JPH02268912A - Method for controlling plate thickness in unsteady rolling area in tandem cold rolling - Google Patents

Abstract

PURPOSE:To minimize the off gate quantity of every rolled coil and to improve the yield and quality by controlling the mass flow on the inlet side of a last stand and controlling the plate thickness on the outlet side of the last stand to a target set value. CONSTITUTION:The tension between a last stand k of a tandem cold rolling mill and a stand k-1 directly before the last stand is monitored by a tension meter installed on occasion between the stands, a deviation is detected from a certain reference set value and a control output is obtained from a series of operation. Then, the speed of the roll of the stand k-1 directly before the last stand is modified and the mass flow on the inlet side of the last stand is controlled to control the plate thickness of a formed product on the outlet side. Especially, since a tuning parameter is provided as one element in this control loop and a certain suitable dependency is given, the effect to the accuracy of the plate thickness of a formed product accompanied by factors deteriorating accuracy of various plate thickness is removed in time of an unsteady rolling state composed of an acceleration and deceleration part and a lower speed part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling plate thickness during unsteady rolling involving acceleration/deceleration and low-speed operation in a continuous or discontinuous tandem cold strip mill.

[Prior Art] Regarding the plate thickness control method for conventional tandem cold rolling mills, various AGC (Aut, Omatic Ga
ugeCont, rol) has been proposed, and the technology has been established to achieve accuracy within ±1% of the target plate thickness in the longitudinal direction of the coil during steady high-speed rolling.

[Problem to be solved by the invention] However, during unsteady rolling that involves acceleration and deceleration of the rolling speed, with the current technology, the error in plate thickness accuracy is on the order of several times (~6%). .

In order to guarantee constant quality to users over the entire length of the coil, we have no choice but to cut the parts where the plate thickness accuracy deteriorates, resulting in a significant drop in yield and deterioration in unit consumption. . The following four facts can be cited as factors contributing to the deterioration of the plate thickness accuracy in the unsteady rolling section.

(A) Normally, when accelerating and decelerating the rolling speed of a tandem mill, the speeds of the drive systems of each stand do not match, and therefore the rotation speed vs. torque characteristic of the drive motor has a large droop characteristic in order to control stable sheet threading. This fact changes the load distribution of each stand, and as a result, the thickness of the finished product at the exit of the final stand is greatly deteriorated.

(B) When the rolling speed changes from a steady high speed state to a low speed state or in the opposite direction, the mass flow on the entrance side of the tandem mill changes in terms of rolling phenomena. In addition, the lower the rolling speed, the larger the friction coefficient becomes, which causes the advance rate of each stand to move to a new equilibrium point, and from the mass flow balance at that time, the plate thickness at the exit of the final stand at low speeds becomes higher. The thickness becomes larger than the original thickness, and the accuracy of the plate thickness deteriorates.

(C) When the rolling speed changes from high speed to low speed.

The thickness of the backup roll bearing oil film changes. Since this causes the roll opening degree to fluctuate (increasing direction), a compensation circuit is usually provided, but it is difficult to completely eliminate this effect, so the plate thickness deteriorates.

(D) The speed monitor AGC that controls the absolute plate thickness on the exit side of the final stand is a feedback control system that has a dead time corresponding to the distance from directly below the final stand to the thickness gauge installed on the exit side of the final stand.

In the transition of the rolling state from high-speed rolling to low-speed rolling where dead time increases, if the optimum gain during high-speed rolling is maintained, the speed feedback control system exhibits an unstable phenomenon and the product plate thickness hunts. Therefore, in order to ensure the stability of the control system, it is necessary to reduce the rolling speed and the gain of the control system to suppress the performance of the control device to a low level.

The board thickness deterioration factors listed in (A), (B), and (C) above and (D)
Due to the constraints on the performance of the control device described in Section 1, the finished product thickness at the exit of the final stand during unsteady rolling conditions (including quasi-steady low-speed rolling sections) that transition from high-speed rolling to low-speed rolling or in the opposite direction is It is difficult to maintain the same accuracy as during steady rolling.

Therefore, it is necessary to implement a control system that can eliminate the influence of fluctuations in the coefficient of friction, which is the main cause of deterioration of sheet thickness accuracy during acceleration/deceleration and low-speed rolling, and at the same time ensure high responsiveness during acceleration/deceleration and low-speed rolling.

