JPH0798248B2 - Slag cutting method and device in continuous casting - Google Patents

Description

TECHNICAL FIELD The present invention relates to a slag cutting method and device for ladle in continuous casting operation of molten metal.

[Conventional technology]

In the operation of pouring molten metal from the ladle to the tundish in the continuous casting operation, when molten slag in the ladle was injected together into the tundish, SiO ₂ and MgO were cast into the cast slab.
Non-metallic inclusions, such as, are mixed in and appear as defects in the rolled product after rolling the slab, which adversely affects quality or yield. Therefore, in the continuous casting operation, a method is generally used in which the slag is cut by visually recognizing the color difference between the molten metal and the molten slag during the pouring operation from the ladle to the tundish. Open injections are generally required to make this identification. In this open pouring method, molten steel comes into contact with air between the ladle and the tundish, and a nitrifying action of about 10 ppm usually occurs. Such nitrifying action is mixed with TiN-based inclusions in cast slabs, especially in special steel grades such as Ti-containing grades.
This leads to deterioration of quality and yield.

In order to prevent such a nitrifying effect, the open injection is stopped and a long nozzle (hereinafter sometimes abbreviated as LN) that is conventionally sealed with Ar is used for that portion. If used, the above-mentioned visual slag cut becomes impossible. Therefore, various slag cutting methods have been developed to replace visual inspection.

For example, in JP-A-60-148652, slag outflow is detected by detecting the vibration of LN with a vibration detector and detecting the change in frequency due to the difference in specific gravity and viscosity of the molten metal and molten slag. Disclose how to detect. In addition, JP-A-55
Japanese Patent Publication No. 97847 discloses a method of detecting a slag outflow by providing a detection coil in a nozzle and capturing a difference in electrical conductivity between molten metal and molten slag as impedance change. In addition, a method using vibration of a tundish disclosed in JP-A-57-112964, or a method based on a difference in electric conductivity between molten metal and molten slag disclosed in JP-A-55-159145 has been proposed. .

[Problems to be solved by the invention]

Although the slag cut detection methods proposed in the above publications each have a loss, the vibration measurement method disclosed in Japanese Patent Laid-Open No. 60-148652 picks up vibrations in the factory from the LN support part, ladle, etc. Becomes noise, and the problem that the target vibration cannot be accurately detected is accompanied. JPA
The measurement method based on impedance change disclosed in JP-A-55-97847 is accompanied by a problem that the detection sensitivity decreases as metal or alumina adheres to the inner surface of the nozzle. In addition, it cannot be denied that the reliability and stability of the measurement are similarly lacking in the methods of measuring the conductivity disclosed in JP-A-57-112964 and JP-A-55-159145.

[Means for solving problems]

According to the present invention made to solve the above-mentioned problems, in a continuous casting method of supplying a molten metal from a ladle to a mold through a tundish, a nozzle at the bottom of the ladle for pouring the molten metal from the ladle into the tundish. A constant magnetic field is formed in the inside of the nozzle, and when the molten metal passes through the magnetic field in the nozzle, the electromotive force generated in the molten metal in the direction orthogonal to the direction of the magnetic field is detected. The present invention provides a slag cutting method in continuous casting, characterized in that the pouring operation from the ladle to the tundish is stopped. As a device for carrying out this method, a long nozzle extending downward is detachably connected to a fixed nozzle installed at the bottom of a ladle for accommodating molten metal, through a sliding nozzle that performs a valve function. In the pouring device, the magnetic pole for forming a constant magnetic field inside the fixed nozzle is arranged outside the fixed nozzle, and the electrode is arranged in the direction orthogonal to the direction of the magnetic field inside the nozzle formed by this magnetic pole. Disclosed is a slag cutting device in continuous casting, in which the electromotive force induced in the electrode is used as a detection signal to open / close the sliding nozzle. In that case, preferably, the magnetic pole is composed of an electromagnetic coil, the electromagnetic coil is detachably installed on the fixed nozzle, and the electromagnetic coil is set on the fixed nozzle when the slag cut time approaches.

The present invention can be applied to all continuous castings targeting a conductive metal melt, but the embodiments of the present invention will be described below taking the case of targeting molten steel as an example.

