JPH08243703A - Level control method in continuous casting - Google Patents

Abstract

(57) [Summary] [Purpose] It is possible to prevent an error in the estimated disturbance value from occurring due to a disturbance that fluctuates in a short cycle, causing unnecessary fluctuations in the output of the inflow flow rate control actuator. When the level difference Lerr between the predicted molten metal surface level Le and the detected value L is large, the correction value u _c corresponding to the disturbance equivalent actuator control command value u _De is made smaller than a predetermined value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten metal level control method for continuous casting, and more particularly to a continuous casting machine equipped with an actuator for controlling the flow rate of molten metal into a mold, such as a stopper or a sliding nozzle. ,
Stable and good against unsteady disturbance called bulging, nozzle clogging that requires fast response, and its separation, which is suitable for continuous production of slabs such as slabs and billets. The present invention relates to a molten metal level control method capable of realizing a high molten metal level controllability and suppressing fluctuations in the molten metal level within a mold.

[0002]

2. Description of the Related Art A continuous casting machine (hereinafter referred to as a continuous casting machine) for continuously producing cast pieces such as slabs and billets from molten metal is constructed, for example, as shown in FIG. The molten steel 10 is poured into the mold 18 through the tundish 14 and the nozzle 16. For example, the molten steel whose surface layer is solidified in the water-cooled mold 18 is
After being pulled out by the pinch roll 20, further cooled and solidified, it is cut into a predetermined length by the cutter 22 and turned into a slab 24 to be sent to the subsequent rolling step.

In this continuous casting machine, it is extremely important to maintain a stable level of the molten steel 10 in the mold 18 in order to ensure good cast slab quality. That is, fluctuations in the molten metal level cause inclusions such as refractories and molten slag into the molten steel, and are trapped by the skin portion of the solidified slab 24 to cause defects such as pinholes and subcutaneous inclusions. It may cause cracking due to uneven heat removal.

Therefore, in continuous casting, generally, the level of molten metal level gauge 26 for detecting the level of molten metal in the mold 18 receives a constant level of molten metal level using a stopper 28, a sliding nozzle or the like as a flow rate control actuator. Has been done. In particular, due to the recent increase in casting speed, the importance of the level control of the metal surface is increasing more and more.

Conventionally, the level control of the molten metal is performed, for example, in Japanese Patent Laid-Open No.
As disclosed in 9-30460 and Japanese Patent Laid-Open No. 63-192545, as shown in FIG. A stopper controller 30 for controlling the stopper 28 to a desired position, the melt level meter 26 for detecting the melt level in the mold 18, a melt level target setter 32, and a melt level target value and measurement. Comparing the values, a comparator 34 that outputs the deviation e, and a preset control parameter are used to calculate a stopper position command value u that makes the deviation e zero,
PID controller 36 that performs proportional-integral-derivative (PID) control
It was generally carried out using a molten metal level control system consisting of

The operation of such a molten metal level control system is as shown in FIG. That is, the molten metal level meter 26 measures the molten metal level L, and the comparator 34 deviates the target value Lref of the molten metal level from the measured value L (= Lref-L).
Is calculated, and based on this deviation e, the PID controller 36
Sends the stopper position command value u to the stopper controller 30. The stopper controller 30 controls the stopper 28 to a predetermined position according to the command value u, and the relationship between the stopper position x (in the example of FIG. 3, the output itself of the stopper controller 30) and the molten steel flow rate flowing into the mold. Flow rate gain Gc
By adjusting the molten steel inflow rate q determined by
The surface level L is controlled. That is, the surface level measurement value L is constantly monitored, and the value is fed back for control. In Fig. 3, ∂Qo / ∂V is the casting speed V
Represents the coefficient of influence on the molten steel flow rate Qo flowing out of the mold.

An actuator for controlling the flow rate of molten steel flowing into the mold is called a sliding nozzle.
There is also a method of combining two plates with round holes and sliding them, but the basic control method is the same as that of the stopper.