The present invention appropriately controls the finished plate thickness at the exit side of the final stand during acceleration/deceleration of the rolling speed and unsteady rolling conditions at low speeds, and is positioned as a complementary relationship to the conventional technology, the speed monitor AGC installed at the final stage. The aim is to propose a new AGC that eliminates wasted time, and to significantly improve yield and quality by minimizing the amount of off-gauge for each rolled coil.

[Means and effects for solving the problem] In order to solve the above problem, in the present invention, the tension between the final stand and the (final-1) stand of the tandem cold rolling mill is adjusted by setting the tension between the stands at any time. monitor with a tension meter, detect the deviation from a certain reference set value, obtain the control output from a series of calculations, (final-1) correct the roll speed of the stand, and control the mass flow on the entrance side of the final stand. This controls the thickness of the finished product on the exit side.

Especially as one element within this control system loop.

By setting tuning parameters and giving a certain appropriate speed dependence, the above-mentioned new A
To make the GC function effectively, eliminate the influence on finished plate thickness accuracy due to various factors that deteriorate plate thickness accuracy at this time, and at the same time smoothly compensate for functional decline due to dead time of the speed feedback monitor AGC system. be able to.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The AGC system, which is a main part of an apparatus implementing the present invention, will be described in detail below with reference to the drawings.

[Example] FIG. 1 shows an apparatus according to one embodiment of the invention.

This equipment consists of fully continuous equipment.

In the figure, 1 to 6 are stands of the rolling mill, 11 to 16 are roll drive monitors for each stand, 21 to 26 are rotation speed detectors including a pulse generator, 31 to 36 are mill reduction devices, and 41 is a roll drive monitor of each stand. Rewinding reel, 42, automatic welding machine, 4
3 and 45 are pride rolls, 44 is a loop car, 4
6 is a take-up reel, 51 to 54 are priddles or reel drive motors, 61 and 62 are rotational speed meters attached to the priddle drive motors, 71 is a shear, 72 is a shear drive device, and 80 is a high-performance control computer It is. In addition, a load cell 91. is used as a control detection end. Plate thickness total 92~
94. A tension meter 95 is installed.

As a plate thickness control device, the No. 1 stand is a Bisla AGC using a load cell, assuming a compact tandem rolling mill.
The roll monitor AGC1 returns the deviation of the No. 11 outlet plate thickness gauge to the No. 1 stand roll-down system, and the control output based on the plate thickness deviation detected from the No. 1 outlet plate thickness gauge and the No. 2 outlet plate thickness gauge is sent to the No. 2 stand roll-down system, respectively. The No. 1 and No. 2 speed feedforward A returns to the No. 1 and No. 2 speed control system at the timing of reaching the No. 23 stand and controls the plate thickness by correcting the roll speed.
GC1 and speed monitor AGC that controls the absolute value of finished product thickness by correcting the speed of the final stand or (final-1) stand based on the deviation signal of the thickness gauge installed on the output side of the final stand (stand No. 6). It is assumed that

The detailed contents of each of these AGCs are omitted because they are existing technologies.

Acceleration and deceleration of the rolling speed is essentially something that is normally done not only in continuous mills but also in the operation of general mills.
In particular, in a completely continuous mill like the one shown in this figure, due to the handling process of changing the exit ring as shown in Figure 2, acceleration and deceleration from high-speed steady rolling to reel switching speed, or vice versa, is required. Perform the action. At this time, the value of the friction coefficient increases exponentially as the speed decreases.

In the rolling phenomenon, the friction coefficient μ and the advance rate f are related by the following equations (1), (2), and (3).

f = tan” 0
・”(1)0= (+-In/2) fT1077 positive
−・−(2) Hn=J〆R'/Ho)
AHz a 11;5-(1/2μ) at tan-1〆
n n (lli(1-Tf/llo・I? Sf)/
l1o(1-Tb/I(i-fil' Sb)]...
(3) However, O: Neutral angle, R': Flat roll radius Hi: Plate thickness on the entrance side of the stand Ho: Thickness on the exit side of the stand ΔIT - T = Hi - Ho: Thickness deviation Tb, Tf on the exit side of the stand Total tension W on the entrance and exit sides of the stand: Plate width Sb, sf: Deformation resistance on the entrance and exit sides of the stand Here, the behavior of the plate thickness in the unsteady rolled portion in Fig. 2a will be explained based on Fig. 3. . Figure 3 shows the exit plate thickness h ok, h at the final stand k and the stand (k-1) in the preceding stage.
ok-+ r entry side plate thickness hik, hjk and advance rate fk
, fk-+ and the roll circumferential speed Vrk.

