JP2839637B2 - Continuous casting equipment for molten metal - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to continuous casting of molten metal, and more particularly to improving the quality of cast slabs.

[Prior Art] In a continuous casting facility for molten metal, conventionally, a force called a pinch force is applied to molten steel in a mold by an electromagnetic coil arranged outside the mold.
That is, an AC magnetic field generated by an AC current applied to the electromagnetic coil generates a circumferential eddy current in the molten steel,
Due to the interaction between the eddy current and the external magnetic field, a pinch force is applied in a direction toward the center of the molten steel, that is, in a direction to narrow down the molten steel. As a result, the central part of the molten steel rises more than the surroundings on the molten metal surface, and the molten steel has a dome-shaped curved surface.
As a result, the opening between the depressed portion in the periphery of the meniscus and the inner wall surface of the mold is widened, so that powder accumulates in this portion and the powder easily flows into the boundary between the molten steel and the inner wall surface of the mold.

By the action of such a pinch force, even when high-speed casting is performed, relatively good slab surface quality is obtained and productivity is improved.

In general, an oscillation mark (a streak-shaped depression extending in the circumferential direction) is easily formed on the surface of the slab (a portion in contact with the mold wall) due to the vertical vibration of the mold, but when a pinch force is applied, a meniscus is formed. Since the contact angle between the mold and the mold becomes smaller, the depth of the oscillation mark becomes shallower, and desired surface quality can be obtained.

This type of technique is disclosed, for example, in Japanese Patent Publication No. 57-21408.

[Problems to be Solved by the Invention] By the way, even when the pinch force as described above is applied, an oscillation mark is conspicuously partially shown on the surface of the slab, or component segregation or the like is caused in the oscillation mark. Defects may occur.

This is because when a pinch force acts, an upward flow occurs in the molten steel, which causes the shape of the molten metal surface (the upper surface of the molten steel) to become unstable, and the molten metal surface to undulate. Is considered as.

Accordingly, 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 a slab.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, in a continuous casting apparatus for molten metal, which performs casting while applying electromagnetic force to molten steel injected into a mold: A first electromagnetic coil that is arranged near the molten metal surface in the mold, is connected to an AC power supply, and applies a force toward the center of the mold to molten steel in the mold; and the first electromagnetic coil; Below the electromagnetic coil, there is provided a second electromagnetic coil that is arranged so as to surround the mold, is connected to an AC power supply, and applies a rotating force to the molten steel in the mold in a circumferential direction of the mold.

[Operation] According to an experiment conducted by the present inventors (using mercury instead of molten steel and a transparent beaker instead of the mold), a casting apparatus provided with an electromagnetic coil for applying a pinch force to molten steel in the mold was used. In the state where the electromagnetic coil is energized and the pinch force is applied, as shown in FIG. 5a, the flow flowing upward and downward from the center in the height direction of the electromagnetic coil in the molten steel (actually, mercury). Both were confirmed. Then, it is considered that the upward flow exerts ripples and fluctuations on the molten metal surface.

In the present invention, the first electromagnetic coil acts to apply a force for pinching the molten steel toward the center, that is, a pinch force, while the other second electromagnetic coil applies the force to the molten steel. Generates a force that rotates in a horizontal plane.
Therefore, a vertical flow and a rotational flow in a horizontal plane are simultaneously generated in the molten steel, and the overall flow is a composite of them. For this reason, even if an unstable wave is to appear on the surface of the molten metal due to the upward flow due to the pinch force, the unevenness of the surface is diffused in the horizontal direction, so that the degree of the wave becomes small. Therefore, the shape of the molten metal surface is stabilized, and oscillation marks are reduced.

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

Embodiment FIG. 1 shows a longitudinal section of a main part of a continuous casting apparatus according to an embodiment. In this embodiment, the mold 1 is formed in a cylindrical shape, and the inner diameter is about 190 mm. At the top of the mold 1,
A first set of coils 2 is arranged so as to surround it, and below it, a second set of coils 6 is arranged so as to surround the mold 1 with a shielding plate 8 interposed therebetween.

