JPH02224857A - Method for controlling molten metal surface in continuous casting mold - Google Patents

Abstract

PURPOSE:To execute continuous casting without any trouble by comparing oscillation characteristic of flow rate controlling mechanism which oscillation characteristic of molten metal surface level, assuming cause of variation of the molten metal surface level and suppressing the variation according to this assumed result. CONSTITUTION:A molten metal surface level instrument 7 measures the molten metal surface level in a mold 4 and the measured value is outputted. A cylinder rod position detector 8 detects position of a hydraulic cylinder 6 corresponding to opening degree of a gate 3 and this is outputted as a signal for gate opening degree or a signal for rod position. A computing element 9a calculates value corresponding to the target opening degree value of the gate 3 based on outputs of the molten metal surface level instrument 7 and the position detector 8, and this is outputted as a calculating value. An oscillator 9b generates periodical signal and this is outputted as exciting signal. A servo-amplifier 10 controls a hydraulic unit 6b based on the signals from the gate opening degree or the rod position detected with the position detector 8 and the controller 9, and opening degree of the gate 3 is oscillated as centering the target value corresponding to the calculating value of the computing element 9a.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for controlling the level of a molten metal poured into a mold during continuous casting.

[Conventional technology]

In continuous casting, it is generally known that fluctuations in the level of the molten metal in the mold are one of the causes of operational troubles such as surface scratches and breakouts on the slab. Controlling and keeping it constant improves quality.
It is an important element essential for stable operations. To control the hot water level, the hot water level in the mold is measured using a hot water level meter such as a gamma ray level needle or an eddy current level meter, and the obtained level signal is fed back to the PID adjustment needle to adjust the level to the set value. If there is a deviation between the two, PID calculation is performed and the output is transmitted to the servo unit, and the flow rate of the molten metal flowing from the tundish into the mold is adjusted by changing the opening degree of a flow rate adjustment mechanism such as a sliding gate (hereinafter simply referred to as a gate) or a stopper. The basic method of doing so is generally adopted.

The parameters of a PID controller are usually the stability of the control system,
The center is set optimally in consideration of responsiveness, and normally it is rarely changed during casting, but if the characteristics of the control system change and the level controllability worsens, the operator etc. reset to provide proper control. This condition often occurs due to changes in casting speed or slab size, nozzle clogging, or nozzle melting. Therefore, although it is a technology related to stopper control,
Publication No. 9-27762 discloses a method of compensating in advance for changes in molten metal flow rate characteristics due to nozzle clogging by calculating the ratio of the differential coefficient between the ring spacing and the actual opening and multiplying the ratio by a parameter. There is. Apart from this, JP-A-59-3
Publication No. 0460 discloses a method of compensating for changes in flow characteristics by making the molten metal flow rate proportional to the effective opening area of the gate without changing the parameters of the PID controller.

When implementing such a method, after starting casting or restarting casting after replacing the tundish, check the level based on the level measured by the level meter after the casting has reached a stable period. The opening degree of the gate or stopper is adjusted. When making such adjustments, the operator presets parameters such as the proportional gain, integral time, and differential time of the PIDJ meter in the control system in accordance with conditions such as casting size and casting speed.

When the above-mentioned PID control or the like is performed, when the gate operates according to the opening command based on the PID calculation result, the hot water level control should be performed reliably. However, in reality, the gate does not follow the opening command accurately. In other words, when the opening command is changed, the gate opening does not follow the opening command exactly. There is a deviation from a perfect proportional relationship between the amount of change in degree and the degree of change.

FIG. 8 is a graph showing the relationship between the two, where the horizontal axis shows the amount of change in the opening degree command, and the vertical axis shows the amount of change in the actual gate opening degree. As can be understood from Fig. 8, when the amount of change in the opening command is within ±a%, the amount of change in the gate opening accompanying this remains within an extremely small range of ±b%; When the amount of change in the command exceeds ±a%, the amount of change in the gate opening changes rapidly accordingly. In other words, the relationship between the two is nonlinear, and when the opening degree command changes, the gate opening degree follows it with a certain delay, that is, a hysteresis characteristic.

Figure 9 diagrammatically shows the nonlinear, hysteresis characteristics of the actual change in gate opening when the opening command shown on the horizontal axis increases from a constant value C to d and decreases from a constant value d to C. This is what is shown.

Therefore, in order to compensate for the above-mentioned hysteresis characteristics and make the time average value of the gate opening match the target value, a control method has conventionally been used in which an excitation signal is added to the opening command signal. .

