JP3041124B2 - Control method of hot strip mill finishing mill - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to tension control of a tandem rolling mill, and more particularly, to joining a tail end of a preceding rolled material and a leading end of a succeeding rolled material on the entry side of a hot strip mill finishing mill. The present invention relates to a control method of a hot strip mill finishing mill for rolling.

[0002]

2. Description of the Related Art A hot strip mill finishing mill is arranged behind a rough mill. In this case, the rolled material extracted from the heating furnace is repeatedly rolled for several passes in a rough rolling mill, and then rolled to a predetermined size in a finishing rolling mill,
It is wound by a down coiler. These series of operations were generally performed for each rolled material. At the time of such rolling, the rolled material that has been rolled by the rough rolling mill is kept on standby at the entry side of the finish rolling mill while the preceding rolled material (preceding material) is being rolled by the finish rolling mill.

By the way, in recent years, the above-mentioned rolling method has been
(1) Want to improve productivity by reducing idle time, (2) Reduce the so-called unsteady part where the dimensions of the front and rear ends do not match the target value, and There is a strong demand to improve dimensional accuracy and (3) to stabilize the rolling operation by eliminating biting and trailing of material, and new rolling methods have been considered to meet this demand.

FIG. 6 shows one of the new rolling methods, in which a joining device 18 is provided in front of a finishing mill having respective rolling stands # 1, # 2,... While being rolled by the finishing mill, the rear end of the preceding material 1a and the front end of the succeeding material 1b that has been rolled by the rough rolling machine 17 are joined and tandem-rolled, and are rolled to a predetermined size. The rolled material is taken up by the down coiler 19.

[0005]

In the conventional rolling method shown in FIG. 6, the rear end of the preceding material and the front end of the following material are joined to perform tandem rolling, so that the idle time can be reduced and the unsteady portion can be reduced. Although it is effective in eliminating and stabilizing the rolling operation, the control method for the finishing mill has not been established, and the tension and compression force generated during rolling were likely to cause adverse effects such as breakage and buckling at the joints .

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a method of controlling a hot strip mill finishing mill capable of performing stable rolling by eliminating an adverse effect on a joining point. And

[0007]

SUMMARY OF THE INVENTION The present invention relates to a hot strip in which a tail end of a preceding rolled material and a front end of a succeeding rolled material are joined and rolled at the entry side of a hot strip mill finishing mill having a plurality of stands. In the control method of the mill finishing mill, a looper is disposed between stands, a looper control for controlling a height of the looper so that an angle of the looper and a tension applied to a rolled material respectively match target values, and Calculate the tension applied to the rolled material from the rolling torque and rolling load of the stand without using it, and enable switching to looperless control that controls the rolling roll speed so that this tension matches the target value. When the looper control is executed, the looper control is executed immediately before the joining point of the preceding material and the succeeding material reaches the entrance side of the upstream stand as viewed from the looper. Along with the switch to the Paresu control,
The target value of the tension is changed to substantially zero, and when the joining point reaches the stand located downstream from the looper, the looper control is switched from the looperless control to the looper control, and each of the looper angle and the tension applied to the rolled material is changed. The target value is changed to the target value at the time of steady rolling of the succeeding material.

In the looperless control, the tensionless arm arm coefficient of the istand is A _0i , the actual tension value in front of the istand immediately before switching from the looper control to the looperless control is T _iM , and the actual rolling torque value is Gm. _iM, rolling load actual value P _iM, (i-1) forward tension actual value of the stand T _{(i-1) M,} a constant determined by the rolling schedule alpha _i,
As β _i , γ _i , δ _i , the forward tension T _i of the i-stand is expressed by the following equation.

[0009]

(Equation 3) And the torque arm coefficient A _0i of the i-stand when there is no tension is expressed by the following equation.

[0010]

(Equation 4) Is used to calculate and store, and the stored value is used for calculating the forward tension T _i of the i-stand from the next time.

At the time of changing the set values such as the roll gap and the roll speed of each stand at a joint point where the rolling schedule of the preceding material and the succeeding material are different from each other with a predetermined set value change time, the i-stand is changed. the variation .DELTA.A _0i of no tension during torque arm coefficient before and after the set value change is calculated storage, a _0i instead of the tension-free time torque arm coefficient a _0i
The forward tension T _i of the i-stand is calculated using + ΔA _0i .

