JPH09164462A - Continuous casting method of steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably cast the slab of excellent quality by controlling the dipping depth of a dipping nozzle by the output signal from a dipping type electromagnetic flow rate sensor dipped in the molten steel in a mold to control the flow of the molten steel in the mold. SOLUTION: A dipping type electromagnetic flow rate sensor 7 is dipped in a mold 6 to detect the power supply to a solenoid magnet and the electromotive force associated with the flow, and the dipping depth of a dipping nozzle 5 is controlled by a tundish elevating/lowering device 3 so that the flow rate of about 10-60cm/sec. toward the dipping nozzle side is obtained based on the signal. The slab of excellent quality can stably be cast thereby.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a signal from an immersion type electromagnetic flow sensor immersed in molten steel in a mold to control the immersion depth of an immersion nozzle and the output of an electromagnetic brake in a mold or an electromagnetic stirrer. Then, the present invention relates to a continuous casting method of steel for optimizing a molten steel flow pattern in a mold.

[0002]

2. Description of the Related Art In continuous casting of steel, controlling molten steel flow in a mold to an optimum value is extremely important for quality control. Conventionally, for example, as disclosed in Japanese Unexamined Patent Publication No. 7-24558. A method of empirically determining the optimum value of the flow pattern, uniquely determining the flow control condition, and simply rotating and stirring in one direction under a constant condition, and JP-A-6-1818.
As disclosed in Japanese Patent No. 2511, a signal from a thermometer or a heat flux meter set in a mold is spectrally analyzed, and electromagnetic stirring propulsion force is controlled according to the result, and Japanese Patent Laid-Open No. 63-212051. As disclosed in, there is proposed a method of measuring the liquid surface position variation in the meniscus and controlling the flow velocity in the mold by braking or acceleration.

[0003]

However, since these do not directly measure the flow rate of molten steel or control the flow based on a wide range of averaged information, a dynamic molten steel flow control mechanism. I was not satisfied with it.

In contrast to the conventional method for controlling the flow of molten steel in a mold which is controlled on the basis of indirect information on the molten steel flow in the mold, or a wide range of average information, in the present invention, in the molten steel, direct current or In the presence of any external magnetic field of alternating current, by using the immersion type electromagnetic velocity sensor that can accurately measure the local molten steel flow velocity with high accuracy, the flow velocity at the required location in the mold can be accurately measured, and based on that information Another object of the present invention is to provide a continuous steel casting method capable of dynamically controlling the flow of molten steel with high accuracy.

[0005]

A method for continuously casting steel according to a first aspect of the present invention controls an immersion depth of an immersion nozzle by an output signal from an immersion electromagnetic flow velocity sensor immersed in molten steel in a mold. , Controlling the flow of molten steel in the mold.

The continuous casting method for steel according to the second invention is
In the first invention, the output of the mold flow control device is controlled.

A third invention is characterized in that, in the first or second invention, the magnetic field generating means of the immersion type electromagnetic velocity sensor is an air-core solenoid magnet.

In continuous casting of steel, there is an extremely high demand for optimizing the flow pattern of molten steel in the mold from the viewpoint of stability of operation and ensuring of quality.

However, generally, when the casting conditions such as the discharge angle of the immersion nozzle, the nozzle opening diameter, the slab size, the pouring speed, and the immersion depth of the immersion nozzle are determined, the molten steel flow pattern in the mold is determined. Is almost decided.

However, as the casting progresses, deoxidation products such as alumina adhere to the inner surface of the immersion nozzle, and the flow pattern gradually changes from that at the beginning of casting. Therefore, it is optimum for stabilizing casting and ensuring quality. The need arises to restore the correct flow pattern.

Among the conditions for determining the flow pattern of molten steel described above, what can be changed during casting is the immersion depth of the immersion nozzle and the output of the mold molten steel flow control device using electromagnetic force. Therefore, if information about the flow condition in the mold is available in some form, this can be dealt with by changing the immersion depth of the immersion nozzle and the output of the flow control device using electromagnetic force.

