Title of invention: Control method, apparatus and program of continuous casting process of multi-layer slab
Technical field
[0001]
　The present invention relates to a control method, apparatus and program for a continuous casting process of a MULTILAYERED SLAB.
　The present application claims priority based on Japanese Patent Application No. 2018-110356 filed in Japan on June 8, 2018, the contents of which are incorporated herein by reference.
Background technology
[0002]
　Conventionally, it has been practiced to produce multi-layer slabs in which the composition of the surface layer and the composition of the inner layer are different. For example, Patent Document 1 discloses a configuration in which molten metals having different compositions in a mold are separated by magnetic means, and molten metals having different compositions are supplied above and below this boundary. More specifically, a static magnetic field zone is formed between the relatively upper molten metal supply position and the relatively lower molten metal supply position in the mold so that the magnetic field lines extend in the direction perpendicular to the casting direction. By doing so, it is possible to prevent molten metals having different compositions having different supply positions from being mixed.
　In the continuous casting process of multi-layer slabs, for the surface layer, the position of the boundary (hereinafter referred to as the boundary layer level) that separates the molten metal (molten steel) on the surface layer and the molten steel on the inner layer is kept in the static magnetic field zone. It is necessary to appropriately control the molten steel supply flow rate by the immersion nozzle and the molten steel supply flow rate by the immersion nozzle for the inner layer.
　To solve this problem, for example, Patent Document 2 discloses a method of controlling the mold molten metal level by the injection amount sum operation while keeping the ratio of the inner layer molten steel injection amount and the outer layer molten steel injection amount constant.
　Further, in Patent Document 3, the surface injection amount set value obtained by calculating the set value based on the surface injection amount measured by the electromagnetic flow meter attached to the injection nozzle on the surface tundish side and the surface shell thickness and the casting speed. The stopper of the surface injection nozzle is opened and closed to adjust the surface injection amount so that the two match, while the molten metal level detected by the molten metal level meter and the surface shell thickness and casting speed are used. A method is disclosed in which the stopper of the injection nozzle for the inner layer is opened and closed to adjust the injection amount of the inner layer by comparing with the set value of the molten metal level obtained by calculating the set value.
Prior art literature
Patent documents
[0003]
Patent Document 1: Japanese Patent Application
Laid-Open No. 63-108947 Patent Document 2: Japanese Patent Application Laid-Open No. 3-243262
Patent Document 3: Japanese Patent Application Laid-Open No. 5-104223
Non-patent literature
[0004]
Non-Patent Document 1: Ironmaking & Steelmaking 1997 Vol.24 No.3 "Novel continuous casting process for clad steel slabs with level dc magnetic field"
Non-Patent Document 2: Ikeda, Fujisaki "Multivariable System Control", Corona Publishing Co., Ltd., p. 95
Outline of the invention
Problems to be solved by the invention
[0005]
　However, in any of the conventional methods, the boundary layer level is not directly controlled. Therefore, for example, if the boundary layer level fluctuates due to fluctuations in the molten steel injection amount due to changes in flow rate characteristics such as nozzle clogging and clogging peeling during casting, it takes a long time to recover this to the target value. During this time, the molten steel in the surface layer and the molten steel in the inner layer are mixed, and the quality of the multi-layer slab may deteriorate.
[0006]
　The present invention has been made in view of the above points, and an object of the present invention is to enable highly accurate control of the boundary layer level in the continuous casting process of multi-layer slabs.
Means to solve problems
[0007]
　The gist of the present invention for solving the above problems is as follows.
(1) In the first aspect of the present invention, molten metal is injected into a mold from a surface layer nozzle and an inner layer nozzle, and the molten metal on the surface layer and the molten metal on the inner layer are vertically and vertically sandwiched in the mold. It is a control method of a continuous casting process for producing a multi-layer slab having a composition of the surface layer and a composition of the inner layer different from each other by separating the molten metal, and measuring the surface layer level which is the position of the molten metal in the mold. Using a level meter and a flow meter installed on either one of the surface layer nozzle and the inner layer nozzle to measure the supply flow rate of the molten metal, the measured value of the surface layer level by the molten metal level meter and the said The measured value of the supply flow rate of the molten metal of either the surface layer nozzle or the inner layer nozzle by the flow meter, and the supply flow rate of the molten metal of the surface layer nozzle and the inner layer nozzle to which the flow meter is not installed. The boundary layer level, which is the position of the boundary, is estimated by the observer based on the calculated value of, and the measured value of the surface layer level by the molten metal level meter and the estimated value of the boundary layer level by the observer are obtained. It is a control method of a continuous casting process of a multi-layer slab that controls the supply flow rate of the molten metal of the surface layer nozzle and the supply flow rate of the molten metal of the inner layer nozzle so as to keep the target value.
(2) In the method for controlling the continuous casting process of the multi-layered slabs described in (1) above, the Ruenberger type observer is used as the observer by using a linear approximation model of the continuous casting process of the multi-layered slabs. May be configured.
(3) In the method for controlling the continuous casting process of the multi-layer slab according to the above (1) or (2), the observer is the surface layer level, the boundary layer level, the surface layer nozzle, and the inner layer nozzle. Of these, the disturbance corresponding to the calculation error of the calculated value of the supply flow rate of the molten metal on the side where the flow meter is not installed may be used as a state variable.
(4) In the method for controlling the continuous casting process of the multi-layer slab described in (3) above, a step-like disturbance or a ramp-like disturbance may be given as the disturbance.
(5) In the method for controlling the continuous casting process of the multi-layer slab according to any one of (1) to (4) above, the flow meter may be installed in the inner layer nozzle.
(6) In the method for controlling the continuous casting process of the multi-layer slab according to any one of (1) to (4) above, the flow meter may be installed on the surface nozzle.
(7) In the second aspect of the present invention, the molten metal is injected into the mold from the surface nozzle and the inner layer nozzle, and the molten metal on the surface layer and the molten metal on the inner layer are vertically and vertically sandwiched in the mold. It is a control device that controls a continuous casting process that separates and produces a multi-layer slab having a composition of the surface layer and a composition of the inner layer different from each other, and is a position of the molten metal in the mold by a molten metal level meter. An input means for inputting a measured value at the surface layer and a measured value of the supply flow rate of the molten metal by a flow meter installed in either the surface layer nozzle or the inner layer nozzle, and the molten metal level meter. The measured value at the surface layer level, the measured value of the supply flow rate of the molten metal of either the surface layer nozzle or the inner layer nozzle by the flow meter, and the flow meter of the surface layer nozzle and the inner layer nozzle are not installed. An estimation means for estimating the boundary layer level at the boundary position by an observer based on the calculated value of the supply flow rate of the molten metal, the measured value of the surface layer level by the molten metal level meter, and the estimation. A control means for controlling the supply flow rate of the molten metal of the surface layer nozzle and the supply flow rate of the molten metal of the inner layer nozzle so as to keep the estimated value of the boundary layer level by the means at each target value is provided. It is a control device for the continuous casting process of multi-layer slabs.
(8) In the third aspect of the present invention, the molten metal is injected into the mold from the surface nozzle and the inner layer nozzle, and the molten metal on the surface layer and the molten metal on the inner layer are vertically and vertically sandwiched in the mold. A program for controlling a continuous casting process of separating and producing a multi-layer slab having a composition of the surface layer and a composition of the inner layer different from each other at the position of the molten metal in the mold by a molten metal level meter. A step of inputting a measurement value of a certain surface layer and a measurement value of a supply flow rate of the molten metal by a flow meter installed in either the surface layer nozzle or the inner layer nozzle, and a surface layer by the molten metal level meter. The measured value of the level, the measured value of the supply flow rate of the molten metal of either the surface layer nozzle or the inner layer nozzle by the flow meter, and the one of the surface layer nozzle and the inner layer nozzle where the flow meter is not installed. Based on the calculated value of the supply flow rate of the molten metal, the step of estimating the boundary layer level at the boundary position by the observer
　, the measured value of the surface layer level by the molten metal level meter, and the said by the estimation. Let the computer execute the step of controlling the supply flow rate of the molten metal of the surface layer nozzle and the supply flow rate of the molten metal of the inner layer nozzle so as to keep the estimated value of the boundary layer level at each target value. It is a program configured in.
The invention's effect
[0008]
　According to the present invention, the boundary layer level can be controlled with high accuracy in the continuous casting process of multi-layer slabs. This makes it possible to suppress mixing of the molten metal in the surface layer and the molten metal in the inner layer, and to produce a multi-layer slab of good quality.
A brief description of the drawing
[0009]
[Fig. 1] Fig. 1 is a diagram showing an outline of a continuous casting facility for casting multi-layer slabs.
FIG. 2 is a diagram showing a functional configuration of a control device for a continuous casting process of a multi-layer slab according to an embodiment.
FIG. 3 is a block diagram of a control system for surface flow rate and inner layer flow rate in the embodiment.
FIG. 4 is a characteristic diagram showing the flow rate characteristics of the inner layer stopper in Example 1, the fluctuation of the surface layer level, and the fluctuation of the boundary layer level.
FIG. 5 is a characteristic diagram showing a change in the opening degree of the surface layer stopper and a change in the opening degree of the inner layer stopper in the first embodiment.
FIG. 6 is a characteristic diagram showing a change in surface flow rate and a change in inner layer flow rate in Example 1.
FIG. 7 is a characteristic diagram showing the casting speed in Example 2, fluctuations in the surface layer level, and fluctuations in the boundary layer level.
FIG. 8 is a characteristic diagram showing a change in the opening degree of the surface layer stopper and a change in the opening degree of the inner layer stopper in the second embodiment.
FIG. 9 is a characteristic diagram showing a change in surface flow rate and a change in inner layer flow rate in Example 2.
Mode for carrying out the invention
[0010]
　Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
　FIG. 1 shows an outline of a continuous casting facility for casting multi-layer slabs.
　As shown in FIG. 1A, the continuous casting facility includes two immersion nozzles (hereinafter referred to as surface layer nozzle 1 and inner layer nozzle 2) having different discharge positions in the casting direction, and molten steel having different compositions. Are injected into the mold 5 from the surface layer tundish 3 and the inner layer tundish 4, respectively, via the surface layer nozzle 1 and the inner layer nozzle 2. FIG . 1B is a schematic view showing a surface layer cross-sectional area A 1 and an inner layer cross-sectional area A 2 .
