JPS61129217A - Method for controlling sheet thickness of tandem rolling mill - Google Patents

Abstract

PURPOSE:To improve sheet thickness accuracy by detecting the sheet thickness on the outlet side or inlet side of a stand, inputting the sheet thickness signal to rolling down control devices and speed control devices and operating the rolling down devices of the respective stands in accordance with the devaition from the target sheet thickness value. CONSTITUTION:Roll speed control devices 13-16 are provided to the respective stands of a tandem rolling mill and low-pass filters 20-22 for low-frequency AGC of Nos. 2-4 stands and high-pass filters 32-34 for high-frequency AGC are respectively provided. The high-frequency component and low-frequency component of the sheet thickness fluctuation of the previous stand are separated. Only the high-frequency component is removed by the high-frequency AGC device of that stand and the low-frequency component is removed by the low-frequency AGC of the respective other stands. The sheet thickness fluctuation over the entire frequency region of the material 31 to be rolled is removed by the above-mentioned method. The sheet thickness accuracy is thus improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to a metal tandem rolling mill that is not equipped with a device for mechanically controlling the strip tension between the stands, such as a tandem cold rolling mill. The present invention relates to a highly accurate plate thickness control method.

[Conventional technology]

It is common knowledge that in conventional cold tandem rolling mills, even if the rolling device of the stands other than the No. 1 stand (hereinafter referred to as intermediate stand) is operated to open or close the gap in the rolling rolls, the plate thickness at the exit side of the stand will hardly change. Met. The reason for this will be explained qualitatively with reference to FIG. 1 is a No. 1 stand roll, and 2.3 is a No. 2.3 stand roll. Stand No. 2.3 corresponds to what is called an intermediate stand. 9 to 11 are the rolling down devices of stands No. 1 to 3. It is now assumed that the roll gap of the stand is narrowed by the No. 2 stand lowering device 5.

Let the inlet side plate thickness of No. 2 stand before narrowing be HI', the outlet side plate thickness as H2, the inlet side speed as v1', and the exit side speed as ■2.1 stand exit speed as vl. At that time, the following equation holds between these quantities due to the constant mass flow law.

H+' v I' = H2V 2 - (1)
Assuming that H2 becomes smaller when the roll gap of the No. 2 stand is narrowed, and setting the change as ΔH2, the thickness of the exit side of the No. 2 stand becomes H2 - ΔH2.

Each stand roll circumferential speed Vl, V2°V3 in Fig. 5
does not change. For example, there is a relationship expressed by equation (2) between the No. 2 roll peripheral speed v2 and the No. 2 outlet plate thickness v2 (however, λ2 is 2
No. stand advanced rate, usually a few percent).

V2=(1+λ2) V2−−(21λ
2 hardly changes due to the operation of the No. 2 reduction device 5, so v2 does not change. H+' also does not change, so +1
In Equation 1, / will change, and if the amount of change is set as Δv1, Equation (1) becomes (1').

H1'(v I'-ΔV)=(H2-ΔH2)V2
(1') Here, the tension T12 between the No. 1 stand and the No. 2 stand is expressed by the following equation.

From formula (1'), No. 2 stand entrance speed Vl after tightening is
-Δv1' is expressed as follows.

That is, the tension T12 between the 1.2 stands and the equation (3) decreases dramatically. When the tension T I 2 decreases, the plate thickness on the exit side of the No. 2 stand mainly increases. As a result, the thickness of the plate on the exit side of the No. 2 stand did not change even when the pulling down device of the No. 2 stand was tightened. Expressed in another way, if the plate thickness on the exit side of the No. 1 stand is Hl, and the plate thickness on the inlet side of the No. 1 stand is constant, the relationship H+ v + = H2V 2 holds true.

v + =V + (1+λ+), V 2 =V
2 (1+λ2)...(3)' (However, λ1.λ2 is the advance rate of No. 1 and No. 2 stands), so Vl (1+λ+)HI=V2 (1+λ
2) It becomes H2. That is, H2=V t (1+λ1)H1/V2(1+λ2)
......(4) It is expressed as follows. Even if you operate the lowering of the No. 2 stand, Vl,
V2. Since Hl, λ2, and λ2 hardly change, the No. 2 outlet side plate thickness hardly changes as a result. Strictly speaking, Hl and λ2 become slightly larger, λ1 becomes slightly smaller, and as a result, H2 hardly changes. To explain this using the mill elasticity curve and strip plasticity curve according to Figure 2, if the mill elasticity curve before No. 2 stand is tightened is CI and the strip plasticity curve is 03, then the plate thickness at the exit side of No. 2 stand is the mill It is determined at the intersection of C1 and 03, where the rolling force required for elongation and the rolling force required for compression of the strip knob match, and becomes H2. At this point, tighten the reduction of the No. 2 stand and change the mill elastic curve from CI to 0.
If you move to 2, the thickness of the exit side of the 2nd stand is C2 and C.
H2 - ΔH2 determined by the intersection of 3, but as mentioned above, the tension between the No. 1 and No. 2 stands becomes small because of this. As a result, the strip plasticity curve moves from C3 to C4, and eventually the thickness of the exit side of the No. 2 stand returns to approximately H2.

Strictly speaking, even if the tension between No. 1 and No. 2 stands is loosened, it does not completely move from C3 to C4, but only moves to C5, but because the tension between No. 1 and No. 2 stands is loosened, Hl becomes thicker, and its As a result, H+' is large (H+' +ΔH+
', and in the end, the thickness of the exit side of the No. 2 stand returns to H2.

As mentioned above, it has been said that even if the intermediate stand is lowered, the plate thickness at the exit side of the stand does not change, and 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 shown in No. 1 will be explained. The plate thickness signal (ΔH[l') (plate thickness reference is given to 35 in advance) detected by the plate thickness deviation detection device 35 on the entrance side of the No. 1 stand is input to the No. 1 stand reduction feedforward ACC device 27, and at the same time The speed meter 39 detects the plate speed on the entrance side of the No. 1 stand and inputs it to the 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+ becomes a rolling force change command value ΔPR+), but in this example, the case of a rolling force control device will be described. The method for calculating ΔSR1 will be described. In general, plate thickness variation ΔH1 on the exit side of the mill is expressed as plate thickness variation ΔH1 on the mill entry side.
When expressed in terms of Ha' and the rolling position variation ΔS, it is expressed by the following equation.

However, M is the mill elastic deformation coefficient and Q is the strip plastic deformation coefficient.

In order to make 8H+ zero even if 8HQ' changes in equation (5), ΔH+ should be set to zero and ΔS should be operated according to the following equation.

Therefore, ΔSR+ is expressed by the following equation according to ΔHo'.

The rolling down control device 23 in FIG. 3 moves the rolling down device 9 according to ΔSR+ to open and adjust the roll gap.
The thickness deviation on the outlet side of the No. 1 stand based on the variation in the plate thickness on the entrance side of the No. 1 stand is made zero. No. 2 stand entry side plate thickness deviation ΔI (+'
is detected by the detection device 36 and input to the AC, C device 17. In the AGC device 17, the No. 2 inlet side plate speed is obtained from the sheet speed meter 40, and the timing is determined when the part of the strip having the thickness deviation detected by the detection device 36 arrives at the No. 2 roll bite, and the No. 1 inlet side plate speed is determined according to ΔH+'. A roll speed change command ΔVIR is given to the stand roll speed control device 13.

ΔVOR is calculated as follows. In Figure 5, H1'
In order for H2 to remain unchanged when the curve is curved by ΔH+', the roll circumferential speed V must change to -Δ■, assuming that the plate speed V does not change. Therefore, equation (1) becomes equation (1).

