KR100325334B1 - Method for controlling thickness of strip in continuous cold rolling - Google Patents

Abstract

PURPOSE: A method for controlling thickness of strip in continuous cold rolling is provided to obtain strip thickness having higher accuracy by obtaining modulus of plasticity, one of important control factors in a strip thickness control system, in such a way that physical rolling effect is reflected in the low speed normal rolling section. CONSTITUTION: In controlling a rolling mill using an AGC (automatic gauge control) system to which an ordinary setup model is applied in cold rolling process, the method for controlling thickness of strip in continuous cold rolling comprises the steps of obtaining an initial roll force during low speed normal rolling P0 by substituting actual data and operation data during low speed normal rolling for a roll force prediction equation; obtaining an initial roll gap value S0 of a hydraulic cylinder on the setup model by substituting the obtained initial roll force P0 for an elasticity deformation equation of the rolling mill; obtaining modulus of plasticity M using the obtained initial roll force P0 by perturbation; and obtaining a roll gap control amount using the obtained modulus of plasticity M, wherein the operation of the rolling mill is controlled in the section where low speed normal rolling is carried out by the initial roll gap value (S0) obtained in the low speed normal rolling conditions and a roll gap control amount (ΔS).

Description

Plate thickness control method in continuous cold rolling

The present invention relates to a method for controlling the plate thickness of a cold rolled steel sheet using an automatic plate thickness control system in a continuous cold rolling process, and in particular, a low plasticity factor, which is one of the important control factors in the plate thickness control system, It was obtained by a method that reflects the effect of physical rolling phenomenon during the steady pressure study, so that a higher plate thickness can be obtained.

Generally, an automatic gauge control (AGC) system is provided to achieve the desired sheet thickness quality in the continuous coil rolling.

Among the AGC systems, there are FF (Feed Forward) AGC and FB (FeedBack) AGC. The former uses plate thickness deviation disturbance of the base material coming from the # 1 stand entrance, and the latter uses the plate thickness deviation generated from the exit # 1 stand. Finally, the roll gap control amount for minimizing the # 1 stand exit plate thickness variation is determined.

The general configuration of the AGC system is as follows.

In a typical cold rolling process, a plurality of rolling mill stands are sequentially installed to sequentially reduce the thickness of the rolled sheet, and in particular, an AGC system is intensively installed so that a roll gap of an appropriate size may be formed in the first stand.

In other words, under the given rolling conditions, the roll gap of the No. 1 stand rolling mill calculated by the uppermost computer, that is, the gap between the upper and lower working rolls, is controlled by the screw down installed on the upper part of the upper working roll. When rolling proceeds after the initial value is set in this way, the thickness of the rolled plate is measured by a thickness measuring instrument installed at the rear end of No. 1 stand, and the rolling is continued if the error is within the allowable range compared to the target thickness. However, if the error is large, the process control computer performs real time control to reduce the error.

The process control computer calculates the control amount of the hydraulic system to be operated in order to reduce the plate thickness error, and commands the hydraulic system installed under the lower work roll. Will be repeated. Real-time control of such plate thickness control is commonly referred to as AGC.

In order to obtain an appropriate roll gap control amount (ΔS) in this AGC, the plasticity coefficient (M), which is a parameter used to obtain the roll gap control amount (ΔS), should be obtained, and the rolling load prediction is used to obtain the plasticity coefficient (M). The formula will be used.

As described above, in the AGC control block for determining the roll gap control amount, there is a factor of plasticity factor (M), which reflects the state of rolling, and conventionally, high-speed normal rolling before rolling starts. As a standard, only one coil has been calculated and used.

However, in continuous cold rolling, the coils are continuously connected to each other, so not only high speed normal rolling (1000 m / min) but also low speed normal rolling (about 100 to 200 m / min) for welding and winding between coils is performed. To perform.

However, since the coefficient of plasticity required for AGC is calculated only once per coil on the basis of high-speed normal rolling, AGC control can only be performed with the plasticity coefficient obtained on the basis of high-speed rolling at low rolling speed, which is not suitable for the physical rolling situation. By using coefficients

The efficiency of the plate thickness control was deteriorated.

The present invention relates to a method for controlling the plate thickness of a cold rolled steel sheet using an automatic plate thickness control system in a continuous cold rolling process, and in particular, a low plasticity factor, which is one of the important control factors in the plate thickness control system, The purpose of this study is to provide a method to obtain a higher plate thickness by obtaining a method that reflects the effect of physical rolling phenomenon during the steady pressure study.

