JP2846143B2 - Control device for hot rolling mill - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control apparatus for a hot rolling mill in which a looper is disposed between tandem stands.

[0002]

2. Description of the Related Art As a sheet thickness control in a hot rolling mill, there is an automatic sheet thickness control (hereinafter abbreviated as AGC) in which an operation end is set to a roll gap by a rolling-down device.
Gauge meter AGC method and MMC (Mill Modulas Contr.
ol) systems are known. In order to improve the accuracy with respect to the target plate thickness with these control methods, it is important to improve the setting accuracy and the responsiveness of the roll gap,
At the same time, it is important to suppress the fluctuation of the tension of the rolled material.

[0003] In particular, the rolled material in hot rolling is susceptible to breakage due to low deformation resistance due to high temperature treatment, and a large loop occurs between rolling mill stands unless tension is properly controlled. Easy to cause.

For this reason, a looper is provided between stands in a hot rolling mill, and the tension is controlled by the looper.

On the other hand, in the cold rolling process, a mass flow AGC, in which the thickness is controlled by the number of rotations of a rolling roll driving main motor, is adopted, and a great effect is obtained. This is disclosed in, for example, JP-A-59-21423.
Recently, attempts have been made to apply this mass flow AGC to a hot rolling process.

[0006]

Control combined with mass flow AGC and tension control by a reduction device is a technique often used in a cold rolling process without a looper, and this tension control is applied to a hot rolling process. The operation method or control method of the looper in this case has not been established, and has the following problems.

That is, in hot rolling, a looper is rarely used because the looper plays a role of supporting the material between stands and facilitating the passage of the sheet to the next stand. Also,
The installation place of the contact type tension meter was limited, and it had to be installed on the looper.

Therefore, a contact-type tensiometer attached to a looper receives an impact when the looper is lifted up and comes into contact with a rolled material, and the measured tension often includes a large error. When the tension was controlled in such a manner, the tension immediately after the threading was likely to be unstable.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems.
It is an object of the present invention to obtain a control device for a hot rolling mill capable of suppressing the instability of the tension immediately after the passing of a sheet even when the tension control such as the above is performed by a reduction device.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a hot rolling mill in which a looper is arranged between i (i = 1 to n-1) stands and i + 1 stand among n stands arranged in tandem. A tension control system for generating a current reference of the looper driving motor so as to maintain the tension of the rolling material between the i-stand and the i + 1 stand at a reference value, and controlling the current of the looper driving motor according to the current reference. A looper height control system for measuring the height of the looper and correcting the speed of the rolling roll drive main motor of the i-stand so as to keep the height of the looper at a reference value; Measure the tension of the rolled material,
A tension feedback control system for controlling the rolling force of the i + 1 stand so as to keep the tension of the rolled material at a reference value; and the tension control system until a certain time has elapsed after the rolled material is caught in the i + 1 stand. And the looper height control system in the operating state, the tension feedback control system in the inactive state, and after a certain period of time has elapsed since the rolling material was caught in the i + 1 stand, the tension control system and the looper height And a control operation switching means for bringing the control system into an inoperative state and bringing the tension feedback control system into an operating state. In addition, each rolling roll rotation speed of the i stand and the i + 1 stand,
An automatic mass flow thickness control system that detects the thickness of the i-stand exit side and corrects the speed of the rolling roll drive main motor of the i-stand based on the detected values,
The automatic mass flow thickness control system is switched between an operation state and a non-operation state in accordance with the tension feedback control system.

[0011]

According to the present invention, a predetermined value is set such that the tension of the rolled material between the stands is maintained at a reference value until a lapse of a predetermined period of time when the tension is predicted to be stable after the rolled material is caught in the i + 1 stand. The current of the looper drive motor is controlled by the current reference, and the speed of the rolling roll drive main motor of the i-stand is corrected so that the height of the looper is maintained at the reference value. After a certain period of time, the rolling force of the (i + 1) -th stand is controlled so as to maintain the tension of the rolling material at the reference value, so that the tension is not destabilized immediately after the rolling material is caught in the (i + 1) -th stand. be able to.

