KR20010036626A - Method for setting control gain for the shape of strip in hot rolling mill - Google Patents

Abstract

PURPOSE: A method for setting the shape control gain of a strip in a hot finishing mill is provided to effectively control the shape of the strip by selecting an appropriate calculating method of the various calculating methods calculating a feedback control gain. CONSTITUTION: The method comprises the steps of measuring crown ratio and elongation of a strip passing through a final rolling machine from instruments (310); obtaining a deviation between a target elongation difference and an actual resulting elongation difference, and a deviation between a target crown ratio and an actual resulting crown ratio from a calculator (320); judging a high crown and a low crown, and both side wave and medium wave using the measured crown and elongation (410); deciding any one calculating method of feedback control gain out of a certain crown ratio equation or a certain bending force equation depending on types of the judged strip shapes (420); calculating control gains according to the decided calculating methods (430,440); calculating bending control amount according to the calculated control gains (340); and compensating roll bending force with the amount of bending compensation (350).

Description

METHOD FOR SETTING CONTROL GAIN FOR THE SHAPE OF STRIP IN HOT ROLLING MILL}

The present invention relates to a method for controlling the shape of a strip in a finishing mill during a hot rolling process of a steel mill, and more particularly, a medium wave, an onion, and a crown, which are waves in the strip generated during the finishing rolling of the strip. Is detected from the back of the final stand and feedback control is performed according to its performance, and a method of selecting an appropriate calculation method among various calculation methods for calculating the feedback control gain is applied in hot rolling that can effectively control the strip shape. The present invention relates to a strip shape control gain setting method.

In general, the shape of the steel strip is divided into a crown and a onion which is a wave due to the difference in elongation in the longitudinal direction of the plate and the crown, which is a thickness deviation in the plate width direction. Such examples are shown in FIG. 2. In Figure 2, the crown of the strip is the cross-sectional view of the strip as the center portion of the thickness of C, the thickness of the left and right sides of the strip A and B, respectively, the strip crown is represented as follows.

Crown = C-(A + B) / 2. In addition, the medium wave refers to the waveform formed in the center of the strip, the onion refers to the waveform formed on both sides of the strip, the flatness of these waveforms, as shown in Figure c) of FIG. If the height of the waveform is H,

Flatness = P / H.

The control of the board for controlling the shape of the strip having the defect as described above is usually controlled by a feedback control method. An example of a feedback control device for performing such feedback control is shown in FIG.

This conventional feedback control device is installed between the final stand 10c of the rolling mill 10 having the multi-stage stands 10a, 10b and 10c and the winding machine 20, as shown in FIG. Crown gauge 12, the flatness measuring instrument 14 configured to measure the elongation difference in the longitudinal direction of the steel strip S, and the measuring instruments 12, 14 adapted to measure the crown, which is the widthwise thickness deviation of S). A roll configured to operate the bender pressure control cylinder 32 to be compensated by the roll bending force compensation amount calculated by the calculator 30 and the calculator 30 configured to obtain the roll bending force compensation amount using the measured value measured from It comprises a bender force control device 34.

Typically, the stand to be implemented is the rear stand 10, the crown measuring instrument 12 measures the shape of the strip S every 2 seconds, the flatness measuring instrument 14 measures every 0.1 seconds, and the control is performed every 0.2 seconds. Is carried out.

A conventional process flow chart for performing feedback control using such a feedback control device is shown in FIG.

In the conventional feedback control process shown in FIG. 3, starting from the start step 300, the next plate crown and wave are measured, and in this step 310, the thickness deviation of the strip S is measured. The crown is measured by the crown measuring instrument 12, the elongation difference in the longitudinal direction of the strip S is measured by the flatness measuring instrument 14, and the measured value measured from the measuring instruments 12 and 14 is calculated. Will be sent out.

Then, the crown deviation and the elongation deviation is calculated in the next step 320, which receives the crown and the elongation difference measured from the shape measuring machine 12, 14 in the calculator 20 based on this equation The deviation (ΔE) of the target elongation difference and the performance elongation difference is calculated by (1), and the deviation (ΔK) between the target crown ratio and the performance crown ratio is obtained.