[Problem to be solved by the invention]

Even when performing PID control as described above, problems such as clogging of the gate due to temperature drop of the molten metal during the casting process, changes in the amount of molten metal supplied due to melting of the gate or differences in the solidity of each gate, etc. If a disturbance such as a change in the withdrawal amount due to a slip of a piece or a change in casting speed occurs, each parameter of the PID adjustment needle set in advance will become inappropriate, and the level of the molten metal will fluctuate violently. A problem arises. Note that if such disturbances are temporary, the fluctuations in the hot water level will also be temporary, but if the disturbance continues over a long period of time, the fluctuations in the hot water level will also be continuous. In extreme cases, a so-called overflow phenomenon occurs, in which the molten metal overflows from the upper end of the mold. Furthermore, even if such a state does not occur, a problem arises in that the quality of the slab deteriorates due to factors such as powder entrainment due to fluctuations in the level of the molten metal.

Furthermore, even when a method of adding excitation signals is implemented to compensate for the hysteresis characteristic of the gate, the level of the hot water may not be constant. As shown in Figure 8.9 and described above, the gate opening degree has a nonlinear response characteristic to the control signal (related command), and the change in the value of the control signal is ±a.
%, the gate opening degree does not follow this sufficiently (see Figure 8). However, this value a is a sliding gate cassette consisting of a gate, a cylinder that drives it, and a transmission mechanism that connects the two. Each cassette has a different unique value, and it changes depending on the usage time of the cassette.

The cause of such changes is that the sliding resistance changes due to changes in the state of molten metal adhering to the sliding portion of the gate.

Incidentally, the excitation signal added to compensate for the nonlinear response of the gate is always fixed at a constant period and amplitude. Therefore, if the value a becomes larger than a certain level, the excitation signal whose characteristics are fixed will not sufficiently compensate for the nonlinear response of the gate, and depending on the amplitude of the control signal, the gate opening may oscillate irregularly. There is a problem.

As described above, in the control method that eliminates the gate dead zone by adding excitation signals in continuous casting, changes in the molten metal supply amount due to gate clogging or melting damage, slab slip or changes in pouring speed, etc. If disturbances occur such as changes in the amount of melt drawn out due to changes in the amount of melt drawn, gate play, or changes in the operating characteristics of the gate due to changes in sliding resistance, etc., the problem is that it may not be possible to properly control the level of the molten metal. be.

The present invention has been made in view of the above circumstances, and it estimates the cause of the fluctuation in the hot water level based on the signal indicating the gate opening degree and the signal indicating the hot water level, and adjusts the control signal according to the estimation result. By adjusting the parameters and/or the excitation signal, no matter what disturbance occurs,
It is an object of the present invention to provide a method for controlling the level of hot water in a continuous casting mold that can stably control the level of hot water.

[Means to solve the problem]

The method for controlling the level of hot water in a continuous casting mold according to the present invention includes:
Flow I that adjusts the amount of molten metal supplied into the continuous casting mold by its opening degree! In the control method for controlling the level of hot water in the mold by adding an excitation signal to the control signal for the 11-node mechanism, the flow i! The cause of the fluctuation in the level of the molten metal is estimated based on the signal indicating the opening of the adjustment mechanism and the signal indicating the level of the molten metal in the continuous casting mold, and the excitation signal and/or Alternatively, the control signal may be adjusted.

[Effect]

In the control method of the present invention, when a change in the hot water level occurs, first a signal indicating the opening degree of the flow rate adjustment mechanism (gate) (in particular, one cycle of the amplitude of this signal) is used.

The cause of the fluctuation in the hot water level is estimated based on the irregularity) and the signal indicating the hot water level (in particular, the two amplitude cycles of this signal, the deviation from the target value, and the amplitude attenuation ratio). Then, according to this estimation result, adjustment of control operation parameters (specifically, changes in proportional gain, integral time, and derivative time in PID control) and/or adjustment of excitation signals (specifically, changes in excitation signals) (Change of the excitation amplitude by one cycle) Then, in the present invention, the hot water level control is performed according to the cause,
Fluctuations in the hot water level are reduced in any disturbance situation.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on drawings showing embodiments thereof.

FIG. 1 is a schematic diagram showing the configuration of an apparatus for carrying out the control method of the present invention, and 1 in the figure indicates a tundish. Molten steel 2, which is the molten metal in the tundish 1, is supplied to a mold 4 via a gate (sliding gate) 3.

As the cast slabs 5 are continuously pulled out from the mold 4, a corresponding amount of molten steel 2 is supplied into the mold 4, so that the molten steel liquid level (molten metal level) in the mold 4 is increased. remains constant. The opening degree of the gate 3 that adjusts the amount of molten steel supplied is controlled by a hydraulic cylinder 6 driven by a hydraulic unit 6b.

