical model representing forward elongation difference after rolling with respect to the center of the sheet width and forward tension for a plurality of positions with different distances from the sheet edge, with the difference in elongation of the material before rolling relative to the center of the sheet width at a plurality of positions with different distances as variables. A mathematical model representing the rolling load with the back tension as a variable is created in advance, and the measured values of the material crown amount, the work roll crown amount, and the elongation difference of the material before rolling are substituted into the mathematical model representing the elongation difference after rolling. , calculates the control amount and the rolling load of the shape control means such elongation difference after rolling coincides with the target value, the formula represents the rolling load and the calculated rolling load mode Calculate the front tension and the rear tension so that the rolling loads obtained from the lines coincide with each other, initialize the calculated control amount of the shape control means, the front tension and the rear tension, and then measure the rolling load continuously during rolling. And substituting the measured value into a mathematical model representing the amount of change in the rolling load, and correcting the front tension and the rear tension so that the rolling load matches the target value. .

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