JP2634108B2 - Metal surface level control method in continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a molten metal level in continuous casting, and more particularly to a continuous casting machine provided with an actuator such as a stopper or a sliding nozzle for controlling the flow rate of molten metal into a mold. Thus, slabs, suitable for continuous production of slabs such as billets, unsteady disturbance called bulging, and nozzle clogging and peeling required fast response is stable and stable. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the level of a molten metal, which can achieve good level control of the molten metal level and can suppress fluctuations in the molten metal level in a mold.

[0002]

2. Description of the Related Art A continuous casting machine (hereinafter referred to as a continuous casting machine) for continuously producing slabs, billets and the like from molten metal is constructed as shown in FIG. The molten steel 10 is injected into a mold 18 through a tundish 14 and a nozzle 16. For example, molten steel whose surface layer has solidified in a 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, the fluctuation in the level of the molten metal causes inclusions such as refractories and molten slag to be entangled in the molten steel, and is caught by the skin portion of the solidified slab 24 to generate defects due to pinholes and subcutaneous inclusions. Or cracks due to uneven heat removal. Therefore,
Generally, in continuous casting, a level control is performed by receiving a signal from a level gauge 26 for detecting a level in the mold 18 and using a stopper 28, a sliding nozzle or the like as a flow rate control actuator. 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 a molten metal is disclosed in, for example,
As disclosed in JP-A-9-30460 and JP-A-63-192545, as shown in FIG. 4, the stopper 28 which is an actuator for controlling a flow rate by restricting a flow path from the tundish 14 to the mold 18; A stopper controller 30 for controlling the stopper 28 to a desired position; a level gauge 26 for detecting the level of the level in the mold 18; a target level setting device 32; The comparator 34 compares the values and outputs a deviation e, and the deviation is determined by a predetermined control parameter.
Calculate the stopper position command value u that makes e zero, and
PID controller 36 that performs proportional-integral-derivative (PID) control
In general, it is carried out using a level control system consisting of

The operation of such a level control system is as shown in FIG. That is, the level gauge 26 detects the level L, and the comparator 34 calculates the deviation e (= Lref-L) between the target level Lref and the detected level L.
Is calculated, and based on the deviation e, the PID controller 36
Sends a stopper position command value u to the stopper controller 30. The stopper controller 30 controls the stopper 28 to a predetermined position in accordance with the command value u, and the relationship between the stopper position x (the output itself of the stopper controller 30 in the example of FIG. 5) and the flow rate of the molten steel flowing into the mold. Flow gain Gc
The molten metal level L is controlled by adjusting the molten steel flow rate q determined by the flow rate. In other words, the detected level L is constantly monitored, and the feedback is fed back to perform control. In FIG. 5, ∂ Qo / ∂ V (partial differentiation of Qo by V ; also referred to as dee Qo / dee V ) is the casting speed V
Represents the coefficient of influence on the flow rate Qo of molten steel flowing out of the mold.

As an actuator for controlling the flow rate of molten steel to the mold, there is an actuator which combines two plates having round holes called a sliding nozzle and slides them, but the basic control method is that of a stopper. Are identical.

In an actual continuous casting machine, alumina adheres to the nozzle 16 at the outlet of the tundish 14 to cause clogging of the nozzle, the adhered material is suddenly peeled off, or the stopper 28 and the tundish 14 Disturbance due to adhesion of alumina to the vicinity of the contact portion, melting of the stopper 28 and the nozzle 16 and the like occurs. For this reason, the flow rate gain Gc, which represents the characteristic from the stopper opening to the flow rate flowing into the mold, greatly fluctuates. Further, below the continuous casting machine, the molten steel in the slab is pushed up due to an unsteady phenomenon called bulging in which the slab 24 periodically expands and contracts between the pinch rolls 20 supporting the slab, and the molten steel in the slab is pushed up. May cause surface level fluctuations. However, when these phenomena occur, it cannot be dealt with by the ordinary PID control system as described above, which has been a serious problem. In other words, the control model of the molten metal level in continuous casting is a model in which the flow rate flowing into the mold is integrated to become the molten metal level, and the integration governs the characteristics of the system. Therefore, although the differential operation is effective for maintaining the level of the molten metal, it is difficult to use a desired high gain because the differential operation is generally strongly affected by noise. And good results could not be obtained.