ΔE = Es-Em

ΔK = Cs / h-Cm / h

(Em: target elongation difference, Es: performance elongation difference,

Cm: target crown ratio, Cs: performance crown ratio,

h: final target thickness of steel strip (S)

In the next step 330, the roll bender force compensation control gains (Gei, Gci) at each stand are calculated, and in the next step 340, the roll bender force compensation amount Fi is obtained by the following equation (2). Calculate

Fi = Gei × ΔE + Gki × △ K

Here, Fi is the roll bending force compensation amount of the i-th stand of the rolling mill 10 having a multi-stage stand, Gei is the wave compensation control gain of the i-th stand, and Gki is the crown non-compensation control gain of the i-th stand.

On the other hand, in the method of calculating the roll bender force compensation control gains (Gei, Gci) in each stand in the step 330, in the case of non-intrusive feedback control, one of the following two methods.

[Method 1]

The present method 1 is a constant crown ratio, which assumes that the crown ratio of each stand in the previous stands 10a and 10b except for the rear of the last stand 10c that the crown and the wave can be measured is constant. The performance of the previous stands 10a and 10b excluding the back of the last stand 10c where the wave is measurable is a way of assuming that the crown ratio in the continuous stands 10a and 10b does not change.

[Method 2]

This method 2 is a constant bender force ratio, which is a method in which the bending force ratio of each stand 10a, 10b, 10c is assumed to be constant, i.e., roll bending at each rear end stand 10a, 10b, 10c. The gain is calculated by assuming that the force is in a constant ratio relationship.

The conventional method of calculating the gain according to the method (1) will be described according to the equation.

For convenience of explanation, assuming that the control target stands 10a, 10b, and 10c are four to six stands, the stand 10a is the fourth stand, the stand 10b is the fifth stand, and the final stand. Assume 10c as the sixth stand. The shape of the strip can be measured from the back of the final stand 10c.

First, the basic relationship between wave and crown is used in the following equation (3).

E _i = ξ _i × (K _i -K _i-1 ) + η _i × E _i-1

Where Ki is the crown ratio at the i-th stand, Ei is the elongation at the i-th stand, ξi is the crown influence coefficient of the i-th stand, and ηi is the shape dielectric constant of the i-th stand.

Here, the crown ratio is represented by the following equation (4) as a function of the crown ratio of the entire stand and the roll bending force.

K ₄ = a ₄ × K ₃ -b ₄ × F ₄

K ₅ = a ₅ × K ₄ -b ₅ × F ₅

K ₆ = a ₆ × K ₅ -b ₆ × F ₆

Fi is the roll bending force of the i-th stand, and ai and bi are the mathematical model coefficients of the i-th stand.

The following equation (5) holds from the above equations (3) and (4).

E₄= ξ₄× (K₄-K₃) + η ₄× E₃

E ₅ = ξ ₅ × (K ₅ -K ₄ ) + η ₅ × E ₄

K ₆ = ξ ₆ × (K ₆ -K ₅ ) + η ₆ × E ₅

Assuming that the crown ratio is constant in Equation (5), that is, K ₄ = K ₅ , the equation is summarized as in Equation (6) below.

E ₆ = ξ ₆ × (K ₆ -K ₅ ) + η ₄ η ₅ η ₆ × E ₃

The second term represented by the product of permittivity from Equation (6) is negligible because its value is negligible.

K ₅ = K ₆ ⁿ -E ₆ ⁿ / ξ ₆

Where K ₆ ⁿ is the crown ratio deviation and E ₆ ⁿ is the wave deviation.

Substituting K ₄ = K ₅ conditions and the above equation (7) into equation (4), in summary, the bender force at each stand is expressed as in the following equation (8).

F₄ =-(1-a₄) / b₄ (K ₆ ⁿ -E ₆ ⁿ / ξ ₆ )

F ₅ =-(1-a ₅ ) / b ₅ (K ₆ ⁿ -E ₆ ⁿ / ξ ₆ )

F ₆ =-(1-a ₆ ) / K ₆ ⁿ + (-a) × E ₆ ⁿ / (bξ ₆ )

When K ₆ ⁿ = DELTA K, E ₆ ⁿ = DELTA E, comparing Equation (8) with Equation (1) yields the values of Gki and Gei at each stand.

On the other hand, the vendor power ratio constant method is calculated | required as follows.

F6 stand exit side crown / flatness deviation from the ratio of the target value (target value-actual performance value) K ₆ ^n, E ⁿ ₆ a quantitative ratio can bending force to a 0 F4 = Assume F × F5 to determine F4 to F6. Where only Denotes a bending force correction amount distribution ratio.

