JP2920897B2 - Method and apparatus for controlling flow of molten steel in mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for controlling the flow of molten steel in a mold, and more particularly to a method and apparatus for controlling the flow of molten steel by generating a static magnetic field in a mold of a continuous casting facility.

[0002]

2. Description of the Related Art In a continuous casting facility, molten steel is injected into a mold from an immersion nozzle to perform casting.

At this time, non-metallic inclusions and air bubbles are usually present in the molten steel to be injected. It is known that the non-metallic inclusions and the like are trapped in the solidified slab (shell) due to the flow action of the molten steel in the mold and cause defects in the rolled product, for example, blister defects in the coil.

Various techniques have been conventionally proposed to prevent such product defects. For example, JP-A-2-28
No. 4750 proposes a technique for controlling the flow of molten steel in a mold using a static magnetic field (static magnetic field).

[0005] That is, in the above-mentioned technique, as shown in FIG. 5, a mold composed of a mold short side 2 and a mold long side 3 is provided on both outer sides of the mold long side 3 and in a vertical direction of the mold 3. The magnetic poles 6A and 6B are arranged at the upper part and the lower part. A coil 7 forming a closed loop is provided for each of the magnetic poles 6A and 6B,
An electromagnet is constructed such that a current flows through the coil 7 and the magnetic flux of the static magnetic field spreads horizontally over the entire width of the mold (width direction of the long side 3 of the mold).

[0006] When the molten steel flows out of the discharge holes 5A and 5B of the immersion nozzle 1 in the two short sides of the mold, a static magnetic field generated by the electromagnet acts on the molten steel to apply a braking force by Lorentz force to control the flow of the molten steel. .

Accordingly, since the electromagnet generates a static magnetic field at the upper and lower portions, braking is applied to the molten steel flow at the upper and lower portions in the molds 2 and 3 to form a molten steel flow as indicated by arrows in the figure. .

FIG. 5A is a sectional view of the molds 2 and 3 as viewed from the long side of the mold 3 and FIG. 5B is a cross-sectional view of the molds 2 and 3 as viewed from the short side 2 of the mold. It is sectional drawing. or,
Reference numeral 4 denotes a shell in which the molten steel has cooled and solidified, and reference numeral 8 denotes a meniscus of the molten steel. The magnetic poles 6A and 6B are magnetically integrally formed with a yoke 6C.

[0009]

However, in the prior art, the magnetic flux density of the static magnetic field generated from the magnetic poles 6A and 6B is adjusted by the magnitude of the current flowing through the coil 7. Since the number of closed loops is 1, the magnetic flux density in the entire width direction of the mold long side 3 can be changed, but the magnetic flux density cannot be partially adjusted in the width direction.

Therefore, the following problems occur in the prior art.

That is, in the molds 2 and 3 of FIG. 5, the molten steel flow may not be uniformly injected in both directions of the mold short side 2 from the discharge holes 5A and 5B due to non-metallic inclusions adhering in the nozzle. . In such a case, the state of the molten steel flow in the molds 2 and 3 changes, and the nonmetallic inclusions are easily captured by the solidified shell 4. Also, for example, in a flow pattern in which breakout due to meniscus fluctuation is likely to occur,
Since it was impossible to change the braking force by partially adjusting the magnetic flux density, the flow of molten steel in the mold could not be properly maintained.

Further, the magnetic flux density distribution is not uniform in the width direction of the long side 3 of the mold. For example, as shown in FIG. 6, the magnetic flux density near the short side 2 of the mold is lower than the magnetic flux density at the center of the long side 3 of the mold. It is remarkably reduced in comparison. This is caused by the end effect of the iron core.

Therefore, in the width direction of the mold long side 3, the descending flow velocity of the molten steel is small at the center thereof due to the large Lorentz force due to the magnetic field, and the descending flow velocity is large near the mold short side 2 because the Lorentz force is small. As a result, the penetration depth of the nonmetallic inclusions in the molten steel flow in the vicinity of the short side 2 becomes larger as compared with the central portion in the width direction, and the nonmetallic inclusions and the like are easily captured by the solidified shell. Defects may occur.