Therefore, the present invention controls the immersion depth of the immersion nozzle based on the signal from the immersion electromagnetic flow velocity sensor so as to obtain an optimum molten steel flow pattern in the mold.

Further, in the case of high-speed casting, it is difficult to obtain the optimum flow pattern only by controlling the immersion depth of the immersion nozzle. Therefore, the signal from the immersion type electromagnetic velocity sensor is applied to the electromagnetic brake arranged on the back surface of the long side mold. Alternatively, it is necessary to consider that feedback is also applied to the output control mechanism of the flow control device such as the electromagnetic stirring device.

Optimum empirically determined based on the signal from the immersion type electromagnetic flow velocity sensor which is immersed in a place near the meniscus in the mold, which is most sensitively reflected to the stability of operation and the quality of the slab. By dynamically controlling the output of the mold flow control device for various patterns, high quality slabs can always be stably cast.

That is, it is well known that by giving an optimum flow velocity to the solidification interface, bubbles and inclusions are discharged to the molten steel side due to their cleaning effect and prevented from adhering to the solidification shell. is there.

Further, stirring the molten steel in the mold for the purpose of controlling the solidification structure and preventing unevenness of the solidification shell thickness is also used as a usual means. However, if the degree of agitation is excessive, a white band, which is a negative segregation zone, and instability and fluctuation of the meniscus are generated, which causes a serious problem in terms of operation stability and quality. Therefore, in order to solve these problems, the present invention attempts to dynamically control the output of the flow control device so as to optimize the flow pattern in the mold based on the information on the quantitative flow condition. Is.

Next, in the present invention, the immersion type electromagnetic flow velocity sensor developed for molten steel was adopted as a means for accurately measuring the flow velocity in the mold.

The immersion type electromagnetic velocity sensor used in the present invention is one in which the magnetic field generating means and the electrode are immersed in molten steel. Since the relative distance between the electrode and the magnetic field generating means is close, the electromotive force increases. It enables stable measurement.

As the magnetic field generating means, an air-core solenoid magnet is used instead of the conventional permanent magnet having a large temperature restriction. In the case of air-core solenoid magnets, the heat resistance is governed only by the heat resistance of the winding material and the insulation of the bobbin, so these materials can be optimized according to the operating temperature.

However, when the liquid to be measured is molten steel,
Since it reacts with the lead wire for measuring the electromotive force and melts, it must be brought into contact with the molten steel through a conductive substance that does not react with the lead wire.

On the other hand, when it is attempted to measure a minute flow velocity fluctuation in a high temperature state, it is necessary to suppress the fluctuation of the generated magnetic flux density as much as possible. In the case of the immersion electromagnetic flow velocity sensor according to the present invention, the generated magnetic flux density fluctuates due to the fluctuation of the impedance Z represented by the equation (1) accompanying the temperature change of the solenoid coil.

[0022]

[Equation 1]

Here, R is the DC resistance of the winding, ω is the frequency of the applied AC current, and L is the self-inductance of the solenoid coil.

As long as the form of the solenoid coil does not change, the inductance L does not change, and if the oscillation frequency ω of the alternating current is controlled to a constant value, the impedance change is governed only by the DC resistance R of the coil. . Therefore, in order to control the generated magnetic flux density to be constant, a constant current mechanism that changes the output voltage of the AC current supply device according to the impedance change mainly due to the change of the DC resistance component of the coil with the temperature change Should be equipped.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view of the vicinity of the continuous casting equipment mold of the present invention. 1 is a tundish, 2 is molten steel, 3 is a tundish lifting device, 4 is a sliding plate, 5
Is an immersion nozzle, 6 is a mold, 7 is an immersion type electromagnetic flow velocity sensor, and 8 is a flow control device for controlling the flow of molten steel in the mold.

Molten steel 2 in the tundish 1 is poured from a sliding plate 4 into a mold 6 via a dipping nozzle 5. An immersion electromagnetic flow velocity sensor 7 is installed in the mold 6, and a flow controller 8 for controlling molten steel flow in the mold is installed on the back surface of the long side of the mold 6. As the flow control device 8, an electromagnetic brake or an electromagnetic stirring device is used.