F4 above × F5 is replaced by Equation 4

K ₄ = a ₄ K ₃ -b ₄ F ₅

K ₅ = a ₄ a ₅ K _3- (a ₅ b ₄ + b ₅ ) F ₅

K ₆ = a ₄ a ₅ a ₆ K _3- (a ₅ a ₆ b ₄ + a ₆ b ₅ ) F ₅ -b ₆ F ₆

In Equation 5, K3 and E3 are insignificant, so ignore them and substitute the above Equation 5 into Equation 5 to calculate the deviation.

K ₅ = -A ₀ F _5, E ₆ ⁿ = ξ ₆ K ₆ ⁿ + (A ₁ + A ₂ ) F ₅

Where A ₀ = a ₅ b ₄ + b _5, A ₁ = (ξ ₆ -η ₆ ξ ₅ ) (a ₅ b ₄ + b ₅ )

A ₂ = (η ₆ ξ ₅ -η ₆ η ₅ ξ ₄ ) (b ₄ )

Defined as

The following F4, F5, F6 can be obtained from the above equation.

In this way, the gain is calculated using the Crown Ratio constant method (method 1) and Bender Force ratio method (method 2).

Therefore, after calculating the gain in step 330, and calculating the roll bender force compensation amount Fi according to equation (2) in step 340, in step 350, the vendor pressure control cylinder 32 And the roll bender force control device 34 to control the rolling mill 10.

However, in the conventional feedback control process as described above, in the process of calculating the roll bender force compensation control gains (Gei, Gci) at each stand in step 330, the above two methods, namely method (1) and method Since there is no criterion on which method to use (2), the conventional method of controlling the shape of the strip (S) is to select one of the two methods arbitrarily or empirically regardless of the shape performance in calculating the control gain. have. That is, in the conventional feedback control method of the strip S shape, the feedback control gain calculation method is not determined according to the shape detected by the shape measuring device of the strip S, but by arbitrarily selecting one of two methods and using it fixedly. There was a problem that the shape control of the strip (S) can not be performed effectively.

For example, if the measured values of the measuring instruments 12 and 14 occur at the same time as the onion wave and the large crown, the gain of each other is canceled when using the method 1, and the adverse effect of the control is shown.

Accordingly, the present invention has been proposed to solve the above problems, and in the process of calculating the roll-bender force compensation control gains at each stand, an appropriate criterion for selecting one of the two methods is used. The purpose of the present invention is to provide a method for setting strip shape control gains in hot rolling, which effectively controls the wave and crown shapes of the strip and minimizes the adverse function of the control.

1 is an overall configuration diagram showing an example of a strip shape control device for controlling the shape of a strip;

Figure 2 is a schematic diagram for defining the shape of a typical strip,

a) perspective view of turning strips,

b) cross section of the strip showing the crown being turned,

c) side cross-sectional view showing strip flatness;

3 is a flow chart showing a step by step method of controlling the strip shape according to the conventional method;

Figure 4 is a flow chart illustrating a step-by-step method of feedback control the strip shape according to the present invention.

<Explanation of symbols for main parts of drawing>

10: continuous rolling mill 12: crown measuring instrument

14 wave measuring instrument 20 winder

30: upper calculator 32: cylinder for bender pressure control

34: roll bender force control device S: strip

In order to achieve the above object, the present invention, in the method of controlling the shape of the hot rolled strip by controlling the roll bending force of the after-rolling mill of the hot finishing rolling line,

Measuring the crown ratio and elongation of the strip passing through the final mill from the meters; Obtaining a deviation between a target elongation difference and a performance elongation difference and a deviation between a target crown ratio and a performance crown ratio based on the crown and the elongation difference measured by the shape measuring instrument; Determining a high crown and a low crown and an onion and a medium wave by using the crown and the elongation measured as described above; Determining a feedback control gain calculation method of either the crown ratio constant method or the bender force ratio constant method according to the determined strip shape; Calculating a control gain according to the calculation method determined above; Comprising: calculating a vendor control amount according to the calculated control gain; and compensating the roll bender force with the vendor compensation amount; to provide a method for setting the strip shape control gain in hot rolling By.

