JPH01309767A - Method and device for cutting slag in continuous casting - Google Patents

Abstract

PURPOSE:To surely execute slag-cut in continuous casting by forming magnetic field in a nozzle at bottom part of a ladle, detecting electromotive force generating at the time when molten metal passes through the magnetic field and stopping pouring apparatus into a tundish from the ladle at the time of charging the electormotive force. CONSTITUTION:The magnetic field is generated in the nozzle 4 at the bottom part of the ladle 1 with an exciting unit 22 and magnetic poles 16a, 16b. The electromotive force generating at the time when the molten metal passes through the magnetic field in the nozzle 4, is detected with an electrode 17. The change of the electromotive force is gotten with an amplifier 23, filter 24 and computing element 25 ad the pouring operation into the tundish from the ladle 1 is stopped at the time of changing the electromotive force. The magnetic pole is used with an electromagnetic coil and set as attachable/detachable to the fixed nozzle. By this method, the slag-cut in the continuous casting can be surely executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for cutting slag in a ladle in continuous casting operation of molten metal.

[Conventional technology]

During the pouring of molten metal from the ladle into the tundish during continuous casting operation, when the molten slag in the ladle is entrained and injected into the tundish, SiO,
, non-metallic inclusions such as MgO are mixed in, and these appear as defects in the rolled product after rolling this slab, resulting in adverse effects such as a decrease in quality or yield, and this causes problems in the continuous casting operation. In this case, one ship uses a method in which the slag is cut by visually identifying the difference in color between the molten metal and molten slag during pouring from the ladle into the tundish. An open injection is generally required to make this identification. In this oven pouring method, molten steel is exposed to air between the ladle and the tundish, and a nitrogen absorption effect of about 10 ppm usually occurs. Particularly in special steel grades such as Ti-containing steel grades, such nitrogen absorption becomes TiN-based inclusions that are mixed into the cast slab, resulting in (1) a decrease in quality and (2) a decrease in yield.

In order to prevent such nitrogen absorption, open injection has been stopped and a long nozzle (hereinafter sometimes abbreviated as LN) sealed with Ar has been used for that part. If used, it becomes impossible to cut the slag visually. Therefore, various slag cutting methods have been developed to replace visual inspection.

For example, Japanese Patent Application Laid-Open No. 60-148652 detects the vibration of LN with a vibration detector, and detects changes in the frequency caused by the difference in specific gravity and viscosity between molten metal and molten slag, thereby detecting slag outflow. Disclose the method of detection. Further, Japanese Patent Application Laid-open No. 55-97847 discloses a method of detecting slag outflow by providing a detection coil in a nozzle and capturing the difference in electrical conductivity between molten metal and molten slag as an impedance change. In addition, a method using vibration of a tundish as shown in JP-A-57-112964, and a method based on the difference in conductivity between molten metal and molten slag as shown in JP-A-55-159145 have also been proposed.

[Problems to be solved by the invention C] Each of the slag cut detection methods proposed in the above-mentioned publications has its advantages and disadvantages, but the vibration measurement method proposed in Japanese Patent Application Laid-Open No. 60-148652 detects slag cut detection from the LN support part, ladle, etc. The problem is that vibrations within the factory are picked up and become noise, making it impossible to accurately detect the target vibrations. The measurement method based on impedance changes disclosed in Japanese Patent Application Laid-Open No. 55-97847 has a problem in that the detection sensitivity decreases due to the adhesion of metal, alumina, etc. to the inner surface of the nozzle. Also, JP-A-57-112964 and JP-A-5
It cannot be denied that the conductivity measurement method disclosed in No. 5-159145 similarly lacks measurement reliability and stability.

[Means to solve problems]

According to the present invention, which was made to solve the above problems, in a continuous casting method for supplying molten metal from a ladle to a mold via a tundish, a nozzle at the bottom of the ladle for pouring metal from the ladle to the tundish is provided. Form a magnetic field within the
Provided is a slag cutting method in continuous casting, which is characterized by detecting the electromotive force when the molten metal passes through the magnetic field inside the nozzle, and stopping the pouring operation from the ladle to the tundish at the point at which the electromotive force changes. do. As a device for carrying out this method, a long nozzle extending downward is removably connected to a fixed nozzle installed at the bottom of a ladle for storing molten metal through a sliding nozzle that functions as a valve. A slag in continuous casting, in which a magnetic pole and an electrode are arranged perpendicularly to each other on the outside of the fixed nozzle, and the electromotive force induced in the electrode is used as a detection signal to open and close the sliding nozzle. Provide cutting equipment. In this case, preferably the magnetic pole is composed of an electromagnetic coil, and the electromagnetic coil is removably installed in a fixed nozzle, and when the time for slag cutting approaches, the electromagnetic coil is set in the fixed nozzle. .