[0011]
　Each molten steel injected into the mold 5 receives a braking force in a static magnetic field band formed by the magnetic field generator 6, and the molten steel in the surface layer and the molten steel in the inner layer are separated vertically in the mold 5 with a boundary 7 in between. Will be done. The molten metal surface 8 in the mold 5 is a position where the molten steel in the surface layer comes into contact with the molten powder, and the boundary 7 is a separation position between the molten steel in the surface layer and the molten steel in the inner layer. Hereinafter, the position of the molten metal surface 8 is referred to as a surface layer level, and the position of the boundary 7 is referred to as a boundary layer level. Although the boundary 7 is actually formed as a transition layer between both layers, it is treated as a boundary line. The line 15 indicates the solidification shell position.
[0012]
　A molten metal level meter 9 for measuring the surface layer level in the mold 5 is installed. Further, in any one of the surface layer nozzle 1 and the inner layer nozzle 2, in the present embodiment, only the inner layer nozzle 2 is provided with an in-nozzle flow meter (hereinafter, simply referred to as a flow meter) 10 for measuring the molten steel supply flow rate. In addition, in any one of the surface layer nozzle 1 and the inner layer nozzle 2, in the present embodiment, the flow meter is not installed in the surface layer nozzle 1. As the flow meter 10, for example, an electromagnetic flow meter is used. When using an electromagnetic flowmeter, it is desirable that the immersion nozzle is filled with molten steel. Therefore, in the present embodiment, the flowmeter 10 is installed in the inner layer nozzle 2 having a relatively large flow rate.
[0013]
　The flow rate of molten steel supplied by the surface nozzle 1 (hereinafter referred to as the surface flow rate) is adjusted by opening and closing the surface stopper 11. Similarly, the flow rate of molten steel supplied by the inner layer nozzle 2 (hereinafter referred to as the inner layer flow rate) is adjusted by opening and closing the inner layer stopper 12. The opening / closing operations of the stoppers 11 and 12 are executed under the control of the controller 13. In this embodiment, a stopper (hereinafter, also referred to as ST) is used, but a sliding nozzle may be used to adjust the flow rate of molten steel supplied from each of the nozzles 1 and 2.
[0014]
　In the continuous casting process of multi-layer slabs by the continuous casting equipment as described above, it is necessary to appropriately control the surface layer flow rate and the inner layer flow rate in order to keep the surface layer level and the boundary layer level at appropriate positions.
　With reference to FIG. 2, the functional configuration of the controller 13 that functions as a control device for the continuous casting process of the multi-layer slab in the present embodiment will be described.
　The input unit 201 inputs the measured value of the surface layer level by the molten metal level meter 9 and the measured value of the inner layer flow rate by the flow meter 10.
[0015]
　The control unit 202 determines the opening operation amount of the surface layer stopper 11 by PI control (Proportional Integral control) so as to keep the surface layer level measured value by the molten metal level meter 9 at the surface layer level target value, and the surface layer flow rate. To control.
[0016]
　In addition, a Luenberger-type observer will be constructed using a linear approximation model of the continuous casting process of multi-layer slabs. The estimation unit 203 uses the surface level measured value by the molten metal level meter 9, the inner layer flow rate measured by the flow meter 10, and the calculated surface flow rate, which is the molten steel supply flow rate of the immersion nozzle on which the flow meter is not installed. Based on, the boundary layer level is estimated by this observer. Then, the control unit 204 determines the opening operation amount of the inner layer stopper 12 by PI control so as to keep the boundary layer level estimated value by the estimation unit 203 at the boundary layer level target value, and controls the inner layer flow rate. .. In estimating the state variables, a non-linear filtering method (ensemble Kalman filter, etc.) for a non-linear model may be used instead of using a linear approximation model, but in the present embodiment, continuous multi-layer slabs are used. A case where a Ruenberger type observer is constructed by using a linear approximation model of the casting process will be described.
[0017]
　In the present embodiment, the input unit 201 corresponds to the input means referred to in the present invention, the estimation unit 203 corresponds to the estimation means referred to in the present invention, and the control units 202 and 204 correspond to the control means referred to in the present invention. To do.
[0018]
Models expressing the continuous casting process for multi-layer slabs are shown in, for example, Patent Document 3 and Non-Patent Document 1.
　In this model , the meniscus position (surface layer level) y 1 (t) and the boundary layer level y 2 (t) are given by the equation (1) according to the fluctuations of the surface flow rate Q 1 (t) and the inner layer flow rate Q 2 (t). ) Varies according to equation (5). As shown in FIG. 1, s (t) is the surface thickness of the multi-layer slab, A 1 (t) is the surface cross-sectional area of ​​the multi-layer slab, and A 2 (t) is the inner cross-sectional area of the multi-layer slab. A is the total cross-sectional area of ​​the multi-layer slab (A 1 (t) + A 2 (t)). V c is the casting speed. W is the mold width, D is the mold thickness, and K is the solidification coefficient.
[0019]
　In the continuous casting process of multi-layer slabs , the surface layer thickness s (t) and the boundary layer level y 2 (t) are "self-healing" as the surface layer level y 1 (t) and the boundary layer level y 2 (t) fluctuate. Has the function of ". 　Here, the inner layer cross-sectional area A 2 (t) and the surface layer thickness s (t) vary according to the equations (3) and (4). τ is the dead time from the meniscus position to the boundary layer level, and satisfies Eq. (5).
[0020]
[Number 1]