1 is a schematic diagram of a plate thickness control device of a strip in continuous cold rolling;

Figure 2 is a state diagram showing the rolling speed in continuous cold rolling,

3 is a graph showing an elasticity curve showing the physical phenomenon of rolling;

4 is a graph for explaining the calculation of the plasticity coefficient by the perturbation method in the plasticity curve,

Fig. 5 is a graph showing the exit plate thickness deviation controlled by the method according to the present invention and the conventional method.

In order to achieve the above object, the present invention, in the cold rolling process to control the rolling mill using an AGC system to which a conventional setup model is applied,

Calculating the initial value rolling load Po at the time of low-speed normal rolling by substituting the performance data and the operation data at the time of low-speed normal rolling into the rolling load prediction equation represented by the following equation (2).

(B, width of the rolled sheet

k: strain resistance of rolled material

Kt: Influence term due to tension in front and rear of rolling mill

Dp: Friction coefficient influence term

R: working roll radius of rolling mill

H, h: mouth of the rolling mill. Published thickness):

Obtaining the roll gap initial value So of the hydraulic cylinder on the set-up model by substituting the elastic deformation equation of the rolling mill represented by the following formula (3) using the initial value rolling load Po obtained as described above;

(However, So: Roll gap initial stage

h: Outer plate thickness of rolling mill

Po: Initial value rolling load

K: Elastic modulus):

Obtaining a plasticity coefficient M by a perturbation method represented by Equation (4) below the obtained rolling load initial value Po,

(However, P: rolling load function (rolling load prediction formula)

α: perturbation coefficient (0.001)

Obtaining the roll gap control amount by substituting the obtained plasticity coefficient M into the following equation (1a) (1b),

(However, roll gap control amount of ΔS _FF : FF AGC

△ S _FB : Roll gap control amount of FB AGC

ΔH: Depth of plate thickness

△ h: deviation of the thickness of the plate

K: modulus of elasticity

M: plasticity coefficient);

And a roll gap initial value (So) and a roll gap control amount (ΔS) obtained under the conditions of the low speed normal rolling in the section for performing the low speed normal rolling.

As mentioned above, the rolling work in the automated continuous cold rolling mill is controlled by a calculator. In particular, the initial value of the actuator (roll gap, roll speed) is determined before rolling starts in order to secure the longitudinal thickness of the product. A set up system for determining and an AGC control system for effectively controlling various appearances during rolling operations are commonly used.

A typical AGC system is concentrated in the first stand as shown in FIG. 1 and is composed of FF (Feed Forward) and FB (Feed Back).

FF is generally composed of the following logic to control the plate thickness deviation existing on the stand 1 side and the FB plate thickness deviation on the stand 1 exit.

However, △ S _FF : Roll gap control amount of FF AGC

△ S _FB : Roll gap control amount of FB AGC

ΔH: Depth of plate thickness

△ h: deviation of the thickness of the plate

K: modulus of elasticity

M: plasticity coefficient

At this time, in order to determine the roll gap control amount, ΔH and Δh are values measured by the entry and exit plate thickness sensors, respectively, and K is a value representing the mechanical properties of the rolling mill, and is a value measured and determined in advance. The plasticity coefficient M is a value that represents the physical properties of the strip and changes with strip and rolling conditions.

On the other hand, since continuous cold rolling continuously performs the rolling by welding the strip, the rolling speed is repeated by repeating the low speed, acceleration, high speed, deceleration, and low speed as shown in FIG. 2 for welding time and winding. .

In the related art, the plasticity coefficient M has been calculated and used only once per coil based on the high-speed normal, and has been applied to all sections.

Therefore, the use of the plasticity coefficient M that does not match the physical phenomenon in the section out of the high-speed normal has a disadvantage that the thickness control accuracy can not be reduced.

The present invention is to solve the problem of the conventional method in controlling the plate thickness in continuous cold rolling, to obtain a plastic coefficient M that can predict the physical phenomenon more accurately and to substitute the AGC method to increase the plate thickness degree It is presented.

Hereinafter, the present invention will be described in more detail.

First, the initial rolling load Po was physically developed by using low-speed normal rolling performance data (data accumulated by actual operation experience) as shown in Table 1 and a conventional elastoplastic curve as shown in FIG. Obtain

In this case, the calculation using the conventional elasto-plastic curve of FIG. 3 means that the low-speed normal rolling performance data and necessary operation data are obtained by direct calculation into the rolling load prediction equation for deriving the elasto-plastic curve. You may also

The rolling load P can be obtained by using the rolling load prediction equation, also known as the Hill equation. The rolling load prediction formula is a formula generally used for a process and control in a cold rolling process, in particular, a process to which an AGC system is applied, and is represented by Equation 2 below.

