JPS61129218A - Control method of sheet thickness by using rolling down device of tandem rolling mill - Google Patents

Abstract

PURPOSE:To improve sheet thickness accuracy by detecting the sheet thickness on the inlet side or outlet side of a stand, inputting the sheet thickness signal thereof to a rolling down control device then controlling the rolling down of each stand in accordance with the deviation between the sheet thickness signal and target value. CONSTITUTION:Rolling down devices 9-12, rolling down control devices 23-26, sheet thickness control devices 27-30 and sheet thickness deviation detectors 35-38 are respectively disposed to rolling rolls 1-4 of the respective stands. Thesheet thickness deviation remaining in the No.2 stand and the sheet thickness deviation generated therein are detected by the detector 37 and is inputted to the device 29. The device 29 emits a roll gap change command to the device 25 by measuring the timing with a sheet speedometer 41 and inputs the roll gap change command to the device 24 so as not to change the sheet thickness on the outlet side of the No.2 stand. The roll gap change commands are emitted similarly to the respective stands, by which the sheet thickness deviations of high-frequencies are eliminated and the sheet thickness accuracy is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to metal tandem rolling mills which are not equipped with a device for mechanically controlling tension between stands, such as tandem cold rolling mills. This invention relates to a plate thickness control method using a rolling down device.

[Conventional technology]

Conventionally, in a tandem rolling mill such as a cold tandem rolling mill that does not have a mechanical inter-stand tension control position between the stands, 1
Stands other than the stand (hereinafter referred to as intermediate stands)
It was common knowledge that even if the rolling roll device was operated to open and close the gap between the rolling rolls, the thickness of the sheet exiting from the stand would hardly change.

The reason for this will be explained with reference to FIGS. 3 and 4. In Fig. 3, 1 is a No. 1 stand rolling roll; 2. Suyo No. 2 and No. 3 stand rolling rolls become so-called intermediate stand rolling rolls. 9, 10 and 11 are stands STI from 1 to 3 respectively.
-This is the rolling down device of ST3. Also, 31 is a strip,
Hle, H2S, H2S' are 1, 2.3 stand entry side board thickness, Hld" 2d 'H3d is 1, 2.3
No. stand exit side plate thickness, ■1e, V2e.

■3e is 1.2.3 stand entrance strip speed,■
1d, ■2d" 3d is the strip speed at the exit side of stands No. 1, 2 and 3, TOI is the strip tension at the entrance side of stand No. 1 1. T12 and T23 are the strip tension between stands No. 1 and 2 and between stands No. 2 and 3, L is the distance between stands, V;, V2.V3 is the circumferential speed of No. 1, 2.3 rolling rolls. Figure 4 shows the mill elastic curves a, b and strip plasticity curves 01 to C3 in No. 3 stand ST3. Assuming that the plate thickness at the entrance of the No. 3 stand is H3e and the roll gap of the No. 3 stand without chewing the strip is 33, the mill elastic curve is a, the strip plasticity curve is cl, and the curve appears at their intersection. Therefore, the thickness of the exit side of the No. 3 stand is H3d.Here, the thickness of the exit side of the No. 3 stand is H3dn.
In order to achieve this, the No. 3 stand lowering device 11 shown in Fig. 3 is operationally tightened.) When the roll gap is increased from 83 to 83n, the mill elastic curve becomes b, and the No. 3 stand outlet plate thickness is determined from the intersection of curve 1 and the curve. seems to be H3dn. However, in FIG. 3, the law of constant mass flow (formula (1) below) before tightening the reduction device must also hold after tightening.

H3d ・■3d ” H3e ”3e
””...(H3e, ■3d even after tightening 11)
does not change, so let the entry speed of No. 3 stand after tightening be ■ en H3dn ``3d'' H3e v3en
・・・・・・(2) becomes H3d>H3dn
Therefore, V3d>”3en.