In order to solve such a problem, Japanese Patent Laid-Open Publication No.
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 using the detected values of the molten metal level, the stopper opening degree, and the slab pouring speed. It has a gain compensating means for calculating.

U ′ = (K10 / G1) u (1)

Here, K10 is a positive constant.

[0011] In addition, a draft (hereinafter referred to as CAMP-) of the 117th (spring) lecture meeting of the Iron and Steel Institute of Japan (April 4-6, 1989), a lecture of lecture number 245 on page 308 of the proceedings.
In ISIJ-245), in order to cope with the periodic level change caused by the unsteady bulging, the level and the amount of change of the level are calculated from the detected value of the eddy current level meter. Is within the set range, a correction output is calculated so as to cancel the level change, and the corrected output is added to the output of the PID controller in accordance with the cycle of the level change, thereby stabilizing the level change. What was made to do is disclosed.

In Japanese Patent Publication No. 60-144, an exciting coil and a detecting coil driven by an alternating current are used to detect the flow velocity in the nozzle corresponding to the differential of the level of the molten metal to control the level of the molten metal. According to this method, it is possible to cope with a change in the flow rate in the nozzle, such as clogging of the nozzle or peeling of the nozzle clogging.

[0013]

However, in this method, it is difficult to obtain high measurement accuracy because of the flow velocity measurement, and it is not possible to cope with bulging caused by a phenomenon in the slab. Furthermore, in addition to the bad measurement environment of high temperature, the equipment is placed in a narrow space, and the equipment becomes expensive even though high detection accuracy and long life of the equipment cannot be expected. Had.

Furthermore, none of the above-described methods for controlling the level of the molten metal can uniformly cope with all of the various disturbances described above such as nozzle clogging, separation, and unsteady bulging. There was a problem that the surface level fluctuation still remained.

In the level control, the quantity that can be directly operated is the flow rate of the molten steel, and the quantity accumulated in the mold, that is, the integral quantity, is the value of the 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 adhered in the nozzle is suddenly peeled off, the flow rate gain Gc suddenly increases, and the flow rate flowing into the mold changes stepwise as shown in FIG. On the other hand, if no treatment is performed, the molten metal level rises in a ramp shape as shown in FIG. A desirable measure against this is to use a flow control actuator such as a stopper as shown in FIG.
This is to operate in a step-like manner to cancel the flow rate fluctuation due to disturbance. However, in a feedback control system such as a PID control system, the treatment is performed only after a change in the molten metal level appears, so that the flow control actuator Operation is shown in FIG.
As shown in FIG. 6 (D), it becomes slow, and as shown in FIG.

The level control apparatus proposed in Japanese Patent Application Laid-Open No. 63-192545 is characterized in that it is provided with a gain compensation means for estimating such a variation in the flow rate gain and correcting the feedback control output. This works effectively only when the change in the flow rate gain is extremely slow, such as when alumina adheres to the nozzle. Therefore, even if the compensation means is provided, the feedback control does not change, and it is impossible in principle to cope with the sudden fluctuation of the flow rate gain as described above. Further, this method has no difference from a normal PID control system for disturbances other than the flow rate gain fluctuation, such as unsteady bulging, so that it can have exactly the same controllability.

On the other hand, the level control method proposed in the CAMP-ISIJ-245 has a means for calculating a correction output separately from the PID control system. The fluctuation amount and the period of the period fluctuation due to the bulging are calculated, and the calculated fluctuation amount and the period are added to the output of the PID controller in accordance with the period of the molten metal level fluctuation, thereby canceling the fluctuation. However,
In this method, once the control is started and the periodic fluctuation of the bath level is reduced, if the bath level is measured only, the unsteady bulging is observed as if it seemed to have converged. There is a problem that the momentary correction value cannot be calculated accurately. Also, it goes without saying that this method cannot deal with any disturbance other than the unsteady bulging.

