JPH0368775B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a method for controlling the level of hot metal in continuous casting of thin slabs, and in particular, a method for continuously casting thin slabs in which the pouring amount is adjusted according to fluctuations in the level of the hot slab. This paper relates to a method for controlling the hot water level.

(Prior art) Continuous casting has traditionally been an important part of steelmaking technology, and the current general trend is that there is a shift from large slabs to continuous casting of small, thin slabs. . However, when casting such thin slabs, the cross section is not only small, but also the thickness is thin compared to the width, so even slight changes in casting conditions can cause fluctuations in the level of the molten metal during pouring. In addition, since high-speed casting is required to increase productivity, level control that is highly responsive to the above-mentioned large fluctuations in the level of the molten metal is required.

Even in the conventional continuous casting method, when large slabs are to be produced, for example, as shown in FIG. , the level 5 of the molten metal is appropriately detected by the detection means 6, and when a deviation from the target value, that is, a disturbance occurs due to fluctuations in the casting conditions, the signal is sent to the controller 7, and the level 5 is detected according to the amount. The hydraulic servo valve mechanism 8 is driven to adjust the valve opening degree of the sliding nozzle 9 of the tundish 3. As a result, the flow rate of the molten steel flow 1 from the tundish 3 is adjusted, and the level of the molten steel is controlled.

(Prior Patent Application) The present inventors have previously developed a thin slab continuous casting method in which molten metal is injected from a large tundish into a small tundish through a sliding nozzle, and then allowed to overflow from this small tundish. We proposed a continuous casting method for thin slabs, which can be called a three-stage hot-water supply method, in which cast slabs are poured into a belt-type continuous casting machine through a pouring trough and solidified slabs are pulled out by the movement of the belt.

When the conventional hot water level control technology described above is applied to such a continuous casting method for thin cast slabs, the hot water level in the casting machine is first measured, and the level at the outlet of the large tundish is adjusted according to the amount of deviation from the target setting value. It is conceivable to control the flow rate by adjusting the opening of the nozzle valve, but according to experiments conducted by the present inventors, there is a delay in the response time of the melt level to the valve opening of the sliding nozzle in a large tundish. Because it is large, the first
While the conventional method shown in the figure only requires a delay of about 0.1 to 0.3 seconds, the three-stage hot water supply method described above has a response time delay of more than 10 times that amount.
As described above, it has been found that as long as the conventional simple control method is used, no matter how the control gain of the controller is adjusted, the control accuracy is poor and stable operation is practically impossible. Furthermore, according to the experimental results of the present inventors, for example, when a disturbance occurs in which the nozzle cross-sectional area suddenly expands or contracts by 15%, the control method based only on the simple sliding nozzle valve opening cannot achieve the required accuracy ± The minimum level fluctuation of 17 mm occurred compared to 3 mm. When casting slabs that are thinner than the width at high speed, such as with a belt-type continuous casting machine,
If the level of molten metal in the mold drops rapidly like this, it will become uncontrollable if the response delay is large as mentioned above, and in extreme cases, the mold will become empty and continuous casting will be impossible, or melting will occur from the mold. It was discovered that metal could overflow and become extremely dangerous.

(Objective of the Invention) One object of the present invention is to provide a method for controlling the level of hot water in a belt-type continuous casting machine in a continuous thin slab casting method with good responsiveness.

Another object of the present invention is to respond to a target set value by adjusting the level of the casting machine, which fluctuates in response to various disturbances caused by fluctuations in casting conditions, when casting into a belt-type continuous casting machine in a continuous thin slab casting method. The objective is to provide a method for controlling the process with ease.

Still another object of the present invention is to control the casting process in response to various disturbances caused by fluctuations in casting conditions that occur in the hot water supply system and the drawing system, respectively, during casting into a belt type continuous casting machine in a thin slab continuous casting method using a three-stage hot water supply system. It is an object of the present invention to provide a method for controlling the level of molten metal in a casting machine to a target established value with high precision and responsiveness by adjusting the pouring amount.

(Summary of the Invention) Herein, the present invention provides a belt-type continuous casting system in which molten metal is injected from a large tundish through a sliding nozzle into a small tundish, and then overflows from the small tundish through a tiltable casting trough. In continuous casting of thin cast slabs, in which the molten metal is poured into a casting machine, the molten metal is solidified by moving a belt, and the resulting slab is pulled out, the level of the melt in the belt-type continuous casting machine is measured and the deviation from a preset target value is measured. is detected, and based on this deviation signal, the gutter tilting angle of the tiltable casting gutter is adjusted, thereby controlling the amount of casting from the small tundish into the belt-type continuous casting machine, and at the same time, the gutter tilting angle is adjusted. angle is measured, the deviation from the horizontal angle is detected, and based on this deviation signal, the opening degree of the valve of the sliding nozzle of the large tundish is adjusted to control the amount of hot water supplied to the small tundish; The hot water level in continuous casting of thin slabs is characterized in that the hot water level is stably and precisely controlled to a set target value by controlling the tilting angle of the gutter displaced by controlling the hot water level to always be at a horizontal level. This is a level control method.

