JPH04262845A - Method for controlling mold level in continuous casting - Google Patents

Abstract

PURPOSE:To accurately control a molten metal surface in a mold in a continuous casting. CONSTITUTION:Deviation between the measured value of a molten metal surface meter 33 and the molten metal surface level aimed value is inputted to a PI controller 34 and by activating a stopper controller 20 with stopper opening degree command outputted from there, the stopper 21 is driven to control a molten steel flow rate into the mold. In this case, in a gain adjustor 31, the measured values of the molten metal surface level and the stopper opening degree are inputted and the ratio of the variations of the them is calculated, and this is averaged for the prescribed time to make the molten steel discharging gain. By using gain variating quantity obtd. from this molten steel discharging gain, the above-mentioned stopper opening degree command is compensated. The variation quantity of the molten metal surface in the mold is reduced.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to a method for controlling the level of molten steel in a mold in continuous casting.

0002

[Prior Art and Problems] Improvements have been made in hot water level control, such as model-based adaptive control devices and two-degree-of-freedom PiD control, but the responsiveness is not good and it is difficult to determine the optimal parameters. be. In addition, level control of small-section molds such as those used in continuous billet casting is difficult to control using conventional stoppers, but by using highly responsive and highly accurate actuators, it is possible to appropriately select the gain. For example, highly accurate level control can be achieved. The problem at this time is that if you want to keep the level fluctuations small, you have to increase the control gain, but as the stopper outflow gain fluctuates, the control loop gain becomes abnormally high and the control There is a risk that it may diverge. In order to suppress such divergence, a method of estimating the gain has been proposed (Japanese Unexamined Patent Publication No. 192545/1983), but sufficient accuracy is not necessarily obtained. Particularly in the case of a small-section mold such as continuous casting of billets, the level fluctuation is larger than in the case of a large-section slab mold, and therefore it is difficult to control accurately.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for controlling the level of molten steel in a mold in continuous casting, which improves accuracy even in the case of small-section molds.

0004

[Means and effects for solving the problem] The method for controlling the mold level in continuous casting of the present invention is based on the method of controlling the mold level in continuous casting. A control method that uses a controller that outputs an opening command for a stopper nozzle provided in a tundish according to a deviation from the tundish, and a stopper control device that adjusts the opening of a stopper in response to the opening command. , for the hot water level and stopper opening measured N+1 times in chronological order, the difference from the previous measurement value is ΔL(
i), ΔS(i), and the ratio ΔL(i)/ΔS
(i) Let the average of the above N times be the molten steel outflow gain Gj,
The present invention is characterized in that, with α and β as correction coefficients and G0 as an initial value of Gj, the gain change amount Rj is determined from Rj=α(Gj/G0)+β, and the opening degree command is corrected using the Rj.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram of a control device showing one embodiment of the present invention, and FIG. 2 is a control block diagram of the control device shown in FIG. In FIGS. 1 and 2, 11 is a tundish into which molten steel 13 is charged from a ladle (not shown), and 12 is a tundish into which molten steel 13 is charged from a ladle (not shown), and 12 is a tundish in which the molten steel in the tundish is transferred to a mold 14.
It is an immersion nozzle for casting. Molten steel 15 is poured into a mold, and is cooled in the mold or a cooling zone (not shown) to form a solidified shell 16.

21 is a stopper that adjusts the flow rate of molten steel flowing out from the tundish 11 to the mold 14; 22 is an inverted L-shaped lever that is fixed to the top of the stopper and moves up and down the stopper 21; its vertical portion is connected to the tundish 11; It is supported on the side wall so that it can be raised and lowered freely. 20 is stopper 2
A stopper control device that controls the lifting and lowering of the lever 22.
As an actuator for driving the stopper 21, a stepping cylinder 23,
Although it has a hydraulic unit 24 and a stepping motor 25, the actuator is not limited to this. Further, 34 is a PI controller that measures the deviation between the molten metal level L from the molten metal level gauge 33 that measures the molten steel level in the mold and the target value L0 of the molten metal level from the target setting device 32, and other control parameters. It is entered here. 31 is a gain adjuster, where the stopper control device 20 is connected to the stopper 21.
The opening degree S, the hot water level L, and other necessary control parameters are input. Reference numeral 36 denotes a computer into which data necessary for operation is input, from which control parameters necessary for stopper control are input into the regulator 31.

The operation of the mold level control mechanism in continuous casting used in the method of the present invention constructed as described above will be explained. The molten steel poured into the mold 14 from the immersion nozzle 12 maintains a substantially constant level in the mold depending on the balance between the amount of the cast and the amount of the slab pulled out. In order to maintain this balance, there are many operational parameters that fluctuate during operation, such as the amount of slab withdrawn and the amount of cast, and control methods are devised for each variable factor.

[0008] In mold level control by adjusting the opening of a refractory nozzle such as the stopper 21, a problem arises in that the melt level fluctuates due to a change in the molten steel outflow gain due to melting or clogging of the nozzle. In order to maintain optimal controllability, it is necessary to always maintain a constant cycle transfer gain even with fluctuations in the molten steel outflow gain, but prediction is difficult due to the wide variety of fluctuation factors. Therefore, in the present invention, the amount of change in stopper opening, which is important as a factor in fluctuations in molten steel, is predicted from the actual value, and this is used as an estimated gain fluctuation value to compensate for it. As a result, good molten metal level control results are obtained. It is.

[0009] The target value L of the hot water level is obtained from the target setting device 32.
The difference ΔL between 0 and L measured by the hot water level gauge 33 is input to the PI controller 34. The gain change amount and control parameters are inputted here from the gain adjuster 31, and an opening command is inputted to the stopper control device 20 as an output. The stepping cylinder 23 receives hydraulic pressure from the hydraulic unit 24 according to the rotational speed of the stepping motor 25 of the stopper control device 20, and the piston rod 28 is driven up and down by a predetermined distance. As a result, the lever 22 and the stopper 21 connected thereto move up and down, and the opening degree of the stopper 21 is adjusted.

The gain regulator 31 receives L from the water level gauge 33 and S from the stopper control device 20, and also receives necessary control parameters from the computer 36. Control parameters are also supplied to the device 34 as appropriate. N in chronological order within a predetermined time
The L and S measured times are L(i) and S(i), respectively.
(i=1 to N+1), the level change ΔL(i) and the stopper opening change ΔS(i) are defined by the following equation (1).

ΔL(i)=L(i)−L(i−1), Δ
S(i)=S(i)-S(i-1)...(1)
However, i=2 to N+1, where i is an index indicating the time of measurement. Below (2
) defines the molten steel outflow gain Gj from the above ΔL(i) and ΔS(i).

Gj=Σ(ΔL(i)/
ΔS(i))/N...(
2) As shown in equation (2), Gj is the ratio of N values obtained from the past N+1 measurement values measured at predetermined intervals, Δ
This is the average of L(i)/ΔS(i). Therefore, Gj is calculated from past ΔL and ΔS at each N+1 measurement time of L and S, and j is an index indicating the current time. From the above Gj, the gain change amount Rj at j is determined by equation (3).

Rj=α(Gj/G0)
+β...
(3) Here, G0 is the initial value of Gj, and α and β are correction coefficients that are determined by operational parameters, manufacturing equipment, control equipment, or actual values related to the operation. In equation (3), Rj
Once Pj is determined, the corrected controller proportional band Pj is determined from equation (4) using P0 as the initial value.

Pj=RjP0

(4) Fig. 3 shows the results according to the embodiment of the present invention, showing temporal changes in the melt level fluctuation, tundish weight, drawing speed, and stopper opening degree. Further, in the figure, the gain Gj is defined by the above equation (3). The mold size is 230 mmφ and is shown for continuous casting of round billets. FIG. 4 shows a comparative example in which the molten steel outflow gain is not compensated for, and the other conditions are the same as those in FIG. 1. Comparing Figures 3 and 4, we can see that in the present example, the level fluctuation was within ±1 mm, while in the comparative example, this was within ±2 to 5 mm.
Therefore, the advantage of this embodiment is clear.

[0015]

[Effects of the Invention] The stopper opening command is compensated by the molten steel outflow gain obtained by measuring the changes in the hot water level and the stopper opening and averaging the ratio over a predetermined period of time, so fluctuations in the hot water level are prevented. Reduced.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a control device of this embodiment.

FIG. 2 is a control block diagram of the control device shown in FIG. 1.

FIG. 3 is a graph diagram showing fluctuations in hot water level and other operating conditions in this example.

FIG. 4 is a comparative example in which no gain compensation is performed, and is a graph diagram showing fluctuations in the hot water level and other operating conditions as operating conditions otherwise similar to those in FIG. 3;

[Explanation of symbols]

11 Tundish 12 Immersion nozzle 13, 15 Molten steel 16 Solidified shell 20 Stopper control device 21 Stopper 22 Lever 23 Stepping cylinder 24 Hydraulic unit 25 Stepping motor 28 Piston rod 31 Gain adjuster 32 Level goal setter 33 Water level gauge 34 PI controller 36 Calculator

Claims (1)

[Claims] Claim 1: The opening command of a stopper nozzle provided in a tundish is determined according to the deviation between the molten steel level in the mold measured by a molten metal level gauge and a target molten steel level in continuous casting. In a method of controlling using a controller that outputs an output and a stopper control device that adjusts the opening degree of the stopper in response to the opening command, N+1
The difference between the previously measured hot water level and stopper opening is ΔL(i) and ΔS(i), respectively.
, the average of N times of the ratio ΔL(i) /ΔS(i) is taken as the molten steel outflow gain Gj, and α and β are correction coefficients, G
0 as an initial value of Gj, a gain change Rj is determined from Rj=α(Gj/G0)+β, and an opening command is corrected using Rj.