As described above, in the prior art, there is no effective level control method for all of the various disturbances as described above. Therefore, the level change is still large, and the slab remains. The quality has been reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and has a stable and good surface finish even with respect to unsteady disturbances such as bulging, clogging of nozzles which require fast response, and peeling. It is an object of the present invention to provide a method for controlling the level of a molten metal in continuous casting, which realizes level controllability and suppresses fluctuations in the level of the molten metal.

[0020]

In order to achieve the above object, the present invention provides a feedback control loop for continuous casting of a slab by a continuous casting machine having an actuator for controlling the flow rate of molten metal into a mold. But the fee
Together they act to match the melt-surface level actual value in molten metal surface level target value based on Dobakku operation signal, disturbance residual
The cancellation control loop is included in the feedback control loop.
In the method for controlling the level of the metal surface acting on the side,
The total inflow into the pump is determined by the disturbance flow rate and the
To the mold, and
The level where the total inflow is integrated by the mold to reach the level
As a level fluctuation model, the feedback operation signal and
Estimate disturbance residual value based on actual surface level
And a correction signal for canceling the disturbance flow rate from the disturbance residual estimation value.
And the correction signal and the feedback operation signal
And the position command value of the actuator,
Input a command value to the actuator,
Is controlled .

[0021]

According to the present invention, a method for controlling a level of a molten metal in a mold is provided.
In the model, the molten metal level fluctuation model was
The input amount Q is controlled by the disturbance flow rate Qω and the actuator.
Of the flow rate q flowing into the mold
The total inflow Q is integrated by the mold and changes in the level
It is configured as Therefore, the physical
Disturbance is quantified as the disturbance flow Qω it brings
When adjusting the control system, the disturbance flow rate Q
The validity of the manipulated variable can be confirmed while actually observing ω,
Can be adjusted easily and accurately.

Further, the disturbance residual of the disturbance residual canceling control loop is obtained.
Of the correction signal for canceling
The sum is used as the position command value of the actuator, and the position command value is
Input to the actuator to control the actuator
ing. At this time, based on a correction signal for canceling the disturbance residual,
Is estimated by the disturbance residual calculator 50.
However, the input to the disturbance residual calculator 50 is
These are the feedback calculation signal and the actual level of the metal surface. So
, The disturbance residual estimation estimated by the disturbance residual calculator 50
The value is the feedback operation of the feedback control loop.
It is assumed that the level control is performed only by the signal.
Is determined.

[0023] Accordingly, nozzle clogging Ya its peeling, unsteady while bulging disturbance caused by such that will be feedback-controlled by a feedback control loop, the residual amount estimation of the disturbance which can not be feedback controlled
Since the level is canceled by the correction signal of the disturbance residual cancellation control loop, the level of the molten metal is always kept stable without being affected by the disturbance.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a method for controlling a molten metal level in continuous casting according to the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In this embodiment, the above-described continuous casting machine shown in FIG. 3 is applied.

[0026] In this example, the inflow rate control actuator is stopper 28, molten metal surface level feedback control PI adjusting meter 40, the stopper dynamics 46 primary lag,
The case where the actual value x of the stopper position and the inflow flow rate q into the mold 18 are in a proportional relationship (proportional coefficient Gc (flow rate gain)) and the phenomenon 48 in the mold is expressed by integration will be described as an example.

In FIG. 1, reference numeral 34 denotes a target value Lref of the molten metal level.
And a comparator for comparing the detected level L detected by the level gauge 26 and outputting a deviation e (Lref-L).

Reference numeral 40 denotes a PI for performing a comparative integration (PI) control.
The controller calculates a stopper position command value Uo for commanding the position of the stopper 28 so that the deviation e input from the comparator 34 becomes zero according to predetermined control parameters (proportional gain Kp and integration time T _I ). And outputs the result to the adder 42.

The PI controller 40 forms a feedback control loop that acts to match the detected level L with the target level Lref. In this embodiment, however, the disturbance residual calculator 50 and A disturbance residual cancellation control loop constituted by the correction signal calculator 52 is included.

The disturbance residual calculator 50 calculates the residual amount γω of the disturbance Qω that cannot be feedback-controlled by the PI controller 40 alone, based on the stopper position command value Uo input from the PI controller 40 and the molten metal level detection value L. To estimate the disturbance residual

[Outside 1] (Hereinafter also referred to as γω hat ) to the correction signal calculator 52.

