JPH0751259B2 - Twin-belt continuous casting level control method - Google Patents

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 twin belt continuous casting.

[0002]

2. Description of the Related Art There are the following methods for detecting the molten metal level.

1. Method of using a float A method of floating a float on the surface of the molten metal and detecting the position of this float with a stick or a chain.

2. Optical (photoelectric conversion) method Focusing on the difference in brightness at the contact position between the molten metal surface and the container,
A method of measuring this boundary line by triangulation using an array sensor or a television camera, for example.

3. Method using ultrasonic wave A method of measuring the distance to the molten metal surface by irradiating it with ultrasonic waves and measuring the time it takes for the reflected sound waves to return.

4. Method of using radiation A method of transmitting radiation diagonally to the surface of the molten metal and detecting the level of the molten metal by the attenuation of this radiation.

5. Immersion electrode method A method of detecting the level of the molten metal by creating an ON-OFF state of the electric circuit with the electrode and the molten metal.

6. Electromagnetic induction method In Japanese Patent Laid-Open No. 48-93539, a coil long in the depth direction is provided on the outer wall surface of the mold, and this coil is connected to one side of an impedance bridge circuit. There is a method of detecting the change of the molten metal level as the change of the mold wall temperature and detecting the molten metal level by utilizing the change of the eddy current generated in the mold due to the change of the specific resistance of the mold wall caused by this change. Has been presented.

As a method for controlling the molten metal level in twin belt continuous casting, PI is calculated from the difference between the measured molten metal level at one location measured by the above-mentioned molten metal level detector and the molten metal level target value.
It is a general conventional technique that a pouring amount command value is calculated by a controller or a PID controller and the pouring amount command value is output to a pouring amount operation device.

[0010]

In the twin-belt continuous casting level control method using the PI controller or the PID controller based on the level measurement value at one location, vibration of the level may be taken into consideration. Since it is not possible, changes in the pouring amount due to the calculated pouring amount command value may cause vibration of the molten metal surface,
This causes problems in terms of product quality or yield, operating rate, and safety during operation.

It is an object of the present invention to provide a control method for compensating for disturbances that affect the average level of the molten metal surface so that the average level of the molten metal surface follows the target value.

[0012]

According to the present invention, in a molten metal level control method for twin-belt continuous casting, (a) the molten metal level is measured at two or more positions horizontally different from each other; the modal filter from the molten metal surface level measurements at two or more calculates the mode displacement of the vibration modes of the mean level and one or more molten metal surface of the molten metal surface, (c) melt-surface level target value and the molten steel surface By calculating the pouring amount command value from the average level, and (d) outputting the pouring amount command value to the pouring amount operation unit, the disturbance affecting the average level of the molten metal level is compensated, and the average level of the molten metal level is compensated. Is made to follow the target value.

[0013]

The present invention will be described in detail below.

1 on the left end of the mold towards the mold
With the point as the origin, the y-axis is set horizontally and the z-axis is set vertically upward, and the molten metal level at time t and position y is z = ζ (y,
t) [m], ζ (y, t) is the N + 1 term (N ≧
Sum of 1)

[0015]

[Equation 1]

Is approximated by “D” represents time derivative.
k _n [1 / m] is represented by the following equation.

K _n = nπ / L (1 ≦ n ≦ N)
(2) L [m] is the mold width.

X ₀ (t) [m] is the average level of the molten metal surface, d
x _n (t) [m] is the mode displacement of the n-th order vibration mode of the molten metal surface and is represented by the following differential equations.

[0019]

[Equation 2]

G is a gravitational acceleration, and g = 9.8 [m / s ² ].
Is.

V (t) [m / s] is the drawing speed.

W ₀ (dimensionless) and w _n (dimensionless) are expressed by the following equations.

[0023]

[Equation 3]

W (y) (dimensionless) is a distribution of the pouring speed from the nozzle in the y direction and is determined by the size and shape of the nozzle. u (t) [m / s] is the average pouring speed from the nozzle.

The present invention is based on the above findings.

The operation of the present invention will be described in detail below with reference to FIG.

FIG. 1 shows the construction of a pouring amount control system for controlling the molten metal level when the measured molten metal level values at two locations are used in the present invention. This is based on the case of N = 1 in the above model. In FIG. 1, a variable written in a large circle represents a multiplier that multiplies the value of the variable, and a symbol added in a small circle represents an adder. The "plant" is composed of a pouring amount operation device for inputting a pouring amount command value, a nozzle, a mold, a molten metal level process, and a molten metal level detector for outputting a molten metal level measured value.

The "main pouring amount calculator" is a PI controller or PI.
It is realized by using a linear controller such as a D controller or a non-linear controller such as a fuzzy controller.

By using the two-level level detectors, the two levels of the level are horizontally different from each other, y = y ₀ ,
y = y ₁ (y ₀ ≠ y ₁ ), and the melt level measurement values are measured as melt level measurement values 0 ζ ₀ (t) = ζ (y ₀ , t) (5) Level measurement value 1 ζ ₁ (t) = ζ (y ₁ , t) (6) Surface level measurement value 0 and surface level measurement value 1
Is from equation (1)

[0030]

[Equation 4]

It is expressed as From this, x ₀ (t), dx _n
(T) is

[0032]

[Equation 5]

It is expressed as follows. here

[0034]

[Equation 6]

It is

The molten metal level measured value 0 and the molten metal level measured value 1 are input to the modal filter and a of the equation (9) is used.
_The multiplier and the adder that multiply by ₀ and a ₁ are operated as in the equation (8) to output the average level x ₀ (t) of the molten metal surface.

Target surface level and average surface level x ₀
From (t), the pouring amount calculator calculates a pouring amount command value. The purpose of the molten metal level control is to make the molten metal level follow the given target value and to compensate for disturbances that affect the molten metal level. Since the vibration mode displacement of the molten metal level is attenuated, the target control is achieved by compensating for the disturbance that affects the average molten metal level and making the average molten metal level follow the target value. To be done. In the present invention, since the average level of the molten metal surface is calculated by the modal filter, the above control can be realized without being affected by the mode displacement of the vibration mode of the molten metal surface.

With the above, the level of the molten metal is measured at two places, and
The case of using the measured values at the locations has been described with reference to FIG. FIG. 3 shows a case where the molten metal level is measured at three points and the measured values at three points are used. This is N =
Based on case 2.

In this case, the modal filter has three multipliers and two adders, the level of the molten metal measured at three points is input, and the average level of the molten metal is output. The pouring amount command value is calculated from the pouring level target value and the average level of the pouring level by the pouring amount calculator.

The above development is expanded for general N (N ≧ 1) when using the melt level at N + 1 places. In this case, the modal filter has N + 1 multipliers and N adders, inputs the molten metal level measured at N + 1 places, and outputs the average molten metal level. The pouring amount command value is calculated from the pouring level target value and the average level of the pouring level by the pouring amount calculator.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0042]

FIG. 2 shows an example of implementing the present invention. Figure 2
This is an example in which the case where the measured values of the molten metal level at two locations are used. A subtractor and a PI controller were used as the pouring amount calculator.

FIG. 3 is a simulation shot of FIG.
The solid line shows the level transition in the case of the molten metal level control method of the present invention, and the broken line shows the transition in the level of molten metal level in the case of the conventional PI control method.

After the steady state at t <0, in FIG. 3A, at t = 0 [s], the molten metal level target value is +10 [mm].
In FIG. 3B, the level of the molten metal at the left end of the mold when changed is +0.01 at the drawing speed at t = 0 [s].
It shows the molten metal level at the left end of the mold when a disturbance of [m / s] is applied. The horizontal axis represents time and the unit is [s], and the vertical axis represents the molten metal level and the unit is [mm]. The width of the mold is L = 1 [m], and a nozzle having a width of 0.25 [m] is positioned so that the left end of the nozzle and the center of the mold coincide with each other. In the control method of the present invention (example of the present invention), the molten metal level is measured at both ends of the mold.

Therefore, in the equation (9), y ₀ = 0, y ₁ =
If L is set, a ₀ = 0.5, a ₁ = 0.5
.. (10) is obtained. PI transfer function of the controller K _p [1+ (1 _{/ T} i p)] -
・ ・ (11) Various simulations were performed, and in consideration of the stability and responsiveness of the measured value of the molten metal surface level, the respective parameters were: K _p = 4, T _i = 2.5
・ ・ (12) was set. In the PI control method (comparative example), the molten metal level is measured at one left end of the mold. The parameters of the PI controller were set to the same values as above.

FIG. 3A shows how the target value is followed, and FIG. 3B shows how the disturbance is compensated. P
In the I control method (comparative example), the measured value of the molten metal level is oscillating in both cases of following the target value and compensating for the disturbance, whereas in the control method of the present invention (inventive example), Both the tracking of the value and the compensation of the disturbance are performed promptly, and the molten metal level does not substantially vibrate.

[0047]

According to the present invention, the average level of the molten metal surface can be made to follow the target value and the disturbance can be compensated for. In continuous casting, the product quality and yield are improved, the operating ratio is improved, and during operation. Has the effect of safety.

[Brief description of drawings]

FIG. 1 is a block diagram showing a case where a melt level measurement value at two locations is used in the present invention.

FIG. 2 is an embodiment in which a subtracter and a PI controller are used as a pouring amount calculator in FIG. 1, that is, when the measured values of the molten metal level at two locations are used.

FIG. 3 is a diagram showing changes in the molten metal level when the example of the present invention is carried out and when the conventional example is carried out, (a) shows the molten metal level fluctuation when the target value is changed, and (b) shows The fluctuation of the molten metal level when the drawing speed is changed is shown.

FIG. 4 is a block diagram showing a case where measured values of molten metal level at three points are used in the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Tokuda Hiroshi Nishinosu, Oita City, Oita Prefecture 1st Nishinosu Nippon Steel Co., Ltd. Oita Works (72) Kei Kei Mori 1st Nishinosu, Oita City, Oita Prefecture Nippon Steel Co., Ltd. Oita Works

Claims (1)

[Claims] 1. A molten metal surface level control method for a twin-belt continuous casting, (b) molten metal surface level measurements at different two or more positions in the horizontal direction, molten metal surface in (b) above two or more The average level of the molten metal surface is calculated from the level measurement value by a modal filter, (C) the molten metal amount command value is calculated from the molten metal level target value and the average level of the molten metal surface, and (D) the molten metal amount command value is poured. A twin-belt continuous casting molten metal level control method comprising: compensating for disturbances that affect the average molten metal level by outputting the molten metal to a molten metal controller, and causing the average molten metal level to follow a target value.