Even though the No. 3 stand entrance speed has become smaller, the No. 2 stand exit speed V2d does not change, so the tension T23 between the No. 2 and No. 3 stands becomes loose. That is, the tension between the stands changes from T23 in the following equation (3) to T2 in the following equation (4).

3n However, E is a Young's modulus of 2.3 Due to a change in the tension between the stands, the slope of the strip plasticity curve in FIG. 4 changes from curve C1 to curve C2. As a result, the plate thickness on the exit side of the No. 3 stand becomes the plate thickness determined by the intersection A of the curve C2.

Furthermore, as a result of the loosening of the tension between the No. 2 and No. 3 stands, the thickness of the plate on the exit side of the No. 2 stand also becomes thicker. When this thickened portion reaches the entrance side of stand No. 3, H3e in Fig. 3 becomes thicker.

As shown in Figure 4, if H3e changes to H'3°, the mill elastic curve moves from curve C2 to curve C3, and the plate thickness at the exit side of No. 3 stand is determined by the intersection of curve 3 at H'3.
．． 3 despite the operation of the No. 3 stand lowering device.
The thickness of the plate on the exit side of the stand does not change much.

As mentioned above, even if the intermediate stand is lowered, the plate thickness at the exit side of the stand does not change, so automatic plate thickness control (AGC) devices have been constructed on this premise.

For example, in a four-stand tandem cold rolling mill according to FIG.
The configuration of a typical conventional AGC device shown in No. 1 will be explained. No. 1 stand entrance plate thickness deviation detection device 3
The board thickness deviation signal ΔH1e (the board thickness reference is given to the device 35 in advance) detected by the board 5 is input to the No. 1 stand reduction feedforward AGC device 27, and at the same time, the board speed at the entrance of the No. 1 stand is measured by the board speed meter 39. This is detected and inputted to the AGC device 27. The AGC device 27 calculates to which position the strip having the plate thickness obtained by the detection device 35 is moving based on the plate speed, and when the position reaches the No. 1 stand roll bite, the reduction position change command value ΔSR+ is calculated. is given to the reduction control device 23. 23 to 26 may be a rolling position control device or a rolling force control device (in the case of a rolling force control device, ΔSR+ is the rolling force change command value ΔPR+
In this example, the case of a lowering position control device will be explained. First, to explain how to calculate the command value ΔSR+, generally the plate thickness variation ΔH1d on the mill outlet side is expressed as the plate thickness variation ΔH on the mill inlet side.
1e and the rolling position variation ΔS, it is expressed by the following equation.

ill 't Q IVL f +=1 where M is the mill elastic deformation coefficient and Q is the strip plastic deformation coefficient.

In order to make ΔH1d zero even if ΔH1e changes in equation (5), ΔH1 should be set to zero and ΔS should be operated according to the following equation.

Therefore, ΔSRI is expressed by the following formula according to ΔH1e.

The rolling control device 23 in FIG. 5 moves the rolling device 9 according to ΔSR+ and adjusts the roll gap, thereby zeroing out the thickness deviation on the exit side of the No. 1 stand based on the variation in the thickness on the entrance side of the No. 1 stand. The plate thickness deviation ΔH2e on the entrance side of the No. 2 stand is detected by the detection device 36 and input to the No. 2 stand speed feedforward AGC device 17. The AGC device 17 obtains the board speed at the entrance of the No. 2 stand from the board speed meter 40 and sends it to the detection device 3.
6, the No. 1 stand roll speed control device 1 measures the timing when the part of the strip having the plate thickness deviation detected by 6 arrives at the No. 2 stand roll bite, and according to ΔH2e.
3Give the roll speed change command ΔVIR. ΔVIR is calculated as follows. In Figure 3, H2e is ΔH2e
■2d because H2d does not change when
If "2e does not change," 2e changes and V2e - ΔV2
e, it is necessary to keep the mass flow constant, and therefore the equation (6) holds true.

(H28+ΔH2e) ("2e-Δ"2e)
= H2d V2d... (6)' Constant mass flow law H2e in the state shown in Figure 3 ``2e = H2d Substitute V2d into (6) 'El'' to obtain the second-order minute term ΔH2eΔV2e
If is omitted, the formula becomes (7)'.

■2.3 is almost equal to the No. 1 roll circumferential speed v1 (7)
'Equation becomes Equation (8).

ΔV, =-ΔH2e...
(8) 2e Therefore, the No. 1 stand roll speed change command ΔVIR can be expressed by the following formula.

According to this ΔVIP, the speed control device 13 shown in FIG. 5 changes the rotational speed of the roll drive electric motor 5 to zero the variation in the plate thickness on the outlet side of the No. 2 stand based on the variation in the plate thickness on the inlet side of the No. 2 stand. Similarly, in FIG. 5, the plate thickness deviation on the entrance side of the No. 3 stand is detected by the detection device 37 and input to the AGC device 18.

The AGC device 18 synchronizes the timing with the No. 3 stand entry plate speed (detected by 41) and gives the No. 2 stand roll speed change command ΔV2R to the roll speed control device 14, and the device 14 changes the rotation speed of the electric motor 6 according to ΔV2R. By changing the rotation speed of roll 2, 3
The variation in plate thickness on the exit side of the No. 3 stand, which is based on the variation in the plate thickness on the entrance side of the No. 3 stand, is made zero. The AGC device 18 also sends a speed change command to the roll speed control device 13, so that the speed ratio of rolls 1 and 2 is maintained so that the tension between stands No. 1 and No. 2 does not change due to changing the speed of roll 2. Change the speed of roll 1 so that Similarly, for the No. 4 stand, the signals from the plate thickness deviation detection device 38 and plate speed meter 42 are input to the AGC device 19, and the AGC device 19 zeroes out the plate thickness variation on the exit side of the No. 4 stand based on the plate thickness variation on the input side of the No. 4 stand. While giving the No. 3 stand roll speed change command ΔV3R to be changed, the roll speed control device 1
No. 1 on 3.14.

Each roll speed change command is given so that the No. 2 and No. 3 stand roll speed ratios do not change due to ΔV3R.

As mentioned above, the plate thickness variation on the exit side of the No. 1 stand is controlled by operating the No. 1 stand lowering device, the plate thickness variation on the exit side of the No. 2 stand is changed by changing the No. 1 stand roll speed, and the plate thickness variation on the exit side of the No. 3 stand is controlled by the No. 1 and 2 stand roll speeds. In conventional AGC, the stand roll speed is changed to reduce the thickness variation on the exit side of the No. 4 stand to 1.2°, while the No. 3 stand roll speed is changed to zero.

[Problem that the invention seeks to solve]

Conventional AGC has a limited control ability and cannot achieve sufficient plate thickness accuracy. The reason for this is that the response speed of the roll speed control devices 13 to 16 shown in FIG. 5 is slow. Normally, in the speed control system of large rolling rolls such as the rolling roll drive device of a tandem cold rolling mill, the moment of inertia of the rolls and electric motor is large, so the response speed is at most about 2 Hz, and it cannot be used for frequencies higher than this. The phase shift and gain decrease will increase. Frequency analysis of the plate thickness variation on the exit side of the one-way stand reveals that there is a frequency component of Om10Hz. It is believed that the plate thickness variation between IHz and 10 Hz is printed plate thickness variation due to the eccentricity of the rolling roll in the previous process (hot rolling). Roll eccentricity in tandem cold rolling is also thought to be caused by plate thickness fluctuations of 1 to 10 Hz, and this is supported by the fact that the plate thickness variation frequency is the frequency of roll rotation in hot rolling and cold rolling and its harmonics. It will be done. In conventional AGC, except for controlling the plate thickness on the exit side of the No. 1 stand by using the No. 1 stand reduction control, the thickness on the exit side of the stand after the No. 2 stand is controlled by controlling the roll speed of each stand. Among plate thickness fluctuations that remain unremoved and plate thickness fluctuations caused by eccentricity of each roll of the pressure feeding machine, it is impossible to remove thickness fluctuations that exceed 2 Hz, which is the response speed of the roll speed control device. Strip thickness fluctuations of 2 Hz or more were about ±1% of the strip thickness, which was within the tolerance range, but as the manufacturing process using metal strips and knobs becomes more automated and faster, strip thickness accuracy has become smaller. As the requirements for
GC was no longer able to meet that demand.

