JPH01245909A - Method for controlling sheet thickness for thin sheet cold rolling - Google Patents

Abstract

PURPOSE:To improve the sheet thickness accuracy at the top and rear ends of a coil and to improve the quality and yield by bringing a difference between both peripheral speeds of upper and lower work rolls to be large when a rolling speed of a thin sheet stock is small and bringing a difference between the speeds to be small when a rolling speed is large. CONSTITUTION:A difference between a peripheral speed of an upper work roll 2a and a peripheral speed of a lower work roll 2b is brought to be large when a rolling speed is small. A difference between both the peripheral speeds is brought to be small when a rolling speed is large. Or together with the above method, one or more AGC methods of feedforward AGC using an inlet side sheet thickness gage 5, feedback AGC using an outlet side sheet thickness gage 6, BISRA AGC using a rolling load gage 3, and tension AGC adjusting tensions of a rolled stock 1 are performed. By that, the sheet thickness accuracy at both the top and rear ends of the stock 1 is markedly improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for controlling plate thickness in cold rolling of thin plates.

[Prior Art] Customers' demands on the thickness accuracy of cold-worked thin plate products are becoming increasingly strict. In order to meet that demand,
Various improvements have been made to control the thickness of thin plates during cold rolling.

Control methods currently in use include feedforward control, BISRA type reduction control, X-ray monitor control, and tension control.

Taking the example of a reverse rolling mill, the rolling operation takes a speed pattern in which the speed is accelerated from a low speed, held at a constant speed, and then decelerated and then stopped near the end of the coil. Then, the next pass of rolling is performed using the same speed pattern, and several passes are performed to finish the sheet to a predetermined thickness.

In a state where the speed is maintained at a constant speed (steady state), the above control method achieves a nearly satisfactory plate thickness accuracy, but in response to the strict demands of recent customers, the plate thickness accuracy during acceleration and deceleration is still not satisfactory. In particular, as the plate becomes thinner, controlling the plate thickness in this area becomes increasingly difficult.

The reason is that as the rolling speed changes, the coefficient of friction changes, and this change changes the rolling load.As the plate becomes thinner, the change in the rolling load increases due to the change in the friction coefficient.
Control becomes difficult.

Feedforward control, which is one of the conventional techniques, is a method in which the plate thickness variation is measured with a plate thickness gauge on the entry side and the roll reduction amount is adjusted according to the variation, and cannot cope with load changes.

The BISRA method of rolling down control is a method that adjusts the amount of roll rolling down according to a change in load, and can, in principle, cope with changes in load due to changes in the friction coefficient.

ΔS=-β(P-Pe)/K-・" (1
) Here, ΔS: Roll gap control amount.

P: Rolling load.

Pe: Reference load.

K: Mill constant, Beta gain.

As shown in equation (1), this method changes the roll gap Δ according to the change from the reference load Pe = P − Pe.
This method controls S, but if the gain β is increased, the roll eccentricity will be controlled inversely, so β cannot be increased too much, and if β is made small, sufficient accuracy cannot be obtained.
In addition, there is a problem in how to select the reference load Pe, and as the plate becomes thinner, load fluctuations due to changes in the friction coefficient are large, which tends to cause deterioration of the shape.

X-ray monitor control (feedback control)
This method uses a wire thickness gauge to measure plate thickness fluctuations and then rolls down the plate, but since there is a distance from the roll bite to the plate thickness gauge and there is a time delay, we tried increasing the gain to improve plate thickness accuracy. If this happens, a hunting phenomenon will occur and sufficient plate thickness accuracy will not be obtained.

Tension control is a method of actively changing the tension to increase or decrease the rolling load to control the exit plate thickness.If the load change due to the friction coefficient is large, the control range will be exceeded and sufficient control cannot be achieved. The reality is that sufficient accuracy cannot be obtained even by combining methods.

As a countermeasure to this problem, there is a method of controlling the roll gap using a function of speed. That is, as shown in FIG. 7, when the rolling speed changes from low speed to high speed, the friction coefficient changes from large to small, and accordingly, the rolling load changes from large to small. Assuming that the roll gap is constant, as the rolling load decreases, the exit side plate thickness decreases according to the gauge meter formula (2), and becomes a curve Δh in FIG. 8.

h = S + (P/K)...
・(2) h: outlet plate thickness, S: roll gap, P: rolling load, K: mill constant.

For this reason, a method is adopted in which the roll gap is changed as the rolling speed increases, as shown by the curve ΔS in FIG.