Therefore, conventionally, the casting width of a mold (slab) has been limited in order to obtain a good cast piece.

Incidentally, in order to solve the above problem, Japanese Patent Laid-Open No.
JP-A-89550 proposes a magnetic force control device for a molten steel flow in a mold that uses a movable iron core divided into a plurality of pieces in a casting width direction to obtain a desired magnetic flux distribution in the width direction.

However, this device has a drawback that the device is complicated and expensive because it requires an iron core longitudinal movement mechanism and an actuator.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and it is possible to arbitrarily adjust the magnetic flux density distribution in the longitudinal direction of the mold with a relatively simple structure so that a desired braking force can be applied to the flow of molten steel. It is an object of the present invention to provide a method and an apparatus for controlling the flow of molten steel in a mold that can exert the following effects.

[0018]

SUMMARY OF THE INVENTION The present invention relates to a method for controlling the flow of molten steel by generating a static magnetic field from a magnetic pole in a mold of a continuous casting facility. By providing a magnetic pole made of a coil, a static magnetic field is generated from the main coil magnetic pole over the entire width of the mold long side, and a static magnetic field is also generated from the auxiliary coil magnetic pole near the short side of the mold, thereby solving the above-mentioned problem. is there.

In the present invention, the current supplied to the auxiliary coil can be controlled according to the strength of the molten steel flow. In this way, an appropriate braking force can be exerted on the molten steel flow.

In the present invention, the current flowing through at least one of the main coil and the auxiliary coil can be controlled so that the magnetic flux distribution in the width direction of the mold becomes uniform. In this way, a constant braking force can be exerted on the molten steel flow in the width direction.

The present invention also provides an apparatus for controlling the flow of molten steel by generating a static magnetic field from a magnetic pole in a mold of a continuous casting facility, comprising a main coil for generating a static magnetic field over the entire width of the mold. By providing a magnetic pole and a magnetic pole comprising an auxiliary coil for generating a static magnetic field near the short side of the mold at the upper and / or lower part outside the long side of the mold,
This is to solve the above problem.

[0022]

In the present invention, when controlling the flow rate of molten steel in the mold, a magnetic pole composed of the main coil and a magnetic pole composed of the auxiliary coil are provided outside the long side of the mold, and the magnetic pole composed of the main coil is extended over the entire width of the long side of the mold. In addition to generating a static magnetic field, a static magnetic field is generated near the short side of the mold from the magnetic pole formed by the auxiliary coil.

Accordingly, when the molten steel flow is injected from the plurality of openings of the immersion nozzle toward the short side of the mold, non-metallic inclusions adhere to the inside of the immersion nozzle, and the molten steel is uniformly discharged from each opening. Even when not injected, by controlling the current supplied to each of the main coil and the auxiliary coil,
Since the desired magnetic flux density distribution can be adjusted by adjusting the partial magnetic flux density in the width direction and the molten steel flow braking force can be changed, the flow of molten steel in the mold can be desirably and appropriately controlled.

Therefore, since the penetration depth of the non-metallic inclusions is made uniform in the width direction and the breakout due to the suppression of the fluctuation of the meniscus can be prevented as a uniform descending flow velocity over the entire area in the width direction of the mold, A slab with good internal quality can be obtained. Also, when casting a wide cast slab, the penetration of nonmetallic inclusions can be prevented, and the internal quality can be improved.

In addition, since a static magnetic field having an arbitrary magnetic flux distribution can be generated by a magnetic pole composed of a main coil and a magnetic pole composed of an auxiliary coil, which is a stationary device, a conventional magnetic field (for example, Japanese Patent Application Laid-Open No.
No need for a movable part such as a movable iron core as disclosed in Japanese Patent Application Laid-open No. 9550), the configuration is simple and the price is low.

[0026]

Embodiments of the present invention will be described below in detail with reference to the drawings.

This embodiment is a molten steel flow control apparatus for controlling the flow of molten steel by controlling the static magnetic field according to the present invention, as shown in FIGS.

