JPH07256410A - Method for continuously casting molten metal - Google Patents

Abstract

PURPOSE:To prevent the development of stagnation and eddy current by making a spouted flow from a pouring nozzle for molten metal flat in shape and flow downward and avoiding the interference of the poured flow with a circulation stirring flow by an electromagnetic coil. CONSTITUTION:At the time of impressing shifting magnetic field 6 to the molten steel 7 in a mold 2 through electromagnetic coils 1 arranged so as to confront each other along the long sides of the mold 2, the circulation stirring flow 4 is developed in a horizontal direction. The shape of the pouring nozzle 3 is made flat while matching the cross sectional shape of the mold 2 and the spouting hole is made a slit type with opened lower end. The molten steel 7 is poured downward from the spouting hole so that the poured flow does not interfere with the circulation stirring flow 4. In order to avoid the interference, the tip of the nozzle 3 is preferably positioned below the lower end of the coil 1. By this method, the uniform cast slab without defect can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method for molten metal, and more particularly to a continuous casting method suitable for casting a slab such as a steel slab from molten steel.

[0002]

2. Description of the Related Art For example, when continuously casting a slab,
It is known that molten steel injected into a rectangular mold is agitated by an electromagnetic coil installed in the width direction of the mold to prevent segregation in the molten steel (see JP-A-57-17355). The electromagnetic stirring of the molten steel is performed by applying an alternating magnetic field to the molten steel and applying moving magnetic fields in opposite directions by electromagnetic coils arranged to face each other across the mold in the width direction of the mold, thereby causing a horizontal swirling flow in the molten steel. Is generated and stirred.

The above electromagnetic stirring will be described with reference to FIG.
Electromagnetic coils are arranged so as to face each other along the width direction of the mold having a rectangular cross section, and thereby a swirling stirring flow due to electromagnetic force is generated in the molten steel. It is known that such horizontal swirling stirring cleans, for example, alumina inclusions captured in the surface layer of aluminum-killed steel, thereby reducing flaws during rolling.

However, as shown in FIGS. 4 (a) and 4 (b), the molten steel flow discharged downward from the discharge port of the injection nozzle 10 having a circular cross section at a short angle hits the short side and is divided into a downward flow and an upward flow, and an upward flow. The flow interferes with the stirring flow, and stagnation due to this interference (a pool for impurities, shaded area A in the figure)
To hinder the cleaning effect of the electromagnetic stirring flow described above. Further, a vortex is likely to be generated at a position directly above the discharge port of the injection nozzle (the cross portion B in the figure), and this vortex causes a problem that the lubricant for casting is caught in the molten steel.

[0005]

The present invention solves the problems of the conventional electromagnetic stirring technology and suppresses the interference between the stirring flow and the injection flow from the nozzle as much as possible.
An object of the present invention is to provide a continuous casting method for molten metal, which can obtain a slab of uniform quality without defects in the slab circumferential direction.

[0006]

The gist of the present invention is as follows. (1) A moving magnetic field is applied to the molten metal in the mold by an electromagnetic coil installed in parallel with the width direction of the mold having a rectangular cross-section for injecting the molten metal, and the molten metal is swirled and stirred horizontally to perform casting. In the continuous casting method of the molten metal, the discharge flow from the injection nozzle of the molten metal is flat and downward corresponding to the shape of the mold, so that the flow by the injection from this nozzle and the swirling stirring flow do not interfere with each other. A method for continuously casting molten metal characterized. (2) The continuous casting method for molten metal according to (1), wherein the molten metal is discharged such that the discharge port of the injection nozzle is located below the lower end of the electromagnetic coil.

[0007]

The function of the present invention will be described in detail below. As shown in FIG. 1, when electromagnetic coils 1 are arranged so as to face each other along a long side of a continuous casting mold 2 having a rectangular cross-sectional shape, and a moving magnetic field 6 by the coil is applied to molten steel 7 in the mold, a horizontal direction is obtained. The swirling agitated flow 4 is generated at. The installation position of the coil 1 is shown in FIG.
Also, as shown in FIG. 3, the upper end is located near the molten steel meniscus, and the coil height is preferably about 200 mm.

According to the present invention, in such electromagnetic stirring of molten steel, the nozzle 3 for injecting the molten steel 7 into the mold 2 is devised to obtain a discharge flow which does not diminish the function of the swirling stirring flow 4. To do. That is, as shown in the drawing, the injection nozzle has a flat shape that matches the cross-sectional shape of the mold, and the molten steel discharge port has a slit shape with an open lower end. Molten steel is injected downward from this discharge port, and this injection flow does not interfere with the swirling stirring flow 4. In order to avoid this interference as much as possible, it is desirable that the tip position (nozzle depth) of the nozzle 3 be below the lower end of the coil 1. In the figure, 5 is the injection flow from the nozzle, and 8 is the solidified shell.

The molten steel injection flow 5 from the nozzle 3 is
The flow is not limited to the downward flow in the vertical direction as shown in the figure, and any flow may be applied as long as the flow of the downward component is given, and the nozzle outlet may have a structure having an angle to some extent. In short, the downward flow of the discharge in the present invention means that the injection flow of the upward component does not have to occur.

Further, as the discharge port of the nozzle, a plurality of slits may be arranged in a row other than one slit, and the shape of the nozzle is not limited to the rectangular cross section shown in the drawing, and the outer wall on the short side of the nozzle may be formed. The molten metal may be formed in an arc shape so that the molten metal can easily be swirled, or the nozzle tip may be formed in a wide slit shape.

By using the flat, downwardly-directed discharge flow generating nozzle of the present invention, this discharge flow hardly interferes with the swirling agitation flow by the coil, and as a result, the horizontal swirling flow is smooth and smooth. Therefore, it becomes possible to cast a good slab without any defects in the circumferential direction, by maximizing the cleaning effect. Further, no vortex around the nozzle is generated, and the defects of lubricant entrainment are reduced.

[0012]

EXAMPLE Casting was carried out using the method of the present invention (nozzle width 800 mm, thickness 150 mm) in a curved slab continuous casting machine (radius 10.5 m) having a cross section of width 1380 mm and thickness 250 mm. As the condition of electromagnetic stirring, an alternating magnetic field of 3 Hz (a magnetic flux density of 600 Gauss in the width direction ¼ part of the inner surface of the long side of the mold) was used. When the number of bubbles and inclusions up to the surface depth of the cast slab after casting of 10 mm was investigated, the results shown in Table 1 were obtained at 1/4 part from the end in the width center / long side width direction. Table 1
For comparison, the case of the conventional method using a round nozzle is also shown.

From Table 1, in the method of the present invention, the flow stagnation did not occur at any position of the width center and the widthwise end from the end in the width direction, and the number was small. It can be seen that there was a large number of stagnation phenomena in the central part.

[0014]

[Table 1]

[0015]

As described above, according to the casting method of the present invention, the horizontal electromagnetic stirring flow can be satisfactorily swirled without stagnation. Generation of eddies and vortices can be prevented, and uniform cast pieces without defects can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory plan view showing a specific example of a continuous casting mold for carrying out the method of the present invention.

FIG. 2 is a front sectional view of FIG.

FIG. 3 is a side view of FIG.

FIG. 4 is a schematic plan view and a schematic front view for explaining the outline of conventional electromagnetic stirring.

[Explanation of symbols]

 1 Electromagnetic Coil 2 Mold 3 Injection Nozzle 4 Swirling Stirring Flow 5 Injection Flow 6 Moving Magnetic Field 7 Molten Steel 8 Shell

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keisuke Fujisaki 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd. Technology Development Division

Claims (2)

[Claims] 1. A moving magnetic field is applied to a molten metal in a mold by an electromagnetic coil installed in parallel with the width direction of the mold having a rectangular cross-section for injecting the molten metal, and the molten metal is swirled and stirred in the horizontal direction to cast. In the continuous casting method of the molten metal, the discharge flow from the injection nozzle of the molten metal is flat and downward corresponding to the mold shape, so that the flow due to the injection from this nozzle and the swirling stirring flow do not interfere with each other. A continuous casting method for molten metal, comprising: 2. The continuous casting method for molten metal according to claim 1, wherein the molten metal is discharged such that the discharge port of the injection nozzle is located below the lower end of the electromagnetic coil.