FIG. 9 is a block diagram of an example of a plate thickness control device for a cold rolling mill, in which 1 is a rolled material, 1a is a payoff reel, and 1b is a block diagram of an example of a plate thickness control device for a cold rolling mill.
1 is a take-up reel, 2a is an upper work roll, 2b is a lower work roll, 3 is a rolling load detector, 4 is a rolling device, 5 is an inlet thickness gauge, 6 is an outlet thickness gauge, 7a is an upper rolling motor, 7
b is the lower rolling motor, 8a is the payoff reel motor,
8b is a motor for the take-up reel, 9a is an upper rolling pulse generator, 9b is a lower rolling pulse generator, 10
11 is a rolling speed adjustment unit that averages the signals from the upper rolling pulse generator and the lower rolling pulse generator and adjusts the electric power of the upper and lower rolling motors so that the average signal matches the command value from the rolling condition setting unit; 12 is a rolling condition setting unit that receives rolling schedule commands from the process computer, calculates rolling conditions and instructs each control unit; 13 is a feedback control unit that performs feedback control; 14 is a BISR
A BISRA control unit that performs AGC; 15 is a feedforward control unit that performs feedforward control; 16
is a tension control section that performs tension control.

The rolling conditions are given to the rolling condition setting section 12 from the process computer 11, and the rolling conditions setting section 12 is configured to control each control section (rolling speed adjustment section 10, feedback control section 13, BIS
RA control unit 14. Feedforward control section 15. Control targets, control constant values, etc. are commanded and output to the tension control unit 16). The speeds of the upper and lower rolling motors 7a and 7b are set to be low at the start of rolling, and are gradually increased as time passes, but in synchronization with this, the control target value of the BISRA control unit 14 is adjusted so that the control target of the rolling load is also sequentially decreased. A change command is given, and plate thickness control is performed so as to satisfy the relationship of the curve ΔS in FIG.

[Problem to be Solved] However, in the method of changing the roll gap as the rolling speed increases, it is difficult to accurately estimate the change in friction coefficient due to speed change. The reason for this is that the coefficient of friction is determined not only by the speed, but also by many factors such as the concentration of lubricating oil, temperature, temperature of the roll and plate, and surface condition of the plate and roll. Even if it could be perfectly controlled, the load fluctuations would be large, leading to shape changes, which would cause rolling problems such as drawing and other negative factors in quality stability.

The present invention attempts to solve the above-mentioned problems and provides a method for improving rolled plate thickness accuracy in areas where plate thickness control is difficult with conventional techniques, that is, areas where load changes are large due to changes in rolling speed. It is something.

[Means to solve the problem] The method of controlling the thickness of cold rolled thin plate according to the present invention is as follows.

(1) When the rolling speed is low, the difference between the peripheral speed of the upper work roll and the lower work roll is increased, and when the rolling speed is high, the difference between the peripheral speed of the upper work roll and the lower work roll is increased. (2) In addition to the method described in (1) above, feedforward AGC, feedback AGC, and BISRA
At least one AGC method of AGC and tension AGC is performed in parallel, or.

(3) In the method of item (2) above, any one or more of the control constant of feedforward AGC, the control constant of feedback AGC, and the control constant of tension AGC are set around the circumference of the upper and lower work rolls. It is characterized by changing depending on the speed difference.

' [Function] When rolling is performed by upper and lower work rolls, the output of the drive motor is usually adjusted so that the circumferential speeds of the upper and lower work rolls are equal (hereinafter, this state is referred to as uniform circumferential speed rolling). , but if we make a difference in the circumferential speed of the upper and lower work rolls (
In this state (hereinafter referred to as "different peripheral speed rolling"), it has been recognized that the rolling load is lower than in normal conditions.

The present invention is based on the above-mentioned findings, and in order to keep the exit side plate thickness deviation constant when the rolling speed is low compared to the steady operating state, conventionally the roll gap is reduced and the rolling load is reduced. In order to reduce the rolling load even if it has to be significantly increased, the rolling speed is detected and depending on the rolling speed, the circumferential speed, which is the ratio of the circumferential speed of the upper work roll to the circumferential speed of the lower work roll, can be adjusted. The speed ratio is made to change from small to large.

[Example] Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

Note that the reference numerals already mentioned indicate the same parts, and the explanation will be omitted.

FIG. 1 is a block diagram of a plate thickness control device according to a plate thickness control method for cold rolling a thin plate as an embodiment, in which 17 receives an average value of signals from pulse generators 9a and 9b to perform upper and lower rolling. A circumferential speed difference calculator 18 calculates and sets the speed difference between the motors 7a and 7b, and a peripheral speed difference calculator 18 receives a rolling schedule command from the process computer 11, calculates rolling conditions, and issues instructions to each control section. After receiving the signal from 17, AG
This is a rolling condition constant setting section that changes C control constants.

Here, the function of the circumferential speed difference calculator 17 will be explained.