It is expressed as Vrk-1.

According to the above equation (3), if the friction coefficient μ changes from 0 to 1 (μk''>μ') as the rolling speed decreases, the advance rate increases from fk' to fk'' and fkl )fk'
), at the final stand, the following equation holds from the mass flow law.

Vrk (1+fk') hok==Vrk-
+ (1+fk-i') hok-+ ・-(
4) In this process, the roll opening remains unchanged, so
hok and hok-+ maintain their values before the change, and try to reach a quasi-equilibrium state with the speed ratio between the th and (k-1)th stands increasing by the amount of the advance rate change. However, in response to the change in speed ratio, an increase in the tension between the -1 stands results in an increase in the entry side tension at the final stand, which prompts a decrease in the advance rate fk1 from equation (3). As a result, the mass flow equilibrium shifts to a new child spar state. Assuming that the mass flow ratio remains unchanged during this transition process, the following equation holds true at the final stand.

Vrk(1+fk1)hok=Vrk(1+fk2)h
ok' ・Mountain (s) fk": Advanced rate value when the tension on the entry side increases (fk"<fk")hok": From the stand exit side plate thickness No. (5) when the advanced rate fk'', the stand exit side plate The change in thickness can be determined by the first-order equation (6) by expressing the change in advance rate as A fk=fk1-fk2 (>O).

hok'=hok・(1,+fk")/(1+f
k2)=hok-+(Vrk-+/Vrk)(1+fk
−+”)/(1+fk”)=hok−+(Vr
k-+/Vrk) (1+fk-1")/(1+fk1
−Δfk) However, (hok'>hok)
・・・(6) That is, in terms of the rolling phenomenon with deceleration, k, (k-1) the tension of the stand and the plate thickness hok on the exit side of the final stand are It exhibits a tendency as shown by the broken line. If the above is described using conventional P-H characteristics, it becomes FIG. 4. In addition, in the continuous tandem strip mill with the AGC system described earlier in Fig. 1, there are functional limitations of the speed feedback AGC installed in the final stand (the lower the rolling speed, the more control is required to ensure stability). Therefore, the actual thickness behavior of the finished product is shown by the solid line in Figure 2, which causes low-frequency plate thickness fluctuations due to the lack of 1M gain, and eventually the plate thickness in the high-speed steady rolling section. Compared to the accuracy of ±0.8%, the accuracy in the unsteady rolling portion is significantly worse at ±6.0%. Therefore, in order to compensate for the speed feedback AGC in which controllability deteriorates due to dead time during unsteady rolling, speed system feedback AGC in which there is no dead time was introduced. Its effect 4
The f1 structure will be explained next based on FIG.

During unsteady rolling, (k-4) stand roll circumferential speed vrk
-+ is decreased by ΔVrk-+, the following equation (7) is obtained from equation (6).

h ok' = h ok-+ ・((Vrk-+-Δ
Vrk-+ )/Vrk)X (1+fk-+ 1)/
(1+fk-+ -Δfk)...(7) Therefore,
In order for hok and hok' to have the same value, the following relationship (8) is required.

(Vrk-+-ΔVrk-+)/(1+ f kl
-Δfk)=Vrk-+/(1+f kl)
- Self' (8) The manipulated variable ΔVrk-+ is obtained from the following equation (9).

AVrk-+=ΔfkXVrk-+/(1+fk')"
・(9) If it is assumed that the relationship between the amount of change T in the final stand entrance tension and the amount of change Δfk in the advance rate is approximately described as a linear relationship, then @setting ΔVrk-+ will be the following equation (
10) Expressed by the formula.

ΔVrk-+ = K u-K t ・ΔT=to ΔT
−...(10) However, K u = Vrk−+ /
(1+fk1)Δfk=KtΔT Equation (10) detects the amount of tension change during unsteady rolling, calculates the equivalent speed change ΔVrk-+ using the conversion coefficient, and returns it to the speed command of the (k-1) stand. This means that the plate thickness accuracy is improved.

