JP2012170984A - Apparatus and method for controlling molten metal surface level within continuous casting machine mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and method for controlling the molten metal surface level within a continuous casting machine mold, capable of appropriately suppressing fluctuations of the molten metal level having different frequency bands.SOLUTION: By performing PI control by obtaining a deviation of a detection value of a molten metal surface level detected by a molten metal surface level meter 21 from its target value, fluctuation of a molten metal surface level in a mold 3 is suppressed. By subjecting a molten metal surface level detection signal to a frequency spectrum analysis then, a peak frequency between fluctuation of a bulging molten metal surface level and fluctuation of a dummy bar-nature molten metal surface level is detected, and a differential filter 12 functioning as a disturbance compensator is switched by the peak frequency. The differential filter 12 has a characteristic for extracting an signal component of a frequency (peak frequency) intended to be suppressed from the deviation to be output by advancing its phase characteristic by 90°.

Description

  The present invention relates to a mold level control apparatus and a control method for controlling a mold level in a mold of a continuous casting machine.

In a continuous casting machine, controlling the molten metal level in molten metal (molten steel) to keep the molten metal level constant and controlling the molten metal level to be constant is not only stable, but also the quality of the slab. This is also extremely important from an administrative standpoint.
Conventionally, as the mold level control method in the mold, the molten metal level in the mold is measured by a molten metal level meter, and the opening of the sliding nozzle is adjusted based on the measured value, and the mold is pulled out of the mold. The method of balancing the mass balance between the molten steel and the molten steel injected from the tundish is taken.

The biggest factor that fluctuates the molten steel surface level in the mold is the fluctuation of the molten steel surface level caused by bulging in the thickness direction of the slab that occurs between the slab support rolls such as guide rolls and pinch rolls (bulging) ( It is said that this is a vardinque hot water surface fluctuation).
As a technique for suppressing such bulging surface level fluctuation, for example, there is a technique described in Patent Document 1. This technology is based on the deviation between the target value and the detected value of the molten metal level, and outputs a sliding nozzle opening command, extracts the bulging fluctuation level from the deviation, and its phase characteristics Is used together with a disturbance compensator using a band derivative having the characteristic of advancing the angle 90 degrees and outputting so as to control the molten metal surface level to be constant. Here, using the data of the past casting speed, the frequency of the bulging hot water surface fluctuation was obtained, and the disturbance compensator was controlled using that frequency, so that the bulging hot water surface fluctuation occurred during the casting speed change. Even in this case, disturbance compensation is effectively performed.

JP 2009-160647 A

  However, the factors that cause the molten steel surface level of the molten steel in the mold to fluctuate include a dummy bar property surface variation in addition to the bulging property surface variation. The variation in the molten metal level of the dummy bar is a variation in the molten metal surface level caused by the dummy bar being caught by the slab support roll at the start of continuous casting in which the slab is pulled out by the dummy bar to start continuous casting. This frequency band of the dummy bar level fluctuation is different from the frequency band of the bulging level fluctuation.

Therefore, in the mold level control method described in Patent Document 1, bulging level fluctuation in a low frequency band can be suppressed, but dummy bar characteristics in a frequency band higher than the frequency band of bulging level fluctuation. It is not possible to suppress the hot water level fluctuation.
Then, this invention makes it the subject to provide the mold level control apparatus and the control method in a mold of the continuous casting machine which can suppress appropriately the mold level fluctuation | variation which has a different frequency band.

  In order to solve the above problems, a mold level control apparatus in a mold of a continuous casting machine according to the present invention is a mold level control apparatus in a mold of a continuous casting machine that controls the mold level in a mold of a continuous casting machine. The hot water level meter for detecting the hot water surface level in the mold, and a tundish provided based on a deviation signal between the hot water surface level detection signal detected by the hot water surface level meter and a predetermined hot water surface level target value. The PI controller that outputs the sliding nozzle opening command and the frequency range including the frequency band of the bulging hot water surface fluctuation and the frequency band of the dummy bar hot water surface fluctuation are detected by the hot water level meter. A frequency spectrum analysis is performed on the molten metal level detection signal to detect the peak frequency of the molten metal level fluctuation, and the deviation frequency signal is detected by the peak frequency detector. A disturbance compensator that extracts a signal component having a peak frequency and outputs the phase characteristic by 90 degrees, and adds the output signal of the disturbance compensator to the opening command output by the PI controller. A sliding nozzle controller that adjusts the opening of the sliding nozzle as the final opening command is provided.