In an actual continuous casting machine, alumina adheres to the nozzle 16 at the outlet of the tundish 14 to cause nozzle clogging, the adhered material is suddenly peeled off, or the stopper 28 and the tundish 14 are separated. Disturbance occurs due to adhesion of alumina near the contact portion, melting damage of the stopper 28 and the nozzle 16, and the like. Therefore, the flow rate gain Gc, which represents the characteristic from the stopper opening degree to the flow rate flowing into the mold, largely changes. Further, below the continuous casting machine, due to an unsteady phenomenon called bulging in which the slab 24 cyclically expands and contracts between the pinch rolls 20 supporting the slab 24, the molten steel in the slab is pushed up, and It may be pushed down and cause fluctuations in the molten metal level.

However, when these phenomena occur,
The conventional PID control system as described above cannot deal with the problem, which is a big problem. That is, the molten metal level control model in continuous casting is a model in which the integral governs the characteristics of the system, because the molten steel inflow flow rate into the mold becomes the molten metal level. Therefore, although the differential operation is effective for maintaining the molten metal level, it is generally difficult to use a desired high gain because the differential operation is strongly influenced by noise, and it is not always possible to use a simple PID controller.
Stable and good results could not be obtained.

With respect to such a problem, Japanese Patent Laid-Open No. 63-63
In −192545, the correction value u ′ of the output u of the feedback control means is calculated by the following equation using the flow rate gain estimated value G1 estimated by using the measured values of the molten metal level, the stopper opening and the cast-in casting speed. A gain compensating means for calculating is provided.

U '= (K10 / G1) u (1)

Here, K10 is a positive constant.

[0013] Further, the proceedings of the 117th (spring) lecture meeting of the Iron and Steel Institute of Japan (April 4-6, 1989) to the lecture of the lecture number 245 on page 308 (hereinafter referred to as CAMP-
In ISIJ-245), in order to deal with the periodic fluctuation of the molten metal level caused by the unsteady bulging, the fluctuation amount of the molten metal level and the cycle are calculated from the measured values of the eddy current level meter, and Is within the set range, the correction output is calculated so as to cancel the fluctuation of the molten metal level, and the corrected output is added to the output of the PID controller in accordance with the cycle of the fluctuation of the molten metal level to stabilize the fluctuation of the molten metal level. What has been done is disclosed.

However, none of the above-mentioned molten metal level control methods can uniformly deal with all of the various disturbances described above, such as nozzle clogging, separation, and unsteady bulging. There was a problem that fluctuations in the level of the molten metal still remained.

In the melt level control, the amount that can be directly manipulated is the flow rate of molten steel, and the amount accumulated in the mold, that is, the integrated amount, is the level of the melt level to be controlled.
In other words, since the system is originally a system with a large phase delay, it takes time for the effect of disturbance to appear as a result, and if feedback control is performed by looking only at the level of the molten metal level, the control will follow up, It has the property that the influence of disturbance remains largely. For example, when the alumina adhering to the inside of the nozzle suddenly peels off, the flow rate gain Gc suddenly increases, and the flow rate flowing into the mold changes stepwise as shown in FIG. On the contrary, if nothing is done, the molten metal level rises like a ramp as shown in FIG. 4 (B). A desirable measure against this is to operate the flow rate control actuator such as a stopper in a stepwise manner as shown in FIG. 4C to cancel the flow rate variation due to disturbance, but in a feedback control system such as a PID control system. Since the treatment is performed for the first time after the change in the molten metal level appears, the operation of the flow rate control actuator is as shown in FIG.
As shown in FIG. 4 (D), it becomes slow, and as shown in FIG.

The molten metal level control device proposed in the above-mentioned Japanese Patent Laid-Open No. 63-192545 is characterized by including a gain compensating means for estimating such a variation in the flow rate gain and correcting the feedback control output. However, this works effectively only when the change in the flow rate gain is extremely slow, such as the process in which alumina adheres in the nozzle. Therefore, even if the compensation means is provided, the feedback control is basically the same,
In principle, it is impossible to deal with the sudden fluctuation of the flow rate gain as described above. Further, with respect to disturbances other than fluctuations in flow rate gain, such as unsteady bulging, this method has no difference from a normal PID control system, and therefore it can have exactly the same controllability.

