JPS6255942B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to an electromagnetic system applied to a mold copper wall having a rectangular horizontal cross section or a steel billet drawn from the mold copper wall in continuous casting equipment used for producing steel billets with a rectangular cross section. Regarding a stirring device.

In recent years, in continuous casting equipment for high-grade steel grades, electromagnetic stirring devices have been provided that apply horizontal rotational motion to molten steel within a billet to improve equiaxed crystallinity and float inclusions.

This electromagnetic stirring device applies the principle of an induction motor, and a stator that generates a rotating magnetic field is placed in a steel billet, and the rotating magnetic field gives horizontal rotational motion to the molten steel inside the steel billet. This is how it was done.

As mentioned above, using an electromagnetic stirring device can improve the equiaxed crystallinity and float inclusions.
In conventional cylindrical core electromagnetic stirrers, when the copper mold wall has a rectangular or square horizontal cross section, turbulence tends to occur at the corners of the copper mold wall and the steel billet. There are problems such as the flux on the liquid surface of the molten steel in the mold getting caught up in the molten steel, or the amount of negative segregation occurring at the stirring position of the manufactured steel bill becoming noticeable.

In particular, if the molded copper wall has a rectangular horizontal cross section,
Because the rotational speed of the flow along the long side of the steel piece is faster than the rotational speed of the flow along the short side of the piece, the turbulence at the two corners from the long side to the short side when viewed in the direction of rotation of the molten steel is intense, and the steel There was a problem that smooth horizontal rotation of the molten steel within the piece could not be achieved.

The purpose of the present invention is to improve an electromagnetic stirring device that is applied to a copper mold wall having a rectangular horizontal cross section or a steel billet drawn from the copper wall. From the side to the short side 2
By controlling the flow direction of the molten steel at the two corners, the turbulence of the molten steel at the corners is alleviated and smooth horizontal rotational movement is achieved, thereby preventing steel quality deterioration due to slacks getting caught. This is an attempt to improve the band.

The electromagnetic stirring device according to the present invention has an iron core having a rectangular horizontal cross section and one convex magnetic pole on the inner surface of each side wall, and the convex magnetic pole of each long wall is connected to the molten steel or steel in the mold copper wall from a neutral position. One electromagnetic coil is wound around the convex magnetic pole of each long wall, while the convex magnetic poles of each short wall are unevenly distributed in the neutral position or in the direction opposite to the rotational direction of the molten steel. On the other hand, an electromagnetic coil is wound around the convex magnetic poles of each of the short walls, and a two-phase alternating current having a phase difference of approximately electrical angle π/2 is transmitted, one of which is connected to the convex magnetic poles of each long wall. The molten steel is characterized in that the molten steel is given horizontal rotational motion by flowing the current into one electromagnetic coil and the other into an electromagnetic coil having convex magnetic poles on each short wall.

According to this electromagnetic stirring device, the magnetic field from the center to the corner becomes stronger at the two corners, and as a result, the strong electromagnetic force is directed in a direction perpendicular to the direction of the magnetic field, that is, in a direction that deviates from the corner. Therefore, the entrainment of the molten steel at the corner portions is alleviated, and the overall rotational movement of the molten steel becomes smooth. Therefore, it is possible to reduce wear on the corner portions of the mold copper wall and to prevent white bands.

In the other pair of corners of the copper mold wall, that is, the corners extending from the short side to the long side of the billet when viewed in the direction of rotation of the molten steel, the flow of the molten steel is less likely to be accelerated, so turbulence is less likely to occur.

The present invention will be specifically described below with reference to illustrated embodiments. Although this embodiment is an example in which the electromagnetic stirring device is applied to a copper mold wall, it can also be applied to a steel piece drawn from a copper mold wall.

FIG. 1 shows the electromagnetic stirring device 1, and FIG. 3 shows the state in which the electromagnetic stirring device 1 is fitted into the outer periphery of the mold copper wall 5. The electromagnetic stirring device 1 has a similar shape to the mold copper wall 5, and both have a rectangular horizontal cross section.

