JP2007268559A - Method and apparatus for controlling solidification completion position of continuously cast slab and method for producing continuously cast slab - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for controlling the solidification completion position of a continuously cast slab, which materialize accurate control of the solidification completion position even in unsteady time at which the deceleration and reacceleration of a casting velocity are performed at pan exchange or the like in continuous-continuous casting, and to provide a method for producing a continuously cast slab. <P>SOLUTION: The method for controlling the solidification completion position of the continuously cast slab is provided in which the solidification completion position of the continuously cast slab is controlled by manipulating a casting velocity and/or a cooling water quantity, and the method is characterized in that response models expressing the relation of the moving response of the solidification completion position of the slab to the change of the casting velocity and/or cooling water quantity are created as a plurality of models in accordance with casting conditions, and are retained in a data base, the response model in accordance with a need is read out from the data base, and using the read-out response model, a filtering processing of a slab moving speed change command signal for allowing the same to coincide with the response of a desired slab solidification completion position is performed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a solidification completion position control method and apparatus for a continuous cast slab that controls the solidification completion position of a continuous cast slab cast by a continuous casting machine online, and a method for manufacturing a continuous cast slab.

  In continuous casting of steel, it is extremely important to determine where the solidification completion position of the continuous cast slab (also referred to as “crater end position”) is in the slab, and to keep it at an appropriate position. Significantly affects slab productivity and quality improvement.

  For example, when the casting speed is increased in order to improve productivity, the solidification completion position moves to the downstream side in the casting direction of the slab. When the solidification completion position exceeds the range of the slab support roll, the slab swells due to the action of static iron pressure (hereinafter this phenomenon is referred to as “bulging”). Problems such as casting stop occur. Therefore, it is extremely important to keep the solidification completion position within an appropriate range.

  Further, in the light reduction operation for improving the quality by reducing the center segregation of the slab, it is necessary to control the casting speed and the strength of the secondary cooling water so that the solidification completion position is located in the light reduction zone. Furthermore, since the cross section of the slab slab is flat, it is known that the solidification completion position is not uniform in the width direction of the slab and the shape varies with time. The shape of the solidification completion position that varies in the width direction is also a major factor that determines the quality and productivity of the slab.

  In order to meet these requirements, it is necessary to first grasp the solidification state of the slab, and methods for estimating the solidification state of the slab and controlling the position of the solidification point have been proposed.

  For example, in Patent Document 1, the solidification thickness is measured using an electromagnetic ultrasonic meter, and the solidification speed of the slab is calculated using the measured solidification thickness and the elapsed time from the meniscus to the electromagnetic ultrasonic meter. Is used to control the casting speed so that solidification is completed when the slab part reaches the position of the electromagnetic ultrasonic meter.

Further, in Patent Document 2, the calculation formula for obtaining the coagulation position from the propagation time of the longitudinal wave ultrasonic wave is calibrated with the value of the transverse wave ultrasonic sensor using both the transverse wave ultrasonic sensor and the longitudinal wave ultrasonic sensor, and the longitudinal wave ultrasonic sensor is calibrated. It is disclosed that a solidification position is estimated from the propagation time of a sound wave, a casting speed based on the estimated position, and spray control.
JP-A-2-55652 JP 2005-177860 A

  However, the above disclosed technique has the following problems.

  First, the technique disclosed in Patent Document 1 uses the calculated value of the solidification rate, but accurate solidification rate estimation during non-steady times such as when the casting rate is reduced and re-accelerated as when the pan is changed during continuous casting. This may cause a phenomenon that the coagulation position goes out of the machine edge. In fact, when the casting speed is changed suddenly, the secondary cooling is also changed at the same time, so the cooling history of the slab immediately below the mold and the slab near the machine end is greatly different. For this reason, there is a problem that how to change the solidification position after the speed change cannot be determined accurately unless a model such as a response model is used.

  In addition, in the technique disclosed in Patent Document 2, it is explained that the casting speed or the secondary cooling spray is controlled using the solidification position accurately estimated by two types of ultrasonic sensors. Is not mentioned.

  The present invention has been made in view of the above circumstances, and is capable of accurately controlling the solidification completion position even in an unsteady state where the casting speed is reduced and re-accelerated, such as when changing the pan during continuous casting. It aims at providing the solidification completion position control method and apparatus of a slab, and the manufacturing method of a continuous cast slab.

  The invention according to claim 1 of the present invention is a solidification completion position control method for a continuous cast slab in which the solidification completion position of the continuous cast slab is controlled by operating the casting speed and / or the amount of cooling water. A response model representing the relationship of the movement response of the slab solidification completion position to changes in the casting speed and / or cooling water volume is created as multiple response models according to the casting conditions, stored in the database, and the response model as required Is cast from the database, and a slab moving speed change command signal is filtered to match the response of the desired slab solidification completion position using the read response model. This is a solidification completion position control method.

  The invention according to claim 2 of the present invention is the solidification completion position control method of the continuous cast slab according to claim 1, wherein the response model representing the relationship of the movement response of the slab solidification completion position is a dead time. This is a solidification completion position control method for a continuous cast slab characterized by being represented by a linear dynamic characteristic model.

  The invention according to claim 3 of the present invention is the solidification completion position control method of the continuous cast slab according to claim 1 or claim 2, wherein the solidification completion position of the continuous cast slab is estimated or detected. A continuous cast slab characterized by obtaining a solidification completion position change obtained by operating a casting speed and / or a cooling water amount, and correcting a response model stored in the database based on the obtained solidification completion position change. This is a solidification completion position control method.

  The invention according to claim 4 of the present invention is characterized in that a continuous cast slab is manufactured using the solidification completion position control method for a continuous cast slab according to any one of claims 1 to 3. It is a manufacturing method of the continuous casting slab which becomes.

  Furthermore, the invention according to claim 5 of the present invention stores a response model representing the relationship of the movement response of the slab solidification completion position to the change in the casting speed and / or the cooling water amount as a plurality of response models corresponding to the casting conditions. A database and a response model as needed are read from the database, and the slab moving speed change command signal is filtered to match the response of the desired slab solidification completion position using the read response model. It is a solidification completion position control apparatus of the continuous cast slab characterized by including a compensator.

  In the present invention, the solidified point position change response model when the casting conditions such as casting speed are changed is managed with parameters in the database, and the non-stationary model is considered in detail. Even in unsteady situations such as when the casting speed is reduced and re-accelerated as in the case of time, the solidification point position can be set to a predetermined position in the shortest time without causing a phenomenon that the solidification position goes out of the machine end. It becomes possible to return the operation, and it is possible to continue the operation while maintaining high productivity. In addition, it is possible to manage the freezing point position with the best quality of the slab.

  The best mode for carrying out the present invention will be described below with reference to the drawings and mathematical expressions. FIG. 1 is a diagram showing the entire basic control system according to the present invention. In the figure, 1 is molten steel, 2 is a tundish, 3 is an immersion nozzle, 4 is a mold, 5 is a shell, 6 is a sliding nozzle, 7 is a pinch roll, 8 is a solidification position detector, 9 is a casting condition database, 10 is Filter processing devices 11 and 11 respectively represent pinch roll speed control devices.

  The tundish 2 is disposed on the upper part of the mold 4, the sliding nozzle 6 is disposed on the bottom of the tundish, and the immersion nozzle 3 is disposed on the lower surface side of the sliding nozzle 6. The molten steel 1 filled in the tundish 2 is injected into the mold 4 through the sliding nozzle 6 and the immersion nozzle 3.

  The molten steel 1 injected into the mold 4 is cooled from the side surface of the mold and solidifies from the surface to form a shell 5, and is drawn downward by a pinch roll 7 to become a cast piece. At this time, the drawing speed, that is, the casting speed is controlled by the pinch roll (P / R) speed control device 11. In addition, the amount of molten steel injected into the mold 4 is determined by the opening degree of the sliding nozzle 6.

  The present invention provides a secondary cooling control method. At this time, it is assumed that there is a separate control system (not shown) in which the spray water amount is automatically changed according to the casting speed level.

  When the casting speed is changed as when the pan is changed, the casting speed can be changed by giving a speed change command to the P / R speed controller 11. At this time, the amount of spray water is automatically increased to an appropriate amount when the speed is increased, and similarly reduced to an appropriate amount of water when the speed is reduced. Thereby, the solidification completion position dynamically changes.

  In the present invention, the dynamic change of the solidification completion position is described as a dynamic characteristic model and stored in the casting condition database 9. Next, the compensator 10 is designed and installed so that the dynamic characteristic model has an ideal response. The compensator 10 performs P / R speed change command filtering using a dynamic characteristic model that meets the operating conditions. However, the compensator 10 can be realized without the solidification position detection device 8 at the solidification completion position. By filtering the R speed change command and giving it to the P / R speed control device 11 as a new P / R speed command, an ideal response can be obtained.

  The filter processing in the compensator 10 will be described below. First, FIG. 2 is a diagram showing how the solidification completion position changes when the casting speed increase is changed.

  In general, when the casting speed is changed as shown in the upper diagram of FIG. 2, the position of the solidification completion point starts to change after the dead time associated with the change in the condition of the spray water amount elapses as shown in the lower diagram of FIG. The change sometimes behaves as if the solidification completion position shown in FIG. 2 once overshoots. For this reason, a speed change that does not overshoot is required.