The present invention aims to eliminate plate thickness fluctuations in the entire frequency range included in the rolled material of tandem rolling mills, which could not be removed by conventional plate thickness control devices. It is intended to provide a control device.

[Means for solving problems]

A condition that a metal strip rolling mill, which is a premise of the present invention, must have is that the response speed of the rolling reduction control device is faster than the response speed of the roll speed control device. For example, the rolling down device may be a hydraulic rolling device, and the roll driving device may be a Siris-Cleonard device using a direct current motor. As mentioned above, the response frequency of the roll speed control device is approximately 2Hz.
On the other hand, the response frequency of the hydraulic pressure reduction control device is about 20 Hz, which is much faster.

The focus of the present invention is that in conventional tandem cold rolling, it was thought that there was almost no change in the plate thickness at the exit side of the stand due to the operation of the rolling device of the intermediate stand, but in reality,
The fact is that the thickness of the exit side plate can be changed by operating at a relatively high frequency of 2 Hz. Curve A shown by the solid line in Figure 6 shows the variation in the thickness of the exit plate when the rolling device of the second stand is operated at various frequencies in actual S-cross-end cold rolling.
It is 1. The vertical axis indicates gain - amount of change in plate thickness on the exit side of the stand/amount of instruction for changing the rolling position, and indicates the degree of change in plate thickness on the exit side of the stand due to the rolling operation. The horizontal axis is frequency, expressed on a logarithmic scale. The degree of influence on plate thickness variation due to rolling operation is 2
It is maximum at ~4 Hz, and at frequencies higher than this range, the response of the rolling device becomes poor and the rolling device itself does not move despite instructions to change the rolling position, so the gain decreases.

The reason why the gain decreases in the low frequency region is as follows. In Figure 4, even if the No. 3 stand roll gap is changed from S3 to S3n, the mill elastic curve moves from CI to 02 and then to 03, so the thickness at the exit side of No. 3 stand changes little from H3d. Then H'3. Therefore, there is almost no change. However, from C1 to 02, the Mill elastic curve is from a to b.
1. Tension between No. 2 stands (Tl2 in Figure 1)
It only moves when the changes. This takes about 0.2 seconds.

Also, the phenomenon of transition from 02 to 03 in Figure 2 is that the tension TI2 changes, the thickness H2d of the exit side of the No. 2 stand changes, and the changed strip is transferred and reaches the No. 3 stand roll, H3.
It only happens when e. The strip transfer time takes 0.5 seconds, for example, when the distance between the stands (L in Figure 1) is 5 m and V2,1 in Figure 3 is 600 mpm (L Omps). Therefore, it takes 0.7 seconds to move from 01 to 03 in FIG. 4, and changes in rolling reduction with a period longer than that do not appear as changes in the plate thickness on the outlet side of the stand, resulting in the characteristics shown in FIG. 6. Conversely, fluctuations in the rolling position with a period of 0.7 seconds or more can change the thickness of the plate on the outlet side of the stand.

Here, if the strip plasticity curve does not move from C1 to C2 and C3 even if the rolling operation moves from curve a to curve A in FIG. 4, dotted line curve A2 in FIG. Side plate thickness varies. The present invention prevents or eliminates the effect of movement from C1 to C2 and C3 in FIG. 4 by operating the rolling down devices of the stand and the upstream stand, and utilizes a rolling down device that is more responsive than the roll speed control device. This allows the plate thickness to be controlled with high precision.

The principle of the method of the present invention will be explained according to FIG.