The above-mentioned level type continuous casting machine is a casting machine that has a wide mold that is tilted downward from horizontal and partitioned by opposing twin belts, and is particularly suitable for continuous casting of thin slabs that are thinner than their width. I say. Furthermore, a thin slab generally refers to a slab that is thinner than its width, but in a narrow sense it includes slabs with a thickness of about 5 to 100 mm.

(Aspects of the Invention) The present invention will be described in more detail below with reference to the accompanying drawings.

FIG. 2 is a schematic diagram showing the configuration of continuous thin slab equipment to which the method of controlling the level of hot water according to the present invention is applied.

That is, the molten metal (molten steel) 22 in the ladle 21 is injected into the large tundish 24 through a sliding nozzle or stopper nozzle 23, and further into the small tundish 24 through the sliding nozzle 25 attached to the bottom of the large tundish 24. 26. An overflow port 27 and a casting gutter 28 are provided on the outlet side of the upper edge of the small tundish 26, and the molten metal 22 passes through the casting gutter 28 into a belt-type continuous casting machine (hereinafter simply referred to as a caster or casting machine). 29 is injected. Casting machine 2
9, the entrance side of the upper and lower belt roll mechanisms 30 and 31;
Belts 32 and 33 are stretched between the outlet sprockets, and the molten metal 22 from the small tundish 26 is injected between both belts, and after being injected, the molten metal 22 is sent to a primary cooling spray zone (not shown). It is cooled and solidified. A drive motor 35 is connected to the entrance sprocket 34 of the upper and lower belt roll mechanisms 30 and 31, and the rotation of this motor causes the primarily solidified slab to be placed on the downstream side of the casting machine 29. The current is sent to a secondary cooling zone 36 consisting of a plurality of rolls.

Since the casting gutter 28 is intended to control the amount of casting from the small tundish 26 by adjusting its tilt angle, it is preferably formed integrally with the small tundish 26 as shown in the illustrated example.
In that case, the gutter tilting angle is adjusted by tilting the entire small tundish 26 using the casting tip of the casting gutter 28 as a fulcrum. In this way, the gutter tilting mechanism uses the casting tip as a fulcrum to move the small trough 2.
There is no particular restriction as long as the entire 6 can be tilted freely,
It is sufficient if a drive mechanism such as a motor or hydraulic pressure is provided to enable the tilting as appropriate, and in that case, for example, the entire small tundish 26 may be supported so as to be swingable. In the illustrated example, the gear mechanism 3 supports the small tundish 26 from the bottom at positions A and B, and is driven by the rotational force of a motor 37 to adjust the height of the bottom of the tundish at each position A and B.
8 and 39, respectively. By moving the small tundish 26 up and down while keeping the heights at both positions at a constant ratio, the whole can be tilted using the tip of the casting gutter as a fulcrum. Therefore, the tilting angle of the small tundish 26 itself becomes the same as the gutter tilting angle, and the tilting angle of the small tundish 26 can be replaced by the gutter tilting angle. In addition,
In the figure, reference numeral 40 is a slag cutting plate, which serves to prevent fluctuations in the level of hot water on the inlet side of the small tundish from being transmitted onto the gutter 28.

FIG. 3 is a schematic explanatory diagram showing an enlarged view of the tilting angle adjustment mechanism of the small tundish 26 mentioned above.
The same reference numerals represent the same members. The small tundish 26, which is pivotally supported by movable struts 43 and 44 at points 41 and 42, is moved up and down at a constant ratio by gears 38 and 39 driven by a motor 37 via a worm mechanism. Tilt angle θ of the small tundish 26 corresponding to the gutter tilt angle of the casting gutter 28
can be quickly adjusted according to fluctuations in the hot water level by operating the above-mentioned mechanism.

The present invention relates to a method for controlling the level of molten metal on the inlet side of the casting machine in the continuous thin slab casting apparatus as described above, and the specific control operation will be explained as follows.