Hereinafter, the present invention will be described in detail with reference to the drawings and formulas.

Strip shape control gain setting method in the hot rolling of the present invention is subjected to a step-by-step process as shown in FIG. Although the present invention is largely identical to each step of the strip shape control process shown in FIG. 3, the method of calculating roll bender force compensation control gains (Gei, Gci) at each stand in the conventional step 330 is different. .

Therefore, hereinafter, the present invention will be described with reference to the process of FIG. 4, and a detailed description thereof will be omitted for the process steps consistent with FIG. 3.

First of all, the present invention starts from the start step 300, and then the next plate crown and wave are measured. In this step 310, the crown, which is a thickness deviation of the width S of the strip S, as in the conventional crown gauge (12) to measure the elongation difference in the longitudinal direction of the strip (S) by the flatness measuring instrument (14), and to send the measured value measured from the measuring instruments (12) (14) to the calculator (30). do.

Then, in the next step 320, the calculator 20 calculates the crown deviation and the elongation deviation, and calculates the deviation (ΔE) between the target elongation difference and the performance elongation difference by the following equation (1), Find the deviation (△ K) from the performance crown ratio.

[Equation 1]

ΔE = Es-Em

ΔK = Cs / h-Cm / h

(Em: target elongation difference, Es: performance elongation difference,

Cm / h: target crown ratio, Cs / h: performance crown ratio,

ΔK: Crown ratio deviation, h: final target thickness of steel strip (S).

In addition, a step 410 of determining a high crown, a low crown, an onion, and a medium wave is performed by using the crown and the elongation measured as described above, and the step 410 is from Equation 1, when ΔE> 0. If onion, ΔE <0, it is determined to be medium wave (target elongation Em = 0), and if ΔK> 0, it is determined as high crown, and if ΔK <0, it is determined as low crown.

Herein, when ΔE> 0, the onion is an onion because Ei> 0 when K increases from the equation (6), assuming that the crown ratio is constant. However, the dielectric constant η ⁱ is ignored, and the crown influence coefficient ξ ₆ is a positive value between 0 and 1.

[Equation 6]

E ₆ = ξ ₆ × (K ₆ -K ₅ ) + η ₄ η ₅ η ₆ × E₃

Therefore, onions should occur when high crowns come out. This means that the crown ratio constant formula (method 1) does not fit when the high crown and midwave appear at the same time. This is not true by the same principle when both the crowns and onions appear at the same time as a result. Therefore, the determination of the high crowns and medium onions and the low crowns and onions is made, and if derived from the crown ratio constant formula (method 1) When the rolling mill is controlled by using the obtained control gains, the bender force feedback amounts enter into mutual control or reverse operation, and the control operation becomes poor. Therefore, in this case, the gain should be calculated by selecting a constant vendor power ratio method (method 2).

The feedback control gain calculation method selected according to the strip shape determined as described above is classified as shown in Table 1 below.

Crown wave Calculation method High crown onion 1 (Crown rain schedule) High crown Medium wave 2 (vendor power ratio constant method) Jerusalem onion 2 (vendor power ratio constant method) Jerusalem Medium wave 1 (Crown rain schedule)

After the step 410, the feedback control gain of either the crown ratio constant method (method 1) or the bender force ratio constant method (method 2) is calculated according to the strip shape determined in the step 410. Step 420 is determined to determine the manner. These steps 420 are also executed automatically by the program input to the calculator 30.

Then, according to the determination of the step 420, the control gain is calculated according to the feedback control gain calculation of any one of the above-described calculation method, that is, the crown ratio constant method (method 1) or the bender force ratio constant method (method 2). Steps 430 and 440 are made.

As described above, the step 430 is a constant crown ratio, which uses a method of assuming a constant crown ratio of each stand in the previous stand except for the rear of the last stand where the crown and the wave can be measured. Equations 3 to 8 are used.

In addition, the step 440 is a constant bender force ratio method, which assumes a constant bending force ratio of each stand, and calculates a gain by assuming that the roll bending force at each rear stage is in a constant ratio relationship. .

Then, after any one of the steps 430 and 440 is executed, calculating a vendor control amount according to the calculated control gain 340 and compensating a roll vendor force with the vendor compensation amount. 350 is executed as usual.