〔Example〕

FIG. 1 shows a typical example of equipment for continuous casting of molten steel, in which the molten steel 3 present in the lower layer of the molten slag layer 2 in the ladle 1 is a long nozzle attached to the bottom of the ladle 1. Hot water is supplied to the tundish 5 through the (LN) 4, continuously poured into the mold 7 through the injection nozzle 6 at the bottom of the tundish 5, and the cast piece 8 is continuously cast. LM4 is ladle 1
It is removably attached to a fixed nozzle 9 fixed to the bottom of the device via a sliding nozzle 10 that functions as a valve.
The molten steel in the tundish 5 is adjusted in amount and started / stopped by a stopper 11 that opens and closes the upper opening of the injection nozzle 6.

In such continuous casting, it is desirable that substantially all of the molten steel 3 contained in the ladle 1 is supplied to the tundish 5 while being separated from the molten slag 2. The present invention makes the slag cut accurately and easily.

FIG. 2 shows a main part of the slag cutting device according to the present invention.
At the bottom of the ladle 1, a fixed nozzle 9 whose upper end communicates with the bottom opening 12 of the ladle and whose lower end is connected to the sliding nozzle 10 is fixed so as to project downward from the outer surface 13 of the ladle bottom. A flange portion 14 is fixedly provided on the lower end side of the fixed nozzle 9. The body of the sliding nozzle 10 has an opening 15 in the center.
It consists of a disk-shaped board with a fixed nozzle 9
It is set to be slidable in the horizontal direction with respect to the flange portion 14 of the. This sliding operation is performed by the reciprocating motion of the piston P by the cylinder C. The long nozzle (LN) 4 is detachably connected to the sliding nozzle 10 so that the opening 15 of the sliding nozzle 10 and the upper end opening of the long nozzle 4 are aligned with each other. In the present invention, the magnetic pole 16 and the electrode 17 are arranged in the fixed nozzle 9 so as to be orthogonal to each other, and a magnetic field is formed in the fixed nozzle 9 by the magnetic pole 16 and generated by molten steel and molten slag passing across the magnetic field. Electromotive force (usually a voltage signal) due to electromagnetic induction is detected by the electrode 17.

FIG. 3 is a perspective view showing a mounting state of the magnetic pole 16 and the electrode 17. As shown in the figure, magnetic poles 16a and 16b are installed opposite to each other with the fixed nozzle 9 interposed therebetween, and the magnetic poles 16a and 16b are magnetized by energizing the electromagnetic coil 18. Since the fixed nozzle 9 is a refractory, its magnetic flux passes through the refractory wall, and a magnetic field is formed in a direction traversing the fixed nozzle 9. And this magnetic pole 16
Electrodes 17a and 17b (17
The side of b is hidden and invisible) is placed. 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 to the electromagnetic coil 18 are integrally supported by a support rod 20.
The magnetic poles 16a and 16b can be freely attached to and detached from the fixed nozzle 9 by reciprocating in the horizontal direction indicated by the arrow. In the illustrated example, the electrodes 17a and 17b are fixed to the outer wall of the fixed nozzle 9, but may be fixed to the flange portion 14 of the fixed nozzle 9 or may be attached to the support rod 20 to form the magnetic poles 16a and 16b. Similarly, it may be detachable. In addition,
It is convenient to mount the supporting rod 20 on a supporting frame (not shown) of the long nozzle 4. Long nozzle 4
Is set and the injection of molten steel is started, and when the end of injection is approached, the support rod 20 is advanced and set on the fixed nozzle 4. After this setting is completed, a current is passed through the electromagnetic coil 18 to generate a magnetic field between the magnetic poles 16a and 16b, and the slug cut is performed by the above-described method. After the slug cut is completed, the electromagnetic coil supported integrally with the magnetic pole 16 is formed. Retreat 18 and make it stand by. In this way, by mounting only when necessary,
Deterioration of the electromagnetic coil due to heat in a high temperature environment can be prevented, the lifespan can be greatly extended, detection accuracy can be improved, and reliability and stability can be improved.

As shown in FIGS. 1 and 2, the ladle 1 usually has a fixed nozzle 9 at its bottom, a flange portion 14 thereof, a sliding nozzle 10 and a cylinder C for slidably reciprocating the nozzle 10. And are integrally supported and formed.

As mentioned before, the ladle 1 is detachably connected to the long nozzle 4 which is positioned and supported by the tundish 5. Therefore, the ladle 1 is successively exchanged and supplied to the long nozzles 4 supported in this way, and the molten steel 3 in each ladle 1 is injected into the tundish 5 through the long nozzles 4. , Continuous casting is performed.