The stator 1 is made of a laminated core of silicon steel plates, and each of its walls 2a, 2a'; 2b, 2b' has convex magnetic poles 3a, 3a'; 3b, 3b' on its inner surface. Further, each of the convex magnetic poles 3a, 3a'; 3b, 3b' is unevenly distributed in one direction from the neutral position (on the center line 0, 0') of each wall 2a, 2a'; 2b, 2b'. That is, as shown in FIG. 3, if the rotation direction of the molten steel in the mold copper wall 5 is the arrow
The convex magnetic poles 3a, 3a' of a' are unevenly distributed in the direction of rotation from the neutral position, while the convex magnetic poles 3b, 3b' of each short wall 2b, 2b' are unevenly distributed in the anti-rotation direction from the neutral position. Incidentally, the convex magnetic poles 3b, 3b' may be in neutral positions.

Opposing convex magnetic poles 3a, 3 of the long walls 2a, 2a'
One electromagnetic coil 4a is wound in the same direction on a',
Moreover, the opposing convex magnetic poles 3b, 3 of the short walls 2b, 2b'
Another electromagnetic coil 4b is wound around b' in the same direction. Note that these electromagnetic coils 4a and 4b are of a self-cooling type, and as shown in FIG.
The center of c is hollow, and cooling water is allowed to flow into the hollow part 4d. An insulating layer 4e is formed on the outer periphery of the main body 4c.

In addition, each of the above convex magnetic poles 3a, 3a'; 3b, 3
b' reduces the air gap for each wall 6a, 6a'; 6b, 6b' of the mold copper wall 5 in order to reduce the magnetic resistance.

Two-phase alternating currents u and v are passed through the electromagnetic coils 4a and 4b of each convex magnetic pole with a phase difference of electrical angle π/2 as shown in FIG. That is, U-phase alternating current is passed through the electromagnetic coils 4a of the magnetic poles 3a, 3a' of the long walls 2a, 2a', while the short walls 2b, 2a'
V-phase alternating current is applied to the magnetic pole 3b of b' and the electromagnetic coil 4b of 3b'.

Now, the flow direction of each phase of alternating current in the electromagnetic coil is, for example, the direction shown in Figure 4 (the marks in the figure indicate the flow toward the back of the page, and the ○ marks indicate the flow toward the front of the page). Then, the u-phase alternating current flow produces a magnetic field φu, and the v-phase alternating current flow produces a magnetic field φv. In other words, the magnetic field φu based on the electromagnetic coil 4a within the mold copper wall 5
The direction is an oblique direction from the convex magnetic poles 3a' to 3a, and the direction of the magnetic field φv based on the electromagnetic coil 4b is an oblique direction from the convex magnetic poles 3b to 3b'.
If the flow direction of each phase of alternating current in the electromagnetic coil is reversed, the direction of the magnetic field is also reversed. However, in either case, a certain amount of leakage flux occurs.

The u-phase current Iu and the v-phase current Iv are respectively expressed by the following formulas (where Im: maximum current) Iu = Im sinωt Iv = Im sin (ωt-π/2) The strengths of the magnetic fields φu and φv are respectively expressed by the current Corresponding to Iu, Iv, the magnetic field at each electrical angle π/4, π... and the electromagnetic force based on the magnetic field are shown in FIG. In the figure, the single-line arrow represents the magnetic field distribution, and the double-line arrow represents the electromagnetic force as a vector.

Now, considering the case where the electrical angle ωt is 0,
The current in the u phase is 0, and the current in the v phase is negative.
Im. Therefore, only the magnetic field φv acts in the direction shown in A, that is, in the direction from the convex magnetic poles 3b to 3b', and the electromagnetic force _F1 acts in the direction orthogonal to the magnetic field φv, that is, in the short wall 6b' of the mold copper wall 5 ( or the short side of the steel piece) toward the corner A of the short wall 6b' and the long wall 6a (or the long side of the steel piece).

When the electrical angle ωt becomes π/4, the current in the u phase becomes a positive current, while the current in the v phase becomes a negative current. Therefore, both the magnetic fields φu and φv are generated, and the resultant magnetic field φuv is a vector combination of the magnetic fields φu and φv, as shown in FIG. The electromagnetic force F ₂ based on this composite magnetic field φuv is
In A, the electromagnetic force _F1 acts in a direction to change the direction of the molten steel inside the mold copper wall, which has been moved toward the corner A, and to move it along the long wall 6a.

When the electrical angle ωt becomes π/2, the u-phase current becomes a positive current, while the v-phase current becomes 0.
Then, as shown in _FIG .
Acts in the direction away from a. Therefore, the molten steel inside the mold copper wall is moved in a direction slightly warped from the corner B between the long wall 6a and the short wall 6b by the magnetic force _F3 .