As shown in FIG. 1 and FIG.
In an electromagnet that generates a static magnetic field in the mold from three directions of the long side of the mold, a main coil 11 for generating a static magnetic field over the entire width of the mold, and first and second coils for generating a static magnetic field near the short side 2 of the mold. And second auxiliary coils 12 and 13.

FIG. 1A is a cross-sectional view as viewed from three directions of the mold long side, FIG. 1B is a coil plan view as viewed from above, and FIG. FIG. 3 shows a cross-sectional view from the side.

As shown in FIGS. 1A and 2, the first and second auxiliary coils 12 and 13 are located in the vicinity of the short side 2 of the mold. A main coil 11 is provided on one side and on the outside overlapping therewith. The main coil 11 and the auxiliary coil 12
And 13 correspond to the mold 2 as shown in FIGS.
And 3 are provided at two places, an upper part and a lower part. Further, as shown in FIG. 1B, the main coil 11 and the auxiliary coils 12 and 13 have a portion (lap portion) 9A that shares the iron core in each of the upper iron core 9 and the lower iron core 10.
And 10A, and iron core portions 9B and 10B having only the main coil 11 are integrally formed. As shown in FIG. 2, the upper iron core 9 and the lower iron core 10 are magnetically integrated by a yoke 14.

The operation of the embodiment will be described below.

In the molten steel flow control device according to the embodiment, the magnitude of the current flowing through the main coil 11 and each of the auxiliary coils 12 and 13 can be freely selected.

Accordingly, a combined magnetic field of the static magnetic field generated when the current flows only through the main coil 11 and the static magnetic field generated when the current flows only through the auxiliary coils 12 and 13 is obtained.

FIG. 3 shows an example of a magnetic flux density distribution in three directions of the slab long side when the static magnetic field is generated in this way. In FIG. 3, a chain line 15 is a magnetic flux density distribution by the main coil 11, and a broken line 16 is a magnetic flux density distribution by the first and second auxiliary coils 12 and 13. As shown in FIG. 6, the magnetic flux density distribution is not constant in the width direction only with the main coil magnetic flux 15, but in the present embodiment, the magnetic field is generated from each of the auxiliary coils 12 and 13 so as to be indicated by a solid line 17 in the drawing. Thus, the composite magnetic flux density distribution is averaged.

Therefore, a uniform magnetic field can be formed in the longitudinal direction of the mold, that is, in the width direction of the slab, and a uniform downward flow can be obtained in the flow direction of the molten steel, thereby preventing intrusion of nonmetallic inclusions and the like. Can be achieved.

Next, a second embodiment will be described.

In the second embodiment, the first and second auxiliary coils 12 and 13 are used in the flow control of molten steel shown in FIG.
Is controlled according to the strength of the molten steel flow.

For example, the direction of the current supplied to the right first auxiliary coil 12 shown in FIG. In this case, for example, as shown in FIG.
5 and the magnetic flux density distribution 18 generated by the first auxiliary coil 12 cancel each other out, so that the magnetic flux density of the portion where the first auxiliary coil 12 is provided becomes low. If a current in the same direction as that of the main coil is supplied to the other second auxiliary coil 13, the magnetic flux density distribution 19 of the portion where the second auxiliary coil 13 is provided increases. The synthesized magnetic flux density distribution is as shown by a solid line 20 in FIG.

Therefore, the discharge holes 5A and 5A of the immersion nozzle 1
B can control the molten steel flow by changing the braking force by independently applying a static magnetic field having an appropriate magnetic flux density to the molten steel injected from B according to the flow velocity. For example, non-metallic inclusions adhere to either of the discharge holes 5A or 5B of the immersion nozzle, and the flow rate of the molten steel is reduced by the discharge holes 5A and 5B.
In this case, the magnetic flux density distribution can be changed in accordance with the molten steel flow velocity to make the molten steel flow injected into the mold a desired one.

In the above embodiment, the main coil 11
The arrangement of the auxiliary coils 12 and 13 is shown in FIG. 1, but the present invention is not limited to the arrangement shown in FIG. And 13 may be provided on the side far from the nozzle 1.

