JP7294278B2 - Strip thickness control method in cold rolling mill - Google Patents

Description

The present invention relates to a strip thickness control method in a steel strip cold rolling mill.

In a cold rolling line that continuously rolls a steel strip, the roll gap of a rolling stand is used as an operating end, and the measured strip thickness on the delivery side measured by a strip thickness gauge on the delivery side of the rolling stand is returned as a feedback amount. (Also referred to as monitor AGC. AGC=Automatic Gauge Control) is generally performed to control the delivery side strip thickness of the rolling stand according to the set value of the target strip thickness.

In the proportional-integral control (hereinafter also referred to as PI control) used for the proportional-integral feedback control, the control output V(t) is expressed by the following equation (1).
V(t)=Kp×e(t)+Ki× _∫0t e( ^τ )dτ (1)
Here, e(t) and e(τ) are plate thickness deviations at times t and τ, respectively, and represent the deviation between the measured plate thickness by the plate thickness meter and the target plate thickness. Kp and Ki are called proportional gain and integral gain, respectively, and are set to adjust the amount of response of the control output. ∫ ₀ ^t e(τ)dτ is the time integral of the plate thickness deviation e(τ) from time 0 to t, and is called an integral term.

PI control is a combination of proportional control (P control) and integral control (I control). In the case of only P control, if the proportional gain Kp is too small, an offset, which is a deviation between the target plate thickness and the measured plate thickness, will occur, and if it is too large, overshoot and hunting will occur. By combining with , the offset can be eliminated. Therefore, PI control in which both are combined is widely applied to thickness control in cold rolling of steel strips.

By the way, some cold-rolled steel strips have a welded portion where a preceding material and a succeeding material are joined.

Before welding, the preceding material and the succeeding material are composed of a section called a stationary part that is rolled under tension during hot rolling, and a section on the central side in the longitudinal direction called a stationary part, and one end that is connected to the stationary part and becomes a free end without tension. It has two sections called the unsteady section rolled in the state, one on the longitudinal tip side and the other on the tail end side. In addition, since the temperature at the tip and tail ends of the steel plate tends to decrease during hot rolling, the deformation resistance in hot rolling is greater than that in the stationary part, and the rolling load increases, so the tip and tail ends of the steel plate There is a tendency for the plate thickness to increase at the part.

Usually, the length of the unsteady portion is about 5 to 20 m, the plate thickness of the unsteady portion is thicker than the steady portion, and the plate thickness difference from the steady portion is about 100 μm at maximum.

When welding the preceding and succeeding materials on the entry side of the cold rolling line, the trailing edge of the preceding material and part of the leading edge of the succeeding material (truncated part) are cut off with a shear, and the preceding and following materials are separated. In general, the length of the truncated part in the rolling direction is about 100 mm at most, which is shorter than the unsteady part, so as shown in FIG. Both the trailing end side of the preceding material 6 ₁ and the leading end side of the following material 6 ₂ include the unsteady portion 21 .

In some cases, the target of PI control is a steel strip having a welded portion where a preceding material and a succeeding material are joined, and control is performed to change the running strip thickness before and after the welded portion. In this case, due to changes in the rolling conditions (target thickness, width, strip tension, etc.) from the preceding material to the succeeding material, the automatic strip is PI control in thickness control is temporarily turned OFF (stopped). On the other hand, if the amount of change in rolling conditions before and after the welded part including the welded part is small and there is no need to change the running strip thickness before and after the welded part, the unsteady part including the welded part is steady while passing through the rolling stand. As in the case of the welded portion, the PI control is kept ON, and the PI control is continued for the unsteady portion before and after the welded portion including the welded portion.

However, even in such an unsteady section including a weld that does not need to change the strip thickness between runs, the thickness deviation is larger than that in the steady section. The integral term of equation (1), which is given by the time integration of , may not converge even if the strip threading object moves from the unsteady section to the steady section. In this case, the plate thickness control overshoots at the steady portion on the leading end side of the trailing material, and a phenomenon occurs in which the plate thickness after rolling deviates from the tolerance of the target plate thickness (hereinafter also referred to as off-gauge). This generated portion is called an off-gauge generation area, and it becomes a problem because the product yield of the cold-rolled steel sheet deteriorates.

In FIG. 8, if the unsteady portion 21 of the preceding material and the succeeding material is cut off before joining the preceding material and the succeeding material, it is expected that the above-described off-gauge will not occur. However, in that case, even the unsteady portion that does not lead to off-gauge generation after rolling is discarded before rolling, and the product yield of the cold-rolled steel sheet is rather deteriorated.

On the other hand, the following patent documents disclose countermeasures for reducing the off-gauge of the unsteady portion of the distal end and/or the tail end.

