JP2001334352A - Electromagnetic stirring device in mold for billet and stirring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform electromagnetic stirring while giving sufficient circulating flow to molten metal below a meniscus even in the case of being high speed casting for improving the surface flaw on a billet, center segregation and the solidified structure, in a continuous casting. SOLUTION: In this device, in a mold, horizontal plane circulating flow type electromagnetic stirring coils are disposed by (n) steps and magnetic poles at these (n) steps of the coils are shifted in order at each 360/n deg.. In this stirring method, the spiral-state circulating flow is generated in the molten metal in the mold by disposing the (n) steps of the horizontal plane circulating type electromagnetic stirring coils to the mold below the meniscus level in the mold and shifting the magnetic poles of the (n) steps of the coils at each 360/n deg. in order to stir the molten metal below the meniscus. The billet in which the development of the surface flaw and the center segregation are sufficiently restrained and which is excellent in the solidified structure, can stably be produced at high speed casting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic stirring device and a stirring method for a billet in a mold for continuous casting of billets and blooms (hereinafter referred to as billets) such as billets. .

[0002]

2. Description of the Related Art As shown in FIG. 5, in a continuous casting of a billet, a molten metal in a tundish 1 (hereinafter referred to as a "molten metal") is cooled through a nozzle 4 provided below the tundish into a cooled tubular mold. 5 is performed. The injected molten metal 7 is solidified along a solidified shell 8 along the inner surface of the mold 5.
Which is drawn out into a billet.

In the continuous casting of such billets,
Electromagnetic stirring of the molten metal 7 in the mold is performed to prevent the generation of flaws and pinholes on the billet due to nonmetallic inclusions in the molten metal 7 and to improve segregation and solidification structure of the billet center. I have. The electromagnetic stirring in this case is called a horizontal swirling flow type, in which a magnetic field is formed in the horizontal direction in the mold by the coil 3 and the magnetic field is swirled in the horizontal plane to give the swirling flow 9 in the horizontal plane to the molten metal. Is what you do.

[0004] Japanese Patent No. 2779344 discloses this technology. A coil for electromagnetic stirring is provided around the meniscus 6.
Disclosed below is a technique for controlling the stirring of the molten metal 7 including the free surface in the mold 5 to improve the solidified structure of the billet and the overall quality.

[0005]

In billet continuous casting equipment, high-speed casting for improving productivity is spurred year by year, and casting at a maximum of 6 m / min has recently been performed. However, a phenomenon occurs in which the stirring flow rate under the meniscus decreases with the increase in speed, and a problem arises in that a sufficient quality improvement effect cannot be obtained. Therefore, the problem to be solved by the present invention is to improve the surface defects of the billet, the segregation at the center, and the solidification structure in the continuous casting of the billet. And magnetic stirring.

[0006]

According to the present invention, there is provided an apparatus for solving the above-mentioned problems, in which a mold is provided with n stages of a horizontal plane swirling flow type electromagnetic stirring coil, and the n-stage coil has a magnetic pole of 360 / n °.
This is an electromagnetic stirring device in a billet mold, which is shifted in order. According to the method of the present invention for solving the above-mentioned problems, an n-stage horizontal swirling flow type electromagnetic stirring coil is arranged in a mold below a meniscus level in the mold,
The magnetic stirring in the billet mold is characterized by generating a spiral swirling flow in the molten metal in the mold by agitating the magnetic poles of the coils of the steps in order of 360 / n ° and stirring the molten metal under the meniscus. Is the way.

[0007]

FIG. 1 shows an example of the apparatus of the present invention. The molten metal 7 injected from the nozzle 4 of the tundish 1 into the tubular mold 5 is cooled and forms a solidified shell 8 along the inner surface of the mold 5, which is pulled out to become a billet. In the apparatus of the present invention, n stages (n = 3 in this example) of a horizontal plane swirling flow type electromagnetic stirring coil 3 are arranged on a mold 5, and the magnetic poles of the n stages of coils are shifted in order by 360 / n °. In this example, the coils 3a, 3b, 3c are 120 ° (= 360 °).
/ 3). Reference numeral 2 denotes a level meter 2 for detecting the level of the meniscus 6, and a gamma ray level meter or the like can be employed.

FIG. 2 shows an example of magnetic pole arrangement of the coils 3a, 3b, 3c. The first-stage coil 3a includes three-phase U, V, and W windings 10 arranged as shown in FIG.
b, each winding 10 is connected to the first-stage coil 3a as shown in FIG.
And the third-stage coil 3c disposes each winding 10 by 120 ° with respect to (b) as shown in (c).

When a current having a phase difference of 120 ° is applied to the U, V, and W windings 10, magnetic lines of force are formed in the electromagnetic stirring coils 3a, 3b, and 3c, respectively, and the magnetic lines rotate with time. At the moment when the electromagnetic stirring coil 3a forms magnetic lines of force going upward from the bottom of the figure as shown in FIG. 2A, the magnetic lines of force formed by the coils 3b and 3c are respectively shown in FIGS. As shown in c), the direction is from the upper left to the lower right and from the upper right to the lower left.

By sequentially shifting the windings 10 of the coils 3 arranged in three stages by 120 ° in this manner, the lines of magnetic force formed by the coils 3a, 3b, 3c are shifted by 120 °.
Shift in order. When a three-phase alternating current is applied to each of the coils 3a, 3b, 3c, the lines of magnetic force formed by the coils 3a, 3b, 3c rotate while being shifted by 120 °. That is, the lines of magnetic force formed by the three coils 3a, 3b, and 3c rotate upward at the same time as rotating in the horizontal direction. Therefore, the molten metal 7 in the mold 5 is spirally extended below the meniscus as shown in FIG. A swirling flow 9 is generated.

In the conventional electromagnetic stirrer, the strong rotational potential at the center of the coil is transmitted to the meniscus 6 due to the viscosity of the molten metal. In the present invention, the strong rotational potential at the center of the coil is reduced by the spiral swirling flow 9. It can move to the meniscus 6 directly. Therefore, in the apparatus of the present invention, a swirling flow velocity stronger than that of the conventional electromagnetic stirring apparatus is generated for the molten metal under the meniscus.

The generation mechanism of the spiral swirling flow 9 will be described with reference to FIG. 3 by taking as an example a case where n = 6, that is, six stages of coils are provided. The positions of the magnetic poles of each coil are shown in a cut-out form in FIG. 2, and the first row is U, -W, V, -U, W,
−V, U. The second stage is 60 ° (=
360 ° / 6) shift, -V, U, -W, V, -U,
W, −V, and the third stage is further shifted by 60 °, and W, −V
V, U, -W, V, -U, W. Hereinafter, it is sequentially shifted by 60 ° to the sixth stage.

When an alternating current of three phases and a phase difference of 120 ° is applied to each of the six-stage coils, the positions of the magnetic poles N and S generated in each of the coils become the first, second,. Are sequentially shifted by 60 °. That is, the lines of magnetic force from the magnetic poles N to S are also sequentially shifted by 60 ° from the first stage to the sixth stage. As a result, as described above, the lines of magnetic force in the coils of each stage rotate in the horizontal direction and simultaneously move upward,
A spiral swirling flow 9 is generated in the molten metal 7.

In such an apparatus of the present invention, in high speed casting, a strong spiral swirling flow 9 can be generated in the molten metal 7 by the multi-stage horizontal swirling type electromagnetic stirring coil 3, and the molten steel under the meniscus can be produced. It can be sufficiently stirred.

Next, in the method of the present invention, using the above-described apparatus of the present invention, as shown in the example shown in FIG. 1, a horizontal plane swirling flow type electromagnetic stirring coil 3 is placed in the mold 5 below the meniscus level in n stages (FIG. 1). N = 3), and the magnetic pole of the n-stage coil is 3
By shifting the molten metal 7 in the mold 5 sequentially by 60 / n °, a spiral swirling flow 9 is generated, and the molten metal below the meniscus is stirred. In this example, three-stage coils 3a, 3
The magnetic poles of b and 3c are sequentially shifted by 120 °.

The arrangement of the magnetic poles of each electromagnetic stirring coil 3 and the mechanism of generation of the swirling flow 9 are as described in the above-described apparatus of the present invention. According to the method of the present invention, in the high-speed casting, the molten metal under the meniscus can be sufficiently stirred by the horizontal plane swirling flow type electromagnetic stirring while the meniscus level in the mold is controlled to be constant.

In the above-described apparatus and method of the present invention, the billet includes a so-called bloom, and the cross-sectional shape can be various shapes such as a square, a rectangle, a circle, an ellipse, and an H-shape. The target material can be various metals or alloys made of a magnetic material in addition to steel. Further, the number of the electromagnetic stirring coils 3 can be appropriately set according to the billet size, the casting speed, and the like, in addition to the above-described three and six stages.

[0018]

EXAMPLE A carbon steel billet having a square shape of 150 mm on a side was continuously cast by the apparatus of the present invention as shown in FIG. The distance between the coil center of the uppermost coil 3a and the meniscus 6 was 370 mm. As an example of the present invention, each coil 3a,
The magnetic poles of 3b and 3c were sequentially shifted by 120 ° as shown in FIG. 2 to perform electromagnetic stirring. As a comparative example, electromagnetic stirring was performed without shifting the magnetic pole of each coil. The casting speed was set to two levels of 3 m / min and 5 m / min in both the present invention example and the comparative example,
The flow velocity of the swirling flow 9 generated in the molten metal 7 was measured up to the position of the meniscus 6 above the uppermost coil 3a.

As a result, as shown in FIG. 4, in the comparative example, the swirling flow rate sharply decreases when moving away from the center of the coil, and when the casting speed is 5 m / min, the swirling flow rate at the meniscus position is about 5 cm. / sec, and no stirring effect was observed. On the other hand, in the example of the present invention, the casting speed was 5 m / m
In the case of in, the swirling flow rate was 26 cm / sec even at the meniscus position, the molten metal under the meniscus could be sufficiently stirred, and a billet having no surface flaws and center segregation and having an excellent solidification structure was obtained.

[0020]

According to the present invention, in continuous casting of billets such as billets, at the time of high-speed casting, the meniscus level is detected by the level meter, and even when the meniscus level constant control is performed, it is disposed below the level meter. By generating a strong spiral swirling flow in the molten metal by the horizontal horizontal swirling flow type electromagnetic stirring coil, the molten metal below the meniscus can be sufficiently stirred. Therefore, generation of surface flaws and center segregation can be sufficiently suppressed, and a billet excellent in solidification structure can be stably manufactured by high-speed casting.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of the present invention.

FIG. 2 is an explanatory diagram showing an example of a magnetic pole arrangement of an electromagnetic stirring coil according to the present invention.

FIG. 3 is an explanatory view showing an operation example of the electromagnetic stirring coil in the present invention.

FIG. 4 is a graph showing a change in swirling flow rate in the embodiment.

FIG. 5 is an explanatory view showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Tundish 2 ... Level meter 3 ... Electromagnetic stirring coil 4 ... Nozzle 5 ... Mold 6 ... Meniscus 7 ... Molten metal 8 ... Solidified shell 9 ... Swirling flow 10 ... Winding

Continued on the front page (72) Inventor Toshiro Fukuokaya 46-59 Ohara Nakahara, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corporation Engineering Business Headquarters (72) Inventor Toyohiko Kamiyoshi 46-46 Nakahara Oaza, Tobata-ku, Fukuoka Prefecture 59 F-term (reference) in Nippon Steel Plant Design Co., Ltd. 4E004 AA09 MB12 NB02 NB04

Claims (2)

[Claims] 1. An electromagnetic stirrer in a billet mold, comprising n stages of horizontal-stirring flow type electromagnetic stir coils arranged in a mold, wherein magnetic poles of the n-stage coils are sequentially shifted by 360 / n °. apparatus. 2. A horizontal plane swirling flow type electromagnetic stirring coil is provided in the mold below the meniscus level in the mold in n stages, and the magnetic poles of the n-stage coils are sequentially shifted by 360 / n ° in order to reduce the number of coils in the mold. A method of electromagnetically stirring in a billet mold, wherein a spiral swirling flow is generated in the molten metal and the molten metal under the meniscus is stirred.