A hot water level meter 7 equipped with a detection head 7a measures the hot water level in the mold 4, which is an amount corresponding to the average supply amount of molten steel 2, and outputs the measured value.

On the other hand, a cylinder rond position detector (hereinafter simply referred to as a position detector) 8 detects the position (cylinder stroke) of the hydraulic cylinder 6 corresponding to the opening degree of the gate 3, and uses this as a gate opening degree signal or a rond position signal. Output.

The controller 9 includes an arithmetic unit 9a, an oscillator 9b, and an adder 9c. The calculator 9a performs a proportional-integral-differential operation (PID operation), and calculates a value corresponding to the target opening value of the gate 3 based on the outputs of the hot water level meter 7 and the position detector 8, and calculates the value corresponding to the target opening value of the gate 3. Output as a calculated value. The oscillator 9b has a predetermined period and amplitude, for example, S
A periodic signal such as an iN wave or a rectangular wave is generated and output as an excitation signal. The period and amplitude of this excitation signal and PID
Each operating parameter is fixed at a constant value while the hot water level in the mold 4 is stable, but when the hot water level changes, it automatically changes to the optimum value according to the command from the controller 11. I am made to do so. The control details of this controller 11 will be described later. The calculated value output by the calculator 9a and the excitation signal output by the oscillator 9b are added together by an adder 9c, and the result is output from the controller 9 as a controller signal.

The servo amplifier 10 controls the hydraulic unit 6b based on the gate opening degree or rod position (cylinder stroke) detected by the position detector 8 and the controller signal output from the controller 9, and calculates the opening degree of the gate 3 by using the calculator 9a. The nonlinear response characteristics of the gate 3, the transmission mechanism 6a, etc. are effectively compensated for by vibrating around a target value corresponding to the calculated value of.

Hereinafter, the control contents of the controller 11, which constitute the gist of the present invention, will be explained in detail. FIG. 2 is a block diagram showing an example of the control contents of this controller 11.

If the conditions for entering automatic control are satisfied, the controller 11
First, the output of the position detector 8 (cylinder stroke of the hydraulic cylinder 6 corresponding to the opening degree of the gate 3) and the output of the molten metal level meter 7 (molten steel level of the molten steel 2) are measured at regular intervals. Sample (Figure 2 2A).

Next, the controller 11 controls the amplitude (s+), period (S2), and irregularity (s) of the waveform sampled from the position detector 8.
S,) is detected (Fig. 2, 2B).

FIG. 3 is a waveform diagram showing the waveform obtained by the position detector 8. As shown in the figure, this waveform has n maximum points,
There is a minimum point. In the figure, the maximum point Max (
t i, Aj) + minimum point win(t i, BJ
) (l is a natural number up to 2n, j is a natural number up to n)
, ti represents the time, Aj represents the local maximum value + BJ represents the local minimum value, respectively. As the amplitude of the cylinder stroke, use the average value within the sampling period of the absolute value of the difference between adjacent maximum and minimum values of the waveform, and as the period, use the average value of the intervals between adjacent maximum and minimum points. This year,
Further, as the irregularity, the absolute value of the difference between adjacent minimum values and the average value of the absolute value of the difference between adjacent maximum values are used. Therefore, the amplitude SI + period S and the irregularity S
, are shown below +1) to (3) formula % formula % Next, the fluctuation amplitude (L,) of the output waveform from the hot water level meter 7
and detect the circumference Q (Lx). In this case, the fluctuation amplitude shall be the average value within the sampling period of the absolute value of the difference between adjacent maximum and minimum values of the output waveform, and the period shall be the average value of the intervals between adjacent maximum and minimum points. will be used.

On the other hand, the current state of the hot water level is detected based on the detection signal of the hot water level meter 7 (FIG. 26, 20 and 2E).

Specifically, as shown in the invention proposed in Japanese Patent Application No. 63-238354, for example, the signal waveform obtained by filtering the detection signal of the hot water level meter 7 is sampled, and the hot water level of these processed data is At least three or more peak positions and peak values of level fluctuations are detected, and a plurality of parameters indicating the hot water surface condition are determined from these. As the plurality of parameters, five parameters can be considered: number of peaks N2, overshoot ratio C1, amplitude attenuation ratio, hot water level fluctuation period E, and offset MF.

The number of peaks N is the number of peaks that appear within a predetermined time in the detection signal of the hot water level meter 7, and is directly determined from the signal from which minute fluctuation components in the original waveform have been removed.