In addition, by operating the mass flow automatic thickness control system after a certain time has elapsed after the rolling material is caught in the i + 1 stand, it is easy to apply the mass flow automatic thickness control to the hot rolling process. Becomes

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. Normally, a tandem rolling mill has 6 to 7 stands. Hereinafter, the i stand and the i + 1 stand will be described.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention together with an applicable stand. In the figure, a rolled material 1 is an i (i = 1 to n) stand 2 (hereinafter, referred to as i).
Rolling is performed in order at an i-stand 3 and an i + 1-stand 3 (hereinafter, simply referred to as an i + 1-stand). A looper 4 driven by a looper drive motor 5 is provided between the i stand and the i + 1 stand. A rotation speed measuring device 6 for measuring the rotation speed is connected to the looper drive motor 5. This rotation speed measuring device 6
, The speed control device 7 generates a current reference for setting the looper drive motor 5 to the reference rotation speed, while the current reference generation device 8 independently controls the current to maintain the tension of the rolling material 1 at the reference value. A reference is generated. The current control device 9 controls the current of the looper drive motor 5 according to these current references, and the normally open contact of the control changeover switch SW1 is connected to the output circuit of the looper drive motor speed control device 7.
The control switch SW is connected to the output circuit of the current reference generator 8.
One normally closed contact is provided. The control changeover switch SW1 is switched by a control changeover circuit (not shown) based on a load detection signal of the rolling mill. The control changeover switch SW1 is shown until a predetermined time elapses after the rolling material 1 is caught in the i + 1 stand. This state is maintained, and when a certain time has elapsed, the state is switched to the state opposite to that shown in the figure.

On the other hand, in order to control the height of the looper 4,
Looper height controllers 10 and 11 are provided, each of which receives an output of the looper angle measuring device 12 and outputs a speed correction signal. In this case, the looper height controller 10 outputs a speed correction signal to the looper drive motor 5, and the looper height controller 10
Reference numeral 11 outputs a speed correction signal to a rolling roll drive main motor of an i-stand described later. Then, the control changeover switch SW that operates synchronously with the control changeover switch SW1 described above.
The normally open contact 2 is connected to the output circuit of the looper height controller 10, and the normally closed contact of the control changeover switch SW2 is connected to the output circuit of the looper height controller 11. Thus, the speed correction signal of the looper height controller 11 is applied to the speed control system of the rolling roll driving main motor until a certain period of time has elapsed after the rolling material 1 is caught in the i + 1 stand, and a certain period of time is passed. After the elapse, the speed correction signal of the looper height controller 10 is applied to the speed control device 7.

Further, the rolling roll of the i-stand is i + 1 by a rolling roll driving main motor (hereinafter referred to as main machine) 15.
The rolling rolls of the stand are driven by rolling roll driving main motors (hereinafter referred to as main machines) 16, respectively, and the speed of each rolling roll is measured by rolling roll rotation speed measuring devices 13 and 14. The main engine 15 has a main engine rotation speed measuring device.
The main unit speed controller 19 controls the speed of the main unit 15 according to the speed measurement signal and the above-described speed correction signal. Similarly, the main engine 16 is coupled to a main engine rotation speed measuring device 18, and the main engine speed control device 20 controls the speed of the main engine 16 according to the speed measurement signal.

Here, the rolling load is detected by the load cell 21 at the i-th stand and by the load cell 22 at the i + 1-th stand, and the detected value is used for rolling control. On the other hand, based on the output signals of the rolling roll rotation speed measuring devices 13 and 14 and the output signal of the thickness measuring device (or the exit side thickness estimating device) 29 for detecting the thickness at the exit side of the i-stand, The mass flow AGC main controller 23 calculates the speed correction of the rolling roll and outputs a speed correction signal. The main engine speed control device 19 is controlled by the control switch S so that the output signal of the mass flow AGC main controller 23 and the output signal of the looper height controller 11 are switched.
The normally open contact of the control changeover switch SW3 operating in synchronization with W1 is connected to the output circuit of the mass flow AGC main controller 23,
The normally closed contact of the control switch SW3 is a looper height controller
11 output circuits.

