JPH0413442A - Apparatus for continuously casting molten metal - Google Patents

Abstract

PURPOSE:To improve casting quality by constituting projecting part of electro- conductive body on outer peripheral wall part in a mold faced to electromagnetic coil in a continuous casting apparatus for molten metal set with the electromagnetic coil in shape surrounding the mold at outside of the mold. CONSTITUTION:In the continuous casting apparatus for casting while giving electromagnetic force to molten steel in the mold by setting the electromagnetic coils 1, 2 in the shape surrounding the mold at the outside of mold 3, the projecting part 3a constituted of the electro-conductive body is formed at the outer peripheral wall part faced to the electromagnetic coils 1, 2 in the mold 3. By this method, magnetic flux density distribution in the mold 3 can be flattened and by this, the developments of oscillation on the cast billet and component segregation are prevented and the casting quantity can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the continuous casting of molten metal, and in particular to the continuous casting of molten metal, in which magnetic flux is applied to the molten steel by an electromagnetic coil placed outside the mold in order to apply a pinch force to the molten steel. Regarding equipment that supplies

[Prior Art] In continuous casting equipment for molten metal, a force called a pinch force has been conventionally applied to the molten steel in the mold using an electromagnetic coil placed outside the mold. That is, an alternating current magnetic field generated by an alternating current applied to an electromagnetic coil generates an eddy current that goes in the circumferential direction in the molten steel, and the interaction between this eddy current and the external magnetic field causes the molten steel to move toward the center, that is, the molten steel. Apply a pinch force in the direction of narrowing down. As a result, the center of the molten steel swells up compared to the surrounding area, creating a dome-like curved surface. As a result, the opening between the depressed part around the meniscus and the inner wall surface of the mold is widened, so that powder accumulates in this part and it becomes easier for the powder to flow into the boundary between the molten steel and the inner wall surface of the mold.

Due to the action of such a pinch force, even when performing high-speed casting, relatively good surface quality of the slab can be obtained and productivity is improved.

Generally, the surface of the slab (&8) is caused by the vertical vibration of the mold.
Oscillation marks (sushi-shaped depressions extending in the circumferential direction) are likely to occur in the area (the part that made contact with the mold wall), but when a pinch force is applied, the contact angle between the meniscus and the mold becomes small, so oscillation marks The mark depth is reduced and the desired surface quality is achieved.

Regarding this type of technology, for example, Japanese Patent Publication No. 57-2140
It is disclosed in Publication No. 8.

[Problems to be Solved by the Invention] By the way, even when the above-mentioned pinch force is applied, oscillation marks may appear partially on the surface of the slab, and component segregation may occur in the valleys of the oscillation marks. Defects may occur.

The reason for this is that when the pinch force is applied, the hot water surface (
It is thought that the shape of the top surface of the molten steel becomes unstable, causing ripples and fluctuations in the molten metal level.

Therefore, an object of the present invention is to stabilize the shape of the molten metal surface when a pinch force is applied, and to further improve the surface quality of the slab.

[Means for Solving the Problems] In order to solve the above problems, the present invention includes an electromagnetic coil disposed outside and surrounding the mold into which molten steel is injected, and an electromagnetic coil is provided to surround the molten steel in the mold. In a continuous casting device for molten metal that performs casting while applying force: a convex portion made of a magnetic material is formed on an outer peripheral wall portion of the mold facing the electromagnetic coil, and a convex portion made of a magnetic material is formed in the convex portion. The portion facing the center portion of the electromagnetic coil in the height direction of the mold is configured to protrude further outward than the portion facing the upper and lower ends of the electromagnetic coil.

[Function] According to experiments conducted by the present inventor (using mercury instead of molten steel and transparent bead force instead of a mold), in the environment of a conventional device, the pinch force was applied by energizing the electromagnetic coil. In this state, as shown in FIG. 4a, both an upward flow and a downward flow from the center of the electromagnetic coil in the height direction were observed in the molten steel (actually mercury). The upward flow is thought to cause ripples and scene changes on the hot water surface.

By the way, conventionally used electromagnetic coils have a structure in which the wires are evenly wound to form an accurate cylindrical shape, and the height direction (direction perpendicular to the circumferential direction of the coil windings) At any position, the number of turns of the coil is substantially the same.

When the magnetic flux density distribution in the height direction inside the mold was measured in an apparatus in which such an electromagnetic coil was arranged to surround a cylindrical mold, the results shown in FIG. 3 were obtained. That is, the magnetic flux density is highest at the center of the coil, and decreases as it approaches both ends. Further, the magnitude of the pinch force acting on the molten steel is proportional to both the magnitude of the eddy current and the magnitude of the magnetic flux density in the molten steel. Therefore, in conventional devices, the greatest force acts on the molten steel at the height of the central portion of the electromagnetic coil, and the force decreases upward and downward from that point. For this reason, it is thought that a flow as shown in FIG. 4a occurs from the central portion where the force is large to the upward and downward directions where the force is small.

However, in the present invention, a convex portion made of a magnetic material is formed on a portion of the outer wall of the mold that faces the electromagnetic coil, and in the convex portion, a portion that faces the center portion of the electromagnetic coil in the height direction of the mold is electromagnetic. The coil is configured to have a shape that projects outward from the portions facing the upper and lower ends of the coil. Generally, magnetic flux has the property of passing through the path closest to it if the magnetic resistance is the same.

Therefore, in the part of the mold wall (generally made of copper) that faces the electric coil, the magnetic flux is most likely to pass through the outwardly protruding part of the central part, and it is relatively difficult for the magnetic flux to pass through the parts above and below that part. However, since the total amount of magnetic flux flowing in and out of the electric coil is constant, the magnetic flux passing through the mold wall increases and the magnetic flux passing through the molten steel inside the mold decreases. Therefore, in the molten steel inside the mold, the magnetic flux density is lower in the center of the electromagnetic coil in the height direction than in the upper and lower parts, and as a result, the distribution of magnetic flux density in the height direction is uniform as shown in Figure 2. become. As a result, the distribution of the pinch force according to the position in the height direction can be made uniform and the upward flow of molten steel can be suppressed, so that the shape and level of the molten metal surface can be stabilized as shown in Figure 4b. I can do it.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[Example 1] Fig. 1 shows a longitudinal section of a mold portion of a continuous casting apparatus according to an example. In this example, the mold 3 has a roughly cylindrical shape. The material of the mold 3 is copper.

Referring to FIG. 1, two electromagnetic coils 1 and 2 are placed outside the mold and surrounding it.

The electromagnetic coils 1 and 2 are in-shell cylindrical coils, and are configured so that the number of turns in the circumferential direction of the coil windings (4, 5) is the same at any height position. The two electromagnetic coils 1 and 2 are arranged one above the other so as to be adjacent to each other. In this example, the inner diameter of mold 3 is approximately 190 mm.
It is. The electromagnetic coils 1 and 2 are used to apply a pinch force to the molten steel 6 filled inside the mold 3. Note that these electromagnetic coils can also be configured as a single one.

The peripheral wall of the mold 3 has a special shape at the portion facing the electromagnetic coils 1 and 2. Specifically, regarding the whole coil composed of two electromagnetic coils 1 and 2, the part facing the center in the height direction, that is, the part facing the lower end of the electromagnetic coil 1 and the upper end of the electromagnetic coil 2 is the outer side. The mold is thicker at this protrusion 3a. Further, the protrusion 3a is formed uniformly over the entire circumference of the mold 3, and its outer surface is formed into a shape that draws a smooth curve in the height direction, as shown in FIG. There is.

The electromagnetic coils 1 and 2 each include one coil winding 4 and 5, and both ends of the electromagnetic coils 1 and 2 are connected in parallel to an AC power source.

An experiment was conducted to clarify the difference between the case where the mold 3 of Example was used for continuous casting and the case where a conventional mold was used. The conditions for this experiment were as follows.

Steel type: 5US304 (18Cr-8Ni) Magnetic flux density: 0, 1000.2000.3000.400
0 (Gauss) Casting speed: 2000 mm/min Thickness of protrusion 3a: 9 mm (maximum) Thickness of mold wall 3: 6 mm Thickness of conventional mold wall: 6 mm The results of this experiment are shown in Figures 5a and 5b.

That is, Fig. 5a shows the results of measuring the depth of the oscillation mark at each magnetic flux density, and Fig. 5b shows the results of measuring the depth of component segregation of the slab at each magnetic flux density. The black circles indicate the case of the electromagnetic coil of the example of the present invention, and the white circles indicate the case of the conventional electromagnetic coil.

From all the results, it can be seen that the mold of the present invention provides much more favorable casting results, especially under conditions where the magnetic flux density is high.

Modified embodiments are shown in Figures 6a and 6b, respectively. In these embodiments, the mold 3B itself has a uniform peripheral wall thickness like a general mold. Instead, in the embodiment of FIGS. 6a and 6b, annular conductors (composed of copper) 7 and 8 are arranged around the outer periphery of mold 3B, respectively. In the example shown in FIG. 6a, the cross-sectional thickness of the magnetic body 7 is constant, and the magnetic body 7 forms a step on the outer periphery of the mold. This produces the same effect as the protrusion 3a in FIG. 1 of the embodiment described above, so that the magnetic flux density distribution in the molten steel can be made uniform.

Although the magnetic flux density distribution in this example is not as flat as in the embodiment shown in FIG. 1, it is sufficiently effective in preventing upward flow in the molten steel. In the embodiment shown in FIG. 6b, the thickness of the magnetic body 8 is formed so that it is large in the center and gradually decreases toward both ends, so that the distribution of magnetic flux density is flattened as in the embodiment shown in FIG. It can be done.

[Effect of the invention] As described above, according to the present invention, the electromagnetic coil (1,
Since a convex portion (3a, 7°8) is formed in the part facing 2), the magnetic flux density distribution within the mold can be made flatter than before, thereby reducing oscillation marks on the slab. The quality of casting can be greatly improved by suppressing the occurrence of component segregation.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing the main parts of the casting equipment of the embodiment. FIGS. 2 and 3 are graphs showing the distribution of magnetic flux density when using the electric coils of the example and the conventional example, respectively. FIG. 4a and FIG. 4b are longitudinal sectional views showing the flow state of molten steel in the conventional example and the example, respectively. Figures 5a and 5b are graphs showing the results of the experiment. FIGS. 6a and 6b are longitudinal sectional views each showing a modified embodiment of the present invention. 1.2: Electromagnetic coil 3: Mold

Claims (1)

[Claims] A continuous casting device for molten metal, which includes an electromagnetic coil placed outside and surrounding a mold into which molten steel is poured, and performs casting while applying electromagnetic force to the molten steel in the mold. In: an outer peripheral wall portion of the mold facing the electromagnetic coil,
A convex portion made of a conductor is formed, and in the convex portion, the portion facing the center portion of the electromagnetic coil in the height direction of the mold is shaped to protrude further outward than the portion facing the upper and lower ends of the electromagnetic coil. A continuous casting device for molten metal, characterized in that: