JPH03285707A - Control method of sheet crown at the time of hot rolling - Google Patents

Abstract

PURPOSE:To improve the control accuracy of sheet crown over the entire length of rolled stock by correcting the controlled variable of a crown control mechanism in rolling taking the relation among the transformation temp. of rolled stock, the estimated value and the measured value of rolling temp. into consideration. CONSTITUTION:Taking the transformation temp. of rolled stock that is fixed basing on the kinds of steel of rolled stock, i.e., carbon content and other contained elements and the high or the low of rolling temp. at each position in the width direction of rolled stock into consideration, the deviation from the target value of sheet crown due to the difference between the measured value and the estimated value of rolling temp. is determined. By correcting the controlled variable of the crown control mechanism in accordance with the deviation in rolling, the deviation from the target value of sheet crown is reduced and the control accuracy of sheet crown over the entire length of rolled stock is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the crown of a plate in hot rolling, particularly by computer control.

[Prior Art] In order to obtain the target plate crown over the entire length of the rolled material in the longitudinal direction, in addition to appropriately setting the control amount of the crown control mechanism before starting rolling, it is necessary to adjust the actual rolling conditions and settings. It is necessary to correct the control amount of the crown control mechanism during rolling so as to reduce the amount of deviation of the sheet crown from the target value caused by the difference from the rolling conditions predicted during calculation.

Regarding this, - numerically, a plate crown detector is installed at the exit side of the final stand of the hot rolling mill row, and feedback control is performed based on the difference between the actual value and target value of the plate crown. .

However, the feedback control described above has the disadvantage that no correction is made to the deviation amount of the plate crown from the target value for the part that is rolled before the plate crown is first measured and the control is started. . Moreover, the common method for measuring the plate crown is to scan a thickness gauge in the width direction of the plate and calculate the plate crown based on the plate thickness measurement results at each position in the width direction. The initial measurement of the plate crown will take a considerable amount of time. Therefore, if the plate crown in this area deviates significantly from the target value and the plate thickness at the edge of the plate width does not fall within the tolerance, the yield will drop significantly due to the cutting of this area.

One possible solution to this problem is to introduce a type of plate crown measuring device that can continuously measure the plate crown from the tip of the rolled material.

Furthermore, JP-A-60-5/1.216 discloses means for correcting work roll pending force based on the difference between predicted values and actual measured values (or estimated values during rolling) of rolling load and work roll crown amount. is proposed. With this means, control can be performed immediately after the rolling mill is caught in each stand.

[Problems to be Solved by the Invention] However, the former method of introducing a plate crown measuring device that can continuously measure the plate crown has a drawback in that it requires a large amount of equipment cost.

Furthermore, the latter method (JP-A-60-5421.6) does not consider rolling conditions other than rolling load and work roll crown amount, and this alone cannot be said to be sufficient. In particular, depending on the steel type of the rolled material, if the actual value of the rolling temperature deviates from the predicted value, there is a problem that the plate crown deviates significantly from the target value.

The present invention aims to solve such problems,
The deviation amount of the plate crown from the target value due to the difference between the measured value and the predicted value of the rolling temperature is reduced, and the accuracy of plate crown control over the entire length of the rolled material is improved at a low cost.
The object of the present invention is to provide a method for controlling plate crown during hot rolling.

[Means for Solving the Problems] In order to achieve the above object, the method for controlling the plate crown during hot rolling of the present invention (Claim 1) includes a method for controlling the crown of a plate during hot rolling according to the present invention. The amount of deviation from the target value of the plate crown due to the difference between the predicted rolling temperature value and the measured value is calculated as follows:
The transformation point of the rolled material determined by the steel type of the rolled material and the magnitude of the rolling temperature at each position in the width direction of the rolled material are determined, and the control amount of the crown control mechanism is determined during rolling according to the amount of deviation of the plate crown. It is characterized by correction.

Further, the method for controlling the plate crown during hot rolling of the present invention (claim 2) calculates the deviation amount of the plate crown from the predicted value and the actual measurement value of the rolling temperature for each rolling pass, and The present invention is characterized in that a correction amount of the control amount of the crown control mechanism is calculated from the deviation amount using a plate crown estimation model.

Furthermore, the method for controlling plate crown during hot rolling of the present invention (
Claim 3) calculates the deviation amount of the sheet crown after the final pass from the predicted value and the actual measurement value of the rolling temperature of at least one pass, and calculates the deviation amount of the sheet crown after the final pass by using a sheet crown estimation model. The present invention is characterized in that a correction amount of the control amount of the crown control mechanism of the two downstream paths is calculated.

