JPH06304719A - Method for braking molten metal in continuous casting mold and electromagnetic stirrer that also serves as brake - Google Patents

Abstract

(57) [Summary] [Purpose] To efficiently and effectively add electromagnetic stirring force and control force to bloom and billet molds. The magnetic field direction that regulates the direction of the braking force can be set depending on the equipment. [Structure] An iron core that surrounds the bloom and billet molds is provided with magnetic poles on the back of the four sides of the mold and having a width approximately the same as the width of each of the four sides by winding the coil. Is within 400 mm from the bottom of the meniscus and 0 to 300 below the center of the immersion nozzle discharge port.
An electromagnetic stirrer that also serves as a brake and is arranged so that the coil is wound around a magnetic pole, and an alternating current and direct current power supply device that supplies alternating current and direct current is provided to the coil. Two orthogonal DC magnetic fields are generated by the orthogonal coils, and the DC magnetic field strengths thereof are relatively adjusted to generate a braking combined DC magnetic field in an arbitrary direction with respect to the molten steel in the mold.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a braking method for positively braking a molten metal poured into a continuous casting mold, and an electromagnetic stirrer that also serves as a brake for actively horizontally stirring and braking the molten metal.

[0002]

2. Description of the Related Art For example, in continuous casting of blooms, billets, etc., in order to improve center segregation and surface quality,
A method of electromagnetically stirring the molten steel injected into the mold in the horizontal direction is adopted. In the conventional electromagnetic stirring method, molten steel is injected into a mold equipped with a plurality of magnetic poles acting as a stator of a motor as an electromagnetic stirring device, and the stirring device is supplied with a three-phase alternating current or a two-phase alternating current. Applying force to molten steel,
A horizontal flow of about 0.1 to 1.0 s / sec is generated (see, for example, JP-A-63-252651 and JP-A-63-286257).

Further, the molten steel injected into the mold contains minute inclusions and bubbles, which remain in the molten steel and solidify, which causes product defects. Therefore, as a method of floating these inclusions and bubbles to the meniscus and removing them from the molten steel, electromagnetic braking is performed. That is, by applying a static magnetic field to the molten steel by using a permanent magnet or an electromagnet arranged on the back of the long side of the mold to positively reduce the molten steel flow rate, inclusions and bubbles are prevented from entering the deep part of the slab. At the same time, they are promoted to float by buoyancy (for example, JP-A-57-173).
56, JP-A-58-188555, etc.).

Further, when continuously casting different types of molten steel without stopping the casting, electromagnetic braking is applied to the molten steel by the above-mentioned device to reduce the range of the region where different types of steel are mixed. Therefore, it has been attempted to improve the yield.

As a combination of these techniques, a mold has also been devised in which an alternating current power source and a direct current power source can be selectively connected to an electromagnetic coil and has both functions of electromagnetic stirring and electromagnetic braking (Japanese Patent Laid-Open No. 63-63). 188461, etc.).

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
As shown in FIG. 6, the electromagnetic stirrer also used as a brake disclosed in Japanese Patent No. 8461 has a linear motor coil installed on the back of the long side of the mold to stir or brake molten steel.
It was a magnetic stirrer that also served as a brake for the slab. In this device, since there is no electromagnetic coil on the back side of the short side, it is not possible to generate a rotating magnetic field. Therefore, the molten steel in the mold for casting the bloom or billet having a small cross section cannot be efficiently stirred. Further, when a DC magnetic field is applied to dampen the molten steel, the magnetic flux must pass through a gap twice the core interval, as shown in FIG. 6, which is a factor that the magnetic flux is greatly attenuated. Further, the DC magnetic field can only be applied to the magnetic field perpendicular to the long side as shown in FIG. It is assumed that a magnetic field perpendicular to the long side is applied to the discharge flow from the two-hole nozzle (immersion nozzle) as shown in FIG. 7A. After the discharge flow collides with the short side, it is divided into an upflow and a downflow. Furthermore, the downward flow forms a circulating flow towards the nozzle. This downward flow is shown in FIG.
When a magnetic field is applied as described above, an induced current conceptually as shown in FIG. 7B is generated in the molten steel based on Fleming's law. In this case, since the current component in the direction perpendicular to the magnetic field is small near the short side, the braking force is not efficiently generated for the downward flow near the short side. Thus, the magnitude of the braking force is closely related to the magnetic field direction and the molten steel flow direction. The direction of molten steel flow in the mold depends on the discharge angle of the immersion nozzle,
Since the size changes intricately depending on the size of the slab, etc., it is considered that there is an optimum DC magnetic field application direction depending on each facility condition. However, the conventional device cannot adjust the application direction of the magnetic field.

When the above-mentioned conventional technique is applied as an electromagnetic stirrer that also functions as a brake for casting blooms, billets and the like, it is difficult to stir and brake molten steel efficiently.