In this way, the ladle 1 is continuously supplied while being exchanged and supplied, but as shown in FIG. 3, the electrode coil 18 is moved forward with respect to the fixed nozzle 4 protruding and fixed to the bottom of the ladle 1. Alternatively, if it is set back so that it can be freely attached and detached, the magnetic pole 16 and the electrode coil 18 will not be damaged,
Moreover, these can be exchanged and supplied with good operability and efficiency without disturbing them.

FIG. 4 is for explaining the principle of the slag cutting device according to the present invention. When a magnetic field is applied to the fixed nozzle 9 through which molten steel flows through the magnetic poles 16a and 16b as shown in FIG. An electromotive force corresponding to the flow velocity of the molten steel is generated in the electrodes 17a and 17b provided. That is, when a conductor moves across a constant magnetic field, an electromotive force in the direction orthogonal to the magnetic field is generated in the conductor, and Faraday's electromagnetic induction law is used to detect this electromotive force with electrodes 17a and 17b. Is. Therefore, the electrodes 17a and 17b need to be in electrical connection with the fluid. The magnitude of the electromotive force generated is proportional to the flow velocity of the fluid, but when pouring from a ladle to a tundish through a nozzle in continuous casting, compared to the variation factor due to this flow velocity, The difference in the specific resistance of the fluid in the case of slag can be detected as a much larger variation factor. That is,
This electromotive force changes depending on the flow rate of molten steel and the nozzle diameter,
It is generally given by

However, in the above equation, E: electromotive force [mV], B: magnetic flux density [gauss], V: average flow velocity of molten steel [cm / s], d: inner diameter of nozzle [cm], K ₁ : correction of short path effect of nozzle wall Number, K ₂ : correction factor for end effect of magnetic field, K ₃ : correction factor for temperature effect of electromagnetic coil, K ₄ : correction factor for thermal expansion of nozzle.

Here, K ₁ is called the Errod correction coefficient and is given by the following equation.

Where D: nozzle outer diameter [cm], ρ _f : specific resistance of molten steel, 140 × 10 ^-6 [Ω.c for molten metal]
m], about 1 to 7 [Ω.cm] for molten slag, τ: molten steel and nozzle contact resistance [Ω. cm ² ], is.

In equation (1), K ₂ is the output reduction coefficient generated by the eddy current generated at the magnetic field terminals at the nozzle entrance and exit, and K ₃ and K ₄ are values determined by the magnetic pole used and the nozzle material. These are difficult to determine by calculation, but can be easily determined by the experimental values of the device several times. However, these numerical values do not change depending on the molten metal and molten slag that pass through the fixed nozzle 9. The only change term that changes with the passage of molten metal and molten slag is K ₁ .

In the equation (2) for calculating K ₁ , since the specific resistance values of the molten metal and the molten slag are greatly different, the value of K ₁ is different between the molten metal and the molten slag. The present invention is characterized in that the change is detected to detect the outflow of slag.
Normally, the opening degree of the nozzle is fixed at the time of performing the slag cut, so that the average flow velocity of the fluid flowing through the fixed nozzle 9 is substantially constant. Therefore, the change in the electromotive force E in the equation (1) is proportional to the change in K ₁ caused by the difference in the specific resistance between the molten steel (metal melt) and the molten slag. If the change in electromotive force E due to the change in K ₁ is captured, the slag outflow can be detected at that time.

The detection operation and the slag cutting operation will be described below with reference to FIG.

As shown in FIG. 2, a predetermined current is supplied from the 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 fixed magnetic field is formed in the fixed nozzle 9, and electromotive force is generated in the electrode 17 when the molten steel passes through the fixed magnetic field. The electrode 17 is connected to the amplifier 23 by a lead wire by a terminal connection. Since the electromotive force E generated at the electrode 17 is a minute signal of about mV, the amplifier 23 amplifies the signal for easy signal processing. This amplified signal is then sent to the filter 24 for waveform shaping. That is, the molten steel flowing in the fixed nozzle 9 may cause a pulsating flow or the like to make the output of the amplifier 23 unstable, so that the filter 24 is used to form a smooth waveform. Then, the output signal of the filter 24 is transmitted to the calculator 25 and its level is judged. This calculator 25 is provided with a comparator which always differentiates the output signal of the filter 24 and preferentially selects a change in its magnitude, and issues a nozzle close command when the differentiation result exceeds the detection level value. . That is, a comparator is provided after the differentiator. Here, the time when the differential result exceeds the predetermined detection level value is determined as the time when the molten slag has passed through the fixed nozzle 9. This is because the electromotive force E generated in the electrode 17 suddenly decreases when the passing fluid changes from molten steel (metal melt) to molten slag. At this time, the nozzle closing command output from the calculator 25 is sent to the hydraulic controller 26, and the hydraulic pressure is supplied from the hydraulic pressure source 27 through the path that can be connected to the cylinder C to drive the piston P and the sliding nozzle 10 To close. As a result, the gap between the fixed nozzle 9 and the long nozzle 4 is closed, and slag cutting is performed.