  In order to realize this, a dynamic characteristic model is created in which the change in casting speed shown in FIG. Then, the response as a result of performing some compensation for the response by this dynamic characteristic model may be a response without overshoot as shown in FIG. 3, for example. In terms of control, this is called model reference control.

  FIG. 4 is a diagram illustrating a configuration example of the model reference control system. In this example, the speed change command given to the secondary cooling process is corrected by putting it in the “P / R speed change pattern filter”, and a corrected new speed change command is given. Instead of the “P / R speed change pattern filter”, a dynamic compensator that changes the dynamic characteristics by observing the solidification position may be inserted. With these processes, the response characteristics of the solidification completion position can be improved as shown in FIG.

  The response characteristic of the solidification completion position is generally made based on a nonlinear heat transfer dynamic characteristic, but is very complicated. For this reason, it is possible to obtain a simpler and more general-purpose model by performing classification based on solidification characteristics depending on the steel type and classification based on the casting speed region, and storing model characteristics according to conditions. Therefore, in FIG. 4, these are extracted from the casting condition D / B (database) and given to the filter. Also, since the characteristics are expected to change over time and casting conditions, update the model parameters for casting conditions D / B by checking the casting speed change record, spray water volume change record and solidification completion position information. It corresponds by adding a mechanism.

  Specific examples are shown below. First, the response of the solidification completion position to the casting speed change is approximated by “dead time + second-order linear response model” G (s) represented by the transfer function shown in the following equation (1).

At this time, the response of the ideal model in which the solidification completion position does not overshoot is given as Gm (s) as shown in the following equation (2).

  Then, the “P / R speed change pattern filter” F (s) shown in FIG. 4 is given by the following equation (3).

  With this configuration, the response of the solidification completion position due to the speed change given to G (s) through F (s) can be realized like the response of Gm (s). This is because F (s) is designed as shown in the following equation (4).

  FIG. 5 summarizes the concept of model compensation described above.

  FIG. 6 is a diagram illustrating an example of a change in the casting speed change command before and after the filter. By passing through the P / R speed change pattern filter, the casting speed command before passing through the upper filter changes to the new casting speed command as shown in the lower stage. In this way, by changing the casting speed through the filter, it is possible to obtain the response of the solidification completion position without the overshoot shown in FIG.

  Here, an example of obtaining a response at a solidification completion position without overshoot has been described as an example. However, by using the above-described method, it is possible to change the response at the solidification completion position with respect to a change in casting speed to an arbitrary response. .

It is a figure showing the whole basic control system concerning the present invention. It is a figure showing the mode of a change of the solidification completion position at the time of a casting speed increase change. It is a figure which shows an example of the ideal response waveform of a casting speed change and a solidification completion point position. It is a figure which shows the structural example of a model reference control system. It is a figure which shows the idea of model compensation. It is a figure which shows an example of the change of the casting speed change command before and behind a filter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Molten steel 2 Tundish 3 Immersion nozzle 4 Mold 5 Shell 6 Sliding nozzle 7 Pinch roll 8 Solidification position detection device 9 Casting condition database 10 Compensator 11 Pinch roll speed control device

Claims (5)

In the solidification completion position control method of the continuous casting slab, the solidification completion position of the continuous casting slab is controlled by operating the casting speed and / or the cooling water amount to control the solidification completion position.
A response model representing the relationship of the movement response of the slab solidification completion position to changes in the casting speed and / or cooling water amount is created as a plurality of response models according to the casting conditions, stored in the database, and the response model as required Is cast from the database, and a slab moving speed change command signal is filtered to match the response of the desired slab solidification completion position using the read response model. Solidification completion position control method. In the solidification completion position control method of the continuous cast slab according to claim 1,
A solidification completion position control method for a continuous cast slab, wherein a response model representing a relationship between movement responses of the slab solidification completion position is represented by dead time and a linear dynamic characteristic model. In the solidification completion position control method of the continuous cast slab according to claim 1 or 2,
By estimating or detecting the solidification completion position of the continuous cast slab, the solidification completion position change obtained by manipulating the casting speed and / or the cooling water amount is obtained, and the database is based on the obtained solidification completion position change. A solidification completion position control method for a continuous cast slab, wherein the stored response model is corrected. A method for producing a continuous cast slab, comprising producing the continuous cast slab by using the solidification completion position control method for the continuous cast slab according to any one of claims 1 to 3. A database that stores a response model representing a relationship of a moving response of a slab solidification completion position to a change in casting speed and / or cooling water amount as a plurality of response models according to casting conditions;
A compensator that performs a filtering process of a slab moving speed change command signal to read out a response model as needed from the database and match the response of a desired slab solidification completion position using the read response model; A solidification completion position control device for a continuous cast slab, comprising:

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