In Patent Document 1, in batch rolling of a steel strip, when controlling the plate thickness of the tip of the steel strip, after the tip passes through one rolling stand, the rolling speed of the one rolling stand reaches a predetermined speed. After reaching the rolling speed and starting operation of the monitor AGC whose control output item is this rolling speed, only P control is performed until the strip thickness deviation of the steel strip converges within the target value, and after convergence within the target value, PI control Disclosed is a method for switching to In this case, the timing of switching from P control to PI control is determined using the actual measurement value of strip thickness on the delivery side of the rolling mill. is also set large.

In Patent Document 2, in continuous rolling of a steel strip, when the strip thickness deviation exceeds a threshold value, the proportional gain Kp of PI control whose control output item is the reduction position or the roll peripheral speed is increased, and the integral gain Ki is decreased. A method for quickly converging the plate thickness deviation is shown. Determination of such a gain manipulated variable is performed using an actual measurement value of the strip thickness on the delivery side of the rolling mill. However, Patent Literatures 1 and 2 do not disclose the rolling control of the welded portion between the preceding material and the succeeding material.

Technologies related to rolling control of the welded portion between the preceding material and the succeeding material are disclosed in the following patent documents.

In Patent Document 3, in order to prevent breakage of the welded part, the undergauge amount of the plate thickness on the delivery side of the final stand is estimated, and if this amount is less than the reference value, the thickness gauge on the delivery side of the first stand is used. is controlled by adding a correction value to the feedforward (FF) AGC for tension control in a predetermined section before and after the welded portion passes through. Gauge meter AGC and monitor AGC are stopped when reaching a predetermined position in front of the stand, the roll gap of the first stand is opened by a predetermined correction amount, and when the welding part passes the first stand, it is closed by the correction amount. A method is disclosed. In addition, FFAGC control is stopped from the position before the thickness gauge until the weld passes through the thickness gauge, and when the weld passes through the thickness gauge, FFAGC is resumed, and the roll gap of the first stand is restored. A method is also disclosed for restarting the gauge meter AGC upon returning to .

In Patent Document 4, the detection value of an entry-side plate thickness gauge provided on the entry side of a continuous tandem rolling mill is tracked to the roll-down position of the first stand (each position in the longitudinal direction of the steel strip corresponding to each detection value is tracked to the first stand). In the plate thickness control method by the so-called roll-down feedforward (roll-down FF) AGC, which operates the roll gap of the first stand (based on each detection value at each time when the roll-down position of one stand is sequentially reached), In order to improve the thickness accuracy without being affected by the thickness variation on the entry side of the rolling mill, the influence coefficient of the rolling load on the thickness deviation on the entry side is calculated before the weld reaches the thickness gauge on the entry side. On the other hand, before the weld passes through the entry thickness gauge and reaches the first stand, the entry thickness deviation before and after the weld is detected and obtained, and based on the entry thickness deviation and the influence coefficient Calculate the load fluctuation amount, calculate and obtain the roll gap change amount to compensate for the fluctuation amount, and change the roll gap of the first stand by the above roll gap change amount immediately after the weld passes the first stand. A method for doing so is disclosed.

JP-A-62-158516 JP-A-63-123504 JP-A-06-079325 JP-A-10-192934

However, when the methods of Patent Documents 1 and 2, which target steel strips without welds, are applied to steel strips with welds, the method of Patent Documents 1 requires integral control in an unsteady portion. cannot be applied, the proportional gain Kp must be set large even in the unsteady part before and after the weld, including the weld, and the control output by the proportional control becomes excessive, resulting in hunting of the operation amount and plate thickness deviation. There is concern about the occurrence of steady-state deviation. In addition, since the actual measurement value of the strip thickness at the delivery side of the rolling mill is used to determine whether to switch between proportional control and proportional integral control, it is necessary to wait until the steady state reaches the thickness gauge at the delivery side of the rolling mill before making a decision. Therefore, the switching timing is delayed, and it is not possible to efficiently prevent the generation of off-gauge at the steady portion on the leading end side of the succeeding material.

When the method of Patent Document 2 is applied to the plate thickness control of the unsteady portion before and after the weld including the weld, proportional control becomes dominant, and there is concern about the occurrence of hunting of the manipulated variable and steady deviation of the plate thickness deviation amount. be. Furthermore, since the gain operation amount is determined using the actual measurement value of the strip thickness on the delivery side of the rolling mill, the gain operation timing is delayed, and it is difficult to reduce the off-gauge generation area of the steady portion on the tip side of the trailing material. Can not.

Further, Patent Document 3 is a technique for preventing breakage of welds by devising an operation method of FFAGC for tension control combined with gauge meter AGC and monitor AGC. No consideration is given to off-gauge occurrence in the stationary portion due to the integral term of PI control not converging on the leading end side of the trailing material. Furthermore, the FFAGC of Patent Document 3 is a means for controlling the plate thickness on the delivery side of the second stand based on the measurement result of the plate thickness gauge on the delivery side of the first stand. As means for controlling the thickness to the target value, feedback control by the monitor AGC is mainly used. Therefore, as for the plate thickness control on the delivery side of the first stand, since it is a normal monitor AGC, it cannot be said that the effect of reducing the off-gauge generation range is sufficient.