Further, the looper 4 has a tension measuring device 24
Is attached, and a tension measurement signal is applied to the draft tension control device 26 via another normally open contact of the control changeover switch SW1. The rolling tension control device 26 outputs a rolling position correction signal for making the detected tension coincide with the reference value. On the other hand, based on the output signal of the load cell 22, the rolling thickness control device 25 similarly outputs a rolling position correction signal for matching the rolling load to the reference value. In addition, i stand and i +
Each stand is provided with a pressing position control device 27, 28 of a hydraulic pressing type or an electric pressing type having a slightly slower response than this. The output signals of the above-described roll-down plate thickness control device 25 and the roll-down tension control device 26 are input to the roll-down position control device 28, and the normally open contact of the control changeover switch SW4 that operates synchronously with the above-described control changeover switch SW1 has a reduction tension. Control device
The normally closed contact of the control switch SW4 is connected to the output circuit of the press-down plate thickness control device 25.

The operation of the present embodiment configured as described above will be described below together with the outline of the mass flow AGC.

Mainly, in the conventional AGC in which the thickness control is performed by using the rolling position control device, the rolling position control device 27 shown in FIG.
The thickness of the strip is controlled by changing the gap opening according to steps 28 and 28.The fluctuation of the rolled material tension and the fluctuation of the looper height that occur at that time are controlled by non-interference control between the main machine and the looper, multivariable control It was common to control by.

On the other hand, in the mass flow AGC, the outlet side plate thickness of the (i + 1) -th stand is controlled by the main unit 15 of the i-th stand using the law of constant mass flow between stands. At this time, the tension needs to be substantially constant, and the tension is controlled by the rolling position control device. Hereinafter, an outline of the mass flow AGC will be described.

Assuming that the width of the rolled material is constant before and after rolling, the constant law of mass flow is expressed by the following equation.

H _i · v _i = h _{i + 1} · v _{i + 1} (1) where h _i : i-stand exit side plate thickness v _i : i-stand exit side material speed h _{i + 1} : i + 1 stand exit plate thickness v _{i + 1} : i + 1 stand exit material speed

By transforming equation (1), the following equation is obtained.

H _{i + 1} = (h _i / v _{i + 1} ) · v _i (2) If the exit material speeds v _i , v _{i + 1} cannot be directly detected, it changes depending on the rolling state. advanced rate to f _i, f _{i + 1}
Is estimated and calculated by the following equation.

V _i = (1 + f _i ) · v _Ri (3) v _{i + 1} = (1 + f _{i + 1} ) · v _{Ri + 1} (4) where v _Ri and v _{Ri + 1} are the main engine rotational speeds. Measuring device 17 and
Roll speed measured at 18.

Here, i stand roll speed change amount Δv
Influence coefficient from _Ri to i + 1 stand exit side thickness variation Δh _{i + 1}

[0028]

(Equation 1) Is obtained as follows.

First, assuming that the thickness is controlled with sufficient accuracy, the following equation is established.

[0030] _{h iref · v i = h i} + 1ref · v i + 1 ... (5) v i in the equation (5), v i _{+ 1,} respectively (3), the value of the equation (4) Substituting gives the following equation: h _iref · v _Ri · (1 + f _i ) = h _{i + 1ref} · v _{Ri + 1} · (1 + f _{i + 1} ) (6) Next, it is assumed that the advance rate does not change because the tension is kept constant. Assuming that when the roll speed of the i-stand changes by Δv _Ri , the plate thickness on the exit side of the ( _{i + 1)} -stand is Δh _{i + 1}
If only the value changes, the following equation holds.

H _iref · (v _Ri + Δv _Ri ) · (1 + f _i ) = (h _{i + 1ref} + Δh _{i + 1} ) · v _{i + 1} · (1 + f _{i + 1} ) (7) From this equation (7) By subtracting equation (6), the following equation is obtained.

H _iref · Δv _Ri · (1 + f _i ) = Δh _{i + 1} · v _{Ri + 1} · (1 + f _{i + 1} ) (8) Accordingly, the influence coefficient is given by the following equation.

[0033]

(Equation 2) The roll peripheral speeds v _Ri and v _{Ri + 1} were measured by the roll speed measuring devices 13 and 14 in FIG.
In addition to the C main controller 23. Mass flow AGC main controller
At 23, the advance rates f _i and f _{i + 1} are estimated,
According to the equations (3) and (4), the material speeds v _i , v
_{Find i + 1} . Next, the mass flow AGC main controller 23
These materials velocity v _i, and v i _{+ 1,} based on the material thickness h _i of the i stand delivery side detected by the thickness measuring device 29, i
The material thickness h _{i + 1} at the +1 stand exit side is obtained. Next, the mass flow AGC main controller 23 controls the outlet side plate thickness h.
_{From i + 1} and the reference value h _{i + 1ref of} the outlet side plate thickness,
The main machine speed correction amount ΔV _Ri of the stand is calculated and added to the main machine speed control device 19.