The peripheral speed ratio X of the upper and lower work rolls is defined as follows.

x = Vrt/Vrb Vrt: peripheral speed of upper work roll 2a, Vrb: peripheral speed of lower work roll 2b, provided that Vrt≧V
r b a When this circumferential speed ratio X is changed, the rolling load changes as shown in Figure 2.6 As the circumferential speed ratio
decreases, but when X exceeds a certain value, the rolling load P
will not change much. This limit value x wax is approximately determined by xmax=H/h H: Inlet side plate thickness, h: Outlet side plate thickness. The amount of load change due to this circumferential speed ratio increases as the roll diameter increases, as the plate thickness decreases, and as the friction coefficient increases.

Using this principle, in the region where the rolling speed is low, the seventh
As shown in the figure, the rolling load increases, so by increasing the circumferential speed ratio X of the upper and lower work rolls 2a and 2b in this region, the rolling load P is reduced, and as the rolling speed increases, the circumferential speed difference is reduced. By doing so, it is possible to reduce rolling load fluctuations from low speed to high speed.

A specific method is shown below.

The rolling load formula Pv when the circumferential speeds of the upper and lower work rolls 2a and 2b are different is as follows.

PV==PV(H, h, R9/Attfltb*Kft
X)...(3) R: Roll radius.

μ: Friction coefficient.

tf: Output tension.

tb: entry tension, Kf: deformation resistance.

becomes.

The relationship between the rolling speed V and the friction coefficient μ is determined in advance through experiments.

μ=μ(V) ・・・・・・(4
)V: Rolling speed.

By substituting the equation (4) into the equation (3) and keeping the rolling load Pv constant, the relationship between the circumferential speed ratio X and the rolling speed V is determined from the equation (3).

x=x(V) ・・・・・・(5
) This equation (5) is set in the memory as a table in the circumferential speed difference calculator 17, and 1. Upper rolling pulse generator 9
The rolling speed V is calculated based on the average of the output of the pulse generator a and the output of the lower rolling pulse generator 9b, and the circumferential speed ratio X is calculated in accordance with the rolling speed V. and the speed of the lower rolling motor 7b is set.

The plate thickness control device of this embodiment is configured as described above,
It works like this:

(1) Rolling condition constant setting section 18 has no circumferential speed difference (X=1)
The rolling operation is commanded, and the rolling load PQ in the low speed region and the rolling load Pu in the steady speed region are determined.

(2) The rolling condition constant setting unit 18 determines xmax determined from the rolling conditions, and calculates the estimated rolling load P x when x=xmax.
Find ysax. At this time, since the conditions of the front and back surfaces are different when different peripheral speed rolling is performed, xmax is determined in consideration of this point of view.

(3) Pxmax) Circumferential speed ratio X at low speed of single rolling for Pu
Let be the above X l1aX. When Pxmax<Pu,
Calculate X maX which becomes Pu4Pv again.

(4) When Pxmax>Pu, the relational expression between X and V that causes the smallest load change during acceleration x = x (V) is expressed as (3
) formula @ When Pxmax<Pu, Pv=Pu
The relational expression x = x (V) between X and V is determined from equation (3). Alternatively, as shown in Fig. 3, an appropriate function 23x between x = xsax and x = 1 may be used as a relational expression. In Fig. 3, 21p is the load change at constant circumferential speed, 22
p is the rolling load P when the circumferential speed ratio X is adjusted and changed so that the load P is constant, 22x is the circumferential speed ratio x when the circumferential speed ratio X is adjusted and changed so that the load P is constant, 23p is xm
The load P when ax is limited, 23x, is the circumferential speed ratio X when X■ax is limited.

(5) From the determined x=x(V), the parallel coefficients aPv/ah and aPv/ah for feedback control and BISRA AGC1 tension control are determined by equation (3).

Find aPv/atb, organize and store each coefficient as a function of V or X.

(6) When the main rolling begins, the circumferential speed ratio X is adjusted by the rolling speed V, and the control constants of each control method are changed depending on the rolling speed V or the circumferential speed ratio X to perform parallel control.

A specific example is shown below. “ Inlet side plate thickness H = 0.296 mm, outlet side plate thickness h = 0.1
89 am.

Output tension tf = 10 kg/m+a'', input tension tb =
7kgf71111” @deformation resistance Kf==70 kg
f/am”, roll radius R = 440 mm, number of friction scratches μ
is μ=0.0691V-'°15...
...(6) shows the case where it changes.

When the upper and lower work rolls are at constant speed, steady area rolling load Pu = 4
25 kgf/+am” and rolling load P Q =803 kgf/amount Ilz in the low speed range v=10 mpm.

The true speed ratio X where Pv=Pu in the low speed range V=10mpm is x
=1.53. Figure 4 shows the relationship between the circumferential speed ratio X and the rolling speed V when the rolling load Pv is constant during acceleration. Due to the huge difference in surface properties on the back side, xmax
The relationship between the circumferential speed ratio
h is the change in plate thickness on the exit side during constant circumferential speed rolling, 25h is xm'ax
When = 1.283, the exit side plate thickness change, 25x is the same x
This is the change in the peripheral speed ratio X when +5ax=1.283.

