KR20060075093A - Robust control method of melt level in the twin roll strip caster - Google Patents

Abstract

The present invention relates to a method of constantly controlling the height of the hot water surface of a mold in a twin roll sheet metal casting process.

The present invention relates to a double roll type sheet metal casting process having a stop surface system for supplying molten steel to a mold and a floor height control system using a camera system for measuring the height of the in-mold surface. The height of the surface in the twin-roll sheet metal casting process is characterized by controlling the height of the surface with a preceding controller for changing the value to match the characteristics of the surface of the floor height control system and a feedback controller for maintaining the surface height constant under normal casting conditions. Provide a robust control method.

Double roll type sheet casting, floor height, control

Description

Robust control method of melt level in the twin roll strip caster

1 is a schematic diagram of a twin roll sheet metal casting process,

2 is a system diagram of a control system of the present invention;

3 is a robust molten steel height control schematic diagram of a twin roll sheet metal casting process,

4 is a distribution coefficient distribution diagram of a stopper and an immersion nozzle in a twin roll sheet casting process;

5 is a casting initial overshoot experimental data of the robust molten steel height control of the twin-roll thin plate casting process,

6 is an experimental data diagram for confirming the disturbance response characteristics of the robust molten steel height control of the twin-roll thin plate casting process.

 -Explanation of symbols for the main parts of the drawing-

1: ladle 2: tundish

3: Stopper system 4: Immersion nozzle

5: camera 6: casting roll

7: edge dam 8: sheet

9: pinch roll 10: rolling roll

11: coiler 12: stopper motor drive system

13: Stopper lever 14: Stopper rod

15: floor height control computer 16: robust floor height controller

17: Molten steel height in tundish 18: Stopper height

19: casting roll speed 20: roll gap

21: Bath surface height 22: Casting roll radius

23: Angle of appearance of immersion nozzle 24: Molten steel height in immersion nozzle

25: Width of immersion nozzle 26: Bottom width of immersion nozzle

27: Installation height of the immersion nozzle

The present invention relates to a method of constantly controlling the height of the hot water surface of a mold in a twin roll sheet metal casting process.

The outline of a twin roll sheet metal casting process is shown in FIG. The molten steel present in the ladle 1 is supplied to the tundish 2 through the slide gate, and is formed into a mold composed of the casting roll 5 and the edge dam 7 through the stopper system 3 and the immersion nozzle 4. Supplied. The hot water level of the molten steel supplied to the mold is measured using the camera 5, and the supplied molten steel is solidified by the water-cooled casting roll 6 to produce a thin plate 8, and the pinch roll 9 and the rolling mill 10 are rolled through the roll mill. ) Is wound up in the coiler 11.

As described above, the system for supplying molten steel to the mold in a twin roll sheet metal casting process is composed of a stopper and an immersion nozzle. And the image processing method using the camera is used as the system to measure the height of the floor. In such a twin roll sheet metal casting process, precise control of the mold height of the mold is a basic requirement for maintaining stable casting. In the twin roll type sheet casting process, the fluctuation of the hot water level causes a change in the contact time with the water-cooled casting roll, which adversely affects the quality of the thin sheet manufactured. If a single mold floor height control failure in a twin roll sheet metal casting process causes significant damage to expensive casting rolls and other machinery, stable floor height control must be established.

In the existing research, numerous applications such as domestic applications 10-2000-80776, 10-1996-57612, Japanese applications 2001-69265, 1999-141926, 1996-167075, 1996-110550, etc. .

Existing papers (Control Engineering Practice, 6 (1998), 191-196) have intensively studied the release coefficients of stoppers and immersion nozzles and the delay of molten steel transmission time as the main obstacles to control the mold height.

In order to overcome such obstacles, a method using a proportional / integral / derivative controller of different characteristics is used at the beginning and the middle of casting (JP-1999-141926). A method of varying the speed of casting rolls is used (US-1998-034239).

However, in the early stage of casting, overshoots exist, overshoots caused by disturbances during casting, and excessive overshoots damage the facilities of the meniscus shield or the casting roll, and deteriorate cast quality and casting stability. . The main cause of such overshoot may be various factors such as change of molten steel supply hardware, refractory machining error, poor zeroing of stopper height, change of molten steel height in tundish, and change of casting speed.

In particular, the release coefficient of the stopper, which is defined by the following equation (1), is not constant during casting, but is scattered and changes. It is very important to control the height of the hot water in preparation for disturbance caused by the change of the release coefficient.

Stopper emission factor = cast steel per hour / maximum molten steel supply per hour at the stopper outlet --------------- (1)

However, the controller for controlling the height of the water so far is a PID controller, which can be expressed by the following equation (2).

(S ² + a ₁ S + a ₂ ) / (b ₁ S + b ₂ ) ----------- (2)

Such PID controller has the advantage of being widely used for general purpose because of its simple design and easy tuning, but it is difficult to cope with a narrow range of environmental changes and accidents, and especially in a field where loss recovery cost is high. It is difficult to use.

On the other hand, the robust controller that can be expressed by the following equation (3)

(S ⁿ + ..... + a ₂ S + a ₁ ) / (b _n-1 S ^n-1 + ... + b ₁ ) ------- (3)

As it can cope with a wide range of environmental changes, respond to sudden situations, and is in the early stages of development, various mathematical models and evaluation criteria are required, but there are no application cases in steelmaking.

In case of double roll type sheet casting machine, even if the molten steel overflows even once, all the equipments are damaged.

The present invention has been made to solve the above problems, and has a main purpose to solve the disadvantages of the PID controller, and to provide a robust controller with no failures once and to apply it to the steelmaking process.

In order to achieve the above technical problem, the present invention uses a stopper system in a tundish to supply molten steel to a mold, and uses a camera system to measure the height of the molten metal in the mold. In the case of initial casting or disturbance of the casting, in the case of initial casting or the disturbance occurs, the height of the floor is controlled by a preceding controller which changes the surface height control system to match the characteristics of the floor height control system, and the level of the floor is maintained by the feedback controller to keep the floor height constant under normal casting. It provides a robust control method of the hot water level in a twin-roll thin plate casting process characterized in that the control.

Investigate the emission range of the stopper and immersion nozzle used in the twin roll type casting process, delay of molten steel transmission time, sheet metal manufacturing speed, etc. from existing casting data, and find out the variable range. Sets the targets to be achieved, and through the design of a robust controller, the hot water level is a double-roll type sheet casting process even in the event of clogging / drilling of the discharge port represented by a sudden change in the discharge coefficient of the stopper and the immersion nozzle. In order to meet the specifications required by the company, it provides a robust controller that ensures the hot water level reaches the target value as quickly as possible with minimum overshoot.

The robust controller designed as above is applied as follows.

In the early stage of casting, deploying the stopper rod, starting the strong preceding controller, applying the preceding controller until the floor height reaches steady state, starting the feedback controller when the floor height reaches steady state, usually Is applied to continue the control of.

In addition, when disturbance occurs during casting, detecting the occurrence of disturbance, starting a strong preceding controller, starting the feedback controller when the hot water level reaches a steady state, and continuing normal control. Apply.

Hereinafter, the design of the robust controller of the present invention will be described in detail with reference to the drawings.

2 is a system diagram of the control system of the present invention.

In the process of FIG. 1, the target floor height is input to the preceding controller, and the feedback controller receives the feedback of the floor height, and the feedback controller gives an output signal to the tundish stopper to adjust the amount of molten steel supplied to the mold through the nozzle. . The part marked P is a mathematical model representing hardware consisting of stoppers, nozzles and molds. From the point of view of a robust controller, the model represents a range of key factors for system development. The preceding controller, represented by F, is the software that plans to reach the initial target floor height, and K is the feedback controller that commands the hardware to maintain the target floor level.

3 shows an enlarged structure of supplying molten steel to a mold in a twin roll sheet casting machine.

First, the stopper system 3 is composed of a stopper motor drive system 12 for driving the stopper up and down, a stopper lever 13 and a stopper rod 14 for adjusting the cross-sectional area of the stopper strip in the tundish.

Here, the flow rate Q _s supplied to the immersion nozzle 4 through the stopper discharge port is related to the molten steel height 17, h _T and the stopper height 18, u in the tundish, and the discharge port of the immersion nozzle 4 is connected. The flow rate Q ₁ supplied to the mold is related to the molten steel height 24 in the immersion nozzle 24 and the area of the discharge port by the following equation.

----- (4)

----- (4)

----- (5)

----- (5)

Here, C _s and C _i represent the emission coefficients of the stopper and the immersion nozzle, and K _s is a linear coefficient calculated from the geometry and has a value between 0.119 and 0.129. C _s and C _i were investigated in the distribution as shown in FIG. 4 from casting data of 500 double roll sheet casting machines. Here, the emission coefficient is defined as (manufacturing amount per hour) / (maximum molten steel supply per hour at the stopper or nozzle discharge port).

In addition, the molten steel amount (V _i ) and the molten steel height (24, h _i ) and the molten steel amount (V _m ) and the molten steel height (21, h _m ) introduced into the immersion nozzle (4) are as follows (6) And (7).

                                    ----------- (6)

------------ (7)

Here, L _i and D _i means the bottom length and width 25 inside the immersion nozzle, L _o and D _o means the width 26 of the outside of the immersion nozzle, L _R and R is the width of the casting roll And a radius 22, r _g means a roll gap 20, θ _o means the angle of the tip of the immersion nozzle appearance, H _o means the installation height (27) from the roll 의 of the immersion nozzle.

In such a system, the dynamics governing the elevation height 21 in the mold are represented by the following equations (8) and (9).

------------- (8)

------------- (8)

------------- (9)

------------- (9)

Here, Q _o means the rate of sheet metal fabrication through roll rolls, and T _s and T _i mean the time it takes for the molten steel to be transferred from the stopper outlet to the immersion nozzle and the time delay for supplying the molten steel from the immersion nozzle to the mold. do. Each of these time delays is unknown, but the sum of the two time delays can be known from the existing casting data since the difference between the time when the stopper starts to close when the casting stops and the time when the surface height of the mold falls. In addition, Q _o It may be seen that the variation range on the basis of existing data casting.

Thus, using the stopper height 18 as a control input, the control model for controlling the height of the in-mold surface 21 is represented in the following frequency domain as a linearized model, and the coefficients shown in the formula are shown in the following table. It has a variable range.

-- (10)

-(10)

Here, Y (s) is a laplacyan of the surface height height measured value in a mold, and R (s) is a laplacyan of a stopper height command value. At this time, the first polynomial of the right term is derived from the above-described equations, and the second polynomial is obtained by linearly modeling the relationship between the stopper height command value R (s) and the stopper height actual value U (s). The reason for modeling the dynamics at the stopper height as an invariant known coefficient is that the dynamics react much faster than the in-mold surface height dynamics in the first term of the formula, so that they exist at the stopper height at that stopper height. This is the result of excluding the uncertainty of the mechanics.

parameter Average Variable range

0.33 (1 / sec ² ) 0.21 ~ 0.44

0.44 (1 / sec) 0.35-0.52

0.023 (1 / sec) 0.019 to 0.026

0.6 (sec) 0.5 to 0.7

The variable range of these parameters is 410 ~ 450mm of hot water level, 375 ~ 425mm of molten steel in tundish, 26 ~ 54mm of molten steel in immersion nozzle, 0.0047 ~ 0.0116 (m ² / sec), It is considered that the stopper release coefficient is 0.41 ~ 0.85 and the immersion nozzle release coefficient is 0.42 ~ 0.92.

The performance criteria that the controller should have in such a control model are expressed by the following three frequency domain performance criteria.

1. Stability Evaluation Criteria:

----- (11)

----- (11)

2. Disturbance Evaluation Criteria:

------ (12)

------ (12)

3. Initial Response Evaluation Criteria:

----- (13)

----- (13)

------ (14)

------ (14)

----- (15)

----- (15)

The robust controller that satisfies such evaluation criteria is composed of the following prior controller and feedback controller.

Leading controller:

----- (16)

----- (16)

Feedback controller:

--- (17)

--- (17)

As described above, the present invention serves to maintain a constant hot water level of the twin-roll thin plate casting process. The performance standard of the toughness controller is set so as to be insensitive to the irregularity of stopper and immersion nozzle emission factor, variable sheet metal manufacturing speed and molten steel transmission time delay which act as obstacles to keep the floor height constant. Designed to control height.

The continuous value leading controller and feedback controller obtained to play the role of maintaining the floor height of the twin roll type sheet casting process are converted into discrete controllers, and are composed of a real-time operating system in which time synchronization of the user's application program is very accurate. Applied to computer systems.

Thus, Figure 5 is a robust molten steel height control experimental data of the twin-roll thin plate casting process to confirm that the water level in the mold at the beginning of the casting is controlled to have an overshoot within 1% with a rise time of 8 to 26 seconds. Can be.

In addition, Figure 6 is a robust molten steel height control experimental data diagram of the twin-roll thin plate casting process can be confirmed to return to the normal state within a short time with overshoot within 3% after the occurrence of disturbance.

 In the present invention, after confirming the release coefficient of the stopper and the immersion nozzle, the variable transmission time of the molten steel and the sheet manufacturing speed, based on the existing experience obtained in the twin-roll sheet metal casting process, it is possible to control the height of the hot water in the variation range of each identified parameter Determining the detailed specifications to be achieved has the following effects:

In the double roll type sheet casting process, it takes 8 ~ 26 seconds for the surface height to rise to the target value at the beginning of casting, and the maximum overshoot that can occur at this time can not be exceeded by more than 1% from the target value.

In the middle of casting, even if the release coefficient of the stopper varies within the range of 0.4 to 0.8 or the immersion nozzle release coefficient changes within the range of 0.45 to 0.85, the water level is controlled not to change more than 5% from the target value.

When the transmission time delay of the stopper system (3) and the immersion nozzle (4) used to supply molten steel is 0.5 to 0.7 seconds, the rise time is 8 to 26 seconds to reach the target value at the initial stage of casting. Overshoot can be controlled within 1% of the target value.

When the discharge coefficient of the stopper system (3) used for supplying molten steel in the middle of casting is suddenly changed from 0.4 to 0.8, or the discharge coefficient of the immersion nozzle is suddenly changed from 0.45 to 0.85, the discharge hole which was clogged slightly is opened. Can be within 0.5% of the target value.

When the floor height control is performed according to the specification according to the present invention, it is possible to achieve casting stability, product quality stability, and high-cost accident prevention.

Claims (6)

In a twin roll sheet metal casting process in which a stopper system in a tundish is used to supply molten steel to a mold, and a bath surface height is controlled using a camera system to measure the height of the mold surface. A preceding controller for changing the target height of the water level to coincide with the operation characteristics of the water level in case of initial casting or disturbance; Robust control method of the floor height in the twin-roll thin plate casting process, characterized in that the control of the floor height with a feedback controller to maintain the constant floor height under normal casting conditions. The method of claim 1, wherein the design of the preceding controller and the feedback controller is carried out by investigating the emission coefficients of the stopper and the immersion nozzle used in the twin roll casting process, the molten steel transmission time delay, the sheet manufacturing speed, and the like, from the existing casting data. The process of determining the range, setting the target to be achieved by the hot water level controller of the twin roll type sheet casting machine in the variable range, and clogging the discharge port represented by the rapid change of the emission coefficient of the stopper and the immersion nozzle to achieve the target Robust control method of the floor height in the twin roll sheet metal casting process, characterized in that it consists of the process of designing a robust controller to meet the specifications required in the double roll sheet metal casting process even in the puncture phenomenon. The method according to claim 1, The process of applying the preceding controller and the feedback controller, the process of starting the robust preceding controller when the initial casting or disturbance occurs, the process of applying the robust preceding controller until the floor height reaches the normal condition, the water surface Robust control method of the hot water level in the twin-roll thin plate casting process, characterized in that the process consists of switching to the feedback controller when the height reaches the steady state. The method according to any one of claims 1 to 3, The preliminary controller takes 8 to 26 seconds to increase the water level to the target value at the beginning of the casting, and satisfies the following formula to prevent the maximum overshoot that can occur at this time from exceeding 1% from the target value. Robust control method of hot water level in twin roll sheet metal casting process.

The method according to any one of claims 1 to 3, The feedback controller changes the water level to within 3% of the target value when the discharge port, which is slightly clogged due to a sudden change in the discharge coefficient of the stopper system from 0.4 to 0.8 or a sudden change in the discharge coefficient of the immersion nozzle from 0.45 to 0.85. Robust control method of hot water level in twin roll sheet metal casting process, characterized by satisfying the equation.

The method according to any one of claims 1 to 3, The feedback controller is a robust control method of the height of the hot water level in the twin-roll thin plate casting process, if the transfer time of the molten steel flowing into the mold through the stopper system and the immersion nozzle is delayed by 0.5 ~ 0.7 seconds.

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