Where B is the width of the rolled plate

k: strain resistance of rolled material

Kt: Influence term due to tension in front and rear of rolling mill

Dp: coefficient of friction influence

R: working roll radius of rolling mill

H, h: mouth and exit plate thickness of rolling mill

Next, the roll gap initial value So of the hydraulic cylinder is calculated | required on a setup model using the initial stage rolling load Po calculated | required as mentioned above. In order to calculate the roll gap initial value So, the setup model uses the elastic deformation formula of the rolling mill as shown in Equation 3 below. The following elastic deformation formula of the rolling mill is a formula generally used to obtain the roll gap initial value So in the setup model of the rolling mill.

Where So: Roll gap initial value

h: Outer plate thickness of rolling mill

Po: Initial value rolling load

K: modulus of elasticity

Next, the plasticity coefficient M is calculated | required by the perturbation method as shown in FIG. 4 centering on the rolling load initial value P calculated | required previously. The expression evolution is as follows.

Where P: rolling load function (rolling load prediction equation)

α: perturbation coefficient (0.001)

Α is a perturbation coefficient, which is a coefficient used in calculating the plasticity coefficient M by a numerical method. That is, in the present invention, the central difference method (central difference method), which is one of numerical methods, is used, which is slightly thicker than the target thickness h of the rolled plate, that is, the rolling load is calculated for h + αh, Again, the rolling load is calculated for h-αh where it is slightly thinner than the target thickness h, where α is 0.001, about 0.1% of the target thickness. The difference between the two rolling loads thus obtained is ΔP corresponding to the molecule of Equation 4, and the distribution of Equation 4 is Δh = 2αh, which is the difference in plate thickness in both cases.

Here, the roll gap initial value (So) obtained under the conditions of low speed normal rolling in the section where the obtained plasticity coefficient M is substituted into Equation (1) to obtain the roll gap control amount (ΔS), and the low speed normal rolling is performed for welding and winding. By applying and controlling the operation with the obtained roll gap control amount (ΔS), it is possible to effectively control the # 1 stand exit plate thickness to a higher degree effectively in response to the change of the rolling speed.

The following is an example carried out under the actual rolling conditions of Table 1 by the method proposed by the present invention.

In the continuous cold rolling mill consisting of five stands, plate thickness control was performed by the method proposed by the present invention to control the exit plate thickness of stand # 1.

5 shows the stand plate thickness deviation of the first stand, the horizontal axis represents the rolling time, the vertical axis represents the plate thickness deviation. Here, the solid line is the value obtained by the method proposed by the present invention, and the dotted line is the plate thickness deviation obtained by the conventional method. At this time, the plate thickness deviation of stand No. 1 shows about 50% improvement.

As described above, the present invention relates to a method of controlling the thickness of a cold rolled steel sheet using an automatic sheet thickness control system in a continuous cold rolling process, and in particular, a plasticity factor, which is one of important control factors in the sheet thickness control system. Is obtained by a method that reflects the effect of physical rolling phenomenon between low-speed steady pressure studies, and it is effective to obtain a higher sheet thickness.

Claims (1)

In controlling the rolling mill using the AGC system to which the usual setup model is applied in the cold rolling process, Obtaining the initial rolling load Po at the time of low speed normal rolling by substituting the performance data and the operation data at the time of low speed normal rolling into the rolling load prediction formula represented by the following formula (2).

(B, width of the rolled sheet k: strain resistance of rolled material Kt: Influence term due to tension before and after rolling mill Dp: coefficient of friction influence R: working roll radius of rolling mill H. h: Rolling mill thickness of rolling mill): Obtaining the roll gap initial value So of the hydraulic cylinder on the set-up model by substituting the elastic deformation equation of the rolling mill represented by the following formula (3) using the initial value rolling load Po obtained as described above;

(So, Roll gap initial value h: Outer plate thickness of rolling mill Po: Initial value rolling load K: modulus of elasticity): Obtaining a plasticity coefficient M by a perturbation method represented by Equation (4) below the obtained rolling load initial value Po,

(However, P: rolling load function (rolling load prediction formula) α: perturbation coefficient (0.001) Obtaining the roll gap control amount by substituting the obtained plasticity coefficient M into the following equation (1a) (1b),

(However, roll gap control amount of ΔS _FF : FF AGC △ S _FB : Roll gap control amount of FF AGC ΔH: Depth of plate thickness △ h: deviation of the thickness of the plate K: modulus of elasticity M: plasticity coefficient; It is configured to include, in the section for performing low speed normal rolling, plate thickness control method in continuous cold rolling, characterized in that the operation control by the roll gap initial value (So) and the roll gap control amount (△ S) obtained under the conditions of low speed normal rolling. .

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