JP2653124B2 - Level control method for molten metal level in continuous casting mold - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlling the level of a molten metal cast into a mold when performing continuous casting.

(Prior art)

In continuous casting, it is generally known that fluctuations in the level of the molten metal in the mold are one of the factors that cause operational troubles such as surface defects and breakout of the slab. Therefore, it is necessary to control the level of the molten metal to keep it constant.
It is also an important factor in quality improvement and stable operation. The level control is performed by measuring the level in the mold using a level gauge such as a γ-ray level meter or an eddy current level meter, and the obtained level signal is fed back to the PID controller, and the level is compared with the set value. If there is a deviation between them, the basic method of calculating the PID, transmitting the output to the servo unit, changing the opening of the sliding gate and stopper, and adjusting the flow rate of the molten metal flowing into the mold from the tundish is generally adopted. Have been.

The parameters of the PID controller are usually set optimally in consideration of the stability and responsiveness of the controller, and usually rarely change during casting, but the characteristics of the control system change, If the level control system deteriorates, the operator resets the system so as to obtain optimal control. These conditions often occur due to changes in casting speed and slab size, nozzle clogging, and nozzle erosion. Therefore,
Although it is related to the control of a stopper,
Japanese Patent Publication No. 762 discloses a method in which the ratio of the differential coefficient between the theoretical opening and the actual opening is determined, and the ratio is multiplied by a parameter to compensate in advance for the flow rate characteristic of the molten metal due to nozzle clogging.
Further, JP-A-59-30460 discloses a method of compensating for a change in flow characteristics by changing the flow rate of a molten metal in proportion to the effective opening area of a sliding gate without changing the parameters of a PID controller. .

When performing such a method, after starting the casting or after replacing the tundish and restarting the casting, in a state where the casting has reached a stable period, based on the level of the molten metal measured by the level gauge. Thus, the opening of the sliding gate and the stopper is adjusted. When the operator performs the adjustment, parameters such as a proportional gain, an integration time, and a differentiation time of the PID controller in the control system are set in advance according to conditions such as a slab size, a casting speed, and the like.

[Problems to be solved by the invention]

However, clogging of the sliding gate due to the temperature drop of the molten metal during the casting process, changes in the molten metal supply amount due to the erosion status of the sliding gate, inherent differences of each sliding gate, etc., slip of the slab and casting speed. When a disturbance such as a change in the amount of withdrawal caused by a change or the like occurs, there arises a problem that preset parameters of the PID controller become inadequate and the level of the molten metal level fluctuates greatly. If the disturbance is temporary, the change in the bath level is also temporary, but if the disturbance is continued for a long period of time, the change in the bath level is also continuous and extremely In this case, a phenomenon that the molten metal overflows from the upper end of the mold, a so-called overflow phenomenon, occurs. Even if such a state does not occur, there is a problem that the quality of the cast slab is deteriorated due to powder entrapment due to fluctuations in the molten metal level.

In order to solve such a problem, the following measures are taken based on the judgment of the operator when the level of the molten metal level fluctuates. That is, the operator checks the fluctuation state (fluctuation width, cycle, etc.) of the bath level using a trend recorder or the like, and according to the fluctuation state, controls the PID controller's control parameters (proportional gain, derivative time, integration time). Etc.), or constantly monitor the change of the bath level, and when the change of the bath level exceeds a certain threshold value, the peak value and the peak position (corresponding to the peak value). Time)
Matching (pattern recognition) with this and a preset fluctuation pattern of the molten metal level is performed, and a measure is taken to adjust each parameter of the PID controller based on the matching. However, even if such measures are taken, the above problem is not sufficiently solved. For example, when the former measure is taken, individual differences in the judgment by the operator become a problem. Further, when the latter measure is taken, there is a problem that the peak value and the peak position cannot be accurately obtained due to the presence of noise or the like. Even if the filtering process is performed to eliminate the influence of the noise or the like, there is a problem that only one of a short cycle and a long cycle of the surface level can be accurately recognized according to the characteristics of the filter used for the processing. .

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for controlling a level of a molten metal in a continuous casting mold that can solve the above-described problems.

[Means for solving the problem]

A method for controlling a level of a molten metal in a continuous casting mold according to claim 1 of the present invention measures a level of a molten metal in a continuous casting mold with a molten metal level gauge, and calculates a difference between the measured level and a predetermined target level. In a method for controlling a level of a level in a continuous casting mold, which performs level control by a control operation of a control controller performed based on the control parameter, an output signal of the level gauge may have at least different filtering performance. A filtering process is performed by using two types of filters. From these processed data, a plurality of variation parameters including the number of peaks of the molten metal level appearing within a predetermined time and respective peak values are obtained. The present invention is characterized in that a change state of a molten metal level is grasped, and a control parameter of the control controller is adjusted based on the result. In the method for controlling the level of the molten metal in the continuous casting mold according to claim 2, a plurality of variation parameters obtained from the processing data are compared with each variation parameter in a memory pattern of the variation of the level of the molten metal, and approximated. The change state is grasped by selecting a storage pattern having a change parameter.