A first object of the present invention is to provide an electromagnetic stirrer which also serves as a brake for efficiently and effectively applying a magnetic stirrer force and a control force to the molten metal in the mold. The second purpose is to provide.

[0009]

According to the braking method of the present invention, an iron core that surrounds a continuous casting mold is provided with a magnetic pole that is the back of the four sides of the mold and has the same width as the width of each of the four sides. It is provided by winding, direct current is made to flow through the coil, two orthogonal DC magnetic fields are generated, and the intensity of the two DC magnetic fields is changed to apply a synthetic DC magnetic field in any direction to the slab. Is characterized by.

The electromagnetic stirrer that also serves as a brake according to the present invention is an iron core that surrounds a continuous casting mold;
The center of the height direction is set within 400 mm from below the meniscus in the continuous casting mold, and the width of each of the four sides of the mold, which is arranged at a position 0 to 300 mm below the center of the discharge nozzle of the dipping nozzle, is approximately the same as the width of each of the four sides of the mold. It has magnetic poles of the same width; a coil wound around the magnetic pole; and an AC / DC power supply device for supplying AC current and DC current to the coil.

[0011]

In the electromagnetic stirrer that also serves as a brake of the present invention, magnetic poles having widths substantially the same as the widths of the four sides of the mold are provided at the backs of the four sides of the mold. The molten metal in the continuous casting mold such as a billet can be efficiently stirred or braked. Since the center position of the magnetic pole in the height direction is within 400 mm from below the meniscus, a sufficient stirring flow rate (0.4
~ 0.5 m / sec) and the center position of the magnetic pole is 0 ~ 300 mm below the discharge nozzle center of the immersion nozzle, so that inclusions and bubbles caused by the nozzle discharge flow penetrate into the deep part of the slab. The maximum braking force that can be generated by the electromagnetic coil acts on the descending flow that is the cause, and as a result, inclusions and bubbles easily float.

Since the alternating current and direct current power supply for supplying alternating current and direct current to the coil is provided, it has two functions of electromagnetic stirring and electromagnetic brake, and both functions are used properly according to the operating conditions such as casting speed. be able to.

Furthermore, since the back magnetic poles on the four sides of the mold are provided, two orthogonal DC magnetic fields are generated by the orthogonal magnetic poles, and the strengths of the two DC magnetic fields are changed to change the strength of the slab in any direction. Since a synthetic DC magnetic field can be formed, optimum electromagnetic braking can be applied to the molten metal flow in accordance with equipment conditions such as the nozzle discharge angle and the size of the slab.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention is shown in FIGS. FIG. 1 is a plan view of a continuous casting mold for blooms and billets, which is equipped with an electromagnetic stirring device that also serves as a brake according to the present invention.
1 is a sectional view taken along the line AA of FIG. 1, and FIG. 3 is a sectional view taken along the line BB of FIG. Referring to FIG. 1, the molds 8 and 9 are inserted into the central openings of the electromagnets (1, 2, 7, 10: FIG. 3). Then, referring to FIGS. 2 and 3, the centers of the electromagnetic coils 1 and 2 are within 400 mm below the meniscus, and 0 to 300 below the center of the discharge port of the immersion nozzle 6.
The insertion depth of the mold is adjusted to be mm by the adjusting bolt 5 (FIG. 1) attached to the mold, and then fixed on the casing 3 (FIG. 1) of the electromagnet. Further, the casing 3 of the electromagnet is fixed on the vibration table 4 (FIGS. 1 and 2) and vibrates together with the molds 8 and 9.

When used as electromagnetic stirring, two pairs of opposed coils 1 and 2 are energized with alternating currents having 90 ° different phases, as shown in FIG. 4 (a). When used as an electromagnetic brake, a direct current is applied to the opposing coils 1 and 2 as shown in FIG. 4 (b). At this time, coils 1 and 2
The direction of the DC magnetic field with respect to the molten steel in the mold is adjusted by changing the current value of.

FIG. 5 shows the structure of the AC / DC power supply device 17 for supplying alternating current and direct current to the coils 1 and 2. The power supply device 17 energizes the coils 1 and 2 with the above-described alternating current or direct current. AC and DC currents can be applied to the coil without changing the cables, and the electromagnetic stirring and braking functions can be used separately.

Specifically, when used as electromagnetic stirring, two pairs of opposing coils 1 and 2 have alternating current V phase and alternating current U phase having different phases of 90 ° as shown in FIG. 4 (a). The electric current of. Then, as shown in the figure, a magnetic field Bu and a magnetic field Bv are generated, and due to an alternating magnetic field with a 90 ° phase difference, the combined magnetic field becomes a rotating magnetic field, and a stirring force that stirs the molten steel horizontally acts.

When used as an electromagnetic brake, a direct current is passed through the opposing coils 1 and 2 as shown in FIG. 4 (b). A DC magnetic field B1 and a DC magnetic field B2 are generated by these currents, and a combined magnetic field B3 is generated by these DC magnetic fields B1 and B2. The direction of the composite magnetic field B3 is determined by the strengths of the DC magnetic fields B1 and B2 (current values converted to the coils 1 and 2). This direction is determined according to the operating conditions. For example, when the nozzle ejection direction is the horizontal direction in FIG. 4B, the DC magnetic field B2 is almost 0, and conversely, when the nozzle ejection direction is the vertical direction in FIG. By setting B1 to 0, a DC magnetic field having a directional component effective for each electromagnetic brake is generated. When the nozzle discharge direction is diagonally directed so that the discharged molten steel does not directly collide with the short side and the long side, the combined magnetic field B3 may be adjusted in a direction in which the DC magnetic field is orthogonal to the molten steel discharging direction. In the alternating-current / direct-current power supply device 17 shown in FIG.
Is an AC conduction control signal whose output is an AC current having a phase difference of 90 ° between the U phase and the V phase, and a DC whose output is a DC current having a required level. A conduction control signal is selectively applied. 15 is commercial 3
A phase alternating current power source, and 18 is a direct current reactor. In Figure 5,
The phase assignment to the coil when electromagnetic stirring is performed is shown by adding to the coil code. FIG. 5 shows a state in which a V-phase AC current flows in the magnetic pole 10 extending in the left-right direction and a U-phase AC current flows in the magnetic pole 10 extending in the vertical direction. If a direct current is applied to the coils 1 and 2 by the thyristor phase shift controller 14,
It becomes an electromagnetic brake.

The mold 8, which is inserted in the opening of the electromagnet,
The material of 9 is, when an alternating current is applied to the coils 1 and 2,
It should have low electrical conductivity in order to suppress the generation of induced current.

[0020]

【The invention's effect】

(1) A direct-current magnetic field in any direction can be applied to the molten metal in the mold, and optimum electromagnetic braking can be applied to the molten metal flow according to equipment conditions such as nozzle discharge angle and slab size.

(2) An electromagnetic stirring force and a braking force can be efficiently and effectively added to the molten metal of the continuous casting mold for blooms and billets, and both functions can be used properly according to the operating conditions such as casting speed. it can.

[Brief description of drawings]

FIG. 1 is a plan view of an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

3 is a sectional view taken along line BB of FIG.

4 is a horizontal cross-sectional view corresponding to FIG. 3, showing a coil energization pattern of the electromagnets (1, 2, 7, 10) shown in FIG. 3, (a) showing an energization pattern during electromagnetic stirring, (b) Indicates an energization pattern during electromagnetic braking.

5 is a block diagram showing the configuration of an AC / DC power supply device 17 for energizing the coils of the electromagnets (1, 2, 7, 10) shown in FIG.

FIG. 6 is a plan view of a conventional electromagnetic stirring device that also serves as a brake.

7 (a) is a vertical cross-sectional view showing a region of a magnetic field applied to molten steel in a mold by the electromagnetic stirrer for brake and shown in FIG. 6, and FIG. 7 (b) is a cross-sectional view taken along line AA (horizontal cross-sectional view) of FIG. ).

[Explanation of symbols]

1, 2: Electromagnetic coil 3: Electromagnetic casing 4: Vibration table 5: Adjuster bolt 6: Immersion nozzle 7: Electromagnetic iron core 8: Mold long side 9: Mold short side 10: Magnetic pole 11: Meniscus 12: Nozzle outlet center 13: Coil center 14: Thyristor phase shift control device 15: AC commercial power supply 16: Thyristor 17: AC / DC power supply device 18: U-phase and V-phase cycloconverter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toyohiko Kamiyoshi 59 Nippon Steel Plant Design Co., Ltd. 46 Nakahara, Tobata-ku, Kitakyushu, Fukuoka

Claims (2)

[Claims] 1. An iron core surrounding a continuous casting mold,
The back of the four sides of the mold, the magnetic pole of approximately the same width as the width of each of the four sides is provided by winding a coil, and a direct current is passed through the coil to generate two direct current magnetic fields that intersect at right angles. A method for braking a molten metal of a continuous casting mold, which comprises applying a synthetic DC magnetic field in an arbitrary direction to a slab by changing a magnetic field strength. 2. An iron core which surrounds the continuous casting mold; the center of the height direction is 400 mm below the meniscus in the continuous casting mold and 0 to 300 mm below the center of the dipping nozzle at the back of the four sides of the mold. And magnetic poles, which are arranged at the following positions and are coupled to the iron core, having approximately the same widths as the width of each of the four sides of the mold; a coil wound around the magnetic pole; and a power supply for both AC and DC that feeds the coil with alternating current and direct current An electromagnetic stirrer that also serves as a brake for the molten metal of the continuous casting mold, which is equipped with a device.