FIG. 6 shows the change in exit side plate thickness over time after the start of rolling when feedback control and BISRA AGC are used together, together with a conventional example. In the figure, 26 is the outlet side plate thickness deviation of this embodiment, and 27 is the outlet side plate thickness deviation in the case of conventional control along the ΔS curve in Figure 8 above. It can be seen from this figure that the variation in plate thickness in this example is smaller than in the conventional case.

In this way, the control device of this embodiment can adjust the circumferential speed according to the magnitude of the rolling speed and reduce the amount of change in rolling load required to achieve a constant plate thickness. Prevents deterioration of product quality during deceleration.

[Effects of the Invention] The thickness control method for cold rolling a thin plate of the present invention includes (1) increasing the difference between the circumferential speed of the upper work roll and the circumferential speed of the lower work roll when the rolling speed is low; , When the rolling speed is high, the difference between the peripheral speed of the upper work roll and the peripheral speed of the lower work roll is reduced, or (2) In addition to the method of item (1) above, feedforward AGC and feedback are used. AGC and BISRA
At least one AGC method of AGC and tension AGC is executed in parallel, or (3) in the method of item (2) above, the control constant of feedforward AGC and the control of feedback AGC are carried out in parallel. Since one or more of the constant and the control constant of the tension AGC are changed depending on the difference in the circumferential speed of the upper and lower work rolls, the plate thickness accuracy at the tip and rear end of the coil can be greatly improved. , significant economic benefits can be obtained by improving product quality and manufacturing yield.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a plate thickness control device according to a plate thickness control method for thin plate cold rolling as an example, Fig. 2 is a graph showing the relationship between circumferential speed ratio and rolling load in the same example, and Fig. 3 The figure is a graph showing the relationship between rolling speed and circumferential speed ratio setting candidate value in the same example, FIG. 4 is a graph showing the relationship between rolling speed and circumferential speed ratio setting decision value in the same example, and FIG. A graph showing the relationship between the rolling speed and the exit side plate thickness deviation in the example, FIG. 6 is a graph showing the transition of the exit side plate thickness deviation with time after the start of rolling in the same example,
Fig. 7 is a graph showing the relationship between rolling speed, friction coefficient, and rolling load in the conventional example, Fig. 8 is a graph showing the relationship between rolling speed and roll gap setting value in the conventional example, and Fig. 9 is a graph showing the relationship between rolling speed and roll gap setting value in the conventional example. FIG. 2 is a block diagram of a plate thickness control device for an inter-rolling mill. 1...Rolled material, 1a...Payoff reel, 1b...Take-up reel, 2a...
Upper work roll, 2b...Lower work roll, 3
...Rolling load detector, 4... Rolling down device, 5... Inlet side plate thickness gauge, 6... Outlet side plate thickness gauge, 7a... ...Upper rolling motor, 7b...
・Lower rolling motor, 8a...Payoff reel motor, 8b...Take-up reel motor, 9a
...Upper rolling pulse generator, 9b...
...lower rolling pulse generator, 11...
Process computer, 13... Feedback control section, 14... BISRA control section, 15.
...Feedforward control section, 16...
・Tension control unit, 17... Circumferential speed difference calculator, 18.
...Rolling condition constant setting section. Patent Applicant Kobe Steel Co., Ltd. Representative Patent Attorney Fu Kobayashi Figure 1 Figure 2 1tii Tatsujohi - Rolling speed (m/m1n) Fig. 5 Pressure it& (r+vmtnt Fig. 6 Fig. 7) Rolling speed (rn/m1n) Fig. 8 Progress to pressure 1 (m/min)

Claims (3)

[Claims] (1) In a plate thickness control method for a rolling mill in which a thin plate material is cold rolled by a pair of upper and lower work rolls, when the rolling speed is low, the circumferential speed of the upper work roll and the circumferential speed of the lower work roll are A method for controlling the thickness of a thin plate in cold rolling, characterized in that the difference between the circumferential speed of the upper work roll and the circumferential speed of the lower work roll is made smaller when the rolling speed is high. (2) Feedforward AGC (
Automatic Gage Control) and
At least one of the following AGC methods: feedback AGC using an exit plate thickness gauge, BISRA AGC using a rolling load meter, and tension AGC adjusting the tension of the rolled material.
2. A sheet thickness control method for cold rolling a thin sheet according to claim 1, characterized in that two AGC methods are carried out in parallel. (3) Any one or more of the control constant of feedforward AGC, the control constant of feedback AGC, and the control constant of tension AGC is changed by the difference in circumferential speed of the upper and lower work rolls. A sheet thickness control method for cold rolling a thin sheet according to claim 2.