JPH0453608B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a method for continuously casting thin slabs using a belt-type continuous casting machine, and more particularly, to a method for continuously casting thin slabs using a belt-type continuous casting machine, and in particular, a method for continuously casting thin slabs using a belt-type continuous casting machine, in which the drawing speed is controlled to control the melt level. This invention relates to a continuous casting method for slabs.

(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, not only the cross section becomes smaller, but also the thickness becomes thinner compared to the width, so even slight changes in casting conditions can cause large fluctuations in the level of the molten metal during pouring. In addition, since high-speed casting is required in order to increase productivity, level control that is highly responsive to the above-mentioned large fluctuations in the level is required.

Even in the conventional continuous casting method, when large slabs are to be produced, for example, as shown in FIG. , the hot water surface level 5 is detected by the detection means 6 as appropriate, 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 oil pressure is adjusted according to the amount. The 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 system, in which the cast slabs are poured into a belt-type continuous casting machine through a pouring trough, and the solidified slabs are pulled out by rolling motion.

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.
It has been found that as long as the conventional simple control method is used, the control accuracy is poor and stable operation is virtually impossible no matter how the control gain of the controller is adjusted. Furthermore, according to the experimental results of the present inventors, for example, when there is a disturbance in which the nozzle cross-sectional area suddenly expands or contracts by 15%, the required accuracy is ±3 mm using a control method based only on the simple sliding nozzle valve opening. However, a minimum level fluctuation of 17 mm occurred. 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 becomes uncontrollable when the response delay is large as described above, and in extreme cases, the mold becomes empty, making continuous casting unnecessary, or melting from the mold. It was discovered that metal could overflow and become extremely dangerous.

On the other hand, it is possible to control the level by adjusting the drawing speed instead of controlling the valve opening, but varying the drawing speed is not desirable in terms of slab quality, and a method of simply adjusting the drawing speed is also considered. Not practically appropriate.

(Object of the Invention) One object of the present invention is to provide a method for continuous casting of thin slabs that realizes responsive control of the level of hot water in a belt-type continuous casting machine in the continuous casting method of thin slabs. be.

Another object of the present invention is to improve the responsiveness of the melt level of the casting machine to a target setting value, 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. It is an object of the present invention to provide a continuous casting method for thin slabs that can be performed with good control.

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 molten metal level of a casting machine to a target setting value with high precision and responsiveness by adjusting the drawing speed.

(Summary of the Invention) Here, the present invention provides a method for injecting molten metal from a large tundish into a small tundish through a sliding nozzle, then overflowing the molten metal from the small tundish, and passing it through a casting trough into a belt-type continuous casting machine. In a continuous thin slab casting method in which the molten metal is solidified and the obtained slab is drawn by casting, motor-driven belt movement, the level of the melt in the belt-type continuous casting machine is measured and the level is adjusted to a preset target value. Based on this deviation signal, the drive speed of the motor that moves the belt is adjusted to control the drawing speed, thereby accurately controlling the level of the melt to the set target, and at the same time controlling the drawing speed. The speed is detected, and the amount of hot water supplied to the small tundish is controlled by adjusting the opening degree of the valve of the sliding nozzle of the large tundish based on the signal of the deviation from the set target value, and the amount of hot water supplied to the small tundish is adjusted to the level of the hot water. The thin slab is characterized in that the molten metal is poured and the slab is pulled out while the level of the molten metal is stably and precisely controlled to a set target value by always controlling the withdrawal speed displaced by the control of This is a continuous casting method.