  Accordingly, the disturbance compensator can be switched so as to appropriately obtain the peak frequency of the bulging hot water surface fluctuation and the peak frequency of the dummy bar hot water surface fluctuation and compensate for the disturbance of the peak frequency. Therefore, by adjusting the opening of the sliding nozzle using this disturbance compensator in combination with the PI controller, it is possible to effectively suppress bulging level fluctuation and dummy bar level fluctuation in different frequency bands. it can. Here, since the frequency characteristic of the disturbance compensator is a characteristic that extracts the signal component of the peak frequency and advances the phase characteristic by 90 degrees and outputs it, the high frequency as in the case where a simple differential controller is applied. The phase delay can be improved by eliminating the influence of noise.

Further, in the above, the disturbance compensator has a characteristic of extracting a signal component of a frequency to be controlled from the deviation signal and advancing the phase characteristic by 90 degrees and outputting the same, and the frequency of the control target is respectively A plurality of different controllers are provided, and only the controller whose peak frequency detected by the peak frequency detector is the frequency to be controlled is made valid.
Thereby, a disturbance compensator can be switched with a comparatively simple structure according to the peak frequency of the molten metal surface level detected by frequency spectrum analysis.

Further, the method for controlling the level in the mold of the continuous casting machine according to the present invention is a method for controlling the level in the mold of the continuous casting machine for controlling the level of the molten metal level in the mold of the continuous casting machine. Based on the deviation signal between the detected molten metal level detection signal and the predetermined molten metal level target value, the opening command of the sliding nozzle provided in the tundish is output by PI control, and the frequency band of the bulging molten metal level fluctuation And frequency band analysis of the molten metal level detection signal detected by the molten metal level meter for the frequency band including the frequency band of the dummy bar characteristic molten metal surface fluctuation, to detect the peak frequency of the molten metal surface fluctuation, The opening command that extracts the signal component of the peak frequency from the deviation signal and outputs a signal obtained by advancing the phase characteristic by 90 degrees by the PI control Adding to the final the opening command, it is characterized by adjusting the sliding nozzle opening.
Thereby, it can be set as the hot_water | molten_metal surface level control method in a mold of the continuous casting machine which can suppress appropriately the hot_water | molten_metal surface fluctuation | variation which has a different frequency band.

  According to the present invention, it is possible to appropriately suppress molten metal surface fluctuations having different frequency bands, such as bulging surface variations with a low frequency (long cycle) and dummy bar surface variations with a high frequency (short cycle). it can. Therefore, the surface level of the molten steel in the mold in the continuous casting machine can be made constant at the target value, and the stability of the slab quality can be improved.

It is sectional drawing which shows the structure of the mold peripheral part of the continuous casting machine in this embodiment. It is a block diagram which shows the mold surface level control system in a mold. It is a figure which shows the frequency analysis result of a hot_water | molten_metal surface level fluctuation | variation. It is a figure which shows the frequency characteristic of a differential filter. It is an example of the simulation result which shows the effect of this embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing the configuration of the mold peripheral part of the continuous casting machine in the present embodiment.
In the figure, reference numeral 1 is molten steel, and reference numeral 2 is a tundish filled with molten steel 1. The tundish 2 is arranged on the upper part of the mold 3, and a sliding nozzle (hereinafter abbreviated as SN) 4 is attached to the bottom of the tundish 2. An immersion nozzle 5 is attached to the lower surface side of the sliding nozzle 4, and the molten steel 1 filled in the tundish 2 is injected into the mold 3 through the sliding nozzle 4 and the immersion nozzle 5.

The molten steel 1 injected into the mold 3 is cooled from the side surface of the mold 3, and is solidified from the surface to form a shell 6, and is drawn downward by a pinch roll 7 to become a slab 8. This drawing speed is controlled to be substantially constant by a pinch roll control device (not shown).
The amount of molten steel injected into the mold 3 is determined by the opening degree of the sliding nozzle 4. Adjustment of the sliding nozzle opening (SN opening) is performed by the control device 10 driving an actuator (sliding nozzle controller) (not shown) such as a hydraulic cylinder.