Although the present invention can be applied to any continuous casting of conductive molten metal, the present invention will be described in detail below using the case of molten steel as an example.

〔Example〕

Figure 1 shows a typical example of equipment for continuous casting of molten steel. The hot water is supplied to the tundish 5 through the nozzle (LN) 4, and the mold 7 is supplied through the injection nozzle 6 at the bottom of the tundish 5.
injected continuously.

The slab 8 is continuously cast. 1M4 is removably attached to a fixed nozzle 9 fixed to the bottom of the ladle 1 via a sliding nozzle 10 that functions as a valve. The injection amount of the molten steel in the tundish 5 is controlled by a stopper 11 which opens and closes the upper opening of the injection nozzle 6, and the injection is started and stopped.

In such continuous casting, it is desirable that the molten steel 3 contained in the ladle 1 is fed into the tundish 5 in a state where the molten steel 3 is separated from the molten slag 2. It is accurate and easy to do.

FIG. 2 shows the main parts of the slag cutting device according to the present invention.
A fixed nozzle 9 is fixedly installed at the bottom of the ladle l, projecting downward from the outer surface 13 of the ladle bottom and having an upper end communicating with the bottom opening 12 of the ladle and a lower end connecting to the sliding nozzle 10. A flange portion 14 is fixedly provided on the lower end side of the fixed nozzle 9. The main body of the sliding nozzle 10 consists of a disk-shaped disk having an opening 15 in the center, and this disk is set so as to be horizontally slidable with respect to the flange portion 4 of the fixed nozzle 9. This sliding movement is performed by the reciprocating movement of the piston P by the cylinder C. The long nozzle (
LN) 4 is detachably connected to the sliding nozzle IO. In the present invention, the magnetic pole 16 and the electrode 17 are arranged perpendicularly in the fixed nozzle 9, and the magnetic pole 16
to form a magnetic field in the fixed nozzle 9 and to pass across this magnetic field? The electrode 17 detects an electromotive force (usually a voltage signal) due to electromagnetic induction generated by the 8W4 and the molten slag.

FIG. 3 is a perspective view showing how the magnetic pole 16 and electrode 17 are attached. As shown in the figure, magnetic poles 16a and 16b are placed opposite each other with the fixed nozzle 9 in between, and these magnetic poles 16a and 16b are magnetized by energizing the electromagnetic coil 18.

Since the fixed nozzle 9 is made of refractory material, the magnetic flux passes through the refractory wall, and a magnetic field is formed in the direction across the inside of the fixed nozzle 9. Electrodes 17a and 17b (the 17b side is hidden and cannot be seen) are placed at horizontal level positions where the magnetic poles 16a and 16b are installed. That is, the magnetic pole 16 and the electrode 17 are arranged orthogonally at the same horizontal level position. The electromagnetic coil 18 and the magnetic poles 16a and 16b attached thereto are integrally supported by a support rod 20, and by reciprocating the support rod 20 in the horizontal direction of the arrow shown in the figure, the magnetic poles 16a and 16b are fixed. It is detachable from the nozzle 9. In the illustrated example, the electrodes 17a and 17b are fixed to the outer wall of the fixed nozzle 9, but they may also be fixed to the flange part 14 of the fixed nozzle 9, or they can be attached to the support rod 20 to form the magnetic poles 16a and L6b. Similarly, the support rod 20 may be made removable; however, it is convenient to attach the support rod 20 to a support frame (not shown) of the long nozzle 4. After the long nozzle 4 is set and injection of molten steel is started, when the end of injection approaches, the support rod 20 is advanced and set in the fixed nozzle 4. After completing this set, a current is applied to the TM and m coils 18, and the Ti1 pole 16a
A magnetic field is generated between the magnetic poles 16b and 16b, and slug cutting is performed using the above-described method. After the slag cutting is completed, the electromagnetic coil 18, which is integrally supported with the magnetic pole 16, is moved back and placed on standby.

By attaching the electromagnetic coil only when necessary in this manner, deterioration of the electromagnetic coil due to heat in a high-temperature environment can be prevented, and the life span can be significantly extended, detection accuracy can be improved, and reliability stability can be improved.

Further, as shown in FIGS. 1 and 2, the ladle 1 usually has a fixed nozzle 9 and a flange portion 14 at its bottom.
A sliding nozzle 10, and a cylinder C that reciprocates this nozzle 10 in a slidable manner are integrally supported.