[0012]

In the following, the operation will be described after the principle of the present invention has been described.

In the tandem rolling of iron or non-ferrous,
Inappropriate rolling and speed setting of each stand causes unexpected tension or compressive force in the rolled material between stands due to disturbances occurring during rolling, such as changes in the longitudinal dimension of the rolled material, changes in the material temperature, etc. . The tension and compression force not only fluctuate the thickness and width of the rolled material, but also may cause abnormal loops and buckling. Therefore, in tandem rolling, the rolled material tension between stands is controlled to be constant in order to prevent these phenomena.

[0014] Conventionally used control methods include:
A looper device is provided between the stands to control the tension between the stands acting on the rolled material to be constant by balancing the force that the looper pushes up the rolled material and the force that the looper receives from the material, and the driving torque and rolling load of the rolling mill. A looperless control that indirectly estimates the tension between stands, calculates the speed correction amount of the rolling roll drive motor from this tension, and controls the tension between stands acting on the rolled material by correcting the motor speed. is there.

Hereinafter, these two control methods will be described with reference to FIG. 3 and FIG. FIG. 3 is a diagram illustrating the principle of looper control. In the drawing, a rolled material 1 is rolled by a roll 2 of an i-stand, and then rolled by a roll 3 of an (i + 1) -th stand. A looper 4 is provided between these stands. Of these, the looper 4 is driven by a looper drive motor 5, and the rolling roll 2 is driven by a rolling roll drive motor 6. A speed control device 7 is provided to control the speed of the looper drive motor 5, and a speed control device 8 is provided to control the speed of the rolling roll drive motor 6. The looper controller 11 includes a looper height controller 9 and a tension controller 10. The looper height controller 9 includes a set looper angle reference θ _iREF and a looper angle actual value θ _iM detected by the looper angle detector 21. The speed command of the looper drive motor 5 is calculated so that the difference with the zero becomes zero and added to the speed controller 7. The tension controller 10 sets the tension reference _TiREF and the _actual tension detected by the tension detector 20. Value T
The speed correction amount of the rolling roll drive motor 6 is calculated so that the difference from _iM becomes zero, and is added to the speed control device 8. Thereby, i acts on the rolled material by balancing the force that the looper pushes up the rolled material and the force that the looper receives from the material.
The tension between the stands in front of the stands can be controlled.

FIG. 4 is a diagram illustrating the principle of looperless control. In the figure, after a rolled material 1 is rolled by a roll 2 of an i-stand, a roll 3 of a (i + 1) stand is rolled.
Rolled in. The rolling roll 2 is a rolling roll driving motor 6
Driven by A speed control device 8 is provided to control the speed of the rolling roll drive motor 6. Further, a load detector 12 for detecting the rolling load of the i-stand is provided, and the detected value is applied to the looperless tension controller 16. The looperless tension control device 16 includes a torque arm coefficient storage device 13, a tension calculation device 14, and a speed correction amount calculation device.
It consists of 15 and.

Here, when the rolled material 1 is rolled only by the i-stand, the state A, the i-stand and (i + 1)
State B is when rolling is performed on both stands.
The torque arm coefficient storage device 13 uses the load detector
Uptake and rolling load actual value P _iM detected by 12, and a drive torque actual value G _iM converted from current value when the speed control device 8 controls the rolling roll drive motor 6, tension-free torque by: The arm coefficient A _0i is calculated and stored.

A _0i = G _iM / P _iM (3) In addition, the tension calculating device 14 calculates the actual rolling load value P in the state B.
_iM , the driving torque actual value G _iM and the _tensionless torque arm coefficient A _0i are taken, and the i stand and (i +
1) The tension T _i between the stands is calculated by the following equation.

[0019]

(Equation 5) Here, P _iM : the actual rolling load value of the i-stand in the state B G _iM : the actual rolling torque of the i-stand in the state B T _{(i-1) M} : the actual value of the rear tension of the i-stand α _i , β _i , γ _i , δ _i : a constant determined by the rolling schedule.

