KR0140331B1 - Prediction method of flatness variation according to strip tension - Google Patents

Abstract

The present invention relates to a method for predicting the change in flatness when a metal strip is subjected to tension, and considers the tensile and compressive stress fields in the strip width direction due to wave generation, and the physical properties and thickness of the strip from the line computer (8). Predicting the flatness change according to the tension change of the strip as the wave height (H) and pitch (P) of the wave due to the stretching of tension and the sinusoidal characteristics of wave And it is possible to improve the precision of the flatness correction control in consideration of the fluctuation value of the wave due to the tension added to the strip.

Description

Estimation method of flatness change according to tension of strip

1 is a schematic view showing a method of measuring flatness in general when a strip tension is applied

2 is a graph showing the relationship between the length of the strip (와 axis) and the height (xy axis), in which flatness typically has sinusoidal characteristics.

3 is an explanatory view showing the internal stress change of the strip according to the form of flatness (a) to (c)

4 is a graph showing the change in the flatness of the strip according to the tension portion in relation to the wavelength and wave height

5 is a graph showing the stress-strain curve of a typical mild steel

6 is a schematic block diagram showing a method for predicting flatness of a strip against a change in tension according to the present invention.

7 is a flowchart illustrating a method for predicting flatness change according to tension of a strip according to the present invention.

* Explanation of symbols for main parts of the drawings

1 strip 2 flatness measuring device

21: flatness measurement computer 5: tension measurement center

51: Flatness Prediction Computer 8: Line Computer

The present invention relates to a method for predicting flatness that changes when a metal strip is subjected to tension, and more particularly, the pitch of strip flatness due to the tension added to the strip when machining or rewinding the metal strip. predicts the behavior of pitch and height depending on the properties and tension of the strip to find the flatness value when it is actually used without tension, or conversely use the measured strip flatness value when there is no tension The present invention relates to a method for predicting flatness change according to tension of a strip for predicting flatness when tension is added.

Recently, the degree of flatness of metal strips has become a very important quality factor due to the trend of high quality metal sheet materials and automation of post processing facilities.

Since the measured value by the conventional well-known flatness measuring method is the flatness value measured in the state in which the constant tension was added when the metal strip progresses in the longitudinal direction, the flatness in the state in which the practical use condition is removed the tension Is different from the measured value, which is judged to be a defective product when the acceptance product is used at the time of measurement, or there are many difficulties in setting an appropriate working standard for flatness inspection.

In addition, when calculating the feedback control amount for flatness correction during feed back control by on-line flatness measurement, the size of tension applied to the strip and the flatness value due to the physical properties of the strip are not considered. There is a limit to precise flatness control by correcting flatness by feedback control according to the size of flatness value.

In addition, in order to check the flatness at the actual tension, there is a method of placing the strip on the off-line plate and measuring it using the difference, or cutting the strip into specimens and measuring it. And many problems in terms of precision of measurement.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. The object of the present invention is to provide a method for accurately and easily predicting the behavior of the flatness variation of the strip according to the tension and the physical properties of the strip. The present invention provides a method for predicting flatness change according to tension.

In order to achieve the above object, the present invention provides a wave height and pitch, which is the flatness of a strip in which tension is applied, is measured by a flatness measuring device and transmitted to a flatness measuring computer, and the tension of the strip is provided on the tension reel. In the method for predicting the change of the wave generated in the strip according to the variation of the tension added to the strip measured by the true tension measuring sensor,

The data of the flatness measuring computer and the tension measuring sensor and the physical property, thickness, and width data of the strip previously inputted to the line computer are transmitted to the flatness predicting computer; The flatness prediction computer, the strip width (WT) of the site where the tensile stress field is formed,

Where W is the width (mm) of the strip without tension, t is the thickness (mm) of the strip without gravity, H2 is the crest of the strip with the tension portion (mm), and T is the tension applied to the strip (ton ), Em: Young's modulus of the metal strip to be tensioned, E _S : Young's modulus of the strip without tension, k: Constant (Onion: 1, Medium: 1, Quarter buckle: 2, Polarization: 0.5) α: Constant (0.1 And elongation ε of the strip due to tension by the value of the strip width W _T calculated in the step;

(Where E is the Young's modulus of the strip); In the step, the crest and the pitch (P₁) at the time of tensionless force are calculated by the calculated value of the elongation (ε) of the strip.