[Action]

In the case of the method according to the present invention, the fluctuation state of the bath level caused by the disturbance as described above is calculated from the data obtained by applying the output signal of the bath level meter through the at least two types of filters to the number of peaks of the bath level. Since a plurality of fluctuation parameters including the peak value are obtained and grasped from the obtained fluctuation parameters, it is possible to accurately grasp any short-term or long-term fluctuation of the molten metal level, and The fluctuation state is grasped by comparing the current fluctuation parameter with the fluctuation parameter in the storage pattern sorted and arranged in advance, and the control parameter of the control controller (PID controller) is made to correspond to the approximate storage pattern. Since the adjustment is performed in accordance with the set contents, the fluctuation of the molten metal level can be reduced quickly.

〔Example〕

Hereinafter, the present invention will be described with reference to the drawings showing the embodiments.

FIG. 1 is a schematic explanatory view showing an apparatus used for carrying out the method of the present invention. In FIG. 1, reference numeral 1 denotes a tundish of a continuous casting apparatus. From the tundish 1, molten metal, that is, molten steel in this embodiment, is cast into a mold 3 through an immersion nozzle 2, and the flow rate is adjusted by a sliding gate 5 driven by a cylinder 4. I have. The sliding gate 5 is controlled so that the level in the mold 3 is constant. The basic configuration of the control is, for example, a level gauge 6 using a gamma ray or an eddy current. The molten metal level is measured, and the measured value is fed back to the molten metal level controller 8 via the molten metal level converter 7. If there is a deviation from the set value, the PID in the molten metal level controller 8 is determined. A method is employed in which a PID calculation is performed by a calculation unit, and the output is transmitted to a servo amplifier 9 to move the cylinder 4 described above. After the signal relating to the measured value is passed through the level controller 7, the filtering process is performed by two types of filters 16 and 17 having different filtering performances. 8 is input. It should be noted that a value measured by a sensor 10 attached to the tundish 1 is input to the molten metal level control device 8 via a tundish weight converter 11 as a signal relating to the tundish weight, and is also input to the continuous casting device. The value measured by the sensor 14 attached to the pinch roll 13 is input to the casting speed converter 15 as a signal related to the casting speed via the casting speed converter 15, and these signals are also used for level control. I have.

When the method of the present invention is performed using such a device, the processing performed by the molten metal level control device 8 will be described in some detail.

The output signal of the level gauge 6 through the level converter 7 has a long-period variation as shown in the waveform on the left side of FIG. 2 [for example, in the case of a wide (1500 mm × 210 mm) cast slab, : 10 to 20 sec], the output signal is filtered by the filters 16 and 17 to perform two filtering processes, thereby obtaining two signals as shown in the waveform on the right side in FIG. That is, by performing a filtering process with a small number of moving averages, a small change at the time of rising or falling of the molten metal cannot be removed as shown in the upper waveform in FIG. By performing a filtering process with a large number of moving averages while obtaining a signal that is smaller than that of FIG. 5, the rough shape of the fluctuation waveform of the water level can be accurately extracted as shown in the lower waveform in FIG. Is obtained, the attenuation of the fluctuation width of which is larger than that of the original waveform.

Also, the output signal of the level gauge 6 shows a short-period variation (for example, in the case of a wide (600 mm × 210 mm) slab, the cycle is 10 sec or less) as shown in the waveform on the left side in FIG. If the output signal is a signal, the output signal is filtered through the filters 16 and 17 to perform a filtering process, thereby obtaining two signals as shown in the waveform on the right side in FIG. That is, by performing the filtering process with a small number of moving averages, it is possible to obtain a signal in which the outline of the fluctuation waveform of the molten metal surface and the fluctuation width thereof are almost faithfully reproduced in the original waveform as shown in the upper waveform in FIG. By performing a filtering process with a large number of moving averages, it is possible to obtain a signal in which the outline of the fluctuation waveform of the molten metal level can be extracted as shown in the lower waveform in FIG. .

Therefore, the peak position of the waveform indicating the level change of the molten metal is obtained from the signal obtained by performing the filtering processing with a large moving average number, and the respective peak positions are obtained from the signal obtained by performing the filtering processing with the small moving average number. Is determined as compared with the conventional case (for example, when the output value of the level gauge 6 is used as it is or when the output value is subjected to a filtering process using a specific filter). Can be more accurately recognized.

By the way, such filtering processing in the filters 16 and 17 is performed for a predetermined time from the time when the output signal of the level gauge 6 after passing through the level converter 7 exceeds a predetermined threshold value. . The execution time of this filtering process is set so that at least three peaks of the fluid level change appear within this time, and differs depending on the shape and size of the slab to be manufactured. When the piece is a round section slab having an outer diameter of 231 mm, the execution time is approximately 20%.
Seconds is enough.

Now, when the two signals subjected to the respective filtering processes in the filters 16 and 17 are input to the liquid level control device 8, the control device 8 generates a plurality of signals indicating the fluctuation state of the liquid level from these signals. (Hereinafter simply referred to as a parameter). Various parameters can be considered as these parameters. For example, the following five parameters are obtained.

(A) Number of peaks; N (b) Overshoot ratio; A (c) Amplitude damping ratio; B (d) Fluctuation cycle of metal surface; C (sec) (e) Offset amount; D (mm) The number of peaks appearing within a predetermined time in the input signal to the surface level control device 8, which is a signal obtained by performing a filtering process with a large number of moving averages as described above, that is, , Are obtained directly from the signal from which the minute fluctuation components in the original waveform have been removed.

As shown in FIG. 4, each of the parameters (b) to (d) is, for example, three consecutive peaks out of N peaks appearing in the input signal to the liquid level controller 8. Find the respective peak positions T ₁ , T ₂ , T ₃ , and the peak values P ₁ , P ₂ , P ₃ ,
Using these and the preset target level L ₀ of the molten metal level, they are respectively calculated by the following equations.

C = T ₃ −T ₁ (3) In FIG. 4, it is as if the peak positions T _{1 to} T ₃ and the peak values P _{1 to} P ₃ are obtained from the same signal. from the signal the minute fluctuation component in the obtained original waveform is removed by the moving average number of large filtering process, firstly obtained peak position T ₁ through T _3, the peak value P ₁ ~
P ₃ is obtained by a filtering process with a small number of moving averages, and from the signal with little attenuation to the original waveform, T ₁
We are determined respectively so as to correspond to the ~T _3.

Furthermore the offset amount D shown in (e) is the instantaneous value L _i of molten metal surface level obtained by sampling the input signal to the molten metal surface level control device 8 at a predetermined period, and accumulated throughout the filtering processing time This parameter is obtained by the following equation.

D = ΣL _i ...... (4) Sampling of the instantaneous value L _i is of course carried out in the signal obtained by the moving average number is less filtering.

Now, the level controller 8 recognizes the current variation pattern from the parameters indicating the variation level of the level thus obtained, and stores the current variation pattern in advance according to various conditions. The control parameters such as the gain, the integration time, and the differentiation time in the PID calculation unit are changed according to a preset procedure corresponding to the storage pattern that matches the pattern.

First, the parameters (a) to (e) are grouped according to their sizes. For example, the overshoot ratio A and the amplitude attenuation ratio B are in the first group when they are 1.25 or more, in the second group when they are in the range of 1.25 to 1.00, and in the range of 1.00 to 0.50. Has a third
If it is less than 0.50, it is grouped into a fourth group.
If this is 10 seconds or more, the first group will be
If it is within the range of ~ 10sec, 5sec
In the following cases, they are grouped into the third group. The same grouping is performed for the peak number N and the offset amount D.

For example, when the current P sensitivity is high, the molten metal level fluctuates in a hunting manner, so that it is classified into a group in which both the overshoot ratio A and the amplitude attenuation ratio B are large, and the fluctuation period C
Is obtained, the convergence to disturbance is slow, the fluctuation period C and the overshoot ratio A are both large, and the amplitude attenuation ratio B is slightly small. A pattern is obtained. In the former case, according to the procedure corresponding to the similar storage pattern, P
The sensitivity is weakened, and in the latter case, the P sensitivity is likewise enhanced. As an example of the former, when a variation pattern in which the overshoot ratio A and the amplitude attenuator B are classified into the first or second group and the fluctuation cycle C is classified into the third group is obtained, the P sensitivity In order to weaken P, the P value in the PID calculation unit is increased by 30%. As an example of the latter, the fluctuation cycle C falls in the first group, and the overshoot ratio A falls in the first or second group. When a fluctuation pattern in which the amplitude attenuator B is classified into the third group is obtained, the P value in the PID calculation unit is reduced by 30% in order to enhance the P sensitivity. .

Also, the case I sensitivity in the PID calculation unit is weak, since convergence to the target value L ₀ of the molten metal surface level is slow, with variation pattern offset amount D is large is obtained, excessive ratio A becomes smaller. As an example of this case, the overshoot ratio A is assigned to a group in which the offset amount D is 300 mm or more.
When a fluctuation pattern that can be classified into the fourth group is obtained, the PID is increased in order to increase the I sensitivity by approximately 20%.
The adjustment of the I value in the calculation unit is performed.

