JPH05318069A - Method for controlling molten metal surface level in mold for continuosly casting small cross-sectional billet - Google Patents

Abstract

(57) [Summary] [Purpose] Even in the case of small-section billets, the establishment of technology for maintaining the molten metal level with high accuracy regardless of the effects of external disturbances such as increased casting speed. [Configuration] When performing control by the PID controller,
K _1D : Introduce an overshoot prevention coefficient and add the change speed of the deviation to the I control term of the PID calculation. [Effect] The fluctuation level of the molten metal surface was ± 2 mm, compared with ± 8 mm in the prior art.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten metal level control method for accurately stabilizing the molten metal level in a mold for continuous casting of small-section billets.

[0002]

2. Description of the Related Art Conventionally, in the casting of a continuous casting machine (hereinafter referred to as CC), stabilization of the molten metal level in the mold has been extremely important in terms of operation and quality of cast slabs. The level control of the molten metal inside the mold is performed by. For example, one of the means for keeping the molten metal level in the mold constant is a method of adjusting the opening of a tundish sliding nozzle (hereinafter referred to as SN) or a stopper. This method is a method of utilizing the detected molten metal level in the mold and automatically and continuously controlling the opening of the SN or the stopper of the tundish by the PID controller so that this level becomes constant.

That is, FIG. 1 shows a case where SN is used and is an explanatory view of the molten metal level control in the mold. In the figure, the molten steel 12 in the tundish 10 is passed through a sliding nozzle 14 for continuous casting. Is injected into the mold 16. At this time, the molten metal level 20 in the mold is constantly measured by the molten metal level gauge 22. When the molten metal level 20 fluctuates, a predetermined signal is sent to the servo amplifier 26 via the PID controller 24, then a command is issued from the hydraulic unit 28 to the work cylinder 30, and the required opening degree of the sliding nozzle 14 is reached.
Secure (a).

In this case, the SNd of the tundish or the opening degree of the stopper is instructed by the PID control based on the deviation between the molten metal level detected by the molten metal level meter and the target level. The calculation of the opening degree instruction at this time is shown by the equation (1).

[0005]

[Equation 2]

However, when this method is applied to the continuous casting of a billet having a small cross section, which is apt to cause a rapid change in the molten metal level, an overshoot phenomenon peculiar to I control occurs and the degree of its attenuation is small, so Can't maintain the level of the water level stably. In other words, it had a problem of poor accuracy. Here, the overshoot phenomenon is a phenomenon that converges to the target level while repeating oscillation, and it takes a long time (30 to 40 seconds) to reach a steady state.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to maintain the molten metal surface level with high precision for a billet having a small cross section, in which the molten metal surface level in the mold is apt to rapidly change due to the influence of disturbance. It is to provide a control method.

[0008]

The inventors of the present invention have conducted a study to achieve the above object, and as a result, I
The present invention has been completed, knowing that it is possible to prevent the overshoot peculiar to I control by adding the change speed of the deviation to the control term and balancing the two.

The present invention is a method for accurately stabilizing the molten metal level in a mold during continuous casting of small cross-section billets, and when performing control by a PID controller, the tundish according to the following equation. To adjust the opening of the nozzle or stopper, I of PID calculation
A method for controlling a molten metal level of a mold for continuous casting of a small cross section billet, which is characterized by adding a changing speed of a deviation to a control term.

[0010]

[Equation 3]

The overshoot prevention coefficient K _ID is obtained by correcting the value obtained by simulation beforehand with actual operation data, since the changing speed of the deviation is added to the term of I control. The "small cross section" billet referred to in the present invention is not particularly limited to it, but generally refers to a billet having a size of 200 x 200 mm or less, and a billet having fluctuations in the molten metal level is a problem. Also in the case, the effect can be seen by applying the present invention.

[0012]

Next, the present invention will be described more specifically with reference to the accompanying drawings.

Fig. 2 shows the PI for a 125 x 125 mm billet.
The simulation result of D control is shown. In case of a sudden change of 10 mm in level,
When the casting speed was rapidly increased to 0.2 m / min,
In the above equation (1) or equation (2), K _P ,
The simulation was performed when the K _I , K _ID , and K _D controls were sequentially superimposed. In the following, they are referred to as P control, I control, ID control, and D control, respectively.

Pattern A: Only when the P control is performed, and in the case, the molten metal level is easily recovered by adjusting the SN opening. But like the case,
Offsets occur as the casting speed increases. As described above, generally, the P level control in which the operation amount is proportional to the deviation amount is used for the molten metal level control, but an offset occurs due to a change in the pouring speed or a change in the molten metal amount from the tundish.

Pattern B: On the other hand, normally, the offset is automatically reset by applying the I control, but the settling time of the I control is worse than that of the P control alone. A small-section billet, which is liable to generate, causes overshoot. Therefore, conventional PI
With control, it was extremely difficult to stabilize the mold level of the small cross section billet with high precision.

Pattern C: In contrast, according to the present invention,
The change speed of the deviation is added to the term of I control which is the integration of the deviation,
By balancing these two, it is possible to prevent the overshoot peculiar to the I control. The calculation of the SN opening in the present invention is expressed by the above-mentioned equation (2). However,
In the case of this pattern C, D control is not performed.

Pattern D: D in case of pattern C
Addition of control further improves the level control. The effect of D control is that the differential element advances the phase by 90 °. In other words, predictive control becomes possible, so the delay factor of the system
This is effective when there is a delay in the hydraulic system, mechanical play, etc. Next, a case where the present invention is applied to a specific operation will be described as an example.

[0018]

[Example] In this example, the diameter is 12 via the tundish SN.
The present invention was applied to the control of the molten metal level in the CC mold in the case of continuously casting a 5 mm billet. That is, the sink roll control method in which the changing speed of the deviation is added to the I control term of the conventional PID control calculation is applied. Conventional example is P
It was ID control itself. A level chart of the molten metal inside the mold is shown in FIG. 3 for both the present invention example and the conventional example. The casting conditions etc. were exactly the same for both methods. With the conventional PID control, the level accuracy was ± 8 mm,
With the control method according to the present invention, extremely high level control of the molten metal surface of ± 2 mm is possible.

[0019]

According to the present invention, the level of the molten metal surface is accurately controlled, and a rapid response can be made even to a sudden change.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a conventional molten metal level control system.

FIG. 2 is a graph showing the result of simulation.

FIG. 3 (a) is a graph showing the result of the conventional example, and FIG. 3 (b) is a graph showing the result of the present invention.

Claims (1)

[Claims] 1. A method for accurately stabilizing the molten metal level in a mold during continuous casting of a small cross section billet, which comprises opening a tundish nozzle or a stopper according to the following formula when controlling by a PID controller. In order to adjust the degree, a method for controlling the level of the mold surface in the small-section billet continuous casting is characterized in that the changing speed of the deviation is added to the I control term of the PID calculation. [Equation 1]