(Where ε² is ignored); By predicting the flatness according to the tension of the strip at the elastic limit by providing a method for predicting the change in flatness according to the tension of the strip.

Hereinafter, the present invention will be described in detail.

6 is a schematic diagram showing a device that can be used in the method for predicting the change in flatness according to the tension of the strip according to the present invention.

When the strip 1 is released from the pay off reel 3 and wound around the tension reel 4, it is located on the upper side of the strip 1 so that the flatness of the tensioned strip 1 can be adjusted. The flatness measuring device 2 which measures continuously is provided, and the flatness prediction computer 51 which receives the flatness actual value from the flatness measuring computer 21 connected to this flatness measuring device 2 is equipped, The flatness prediction computer 51 is attached to one side of the tension reel 4 to measure the tension added to the strip 1 between the pay-off reel 3 and the tension reel (4) The line computer 8 is configured to transmit the thickness, the width and the material performance of the strip to be measured to the flatness prediction computer 51 as well as to receive the measured tension therefrom.

The wave generated in the strip 1, that is, the flatness has a sine wave characteristic. As shown in FIG. 2, the flatness is the length of the strip as the x-axis and the height of the strip with respect to the length is y. If it is an axis, it appears as a sinusoidal wave having a crest (H) and a pitch (P), as shown in Equation 1 below.

It may be represented as.

When a wave is generated in the strip 1, as shown in FIG. 3, the wave generated portion is relatively stretched as compared to the unoccupied portion, and thus a compressive stress field is formed, and the non-waved portion is a tensile stress field. When tension is applied in this state, stretching occurs throughout the strip due to the Young's modulus of the material, and thus the area where the tensile stress field is formed becomes wider and larger in size, while the area of the compressive stress field is narrower and its size is also increased. Becomes smaller.

At this time, the explosive size of the portion where the tension is added to the strip and the tensile stress field is formed may be determined using the flatness in the width direction measured from the flatness measuring device 2, and the portion where the wave is generated is formed with a compressive stress field. The flat and flat part is the part where the tensile stress field is formed. However, the wave measured online by the flatness measuring device 2 should be corrected because it is a measured value in a state where tension is added, and this correction method is measured in a state where tension is added and a state where tension is removed, respectively. The flatness in one width direction is calculated by an empirical formula based on the measured value, which has the relationship of the following equation (2).

Equation 2

From here

W _T : Width of the strip with tensile stress applied (mm)

W is the width of the strip at tension (mm)

t: thickness of the strip at tensionless (mm)

H₂: Crest of strip with tension section (mm)

T: Tension added to the strip (ton)

E _m : Young's modulus of the metal strip to be measured in tension addition

E _S : Young's modulus of strip at tension

k: constant (onion: 1, medium: 1, quarter buckle: 2, polarization; 0.5)

α: constant (0.1 to 0.6)

Equation (2) is applicable to the added tension within the elastic limit of the strip to be measured. If α is less than 0.1, the deviation is large in the measured value of the thin strip, and if α is more than 0.6, the thick strip Since the measurement deviation increases at, apply a value in the range of 0.1 to 0.6.

As the tension is added to the strip as described above, the portion of the tensile stress field becomes wider and the portion of the compressive stress field becomes narrower, so that the amount of excess stretching is reduced in comparison with the non-wave generating portion, and the characteristics of the wave are changed, as shown in FIG. The original wave 6 changes in the form of a wave ₇ where it is dug by the tension portion and H ₆ becomes smaller by H ₇ and the pitch P ₆ becomes longer by P ₇ .

The difference between P ₇ and P ₆ may be calculated as shown in Equation 3 below as the elongation of the strip according to the tension portion.

... Expression 3

Where E is the Young's modulus of the strip.

In order to predict the change of the crest height (H) and the pitch (P) according to the change of stretching as described above, the length of the wave must be calculated.

.... Equation 4

By the above formulas 1 and 4,

..... Equation 5

To obtain an approximate solution of Equation 5, expand to the second term in the Taylor Series.

Equation 6

Can be obtained.

In order to derive the waveform relationship between the tensioned state and the non-tensioned state, H₁: wave height without tension, H₂: wave height with tension, P₁: tension without tension Pitch, P₂: Pitch when tension is applied,

... Equation 7

P₁ · (1ε) = P₂ ... equation 8

Relationship is established, and according to the above equations 7, 8 and 3,

... (Equation (9)

Equation 10

Where ε² is ignored

You get the final equation of.

That is, as shown in FIGS. 6 and 7, the flatness measuring device 2 and the flatness measuring computer 21 measure the flatness change in the width direction and the longitudinal direction while tension is applied online. When transmitting to the flatness prediction computer 51, the flatness prediction computer 51 receives the material, thickness, and width of the strip to be measured from the line computer 8, and calculates the cross-sectional area of the portion where the tensile stress field in the width direction is formed. By measuring the tension applied to the strip from the tension measuring sensor (5) and using the Young's modulus of the strip to be measured, the elongation (ε) of the actual strip can be calculated by Equation 3, and the resulting equations 9 and 10 are obtained. It is possible to accurately predict the amount of change of the wave according to the change of tension.

Using the Young's modulus of various steel strips, the skin pass mill of the hot-rolling mill measures the flatness with 10 tons tension applied during the skin pass operation, and the flatness at the same point of the same strip is removed without tension. The results measured using wires and rulers and the predicted values of the present invention are shown in Table 1, which shows that the predicted values according to the method of the present invention coincide within a small error range with respect to the measured values after tension removal.

However, the materials are calculated by the same Young's modulus as carbon steel.

As described above, according to the present invention, it is possible to accurately predict the flatness when removing tension regardless of the amount of tension applied to the metal strip, thereby enabling online predictive inspection for preventing flatness failure under practical use conditions of the metal strip. Therefore, it is possible to prevent the fall of the product error rate by cutting a separate specimen for the purpose of flatness inspection, improve the workability, and also add tension to the strip during online feedback control for flatness correction. By controlling in consideration of the fluctuation value of the wave, it has an excellent effect of improving the accuracy of the flatness correction control.

Claims (1)

The crest (H2) and pitch (P2), the flatness of the strip (1) in tension, are measured by the flatness measuring device (2) and transmitted to the flatness measuring computer (21). In the method for predicting the change of the wave generated in the strip according to the variation of the tension added to the strip measured by the tension measuring sensor (5) provided in the tension reel (4) of the tension (T) of The data of the measuring computer 21 and the tension measuring sensor 5 and the physical property, thickness, and width data of the strips previously input to the lie computer 8 are transmitted to the flatness prediction computer 51, respectively; The flatness prediction computer 51 measures the width of the strip (WT) at the portion where the tensile stress field is formed. Where W is the width of the strip without tension (mm), t is the thickness of the strip without gravity (mm), H2 is the strip height with the tension portion (mm), and T is the tension (ton) applied to the strip. : Young's modulus of the metal strip to be measured in tension state, ES: Young's modulus of strip in tensionless state, k: Constant (onion: 1, medium wave: 1, quarter buckle: 2, polarization: 0.5, α: constant (0.1 to 0.6) And elongation ε of the strip due to tension by the value of the strip width WT calculated in the previous step, (Where E is the Young's modulus of the strip); In the step, the crest and the pitch (P₁) at the time of tensionless force are calculated by the calculated value of the elongation (ε) of the strip. (Where ε² is ignored); Prediction method of variation in ballistic trajectory according to the tension of the strip, characterized in that it predicts the flatness according to the tension of the strip at the elastic limit by