According to the present invention as described above, when the high crown and medium wave, low crown and onion is generated by using this property, using a method of constant bender ratio method 2, and the crown when the high crown and onion, low crown and medium wave occurs The control gain is calculated by using the method 1, which is a crown ratio constant method that can effectively control the wave and the wave at the same time, derive the vendor control amount from the control gain derived above (340), and perform the vendor control (350). This allows more effective shape feedback control.

Hereinafter, the working effects of the present invention will be described in more detail with reference to Examples.

(Example)

In order to examine the effects of the present invention in more detail, the experiments were conducted in the conventional method and the method of the present invention on the general steel sheet and the electrical steel strip, and the results are shown in Tables 2 and 3 below, respectively. ) And Crown Hit Ratio.

Here, the flatness (P / H) is an average calculated according to the definition shown in FIG. 2 using the steel strip (S) wave data, and the crown hit ratio is the total number of strips (S) and the performance crown The ratio of the number of strips (S) whose deviation of the target crown is within ± 20um is shown.

Flatness average Steel grade 99.1 (Prior) 99.2 (conventional) 99.3 (conventional) 99.4 (Prior) The present invention General steel 146.9 153.3 160.0 140.9 175.4 Electrical steel sheet 125.3 140.2 133.0 121.5 143.1

Crown Hit Ratio% Steel grade 99.1 (Prior) 99.2 (conventional) 99.3 (conventional) 99.4 (Prior) The present invention General steel 86.4 83.2 86.6 83.8 88.1 Electrical steel sheet 92.2 90.0 89.1 92.7 93.9

According to the present invention as shown in Table 2, the flatness is increased by 25.4 and 13.1, respectively, in the general steel and electrical steel due to the reduction of shape defects caused by medium or onion, crown shape quality as shown in Table 3 above As the crown hit ratio due to the improvement was increased by more than 3% in the general steel and the electrical steel sheet, the strip S having good shape quality was obtained.

As described above, the present invention is more elastic in the hot rolling process of the steel sheet strip (S) to suitably change the calculation method of the feedback control gain during shape feedback control during the finishing rolling process according to the shape performance of the strip (S) Through feedback control of the shape, it is possible to obtain a finished product having good shape quality. That is, according to the present invention, in the process of calculating the roll-bender force compensation control gains at each stand, it is possible to effectively control the wave and crown shape of the strip by selecting an appropriate criterion for which of the two methods is selected and used. As a result, the effect of minimizing the adverse function of the control is obtained.

Claims (3)

In the method of controlling the shape of the hot rolled strip by controlling the roll bending force of the after-rolling mill of the hot finishing rolling line, Measuring (310) the crown ratio and elongation of the strip (S) passed through the final mill (10) from the meters (12) (14); The calculator 30 calculates the deviation between the target elongation difference and the performance elongation difference and the deviation between the target crown ratio and the performance crown ratio based on the input of the crown and the elongation difference measured by the shape measuring instruments 12 and 14. Obtaining 320; Determining a high crown and a low crown and an onion and a medium wave by using the crown and the elongation measured as described above (410); Determining a feedback control gain calculation method of any one of the crown ratio constant method and the bender force ratio constant method according to the shape of the strip (S) shape determined above (420); Calculating control gains (430, 440) according to the calculation method determined above; Calculating a vendor control amount according to the calculated control gain (340); and compensating a roll vendor force with the vendor compensation amount (350); strip shape in hot rolling How to set control gain. The method of claim 1, wherein the step 410 is performed using the measured crown and elongation and Equation 1 below. [Equation 1] ΔE = Es-Em ΔK = Cs / h-Cm / h (Em: target elongation difference, Es: performance elongation difference, Cm / h: target crown ratio, Cs / h: performance crown ratio, △ K: deviation of crown ratio, h: final target thickness of steel strip (S)) Determine the high and low crowns of the strip (S), onions, and medium waves, if △ E> 0, then onions, and △ E <0, medium waves (target elongation Em = 0), and △ K> 0, high crowns A strip shape control gain setting method in hot rolling, characterized in that a low crown is determined when? K &lt; The method according to claim 1, wherein the step 420 is a formula of the crown ratio constant method when the shape of the strip S determined in the step 410 is high crown and onion, and low crown and medium wave (method 1). To select; A method for setting strip shape control gains in hot rolling, characterized by selecting a constant bender ratio (method 2) when high crowns, medium waves, and low crowns and onions are determined.