On the other hand, the molten metal level control method proposed in the CAMP-ISIJ-245 has a means for calculating a correction output in addition to the PID control system, and measures the molten metal level to determine the unsteady state. The fluctuation amount and cycle of the cyclic fluctuation caused by bulging are calculated, and the fluctuation amount is added to the output of the PID controller in accordance with the cycle of fluctuation of the molten metal surface level to cancel the fluctuation. However, in this method, once the control starts and the periodic fluctuation of the molten metal level decreases, it is observed that unsteady bulging seems to have converged at first glance if only the molten metal level is measured. However, there arises a problem that the correction value may not be calculated accurately every moment. Also, with this method,
It goes without saying that we cannot deal with disturbances other than unsteady bulging.

As described above, in the conventional technique, there is no effective method for controlling the molten metal level with respect to all of the various disturbances described above. Therefore, the variation in the molten metal level remains large and the slab This has caused a deterioration in quality.

In order to solve the above problems, the inventors of the present invention first calculated a molten metal level predicted value using a molten metal level dynamic characteristic model, and calculated the molten metal level predicted value and the molten metal level. By comparing the level detection values, all the fluctuations in the molten metal level caused by various disturbances result in changes in the specified position value of the inflow rate control actuator, and a correction signal that cancels the command value corresponding to the disturbance is added to the inflow rate control actuator ( Japanese Patent Publication No. 6-264) or a similar method (Japanese Patent Laid-Open No. 3-17496).
1 and Japanese Patent Laid-Open No. 5-31560).

[0020]

However, in the above method, an error may occur in the estimated disturbance value with respect to a disturbance that fluctuates in a short period, causing unnecessary fluctuations in the output of the inflow flow rate control actuator. It has been found.

The present invention has been made in order to solve the above-mentioned conventional problems, and it is possible to deal with unsteady disturbances such as bulging and nozzle clogging, separation and short-period disturbances that require fast response. An object of the present invention is to provide a molten metal level control method in continuous casting, which realizes stable and favorable molten metal level controllability and can suppress variation in molten metal level.

[0022]

SUMMARY OF THE INVENTION The present invention is a continuous casting machine using a continuous casting machine equipped with an actuator for controlling the flow rate of molten metal into a mold and a detector for detecting the level of molten metal in the mold. During casting, an actuator control model showing a variation characteristic of the operation x with respect to a variation of the actual control command value u of the actuator, an inflow flow rate characteristic model showing a variation characteristic of the inflow flow rate q according to the operation x of the actuator, and the inflow A molten metal level dynamic characteristic model constituted by an in-mold phenomenon model representing the variation characteristic of the molten metal level L in the mold relating to the variation of the flow rate q is obtained, and the molten metal level dynamic characteristic is calculated for each control cycle. In the model, the actual control command value u of the actuator
Is input to calculate the molten metal surface level predicted value Le at this time, and the level difference Lerr between the molten metal surface level predicted value Le and the detected value L of the molten metal surface level at this time is calculated from the level difference Lerr. To calculate a virtual disturbance-corresponding actuator control command value u _De that causes Lerr, reduce the level difference Lerr, and cancel the disturbance-corresponding actuator control command value u _De , the disturbance-corresponding actuator control command value u _De
The correction value u _c corresponding to is added to that input to the actuator as the control command value of the actuator, and the value after the addition is input to the actuator as the control command value u of the next control cycle. In the above level control method, when the level difference Lerr is large,
To cancel the disturbance corresponding actuator control command value u _De, a correction value u _c corresponding to the disturbance corresponds actuator control command value u _De, by less than a predetermined value is obtained by achieving the above objects.

[0023]

In the present invention, when controlling the flow rate of the molten metal flowing into the mold by an actuator such as a stopper or a sliding nozzle, the molten metal level predicted value Le is calculated using the molten metal level dynamic characteristic model, The level difference Lerr between the predicted surface level Le and the detected level L is determined, various disturbances that cause fluctuations in the molten level are estimated from the level difference Lerr, and the correction value u _c for canceling it is set as the actuator control command value. In addition. Furthermore, the level difference Ler
When r is large, the correction value u _c is made small in order to prevent overcorrection. Therefore, it is possible to respond quickly and appropriately to disturbances of different properties such as flow rate changes due to nozzle clogging and its separation, unsteady bulging, etc., and it is difficult to estimate disturbances and stable against high-frequency disturbances. The level controllability of the molten metal can be maintained.