FIG. 4 is a waveform diagram of the detection signal of the hot water level meter 7, and shows the peak values 1'r+ and Tz of three consecutive peaks among the N peaks appearing in the signal waveform.

Using T, peak values P+, Pg, Ps, and a preset target value L0 of the hot water level, the overshoot ratio C2 amplitude attenuation ratio and the hot water level fluctuation cycle E are calculated as shown in (4) to (4) below, respectively. 6
) is calculated as follows.

P + L.

5Pz E”T3 Tl (6) Also, the offset ffF is the instantaneous value i of the hot water level obtained by sampling the detection signal of the hot water level meter 7 at a predetermined period, over the entire filtering processing time. It is a parameter obtained by integrating the parameters, and is expressed by the following equation (7).

F=ΣI7□ (7) The controller 11 recognizes the fluctuation pattern of the hot water level from each parameter indicating the fluctuating state of the hot water level obtained in this way, and changes this according to various conditions. The system compares the stored patterns organized in advance with the stored patterns, finds a matching stored pattern, and detects the current fluctuating state of the hot water level.

Finally, based on the information obtained in Fig. 2 2B, 2C, and 2E, the cause of the fluctuation in the hot water level is estimated, and the excitation signal and/or
Or adjust the PID control parameters (Fig. 2 2F)
.

FIG. 5 is a flowchart showing the operation contents in FIG. 2F. First, in step S1, it is determined whether there is a change in the hot water level (fluctuation in the hot water level).

It is determined whether the fluctuation range of the hot water level detected by the hot water level meter 7 is larger than a certain predetermined value. If the hot water level fluctuation width is less than this predetermined value, it is determined that there is no hot water level fluctuation (step S1: NO), and the excitation signal and/or PI
Since there is no need to adjust the parameters of the D control, the process proceeds to step S7, which will be described later.On the other hand, if the hot water level fluctuation width is larger than this predetermined value, it is determined that there is a hot water level fluctuation (
Step S1: YES), the process proceeds to step S2, and the cause is estimated and dealt with in the following steps.

In step S2, the magnitude of the sliding resistance of the gate 3 is determined based on the irregularity value of the cylinder stroke. If the detected irregularity value is less than or equal to a certain predetermined value, it is determined that the irregularity is small (step S2: NO), and the process proceeds to the next step S3.

On the other hand, if the detected irregularity value is larger than this predetermined value, it is determined that the irregularity is large (step S2: YES).
), proceed to the next step S4. If the irregularity of the cylinder stroke becomes large, the sliding resistance of the gate 3 is large and the gate 3 is difficult to move. Fluctuations in the hot water level are suppressed by increasing A0 and period Tc by predetermined amounts ΔA1 and ΔT, respectively, and reducing the sliding resistance of the gate 3 to make the gate 3 easier to move.

This means that the control method for adding the excitation signal performs automatic adjustment to add an amount larger than the fuwa zone of the gate 3 that is originally intended.

In step S3, the hot water level fluctuation cycle, the cylinder stroke cycle, and the maximum point of each waveform are determined.

Based on the position of the minimum point, it is determined whether the amount of excitation is excessive. If the hot water level fluctuation cycle and the cylinder stroke cycle match, and the positions of the maximum and minimum points of their respective waveforms match, then PID! IJ 1
Since the first operation should be performed normally, it is determined that the amount of excitation is excessive at this time. In this case (step S
3: YES), the process proceeds to step S5, and in step S5, the target amplitude A9 and period Tc of the excitation signal are respectively adjusted by predetermined amounts Δ.
It decreases by A0 and ΔT, suppressing the fluctuation of the hot water level. on the other hand,
If the hot water level fluctuation cycle does not match the cylinder stroke cycle, or if the positions of the maximum and minimum points of the respective waveforms do not match, the amount of excitation is determined to be appropriate; In this case (step S3: NO), the process advances to step S6.

If the process proceeds to step S6, it is considered that the cause of the hot water level fluctuation exists outside the gate 3. Therefore, in step S6, as shown in the invention proposed in Japanese Patent Application No. 63-238354, the hot water level fluctuation pattern extraction result is and the pre-arranged hot water level fluctuation patterns, match the matching hot water level fluctuation patterns, and calculate the PID according to the preset procedure.
Fluctuations in the hot water level are suppressed by changing the control parameters of proportional gain, integral time, and differential time in calculations.

In step S7, a feedback operation is performed to match the amplitude A of the cylinder stroke with the excitation (target amplitude A of No. 8).In other words, if the amplitude A is larger than the target amplitude A'', the amplitude of the excitation signal Ac is decreased by a predetermined amount ΔAc, and if the amplitude A is smaller than the target amplitude A8, the amplitude AC of the excitation signal is increased by a predetermined amount ΔAc.

The above-described series of operations is performed at predetermined intervals, and the predetermined interval is set to, for example, 10 to 15 seconds.

Next, an example of actual hot water level control using the control method of the present invention will be described. Figure 6 shows each waveform before control, and Figure 7 shows each waveform after control. Waveform (a) shows the excitation signal, waveform (bl shows the cylinder stroke, and waveform (C) shows the waveform after control. The actual melt level is shown respectively. In this case, the casting size is 1871 round slab casting, the casting speed is 1. Orn/min, and the casting time is 800 m after the start of casting.
After about a minute had passed, the gate 3 was in a state where it was a little difficult to move. Further, at this time, the proportional gain was 500%, the integral time was 0.15 minutes, and the differential time was 0.1 c minutes, and these values were not changed from the start of casting. The amplitude of the excitation signal was 11 mm.

The period was 1 second.

In this case, the waveform of the cylinder stroke signal (in Fig. 6)
), it is determined in the above-mentioned step S2 that the irregularity of the cylinder stroke is large. Therefore, in step S4, the target amplitude and period of the addition signal are increased. In this way, priority is given to increasing the target amplitude of the addition signal, and proportional gain adjustment is not performed. Therefore, when the cylinder stroke signal waveform starts to operate regularly as shown in FIG. As shown in Figure (C), the hot water level becomes stable.

In this example, the increase ΔA* in the target amplitude of the excitation signal is set to 0.
．． 5. Since the period increase ΔT was set to 0.1 seconds, the amplitude change per time was set to 0.25*+■, and the adjustment cycle was set to 15 seconds, it took 1 minute to stabilize. The amplitude and period of the excitation signal after control are respectively ±2fl,
The time was 1.2 seconds.

Although the output waveform is subjected to filtering processing when detecting each parameter of the hot water level waveform, it is not necessarily necessary to perform filtering processing, and the combinations of the parameters may be other than those shown in this embodiment.

Further, as an index indicating the operational characteristics of the gate, other indicators than those shown in this embodiment may be used.

Further, in the flowchart shown in FIG.
2 and step S3 may be reversed.

Further, in this embodiment, a case has been described in which a gate is used as the flow rate adjustment mechanism, but a stopper may also be used. Furthermore, although the two amplitude cycles are changed at the same time, only one of them may be changed.

〔Effect of the invention〕

As described in detail above, in the control method of the present invention, when a change in the level of the molten metal (molten steel) poured into the mold occurs during continuous casting, vibration of the flow rate adjustment mechanism that adjusts the flow rate of the molten metal occurs. The characteristics are compared with the vibration characteristics of the hot water surface level to estimate the cause of fluctuations in the full surface level, and the fluctuations are suppressed according to this estimation result, so if there is a fluctuation in the hot water surface level due to any cause. Even if there is a problem, this fluctuation can be quickly suppressed. As a result, no matter what disturbance causes fluctuations in the hot water level,
The present invention has excellent effects such as suppressing the fluctuation and performing continuous casting without any trouble.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of an apparatus for carrying out the control method of the present invention, FIG. 2 is a block diagram showing the control contents of the controller, and FIG. 3 is a waveform diagram showing the detection signal of the position detector. Fourth
The figure is a waveform diagram showing the detection signal of the hot water level meter, Figure 5 is a flowchart showing the control method of the present invention, Figures 6 and 7 are waveform diagrams in a control example to which the present invention is applied, Figure 8, FIG. 9 is a characteristic diagram showing the responsiveness of the gate. 1... Tandite 3... Sliding gate 4... Mold 5... Cast steel piece 6... Hydraulic cylinder 7... Oil level gauge 8... Cylinder rond position detector 9... Controller 9a...
Arithmetic unit 9b... Oscillator 9c... Adder 10.
...Servo amplifier 11...Controller patent Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent attorney Noboru Kono Funeral map

Claims (1)

[Claims] 1. A control method for controlling the level of molten metal in a continuous casting mold by adding an excitation signal to a control signal for a flow rate adjustment mechanism that adjusts the amount of molten metal supplied into a continuous casting mold by its opening degree. In this step, the cause of the fluctuation in the level of the molten metal is estimated based on a signal indicating the opening degree of the flow rate adjustment mechanism and a signal indicating the level of the molten metal in the continuous casting mold, and the increase is performed according to the estimation result. 1. A method for controlling a liquid level in a continuous casting mold, the method comprising adjusting a vibration signal and/or the control signal.