In addition, when starting the operation of the belt-type continuous casting machine of the present invention, the amount of molten metal injected through the sliding nozzle of the large tundish cannot be accurately measured at first, so it takes time to reach steady operation. During this period, fluctuations in the drawing speed and wide fluctuations in the level of the molten metal may be experienced. Therefore, even in the present invention,
Before starting the operation, the flow rate of molten metal injected from the large tundish to the small tundish was actually measured, and the sliding nozzle was opened to match the amount poured into the caster calculated based on this actual measurement plan with the target pouring amount. In addition, the flow rate of molten metal from the large tundish to the small tundish after control is actually measured, and based on this, the drawing speed of the caster during casting is set by calculation. The levels are automatically and quickly matched to their respective target values, and steady operation is quickly brought about.

() Molten metal level control by tilting the gutter; First, we will explain the casting machine liquid level control by tilting the pouring gutter. In Fig. 2, the detection of the hot water level H in the mold on the entrance side of the casting machine is as follows:
For example, the measurement is performed through an optical measuring device 103 composed of an optical fiber 100, a camera 101, and a position calculation circuit 102. That is, in the illustrated example, changes in brightness near the melt surface on the belt dam block side, that is, in the mold, are captured by the camera 101 through the optical fiber 100, converted into electric current, and inputted to the position calculation circuit 102.
A calculation device 1 that outputs a position signal and controls the signal.
Enter into 04. The control calculation device 104 compares the level with a preset target level H*, and based on the deviation from the target value, controls the motor drive device 105 for tilting the pouring gutter according to the following formula.
Calculate the control signal U ₁ (t) input to the .

U ₁ (t)=Kp ₁ [e ₁ (t) + 1/T _I1 ∫ ^t _p e ₁ (t) dt+T _D1 de ₁ (t)/dt]...(
1) t: Time e ₁ (t)=H*-H(t) H(t): Casting machine entrance side melt level H* : Target melt level Kp ₁ , T _I1 , T _D1 : Proportional, integral , differential control gain U ₁ (t): gutter tilting control signal The signal U ₁ (t) calculated by the above equation (1) is
The input is input to the gutter tilting motor drive device 105, and through the rotation of the motor 37, the casting gutter,
That is, the small tundish 26 is tilted, the amount of pouring from the small tundish is adjusted, and the molten metal level H is controlled to the target level H*. In other words, when the hot water level H rises due to disturbance, the gutter tilting angle is reduced by the amount specified by the signal U ₁ (t) corresponding to the proportional, integral, and differential values of the deviation, thereby reducing the pouring amount. Then, the hot water level H is controlled to the target level. The same is true for the reverse case, except that the gutter tilting angle is increased this time. Since the pouring amount changes very quickly with respect to the tilting of the gutter, rapid level control is achieved.

() Control of the gutter tilting angle θ: Next, the control of the gutter tilting angle θ by operating the valve opening of the sliding nozzle 25 on the outlet side of the large tundish 24 will be explained.

First, the gutter tilting angle θ, that is, the change in the bottom position of the small tundish 26 is detected by the detection device 106, and this detected position is converted into a current signal. A current signal is input to the control calculation device 104. The mechanism of this detection device 106 may be one that optically detects the position, that is, the angle, or a control signal U ₁ to the aforementioned motor 37.
(t) may be obtained by calculation. The control calculation device 104 compares the target angle θ* set in advance, calculates the deviation e 2 '(t) from the target value, and calculates the deviation e ₂ '(t) from the target value based on the following equation (2).
A control signal U ₂ (t) for valve opening/closing input to the hydraulic control device 107 is calculated.

U ₂ (t)=Kp ₂ [e ₂ (t) + 1/T _I2 ∫ ^t _p e ₂ (t) dt+T _D2 de ₂ (t)/dt]...(
2) t: Time e ₂ (t) = θ*-θ(t) θ*: Target gutter tilting angle θ(t): Gutter tilting angle Kp ₂ , T _I2 , T _D2 : Proportional, integral, differential control gain U ₂ (t): Valve opening/closing control signal Valve opening/closing control signal U ₂ calculated using equation (2) above
(t) is input to the hydraulic control device 107. This hydraulic control device consists of a solenoid valve and a pressure control circuit (not shown), and controls the advancement and retraction of the rod 109 into and out of the hydraulic cylinder 108 and the amount of oil sent to each oil chamber based on the control signal described above.
The rod 109 moves back and forth, and the valve slide unit connected to it moves back and forth, causing the sliding nozzle 25
The valve is designed to open and close.