[0024]

[Embodiment] Hereinafter, the inflow flow rate control actuator is a stopper, and the control characteristic (actuator control model) from the stopper position command value u to the operation x of the stopper position is first-order lag 1 / (1 + T · s), and the operation of the stopper position is performed. Taking the case where the dynamic characteristic (in-mold phenomenon model) from the inflow rate q to the molten metal level L is expressed by an integral, the inflow rate characteristic model from x to the fluctuation of the inflow rate q is a constant Gc.
Embodiments of the present invention will be described in detail.

The first embodiment of the present invention, as shown in FIG.
The deviation e is set to zero by the comparator 34 which compares the target value Lref of the molten metal level and the detected value L and outputs the deviation e, and a predetermined control parameter (proportional gain KP and time constant TI). To calculate the stopper position command value u _o to perform proportional integral (PI) control, and to add the stopper command value u _o and the subsequent correction value u _c to obtain the actual stopper position. Of the stopper position command amount u corresponding to the disturbance, and the output of the adder 42.
A stopper dynamic characteristic model 46 showing the relationship between the actual command value u of the stopper position to which _De is added and the inflow flow rate q to the mold, and the inside of the mold showing the relationship between the inflow flow rate q and the level L of the mold surface. Phenomenon model 48 and a disturbance equivalent stopper position for estimating the disturbance equivalent stopper position command amount u _De corresponding to the difference between the molten metal level predicted value Le output from the in-mold phenomenon model 48 and the actual molten metal level detected value L The command amount estimator 50, the error calculator 52 that calculates the error Lerr between the predicted molten metal surface level Le and the detected molten metal surface level L, and the error detector 52 that cancels the disturbance-corresponding stopper position command amount u _De And a correction signal generator 54 that outputs a correction value u _c that changes according to the input level difference Lerr. In the figure, 44 is the adder 4
2 is a virtual adder showing that the stopper position command amount u _De corresponding to the disturbance is added to the output of 2.

In FIG. 5, s is a Laplace operator, Gc
Is a flow rate coefficient of the stopper, T is also a time constant, and A is a mold cross-sectional area.

The operation of the first embodiment will be described below.

Level detection value L and level target value L
The comparator 34 compares the ref values with each other, inputs the deviation e between them to the PI controller 40, and outputs the stopper position command value u _o calculated by the PI controller 40 to the adder 42. Further, in the adder 42, the stopper position command value u
By adding _o and the correction signal u _c to the stopper position command value u and outputting the stopper position command value u to the stopper controller, the molten metal level L is set to a desired value.

A method of creating the correction value u _c will be described below.

Nozzle clogging, separation of nozzle clogging, or unsteady surface vibration called bulging,
Assuming that the disturbance is caused by the behavior of the virtual stopper and the virtual stopper position command amount corresponding to the disturbance is u _D , the control model of the molten metal level is expressed by the following state equation (2). Expressed.

[0031]

[Equation 1] Here, A: Mold cross-sectional area T: Constant expressing dynamic characteristics of stopper Gc: Flow coefficient d / dt: Differential operator

In the above equation (2), first, the actuator control model showing the variation control characteristic of the operation of the actuator to be used, that is, the stopper 28 or the like, with respect to the command amount u _R of the stopper is first-order lag. That is, the following equation is obtained.

Dx / dt =-(1 / T) x + (1 / T) u _R (3) x: stopper position

Further, the inflow flow rate characteristic model showing the change characteristic of the inflow flow rate q related to the change of the stopper position due to the operation of the stopper 28 adopts a value at a typical stopper position x _{o and} is given by the following equation. .

Gc = (∂q / ∂x) | _{x = x.} … (4)

Equations (3) and (4) can be summarized as equation (5).

Dq / dt =-(1 / T) q + (Gc / T) u _R (5)

Since the command value of the stopper is the sum of the disturbance-corresponding command amount u _D for varying the molten metal level and the stopper position command value u calculated from the molten metal level control, the relationship of equation (6) is established. It holds.