[0021]
　If the casting speed V c is constant, the waste time τ can be expressed by Eq. (6). Further, if the surface layer level is maintained at the surface layer level target value, the waste time τ may be approximated as in Eq. (7). y 0 is the steady surface level target value. During steady control, the approximation as shown in Eq. (7) can be performed.
[0022]
[Number 2]

[0023]
<
　Drivation of Linear Approximation Model> In order to construct a Ruenberger type observer, a linear approximation model of the nonlinear models of Eqs. (1) to (4) and Eq. (7) is derived.
　Perturbation amount of each state variable near the set value (y 1 ~ (t), y 2 ~ (t), s ~ (t), A 2 ~ (t), Q 1 ~ (t), Q 2 ~ ( t)) is defined as follows. In addition, for example, in the notation of y 1 to (t), it is assumed that ~ is added above y 1 .
[0024]
[Number 3]

[0025]
　y 1 * and y 2 * are the set values ​​of the surface layer level and the boundary layer level, and s * and A 2 * are the equilibrium points of the nonlinear model determined according to V c , y 1 * and y 2 * , Q 1 * and Q. 2 * is the target value of the molten steel supply flow rate determined according to V c , s * , and A 2 * , and is expressed as follows.
[0026]
[Number 4]

[0027]
　When the nonlinear models of equations (1) to (4) and (7) are linearly approximated in the vicinity of these set values, the perturbation dynamics at the surface layer level and the boundary layer level are obtained by equations (8) and (9). It is expressed as.
[0028]
[Number 5]

[0029]
　Incidentally, the perturbation amount s of the surface layer thickness ~ (t) is expressed by Equation (12), the perturbation amount y of the boundary layer level 2 - to reverse the variation of the (t), the surface layer thickness perturbation amount s - ( It can be seen that t) fluctuates.
[0030]
[Number 6]

[0031]
　The equation (9) expressing the variation at the boundary layer level can be summarized as the equation (14) by using the equations (10) to (13).
[0032]
[Number 7]

[0033]
　When the casting speed V c = 1.0 m / min, the solidification coefficient K = 20.0 mm · min ^ ( -1 / 2), the surface layer level y 1 = -100 mm, and the boundary layer level y 2 = -420 mm, α = 0.4735, β = 0.0177, and the time constant “1 / αβ” of the self-repair function at the boundary layer level is 117 sec.
[0034]
A
　Ruenberger-type observer is constructed to estimate the boundary layer level that cannot be measured directly.
　Here, two flow rates, a surface flow rate and an inner flow rate, are required as the observer input, but since only one flow meter 10 is installed, the molten steel supply flow rate of the immersion nozzle on which the flow meter is not installed is used. A calculated surface flow rate is substituted by a calculated value, and the calculated error is regarded as a step disturbance and is compensated by an observer.
　As the calculated value of the surface layer flow rate, for example, a flow rate target value (a constant value determined according to the casting speed) at the time of steady control may be used, or a nominal model of the flow rate characteristic showing the relationship between the opening degree of the surface layer stopper 11 and the flow rate. And the value calculated based on the actual opening opening value of the surface stopper 11 may be used.
[0035]
　When the flow meter 10 is installed in the inner layer nozzle 2 and the flow meter is not installed in the surface layer nozzle 1 as in the present embodiment, the formulation is as follows.
　Calculated Q of the surface layer flow 1 - stepwise disturbance d as calculated error of (t) 1 in consideration of ^ (t), it is formulated in a state space model (equation (15) from equation (17)). Equation (15) is an addition of step-like disturbance d 1 ^ (t) to equation (8) , and equation (16) corresponds to equation (14). Note that ^ is added to distinguish that it is an observer state variable. For example , in the notation of d 1 ^ (t), it is assumed that ^ is added above d 1 .
　The equations (15) to (17) can be collectively expressed by the state space models of the equations (18) and (19).
[0036]
[Number 8]