[Function] In the above-described method for controlling plate crown during hot rolling of the present invention, the transformation point of the rolling margin determined by the steel type of the rolled material, that is, the amount of carbon contained and other contained elements, and each position in the width direction of the rolled material are determined. Considering the size of rolling temperature.

Therefore, the amount of deviation from the target value of the plate crown due to the difference between the measured value and the predicted value of the rolling temperature is calculated, and the control amount is corrected accordingly during rolling, so that the actual measured value of the rolling temperature By reducing the amount of deviation of the plate crown from the target value due to the difference between the calculated value and the predicted value, it is possible to improve the control accuracy of the plate crown over the entire length of the rolled material.

[Embodiment of the Invention] Fig. 5(a) shows the experimental results by the present inventors, and shows the plate crown estimation error (difference between the actual value and the estimated value) in line with the finish exit temperature of the rolled material. ), and for a certain steel type, the lower the rolling temperature, the larger the actual sheet crown value compared to the estimated value, and this tendency has a significant correlation with the amount of carbon content; The smaller the amount of carbon, the larger the plate crown estimation error. This tendency also occurs with other additive elements and as shown in Figure 5(b).
It also varies depending on whether or not the end of the plate is heated on the entry side of the rolling mill.

In hot rolling, under normal rolling conditions where local heating or cooling is not actively applied in the width direction of the rolled material, the strip temperature is lower at the strip width edges than at the strip width center. The temperature distribution becomes as follows.

As a result, as shown in Fig. 4(a), when the plate temperature is at or above the A3 transformation point of the rolled material over the entire region in the width direction, the distribution of the deformation resistance of the rolled material in the width direction is abrupt. The distribution increases slightly from the center of the sheet width to the ends of the sheet width without any change. However, as shown in Fig. 4(b), if the temperature at the center of the plate width is above the A3 transformation point and the temperature at the edge of the plate is below the A rs transformation point, the temperature near the edge of the plate In this case, the deformation resistance becomes significantly smaller due to changes in the crystal structure due to transformation of the rolled material. Therefore, in this case, the plate thickness near the plate width ends becomes significantly thinner, and the plate crown becomes larger.

In finish rolling, which is the main target of plate crown control, the plate temperature distribution does not change significantly depending on the rolling conditions, so conventional plate crown estimation models either assume that the deformation resistance of the rolled material is constant or 58-4
Even when determining the deformation resistance distribution from the humidity distribution as in No. 7245, the transformation of the rolled material is not taken into account. Therefore, when the temperature distribution in the width direction of the plate and the transformation point of the rolled material have a relationship as shown in FIG. 4(b), the plate crown estimation error increases. That is, even for rolled materials of the same steel type, the lower the rolling temperature is, or even at the same rolling temperature, the higher the transformation point, the larger the plate crown estimation error tends to be.

Figure 5(a) shows the properties of three steel types A, B, and C, which have almost the same compositional system but differ only in the carbon layer.
The results show the results of linear regression of the relationship between the exit side temperature and the plate crown estimation error using the conventional model on data of N number 100 or more. The crown estimation error increases, and this tendency is more pronounced for steel type A, which has a lower carbon content. This tendency is not seen in steel types with a high carbon content. This is because the lower the carbon content, the higher the A, a transformation point, and the easier the transformation of the rolled material to occur at the edge of the plate width.For steel type C, which has the highest carbon content, the finishing exit temperature is normal. It is considered that transformation at the edge of the plate width does not occur within the range of operating conditions. Similarly, for steel types that contain additive elements that affect above and below the A, 3 transformation point, it is easily assumed that the relationship between the finish exit temperature and plate crown estimation error differs depending on the transformation point.

FIG. 5(b) shows the influence of sheet width end heating on the entry side of the rolling mill for the steel type B. In the case of sheet width end heating (see symbol B'), the sheet crown estimation error There is no correlation between the temperature and the finishing outlet temperature. This is because the temperature distribution in the sheet width direction is almost uniform, so even if the finished exit temperature is low, only the sheet width edges do not undergo transformation, and the deformation resistance distribution remains constant regardless of temperature. It is from.

Based on the above considerations, the present inventors estimated the relationship between the temperature distribution of the rolled material and the transformation point, and developed a plate crown that takes into account changes in the deformation resistance distribution due to partial transformation in the width direction of the rolled material. We found that the accuracy of plate crown control can be significantly improved by using the estimation model.

In the present invention, as a plate crown correction method, the following (
1) Use the method expressed by Eq.

CR=CR''+ΔCR (1) Here, CR'' is the plate crown estimated value based on the conventional plate crown estimation model, and ΔCR is the plate crown correction amount due to the influence of metamorphosis.