The flow velocity value of the molten steel 2 is measured by the immersion type electromagnetic velocity sensor 7 by the outflow of the molten steel 2 from the immersion nozzle 5.
The depth of the immersion nozzle 5 is controlled by the tundish lifting device 3.

FIG. 2 (a) is a schematic sectional view of an immersion type electromagnetic flow velocity sensor in a state of being immersed in molten steel used in the present invention, and FIG. 2 (b) is a sectional view taken along line XX of FIG. 2 (a). Is.

The immersion type electromagnetic velocity sensor 7 includes a solenoid magnet 9, a coil protection material 10 for protecting the solenoid magnet 9 from the molten steel 2, a coil protection material 10 and a sensor holding tube 1.
Sensor support rod 11 for supporting 2 and sensor holding tube 1
It is composed of a lead wire 13 that passes through the inside of the sensor holding tube 2, and an electrode 14 that is tightly sealed in the sensor holding tube 12 at the tip of the sensor holding tube 12.

Here, the electrically conductive ceramic or the ceramic containing the refractory metal is electrically conductive even at a high temperature, so that it can be used as the electrode 14. Specifically, the lead wire 1 using zirconium boride as the electrode 14
It was arranged at the tip of No. 3. Other materials for the electrodes include titanium boride and zirconium oxide containing molybdenum. The lead wire was a tantalum wire.

The coil of the magnetic field generating solenoid is tantalum wire of 0.5 mm Φ made of the same material as the lead wire, and outer diameter of 12 mm Φ.
The alumina tube was wrapped 70 times and the outer circumference was coated with heat resistant cement.

An immersion type electromagnetic flow velocity sensor used in another embodiment of the present invention is shown in FIG. FIG. 3 (a)
Is a schematic sectional view, and FIG. 3B is a sectional view taken along line XX of FIG.

The difference between the immersion type electromagnetic flow velocity sensor shown in FIG. 3 and the immersion type electromagnetic flow velocity sensor shown in FIG. 2 is that the sensor protection tube has a U-shape, and in this embodiment, it is conductive. Since the substance may be in a liquid state, fused silver is used as the electrode. The melting temperature of steel is as high as 1500 ° C or higher, and it forms an alloy with most metals. That is, since most metals are dissolved, there is no metal that can be used as an electrode for measuring an electromotive force of an electromagnetic velocity sensor by directly contacting molten steel for a long time in a solid state.

Therefore, as shown in FIG. 3, the steel of the electromotive force measuring portion and the lead wire made of tantalum were electrically connected via silver which did not form an alloy with steel.

As a matter of course, since silver is in a molten state at around 1500 ° C., it is necessary to take special measures as shown in FIG. 3 so that the molten silver does not leak out. That is, in order that the molten silver does not overflow even when the immersion depth of the immersion type electromagnetic flow velocity sensor becomes shallow, the total height of the molten silver must be less than 2H with respect to the U-shaped portion length H. That is,
It is necessary to determine the length H of the U-shaped portion and the heights ha ₁ and ha ₂ of the molten silver on both sides of the U-shaped portion within the range represented by the formula (2).

[0037]

(Equation 2)

In the present embodiment, an alternating current having an oscillation frequency of 18 Hz is supplied from the constant current stabilizing power supply to the solenoid coil, and the electromotive force is detected by the lock-in amplifier while referring to the phase of the supplied current. The strength of the magnetic field generated by the solenoid magnet used this time was 3.5 × 10 ⁴ AT / m, and the relationship between the flow velocity and the electromotive force was investigated using a gutter that secured a predetermined flow velocity. The result is shown in FIG.

As shown in FIG. 5, a very good correspondence was obtained between the flow velocity and the electromotive force. In this figure, the X mark is the measured value in the presence of a DC external magnetic field of 2800 Oersted,
The ● marks are measured values in the absence of an external magnetic field. It has been confirmed that the electromagnetic flow velocity sensor according to the present invention is hardly affected by the external magnetic field.

Although tantalum was used as the winding material of the solenoid coil in the present embodiment, platinum or platinum-rhodium alloy is used as a material having a melting point of 1500 ° C. or higher and resistant to oxidation, and these materials are used instead of tantalum. It goes without saying that you can do it.