As mentioned above, the ladle 1 is detachably connected to the long nozzle 4 which is positioned and supported by the tundish 5. Therefore, such ladle 1 is exchanged and supplied one after another to the long nozzle 4 supported in this way, and the molten steel 3 in each ladle is
Continuous casting is performed while injecting the liquid into the tundish 5 through the long nozzle 4.

In this way, continuous casting is carried out while the ladle 1 is being exchanged and supplied. As shown in FIG. Alternatively, if it is set back and installed in a removable manner, the magnetic pole 16 and the TL+D coil 18 will not be damaged (and they will not get in the way, allowing for good operability and efficient replacement and supply of the ladle 1. I can do it.

FIG. 4 is for explaining the principle of the slag cutting device according to the present invention. As shown in the figure, when a magnetic field is applied by the magnetic poles 16a and 16b to the fixed nozzle 9 through which molten steel flows, the slag cutting device is placed at a position perpendicular to the magnetic field. Provided electrodes 17a, 17
An electromotive force is generated in b according to the flow velocity of the molten steel. This electromotive force changes depending on the flow rate of molten steel, the nozzle diameter, etc., and is generally given by the following formula.

K4...(1) However, in the above formula, E: electromotive force (mV).

B: Magnetic flux density (gauss).

V: Average flow velocity of molten steel (cm/s).

d: Nozzle inner diameter (cm).

K1: Nozzle wall short path effect correction number.

K: Terminal effect correction coefficient of I field.

K: Temperature effect correction coefficient of electromagnetic coil.

K4: Nozzle thermal expansion correction coefficient.

It is.

Here, is called the Elrod correction coefficient and is given by the following formula.

2(d/D) D = nozzle outer diameter [C steel].

ρ: Specific resistance of molten steel, 140×to- for molten metal
- [Ω, cm], 1 to 7 [Ω, cIl for molten slag
] Degree 9 τ: Contact resistance between molten steel and nozzle [Ω, C錡2
].

It is.

In equation (1), 2 is an output reduction coefficient caused by an eddy current generated at the magnetic field end of the nozzle exit portion, and 4 is a value determined by the magnetic pole and nozzle material used. Although these are difficult to determine by calculation, they can be easily determined by several experimental values using the device.

However, these values do not change due to the molten metal and molten slag passing through the fixed nozzle 9.
The only change term that changes due to the passage of the molten metal and molten slag is +.

This is because the specific resistance values of the molten metal and the molten slag are greatly different in the calculation formula (2) of formula 1.

The value of is different for molten metal and molten slag. The present invention is characterized in that the outflow of slag is detected by capturing this change. Normally, the opening degree of the nozzle is fixed at the time of slag cutting, so the average flow velocity of the fluid flowing through the fixed nozzle 9 is approximately constant. Therefore, (I)
The change in the electromotive force E in the equation is proportional to a change of 1 due to the difference in resistivity between molten steel (molten metal) and molten slag. If the change in the electromotive force E due to the change in is detected, the outflow of slag can be detected at that point.

This detection operation and slag cutting operation will be explained below with reference to FIG.

As shown in FIG. 2, a predetermined current is applied from an excitation unit 22 to the electromagnetic coil 18 for exciting the magnetic poles 16a and 16b. The excitation unit 22 is automatically adjusted so that the current flows according to the reference value given by the setting, so that the strength of the magnetic field generated in the electromagnetic coil 18 is constant, that is, the magnetic flux density B is constant. As a result, a constant magnetic field is formed within the fixed nozzle 9, and when the molten steel passes through this constant magnetic field, an electromotive force is generated in the electrode 17. The electrode 17 is connected to the amplifier 23 by a conductive wire through a terminal connection.
The electromotive force E generated at the electrode 17 is a minute signal of about mV.

The signal is amplified by an amplifier 23 to facilitate signal processing.

This amplified signal is then sent to a filter 24 for waveform shaping. That is, since the molten steel flowing through the fixed nozzle 9 may cause pulsating flow and the output of the amplifier 23 may become unstable, the filter 24 shapes the molten steel into a smooth waveform.

Next, the output signal of the filter 24 is sent to the arithmetic unit 25 and its level is determined. This computing unit 25 is equipped with a comparator that constantly differentiates the output signal of the filter 24, selects a change in magnitude preferentially, and issues a nozzle closing command when the result of differentiation exceeds a detection level value. . In other words, a comparator is provided after the differentiator. Here, the time when the first differential result exceeds a predetermined detection level value is determined as the time when the molten slag has passed into the fixed nozzle 9. This is because the electromotive force E generated at the electrode 17 becomes extremely low when the passing fluid changes from molten steel (molten metal) to molten slag. At this point, the nozzle closing command output from the calculator 25 is sent to the hydraulic controller 26, which supplies hydraulic pressure from the hydraulic source 27 via a path that can be freely connected to the cylinder 〇, drives the piston P, and drives the sliding nozzle 10. Operate the closing operation. As a result, the space between the fixed nozzle 9 and the long nozzle 4 is closed, and slag cutting is performed.