(H1'+ΔH+') (v+-ΔVl)=H2V2...
(1) Substituting (1) into (1) and omitting the second-order minute terms ΔH and Δ■ gives equation (8).

However, according to equation (3), v 1 =V + (1+λ
Because of the relationship 1), Δv1=Δ■1・(1+λ1)
(However, ΔV+ is the variation of ■1). Since vl is almost equal to Vl', v +' = V + (1+
λ1) and Δl/l'=:Δv1 (1+λ mouth,
Substituting this into equation (8) yields the following equation.

Based on equation (9), the speed change command ΔVIR to the roll speed control device 13 in FIG. 3 is expressed as follows.

According to this ΔvlR, the roll speed control device 13 of FIG.
changes the rotational speed of the roll drive electric motor 5, and makes the variation in the plate thickness on the exit side of the No. 2 stand, which is based on the variation in the plate thickness on the person side of the No. 2 stand, to zero. Similarly, in FIG. 3, 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 entrance plate speed and gives the No. 2 stand roll speed change command ΔV2R to the roll speed control device 14, and the roll speed control device 14 changes the roll drive electric motor 6 according to ΔV2R.
By changing the rotational speed of the rolling rolls 2 and the rotational speed of the rolling roll 2, 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 gave a speed change command to the roll speed control device 13 to change the speed of the rolling roll 2, so the speed ratio of the rolling rolls 1 and 2 was adjusted so that the tension between the No. 1 and No. 2 stands did not fluctuate. The roll speed of the rolling roll 1 is changed so as to be kept constant. In the same way, the No. 4 stand also inputs the signals from the inlet side plate thickness deviation detection device 38 and the plate speed meter 42 to the AGC device 19, and the AGC device 19 eliminates the No. 4 stand exit side plate thickness variation based on the No. 4 stand inlet side plate thickness variation. 1 and 2 to the roll speed control device 13.14.

Each roll speed change command is given so that the No. 3 roll speed ratio does not change due to ΔV3R.

As mentioned above, changes in the plate thickness on the exit side of the No. 1 stand are controlled by operating the No. 1 rolling down device, changes in plate thickness on the exit side of the No. 2 stand are controlled by changing the speed of the No. 1 roll, and changes in the plate thickness on the exit side of the No.
In conventional AGC, variations in the thickness of the No. 1 and No. 2 rolls are changed for the exit side, and changes in the speed of the No. 1, 2, and 3 rolls are adjusted to zero for the fluctuation of the No. 4 exit side.

[Problem that the invention seeks to solve]

Conventional AGC has limited control capability and cannot achieve sufficient plate thickness accuracy. The reason for this is that the response speed of the roll speed control devices 13 to 15 shown in FIG. 3 is slow. Normally, in the speed control system of large rolling rolls such as the rolling roll driving 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 2Hz, and it is difficult to respond to frequencies higher than this. In this case, the phase shift and gain decrease will be large. On the other hand, frequency analysis of the plate thickness variations on the exit side of each stand reveals that there are frequency components from 0 to L OHz. 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 a cause of plate thickness variation 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 thickness of the No. 1 outlet side under the No. 1 pressure, each stand roll speed is controlled to control the thickness of the stand exit side from the No. 2 stand onwards, so the thickness is not removed until the No. 2 inlet side. 2H, which is the response speed of the roll speed control device, is the remaining plate thickness variation and plate thickness variation caused by the eccentricity of each roll of the rolling mill.
Anything above z cannot be removed. Thickness fluctuations of 2Hz or more were about ±1% of the strip thickness, which was within the tolerance range, but as manufacturing processes using metal strips become more automated and faster, there is a growing demand for strip thickness accuracy. As the requirements have become stricter, conventional AGC has become unable to meet these requirements.

The present invention provides plate thickness control in metal tandem rolling mills with the purpose of eliminating 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 related to the device.