When the electrical angle ωt becomes 3π/4, the u phase and v
The current in either phase is a positive current. Then, a magnetic field φu in the same direction as C and a magnetic field φv in the opposite direction to B are generated, and the resultant magnetic field φuv becomes extremely strong as shown in D. This composite magnetic field φuv acts from the center in the direction of the corner B, and the electromagnetic force _F4 based on this also becomes stronger and moves the molten steel in the mold roughly in the direction of the corner C so as to deviate from the corner B. Therefore, entrainment and turbulence at the corner portion B are less likely to occur.

Ho, He, To, and Chi have electrical angles ωt of π and 5, respectively.
The resultant magnetic field and electromagnetic forces F ₅ , F ₆ , F 7 , and F ₈ are shown in the case of π/4, 3/2·π, and _7π /4. These electromagnetic forces F ₅ , F ₆ , F ₇ , F ₈ are respectively a and
It has the same magnitude as the electromagnetic forces F ₁ , F ₂ , F ₃ , and F ₄ in B, C, and D, and acts in the opposite direction. Therefore, in case 1, as in case d, the molten steel in the mold copper wall is moved away from the corner D,
As a result, entrainment and turbulence of molten steel are less likely to occur.

As mentioned above, at corner parts A and C,
Electromagnetic forces F ₁ and F ₅ move the molten steel in the mold to the corners A and C.
However, since the flow distance along the short walls 6b and 6b' is short, the flow velocity is not very high. Therefore, little turbulence occurs in the corner portions A and C.

By controlling the magnetic field as described above, the molten steel within the copper mold wall rotates smoothly as a whole.

Note that the u-phase and v-phase alternating currents preferably have a low frequency of about 2 Hz to 12 Hz.

In the above embodiment, the two-phase alternating currents u and v have a phase difference of π/2 in electrical angle, but the present invention is not limited to this, and the phase difference between the two-phase alternating currents u and v is π Even if it deviates from /2 to some extent, substantially the same action and effect as above will be produced.

As explained above, the electromagnetic stirring device according to the present invention has a simple structure in which the positions of the two pairs of convex magnetic poles are deviated from the neutral position in a predetermined direction, thereby stirring the molten steel in the billet. The flow in the corners can be controlled and the intended purpose can be achieved.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention, and FIG. 1 is a perspective view showing an electromagnetic stirring device in which an electromagnetic coil is wound around an iron core, FIG. A plan view showing the state in which the stator is fitted, Fig. 4 is an explanatory diagram showing the magnetic field when a unidirectional current flows through the electromagnetic coil, Fig. 5 is a waveform diagram of two-phase current flowing through the electromagnetic coil, 5, 1 to 1 are explanatory diagrams showing the magnetic field and electromagnetic force at each electrical angle in FIG. 5. 1... Electromagnetic stirring device, 2a, 2a'... Long wall of electromagnetic stirring device 1, 2b, 2b'... Short wall of electromagnetic stirring device 1, 3a, 3a'; 3b, 3b'... Convex magnetic pole, 4
a, 4b...Electromagnetic coil, 5...Mold copper wall, 6
a, 6a'...Long wall of mold copper wall 5, 6b, 6b'...
Short walls of the molded copper wall 5, A, B, C, D...corner parts of the molded copper wall 5.

Claims (1)

[Scope of Claims] 1. An electromagnetic stirring device used by being placed around a mold copper wall having a rectangular horizontal cross section in continuous casting equipment or around a steel piece drawn from the mold copper wall, the iron core having a rectangular horizontal cross section. and has one convex magnetic pole on the inner surface of each side wall, and the convex magnetic pole of each long wall is unevenly distributed in the direction of rotation of the molten steel in the mold copper wall or the molten steel in the billet from the neutral position, while the convex magnetic pole of each short wall is The convex magnetic poles are unevenly distributed in a neutral position or in a direction opposite to the rotational direction of the molten steel, and one electromagnetic coil is wound around the convex magnetic poles on each of the long walls, while one electromagnetic coil is wound around the convex magnetic poles on each of the short walls. Two electromagnetic coils are wound, and one of the two-phase alternating current having a phase difference of approximately electrical angle π/2 is sent to the electromagnetic coil of the convex magnetic pole of each long wall, and the other is connected to the convex magnetic pole of each short wall. An electromagnetic stirring device characterized in that a horizontal rotational motion is imparted to molten steel by flowing through the electromagnetic coils of magnetic poles.