Further, if oxidation resistance treatment is performed, high melting point metals such as molybdenum, rhodium, hafnium, niobium,
It is also possible to use tungsten, and also carbon fiber or the like. However, the lead wire material of the sensor shown in FIG. 3 is limited to tantalum, tungsten, or the like, which is a metal that does not form an alloy with molten silver. On the other hand, there is lead in addition to silver as a metal that does not react with molten steel, and molten lead can be used as the contact electrode instead of molten silver.

In each of the embodiments of the present invention, the frequency used for the measurement was 18 Hz, but the measurement system is not disturbed depending on the frequency of the external magnetic field and the surrounding electrical environment. The optimum frequency may be selected.

However, the usable frequency range is that it is necessary to supply a relatively large current to the solenoid coil.
0.1 Hz due to the balance of amplification sensitivity of lock-in amplifier
The limit is about 50 KHz.

As a method of controlling the immersion depth of the immersion nozzle, it is possible to deal with it by raising or lowering the molten steel level in the mold in addition to raising and lowering the tundish by using the tundish raising and lowering device. is there.

[0045]

【Example】

(Example 1) At a superheating degree of molten steel in a tundish of 35 ° C, in a mold of size 220 mm x 1650 mm during casting, as shown in Fig. 1, at a position 150 mm deep from the molten steel surface, the immersion type electromagnetic velocity sensor shown in Fig. 2 was used. Was immersed. Immerse the above electromagnetic flow rate sensor in 1/4 from the short side in the width direction of the mold and 1 in both sides with the immersion nozzle sandwiched around 1/2 in the thickness direction. With the measurement system shown in the block diagram of Fig. 4, the electromotive force associated with the power supply to the solenoid magnet and the flow is detected, and based on the signal, the flow velocity toward the immersion nozzle side becomes 10 to 60 cm / sec. The immersion depth of the immersion nozzle was controlled by a tundish lifting device.

As a result, it was possible to stably cast a high quality slab from the initial stage to the final stage of casting, despite the tendency of clogging of the immersion nozzle.

Example 2 Using the same measuring device for casting size and flow velocity as in Example 1, the immersion depth of the nozzle was controlled while controlling the output of the electromagnetic stirring device of the mold.
In Example 2, when the immersion depth was increased, the molten steel flow rate decreased, and when the immersion depth was decreased, the molten steel flow rate increased.

The electromagnetic stirrer used in this embodiment is a device for stirring the molten steel in the mold in one direction in the horizontal direction by the moving magnetic field, and the stirring strength control output is the same as that in the first embodiment. Optimization was made by the signal from. The immersion type electromagnetic flow velocity sensor is optimally placed at 1/4 position in the mold width direction and 1/4 position in the thickness direction so that the point is centered on the immersion nozzle at a depth of 150 mm from the liquid surface. If the stirring force is controlled so that the flow pattern is 30 to 60 cm / sec, and the control by only adjusting the output of the electromagnetic stirring force is incomplete, immediately set the immersion depth of the immersion nozzle to the tundish lifting device. Adjustment to ensure a stable horizontal rotational flow in one direction at all times. As a result, an extremely clean slab without inclusions or bubbles near the surface layer of the slab could be stably cast from the initial stage to the final stage.

(Example 3) Using the same measuring device for casting size and flow velocity as in Example 1, the output of the mold flow controller and the immersion depth of the nozzle were controlled. In this embodiment, the wiring of the electromagnetic stirrer of the second embodiment is changed so that a driving force from both ends of the mold toward the center in the width direction is generated, and a signal from the immersion electromagnetic flow velocity sensor is fed back to the output control mechanism. did.

The purpose of this embodiment is to optimize the flow in the vicinity of the meniscus in order to prevent the entrainment of mold powder when the pouring speed is high, as compared with the first embodiment. Immersion type electromagnetic flow velocity sensor is located at the depth of 50mm from the liquid surface centering on the immersion nozzle, one on each side at 1/8 from the short side in the mold width direction and 1/2 position in the thickness direction. The output of the flow control device is adjusted based on the signals from them, and when it is insufficient, the immersion depth of the immersion nozzle is adjusted by the tundish lifting device so that the flow velocity at each location is 10 to 10 It was controlled to be 30 cm / sec.