Therefore, the speed correction amount calculating device 15 calculates the speed correction amount of the rolling roll driving motor 6 so that the difference between the tension T _i and the set target tension T _iREF becomes zero, and calculates the speed control device. Add to 8. Thereby, the tension between the stands is indirectly estimated from the driving torque and the rolling load of the rolling mill, and the speed of the rolling roll drive motor is corrected so that the tension matches the set tension value, thereby acting on the rolled material. The tension between stands can be controlled.

In the present invention, these two control methods are skillfully switched, and an outline thereof will be described with reference to FIG. Here, for example, among the seven stands that constitute the finish rolling mill, the switching timing of the tension control method, the timing of changing the looper angle, and the tension value between the stands when the joining point is rolled at three stands on the upstream side are set. In the drawing, X indicates the switching or change position for the tension control between the # 1 stand and the # 2 stand, and Y indicates the switching for the tension control between the # 2 stand and the # 3 stand. Or it indicates the change position.

Now, until the joining point reaches the position X,
Since only the preceding material is rolled, steady rolling is performed by looper control. When the joining point reaches the position X, the actual tension value T _1M during looper control is held, and the torque arm coefficient A ₀₁ at the time of no tension is calculated and stored by the above equation (2).

Calculation of the tensionless arm coefficient A ₀₁
When the storage is completed, it switches the tension control between the # 1 stand and # 2 stand Ruparesu tension control using the tension-free torque arm coefficient A _01. Further, the looper between the # 1 stand and the # 2 stand is lowered to the pass line or below the pass line, and the tension reference of the looperless tension control is changed to substantially zero. In this state, the joining point is rolled in the # 1 stand, and the same point is rolled until the joining point passes through the # 2 stand.

Subsequently, after the joining point is rolled at the # 2 stand, the tension reference between the # 1 stand and the # 2 stand is changed to a target value at the time of steady rolling by looperless control.
Subsequently, the control is switched from the looperless control to the looper control to control the tension between the # 1 stand and the # 2 stand.

On the other hand, the tension control between the # 2 stand and the # 3 stand holds the actual tension value T _2M at the time of the looper control at the time when the joining point reaches the position Y, calculates and stores the torque arm coefficient a ₀₂ at tension.

Calculation of the tensionless arm coefficient A ₀₂
When the storage is completed, it switches the tension control between the # 2 stand and # 3 stand Ruparesu tension control using the tension-free torque arm coefficient A _02. Further, the looper between the stand # 2 and the stand # 3 is lowered to the pass line or below the pass line, and the tension reference of the looperless tension control is changed to substantially zero. In this state, the joining point is rolled in the # 2 stand, and the same point is rolled until the joining point passes through the # 3 stand.

On the other hand, after the joining point is rolled at the # 3 stand, the tension between the # 2 stand and the # 3 stand is switched to looper control.

Hereinafter, the inter-stand tension after the # 3 stand is controlled in exactly the same manner. By the way, the setting change of the roll gap, the roll speed, and the like for the preceding material and the following material is performed at the joining point. As described above, when the set value is changed between the preceding material and the following material, the torque arm coefficient at the time of no tension is also different. As described above, if the non-tension torque coefficient of the i-stand is calculated and stored from the tension immediately before switching from the looper control to the looper-less control, and this is used to calculate the next i-stand rear tension, the roll gap, the roll It is necessary to correct the calculated and stored non-tension torque A _0i in accordance with the lapse of time from the start to the end of the change of the set value such as the speed. This correction will be described in more detail with reference to FIG.

FIG. 5 shows the roll gap S and the no-tension torque coefficient A ₀ when the roll gap is changed.
Is a graph showing a relationship between the time t, when the joining point at time t ₁ passes through the # 1 stand, it takes a set value changing time T straddling both sides of the time t ₁ roll gradually change to S ₂ from S ₁ the gap. At this time, the torque arm coefficient A _01,1 at the time of _tensionless of the preceding material in the # 1 stand gradually changes to the torque arm A _01.2 at the time of tension of the _succeeding material.

In this case, the forward tension T _1,1 of the # 1 stand in the preceding material before the change of the set value is started can be calculated by the following equation.

[0031]

(Equation 6) In addition, in the following material after the change of the set value is completed, #
The forward tension T _1,2 of one stand can be calculated by the following equation.

[0032]

(Equation 7) On the other hand, in the stand # 2, A _02,1 is used instead of the torque arm coefficient A _01,1 at no tension in FIG.
When the front tension T _1,1 of one stand is used, the front tension T _2,1 of the # 2 stand in the preceding material before the change of the set value is started can be calculated by the following equation.

[0033]

(Equation 8) Similarly, in the # 2 stand, A _02,2 is used instead of the torque arm coefficient A _01,2 at the time of no tension in FIG.
# 1 Using a front tension T _{1, 2} of the stand, the front tension T _{2, 2} of the # 2 stand in the row material after subsequent finishing the change of set values can be calculated by the following equation.

[0034]

(Equation 9) Therefore, _assuming that the difference between the torque arm coefficient at no tension A _01,1 and A _01,2 is ΔA ₀₁ , the forward tension T ₁ of the # 1 stand after the end of the change of the set value of the # 1 stand is given by the following equation. Can be calculated by

[0035]

(Equation 10) Similarly, _assuming that the difference between the non-tension torque arm coefficients A _02,1 and A _02,2 is ΔA ₀₂ , the forward tension T ₂ of the # 2 stand after the end of the change of the set value of the # 2 stand is as follows. It can be calculated by an equation.

[0036]

[Equation 11] In this case, the torque arm coefficient correction value ΔA ₀₁ , Δ
_A02 is given after the setting change time T has elapsed.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the drawings. FIG. 2 is a block diagram showing a configuration of an apparatus embodying the present invention. In the figure, rolled material 1 is # 1
The rolls are sequentially rolled by the roll 2 of the stand, the roll 3 of the # 2 stand, and the roll 34 of the # 3 roll stand. At this time, the looper 4 is provided between the # 1 stand and the # 2 stand. The looper 4 is driven by a looper driving motor 5, and the rolling roll 2 is driven by a rolling roll driving motor 6. A speed control device 7 is provided to control the speed of the looper drive motor 5, and a speed control device 8 is provided to control the speed of the rolling roll drive motor 6. The looper controller 11 calculates the speed command of the looper drive motor 5 such that the difference between the set looper angle reference θ _iREF and the actual looper angle value θ _iM detected by the looper angle detector 21 becomes zero, and calculates the speed. In addition to the controller 7, a speed correction amount of the rolling roll driving motor 6 is further calculated so that the difference between the set tension reference T _iREF and the tension T _iM detected by the tension detector 20 becomes zero. It is added to the control device 8.

A load detector 12 for detecting the rolling load of the # 1 stand is provided, and the detected value is applied to a looperless tension controller 16. The looperless tension control device 16 calculates the actual rolling load value P _1M detected by the load detector 12 and the actual driving torque value G _1M converted from the current value when the speed control device 8 controls the rolling roll drive motor 6. The tension-free torque arm coefficient A ₀₁ is calculated, and the rolling load actual value P _1M , the driving torque actual value G _1M, and the tension-free torque arm coefficient A ₀₁ detected by the tension detector 20 are used. The front tension T ₁ of one stand is calculated, and the speed correction amount of the rolling roll drive motor 6 is calculated so that the front tension T ₁ matches the set target tension T _iREF , and is added to the speed control device 8. Has become.

Similarly, a looper 24 is provided between the # 2 stand and the # 3 stand. The looper 24 is driven by a looper driving motor 27, and the rolling roll 3 is driven by a rolling roll driving motor 28. Also, a speed control device for controlling the speed of the looper drive motor 27 is provided.
A speed control device 30 is provided for controlling the speed of the rolling roll drive motor 28. Looper control device
A speed controller 31 calculates a speed command of the looper drive motor 27 such that the difference between the set looper angle reference θ _2REF and the actual looper angle value P _2M detected by the looper angle detector 26 becomes zero. In addition to the set tension reference T _2REF and the actual tension value T detected by the tension detector 25.
The speed correction amount of the rolling roll drive motor 28 such that the difference from _2M becomes zero is calculated and added to the speed control device 30.

A load detector 37 for detecting the rolling load of the # 2 stand is provided, and the detected value is applied to the looperless tension controller 32. Ruparesu tension controller 32 is collected by a rolling load P _2M detected by the tension detector 25, and a drive torque actual value G _2M converted from current value when the speed control device 30 controls the rolling roll drive motor 28 To calculate the tension-free torque arm coefficient A ₀₂ ,
The front tension T ₂ of the # 2 stand is calculated based on the rolling load actual value P _2M , the driving torque actual value G _2M and the tension-free torque arm coefficient A ₀₂ detected at 25, and the front tension T ₂ is set. The speed correction amount of the rolling roll drive motor 28 that matches the target tension T _2REF is calculated and applied to the speed control device 30.