Figure 5 shows typical examples of waveforms for each device. Waveform A is the output waveform of the amplifier 23, and is the electromotive force E generated at the electrode 17.
(usually a voltage signal). Here, due to the pulsating flow inside the nozzle, this electromotive force E, that is, waveform A, causes minute vibrations. Also.

As the amount of molten steel in the ladle decreases, the flow velocity of molten steel passing through the nozzle decreases, and accordingly, the height of the waveform A gradually decreases. The waveform opening is after the waveform has been shaped by the filter 24.

It is smoothed. As shown by the waveform A and B, the level of the f8 molten slag rapidly decreases when it flows out. The arithmetic unit 25 first differentiates the waveform of the output signal of the filter 14 to obtain waveform C.

When molten steel changes to molten slag, a peak occurs in the waveform, so it is compared with a preset detection level using a comparator, and when the differential waveform exceeds the detection level, the nozzle is activated like a crack. A close signal is output from the calculator 25. The hydraulic controller 26 receives this closing signal output from the calculator 25 and drives the cylinder C to close the sliding nozzle 10, thereby preventing molten slag from flowing into the tundish dish 5.

〔Effect of the invention〕

According to the present invention, the end point of injection of molten metal can be detected stably and with high accuracy using a simple device, so that reliable slag cutting can be performed. This eliminates quality defects in slabs caused by T8 molten slag being mixed into the tundish slab and melting of refractories in the tundish, and stabilizes quality in continuous casting of T1 grade steel and other high-grade steels. The production yield can be improved. In addition, the conventional manual slag cutting can be automated, eliminating variations in accuracy due to operator skill levels when cutting slag using visual judgment.

It can save labor and ensure stable work for the operator.

Furthermore, since the electromagnetic coil can be installed only when necessary, the electromagnetic coil will not be damaged and will not get in the way, making it possible to exchange and feed ladles efficiently and continuously casting, while also allowing for continuous casting. This eliminates the reduction in the lifespan and reliability of the electromagnetic coil due to this, making it possible to improve maintainability, reduce costs, and maintain high reliability, making it possible to achieve high precision and high reliability in slag cutting.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an example of continuous casting equipment to which the present invention is applied, FIG. 2 is a schematic cross-sectional view showing the main parts of a slag cutting device according to the present invention, and FIG. FIG. 4 is a conceptual diagram for explaining the present invention in detail, and FIG. 5 is a diagram showing an example of a waveform of an electromotive force detection device. 1... Ladle, 2... Ladle-like molten slag, 3...
Ladle inner bay steel, 4. Long nozzle, 5. Tundish, 6. Injection nozzle, 7. Mold, 8
...Slab, 9..Fixed nozzle 710..Sliding nozzle, 14..Flange part of fixed nozzle, 15.
・Sliding nozzle opening. 16... Magnetic pole, 17... Electrode, 18... Electromagnetic coil. 20... Support rod, 22... Excitation unit, 23... Amplifier, 24... Filter, 25... Arithmetic unit. 26...Hydraulic controller, 27...Hydraulic power source. Column 1-. Wu 2 ("Taka 3.1 Figure 4 Molten Steel Figure 5 Time

Claims (3)

[Claims] (1) In a continuous casting method in which molten metal is supplied from a ladle to a mold via a tundish, a magnetic field is formed in the nozzle at the bottom of the ladle for pouring the metal from the ladle into the tundish, and this magnetic field in the nozzle is applied to the metal. A slag cutting method in continuous casting, characterized in that an electromotive force is detected as the molten metal passes through, and the operation of pouring the metal from a ladle to a tundish is stopped at the point at which the electromotive force changes. (2) A pouring device in which a long nozzle extending downward is detachably connected to a fixed nozzle installed at the bottom of a ladle for storing molten metal through a sliding nozzle that functions as a valve, A slag cutting device for continuous casting, wherein a magnetic pole and an electrode are arranged orthogonally to each other outside the fixed nozzle, and the sliding nozzle is opened and closed using the electromotive force induced in the electrode as a detection signal. (3) The slag cutting device according to claim 2, wherein the magnetic pole is composed of an electromagnetic coil, and the electromagnetic coil is detachably installed on the fixed nozzle.