As a result, it became possible to stably cast a high quality slab without entrainment of powder.

In this embodiment, the electromagnetic control force is an example of control by the flow control device arranged so as to be directed toward the center of the mold, but conversely, the drive force is directed from the center of the width of the mold to both ends. Needless to say, it can be applied to a flow control device in which

(Embodiment 4) When the pouring amount per unit time increases, the necessity of braking the discharge flow rate from the immersion nozzle increases, but the method most suitable for that purpose is the flow control method by the DC magnetic field. In this example, a test was conducted with the aim of optimizing the flow there.

Conventionally, when the output of the electromagnetic brake is too strong, the entrainment of mold powder is reduced, but deoxidation products and bubbles mainly composed of alumina, and in some cases converter slag are trapped under the surface layer of the slab. Many cases were acknowledged.

Therefore, in this embodiment, the same as in the first embodiment,
The casting size and flow velocity measuring device were used to control the output of the electromagnetic brake type mold flow control device by the DC magnetic field and the immersion depth of the immersion nozzle.

The flow velocity sensor was 1/50 from the short side in the mold width direction at a position 50 mm deep from the molten steel surface centering on the immersion nozzle.
8. Placed one on each side at 1/2 position in the thickness direction. By controlling the flow velocity at the measurement position by the electromagnetic brake output and the immersion depth of the immersion nozzle by the tundish lifting device to dynamically control it to 5 to 20 cm / sec, the problems of the conventional technology are solved, It was possible to stably cast extremely high quality slabs in which alumina and air bubbles were not trapped under the surface layer.

In this embodiment, the magnet of the immersion type electromagnetic velocity sensor is an AC solenoid because it is intended to perform measurement in the presence of an external DC magnetic field. The electric power may be detected as a signal corresponding to the flow velocity.

[0058]

INDUSTRIAL APPLICABILITY The present invention directly measures the flow state of molten steel in a mold by an immersion type flow velocity sensor, and based on the measurement result, adjusts the immersion depth of the immersion nozzle and the output of the flow control device, By dynamically controlling the molten steel flow inside, it is possible to stably cast high quality slabs.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of the vicinity of a continuous casting facility mold of the present invention.

FIG. 2 is a schematic view of an immersion type electromagnetic flow velocity sensor in a state of being immersed in molten steel used in the present invention, (a) is a sectional view,
(B) is a XX sectional view of (a).

FIG. 3 is a schematic view of an immersion type electromagnetic flow velocity sensor of another embodiment immersed in molten steel used in the present invention, in which (a) is a sectional view and (b) is a sectional view taken along line XX of (a). It is a figure.

FIG. 4 is a block diagram of a power supply and measurement system for the sensor.

FIG. 5 is a diagram showing a relationship between a flow rate of molten steel and an electromotive force.

[Explanation of symbols]

 1: Tundish 2: Molten steel 3: Tundish lifting device 4: Sliding plate 5: Immersion nozzle 6: Mold 7: Immersion type electromagnetic velocity sensor 8: Flow control device 9: Solenoid magnet 10: Coil protector 11: Sensor support rod 12: Sensor holding tube 13: Lead wire 14: Electrode 15: Molten silver

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Suzuki Marunouchi 1-2-2, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Masayuki Nakata 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Date Main Steel Pipe Co., Ltd.

Claims (3)

[Claims] 1. A steel continuation characterized in that the flow of molten steel in a mold is controlled by controlling the immersion depth of an immersion nozzle by an output signal from an immersion type electromagnetic flow velocity sensor immersed in molten steel in a mold. Casting method. 2. The continuous casting method for steel according to claim 1, wherein the output of the flow control device for the molten steel in the mold is controlled by the output signal of the immersion type electromagnetic flow velocity sensor. 3. The continuous casting method for steel according to claim 1, wherein the magnetic field generating means of the immersion type electromagnetic velocity sensor is an air-core solenoid magnet.