Means for Solving Problem C] As a condition that a metal strip rolling mill, which is a premise of the present invention, must have, the response speed of the rolling reduction control device must be 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 2 Hz, whereas 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,
It is a fact that the exit plate thickness can be changed by operating at a relatively high frequency of 20 Hz. The curve A1 shown by the fourth solid line shows the variation in the exit side plate thickness when the rolling device of the second stand is operated at various frequencies in actual 4-tandem cold rolling. 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 fluctuation due to rolling operation is 2 to 4 HzT: At the maximum, at frequencies higher than this range, the response of the rolling device becomes poor, and the rolling device itself stops moving even when instructed to change the rolling position, so the gain decreases. .

The reason why the gain decreases in a frequency range lower than 2 to 4 Hz will be explained based on FIG. 2.

As already stated, the plate thickness H2 is determined from the intersection of the curves C1 and C3. When changing the rolling position and changing C1 to C2, it changes from C3 to C5 due to the change in back tension, but according to experiments, the rolling movement amount ΔS2 and the bank tension fluctuation amount Δ
There is a relationship with T12 (S nira plus operator, t12: time constant, usually about 0.2 seconds), and it takes time for the change to occur. Also, when the hack tension fluctuation occurs, the thickness H1 on the exit side of the No. 1 stand changes and the change occurs from C5 to 06, but the timing of the change is when the strip whose thickness has changed reaches the No. 2 stand. The strip of No. 1 stand roll bite reaches the entrance side of No. 2 is 1. The distance between No. 2 stands (L in Figure 5) is 5 m, 1
Assuming that the speed at the exit side of the No. stand (v+ in Figure 5) is 300 mpm, this is about 1 second later. In other words, by controlling the pressure reduction, finally 2
It takes approximately 1.5 seconds for the thickness of the exit side of the stand to return to its pre-operation value.
After 2 seconds, it becomes temporarily thinner.In other words, if the rolling cycle is longer than 1.2 seconds, the plate thickness will not change, but if the rolling cycle is less than 1.2 seconds, the plate thickness will not change. This means that the plate thickness fluctuates. Figure 4 shows this quantitatively. This fact means that in the days when the rolling mill's rolling device was electric rolling, rolling was done only slowly. Since it could not be operated, it was not useful for sheet thickness control, but if it becomes a hydraulic rolling down device that can achieve a response speed of about 20 Hz, it will be able to be effectively used as a sheet thickness control device.

However, as can be seen from the above, if the rolling operation is performed at a frequency of 1.2 seconds or less (frequency: 1/12 Hz), the plate thickness at the exit side of the stand will hardly change, but only the tension will fluctuate. It is harmful in terms of board properties. Therefore, the plate thickness control according to the present invention removes only the high frequency component of the plate thickness variation by rolling down, and removes the low frequency component by changing the roll speed ratio. It is a device.

Next, the present invention will be explained in detail based on FIG.

3, 1 to 4 are the rolling rolls of stands 1 to 4, 5 to 8 are the electric motors for driving the rolls, 9 to 12 are the same rolling devices, 13 to 16 are the same roll speed control devices, 17 ~
19 is the low frequency AGC soga of stands 2-4. 2
0 to 22 are low-pass filters for stand No. 2 to 4 low JIAGC, 23 to 26 are down control devices for stand No. 1 to 4, 27 are down feed forward AGC devices for stand No. 1, and 28 to 30 are high frequency for stand No. 2 to 4. AGC device,
31 is a metal strip, 32 to 34 are high frequency AGC bypass filters for stands 1 to 4, and 35 to 38 are 1 to 4.
The board thickness deviation detection device on the entrance side of stand No. 4, 39 to 42, is the same board speed meter. The part surrounded by the dashed line in Figure 1 is the third
This is a part added according to the present invention to the conventional AGC shown in the figure. The board thickness deviation on the entrance side of the No. 1 stand is detected by the detection device 35 and input to the AGC device 27. The AGC device 27 measures the timing based on the plate speed from the plate speed meter 39 (
7) Output the rolling down position change reference ΔSR1 according to the formula and give it to the rolling down control device 23, which moves the rolling down device 9 and moves the roll gap by ΔSR+.
The purpose is to reduce the variation in plate thickness on the exit side of the No. 1 stand to zero, which is based on the variation in the plate thickness on the entrance side of the No. 1 stand. The plate thickness deviation remaining in the No. 1 stand and the plate thickness deviation caused by the roll eccentricity of the No. 1 stand are detected by the detection device 36 and input to the filter 32.