  The SN opening is controlled so that the amount of molten steel injected into the mold 3 and the amount drawn downward are balanced. The control is such that the opening command value (SN opening command value) of the sliding nozzle 4 is set so that the level of the molten metal surface 22 in the mold 3 (the molten metal surface level in the mold) becomes constant at a preset molten metal surface level target value. ) Is set. The hot water level in the mold is detected by the hot water level meter 21, and the detected value is input to the control device 10.

FIG. 2 is a block diagram showing a mold level control system in the mold.
As shown in FIG. 2, the deviation (Lref−L) between the molten metal level L obtained from the molten metal level meter 21 and the predetermined molten metal level target value Lref is determined by the PI (proportional + integral) controller 11 and the disturbance compensation. Are input to the differential filter 12 functioning as a detector. The PI controller 11 outputs an SN opening command value that makes the input deviation zero.

The differential filter 12 extracts a signal component of a specific frequency as a control target from the deviation and performs a process of advancing the phase characteristic by 90 degrees, and is composed of a plurality of controllers having different control target frequencies. Has been. The differential filter 12 is switched according to the frequency analysis result of the FFT analysis 13 so that one of the plurality of controllers becomes effective.
The FFT analysis 13 has an FFT (Fast Fourier Transform) function that inputs the molten metal level L detected by the molten metal level meter 21 and performs frequency spectrum analysis of the molten metal level fluctuation. As described above, online analysis by FFT (analysis while capturing a signal) is performed here. By this FFT analysis 13, the relationship (frequency spectrum) of the fluctuation amplitude with respect to the fluctuation frequency of the molten metal surface level is obtained, and the fluctuation frequency that maximizes the fluctuation amplitude can be specified as the peak frequency of the molten metal surface fluctuation. That is, the FFT analysis 13 functions as a peak frequency detector.

FIG. 3 is a diagram showing an example of the frequency analysis result of the molten metal surface level fluctuation. (A) is the frequency analysis result when the bulging hot water surface fluctuation occurs, and (b) is the frequency analysis when the dummy bar hot water surface fluctuation occurs. It is a result.
Here, bulging means that the shell 6 formed on the surface of the slab 8 supports the slab 8 by the static iron pressure (molten metal pressure) of the unsolidified molten steel inside the slab 8 after passing through the mold 3. This is a phenomenon in which the pinch rolls 7 swell in the thickness direction. Thus, in the process of passing through the pinch rolls 7 arranged at a predetermined interval, the molten metal surface generated due to the shell 6 and thus the unsolidified molten steel inside is repeatedly expanded or pushed in the thickness direction. The level fluctuation is bulging hot water level fluctuation. This bulging level fluctuation is the main cause of the level fluctuation, and the fluctuation frequency is determined by the pinch roll interval and the casting speed.

On the other hand, in the continuous casting machine, casting is started by pulling out the slab 8 with a dummy bar. At the start of casting, the molten metal surface level fluctuation occurs due to the dummy bar being caught by the pinch roll 7. This is the fluctuation of the dummy bar surface. The fluctuation frequency of the dummy bar hot water surface fluctuation is determined by the type of the molten steel 1 and the like without depending on the casting speed.
Fluctuation frequency is different between bulging level fluctuation and dummy bar level fluctuation, the frequency band of bulging level fluctuation is relatively low (about 0.04-0.07 Hz), and the frequency range of dummy bar level fluctuation is Relatively high (about 0.25). Therefore, the frequency spectrum analysis shows that when the bulging hot water level fluctuation occurs, the peak frequency is measured to be relatively low as shown in FIG. 3A (0.05 Hz in this example). As shown in 3 (b), the peak frequency is measured relatively high (in this example, 0.25 Hz).