The plate crown correction amount ΔCR is determined in advance through experiments or off-line theoretical analysis as a function of the Ara transformation point determined from each additive element and the rolling temperature. For convenience, it is calculated as a function of rolling temperature for each steel type.

In the present invention, based on the above formula (1), the plate crown correction amount is calculated from the predicted value of the plate temperature in the calculation of setting the control amount of the crown control mechanism, and the plate crown correction amount is calculated from the actual value of the plate temperature during rolling. and the plate crown correction amount, and the control amount of the crown control mechanism is corrected according to the difference between the two.

Strictly speaking, it is desirable to calculate the plate crown correction amount for each pass, as shown in FIG.

That is, at least one of the steel type and composition and the predicted value of the rolling temperature (center of the sheet width) of each pass used in the setting calculation are read (step Sl), and the A, 8 transformation point is determined from at least one of the steel type and composition. Estimate (step S2). The temperature distribution in the width direction of the strip is estimated from the predicted rolling temperature at the center of the strip width in each pass (step S3).

For the estimation in step S3, any formula may be used, including formulas based on experience, as long as the formula can express the temperature distribution in the board width direction. For example, according to heat transfer theory, it is known that the temperature distribution in the plate width direction can be approximated by a quadratic curve such as the following equation (2).

T=To-a-x-42)
Here, T is the temperature at the center of the board width, To is the temperature at the center of the board width, a is the coefficient, and X is the distance from the center of the board width.

The plate width end temperature estimated in step S3 and the A, 3 transformation point estimated in step S2 are compared for each pass, and the plate crown correction amount (predicted value) ΔCR of each pass is determined. (Step S4.).

Next, read the actual measurement value of the rolling temperature (step S5),
The temperature distribution in the board width direction for each pass (actual value) is estimated (step S6). In step S5, it is desirable to actually measure the temperature distribution in the board width direction for each pass, but the temperature at the center of the board width in at least one pass is actually measured, and based on that, in step S6, the temperature distribution in the board width center of the other passes is measured. The temperature distribution in the board width direction for each pass may be estimated. A method for estimating the temperature at the center of the strip width is disclosed, for example, in Special Report 1-Nα36 "Theory and Practice of Plate Rolling" edited by the Japan Iron and Steel Institute, pages 156 and 159 (published September 1, 1980). There is. In other words, the temperatures of the passes before and after the known pass temperatures can be found in sequence, taking into consideration cooling due to contact with rolls, water cooling, processing heat generation due to rolling, etc. The means for estimating the temperature distribution in the board width direction is the same as that used in step S3.

Then, from the plate width direction temperature distribution estimated in step S6 and the A, 3 transformation point estimated in step S2, the plate crown correction amount (
The actual value) (8CR) is calculated (step S7).

Once the predicted value and actual value of the plate crown correction amount for each pass are determined, the amount of correction of the control amount of the crown control mechanism for each pass can be easily determined (step S8). For example, when performing plate crown control using a work roll bender,
The plate crown CJ of each pass (first pass) is
As a conventional plate crown estimation model in equation 2), the Japanese Journal of Plastic Processing [Plasticity and Processing J vol, 25
(1286 No. 1034-=12-1041 pages (issued November 20, 1980)), if the model proposed is used, it is expressed by the following equation (3).

CR4=(]-5b)(ati4'i+azi°CW1
+a3rF, i+ (other influencing terms)) +9Ir (1
−r i) ・CRj−++ΔcRj −(
3) Here, 9!3 is the crown genetic coefficient, rl is the rolling reduction rate, Pj is the rolling load, CWi is the roll crown of the strip width, F□ is the work roll pending force, aii + a2
□+a3i is the influence coefficient.

'-2 In formula (3), considering the change from the setting calculation by focusing on the pending force Fj and CRj to the plate crown correction amount, δCR1 = (], -'74.)' a3j, 'δF, published It is expressed as ΔCR)−ΔcRs)−(4). Here, δ
represents the deviation from the set calculation.

Therefore, the amount of correction of the pending force for each pass can be determined as shown in the following equation (5) by setting the change δCRj from the plate crown setting calculation to zero in equation (4).

More simply, as shown in Figure 2, the steel type or A,
3. Sheet crown correction amount (ΔCRP and Δ
CR,) may be determined for the predicted value and the measured value of the rolling temperature (steps A1 to A5), and based on the difference, the amount of correction of the control amount of the crown control mechanism for each pass may be determined (
Step A6).

A method for determining the correction amount of the control amount for each pass will be described below, taking as an example the case where plate crown control is performed using a work roll bender.

The influence of the bending force modification of each pass on the plate crown and plate shape after the final pass is expressed by the following equations (6) and (7) from the plate crown estimation model.