In addition, Patent Document 4 discloses an improved technique for plate thickness control by reduction FFAGC, and in the first place does not disclose proportional integral feedback control using PI control. No consideration is given to off-gauge occurrence in the stationary part due to the fact that the integral term of PI control does not converge at . In addition, in strip thickness control by roll reduction FFAGC, the deviation from the target value of strip thickness at the delivery side of the rolling stand cannot be eliminated, so off-gauge may occur.

In view of the above-mentioned problems, the present invention is a cold rolling mill that does not change the running thickness of an unsteady portion including a welded portion of a steel strip and continues proportional-integral control in feedback control. To improve the product yield of cold-rolled steel sheets by reducing the off-gauge generation area of the stationary part on the tip side of the trailing material while maintaining the plate thickness accuracy of the tail end, and reducing the amount of steel strip cut off before and after the weld. To provide a strip thickness control method in a cold rolling mill.

The present inventors have made intensive studies to solve the above problems, and as a result, the proportional integral control is continued without changing the running plate thickness for the unsteady part including the weld, and the weld is the rolling stand. After passing through the reduction position, the present inventors have come up with a method of resetting the integral term for initializing the integral term of the PI control, and have made the present invention having the following gist and configuration.
[1] A thickness control method in a cold rolling mill for a steel strip having a welded portion joining a preceding material and a succeeding material, comprising:
Perform proportional integral control with the roll gap of the rolling stand as the operating end,
continuing the proportional integral control for the unsteady portion before and after the welded portion;
A plate thickness control method in a cold rolling mill, characterized in that after the welded portion passes through the reduction position of the rolling stand, an integral term is reset to initialize the integral term of the proportional integral control.
[2] The strip thickness control method in a cold rolling mill according to [1], wherein the preceding strip and the trailing strip have the same strip thickness and strip width.
[3] The strip thickness control method for a cold rolling mill according to [1] or [2], wherein a difference in tensile strength between the preceding material and the succeeding material is 30 MPa or less.
[4] The cold rolling according to any one of [1] to [3], wherein the rolling stand having the roll gap as an operating end is the first stand of a tandem cold rolling mill. Thickness control method in machine.
[5] Any one of [1] to [4], wherein the resetting of the integral term is performed at the timing when a portion of the succeeding material having a predetermined length L from the welded portion has completed rolling. Sheet thickness control method in the cold rolling mill according to.
[6] The plate in the cold rolling mill according to [5], wherein the predetermined length L is determined based on the measured value of an entry-side plate thickness gauge installed on the entry side of the cold rolling mill. Thickness control method.

According to the present invention, the proportional gain Kp and the integral gain Ki are not operated while the unsteady portion including the welded portion passes through the rolling stand, and the integral term is reset after the welded portion passes through the reduction position of the rolling stand. As a result, without impairing the controllability of the unsteady portion on the tail end side of the preceding material, overshooting of the operation amount in the steady portion on the tip side of the following material after the weld is prevented, and the off-gauge generation area is reduced. There is an effect that the product yield of cold-rolled steel sheets can be improved.

Further, according to the present invention, by determining the timing of resetting the integral term based on the detection of the welded portion at the entry side of the rolling mill, the integral term is reset at the moment when the welded portion has completely passed directly below the first stand. It is possible to update the control, and compared to the case of switching from proportional control using the measured value of the strip thickness on the delivery side of the rolling mill to proportional integral control (Patent Document 1) and determining the gain operation amount (Patent Document 2), There is also the effect that it is possible to update the integral control at a timing that more closely matches the actual situation.

1 is a system configuration diagram showing an example of a strip thickness control method in a cold rolling mill used in an embodiment of the present invention; FIG. 2 is a block diagram of a PI control unit 100 of FIG. 1; FIG. FIG. 4 is a diagram showing an example of transition of delivery side plate thickness deviation [S1−S2] and roll gap change amount S4 before and after a welded portion according to the present invention; FIG. 9 is a diagram showing an example of changes in delivery side plate thickness deviation [S1−S2] before and after a welded portion and roll gap change amount S4 according to a comparative example; FIG. 2 is a system configuration diagram showing an example of a plate thickness control method in which an entry-side plate thickness gauge is added to FIG. 1 to enable use of an entry-side measured plate thickness; 6 is a block diagram of the PI control unit 100 of FIG. 5; FIG. FIG. 6 is an explanatory diagram showing a method of determining an unsteady portion length on the leading end side of a trailing material after a welded portion on-line by the plate thickness control method of FIG. 5 ; It is a schematic diagram which shows the state before welding of a preceding material and a succeeding material, and before cold-rolling after welding.