U _R = u + u _D (6)

The second row in the equation (2) is composed of the equations (5) and (6). That is, it is as follows.

Dq / dt = − (1 / T) q + (Gc / T) u _D + (G / T) u (7)

In the equation (2), an in-mold phenomenon model corresponding to the accumulation of the inflow rate in the mold, which shows the variation control characteristic of the molten metal level L in the mold with respect to the variation of the inflow rate q, That is, (dL / dt) is given by the following equation.

DL / dt = q / A (8)

The dynamic characteristic of the disturbance equivalent command amount u _D is
It is assumed that the third line in the equation (2), that is, the following equation (9). This physically assumes a step-like dynamic characteristic.

Du _D / dt = 0 (9)

As described above, in the present embodiment, the actuator control model, the inflow flow rate characteristic model, and the in-mold phenomenon model are shown in the equation (2). Further, these various models are, as a whole, a molten metal level dynamic characteristic model.

Therefore, in the disturbance equivalent stopper position command amount estimator 50, the actual stopper position command value u is input to the equation (2) to predict the molten metal level, and the predicted molten metal level Le and the molten metal level. By sequentially feeding back the difference Lerr of the surface level detection value L to the model by the following equation, it is possible to make the molten metal surface level detection value L and the predicted value Le coincide with each other. The virtual stopper position command amount u _De for nozzle clogging separation or bulging can be estimated.

[0048]

[Equation 2] Here, G1, G2, G3: constants, subscript e: indicates an estimated value.

Next, the level calculator Lerr, which is one of the inputs to the correction signal generator 54, is calculated by the error calculator 52 by the following equation.

Lerr = L-Le (11)

Next, the above-mentioned disturbance equivalent stopper position command value u
_The stopper correction value u _c that cancels _De is set to the correction signal generator 5
In 4, the calculation is performed by the following procedure.

Δu _D = u _De (i) −u _De (i−1) (12) Δu _c = −Ko * Kc * Δu _D (13) u _c (i) = u _c (i-1) + Δu _c (14) where i is the current value in the calculation for each control cycle, and i−1 is the previous value in the calculation for each control cycle.

Note that Ko is the reference gain and Kc is
Depending on the absolute value of the melt level error Lerr, 0.0 to 1.
The value changes between 0 and an example is shown in FIG. In FIG. 6, when the molten metal level error Lerr = 0 and it is determined that the control reliability is high, Kc = 1.0 is set and the correction value u _{c is set} to u.
The change in _De (Δu _D ) is completely reflected, and Lerr _min ~
If 0 to 0-Lerr _max is given as a straight line and the control reliability is determined to be low due to high-frequency disturbance or the like in other regions, Kc = 0 is set, and the correction value u _c has no Δu _D. It is not reflected.

FIGS. 7A and 7B show a method according to Japanese Examined Patent Publication No. 6-264 for short-period disturbance when there is an error between the molten metal level dynamic characteristic model and the actual molten metal level dynamic characteristic. FIG. 3 shows comparative examples of molten metal level control of the method according to the present invention. Compared to the conventional method, in the present invention, as shown in FIG. 7 (B), unnecessary actuator output fluctuations are suppressed and the change in stopper position is reduced, as shown in FIG. 7 (A). It can be seen that the fluctuation of the molten metal level is small and the stability is high.

As described above, in the first embodiment, the disturbance equivalent strike
Upper position command value u_DAlthough the present invention has been described,
The technology described in Kaihei 5-31560 is also suitable.
It can be used. The present invention applied to JP-A-5-31560
FIG. 8 shows a second embodiment of the above. In FIG. 8, 60 is a mode
Flow rate characteristics, 62 is the disturbance Qw added to the inflow rate q
Therefore, the molten steel with the total inflow flow rate Q will flow into the mold.
The adder indicated by 64 is a strobe input from the PI controller 40.
Upper position command value u_oAnd the surface level detection value L, PI
Disturbance that cannot be fully feedback-controlled by the controller 40 alone
Residual amount of Qw γ _wAnd estimate this disturbance residual estimator γ_we
Is a disturbance residual error calculator that outputs the
It

In the second embodiment, Japanese Patent Laid-Open No. 5-3156 is used.
The expression (4) of 0 is changed to the expression corresponding to the expressions (12) to (14) of the first embodiment.