δCRN=AN5 FN+AN-1δFN-□+...
+A□δF, ... (6) δλ, =]3NδF N +
B N -1δFN-1+・10B1δF1...
(7) Here, A4. Bj (i = 1 to N) is an influence coefficient, which can be expressed using the above-mentioned 'J j, + rj + a3i.

On the other hand, the condition for correcting the amount of deviation of the plate crown from the target value is the following equation (8).

δCRN+ (ΔCR knee ΔCR,:) = O・(8
) Furthermore, in the method of the present invention, the following equation (9) is used, taking into consideration that the plate shape after the final pass is not disturbed by the correction of the plate crown.
Add the condition.

δλ1=0 ・(9)(8),(9)
By substituting the equation (6L(7) into the equation), the two equations (1, 0) which are necessary conditions in the method of the present invention.

(11) is obtained.

(ΔCR knee ΔCRY) = A, δF2+...ten A1δ
F1...(10)0=BN8FN+...10B, δF
1...(11) Therefore, the number of unknowns,
That is, the number of passes for modifying the pending force requires at least two passes, and can be arbitrarily selected from 2 to N. However, if the correction is performed in three or more passes, it is necessary to provide m-2 independent conditions, where m is the number of correction passes. For example, when correction is performed in three passes from the N-2nd pass to the final Nth pass, conditions such as the following equation (12) are given.

δF N-1= d・δFN2...(
12) Here, d is a constant.

(]O), (11), (]2) and δpN-3=...
- From the 15 conditions of δF, =O, the pending force correction amount δFj of each pass can be obtained.

In addition, the m correction passes can be arbitrarily selected from the 1st pass to the Nth pass, but in reality, corrections made in the upstream pass have little effect on the plate crown and plate shape after the final pass. Therefore, it is likely that the determined correction amount will exceed the equipment capacity. Therefore, it is desirable to implement the method of the present invention including at least the downstream path.

FIG. 3 shows the effect when the method of the present invention is applied to the crown control of a 7-stand hot rolling sheet.
The difference between the actual measured value and the predicted value of the finish side temperature at the tip of the rolled material is classified into seven categories, and the actual value of the plate crown in each category (1st measurement value with a crown meter) is calculated. This is a plot of the average value of the difference from the target value. As shown in FIG. 3, when the method of the present invention is not implemented, the larger the difference between the measured rolling temperature value and the predicted value, the greater the deviation of the sheet crown from the target value tends to be. However, by implementing the present invention, a plate crown that was exactly as expected was obtained regardless of the prediction error of the rolling temperature.

[Effects of the Invention] As detailed above, according to the method for controlling plate crown during hot rolling of the present invention (claims - to 3), predicted values and actual measurements of the transformation point and rolling temperature of the rolled material can be improved. The control amount of the crown control mechanism is corrected during rolling by taking into account the relationship between the rolling temperature and the actual value. It is possible to reduce the amount of steel and greatly improve plate crown control accuracy over the entire length of the rolled material at a low cost.

[Brief explanation of the drawing]

Figures 1 and 2 are flowcharts for explaining a method for controlling plate crown during hot rolling as an embodiment of the present invention, and Figure 3 is a flowchart for explaining the effect of the method of this embodiment. Figures 4 (a) and (b) are graphs showing changes in deformation resistance due to the relationship between the temperature distribution in the sheet width direction and the A and 3 transformation points, and Figures 5 (a) and (b). ) is a graph showing the relationship between the finish side temperature and the plate crown estimation error.

Claims (3)

[Claims] (1) In the sheet crown control method during hot rolling using computer control, the difference in the sheet crown from the target value due to the difference between the predicted value of the rolling temperature and the actual value used for calculation of the control amount of the crown control mechanism is The amount of deviation is determined by considering the transformation point of the rolled material determined by the steel type of the rolled material and the magnitude of the rolling temperature at each position in the width direction of the rolled material, and the control amount of the crown control mechanism is determined according to the amount of deviation of the sheet crown. A method for controlling plate crown during hot rolling, characterized by correcting the crown during rolling. (2) Calculate the deviation amount of the plate crown from the predicted value and the measured value of the rolling temperature for each rolling pass, and correct the control amount of the crown control mechanism using the plate crown estimation model from the deviation amount for each pass. Claim 1 characterized in that the amount is calculated.
The described method for controlling sheet crown during hot rolling. (3) Calculate the deviation amount of the plate crown after the final pass from the predicted rolling temperature value and the measured value of at least one pass, and use the plate crown estimation model from the deviation amount after the final pass to calculate at least two downstream passes. 2. The method of controlling a sheet crown during hot rolling according to claim 1, further comprising calculating a correction amount of a control amount of said crown control mechanism.