KR20010058101A - Method for casting speed feed forward for suppressing mold level fluctuation in continuous casting process - Google Patents

Abstract

PURPOSE: A casting speed feed forward method for restraining a change of a mold level in the continuous casting process is provided to speedily compensate the influence of a steel discharge quantity on the change of a mold level in response to the rotation of a driving roll to restrain the mold level change, thereby reducing the surface defect ratio of slab and preventing safety accidents in advance. CONSTITUTION: In a casting speed feed forward method for restraining a change of a mold level in the continuous casting process, a feed-forward controller(15), which reduces a change of a mold level(16) by restraining the influence of a steel quantity discharged out of the mold in association with the rotation of a driving roll on the mold level change, satisfies a formula, GF(s)=(1+TN·s)/Kp, wherein TNN represents a time constant of a slide gate, and KPp represents a coefficient of discharge of a nozzle according to an opened sectional area of the slide gate, and carries out the control by the phase lead/lag method in high and low frequency areas.

Description

Method for casting speed feed forward for suppressing mold level fluctuation in continuous casting process}

The present invention relates to a casting speed feedforward method in a continuous casting process, in particular, in the case of using a casting speed in a feedforward controller during a continuous casting process in a steel mill, the average casting speed is used and the feedforward controller is a mathematical method. The present invention relates to a casting speed feedforward method for suppressing mold level variation in a continuous casting process, which is configured to be suitable for preventing molten steel level fluctuations in a mold.

In general, studies and published results have shown that variation in mold level can cause surface defects in slab products ("Continuous Casting Mold Level Control by Theory ", SICE, Summer Seminar 1992, 5-9 July, 1992, Izu, Japan, pp. 133-140, and" Robust Molten Steel Level Control for Continuous Casting ", Proceedings of the 35 ^th Conference on Decision and Control, Kobe , Japan, Dec. 1996, pp. 1245-1250, etc.)

As the mold level fluctuation increases, the surface defect rate of the slab increases, which greatly affects the subsequent hot rolling process and cold rolling process, making it impossible to produce a good product. There are many types of factors that cause mold level variation and are classified according to the conditions of each player.

Therefore, in the present invention, the semi-solid molten steel (Semi-Solidified) flowing out under the mold (3) by the abnormal bulging (Unsteady Bulging) generated between the drive roll (4) installed in the lower part of the mold (3) Reduce the effect of fluctuations in Solified Steel Quantity) on mold level fluctuations.

By eliminating the effect of the above-mentioned fluctuation of the molten steel under the mold due to the abnormal bulging on the mold level fluctuation, conventionally, the mold casting area 10 is multiplied by the mold cross section 29 and this value is fed to the feedforward controller. Used to enter. However, the prior art has not configured the feedforward controller mathematically, but simply configures the feedforward controller by simply applying iteratively in actual application.

Therefore, if the casting speed 10 fluctuates due to various reasons such as abnormal bulging, if the feedforward controller is not mathematically designed, rather than suppressing mold level fluctuations, the control system may be unstable and amplification of mold level fluctuations may occur. There was a problem that can be impossible to use.

Accordingly, the present invention has been proposed to solve the conventional problems as described above, and an object of the present invention is to use the average casting speed in the case of using the casting speed in the continuous casting process of the steel mill in the feed forward controller and to calculate the feed forward controller The present invention provides a casting speed feedforward method for suppressing mold level fluctuations in a continuous casting process that can be constructed based on conventional methods to prevent molten steel level fluctuations occurring in a mold.

Casting speed feedforward method for suppressing the mold level fluctuation in the continuous casting process according to an embodiment of the present invention to achieve the above object,

It is possible to supply molten steel from the ladle to the tundish by opening a specific position under the ladle and connecting it to the tundish through the nozzle, and to supply molten steel into the mold using the slide gate and the immersion nozzle by opening the specific position under the tundish. And a feedback / feedforward controller configured to input the mold level measurement sensor value and output the slide gate position control value to the servo amplifier by drawing the reaction molten steel in the mold by using the driving roll of the lower part of the mold. In a mold level control system,

The feedforward controller which suppresses the influence of the molten steel flowing out of the mold on the mold level variation in accordance with the rotation of the driving roll, reduces the mold level variation,

(Where T _N is the time constant of the slide gate and K _p is the discharge coefficient of the nozzle formed by the open cross-sectional area of the slide gate), and the control is performed by the phase forward / delay method in the high frequency and low frequency region. It is characterized by the technical configuration.