The same control system as described above is provided for each stand after the # 3 stand. However, for simplification of the drawing and the description, a rolling roll driving motor 35 for driving the rolling roll 34 of the # 3 stand is provided. And its speed control device 36
Only shows.

A junction detector 22 for detecting the junction A is provided on the entrance side of the # 1 stand, and a junction tracking unit 23 tracks its position and outputs a position signal of the junction to a reference generator. Add to 33. The reference generator 33 outputs a different tension reference T _iREF depending on the position of the joint A between the time of steady rolling and the case where the joint is located between the stands, and outputs the looperless tension controllers 16, 32, , And the looper arm angle reference θ _iREF that changes according to each control method is calculated and provided to the looper controllers 11, 31,. Further, changeover switches SW1 and SW1 for switching the control method according to the position of the junction A.
SW2 are provided in front of the speed controllers 8, 30,..., Respectively, and are switched in accordance with the joint positions calculated by the joint tracking device 23.

The operation of the embodiment constructed as described above will be described below. Now, junction A is a junction detector
Until it is detected at 22, since only the preceding material is rolled,
With the changeover switches SW1 and SW2 shown in the figure, a rolling roll speed correction signal of the looper control device 11 is given to the speed control device 8, so that steady rolling is performed by looper control. When the joining point is detected by the joining point detector 22, the looperless tension controller 16 holds the actual tension value T _1M during looper control, and calculates the torque arm coefficient A ₀₁ at the time of no tension according to the equation (2). Is calculated and stored. In the # 1 stand, since the back tension is zero, T _{(i-1) M in} equation (2)
Is zero.

[0044] When the calculation of the torque arm coefficient A _01, the storage is completed, the shown change-over switch SW1 in the opposite state, the tension control between the # 1 stand and # 2 stand Ruparesu control Switch. At this time, the reference generator 33 outputs a looper angle reference θ _1REF that lowers the looper 4 to the pass line or below the pass line, and changes the tension reference T _1REF of the looperless control to substantially zero. In this state, the joining point A is rolled in the # 1 stand, and is rolled in the same state until the joining point passes through the # 2 stand.

Subsequently, after the joining point A is rolled at the # 2 stand, the tension reference T _1REF between the # 1 stand and the # 2 stand is changed to that at the time of steady rolling, and the changeover switch SW1 is set. By changing to the looper control from the looperless control to the state shown in FIG.
Control the tension between the two stands.

On the other hand, the tension control between the # 2 stand and the # 3 stand is performed by switching the changeover switch SW2 to a state opposite to that shown in the figure when the joint A is detected by the joint detector 22. The joining point A is #
When reaching the position immediately before the two stands, the detected tension T _2M during looper control is held, and the torque arm coefficient A ₀₂ at the time of no tension is calculated and stored using the above equation (2).

The calculation of the torque arm coefficient A _02, when the storage has been completed, switches the tension control between the # 2 stand and # 3 stand Ruparesu tension control. Further, the reference generator 33 outputs a looper angle reference θ _2REF that lowers the looper 24 to a pass line or a pass line or less,
Substantially changing the zero tension reference T _2ref of Ruparesu tension control. In this state, the joining point is rolled on the # 2 stand, and the same state is maintained until the joining point passes through the # 3 stand.
> Rolled in state.

Hereinafter, the same control is performed in the stands # 3 to # (n-1), but the description is omitted because they are duplicated.

Next, when there is a change in the setting of the roll gap and the roll speed between the preceding material and the following material, as described above, the looperless tension controller 16 controls the non-tension state given after the elapse of the set value change time T. Torque arm coefficient ΔA
With ₀₁ and .DELTA.A _02, (9) calculates the # front tension T ₁ of the 1 stand after the completion of the change of the set value by type, furthermore, since the completion of the change of the set value by (11) to calculate the forward tension T ₂ of the # 2 stand.

[0050]

As is apparent from the above description, according to the present invention, when the preceding material is being rolled, the looper control is executed, and the joining point between the preceding material and the succeeding material is set on the stand upstream of the looper. The control is switched from looper control to looperless control just before reaching the entry side of the robot, the target value of the tension is changed to substantially zero, and when the junction reaches the stand downstream of the looper, the control is switched from looperless control to looper control. Along with
Since the target values of the looper angle and the tension applied to the rolled material are changed to the target values at the time of steady rolling of the succeeding material, abnormal loops and buckling may occur even when the rolled material is joined and continuously rolled. Stable rolling without fear is possible.

In this case, by calculating the front tension of each stand and the torque arm coefficient at the time of no tension by the above equations (1) and (2), reliable control becomes possible.

When the rolling schedule differs between the preceding material and the succeeding material, the amount of change in the torque arm coefficient at the time of no tension of each stand is sequentially calculated and stored, and the amount of change is added to the original torque arm coefficient at the time of no tension. In this way, it is possible to cope with a change in the rolling schedule at the junction.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a state of control switching and setting value change in which the present invention is associated with a material joining point.

FIG. 2 is a block diagram showing a configuration of an apparatus for implementing the present invention.

FIG. 3 is a block diagram showing a configuration of a looper control device for explaining the principle of the present invention.

FIG. 4 is a block diagram showing a configuration of a looperless control device for explaining the principle of the present invention.

FIG. 5 is a diagram showing a relationship between a roll opening degree, a tensionless torque arm coefficient, and time in order to explain the principle of the present invention.

FIG. 6 is a layout diagram of a general rolling facility that performs rolling by joining a tail end of a preceding rolled material and a front end of a succeeding rolled material.

[Explanation of symbols]

 2,3 Roller roll 4,24 Looper 5,27 Looper drive motor 6,28 Roller roll drive motor 7,29 Speed controller 8,30 Speed controller 11,31 Looper controller 16,32 Looperless tension controller 22 Joint inspection Output device 23 Junction point tracking device 33 Reference generation device SW1, SW2 selector switch

Claims (3)

(57) [Claims] 1. A method for controlling a hot strip mill finish rolling mill in which a tail end of a preceding rolled material and a tip end of a succeeding rolled material are joined and rolled at an entry side of a hot strip mill finishing rolling mill having a plurality of stands. A looper between the stands, looper control to control the height of the looper so that the angle of the looper and the tension applied to the rolled material respectively match the target value, and the rolling torque of the stand without using the looper and Calculate the tension applied to the rolled material from the rolling load, and enable switching to looperless control that controls the rolling roll speed so that this tension matches the target value.When the preceding material is being rolled, the looper control is performed. Execute, and switch from the looper control to the looperless control immediately before the joining point of the preceding material and the following material reaches the entrance side of the upstream stand as viewed from the looper. In both cases, the target value of the tension is changed to substantially zero, and when the joining point reaches the stand downstream from the looper, the looper control is switched from the looperless control to the looper control, and the looper angle and the tension applied to the rolled material are changed. A control method for a hot strip mill finishing rolling mill, wherein each target value is changed to a target value at the time of steady rolling of the succeeding material. In the looperless control, the tension-free torque arm coefficient of the i-stand is A _0i , the actual tension value in front of the i-stand immediately before switching from the looper control to the looper-less control is T _iM , and the actual rolling torque value is G. _iM, rolling load actual value P _iM, (i-1) forward tension actual value of the stand T _{(i-1) M,} a constant determined by the rolling schedule alpha _i,
As β _i , γ _i , δ _i , the forward tension T _i of the i-stand is expressed by the following equation: And the torque arm coefficient A _0i of the i-stand when there is no tension is expressed by the following equation: 2. The control method for a hot strip mill finishing mill according to claim 1, wherein the calculated value is stored by using the following, and the stored value is used for calculating the forward tension T _i of the i-stand from the next time. 3. When changing the set values such as the roll gap and the roll speed of each stand at a joining point where the rolling schedule of the preceding material and the succeeding material are different from each other with a predetermined set value changing time, the i-stand is changed. The change amount ΔA _0i of the torque arm coefficient at no tension before and after the change of the set value is calculated and stored, and A _0i + ΔA is used instead of the torque arm coefficient A _0i at no tension.
Hot strip mill finishing mill control method according to claim 2, characterized in that for calculating the forward tension T _i of i stand with _0i.