The filter 32 extracts only the high frequency component (∆H'1h) of approximately IHz or higher from the plate thickness deviation signal and sends it to the AGC device 2.
Give to 8. The AGC device 28 measures the timing at which the strip having the thickness deviation measured by the detection device 36 reaches the roll hide of the roll 2 based on the signal from the plate speed meter 40, and at the time of arrival, according to equation (7). However, ΔHa' in equation 7) becomes ΔH'lh) The rolling position change standard, Δ
SR2 is outputted and given to the reduction control device 24, and the device 24
By moving the rolling down device 10 and moving the roll gap by ΔSR2, the IH of plate thickness variation on the entrance side of No. 2 stand is
Attempts to make the variation in the plate thickness on the outlet side of the No. 2 stand, which is based on components greater than or equal to z, to zero. Similarly, the high frequency AGC of the No. 3 stand removes the plate thickness fluctuation of IHz or more that could not be completely removed by the No. 2 stand and the high frequency component of the IHz or more of the plate thickness fluctuation caused by the roll eccentricity of the No. 2 stand. Their roles are: the detection device 37 is the same 36, the plate speed meter 41 is the same 40, the filter 33 is the same 32, the AGC device 29 is the same 28, the reduction control device 25 is the same 24, and the reduction device 11 is the same 10. and,
Roll 3 is the same as roll 2. Similarly, components of IHz or higher on the inlet side of the No. 4 stand are removed by the high frequency AGC of the No. 4 stand. Here, No. 1 stand pressure feed forward A
Unlike the No. 2-4 stand high frequency AGC devices, the GC device 27 can also remove plate thickness fluctuations at low frequencies below IHz. This is because the tension of the strip 7 on the entry side of the No. 1 roll is generally kept constant by some means, so by operating the No. 1 stand roll-down device 9, the thickness of the strip on the exit side of the No. 1 stand is changed. Even if the No. 1 stand entry tension does not change, the No. 4
This is because the characteristics are not as shown in FIG. A1, but as shown by the curve A2 indicated by the broken line in the same figure.

The plate thickness variation signal detected by the detection device 36 in FIG. 1 is also input to the filter 20. Reference numeral 20 is a low-pass filter, which passes only the frequency component (ΔH'1z) lower than IHz of the signal obtained by the detection device 36, and supplies it to the AGC device 17. The device 17 uses the plate stray signal detected by the plate speed meter 40 to measure the timing at which the strip with the plate thickness deviation obtained by the detection device 36 reaches the roll bite of the roll 2, and at the time it reaches the roll bite, H1' of the formula according to the formula (however α0) is ΔHt' using the No. 2 entry side plate thickness standard.
is ΔH'+z) No. 1 roll speed change command ΔSR+
is given to the roll speed control device 13. The device 13 changes the rotational speed of the roll drive electric motor 5, and attempts to reduce the plate thickness variation to zero on the exit side of the No. 2 stand based on the component of IHz or less of the plate thickness variation of the No. 2 stand. Similarly, the component below IHz of plate thickness variation on the entrance side of No. 3 stand is low frequency A of No. 3 stand.
Remove with GC. Its role is the entry side plate thickness deviation detection device 37
is the same 36, the plate speed meter 41 is the same 40, the filter 21 is the same 20, the AGC device 18 is the same 17, the roll speed control device 14 is the same 13, the roll drive motor 6 is the same 5, the roll 2 corresponds to 1. However, 18 is 13 at the same time as 14.
A speed change command is also given to the rolls 1 and 2 to keep the speed ratio of rolls 1 and 2 constant. Similarly, the component below IHz of the plate thickness variation on the No. 4 stand person side is removed by the No. 4 stand low frequency AGC.