From the intersection K of a and C1 in the same figure, the thickness of the exit side of the No. 3 stand is H3.
d is determined. Here, the thickness of the exit side of No. 3 stand is H3dn.
In order to do this, operate the No. 3 stand lowering device to change the No. 3 stand roll gap from S3 to 53n (the necessary roll gap assuming no change in tension). However, first, the tension T23 in FIG. 3 changes and moves from 01 to 02 in FIG. 7, and the No. 3 outlet side plate thickness is determined by the intersection A with the curved line. Therefore, according to the change in tension, the No. 3 stand roll gap is moved to 83r in Fig. 7. The tension T23 in Fig. 3 changes further, and 02 in Fig. 7 moves to c3, but the plasticity curve moves from b to C as it moves from S3n to S3r).
Taking this into consideration, the S3
Determine r. Also, the No. 2 stand rolling gap is changed by operating the No. 2 stand rolling device so that the plastic curve does not move from 03 to 04 in FIG. The movement from C3 to 04 occurs when the plate thickness on the entrance side of No. 3 stand changes from H to H2Se, but this is due to the tension T2 being changed by the operation of the rolling down device 11 in Fig. 3.
3 changes, which causes a change in plate thickness H2d (H'2
d), this is what happens when the No. 3 stand roll is reached. To prevent this, the No. 2 roll gap may be changed at the same time as the No. 3 stand roll gap is changed. The phenomenon caused by changing the roll gap of No. 2 stand is the same as when changing the roll gap of No. 3 stand, and in Fig. 7, H3° is changed to H2d, H3e is changed to H2e, H2Se.
It is better to replace S3 with S2° and S3r with S2r.In order to prevent H2d from moving from the value of H3e to H2Se, it is sufficient to change it from 32 to S2r.

By changing the No. 2 stand roll gap, the tension TI in Figure 3
2 will change, so it will be necessary to manipulate the No. 1 stand roll gap in order to negate that effect.

As mentioned above (by changing the No. 3 stand roll gap,
In order to set the thickness of the exit side of No. 3 stand to the target value, move the no. This can be achieved by changing the roll gap of the stand.

An example of application of the plate thickness control method of the present invention based on the above principle will be explained with reference to FIG. Similar to Figure 5, in this figure, 1 to 4 are the rolling rolls of stands 1 to 4, 9 to 12 are rolling devices, 23 to 26 are rolling control devices, and 27 to 30 are plate thickness control devices (rolling devices). feedforward AGC device),
35 to 38 are plate thickness deviation detection devices, and 39 to 42 are plate speed meters.

Plate thickness control device for No. 1 stand (9° 23 in Figure 1)
27, 35, 39) is the same as that in Figure 5 (9,
23, 27, 35, 39). The plate thickness deviation remaining in the No. 1 stand and the plate thickness deviation caused by the eccentricity of the No. 1 stand roll are detected by the detection device 36 and input into the plate thickness control device 2. The device 28 calculates the plate thickness change command ΔSR2 according to equation (7), but the strip plastic deformation coefficient 02 in the No. 2 stand changes by ΔQ2 due to the tension between the No. 2 stands (this is calculated in advance). (actually measured), it is given by the following formula. However, M2 is the No. 2 stand mill plasticity coefficient.

(However, ΔH2 is the reduction amount H2e-H2 at No. 2 stand.
d) The second term on the right side of equation (101) is explained in Figure 2.C1
The thickness H2dn of the exit side of the No. 2 stand determined by the intersection of and a is 2
The strip plasticity coefficient Q2 at the No. stand is Q2ΔP2 is M2ΔS2', and ((Q2+ΔQ2)ΔH2−
It is also expressed as Q2ΔH2)=−ΔQ2·ΔH2. Therefore, M2ΔS2'=゛-ΔQ2ΔH2, that is, the plate thickness control device 28 in FIG.
Also, it is necessary to prevent the plate thickness variation on the outlet side of the No. 1 stand caused by the tension between the No. 1 and 2 stands changing due to the operation of the No. 2 stand reduction, and as a result, the strip plasticity coefficient Q1 in the No. 1 stand changes to Q1 + ΔQ +. The pressure lower position change command ΔSR+' is output according to the following formula.