The first set of coils 2 is configured by stacking two electromagnetic coils 3 and 4 on top of each other, and is formed in a cylindrical shape of each of the electromagnetic coils 3 and 4. The height of the first set of coils 2 is
The molten steel 9 poured into the mold 1 is positioned so that the molten metal surface 9a enters above or inside the first set of coils. Surface of a bath
9a is flat when no electromagnetic force is applied, but when a pinch force is applied by the first set of coils 2, that is, a force in the direction of squeezing the molten steel 9 toward the center side, as shown in FIG. Rises into a dome shape.

The winding 5 of the coil constituting the electromagnetic coil 3 is wound in a direction of circling the outer periphery of the mold 1 as is apparent from the cross section of FIG. The same applies to the other electromagnetic coil 4. These electromagnetic coils 4 are connected in parallel to an AC power supply. Therefore, the operation of the first set of coils 2 can be explained with reference to FIG. 2a. That is,
As shown in FIG. 2a, the current flowing through the electromagnetic coils 3 and 4 flows in the direction of circling the outer periphery of the mold 1, thereby generating an eddy current in the molten steel in the direction circling in a horizontal plane. Due to the interaction between the eddy current and the magnetic fields generated by the electromagnetic coils 3 and 4, a force in the radial direction of the mold 1 (actually a force toward the center) is generated in the molten steel.

Here, the magnitude of the eddy current is J, the magnitude of the magnetic flux density is B,
Assuming that the force is F, the magnitude of the force F can be represented by F = J × B. Further, since the electromagnetic coils 3 and 4 are energized by an AC power supply, assuming that the angular velocity of the power supply is ω and the time is t, B = Bm Sin ωt J = Jm Sin (ωt−ψ), then F = Bm Sin ωt · Jm Sin (ωt−ψ) = Bm · Jm (Sin ωt · Sin (ωt−ψ)) = Bm · Jm (Cosψ−Cos (2ωt−ψ)) / 2 = (1/2) Bm · Jm · Cosψ− (1/2) Bm · Jm · Cos (2ωt−ψ) (1) In the equation (1), the first term on the right side, that is, (1 /
2) Bm ・ Jm ・ Cos ψ is a DC component because it is not affected by time, and it can be seen that a force is always generated in a fixed direction. The direction of the force F is the central direction of the molten steel at any position in the circumferential direction, thereby generating a force in the direction of narrowing the molten steel, that is, a pinch force.

The magnitude of the magnetic field generated by the first set of coils 2 is
The magnetic field is largest at the center in the height direction, and the magnetic field decreases as the distance from the center increases. For this reason, the pinch force generated in the molten steel 9 by the first set of coils 2 is largest at the center of the first set of coils 2, and the force is small above and below. As a result, as shown by an arrow in FIG. 1, a flow flowing upward from the peripheral portion toward the center and a flow flowing downward from the peripheral portion to the center, as indicated by arrows in FIG. Are formed. Among them, the upward flow easily causes ripples on the molten metal surface 9a, and makes the molten metal surface properties unstable.

In this embodiment, in order to prevent the undulation and stabilize the properties of the molten metal, a flow in the circumferential direction as shown by an arrow in FIG. This circumferential flow is generated by the action of the lower second set of coils 6. The action for generating the circulation flow is basically the same as that of the induction motor.

The second set of coils 6 is configured by arranging a large number of electromagnetic coils 7 elongated in the vertical direction like stator windings of an induction motor so as to surround the mold 1 along the outer periphery of the mold 1. Each of a large number of electromagnetic coils 7 is connected in parallel with every third one so that it can be connected to a three-phase AC power supply. Adjacent electromagnetic coils connected to the same-phase power supply are connected so that their directions are opposite to each other. Accordingly, the adjacent ones of the electromagnetic coils 7 are energized with a phase difference of 60 degrees from each other by the three-phase AC power supply.

The operation of the second set of coils 6 can be explained with reference to FIG. 2b. That is, as shown in FIG. 2b, the magnetic field of each of the electromagnetic coils 7 is vertically
Generates a rotating magnetic field in a direction surrounding the mold. Also, the electromagnetic coil 7
The eddy current is generated in the molten steel 9 by the respective magnetic fields. By the action of the eddy current and the rotating magnetic field, a force circulates in the molten steel 9 in the same direction as the rotating magnetic field, that is, along the mold wall in a horizontal plane, thereby generating a circulating flow.

Circumferential flow also affects the upper surface 9a,
Since it acts to agitate the molten steel 9 in the circumferential direction, the height of each position of the molten metal surface is flattened in the circumferential direction. Therefore, even when an upward flow occurs, unstable ripples are unlikely to occur on the molten metal surface.

In the embodiment shown in FIG. 1, a stainless steel shielding plate 8 is arranged between the first set of coils 2 and the second set of coils 6 in order to prevent the magnetic field from interfering with each other. It is.

An experiment for comparing the results of casting was performed between the apparatus of the embodiment shown in FIG. 1 and the apparatus in which the second set of coils 6 were removed (see FIG. 3). The results are shown in FIGS. 5a and 5b. In this example, the steel type is SUS304 and the average magnetic flux density is 0,10
00, 2000, 3000 and 4000 (Gauss), casting speed 2000mm /
Experimented in minutes. FIG. 5a shows the depth of the oscillation mark (OSM) generated under each magnetic flux density condition,
FIG. 5b shows the depth of segregation. The case of the apparatus of the embodiment shown in FIG. 1 is indicated by a black circle, and the case of the apparatus without the second set of coils 6 is indicated by a white circle. 5a and 5b, it is clear that the apparatus of the embodiment using both the first coil 2 and the second coil 6 is superior.

In the above embodiment, the coil 2 for applying the pinch force is configured by combining the two electromagnetic coils 3 and 4, but may be replaced with a single electromagnetic coil.

[Effects] As described above, according to the present invention, since the pinch force is applied to the molten steel in the mold by providing the first electromagnetic coil (2), high-speed casting is possible, and the second electromagnetic coil ( Since 6) is provided to give the molten steel a circumferential flow, it is possible to prevent the undulation of the molten metal surface caused by the pinch force and to stabilize the molten metal surface property, thereby improving the cast slab quality. .

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a main part of a casting apparatus according to an embodiment. 2a and 2b are perspective views showing the direction of the operation of each coil of the device of FIG. FIG. 3 is a longitudinal sectional view showing the device in which a coil for giving a circumferential flow is removed. FIG. 4 is a graph showing distribution of magnetic flux density in molten steel by the first set of coils. 5a and 5b are graphs showing the casting quality of the apparatus of the embodiment and the conventional apparatus in comparison. 1: Mold 2: First set of coils (first electromagnetic coil) 3,4: Electromagnetic coil, 5: Coil winding 6: Second set of coils (second electromagnetic coil) 7: Electromagnetic coil 8: Shielding plate (shielding member) 9: molten steel, 9a: hot water surface

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Eiichi Takeuchi 1-1-1 Edamitsu, Yawatahigashi-ku, Kitakyushu-shi, Fukuoka Prefecture Nippon Steel Corporation 3rd Technical Research Institute (56) References JP-A-46-2054 ( JP, A) JP 4-503482 (JP, B2) JP-B 57-21408 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB names) B22D 11/00-11/22

Claims (2)

(57) [Claims] In a continuous casting apparatus for molten metal, wherein casting is performed while applying an electromagnetic force to molten steel injected into a mold, the molten metal is placed near a surface of a molten metal in the mold so as to surround the mold.
A first electromagnetic coil that is connected to an AC power supply and applies a force toward the center of the mold to molten steel in the mold; and a first electromagnetic coil is disposed below the first electromagnetic coil so as to surround the mold. A second electromagnetic coil that is connected to apply a rotational force to the molten steel in the mold in a circumferential direction of the mold; 2. The continuous casting apparatus for molten metal according to claim 1, wherein a shield member made of a magnetic material is disposed between said first electromagnetic coil and said second electromagnetic coil.