  In the FFT analysis 13, a frequency spectrum analysis is performed for a frequency band (for example, 0.04 Hz to 0.3 Hz) including a fluctuation frequency band of bulging hot water surface fluctuation and a fluctuation frequency band of dummy bar hot water surface fluctuation. I do. In other words, the detection value of the molten metal level detected by the molten metal level meter 21 is passed through a band-pass filter that passes the frequency band to be analyzed, and the frequency spectrum analysis is performed on the result. Thereby, the peak frequency of the bulging hot water surface fluctuation and the dummy bar hot water surface fluctuation can be appropriately measured.

Then, the peak frequency of the molten metal surface fluctuation measured by the FFT analysis 13 is set as the frequency of the molten metal surface fluctuation to be suppressed in the molten metal surface level control, and the differential filter 12 extracts the signal component of the peak frequency from the deviation signal. And the phase characteristics are switched so as to have a characteristic of advancing by 90 degrees.
FIG. 4 is a diagram illustrating an example of the frequency characteristic of the differential filter 12, and illustrates a case where the frequency to be suppressed (the peak frequency of the molten metal surface fluctuation) is 0.3 Hz. As shown in FIG. 4, by setting the gain of the frequency to be suppressed to 0 dB and lowering the gain below 0 dB in the low frequency region and the high frequency region, only the signal component of the frequency to be suppressed is extracted, and the phase is 90 degrees. I am trying to proceed. In the present embodiment, for example, a plurality of controllers having the above-described characteristics in which a frequency to be suppressed every 0.01 Hz is set are prepared, and the validity / invalidity of these controllers is switched according to the peak frequency of the molten metal level fluctuation. .

  The calculation result by the differential filter 12 is added to the SN opening command value output from the PI controller 11 as the SN opening correction value, and the result becomes the final SN opening command value. In other words, the mold level control system in the mold shown in FIG. 2 is used in conjunction with the PI controller 11 so that the deviation between the melt level L and the target value Lref becomes zero. By extracting the components (bulging surface level fluctuation component and dummy bar surface level fluctuation component) and controlling the SN opening by the differential filter 12 having the characteristic that the phase characteristic is advanced by 90 degrees, The fluctuation of the is suppressed.

That is, when the SN opening command value is output, the flow rate of the molten steel 1 flowing into the mold 3 is controlled by adjusting the SN opening after a predetermined dead time (dead time 14) (SN characteristic 15). ). Then, the molten steel 1 of the total inflow flow rate in which the molten metal surface level fluctuation (melt surface level disturbance) is added to the inflow flow rate as a flow rate disturbance flows into the mold 3. At this time, the flow rate level L in the mold 3 is obtained by integrating the flow rate flowing into the mold 3 (flow rate integration 16), and this is detected by the melt level meter 21 (sensor characteristic 17).
In this way, a feedback control loop is formed that acts to make the hot water surface level L coincide with the hot water surface level target value Lref.

  In general, in the mold level control system in the mold, a PI controller is used to make the deviation between the detected value of the mold level and its target value zero, or the inflow flow rate into the mold is integrated and the hot water in the mold is integrated. The integration operation dominates the system characteristics because the surface level is reached. However, since the integration operation is an operation with a phase delay of 90 degrees, in order to improve the phase delay and perform appropriate control, an operation for advancing the phase by 90 degrees is required.

  Normally, D (differential) control is used to achieve 90-degree phase advance. However, since the simple differential operation is susceptible to noise and has a characteristic that the gain increases as the frequency becomes higher, if a PID controller is simply used instead of the PI controller, the high frequency component The signal is unnecessarily suppressed, and appropriate hot water level control cannot be performed.

  Therefore, in the present embodiment, as shown in FIG. 4 as an example of frequency characteristics, a differential filter 12 that advances the phase by 90 degrees at a specific frequency to be suppressed is added as a disturbance compensator. As the differential filter 12, a controller having a characteristic that lowers the gain in a high frequency region than a specific frequency to be suppressed is applied. Thereby, like the case where a simple D controller is applied, the molten metal surface fluctuation | variation of the specific frequency which should be suppressed can be suppressed appropriately, without suppressing the molten metal surface fluctuation | variation of a high frequency component unnecessarily.

FIG. 5 is an example of a simulation result showing the effect of the present embodiment. Here, a solid line a in FIG. 5 is a simulation result in a system in which the SN opening is controlled only by the PI controller 11 without applying the differential filter 12. On the other hand, a broken line b in FIG. 5 is a simulation result in the present embodiment in which the differential filter 12 is applied together with the PI controller 11. As can be seen from FIG. 5, the combined use of the differential filter 12 can provide an effect of reducing the fluctuation level of the molten metal surface level (an effect of reducing the fluctuation range of about 25%).
Thus, in the present embodiment, since the frequency band including the frequency band of the bulging hot water surface fluctuation and the frequency band of the dummy bar hot water surface fluctuation is the object, the frequency spectrum analysis is performed on the signal detected by the hot water surface level meter. It is possible to appropriately detect the peak frequency of bulging level fluctuation and dummy bar level fluctuation in different frequency bands.

  Then, the differential filter is switched according to the detected peak frequency, and the SN opening degree command output from the PI controller is corrected by the output of the differential filter. Here, the differential filter has a characteristic of extracting a signal component of a specific frequency from an input signal and advancing its phase characteristic by 90 degrees and outputting it. By switching such a differential filter according to the peak frequency, it is possible to realize disturbance compensation according to the period change of the molten metal surface fluctuation (cause of the molten metal surface fluctuation), and appropriately suppress the molten metal surface fluctuation with different frequency characteristics. can do.

In addition, since the phase advance of 90 degrees can be realized by the differential filter, the phase delay due to the integration operation of the PI controller can be improved, and the molten metal level control can be performed with an appropriate phase. Furthermore, since the gain characteristic of the differential filter is a characteristic that lowers the gain in a higher frequency region than the specific frequency, it is possible to eliminate the influence of high frequency noise that occurs when a simple D controller is applied.
As described above, it is possible to effectively suppress the fluctuation of the molten metal surface having different frequency characteristics and to keep the molten metal surface level in the mold constant at the target value. Can be manufactured.

  DESCRIPTION OF SYMBOLS 1 ... Molten steel, 2 ... Tundish, 3 ... Mold, 4 ... Sliding nozzle (SN), 5 ... Immersion nozzle, 6 ... Shell, 7 ... Pinch roll, 8 ... Slab, 10 ... Control device, 21 ... Hot water level Total, 22 ...

Claims (3)

A mold level control device in a mold of a continuous casting machine for controlling a mold level in a mold of a continuous casting machine,
A hot water level meter for detecting the hot water level in the mold;
A PI controller that outputs an opening command of a sliding nozzle provided in the tundish based on a deviation signal between a hot water level detection signal detected by the hot water level meter and a predetermined hot water level target value;
For the frequency band that includes the frequency band of bulging level fluctuations and the frequency range of dummy bar level fluctuations, frequency spectrum analysis is performed on the level detection signal detected by the level gauge, and the peak level A peak frequency detector for detecting the frequency;
A disturbance compensator that extracts a signal component of the peak frequency detected by the peak frequency detector from the deviation signal and advances the phase characteristic by 90 degrees and outputs the signal,
A sliding nozzle controller that adds the output signal of the disturbance compensator to the opening command output from the PI controller to obtain a final opening command, and adjusts the sliding nozzle opening. Mold hot water level control device.   The disturbance compensator has a characteristic of extracting a signal component of a frequency to be controlled from the deviation signal and advancing the phase characteristic by 90 degrees and outputting the same, and a plurality of controllers having different frequencies to be controlled 2, wherein only the controller whose peak frequency detected by the peak frequency detector is the frequency to be controlled is configured to be valid. Mold level control device in mold. A mold level control method in a mold of a continuous casting machine for controlling a mold level in a mold of a continuous casting machine,
Based on the deviation signal between the hot water level detection signal detected by the hot water level meter and the predetermined hot water level target value, an opening command of the sliding nozzle provided in the tundish by PI control is output,
By analyzing the frequency spectrum of the molten metal level detection signal detected by the molten metal level meter for the frequency band including the frequency band of the bulging molten metal level fluctuation and the frequency band of the dummy bar type molten metal level fluctuation, Detect the peak frequency of
Extracting the signal component of the peak frequency from the deviation signal and adding a signal obtained by advancing its phase characteristic by 90 degrees to the opening command output by the PI control is used as the final opening command, A mold level control method in the mold, wherein the opening degree of the sliding nozzle is adjusted.

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