In each of the above-described embodiments, the molten metal level dynamic characteristic model is constructed from the command value to the inflow flow rate control device. However, as in Japanese Patent Laid-Open No. 3-146247, the inflow flow rate control device output is used. It is also possible to construct a molten metal level dynamic characteristic model and apply the present invention. Japanese Patent Laid-Open No. 5-
FIG. 9 shows a third embodiment of the present invention applied to a combination of 31560 and Japanese Patent Laid-Open No. 3-146247.

[0058]

As described above, according to the present invention,
Fast and appropriate control is possible for disturbances with different properties such as nozzle clogging and separation, unsteady bulging, etc., and stable even for high-frequency disturbances that are difficult to estimate. Since the molten metal level control can be maintained, good slab quality can be obtained, and the occurrence of quality defects can be prevented, so that the yield can be improved.

[Brief description of drawings]

FIG. 1 is an overall view showing a configuration of an example of a continuous casting machine to which the present invention is applied.

FIG. 2 is a block diagram showing a configuration of a conventional molten metal level control device.

3 is a block diagram of the device of FIG. 2 represented by a transfer function.

FIG. 4 is a diagram showing an example of fluctuations in molten metal level when deposits in the nozzle are peeled off.

FIG. 5 is a block diagram showing the configuration of the first embodiment of the present invention.

FIG. 6 is a diagram showing an example of a relationship between a molten metal surface level error Lerr and a correction coefficient Kc in the first embodiment.

FIG. 7 is a diagram showing a comparison between control examples of the present invention method and the conventional method.

FIG. 8 is a block diagram showing a configuration of a second embodiment of the present invention.

FIG. 9 is a block diagram showing a configuration of a third embodiment of the present invention.

[Explanation of symbols]

10 ... Molten steel 14 ... Tundish 16 ... Nozzle 18 ... Mold 26 ... Level level meter L ... Level level measured value 28 ... Stopper 30 ... Stopper controller x ... Stopper position 32 ... Level level target setter Lref ... Level level Level target value 34 ... Comparator 40 ... PID controller u _o , u ... Stopper position command value 42, 44 ... Adder 46 ... Stopper dynamic characteristic model 48 ... Mold phenomenon model 50 ... Disturbance equivalent stopper position command amount estimator u _D ... flow disturbance corresponding stopper position command value 52 ... error calculator 54 ... correction signal generator u _c ... correction value q ... inflow rate

Claims (1)

[Claims] 1. When continuously casting cast pieces by a continuous casting machine equipped with an actuator for controlling a flow rate of molten metal flowing into a mold and a detector for detecting a molten metal level in the mold, the actual actuator An actuator control model showing a variation characteristic of the operation x with respect to a variation of the control command value u, an inflow flow rate characteristic model showing a variation characteristic of the inflow flow rate q according to the operation x of the actuator, and the inflow flow rate q.
Of the variation level of the molten metal level L in the mold, and a dynamic model of the molten metal level composed of a phenomenon model in the mold that represents the variation characteristic of the molten metal level L in the mold. The actual control command value u of the actuator is input to calculate the molten metal level predicted value Le at this time, and the molten metal level predicted value Le and the detected molten metal level L in the mold at this time L To calculate a virtual disturbance-corresponding actuator control command value u _De that causes the level difference Lerr, reduce the level difference Lerr, and cancel the disturbance-corresponding actuator control command value u _De . the correction value u _c corresponding to the disturbance corresponds actuator control command value u _De, added to what is input to the actuator as a control command value for the actuator, The value after addition, the molten metal surface level control method to be inputted to the actuator as a control command value u in the following control cycle, when the level difference Lerr is large, counteract the disturbance corresponding actuator control command value u _De Therefore, the correction value u corresponding to the disturbance-corresponding actuator control command value u _De
A molten metal level control method in continuous casting, wherein _c is made smaller than a predetermined value.