In the disturbance residual calculator 50, it is assumed that the fluctuation of the molten metal level is caused by the residual of the disturbance that could not be completely controlled by the PI controller 40, and the residual amount of the disturbance is calculated by the following control model. Is calculated.

When the disturbance residual amount γω does not occur, the stopper position command value Uo and the molten metal level detection value L are calculated by the state equation

(Equation 1) Is represented by Here, d / dt is a differential operator. This
The first line of equation (2) is And the sum of the inflow Gc · X and the disturbance flow Qω is the product
And show that it is divided into mold level in the mold
I have. Similarly, the second row is expressed as dx / dt =-(1 / T) .X + (1 / T) .Uo, and is an integral indicating the dynamic characteristic (first-order lag) of the stopper.
It is an equation. Similarly, the third line is expressed as dQω / dt = 0, and represents a differential process representing a disturbance flow rate (step disturbance).
It is an expression.

The disturbance residual operation unit 50 calculates the molten metal level L from the stopper position command value Uo input from the PI controller 40 according to the equation (2).

The calculated level L is an estimated level.

[Outside 2] (Hereinafter also referred to as L hat ) , and the disturbance residual operation unit 5
0 indicates the estimated level L and the level gauge 26.
The difference from the level detection value L input through the

(Equation 2) To calculate the disturbance residual amount estimated value γω hat and output it to the correction signal calculator 52. Here, g1, g2, and g3 are constants. In this equation (3)

[Outside 3] (Also referred to as a hat) represents an estimated value, and is replaced with a disturbance Qω.
The symbol γω is used. The first on the right side of equation (3),
The two terms have the same meaning as in equation (2). The third term on the right is actually
Gain g1, the difference between the hot water level L and its estimated value L hat
This is a term that provides feedback by multiplying g2 and g3.
Therefore, each of the estimated values of the equation (3) converges to the true value.
Guaranteed by observer theory.

The correction signal calculator 52 is a disturbance residual calculator 5.
A stopper correction signal Uc is output to the adder by multiplying the disturbance residual estimated value γω hat from 0 by the correction coefficient −K. That is, the stopper correction signal Uc output from the correction signal calculator 52 is expressed by the following equation.

(Equation 3) Indicated by The constant K in the equation (4) is calculated using a γω hat.
To calculate the stopper correction signal U _C for canceling γω .
It is a coefficient for

The adder 42 adds the stopper position command value Uo and the stopper correction signal Uc and outputs the sum as a total stopper position command value u.

Numeral 46 indicates the dynamic characteristics of the stopper 28 controlled by the total stopper position command value u from the adder 42. The actual position of the stopper 28 controlled by the total stopper position command value u is the actual stopper position value x. Is output as

Reference numeral 47 denotes a flow rate characteristic of the mold 18. The flow rate q of the molten steel 10 flowing from the nozzle 16 into the mold 18 is proportional to the actual value x of the stopper position determined by the stopper dynamic characteristic 46 (the proportional coefficient is a flow coefficient). Gc).

Reference numeral 44 denotes a case where a disturbance occurs, the disturbance Q
ω is added to the inflow q, and the molten steel 1
An adder indicating that 0 flows into the mold 18.

Numeral 48 denotes a phenomenon in the mold 18 into which the molten steel 10 having the total inflow flow rate Q has flowed, and the molten metal level L is determined by the total inflow flow rate Q. Here, A is mold 1
The cross-sectional area of 8, S is the Laplace operator.

Next, the operation of this embodiment will be described.

The detected level L of the molten steel 10 detected by the level gauge 26 and the target level Lref are compared by the comparator 34, and the deviation e is input to the PI controller 40. , The stopper position command value Uo that makes the deviation e zero is output from the PI controller 40 to the adder 42.

When disturbance Qω due to nozzle clogging or the like occurs, even if feedback control is performed only by PI controller 40, disturbance Qω remains, so that the molten metal level cannot be maintained stably.

In order to cope with such a situation, the disturbance residual calculator 50 inputs the stopper position command value Uo and the molten metal level detection value L from the PI controller 40, and calculates the equation (2) and the equation (3).
The estimated disturbance residual value γω hat is calculated according to the model of the equation, and is output to the correction signal calculator 52.
2 outputs the stopper correction signal Uc to the adder 42.

Therefore, the adder 42 outputs a total stopper position command value u obtained by adding the stopper correction signal Uc to the stopper position command value Uo for the stopper dynamic characteristic 46.

As a result, the residual amount γω of the disturbance Qω due to nozzle clogging, separation, unsteady bulging, etc.
Is controlled so as to cancel, and the flow characteristics 47 and the phenomenon 48 in the mold exhibit characteristics and phenomena that cancel the disturbance residual amount γω.

Therefore, as a result of the stopper 28 being controlled by the total stopper position command value u, the molten metal level of the molten steel 10 flowing into the mold 18 from the nozzle 16 has a stable value with respect to any disturbance Qω. Become.

FIG. 2 shows a comparison between the control characteristics according to the present embodiment and the control characteristics according to the conventional example. Was one third of the total.

As described above, the control method of the present embodiment uses the PI
The residual amount of the disturbance that cannot be completely controlled by the controller 40 alone is canceled by the disturbance residual amount estimated value γω hat calculated by the disturbance residual calculator 50 and the correction signal calculator 52. The level of the molten metal in the mold 18 can always be kept stable in a quick and appropriate manner.

[0050]

As described above, according to the method for controlling the level of the molten metal in the continuous casting of the present invention, the residual amount of the disturbance that cannot be completely controlled by feedback is estimated, and the correction for canceling the residual amount is performed. Since a signal is output to the actuator, the level of the molten metal can be constantly maintained in a stable manner in response to any disturbance quickly and appropriately, and as a result, good slab quality can be maintained and quality defects can be maintained. There is an excellent effect that generation can be prevented and the yield can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a method for controlling a metal surface level in continuous casting according to the present invention.

FIG. 2 is a diagram showing a comparison between a response according to an embodiment and a response according to a conventional example.

FIG. 3 is an overall view showing a configuration of an example of a continuous casting machine to which the present invention is applied.

FIG. 4 is an overall view showing a configuration of a conventional molten metal level control device.

FIG. 5 is a block diagram showing the device of FIG. 4 in terms of a transfer function.

FIG. 6 is a diagram illustrating an example of a change in the level of the molten metal when the deposits in the nozzle are separated.

[Explanation of symbols]

10: molten steel, 14: tundish, 16: nozzle, 1
8: mold, 24: cast piece, 26: level gauge, L:
Level detection value (actual level value), 28: Stopper (actuator), x: Actual position value of stopper, Lre
f ... level target value, 34 ... comparator, 40 ... PI controller, Uo ... stopper position command value (command value), u ... total stopper position command value, 42, 44 ... adder, 46 ... stopper dynamic characteristics , 47: Flow characteristics, 48: In-mold phenomenon, 50
… Disturbance residual calculator, Qω… disturbance,

[Outside 4] ... Estimated value of disturbance residual amount (γω hat) , 52... Correction signal calculator, Uc .stopper correction signal (correction signal), q.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaki Takashi 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corp. Inside Chiba Works (72) Inventor Shuji Tanaka 1-Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corp. Chiba Works (56) References JP-A-3-110051 (JP, A)

Claims (1)

(57) [Claims] In a continuous casting of a slab by a continuous casting machine equipped with an actuator for controlling a flow rate of molten metal into a mold, a feedback control loop includes a feedback operation signal.
The feedback control le with acts to match the melt-surface level actual value in molten metal surface level target value, the disturbance residual cancellation control loop based on
In the method for controlling the level of a metal surface acting on the inside of a mold, the total inflow into the mold is determined by a disturbance flow rate and the actuator.
Of the flow rate flowing into the mold from the
The total inflow into the mold is integrated by the mold and
Based on the feedback calculation signal and the actual level
The disturbance residual estimated value is estimated based on the estimated disturbance residual value, and a correction signal for canceling the disturbance flow rate is calculated from the disturbance residual estimated value.
Determined, and the correction signal, the sum of the feedback calculation signal before
A method for controlling a level of a molten metal surface in continuous casting , wherein a position command value of the actuator is set as the position command value , and the position command value is input to the actuator to control the actuator.