1 is a schematic configuration diagram of a tundish, a mold surrounding part, and an associated control system of a general player;

FIG. 2 is a block diagram of a mold level control system in FIG. 1;

Figure 3 is a block diagram of a mold level control system showing a casting speed feedforward method for suppressing mold level variation in a continuous casting process according to an embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

1: slide gate 2: immersion nozzle

3: mold 4: drive roll

5: mold level measuring sensor 6: hydraulic cylinder

7: Servo Valve 8: Servo Amplifier

9: hydraulic cylinder moving distance measuring device 10: casting speed

11: tundish 12: long nozzle

13: ladle 14: feedback controller

15: feed forward controller 16: actual molten steel level of the mold

17: molten steel level of tundish 18: mold level set value

19: Mold level sensor measured value

Hereinafter, an embodiment according to the technical idea of the casting speed feedforward method for suppressing mold level variation in the continuous casting process of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic diagram showing a control system for suppressing ladle 13, tundish 11, mold 3 and mold level 16 fluctuations.

Thus, the molten steel whose components are adjusted in the steel mill is transferred to the performance factory by using the ladle 13, and the work is started, and the molten steel flows into the tundish 11 as the long nozzle 12 of the ladle 13 is opened. do. When the molten steel in the tundish 11 is more than an appropriate level, the lower slide gate 1 of the tundish 11 is opened to fill the molten steel in the mold 3. When the molten steel rises to the appropriate level in the mold 3, the driving roll 4 is driven to draw out the molten steel that has reacted.

When molten steel flows out by the rotation of the driving roll 4, the molten steel level in the mold is lowered, which is detected by the mold level sensor 5 and input to the feedback controller 14, and the feedback / feedforward controllers 14 and 15 ) Is output to the servo amplifier 8 and the output of the servo amplifier 8 is output to the servo valve 7 to drive the hydraulic cylinder (6) to open the slide gate (1). That is, when the mold level 16 is high, the slide gate 1 is closed to block the flow of oil from the tundish 11 to the mold 3 to lower the mold level 16. On the contrary, when the mold level 16 is low, the slide gate 1 is closed. More (1) is opened to allow more molten steel to flow into the mold (3) from the tundish (11).

This series of operations consists of a closed loop system that automatically adjusts the mold level 16 to the desired value 18. In the inner loop, the servo amplifier 8 measures the moving distance of the hydraulic cylinder 6 using the hydraulic cylinder moving distance measuring device (LVDT) 9. The superiority of the method of controlling the mold level 16 to the desired value 18 generally depends on the performance of the feedback / feedforward controllers 14 and 15.

FIG. 2 is a block diagram of a closed loop mold level control system in the schematic diagram of FIG.

In Fig. 2, reference numeral 14 denotes a feedback controller, reference numeral 15 denotes a feedforward controller, and reference numeral 23 denotes a relationship between an output 22 of the feedback / feedforward controller 14 and 15 and a moving distance 24 of the slide gate 1. The transfer function to be indicated, 25 is a transfer function representing the relationship between the molten steel inflow 27 from the tundish 11 to the mold 3 with respect to the moving distance 24 of the slide gate 1, 33 is The transfer function showing the relationship between the difference between the molten steel amount 32 and the molten steel inflow amount 27 caused by the rotation of the driving roll 4 and the mold level 16, (5) is the mold level measurement The transfer function of the sensor.

In the transfer function (23)T _N Is the time constant of the slide gate (1), the transfer function (25)K _p Is the coefficient of discharge of the nozzle configured by the open cross-sectional area of the slide gate 1,T _d Is the time taken from the tundish 11 to reach the mold 3 by the molten steel introduced through the nozzle configured in the open cross-sectional area.K _p AndT _d Is obtained experimentally.

In the transfer function 33, T _m in the mold 3 in constructing the difference between the molten steel inflow 27 into the mold 3 and the molten steel outflow amount out of the mold 3 and the mold level 16 Is a time constant for expressing the effects of molten steel slewing in. In addition, T _L in the transfer function 5 is a time constant of the mold level measuring sensor 5.

In Fig. 2, 30 is the average casting speed, and the actual operation of this value is calculated by the feedforward controller 15 by receiving the instantaneous casting speed 10 value from the drive roll 4. (31) represents the fluctuation of the molten steel flow rate, and the product of the average casting speed (30) and the mold (3) cross-sectional area (29) represents the average molten steel flow rate (28) and the instantaneous molten steel flow amount in combination with the above (31). And (32).

3 is a block diagram of a mold level control system showing a casting speed feedforward method for suppressing mold level variation in a continuous casting process according to an embodiment of the present invention. 2 is a modified block diagram of FIG. 2 configured to move to the rear of the transfer function 33.

In FIG. 3, the error value 20 of the output value 19 of the mold level measuring sensor 5 and the mold level setting value 18 is calculated and input to the feedback controller 14. Meanwhile, the average molten steel flow amount 28 calculated according to the above method is input to the feedforward controller 15 to compensate for the molten steel flow out of the mold 3 according to the rotation of the driving roll 4.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 3, the average casting speed 30 is calculated by receiving the instantaneous casting speed 10 value from the feedforward controller 15, using a moving average method or using a fast fourier transform (FFT). By calculating one harmonic, a low frequency filter having a cutoff frequency lower than that of the first harmonic is designed and implemented in the feedforward controller.

In FIG. 3, the feedforward controller 15 is calculated as follows in order to compensate the molten steel outflow amount due to the rotation of the driving roll 4 using the feedforward controller 15. FIG. The feed forward controller 15 is calculated as follows in order to compensate for the molten steel outflow amount due to the rotation of the drive roll 4 using the feed forward controller 15. In order to accurately compensate the amount of molten steel outflow due to the rotation of the driving roll 4, the following Equation 1 must be established.

The feedforward controller can be calculated from Equation 1 as shown in Equation 2 below.

The feedforward controller is in the form of a proportional-differential (PD) controller and uses the average casting speed 30 to configure the input of the feedforward controller 15.

Since the feedforward controller 15 is in the form of a PD controller, if the input value of the feedforward controller 15 changes momentarily large, the control system becomes unstable and amplifies rather than compensates for the mold level 16 fluctuation due to the amount of molten steel.

It is for this reason that the average casting speed 30 is used as the input value of the feedforward controller 15 in the present invention. In the feedforward controller, the performance of the feedforward controller may be somewhat improved by a phase lead / lag method at high and low frequencies.

The feedforward controller calculated as in Equation 2 is implemented by applying a trapezoidal type discretization method in a personal computer (PC) or a programmable logic controller (PLC).

The output 21 calculated by the feedforward controller 15 is added to the output of the feedback controller 14 and output to the servo amplifier 8 to suppress the influence of the molten steel outflow amount on the mold level variation.

As described above, the present invention uses the average casting speed when the casting speed is used in the feedforward controller during the continuous casting process of the steel mill, and configures the feedforward controller based on a mathematical method to prevent the molten steel level variation of the mold generated in the mold. will be.

Although the preferred embodiment of the present invention has been described above, the present invention may use various changes, modifications, and equivalents. It is clear that the present invention can be applied in the same manner by appropriately modifying the above embodiments. Accordingly, the above description does not limit the scope of the invention as defined by the limitations of the following claims.

As described above, in the continuous casting process according to the present invention, the casting speed feedforward method for suppressing the mold level fluctuations can quickly determine the effect of the molten steel outflow due to the rotation of the driving roll 4 on the variation of the mold level 16. By compensating for mold level fluctuations, the slab surface defect rate is reduced, and safety accidents are prevented and productivity is improved.

Claims (2)

It is possible to supply molten steel from the ladle to the tundish by opening a specific position under the ladle and connecting it to the tundish through the nozzle, and to supply molten steel into the mold using the slide gate and the immersion nozzle by opening the specific position under the tundish. And a feedback / feedforward controller configured to input the mold level measurement sensor value and output the slide gate position control value to the servo amplifier by drawing the reaction molten steel in the mold by using the driving roll of the lower part of the mold. In a mold level control system, The feedforward controller which suppresses the influence of the molten steel flowing out of the mold on the mold level variation in accordance with the rotation of the driving roll, reduces the mold level variation, Where T _N is the time constant of the slide gate and K _p is the discharge coefficient of the nozzle constructed by the open cross-sectional area of the slide gate. A casting speed feedforward method for suppressing mold level fluctuation in a continuous casting process, characterized in that based on the shape of, and performing the control by the phase leading / delay method in the high frequency and low frequency region. The method of claim 1, wherein the input of the feedforward controller uses a value obtained by multiplying an average casting speed and a mold cross-sectional area.