As described above, the liquid level control device 8 determines which parameter should be changed and how much among the control parameters in the PID calculation unit in accordance with various fluctuation patterns of the liquid level based on the operation results of the continuous casting equipment. Filters having different filtering characteristics
Since the current level change pattern can be accurately recognized by the signal from the level gauge 6 input thereto via the channels 16 and 17, the optimum pattern for the current level change is provided. The control operation is performed promptly.

FIG. 5 shows the result of performing the PID control at the molten metal level according to the method of the present invention. That is, (a) in the figure is a scene level obtained by performing PID control by a manual method (conventional example).
The figure (b) in the figure shows the level of the molten metal obtained by performing the PID control according to the method of the present invention as described above. In each case, the casting speed at the time of casting was 2.0 m / min, the slab size was 231 mmφ, and an eddy current type was used as a level gauge for measuring the level of the level. In this figure, since the state of fluctuation of the molten metal level in (a) is a state in which the offset amount D is large, the I sensitivity is first increased with the execution of the method of the present invention, whereby the overshoot ratio A and the amplitude attenuation are increased. by the ratio B obtained both large fluctuation period C is small variation state, then has been allowed to drop P sensitivity variation state to quickly converge to the target value L ₀ is obtained by changing these control parameters ing. From these results, it can be seen that when controlling the level of the molten metal cast into the mold using the method of the present invention, the fluctuation in the level of the molten metal can be greatly suppressed as compared with the conventional method.

In the above-mentioned apparatus, the sliding gate 5 driven by the cylinder 4 is used to perform the above-described PID control to make the level of the molten metal constant, and the casting amount is adjusted by adjusting the sliding gate 5. It goes without saying that the method of the present invention can be applied to an apparatus using a double-cylinder sliding gate instead of the sliding gate 5 or an apparatus using a stopper.

Also, three or more types of filters having different filtering performances may be used instead of the filters 16 and 17. Further, in this example, the moving average number is used as the filtering process, but another digital filter may be used.

In addition, as the parameter indicating the fluctuation state of the molten metal level, a parameter other than that shown in this embodiment may be used, and the classification method according to the magnitude of each parameter is not limited to the one shown in this embodiment. Needless to say.
Furthermore, the convergence time of the change in the level of the metal surface can be reduced by finely setting the type and the amount of change of the control parameter to be changed for each storage pattern of the level of the metal level corresponding to the combination of the size of each parameter. Still further shortening is possible.

〔effect〕

As described above in detail, according to the method of the present invention, when performing continuous casting, fluctuations in the surface level of the molten metal cast into the mold can be accurately grasped for any fluctuations in either a short cycle or a long cycle. Since the level control is performed based on the result, stable level control is possible. In addition, grasping of the fluctuation state of the bath level is performed by comparing the fluctuation parameter including the number of peaks of the bath level fluctuation and each peak value with each fluctuation parameter in a storage pattern stored in advance. Since the control parameters of the control controller are adjusted in accordance with the contents set in correspondence with the storage pattern that coincides with the above, even if there is any fluctuation in the molten metal level, this fluctuation can be reduced quickly. Thus, the present invention provides an extremely powerful means for performing a continuous casting operation.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing an apparatus used for carrying out the method of the present invention, FIGS. 2 and 3 are explanatory views showing a process of performing a filtering process by the method of the present invention, and FIG. FIG. 5 is an explanatory diagram of a method of calculating a parameter indicating a level change state, and FIG. 5 is a graph showing a change in the level of the molten metal level controlled by the method of the present invention in comparison with the conventional technique. 3 ... mold, 5 ... sliding gate 6 ... level gauge 8, 8 level controller 16,17 ... filter

Claims (2)

(57) [Claims] 1. A control operation of a control controller, which measures a level of a molten metal in a continuous casting mold with a molten metal level gauge and performs a control based on a control parameter according to a deviation between the measured level and a predetermined target level. In the method for controlling the level of the molten metal in the continuous casting mold for performing the level control by, the output signal of the level gauge is filtered through at least two types of filters having different filtering performances. Obtain a plurality of variation parameters including the number of peaks and the respective peak values of the bath level appearing in a predetermined time, grasp the fluctuation state of the bath level from the obtained fluctuation parameters, and based on the result. A method for controlling the level of a molten metal in a continuous casting mold, comprising adjusting a control parameter of the control controller. 2. The method according to claim 1, wherein a plurality of variation parameters obtained from the processing data are compared with each variation parameter in a pre-arranged storage pattern of the surface level variation, and a storage pattern having an approximate variation parameter is selected. 2. The method according to claim 1, wherein the fluctuation state is grasped.