Here, the belt-type continuous casting machine is a casting device that has a wide mold that is inclined downward from the horizontal and partitioned by opposing twin belts, and is particularly suitable for continuous casting of thin slabs that are thin in thickness compared to the width. In addition, thin slabs generally refer to slabs that are thinner than their width, but in a narrower sense, they include 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 passed through the sliding nozzle or stopper nozzle 23.
is injected into the large tundish 24 through the
Further, it is injected into the small tundish 26 through a sliding nozzle 25 attached to the bottom of the large tundish 24. Small tandate 26
An overflow port 27 and a casting gutter 28 are provided on the outlet side of the upper edge, and the molten metal 22 is injected into a belt-type continuous casting machine (hereinafter simply referred to as a caster or casting machine) 29 through the casting gutter 28. be done. In the casting machine 29, belts 32 and 3 are installed between the inlet and outlet sprockets of the upper and lower belt roll mechanisms 30 and 31, respectively.
3 is stretched between both belts, and molten metal 22 from a small tundish 26 is injected between both belts. After being injected, the molten metal 22 is cooled and solidified by a primary cooling spray zone (not shown). Inlet sprocket 34 of upper and lower belt roll mechanisms 30 and 31
A driving motor 35 is connected to the casting machine 29, and the rotation of this motor transports the primarily solidified slab to a secondary cooling zone 36 consisting of a plurality of rolls installed downstream of the casting machine 29.

The casting trough 28 is preferably formed integrally with the small tundish 26 as shown in the illustrated example. In the figure, reference numeral 37 is a slag cutting plate, which has the role of not transmitting fluctuations in the molten metal level on the inlet side of the small tundish onto the casting gutter 28.

The present invention relates to a method for continuously casting thin slabs while controlling the molten metal level on the inlet side of the casting machine in the above-mentioned continuous casting machine for thin slabs.The specific control operation thereof will be explained below. Then, it is 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, in the present invention, at the start of operation, the flow rate of molten metal injected from the large tundish to the small tundish is actually measured, and the target amount of poured into the caster is calculated based on the measured results. The opening degree of the sliding nozzle is controlled to match the pouring amount, and then 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 during casting of the caster is set by calculation. As a result, the withdrawal speed of the caster and the molten metal level are automatically and quickly brought into agreement with their respective target values, and steady operation is quickly brought about.

() Molten metal level control by drawing speed; First, casting machine liquid level control by adjusting the drawing speed of a belt-type continuous casting machine will be explained. In FIG. 2, the detection of the hot water level H in the mold on the entrance side of the casting machine is performed using, for example, an optical fiber 10.
0, through an optical measuring device 103 composed of a camera 101 and a position calculation circuit 102.
That is, in the case of the illustrated example, changes in brightness near the melt surface on the belt dam block side, that is, inside 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 to generate a position signal. and inputs the signal to the control arithmetic unit 104. In the control calculation device 104,
A comparison is made with a preset target hot water level H*, and based on the deviation from the target value, a control signal U ₁ (t) to be input to the motor drive device 105 for adjusting the drawing speed is determined by the following formula. calculate.

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 inlet melt level H*: Target melt level Kp ₁ , T _I1 , T _D1 = Proportional, integral, differential control gain U ₁ (t): Drawing Speed Control Signal The signal U ₁ (t) calculated by the above equation (1) is input to the above-mentioned drawing speed adjustment motor drive device 105, and through the rotation of the motor 35, the drawing speed is controlled, that is, the drawing speed from the caster is controlled. The amount of withdrawal is adjusted, and the hot water level H is controlled to the target level H*. In other words, when the hot water level H rises due to a disturbance, the drawing speed is increased by the amount specified by the signal U ₁ (t) corresponding to the proportional, integral, and derivative of the deviation, thereby increasing the drawing amount. control to lower the hot water level H to the target level. The same applies to the reverse case, except that the drawing speed is reduced this time. Since the drawing amount changes very quickly with respect to the drawing speed change, rapid hot water level control is realized.

() Control of drawing speed (v): Next, drawing speed v control by controlling the valve opening of the sliding nozzle 25 on the outlet side of the large tundish 24 will be explained.

First, a change in the drawing speed v, for example, the rotational speed of the motor 35, is detected by the detection device 106, and this detected amount is converted into a current signal. A current signal is input to the control calculation device 104. This detection device 106
The mechanism is, for example, one that optically detects speed, that is, position change, or the above-mentioned motor 35.
It may be obtained by calculation from the control signal U ₁ (t) to the control signal U 1 (t). The control calculation device 104 performs a comparison with a preset target drawing speed v*,
The deviation e ₂ (t) from the target value is calculated, and the control signal U ₂ (t) for opening and closing the valve, which is input to the hydraulic control device 107, is calculated based on the following equation (2).

U ₂ (t) = Kp ₂ [e ₂ (t) + 1/T _I2 ∫ ^t _p e ₁ (t) dt + T _D2 de ₂ (t) / dt] …(2) t: Time e ₂ (t) = v*-v(t) v*: Target drawing speed v(t): Drawing speed Kp ₂ , T _I2 , T _D2 : Proportional, integral, differential control gain U ₂ (t): Valve opening/closing control signal (2) above Valve opening/closing control signal U ₂ (t) calculated by the formula
is input to the hot water pressure 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 valve sliding nozzle 25 moves forward and backward, and the valve sliding portion connected thereto moves back and forth, thereby opening and closing the valve of the sliding nozzle 25.

The valve opening degree is detected by a position detector 110 of the slide portion, and is inputted to the control calculation device 106 as a feedback signal. As described above, the valve opening degree is controlled, the amount of molten metal supplied from the large tundish 24 is adjusted, and the drawing speed (v) is controlled to a predetermined target value (v*).

For example, if the drawing speed v is larger than the target setting value, a signal corresponding to the proportional, integral, and differential of the deviation
The valve closes due to U ₂ (t), the amount of water supplied to the small tundish decreases, and the level of hot water falls, so that the drawing speed v decreases and is controlled to return to the target drawing speed. The same applies to the opposite case.

When performing the first and second two connected controls as described above, first, the level of the molten metal in the casting machine 29 is controlled by a fast-responsive drawing speed adjustment operation, and then the first control controls the molten metal level. By returning the drawing speed to the normal target drawing speed,
This makes it possible to precisely control the hot water level and keep the drawing speed close to the target value at all times.

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 equipment to control the hot water level by simply controlling the drawing speed as a conventional method. The control results according to the conventional method are shown in a graph in FIG. 3, while the control results according to the method of the present invention are shown in the same graph 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 Fig. 3, it was possible to secure the required accuracy of ±3 mm regarding the level of the molten metal, but the drawing speed drifted, which was unfavorable in terms of slab quality. In contrast, in the control method according to the present invention, in response to an increase in the supply amount due to disturbance, as soon as a rise in the level of the hot water is detected, the drawing speed (v) is increased to reduce the fluctuations in the level to a certain level. At the same time, the valve opening of the sliding nozzle of the large tundish is controlled in the closing direction in order to suppress the increase in the drawing speed (v), and the necessary level accuracy is maintained despite the above-mentioned disturbances. It was always possible to fully satisfy ±3 mm and control the drawing speed close to the target value, and overall stable, quick, and accurate control was achieved.

As is clear to those skilled in the art from what has already been explained above, according to the present invention, the drawing speed (v) can be varied in immediate response to variations in the level of molten metal in the mold to compensate for the variations; In response to fluctuations in the amount of hot water supplied to the mold, changes in the amount of hot water received from the large tundish to the small tundish can be immediately responded to the fluctuations in the drawing speed v, so a highly sensitive response can be obtained. This makes it possible to further improve the control accuracy of the molten metal level within the mold, and further improve the quality of the thin slab.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing a conventional control system; Fig. 2 is a schematic diagram of continuous casting equipment used in the present invention; and FIG. 4 are graphs also showing the results 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, 106 ... 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 the thin slab continuous casting method, the molten metal is overflowed from the small tundish and poured into a belt-type continuous casting machine through a casting trough, and the molten metal is solidified and the obtained slab is pulled out by motor-driven belt movement. The level of the melt in the belt-type continuous casting machine is measured, the deviation from the preset target value is detected, and based on this deviation signal, the driving speed of the motor that moves the belt is adjusted to adjust the drawing speed. At the same time, the drawing speed is detected and the opening degree of the valve of the sliding nozzle of the large tundish is controlled based on the signal of the deviation from the set target value. The hot water level is controlled stably and accurately to the set target value by controlling the amount of hot water supplied to the small tundish by adjusting the water level, and by always controlling the drawing speed, which is displaced by the hot water level control, to a constant value. A method for continuously casting thin slabs, characterized by casting molten metal and drawing slabs.