Among the constituent functions of the low frequency AGC, the low pass filter shown at 20.21.degree. 22 in FIG. 1 can be omitted. The reason for this is that, for example, in one stand, the response speed of the roll speed control system consisting of 13 in FIG. This is because even if a speed change command is given, the actual No. 1 roll speed does not respond at 2 Hz or higher.

However, in that case, in the 1 to 2 Hz region, it interferes with the high frequency AGC and the gain cannot be increased sufficiently, so filters 20 to 2 are used.
2, the effect of the present invention can be fully exhibited. Also, among the components of high-frequency AGC, the bypass filter shown in Figure 1 32, 33, and 34 is also used to
It can be omitted if the decrease in gain due to interference with the GC does not cause too much of a problem in operation, but a sufficient effect cannot be expected without it.

The main component of the present invention is that, in a metal tandem rolling mill that is not equipped with a mechanical device for controlling tension between stands, a rolling device including at least one stand other than the first stand is provided with a roll speed control device that controls plate thickness fluctuations. The purpose of the bridge is to provide the ability to remove high frequency components relative to the response speed, and to provide a roll speed control device with a slow response speed to the ability to remove plate thickness fluctuations of relatively low frequency components. Therefore, the embodiment of the present invention need not be limited to the method shown in FIG. 1; for example, the high frequency AGC may be a gauge meter AGC.

〔Effect of the invention〕

The present invention is as described above, and according to the present invention, it is possible to remove plate thickness fluctuations in all frequency ranges included in a rolled material of a tandem rolling mill, which could not be removed by conventional plate thickness control devices. This makes it possible to achieve highly accurate plate thickness control in cases where the stands are not equipped with a device for mechanically manipulating the strip tension between the stands, such as in a tandem rolling mill.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the embodiment of the present invention, Fig. 2 is a schematic diagram showing the rolling situation of the conventional method, Fig. 3 is a block diagram showing the AGC of a conventional tandem cold rolling mill, Figure 4 is a graph showing changes in plate thickness when the rolling device of a specific stand is operated at various frequencies in 80C of Figure 3 to explain the present invention, and Figure 5 is an explanation showing the rolling situation of the conventional method. It is a diagram. In the drawings, 1 to 4 are rolling rolls of the first to fourth stands,
5 to 8 are roll drive electric motors, 13 to 16 are roll speed control devices, 9 to 12 are rolling down devices, 23 to 26 are rolling down control devices, and 36 to 38 are entrance side plate thickness deviation detection devices. Applicant Nippon Steel Corporation Patent Attorney Minoru Aoyagi Figure 1

Claims (1)

[Claims] It is equipped with a roll speed control device that includes a plurality of stands and controls the roll rotation speed of the stand, and a roll-down control device that controls the rolling position or rolling force by operating the roll-down device, and the roll-down control device is controlled by the response speed of the roll speed control device. In a tandem rolling mill for metal strip steel that is constructed with a device with a faster response speed and is not equipped with a mechanical device for controlling inter-stand tension such as a looper between the stands, the entry side plate thickness of at least one stand excluding the first stand Alternatively, the exit side plate thickness is detected directly or by calculation, and the plate thickness signal is input to the reduction control device and the speed control device. The rolling down device of the stand is operated according to the plate thickness deviation signal of the high frequency component, and the roll speed of the downstream including the stand or the upstream not including the stand is operated according to the plate thickness deviation signal of other frequency components. A method for controlling plate thickness of a tandem rolling mill, characterized by making the plate thickness at the exit of a stand constant.