[Cold rolling mill]
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1 and 2 are respectively a system configuration diagram and a block diagram of the PI control unit 100 of FIG. A steel strip 6 is being rolled in a rolling stand 4 of a cold rolling mill. The steel strip cold-rolled by the cold rolling mill has a raw material thickness range of 1.2 to 3.2 mm, a width range of 800 to 1300 mm, and a product thickness range of 0.12 to 1.6 mm. However, the material plate thickness range, the plate width range, and the product plate thickness range of the steel strip cold-rolled by the cold rolling mill are not limited to these ranges.
[Welded part of preceding material and succeeding material]
As described above, the steel strip 6 has the welded portion 11 joining the preceding material 6 ₁ and the succeeding material 6 ₂ . An unsteady portion 21 is formed before and after the welded portion including the welded portion 11 , and the steady portion 20 continues to the unsteady portion 21 on the opposite side of the welded portion 11 . The plate thickness of the unsteady portion 21 is thicker than that of the steady portion 20 . (See the enlarged view of part A in FIG. 1 and FIG. 8).

Welding may be, for example, laser welding, carbon dioxide welding, or other arc welding. In addition, it is preferable to appropriately perform the surplus processing of the welded portion.
[Use the roll gap as the operating end]
In the system configuration of FIG. 1, a pair of entry-side bridle rolls 9 that apply tension to the steel strip 6 on the entry side of the rolling stand 4, the roll peripheral speed of the entry-side bridle rolls 9 is detected, and the bridle roll peripheral speed S5 is detected. A roll peripheral speed detector 10 that outputs a roll gap of the rolling stand 4, a roll gap of the rolling stand 4 as an operating end, a roll gap control device 3 that commands the roll gap change amount S4 to the roll gap cylinder 5, and a delivery side of the rolling stand 4 (Downstream side) detects the plate thickness of the steel strip 6 and outputs the measured plate thickness S2 on the delivery side. It has a weld sensor 12 that outputs a detection signal S6.

Here, the reason why the roll gap is used as the operating end is that the plate thickness can be easily changed by changing the roll gap because the plastic coefficient is relatively small in the front stand of the cold rolling mill. In addition, when the FFAGC is used together, the peripheral speed of the roll is often used as the operating end, and this is to avoid the operating end from interfering with each other.

The system configuration of FIG. 1 further includes a first computer 1 (hereinafter simply referred to as computer 1) having a PI control unit 100 and an integral term reset command unit 101 as means for executing monitor AGC, and a target plate in computer 1. It has a second calculator 2 (hereinafter also simply referred to as calculator 2) for inputting the thickness S1.

An integral term reset signal S7 is input to the PI control unit 100 from the integral term reset command unit 101 through the gate G2.

Calculator 2 also outputs G1 switching signal S8 and G2 switching signal S10, for example, opening/closing gates G1 and G2 with signal values, eg, 1/0, respectively.
[Proportional-integral control for unsteady parts before and after the weld]
In the present invention, there is no need to change the running strip thickness, and the PI control is turned ON during the passage of the unsteady portion 21 before and after the welded portion including the welded portion 11 as well as during the passage of the steady portion 20. It is targeted for the case where it remains (continues). The continuation of this PI control is executed by keeping the gate G1 open.

On the other hand, when changing the running strip thickness, which is not the object of the present invention, the gate G1 is opened while the stationary portion 20 is passing through the rolling stand 4 to continue PI control, and at least the welding portion 11 is passing through the rolling stand 4. During the operation, the gate G1 is closed to temporarily turn off the PI control. During this OFF period, the target plate thickness S1 is changed, or the proportional gain Kp and/or the integral gain Ki are changed as necessary. After that, after the preset section including the welded portion 11 passes through the rolling stand 4, the PI control is turned ON (the gate G1 is opened). Note that the computer 2 detects the time period during which a preset section including the welded portion 11 is passing through the rolling stand 4, which is determined by the welded portion detection signal S6 and the bridle roll peripheral speed S5. It is identified by tracking the position of the longitudinal section along the direction of strip travel.

In the tandem cold rolling mill, when the welded portion 11 passes through the rolling stand, the rolling speed of the stationary portion (final stand or final speed of the steel strip on the exit side of the stand). For example, the rolling speed is appropriately set within the range of 150 to 500 m/min. However, the rolling speed is not necessarily constant over the entire length of the unsteady portion on the trailing end side of the preceding material and the unsteady portion on the leading end portion of the following material. Rolling speed may be increased.
[Integral term reset]
In the present invention, when the gate G1 is opened, the gate G2 is also opened to allow passage of the integral term reset signal S7.

The PI control unit 100 continuously receives the target strip thickness S1 from the calculator 2 and the delivery-side measured strip thickness S2 from the delivery-side strip thickness gauge 7 from the start to the end of the cold rolling of the steel strip 6, and A screw-down amount deviation signal S3 is generated according to the block diagram, and is input to the screw-down cylinder control device 3 through the open gate G1. The screw-down cylinder control device 3 generates a roll gap change amount S4 from the input screw-down amount deviation signal S3 and inputs it to the screw-down cylinder 5 . The reduction cylinder 5 operates the roll gap of the rolling stand 4 by an amount corresponding to the input roll gap change amount S4.

When the PI control unit 100 receives an integral term reset signal S7 from the integral term reset command unit 101 through the open gate G2, the PI control unit 100 resets the integral term to initialize the integral term.

Here, the “integral term reset” means that the PI control unit 100 recognizes the time τ=tr at the time of input of the integral term reset signal S7, and resets the integral term from ∫ ₀ ^t e(τ)dτ to ∫ _tr ^t e(τ)dτ=∫ ₀ ^t e(τ)dτ−∫ ₀ ^tr e(τ)dτ. This is equivalent to switching the integral control transmission element from "Ki/s" to "Ki×(1/s-1/s ^' )" in the block diagram (FIG. 2). Here, "Ki/s ^' " is a transfer element in a transfer function obtained by Laplace-transforming "Ki×∫ ₀ ^tr e(τ)dτ". Note that the time τ=0, which is the lower limit of the integration range of the integral term before resetting the integral term, is the time when the PI control is started.

As a result, the integral term is once returned to zero at the time τ=tr, and from there the time integration of e(τ) is executed with the lower limit of the integral range tr.

In resetting the integral term, as described above, only the lower limit of the integral range of the integral term is changed, and the integral gain Ki and the proportional gain Kp are not changed.
[Action and Effect by Integral Term Reset]
The effect of resetting the integral term of the present invention will be described by comparison with a comparative example.

The example of the present invention is an example in which the gate G1 and the gate G2 are opened in FIG. 1, and the integral term is reset while continuing the PI control. A comparative example is an example in which the gate G1 is opened and the gate G2 is closed in FIG. 1, and the integral term is not reset as in the conventional case while continuing the PI control.

FIG. 4 shows an example of changes in the delivery side plate thickness deviation [S1-S2] before and after the weld and the roll gap change amount S4 according to the comparative example. In the comparative example, the integral term accumulated and remaining from before the welded portion 11 does not converge at the unsteady portion 21 after the welded portion 11, and as a result, as shown in FIG. A large downward deflection (deviation to the thin side) occurs, and after shifting to the steady state 20, the roll gap change amount S4 greatly overshoots to the open side and returns to near zero. (eg about 55m) appeared.

On the other hand, FIG. 3 shows an example of transition of the delivery side plate thickness deviation [S1-S2] before and after the weld and the roll gap change amount S4 according to the present invention. In the present invention, the integral term is initialized after the welded portion 11 passes through the reduction position of the rolling stand 4 . The "rolling position" is a position that defines the roll gap, and corresponds to the position of the intersection of the straight line perpendicular to the upper and lower roll axes and the pass line. By such initialization of the integral term, the residual integral term accumulated from before the welded portion 11 is deleted, and the newly accumulated integral term is accumulated from zero, so convergence is quick, and as a result, as shown in FIG. In addition, the downward deflection (deviation to the thin side) of the delivery side plate thickness deviation [S1-S2] becomes small, and the overshoot to the open side of the roll gap change amount S4 after shifting to the steady section 20 also becomes small, and zero The time to return to the vicinity has been shortened, and the off-gauge generation area has been reduced (eg, about 6m). In the examples of FIGS. 3 and 4, the rolling speed (peripheral speed of the roll at the final stand) was about 300 m/min in the steady portion and the same speed in the unsteady portion, and rolling was performed at a constant speed.

That is, in the present invention, by resetting the integral term after the unsteady portion on the tail end side of the preceding material before the weld passes through the reduction position of the rolling stand, the PI for the unsteady portion on the tail end side of the preceding material before the weld is While maintaining the plate thickness controllability by control, the convergence due to the accumulation and residual of the integral term from the unsteady part on the tail end side of the preceding material before the weld to the steady part on the tip side of the following material after the weld. This has the effect of preventing a delay, thereby exhibiting the effect of reducing the off-gauge generation area.
[Thickness and width of the same class]
As described above, the present invention is directed to a steel strip in which the running strip thickness is not changed before and after the weld. As a steel strip that does not change the thickness between runs before and after the welded portion, for example, there is a steel strip that has "the same section thickness and width". "Thickness and width of the same section" means that the difference in material thickness between the preceding and succeeding materials is 0.1 mm or less, the difference in width is 50 mm or less, and the preceding and succeeding materials and the difference in target product thickness is within ±5%. If the dimensional difference between the preceding material and the succeeding material is within such a range, there is no need to change the running plate thickness, and the unsteady part before and after the weld, including the weld, can be monitored with the monitor AGC turned on. This is because it can be passed through a rolling stand. Therefore, in the present invention, it is preferable that the preceding material and the succeeding material have the same thickness and width.

In addition, there is a case where the running strip thickness is not changed even for a steel strip in which the difference in deformation resistance between the preceding material and the succeeding material corresponds to a difference in tensile strength of 30 MPa or less as a thin steel plate product. Therefore, in the present invention, it is preferable that the difference in tensile strength between the preceding material and the succeeding material is 30 MPa or less.
[First stand of tandem cold rolling mill]
The cold rolling mill used in the present invention may be either a single stand type cold rolling mill or a tandem type cold rolling mill, but the tandem type is preferable from the viewpoint of rolling efficiency. In the case of the single stand type, only one rolling stand is used in the present invention. On the other hand, in the case of the tandem type, if the integral term is reset at the first stand, the delivery side plate thickness deviation at the unsteady portion before and after the weld becomes small from the second stand onwards without resetting the integral term. Therefore, further lengthening of the off-gauge generation area does not occur. Therefore, in the present invention, it is preferable that the rolling stand whose operating end is the roll gap is the first stand of the tandem cold rolling mill. This is also because the roll gap of the first stand has the greatest effect on the strip thickness on the delivery side of the final stand of the tandem cold rolling mill.
[Timing for resetting the integral term: setting the predetermined length L offline]
In the present invention, the reset of the integral term is performed after the welded portion 11 passes the roll-down position of the rolling stand 4. However, the timing of resetting the integral term can be, for example, immediately after the welded portion 11 has passed the roll-down position of the rolling stand 4. I do not care. By initializing the integral term accumulated in the plate thickness control of the unsteady portion 21 on the tail end side of the preceding material 6 ₁ on the leading edge side of the trailing material 6 ₂ , the unsteady portion 21 of the trailing material 6 ₂ This is because delay in convergence of the integral term can be prevented.

On the other hand, the timing of resetting the integral term is even after the unsteady portion 21 of the succeeding material 6 ₂ has been rolled by a predetermined length L after the welded portion 11 has passed the roll-down position of the rolling stand 4. good. Even in the unsteady portion 21 on the tip side of the trailing material 6 ₂ , the integral term is accumulated due to plate thickness control there, and then the convergence of the integral term is delayed when shifting to the following steady portion 20. Therefore, such This is because the delay in convergence of the integral term in the stationary portion 20 of the trailing material 6 ₂ can be prevented by initializing the integral term at the time of transition.

At that time, the predetermined length L can be set in advance, for example, 1 to 5 m. Further, the predetermined length L may be set individually as a table value obtained empirically according to attributes such as thickness, width and steel type of the material to be rolled. The predetermined length L depends on the length of the unsteady portion 21 on the tip side of the trailing material ₆₂ , and this dependent length also changes depending on the manufacturing conditions in the hot rolling line in the preceding process. This is because it often changes depending on the manufacturing specifications of the material.

In the example of FIGS. 1 and 2, the integral term reset command unit 101 outputs the weld detection signal S6 The weld 11 is detected by the input of , and the moving distance of the weld 11 after detection is calculated from the time integration calculation of the bridle roll peripheral speed S5, thereby sequentially tracking the weld 11 (also referred to as weld tracking). , the time when the unsteady portion 21 of the predetermined length L from the welded portion 11 of the succeeding material 6 ₂ completes passing through the roll-down position of the rolling stand 4 is recognized as the timing of resetting the integral term, and at this timing the integral term It is configured to output a reset signal S7.

If the predetermined length L is set to L=0, the integral term can also be reset when the welded portion 11 has completely passed through the roll-down position of the rolling stand 4 .

As the weld zone sensor 12 used for the weld zone tracking, for example, an optical or magnetic detection sensor can be used. The optical sensor, which is an optical detection sensor, emits light from one of the top and bottom sides of the steel strip with a light projector, and the light that has passed through the detection hole drilled corresponding to the weld is installed on the other side. Passage of the welded portion can be detected by detecting it with a light receiver such as a camera attached to it. In addition, the magnetic sensor, which is a magnetic detection sensor, is equipped with, for example, an eddy current sensor. Passage can be detected.

Also, as the delivery side plate thickness gauge 7, an ultrasonic thickness gauge, an X-ray thickness gauge, a gamma-ray thickness gauge, or the like can be preferably used.
[Timing for resetting the integral term: Determining the predetermined length L online]
In addition, from the viewpoint of suppressing as much as possible the delay in convergence in the following steady portion due to the accumulation/remaining of the integral term in the unsteady portion on the leading end side of the following material after the welding portion, the predetermined length L is It is preferable to use the unsteady length of the trailing material tip side after the cut, and it is better to determine this unsteady length online based on the measured plate thickness on the entry side rather than setting it off-line. This is preferable because it allows the use of non-stationary lengths that are close to reality.

The method of determining the length of the unsteady portion on the leading end side of the trailing material after the welding portion online will be described with reference to FIGS. 5, 6 and 7. FIG.

FIG. 5 is a system configuration diagram showing an example of a plate thickness control method in which an entry-side plate thickness gauge 8 is added in FIG. 1 and the entry-side measured plate thickness S9 can be used. 1 is a block diagram of unit 100. FIG. As the entry plate thickness gauge 8, an ultrasonic thickness gauge, an X-ray thickness gauge, a gamma-ray thickness gauge, or the like can be preferably used. FIG. 7 is an explanatory diagram showing a method of determining the length of the unsteady portion on the leading end side of the trailing material after the welded portion on-line by the plate thickness control method of FIG.

In FIG. 7, the curve in the figure is a curve (hereinafter also referred to as S9 curve) showing the transition of the entry-side measured plate thickness S9 measured by the entry-side plate thickness gauge 8 (FIG. 5), and point A on the S9 curve is , when the integral term reset command unit 101 (FIG. 5) receives the weld detection signal S6 output by the weld sensor 12 (FIG. 5) upon detection of the weld 11. FIG. The integral term reset command unit 101 starts a calculation (also referred to as a primary calculation) for successively time-integrating the bridle roll peripheral speed signal S5 with point A as a starting point. The point in time (point B in FIG. 7) when the moving distance of the portion 11 along the direction of movement of the steel strip satisfies the distance from the welded portion sensor 12 to the entry-side plate thickness gauge 8 is specified, and the primary calculation ends.

Then, simultaneously with the end of the primary calculation, a calculation (also referred to as a secondary calculation) for successively time-integrating the bridle roll peripheral speed signal S5 is started with point B as a starting point. tracks the moving distance of the welded portion 11 along the direction of movement of the steel strip. Then, in parallel with the secondary calculation, the value of the S9 curve is sequentially compared with the determination thresholds (+) and (-) of the unsteady length, and the value of the S9 curve is within the determination threshold (between + and -). The point of time (point C in FIG. 7) is specified. Since the moving distance of the welded portion 11 along the direction of movement of the steel strip from point B is equivalent to the distance in the longitudinal direction of the steel strip from the welded portion 11 to the downstream side, point C This corresponds to a point along the longitudinal direction of the steel strip where the plate thickness along the longitudinal direction of the strip falls within the judgment threshold value. corresponds to the unsteady length of Therefore, the distance X is determined as the unsteady length on the leading end side of the trailing material after the welded portion. After that, the second calculation ends.

The process of determining the distance X by the above-described first and second calculations can be performed online by adding the execution means of the process to the integral term reset command unit 101 or by adding it to the computer 2. It can be done prior to the passage of the rolling stand 4 of the section 11 . When the calculator 2 determines the distance X, it transmits the determined distance X to the integral term reset command unit 101 by suitable transmitting means (not shown).

The integral term reset command unit 101 applies the determined distance X to the value of the predetermined length L.

Furthermore, when adopting the thickness control method shown in FIG. 5, an entry side thickness gauge 8 is provided on the entry side of the tandem cold rolling, and tracking means from this entry side thickness gauge 8 to the first stand is provided. Therefore, a strip thickness control system may be configured that also uses the rolling feedforward AGC described in Patent Document 4.

In this embodiment, the unsteady portion on the tail end side of the preceding material and the unsteady portion on the leading end side of the trailing material are thicker than the respective steady portions. However, it goes without saying that the present invention can also be applied to a case where the unsteady portion is thinner than the steady portion.

An example (invention example) in which the present invention is applied to a six-stand tandem cold rolling mill (hereinafter simply referred to as a rolling mill; the entirety is not shown) with the rolling stand 4 shown in FIG. 1 as the first stand , will be compared with an example (comparative example) to which the conventional plate thickness control method is applied. This rolling mill has four stages in each stand and a work roll diameter of 500 to 600 mm. A welding machine (not shown) is installed upstream of the entry-side bridle roll 9 of the rolling mill to join the trailing end of the preceding material ₆₁ and the leading end of the following material ₆₂ by laser welding. The delivery side plate thickness gauge 7 consists of the gamma ray thickness gauge. The weld sensor 12 consists of the optical sensor.

In the example of the present invention, the gate G1 is opened to continue PI control while the unsteady portion 21 including the welded portion 11 is passing through the first stand, and the gate G2 is opened to reset the integral term in the PI control unit 100. passage of the integral term reset signal S7 for prompting the Then, the integral term reset command unit 101 detects the welded portion 11 by inputting the welded portion detection signal S6 from the welded portion sensor 12, and calculates the moving distance of the welded portion 11 after the detection by time integral calculation of the bridle roll peripheral speed S5. , and the time when the unsteady portion 21 of the predetermined length L from the weld 11 of the succeeding material 6 ₂ completes passing through the roll-down position of the rolling stand 4 is the integral term reset This is recognized as timing, and the integration term reset signal S7 is output at this timing. The predetermined length L was set to L=3 m based on the experience value of the length of the unsteady portion in the past.

In the comparative example, in the example of the present invention, the gate G2 is changed from open to closed to disable passage of the integral term reset signal S7 that prompts the PI control unit 100 to reset the integral term so that the integral term reset is not executed. Other than this, it was the same as the example of the present invention.

In the examples of the present invention and the comparative examples, rolling was performed on steel strips to be steel sheets having a product plate thickness of 0.15 to 0.5 mm and a plate width of 650 to 1050 mm. In addition, the target steel strip has the same steel type for the preceding material and the following material, the difference in material plate thickness is 0.1 mm or less, and the difference in product thickness of the succeeding material from the preceding material is within ± 5%. The width difference of the subsequent material with respect to the preceding material was within ±20 mm.

As a result, for example, the material plate thickness is 2.3 mm, the plate width is 1000 mm, the product plate thickness is 0.23 mm, and the rolling speed (roll peripheral speed of the final stand) is about 300 m/min in the range including the unsteady part. Below (Case 1), in the comparative example, after the weld passed through the roll-down position of the first stand, the plate thickness fluctuation in the non-stationary portion of the succeeding material increased, and the steady portion on the tip side of the succeeding material had a thickness of about 780 m. While the off-gauge generation area appeared, in the example of the present invention, the plate thickness fluctuation in the unsteady portion of the trailing material became small, and the off-gauge generation area in the steady portion on the tip side of the trailing material could be reduced to about 200 m. did it.

Also, for example, under the condition that the material plate thickness is 2.6 mm, the plate width is 1000 mm, and the product plate thickness is 0.40 mm, and the rolling speed (roll peripheral speed of the final stand) is about 250 m/min in the range including the unsteady part. In (Case 2), the off-gauge generation area of the stationary portion on the leading end side of the trailing material was about 86 m in the comparative example, whereas it was reduced to about 6 m or less in the example of the present invention.

As described above, by applying the present invention, in the tandem cold rolling mill, off-gauge generation after passing the weld zone is suppressed, and the cutoff amount in the next process is 0.05% on average per weight of the rolled product. have succeeded in reducing

1 1st computer 2 2nd computer 3 Rolling cylinder control device 4 Rolling stand 5 Rolling cylinder 6 Steel strip 6 ₁ Leading material 6 ₂ Subsequent material 7 Exit side thickness gauge 8 Entrance side thickness gauge 9 Entrance side bridle roll 10 Roll Circumferential speed detector 11 Welded portion 12 Welded portion sensor 20 Steady portion 21 Unsteady portion 100 PI control portion 101 Integral term reset command portion G1 Gate G2 Gate S1 Target plate thickness S2 Measured plate thickness S3 Roll-down amount deviation signal S4 Roll gap Change amount S5 Bridle roll peripheral speed S6 Welded part detection signal S7 Integral term reset signal S8 G1 opening/closing signal S9 Measured plate thickness S10 G2 opening/closing signal

Claims (6)

A plate thickness control method in a cold rolling mill for a steel strip having a welded portion joining a preceding material and a succeeding material, comprising:
Perform proportional integral control with the roll gap of the rolling stand as the operating end,
continuing the proportional integral control for the unsteady portion before and after the welded portion;
Integral for initializing the integral term of the proportional-integral control at the timing when the portion of the succeeding material having a predetermined length L from the welded portion of the succeeding material has completed rolling after the welded portion has passed the roll-down position of the rolling stand. A strip thickness control method in a cold rolling mill, characterized by performing a term reset. 2. The strip thickness control method in a cold rolling mill according to claim 1, wherein said predetermined length L is set in advance at 1 to 5 m from said welded portion of said succeeding strip. 2. The strip thickness control method for a cold rolling mill according to claim 1 , wherein the predetermined length L is determined based on the measured value of an entry-side strip thickness gauge installed on the entry side of the cold rolling mill. . The strip thickness control method for a cold rolling mill according to any one of claims 1 to 3, wherein the preceding strip and the trailing strip have the same strip thickness and strip width. The strip thickness control method for a cold rolling mill according to any one of claims 1 to 3, wherein a difference in tensile strength between the preceding material and the succeeding material is 30 MPa or less. Strip thickness control in a cold rolling mill according to any one of claims 1 to 5 , wherein the rolling stand having the roll gap as an operating end is a first stand of a tandem cold rolling mill. Method.

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