The valve opening degree is detected by a position detector 110 of the slide portion, and is inputted to the control calculation device 104 as a feedback signal. The valve opening degree is controlled as described above, and the large tandem
The amount of melt oil supplied from is adjusted, and the gutter tilting angle θ is controlled to a predetermined target value θ*. Usually, the pouring ratio is controlled so as to return to the horizontal (θ*=0).

For example, if the gutter inclination angle θ is a positive value,
The signal U ₂ according to the proportional, integral and derivative of its deviation
At (t), the valve opens, the supply amount to the small tundish increases, and the oil level rises, so that the gutter inclination angle θ decreases and is controlled to return to horizontal. The same applies to the opposite case.

By the first and second two connected controls explained above, firstly, the level of the hot water in the casting machine 29 is controlled by a quick-responsive gutter tilting operation, and then the gutter inclination angle displaced by this first control is By returning the oil level to a normal horizontal level, it becomes possible to control the oil level with high accuracy and keep the gutter tilt angle always close to horizontal.

Next, the present invention will be further explained with reference to Examples.

Example: 600mm x 40mm
Thin slabs with a cross section of mm were continuously cast at a casting speed of 6 m/min. At this time, we looked at the fluctuations in the molten metal level when a disturbance was applied that suddenly expanded the cross-sectional area of the sliding nozzle, which supplies molten steel from the large tandem to the small tandem, by 15%. For comparison, we also used the same device to control the oil level by simply controlling the valve opening as a conventional method. The control results according to the conventional method are shown graphically in FIG. 4, while the control results according to the method of the present invention are also shown graphically in FIG.

As is clear from the results shown, the amount of hot water supplied from the nozzle increases instantaneously due to the above disturbance, and after a certain time delay, the hot water level rises, and then gradually recovers as the control mechanism operates. .

In the conventional method, as shown in Figure 4, no matter how you adjust the control gain, the required accuracy is ±3 mm, but the minimum accuracy is 17 mm.
Level fluctuations of mm occurred. Moreover, it takes more than 80 seconds to recover. In contrast, in the control method according to the present invention, first, in response to an increase in supply amount due to disturbance,
When a rise in the level of hot water is detected, the gutter tilting angle θ is immediately increased to control the pouring amount, and at the same time, the valve of the sliding nozzle of the large tundish is opened in order to suppress the rise in angle θ. The angle was controlled in the closing direction, and as mentioned above, despite disturbances, control that fully satisfied the required accuracy of ±3 mm was always possible, and overall stable, quick, and accurate control was achieved.

As is clear to those skilled in the art from the foregoing description, according to the present invention, it is possible to compensate for changes in the level of molten metal in the mold by increasing or decreasing the amount of molten metal poured into the mold from the small tundish. On the other hand, it is possible to obtain a highly sensitive response because the change in the amount of molten metal received from the large tandem to the small tundish is immediately responded to the change in the amount poured into the mold.
This makes it possible to further improve the accuracy of controlling the level of the molten metal in the mold, and further improve the quality of the thin slab.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram showing a conventional control system; Fig. 2 is a schematic explanatory diagram of continuous casting equipment used in the present invention; Fig. 3 is an enlarged view of a part of the gutter tilting mechanism in Fig. 2. FIG. 4 is a graph showing the results of hot water level control by the conventional control system; and FIG. 5 is a graph showing the results similarly according to the present invention. 21: Ladle, 22: Molten metal, 24: Large tunic, 26: Small tunic, 28: Casting gutter,
29: Casting machine, 102: Position calculation circuit, 104:
Control calculation device, 105: Motor drive device, 10
6: Detection device, 107: Hydraulic control device, 110:
position detector.

Claims (1)

[Claims] 1 The molten metal injected from the large tundish into the small tundish through the sliding nozzle,
Next, in continuous casting of thin slabs, the molten metal is overflowed from the small tundish and poured into a belt type continuous casting machine through a tiltable pouring trough, and the belt movement solidifies the molten metal and draws the obtained slab. The level of the continuous casting machine is measured, the deviation from the preset target value is detected, and based on this deviation signal, the gutter tilting angle of the tiltable casting gutter is adjusted, thereby At the same time, the amount of pouring from the tundish into the belt-type continuous casting machine is controlled, the gutter tilting angle is measured, the deviation from the horizontal angle is detected, and based on this deviation signal, the sliding nozzle of the large tundish is controlled. The opening of the valve is adjusted to control the amount of hot water supplied to the small tundish, and the gutter tilting angle, which has been displaced by the hot water level control, is always kept at a horizontal level, thereby bringing the hot water level to the set target value. A method for controlling the level of hot water in continuous casting of thin slabs, which is characterized by stable and accurate control.