In the above embodiment, the molds 2 and 3 were used.
The coils 11, 12, and 13 of magnetic poles are respectively provided at the upper and lower portions of
Has been described, but the coils and magnetic poles configured when implementing the present invention are not limited thereto. For example, coils and magnetic poles can be provided over the entire upper and lower portions of the mold. Further, a magnetic pole can be provided independently at either the lower part or the upper part. Further, the present invention is not limited to providing the auxiliary coils one by one in the short side direction of the mold. For example, by arranging some auxiliary coils from the main part in the short side direction, the magnetic flux density distribution can be controlled more finely.

[0042]

As described above, according to the present invention, it is possible to control the magnetic flux density distribution to a desired value in the long side of the mold, that is, in the width direction of the slab.

Therefore, a uniform magnetic field can be formed in the width direction, and a uniform descending flow of molten steel can be obtained in the width direction, thereby preventing nonmetallic inclusions and bubbles from entering.

Also, in producing a wider cast piece,
Non-metallic inclusions and air bubbles can be prevented from entering.

According to the investigation by the inventor, as a result of comparison between the case of the conventional method and the case of the present invention in the continuous annealing line inspection, it was confirmed that the blister occurrence rate by the present method was reduced by half.

Further, the magnetic flux density can be partially controlled in the longitudinal direction of the mold. Therefore, it is possible to apply an appropriate braking force even to the transformation of the molten steel flow generated due to clogging of one of the immersion nozzle discharge holes, thereby preventing the breakout by suppressing the fluctuation of the meniscus, and It is possible to prevent metal inclusions from being caught by the solidified shell, and to obtain a slab having good internal quality. Also in this case, an excellent effect such as casting of a cast piece having a wider width and higher quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a configuration of a molten steel flow control device according to a first embodiment of the present invention, as viewed from a long side of a mold,
And a top plan view.

FIG. 2 is a longitudinal sectional view of the control device as viewed from a short side of a mold.

FIG. 3 is a diagram showing an example of a magnetic flux distribution for explaining the operation of the first embodiment.

FIG. 4 is a diagram showing an example of a magnetic flux density distribution for explaining the operation of the second embodiment of the present invention.

FIG. 5 is a sectional view in the direction of a mold slab and a sectional view in the direction of a short side showing a configuration example of a conventional molten steel flow control device.

FIG. 6 is a diagram showing an example of magnetic flux density distribution by the conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Immersion nozzle, 2 ... Mold short side, 3 ... Mold long side, 4 ... Solidified shell, 5A, 5B ... Discharge hole, 8 ... Meniscus, 9A ... Upper iron core common part, 9B ... Upper iron core independent part, 10A ... Lower iron core common part, 10B. ... Auxiliary coil magnetic flux density distribution, 17, 20 ... Synthetic magnetic flux density distribution.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-284750 (JP, A) JP-A-62-207543 (JP, A) JP-A-2-117756 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) B22D 11/10 350 B22D 11/10 B22D 11/04 311 B22D 11/18

Claims (4)

(57) [Claims] 1. A method for controlling the flow of molten steel by generating a static magnetic field from a magnetic pole in a mold of a continuous casting facility, wherein a magnetic pole comprising a main coil and a magnetic pole comprising an auxiliary coil are provided outside the long side of the mold. A flow control method for molten steel in a mold, comprising: generating a static magnetic field from the main coil magnetic pole over the entire width of the mold long side; and generating a static magnetic field from the auxiliary coil magnetic pole near the short side of the mold. 2. The method according to claim 1, wherein the current supplied to the auxiliary coil is controlled according to the strength of the molten steel flow. 3. The method according to claim 1, wherein a current flowing through at least one of the main coil and the auxiliary coil is controlled so that a magnetic flux distribution in a long side width direction of the mold is uniform. To control the flow of molten steel in the mold. 4. An apparatus for controlling a flow of molten steel by generating a static magnetic field from a magnetic pole in a mold of a continuous casting facility, comprising: a magnetic pole comprising a main coil for generating a static magnetic field over the entire width of a long side of the mold; And a magnetic pole comprising an auxiliary coil for generating a static magnetic field in the vicinity of the short side of the mold, provided on the upper and / or lower side of the outside of the long side of the mold.