Figure 5 shows an example of the configuration of this AGC system.
In addition to the conventional velocity feedback loop from 2 to the operating end through the proportional integrator 105, k.

(k-1) A new feedback loop is provided from the tension meter 101, which is a detection end for inter-stand tension, to the operation end 106.

First, the tension meter 101 measures k at any time.

(k-1) Monitor the tension between the stands and lock on the tension value during steady rolling just before the start of deceleration.
Lock on at 1102. During unsteady rolling after the start of deceleration, the lock-on value and the value detected by the tension meter are determined, and the equivalent speed deviation amount is calculated using the conversion coefficient K and the tuning rate η. A
Feedback to SR speed standard. Limiters 10 and 11 are provided to prevent feedback of excessively controlled amounts.

Furthermore, the lock-on value is reset at the end of acceleration. In order for this new feedback loop to operate effectively only during unsteady rolling, the tuning rate η is given an arbitrary speed dependence as shown in FIG.

Since Kt is unknown for the speed conversion coefficient, it is calculated from the first-order equation (11) (basic equation for tension generation).

AT=(A-E/L)/(Vik-Vok-+
) dt, = (11) ΔT: Tension change rate Vik: k Stand entrance side plate thickness Vok: (k-1) Stand exit side plate thickness A: Strip cross-sectional area L: k, (k-1) Distance between stands E: Young When the rate minute time dt is approximated by the calculation time Δτ of the control loop, K is expressed by the following equation (12).

K=to α・(L/Δ・E)/Δτ ・・・(12
) [Effects] The effects of the system 11 having this control system are as shown in FIG. 6, and the thickness accuracy of the unsteady rolling section is as follows.

An improvement of ±0.9% was obtained. In addition, Kα.

η is α according to the table in the calculator for each steel type and coil.
The value of η or the pattern of η can be preset.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of a control system 11 of a fully continuous tandem cold rolling facility to which the present invention is applied. FIGS. 2a and 2b are graphs showing the rolling time including the unsteady and steady rolling regions, the rolling speed at that time, the thickness of the finished product, and the change in tension between the final stand and the (final-1) stand. FIG. 3 is a front view showing the relationship between the outlet side plate thickness, the inlet side plate thickness, and the advance rate in the final stand and the (final-1) stand as a roll circumferential speed. FIG. 4 is a graph showing the tension of the final stand and (final-1) stand and the final exit side plate thickness in terms of P-H characteristics due to deceleration. FIG. 5 is a block diagram showing the control system of the present invention in detail. FIG. 6 shows the rolling time when the present invention is implemented. It is a graph showing changes in rolling speed and finished product plate thickness. FIG. 7 is a graph showing the relationship between the tuning rate and rolling speed, which is used to prevent excessive control output during unsteady rolling. 1 to 6: Stands 11 to 16 Two roll drive motors 21 to 26: Rotation speed detector 31 to 36: Mill reduction device 41: Rewinding reel 42: Welding machine 43.45 nib bridle roll 44: Loop car 51 to 54 nib Bridle and reel drive motor 61.
62: Rotation speed detector 71: Shear 72: Shear drive device 80:
Control calculator 91: Load cells 92 to 94: Plate thickness meter 95 = Tension meter 101: Tension meter 102: Tension lock-on device 103: Tension speed converter (K: conversion coefficient, η: tuning rate) 104.105
: Proportional integrator 106: Speed controller 107: Roll drive motor 108-111: Limiter 112: X-ray plate thickness gauge 11
3: Final stage pre-stage stand (k-1) 114: Final stand (k) 115: Multiplier

Claims (1)

[Claims] Speed monitor A that corrects the speed of the final stand or (final-1) stand based on the deviation output from the target value of the final stand exit side plate thickness gauge and controls the final stand exit side plate thickness.
GC: A control system that detects the tension between the final stand and the (final-1) stand, converts the tension deviation from the reference tension value of the detection result into a speed deviation, and corrects the roll speed of the (final-1) stand. Additionally, a method for controlling plate thickness in an unsteady rolling region in tandem cold rolling, characterized by controlling the mass flow on the entrance side of the final stand and controlling the plate thickness on the exit side of the final stand to a target setting value.