[0034]

(Equation 3) Here, T: delay time for timing synchronization (transfer delay time between materials for stands) S: Laplace operator

This is based on the condition that the tension between the i-th stand and the (i + 1) -th stand is substantially constant. In order to satisfy this condition, in this embodiment, the tension is controlled using the rolling-down position control device 28. . That is, the rolling tension control device 26
Calculates a roll gap opening command value from the deviation between the tension detected by the tension measuring device 24 and the tension reference, and gives the calculated value to the rolling position control device 28 so that the actual roll opening matches the command value. Has become.

While the mass flow AGC has been described above, the overall operation of the embodiment shown in FIG. 1 will be described with reference to the control block diagrams of FIGS. 2 and 3.

When the leading end of the rolled material 1 passes through the i-stand, i
Until the +1 stand bites the looper 4, the rolled material 1
Is made to wait downward so as not to contact with. Then, when the leading end of the rolled material 1 is bitten by the i + 1 stand, that is, when the rolled material 1 is passed through the i + 1 stand, the looper 4 is lifted. At this time, when the tension measuring device 24 comes into contact with the rolled material 1, it receives an impact, which is detected as tension. Therefore, immediately after the sheet is passed through the i + 1 stand, the looper drive motor 5 is controlled so that the reference tension acts without performing the tension feedback control based on the detected tension.

For this reason, the control changeover switches SW1 to SW
The contact No. 4 is held in the illustrated state. Therefore, the current reference of the current reference generator 8 is applied to the current controller 9, and the current controller 9 controls the current of the looper drive motor 5 according to the current reference. As a result, the looper 4 is lifted to generate a tension in the rolled material 1 that matches the tension standard. The angle of the looper 4 is measured by a looper angle measuring device 12, and the looper height controller 11 calculates a main engine speed correction amount Δv _Ri such that the position coincides with the reference value and adds it to the main engine speed control device 19. Thus, the looper 4 is adjusted to the reference height. On the other hand, the rolling load of the (i + 1) th stand is detected by the load cell 22, and the rolling thickness control device 25 gives the rolling gap opening command value for matching the detected value to the reference value to the rolling position control device 28.

As a result, the tension of the rolled material 1 is controlled to the reference value by the current reference of the current reference generator 8, the height of the looper 4 is maintained at the reference value by the rolling roll speed of the i stand, and the i + 1 stand exit side Is controlled by the rolling position control device 28.

A control system in a state where the contacts of the changeover switches SW1 to SW4 are illustrated can be represented by a block diagram of FIG.

In the figure, a reference change amount (hereinafter, change amount) of the looper angle Δθ _iref is represented by a conversion gain unit 30.
Reference rolled material loop amount between the stand through .DELTA.l _iref
And the actual looper angle Δθ _i is converted to a conversion gain 41
Is converted to the reference .DELTA.l _i of the rolling material loop amount through.
A loop amount .DELTA.l _iref and .DELTA.l _i of the rolling material 1
Loop height controller 31 corresponding to middle looper height controller 11
And a command value Δv _Riref of the main engine speed correction amount Δv _Ri of the i-stand is calculated from the difference. 1 is converted into a main engine speed correction amount Δv _Ri by a main engine speed control unit 32 corresponding to the main engine speed control device 19 in FIG. This tension generation process
33 also includes the loop amounts Δl _i and i between the stands.
+1 stand main engine speed Δv _{Ri + 1} is also added, and the total tension Δ
T _i is obtained. The total tension ΔT _i is converted into a torque ΔT _Ti by a tension torque generation gain 34 and applied to a looper drive motor process 35. On the other hand, the actual looper angle Δθ _i is converted to a current reference ΔI _iref by a current reference generation function unit 37 corresponding to the current reference generator 8 in FIG. Then be converted to the looper drive motor current [Delta] I _i which corresponds to the current reference [Delta] I _iref by the current control device 38, further, after the torque constant unit 39 is converted into the looper torque [Delta] T _ai is multiplied by a torque constant to this, looper Drive motor process 35
Is added to Further, the actual looper angle Δθ _i is multiplied by a torque gain in a torque gain unit 40 and converted into a torque ΔT _si by a plate weight, a looper own weight, and a looper acceleration / deceleration, and is applied to the looper drive motor process 35. . The looper drive motor process 35 determines the Δ
The calculation of T _si + ΔT _ai −ΔT _Ti is executed, and the obtained value is converted into the rotation angular velocity Δω _i of the looper drive motor. The rotational angular velocity Δω _i is calculated by a looper angle ΔΔθ _i by a looper angular velocity-looper angle conversion function of the looper drive motor.
Is converted to

The control method shown in the block diagram of FIG. 2 makes it possible to maintain the tension on the basis of the tension from the looper angle without actually measuring the tension, and also to keep the looper height constant. In addition, it is possible to suppress the instability of the tension immediately after passing the i + 1 stand through which the value of the tension measured by the tension measuring device tends to include an error.

On the other hand, in a mass flow AGC or the like, since the plate thickness is controlled using the main unit of the i-stand as the operation end, the main unit cannot be used as the operation end of the looper height. Therefore, when a certain period of time has passed since the rolling material 1 passed through the i + 1 stand and the angle θ of the looper 4 was stabilized to some extent, the control changeover switches SW1 to SW4 were set in the opposite state to that shown in the drawing. Switch.

By this switching, the looper height controller 10 applies a speed correction value to the speed controller 7 so that the measured angle of the looper angle measuring device 12 matches the reference angle. The speed control device 7 generates a current reference corresponding to a value obtained by correcting the difference between the detected value of the rotation speed measuring device 6 and the reference value with a speed correction value, and this current reference replaces the output of the current reference generation device 8. Is input to the current control device 9. Meanwhile, a tension measuring device
The detected value of the material tension by 24 is given to the rolling tension control device 26, which outputs a command value ΔS _oiref of the roll gap opening ΔS _oi , which _{replaces the} output of the _rolling thickness control device 25. Input to the rolling position control device 28. The main machine speed correction amount calculated by the mass flow AGC main controller 23 is the same as the looper height controller 11.
Is input to the main engine speed controller 19 in place of the output of the main engine.

As described above, the control changeover switches SW1 to SW
By switching W4, the tension control is performed by the rolling position control device 28, so that the tension control by the looper 4 becomes unnecessary, and the main function of the looper 4 is to support the rolled material 1 to improve the threadability. Become. That is, the looper height controller 10 _{supplies a} speed correction signal to the speed control device 7 only for the purpose of keeping the height of the looper 4 at the given looper height reference value θ _iref .

A control system in a state where the contacts of the changeover switches SW1 to SW4 are switched to the opposite side to that shown can be represented by the block diagram of FIG.

In the drawing, a _rolling tension control unit 42 corresponding to the rolling tension control device 26 outputs a roll gap opening reference ΔS _{oi + 1ref} corresponding to a deviation between the tension reference value Δt _firef and the detected tension value Δt _fi. , The rolling position control unit 43 corresponding to the rolling position control device 28 sets the roll gap opening to _{ΔSoi + 1} . The roll gap opening-forward tension process 44 generates a forward tension Δt _firef corresponding to the roll gap opening ΔS _{oi + 1} . The conversion gain unit 48 converts the looper angle Δθ into forward tension, and performs a roll speed-forward tension process 49.
Outputs a forward tension corresponding to the roll speed Δv _Ri . On the other hand, the looper height controller 45 outputs the rotation angular velocity reference Δω _iref based on the difference between the looper angle Δθ _i and the angle reference Δθ _iref . The looper drive motor speed controller 46 generates a current reference ΔI _iref corresponding to a difference between the rotation angular speed reference Δω _iref and the detected rotation angular speed Δω _i . This current reference ΔI
looper drive motor current control unit 38 is caused to looper drive motor current [Delta] I _i according _iref, torque constant unit 39 generates a torque [Delta] T _ai. The looper angle Δθ _i is converted into a torque ΔT _si by a torque gain unit 40, and the conversion gain unit 47 converts the tension Δt _fi into a torque ΔT _fi . The looper drive motor process 35 calculates the sum of these torques as the looper angle Δω _i
Convert to

In the tension feedback control system shown in FIG. 3, the tension is controlled by a reference value with respect to a disturbance caused by a change in the speed of the main unit 15 of the i-stand, which is an operation end of the mass flow AGC, and a change in tension caused by a change in the angle of the looper. It has a function to control to keep it. Also, the looper height control system has a function of controlling the looper height to a reference value against disturbances such as a change in the looper height due to a change in tension and a change in the looper height due to the plate weight, the looper's own weight, or the like. .

The timing of switching from the control method shown in FIG. 2 to the control method shown in FIG. 3 is performed at intervals of the sampling pitch. That is, assuming that the control according to the method shown in FIG. 2 is currently performed at the k-th control timing from the start of the tension control, the control is switched to the method shown in FIG. Control is performed by the method shown in FIG. At this time,
ΔI _ref , Δv _ref , Δ which are output of the k-th control signal
_{Soi + 1ref and the} like are held and used at the time of the (k + 1) th control. Also, the command value ω of the looper motor rotation angular velocity
_iref is the k-th looper motor rotational angular velocity omega _i, the value of the integrator included in the controllers or also maintained, or be initialized to appropriate values.

In the above embodiment, a four-high rolling mill and a rolling mill having an electric looper have been described.
It is obvious that the present invention can be applied even if the type of the rolling mill and the looper drive system are changed.

In the above embodiment, the description has been given of the case where the present invention is applied to the two stands.
Needless to say, the present invention can be similarly applied to a multi-stand rolling mill having more than a stand.

[0052]

As is apparent from the above description, according to the present invention, in a hot rolling mill having a looper between stands, activation of the tension control and control of the looper when tension control such as mass flow AGC is performed by a rolling-down device. Can be established, and the instability of the tension immediately after threading can be suppressed, thereby enabling more stable operation of the hot rolling mill.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention, together with an application object.

FIG. 2 is a block diagram showing a configuration of a control system according to one embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a control system according to one embodiment of the present invention.

[Explanation of symbols]

 2 i stand 3 i + 1 stand 4 looper 5 looper drive motor 7 looper drive motor speed controller 8 looper drive motor current reference generator 9 looper drive motor current controller 10 looper height controller 11 looper height controller 12 looper angle measurement Apparatus 13 Rolling roll rotation speed measuring device 14 Rolling roll rotation speed measuring device 15 Rolling roll drive main motor 16 Rolling roll drive main motor 19 Main machine speed control device 20 Main machine speed control device 23 Mass flow AGC main controller 24 Tension measuring device 25 Press down plate Thickness control device 26 Roll-down tension control device 27 Roll-down position control device 28 Roll-down position control device 29 Sheet thickness measurement device

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B21B 37/48-37/52

Claims (2)

(57) [Claims] 1. A hot rolling mill in which a looper is arranged between i (i = 1 to n-1) stands and i + 1 stand among n stands arranged in tandem.
A tension control system for generating a current reference of the looper driving motor so as to maintain the tension of the rolling material between the stand and the (i + 1) th stand at a reference value, and controlling the current of the looper driving motor in accordance with the current reference; Height control system that corrects the speed of the rolling roll drive main motor of the i-stand so that the height of the looper is maintained at a reference value, and a rolling material between the i-stand and the i + 1-stand. And a tension feedback control system for controlling the rolling force of the i + 1 stand so as to maintain the tension of the rolled material at a reference value, and a certain time elapses after the rolled material is caught in the i + 1 stand. Until, while the tension control system and the looper height control system in the operating state, the tension feedback control system in the inactive state,
After a certain period of time has elapsed after the rolled material has been caught in the (i + 1) stand, the control operation switching is performed so that the tension control system and the looper height control system are deactivated and the tension feedback control system is activated. Means for controlling a hot rolling mill. 2. The rotation speed of each of the rolling rolls of the i-stand and the (i + 1) -th stand, and the thickness of the sheet on the exit side of the i-stand are detected. 2. The hot rolling mill according to claim 1, further comprising a mass flow automatic thickness control system for correcting, wherein the automatic mass flow thickness control system is switched between an operation state and a non-operation state in accordance with the tension feedback control system. Control device.