[0037]
　An observer is constructed for this state space model as shown in equation (20).
[0038]
[Number 9]

[0039]
　When the state space model is detectable, the error in estimating the state variable by the observer decreases over time and approaches 0 (see, for example, Non-Patent Document 2). Here, the detection by the state space model means that the condition of the equation (23) is satisfied with respect to the unstable pole λ of the system matrix A of the equations (21) and (22). n is the dimension of the state variable x.
　In the state-space models of Eqs. (18) and (19), for unstable pole 0, Eq. (24) is obtained and the detectability is satisfied. Therefore, the estimation error of the observer constructed by Eq. (20) is It can be asymptotically close to 0.
[0040]
[Number 10]

[0041]
　Based on the above, FIG. 3 shows a block diagram of the control system for the surface flow rate and the inner layer flow rate in the present embodiment.
　As shown in FIG. 3, the surface layer level y 1 is measured, compared with the surface layer level target value (y 1 target value), and the opening degree of the surface layer stopper 11 is adjusted according to the difference under the control of the controller 13. Perform feedback control. As expressed by the equation (1), the fluctuation of the surface layer level y 1 is expressed by the equation obtained by dividing the sum of the surface flow rate Q 1 and the inner layer flow rate Q 2 by the area A and then subtracting the casting speed V c. .. According to this, in the block diagram, the sum of the surface flow rate Q 1 and the inner layer flow rate Q 2 , which are controlled according to the opening degree of the surface stopper 11, is multiplied by 1 / A, and then the casting speed V c is subtracted. The surface layer level y 1 is obtained by integrating the values ​​obtained .
[0042]
　In addition, the boundary layer level perturbation amount y 2 ~ is estimated by the observer, and the boundary layer level set value is added to y 2 ~ ( indicated as the y 2 estimated value in FIG. 3 ) and the boundary layer level target value (y 2). Compared with the target value), under the control of the controller 13, feedback control for adjusting the opening degree of the inner layer stopper 12 corresponding to the difference is executed. The observer estimates the boundary layer level perturbation amount y 2 ~ by inputting the measured value of the surface layer level y 1, the measured value of the inner layer flow rate Q 2 , and the calculated value of the surface layer flow rate Q 1 . As expressed by the equation (2), the fluctuation of the boundary layer level y 2 is expressed by the equation obtained by dividing the inner layer flow rate Q 2 by the inner layer cross-sectional area A 2 and subtracting the casting speed V c . According to this, in the block diagram, the inner layer flow rate Q 2 controlled according to the opening degree of the inner layer stopper 12 is multiplied by 1 / A 2 , and the casting speed V c is obtained from there. The boundary layer level y 2 is obtained by subtracting and integrating .
[0043]
　As described above, a linear approximation model of the continuous casting process of multi-layer slabs is used to construct a Ruenberger type observer, and the boundary layer level to be controlled is estimated in real time. As a result, even if the boundary layer level fluctuates due to changes in flow rate characteristics such as nozzle clogging or clogging peeling during casting, the boundary layer level fluctuation is detected and the boundary layer level target value is quickly restored. Can be done. In this way, in the continuous casting process of multi-layer slabs, the boundary layer level can be controlled with high accuracy, mixing of the molten metal of the surface layer and the molten metal of the inner layer can be suppressed, and the double layer of good quality. It becomes possible to manufacture layered slabs.
　Further, since the flow meter 10 is installed only in one of the surface layer nozzle 1 and the inner layer nozzle 2, the equipment configuration can be simplified.
[0044]
　Even when the flow meter 10 is installed in the surface nozzle 1 and the flow meter is not installed in the inner layer nozzle 2, the observer is configured as shown in equations (25) to (27) by the same formulation. Can be done. Since the state-space models of Eqs. (25) and (26) also satisfy the detectability, the estimation error of the observer constructed by Eq. (27) can be asymptotically approached to 0.
[0045]
[Number 11]

[0046]
　Further, in formulating the disturbance, a step-shaped disturbance is taken as an example, but if the actual change in the flow rate characteristics can be regarded as a lamp-shaped disturbance, a lamp-shaped disturbance may be assumed. When a ramp-shaped disturbance is assumed as the disturbance, the dynamics of the disturbance are formulated as in the equation (28).
[0047]
[Number 12]

[0048]
　When the flow meter 10 is installed in the inner layer nozzle 2 and the flow meter is not installed in the surface layer nozzle 1 as in the embodiment, the state space model in consideration of the lamp-shaped disturbance is formulated by equations (29) and (30). It is shown in the formula. Since this state-space model also satisfies the detectability, it is possible to construct a Ruenberger-type observer as in the case of a stepped disturbance. Even when the flow meter 10 is installed in the surface nozzle 1 and the flow meter is not installed in the inner layer nozzle 2, the Ruenberger type observer can be configured by the same formulation.
[0049]
[Number 13]

Example
[0050]
　Also in the embodiment described below, the flow meter 10 is installed in the inner layer nozzle 2 and the flow meter is not installed in the surface layer nozzle 1 as in the embodiment.
(1) Example 1 (Control simulation when flow rate characteristic changes) In
　Example 1, a control simulation when flow rate characteristic changes is performed assuming casting of a multi-layer slab in a test CC (Continuous casting), and the present invention is performed. Boundary layer level control method to which is applied, and inner layer flow rate constant control method according to the method described in Patent Document 3 (a flow meter is installed in the inner layer nozzle to keep the inner layer flow rate constant, and then the surface layer level is constant. The method of keeping) was compared.
　In the boundary layer level control method, both surface layer level control and boundary layer level control are performed by PI control, and in the inner layer flow rate constant control method, both surface layer level control and inner layer flow rate target value control are performed by PI control.
[0051]
　In this embodiment, it is assumed that the flow rate of the inner layer stopper decreases due to (1) nozzle clogging, (2) clogging peeling, and (3) tundish head lowering (lowering of the hot water surface in the tundish). As shown in FIG. 4A, when the inner layer stopper has a certain opening degree, the flow rate of the inner layer stopper gradually decreases as the tundish head descends. Then, in the middle of the process, nozzle clogging occurs in the inner layer stopper and the flow rate is significantly reduced, and then clogging peeling occurs and the decrease in flow rate is eliminated. The "inner layer ST (stopper) flow rate characteristic change rate" on the vertical axis of FIG. 4A is based on the flow rate characteristic of the inner layer stopper at the start of casting (relationship between the opening degree of the stopper and the flow rate). Represents the relative value of flow rate characteristics.
[0052]
　The simulation conditions are mold width: 800 mm, mold thickness: 170 mm, surface layer level target value: -100 mm, boundary layer level target value: -420 mm, casting speed: 1.0 m / min, solidification constant 20.0 mm / min ^ (-). 1/2).
[0053]
　Further, as the PI control parameters of the boundary layer level control method, the proportional gain was set to 0.30 and the integration time was set to 10.0 [sec] for both the surface layer level control and the boundary layer level control. In addition, as PI control parameters of the inner layer flow rate constant control method, proportional gain: 0.30, integration time: 10.0 [sec] for surface level control, proportional gain: 0.000002, integration time: 10 for inner layer flow rate constant control. It was set to 0.0 [sec].
[0054]

　Fig. 4 (b) shows the fluctuation at the surface layer level, and (c) shows the fluctuation at the boundary layer level. Further, FIG. 5A shows a change in the surface stopper opening degree, and FIG. 5B shows a change in the inner layer stopper opening degree. Further, the surface flow rate Q in FIG. 6 (a) 1 a change in the inner layer flow rate Q in (b) 2 shows changes in. The horizontal axis of each characteristic diagram of FIGS. 4 to 6 is time [sec]. The solid line in the figure shows the characteristic line by the boundary layer level control method, and the dotted line shows the characteristic line by the inner layer flow rate constant control method.
　As shown in FIG. 4B, the surface layer level can be kept substantially constant by any of the methods with respect to the change in the flow rate characteristic of the inner layer stopper in FIG. 4A. On the other hand, as shown in FIG. 4 (c), regarding the boundary layer level, the boundary layer level is kept substantially constant in the boundary layer level control method, but the boundary layer level is maintained in the inner layer flow rate constant control method. Fluctuations cannot be suppressed.
[0055]
　In the boundary layer level control method, by estimating the boundary layer level to be controlled in real time by an observer, it is possible to detect fluctuations in the boundary layer level and quickly recover to the boundary layer level target value.
　On the other hand, in the inner layer flow rate constant control method, the molten steel supply flow rate is restored to the target value and then the multi-layer slab is used in response to the change in the boundary layer level resulting from the change in the flow rate characteristics of the inner layer stopper. It is an indirect control method that restores the boundary layer level to the target value by the self-repair function of the continuous casting process, and it takes a long time to restore the boundary layer level. In the flow rate target value control, the disturbance suppression effect can be enhanced by setting the control gain to a high gain such as shortening the integration time, but the closed loop system may become unstable, so the control gain is excessive. It is difficult to make it high gain.
[0056]
(2) Example 2 (Control simulation at the time of changing the casting speed) In
　the operation of the continuous casting process, the operation of changing the casting speed V c is performed during casting . For example, there is a change in the casting speed V c , such as increasing the casting speed V c from the time of controlling the rise of hot water toward steady operation, or decelerating the casting speed V c when the molten metal level fluctuation becomes severe . Assuming such a situation, a control simulation was performed when the casting speed V c was changed. 　The simulation conditions and control parameters are the same as those in the first embodiment except that the tundish head is kept constant and the casting speed V c is changed.
[0057]
　As shown in FIG. 7 (a), the casting speed V toward 110sec from 100 sec c as to slow down from 16.7mm / sec (1.0m / min) to 13.3mm / sec (0.8m / min) did. In addition, the flow rate target value according to the casting speed V c is set by the boundary layer level control method and the inner layer flow rate by the formulas (1) to (4) and (7) expressing the continuous casting process of the multi-layer slab. It was set as the target value in the constant control method.
[0058]

　FIG. 7 (b) shows the fluctuation at the surface layer level, and (c) shows the fluctuation at the boundary layer level. Further, FIG. 8A shows a change in the surface stopper opening degree, and FIG. 8B shows a change in the inner layer stopper opening degree. Further, (a) of FIG. 9 shows a change in the surface flow rate Q 1 , and (b) shows a change in the inner layer flow rate Q 2 . The horizontal axis of each characteristic diagram of FIGS. 7 to 9 is time [sec]. The solid line in the figure shows the characteristic line by the boundary layer level control method, and the dotted line shows the characteristic line by the inner layer flow rate constant control method.
　In response to the change in the casting speed V c in FIG. 7 (a) , as shown in FIG. 7 (b), with respect to the surface layer level, fluctuations in the surface layer level are quickly suppressed by any method, and the surface layer level target is achieved. Can be converged to a value. On the other hand, as shown in FIG. 7 (c), with respect to the boundary layer level, the boundary layer level control method can quickly suppress the fluctuation of the boundary layer level and converge to the boundary layer level target value. However, in the inner layer flow rate constant control method, the boundary layer level fluctuates greatly, and the recovery to the boundary layer level target value is delayed.
[0059]
　Although the present invention has been described above together with the embodiments, the above embodiments are merely examples of embodiment of the present invention, and the technical scope of the present invention is construed in a limited manner by these. It should not be. That is, the present invention can be implemented in various forms without departing from the technical idea or its main features.
　The control device for the continuous casting process of the multi-layer slab to which the present invention is applied can be realized by, for example, a computer equipped with a CPU, ROM, RAM and the like.
　The present invention also provides software (program) that realizes the functions of the present invention to a system or device via a network or various storage media, and the computer of the system or device reads and executes the program. It is feasible.
　Therefore, in another aspect of the present invention, the molten metal is injected into the mold from the surface nozzle and the inner layer nozzle, and the molten metal on the surface layer and the molten metal on the inner layer are separated vertically in the mold with a boundary. This is a program for controlling a continuous casting process for producing a multi-layer slab in which the composition of the surface layer and the composition of the inner layer are different from each other, and is the surface layer which is the position of the molten metal surface in the mold by the molten metal level meter. The step of inputting the measured value of the level and the measured value of the supply flow rate of the molten metal by the flow meter installed in either the surface layer nozzle or the inner layer nozzle, and the surface layer level by the molten metal level meter. The measured value, the measured value of the supply flow rate of the molten metal of any one of the surface layer nozzle and the inner layer nozzle by the flow meter, and the surface nozzle and the inner layer nozzle of which the flow meter is not installed. The step of estimating the boundary layer level at the boundary position by the observer based on the calculated value of the supply flow rate of the molten metal, the measured value of the surface layer level by the molten metal level meter, and the boundary layer by the estimation. A computer is configured to perform a step of controlling the supply flow rate of the molten metal of the surface layer nozzle and the supply flow rate of the molten metal of the inner layer nozzle so as to keep the estimated value of the level at each target value. A recording medium that can be read by the program or the computer that recorded it.
　The control device for the continuous casting process of the multi-layer slab to which the present invention is applied may be a PLC (Programmable Logic Controller) or may be realized by dedicated hardware such as an ASIC (Application Specific Integrated Circuit). May be good.
Industrial applicability
[0060]
　According to the present invention, it is possible to suppress mixing of the molten metal of the surface layer and the molten metal of the inner layer, and to produce a multi-layer slab of good quality.
Description of the sign
[0061]
1: Surface nozzle
2: Inner layer nozzle
3: Surface layer tundish
4 : Inner layer tundish
5: Mold
6: Magnetic field generator
7: Boundary
8: Hot water surface
9: Hot water level meter
10: Flow meter
11: Surface layer stopper
12: Inner layer Stopper
13: Controller
15: Solidification shell position
201: Input unit
202: Control unit
203: Estimating unit
204: Control unit
The scope of the claims
[Claim 1]
　The molten metal is injected into the mold from the surface layer nozzle and the inner layer nozzle, and the molten metal on the surface layer and the molten metal on the inner layer are separated vertically in the mold with a boundary between them, and the composition of the surface layer and the inner layer are separated. A control method for a continuous casting process for producing multi-layer slabs having different compositions, which is
　a molten metal level meter for measuring the surface layer level, which is the position of the molten metal surface in the mold, and the surface layer nozzle and the inner layer nozzle. Of the
　surface layer level measurement value by the molten metal level meter and the surface layer nozzle and the inner layer nozzle by the flow meter, using a flow meter installed on one of them and measuring the supply flow rate of the molten metal. Based on the measured value of the supply flow rate of the molten metal of either one and the calculated value of the supply flow rate of the molten metal of the surface layer nozzle and the inner layer nozzle on which the flow meter is not installed, the boundary is formed by the observer. The boundary layer level of the
　surface nozzle is estimated so that the measured value of the surface level by the molten metal level meter and the estimated value of the boundary layer level by the observer are kept at their respective target values. A
method for controlling a continuous casting process of a multi-layer slab, which comprises controlling the supply flow rate of the molten metal and the supply flow rate of the molten metal of the inner layer nozzle .
[Claim 2]
　The continuous casting process of a multi-layer slab according to
claim 1 , wherein a Ruenberger type observer is constructed by using a linear approximation model of the continuous casting process of the multi-layer slab as the observer. Control method.
[Claim 3]
　The observer has the surface layer level, the boundary layer level, and the disturbance corresponding to the calculation error of the calculated value of the supply flow rate of the molten metal of the surface layer nozzle and the inner layer nozzle on which the flow meter is not installed. The
method for controlling a continuous casting process of a multi-layer slab according to claim 1 or 2, wherein the state variable is used.
[Claim 4]
　The
method for controlling a continuous casting process of a multi-layer slab according to claim 3, wherein a step-like disturbance or a ramp-like disturbance is applied as the disturbance .
[Claim 5]
　The
method for controlling a continuous casting process of a multi-layer slab according to any one of claims 1 to 4 , wherein the flow meter is installed in the inner layer nozzle .
[Claim 6]
　The
method for controlling a continuous casting process of a multi-layer slab according to any one of claims 1 to 4 , wherein the flow meter is installed on the surface nozzle .
[Claim 7]
　The molten metal is injected into the mold from the surface layer nozzle and the inner layer nozzle, and the molten metal on the surface layer and the molten metal on the inner layer are separated vertically in the mold with a boundary between them, and the composition of the surface layer and the inner layer are separated. A control device that controls a continuous casting process for producing multi-layered slabs having different compositions
　, such as a surface level measured value of the position of the molten metal in the mold by a molten metal level meter, the surface nozzle, and the surface nozzle. An input means for inputting the measured value of the supply flow rate of the molten metal by a flow meter installed on one of the inner layer nozzles, the
　surface layer level measured value by the molten metal level meter, and the said by the flow meter. The measured value of the supply flow rate of the molten metal of either the surface layer nozzle or the inner layer nozzle, and the calculated value of the supply flow rate of the molten metal of the surface layer nozzle and the inner layer nozzle to which the flow meter is not installed. Based on the above, the estimation means for estimating the boundary layer level at the boundary position by the observer, the
　surface layer level measurement value by the molten metal level meter, and the boundary layer level estimation value by the estimation means are obtained.
A series of multi-layered slabs provided with a control means for controlling the supply flow rate of the molten metal of the surface layer nozzle and the supply flow rate of the molten metal of the inner layer nozzle so as to maintain the target value. Control device for the casting process.
[Claim 8]
　The molten metal is injected into the mold from the surface layer nozzle and the inner layer nozzle, and the molten metal on the surface layer and the molten metal on the inner layer are separated vertically in the mold with a boundary between them, and the composition of the surface layer and the inner layer are separated. A program for controlling a continuous casting process for producing multi-layer slabs having different compositions,
　which is a surface-level measured value of the position of the molten metal in the mold by a molten metal level meter, and the surface nozzle and the surface nozzle. The step of inputting the measured value of the supply flow rate of the molten metal by the flow meter installed in one of the inner layer nozzles, the
　surface layer level measured value by the molten metal level meter, and the surface layer by the flow meter. The measured value of the supply flow rate of the molten metal of either one of the nozzle and the inner layer nozzle and the calculated value of the supply flow rate of the molten metal of the surface layer nozzle and the inner layer nozzle on which the flow meter is not installed. Based on this, the step of estimating the boundary layer level at the boundary position by the observer,
　the measured value of the surface layer level by the molten metal level meter, and the estimated value of the boundary layer level by the estimation are set as the respective target values.
A program configured to cause a computer to perform a step of controlling the supply flow rate of the molten metal of the surface layer nozzle and the supply flow rate of the molten metal of the inner layer nozzle so as to maintain the structure.