FIG. 5 shows a typical example of the waveform of each device. The waveform a is the output waveform of the amplifier 23 and corresponds to the electromotive force E (usually a voltage signal) generated in the electrode 17. Here, the electromotive force E, that is, the waveform i, causes a slight vibration due to a pulsating flow in the nozzle. In addition, the flow velocity of the molten steel passing through the nozzle decreases as the amount of molten steel in the ladle decreases, and the height of the corrugated b decreases accordingly. Waveform B is smoothed after being shaped by the filter 24. As shown by the waveforms a and b, the level of molten slag decreases rapidly when it flows out. The calculator 25 first differentiates the waveform b of the output signal of the filter 14 to obtain the waveform c. When molten steel changes to molten slag, a peak occurs like a waveform c, so it is compared with the detection level set in advance by the comparator, and when the differential waveform c exceeds the detection level, the output of the nozzle A close signal is output from the calculator 25. Hydraulic controller 26
In response to this closing signal output from the computing unit 25, the cylinder C is driven to close the sliding nozzle 10, thereby preventing the molten slag from flowing into the tundish 5.

〔The invention's effect〕

According to the present invention, the end point of pouring the molten metal can be detected stably and accurately with a simple device, so that reliable slag cutting can be performed. Therefore, inferior slab quality due to the molten slag being cast into the slab and melting loss of the refractory in the tundish can be eliminated, and quality stabilization in continuous casting of Ti-containing steel grades and other high-grade steel can be realized. The yield can be improved.
In addition, the conventional manual slag cutting can be automated, the accuracy variation due to the operator's skill level at the time of slug cutting by visual judgment can be eliminated, and labor saving and stable work of the operator can be realized. Furthermore, since the electromagnetic coil can be installed only when necessary, the electromagnetic coil is not damaged, and the electromagnetic coil does not get in the way, and the ladle can be exchanged and supplied efficiently and efficiently, and continuous casting is possible. As a result, it is possible to eliminate the deterioration of the life and reliability of the electromagnetic coil, improve the maintainability, reduce the cost and maintain the high reliability, and realize the high precision and high reliability of the slag cut.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of a continuous casting facility to which the present invention is applied, FIG. 2 is a schematic sectional view showing an essential part of a slag cutting device according to the present invention, and FIG. 3 is a slag cutting device according to the present invention. FIG. 4 is a perspective view showing essential parts, FIG. 4 is a conceptual diagram for explaining the principle of the present invention, and FIG. 5 is a diagram showing an example of waveforms of an electromotive force detection device. 1 …… Ladle, 2 …… Molten slag in ladle, 3 …… Molten steel in ladle, 4
…… Long nozzle, 5 …… Tandishyu, 6 …… Injection nozzle, 7 …… Mold, 8 …… Slab, 9 …… Fixed nozzle, 10 …… 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 …… calculator , 26 ...
… Hydraulic controller, 27 …… Hydraulic power source.

Claims (3)

[Claims] 1. A continuous casting method in which a molten metal is supplied from a ladle to a mold through a tundish, and a constant magnetic field is formed in a nozzle at the bottom of the ladle for pouring the molten metal from the ladle into the tundish. When the molten metal passes through the internal magnetic field, it continues to detect the electromotive force generated in the molten metal in the direction orthogonal to the direction of the magnetic field, and when the detected value of this electromotive force changes, the ladle is transferred to the tundish. A slag cutting method in continuous casting characterized by stopping the pouring operation. 2. A pouring method in which a long nozzle extending downward is detachably connected to a fixed nozzle installed at the bottom of a ladle for accommodating a molten metal through a sliding nozzle having a valve function. In the device, a magnetic pole for forming a constant magnetic field in the nozzle is arranged outside the fixed nozzle, and an electrode is arranged in a direction orthogonal to the direction of the magnetic field in the nozzle formed by the magnetic pole. A slag cutting device in continuous casting, in which an electromotive force induced in an electrode is used as a detection signal to open and close the sliding nozzle. 3. The slug cutting device according to claim 2, wherein the magnetic pole is composed of an electromagnetic coil, and the electromagnetic coil is detachably installed in the fixed nozzle.