This idea is similar to equation (11).

(However, M; is the No. 1 stand mill elastic modulus, ΔH+ is 1
The plate thickness deviation remaining at the No. 2 stand and the plate thickness deviation generated at the No. 2 stand are detected by the detection device 37 in FIG. At the same time, the board speed meter 41 measures the timing and outputs a No. 3 stand roll gap change command to the roll down control device 25, and at the same time, the roll down control device 24 so that the plate thickness on the exit side of the No. 2 stand does not change due to the change in the No. 3 stand roll gap. A No. 2 stand roll gap change amount command is output to the No. 2 stand roll gap change command, and a No. 1 stand roll gap change command is output to the reduction control device 23 so that the plate thickness on the exit side of the No. 1 stand does not change due to the change in the No. 2 stand roll gap. Similarly, in the No. 4 stand, the plate thickness control device 30 uses the measured values of the plate thickness deviation detection device 38 and the plate speed meter 42 to output roll gap change commands to the reduction control devices 26, 25, and 2423, respectively.

The rolling down control devices 23 to 26 that have received the roll gap change command operate the rolling down devices 9 to 12, respectively, to change the No. 1 to 4 stand roll gaps as instructed, and make the plate thickness fluctuation on the outlet side of each stand zero.

As mentioned above, conventionally from No. 2 stands onwards, plate thickness was controlled using a roll speed control device with a low response speed.
By using the plate thickness control method of the present invention, high-frequency plate thickness deviations that could not be removed by conventional methods can be removed. Of course, this method can also be used in combination with a conventional sheet thickness control method using a roll speed control device.

In addition, it has been confirmed in experiments that the tension on the exit side of the stand changes slightly when the roll-down operation is performed, and as shown by the broken line in Figure 1, it is also possible to operate the roll-down device of the stand downstream from the stand concerned to improve plate thickness accuracy. Effective for improvement.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2, Fig. 4, Fig. 6, and Fig. 7 are graphs for explaining the operation, Fig. 3 is an explanatory diagram of the tandem mill, and Fig. 5. FIG. 1 is a block diagram illustrating a conventional device. In the drawing, 1 to 4 are the rolls of No. 1 to 4 rolling stands, and 9 to 1
2 is a rolling down device, 23 to 26 are rolling down control devices, 31 is a metal strip, and 35 to 38 are plate thickness deviation detection devices. Applicant Nippon Steel Corporation Patent Attorney Minoru Aoyagi 1st I! 1 1~4 Pressure] E port Figure 3+, 2.3: No. 1, 2.3 Stacido twin ILo-
Le 9.10.14: 1.2.3 stand, pressure setting 4th 13-16 Roll l blow control moxibustion! 17-19 Speed Feedforward 1-'AGC Tiger!
! 23-26: Reduction rate 114 feet table t 39-421 size 27: ff Lower foot "Forward AG"
(J distance 1 [5 to 38: Handling Atsuku cliff pinching device Fig. 6

Claims (1)

[Claims] A tandem rolling mill for metal strip steel that has multiple rolling stands and is equipped with a rolling control device that controls the rolling position or rolling force by manipulating the rolling position, and is not equipped with a mechanical device for controlling inter-stand tension such as a looper between the stands. , the inlet side plate thickness or the outlet side plate thickness of at least one stand excluding the first stand is detected directly or by calculation, the plate thickness signal is input to the rolling control device, and the plate thickness is detected according to the deviation between the plate thickness signal and its target value. By operating the rolling down device of the stand and at the same time controlling the fluctuation in strip tension caused by this operation, the rolling down device of the upstream stand and/or downstream stand is also operated to prevent variations in the thickness of the exit side of the stand upstream and/or downstream of the stand. A method for controlling plate thickness in a tandem rolling mill, characterized in that: