JPH0751258B2 - 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. A method of detecting a change in the melt level as a temperature change in the mold wall and detecting the melt level by utilizing the change in the eddy current generated in the mold due to the change in the resistivity of the mold wall caused by this change Presenting.

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.

The present invention provides a control method that compensates for disturbances that affect the average level of the molten metal surface, makes the average level of the molten metal surface follow a target value, and positively suppresses vibration of the molten metal surface. With the goal.

[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 The main pouring amount command value is calculated from the average level, (d) the auxiliary pouring amount command value is calculated from the mode displacement of the vibration mode of the molten metal surface, and (e) the main pouring amount command value and the auxiliary pouring amount command value are calculated. By calculating the pouring amount command value and (f) 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 set to the target value. And suppress the vibration of the molten metal surface. Is characterized by.

[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 Figure 1, a variable written in a large circle is a multiplier that multiplies the value of the variable, an addition symbol is written in a small circle, and an subtraction symbol is written in a small circle. Represents a subtractor. Of these, the subtractor is provided with an addition symbol and a subtraction symbol to clearly indicate the order of subtraction.

The "plant" is composed of a pouring amount operation device for inputting a pouring amount command value, a nozzle, a mold, a pouring process, a pouring surface detector for outputting a pouring level measurement value, and the like.

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.

The "auxiliary pouring amount calculator" is a P controller, PD
It is realized by using a linear controller such as a controller or a phase compensator, or a non-linear controller such as a fuzzy controller.

By using the two-level level detectors, two levels y = y ₀ , which are different from each other in the level in the horizontal direction,
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)

[0032]

[Equation 4]

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

[0034]

[Equation 5]

It is expressed as follows. here

[0036]

[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 _{00 of the} equation (9) is obtained.
, A ₀₁ , a ₁₀ , and a ₁₁ are multiplied by a multiplier and an adder, and the average level x ₀
(T) and the mode displacement dx of the primary vibration mode of the molten metal surface
_n (t) is output.

Target surface level and average surface level x ₀
From (t), the main pouring amount calculator calculates the main pouring amount command value. From the mode displacement dx _n (t), the auxiliary pouring amount calculator calculates the auxiliary pouring amount command value. A subtracter calculates the pouring amount command value from the main pouring amount command value and the auxiliary pouring amount command value.

The purpose of the molten metal level control is to make the molten metal level follow a given target value, compensate for disturbances that affect the molten metal level, and suppress vibration of the molten metal level. That is,
At x ₀ (t) and dx _n (t), the disturbance affecting the average level x ₀ (t) of the molten metal surface is compensated, and the average level x ₀ (t) of the molten metal surface is made to follow the target value. The desired control is achieved by asymptotically approaching the mode displacement dx _n (t) of the vibration mode of the surface. In the present invention, Shuchu hot water command value to compensate for the disturbance which affects the average level x ₀ of the molten metal surface (t), to follow the average level x ₀ of molten steel surface (t) to the target value, the auxiliary pouring amount The command value achieves the target control by asymptotically bringing the mode displacement dx _n (t) of the vibration mode of the molten metal surface close to zero.

As described 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 nine multipliers and six adders, the levels of the molten metal measured at three points are input, and the average level of the molten metal and the two molten metal levels are input. The mode displacement of the vibration mode is output. The main pouring amount command value is calculated by the main pouring amount calculator from the target level of the molten metal level and the average level of the molten metal level. An auxiliary pouring amount command value is calculated by the auxiliary pouring amount calculator from the two mode displacements. A subtracter calculates the pouring amount command value from the main pouring amount command value and the auxiliary pouring amount command value.

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) ² multipliers and N (N + 1) adders, and the melt level measured at N + 1 places is input, and the average level of the melt level and the N melt levels are input. The vibration displacement mode of the molten metal surface is output. The main pouring amount command value is calculated by the main pouring amount calculator from the target level of the molten metal level and the average level of the molten metal level. An auxiliary pouring amount command value is calculated by the auxiliary pouring amount calculator from N mode displacements. Other objects and features of the present invention for calculating the pouring amount command value by the subtracter from the main pouring amount command value and the auxiliary pouring amount command value will be apparent from the following description of the embodiments with reference to the drawings.

[0044]

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 main pouring amount calculator, and a phase compensator was used as the auxiliary pouring amount calculator.

FIG. 3 is the simulation tune 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 =
Letting L be, a ₀₀ = 0.5, a ₀₁ = 0.5, a ₁₀ = 0.
_{5, a 11 = -0.5 ··· (} 10) is obtained. The transfer function of the PI controller K _p [1+ (1 _{/ T} i p)]
(11) The transfer function of the phase compensator is f [(p + b) / (p + a)].
・ ・ (12) 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, f = -12, a = 9,
b = 3 ... (13) 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.

[0049]

According to the present invention, the average level of the molten metal surface can be made to follow the target value, the disturbance can be compensated, and the vibration of the molten metal surface can be actively suppressed. It also has the effects of improving yield, improving operating rate, and safety during operation.

[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] FIG. 2 shows a subtractor and a PI as a main pouring amount calculator in the case of using the molten metal level measurement values at two places.
This is an embodiment in which a controller is used and a phase compensator is used as an auxiliary pouring amount calculator.

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 From the level measurement value, the average level of the molten metal surface and the mode displacement of one or more molten metal surface vibration modes are calculated using a modal filter, and (c) the main molten metal amount command value from the molten metal surface level target value and the average metal level of the molten metal surface. (D) The auxiliary pouring amount command value is calculated from the mode displacement of the vibration mode of the molten metal surface, (e) The pouring amount command value is calculated from the main pouring amount command value and the auxiliary pouring amount command value, (F) By outputting the pouring amount command value to the pouring amount controller, the disturbance that affects the average level of the molten metal level is compensated, the average level of the molten metal level follows the target value, and Twin belt continuous casting characterized by suppressing vibration Method of controlling molten metal level.