JPH0333055B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides electromagnetic stirring to actively horizontally flow molten steel injected into a continuous casting mold and to actively make it stand still. The present invention relates to an electromagnetic coil device that can perform electromagnetic braking individually or simultaneously.

[Conventional technology]

When molten steel with a low degree of deoxidation is poured into a mold for continuous casting, CO gas and small amounts of H ₂ gas, N ₂ gas, etc. are generated inside the mold. If solidification begins while these gases remain in the molten steel, it will cause defects such as pinholes in the product. Therefore, in the field of continuous casting, a method has long been employed in which molten steel poured into a mold is electromagnetically stirred so that it actively flows horizontally within the mold.

The conventional electromagnetic stirring method involves injecting molten steel into a mold containing a multiphase inductor as an electromagnetic stirring device that acts in the same way as the stator of a linear motor, and feeding three-phase AC or two-phase AC to the electromagnetic stirring device. This method applies electromagnetic force to molten steel and generates horizontal flow of about 0.1 to 1.0 m/sec (Japanese Patent Laid-Open No. 1983-
Publication No. 28034, Special Publication No. 58-52456, Special Publication No. 58
-52457 Publication, Special Publication No. 58-35787, Special Publication Sho
Publication No. 59-5057, Publication No. 59-7536, Publication No. 59-7536, Publication No. 59-7536, Special Publication Sho
58-7537, JP-A-56-41054, JP-A-60-223649, etc.).

Furthermore, the molten steel injected into the mold is accompanied by minute inclusions, and flux is drawn into the molten steel during injection. If such inclusions or fluxes remain in the molten steel and solidification begins, they will similarly cause defects in the product. Therefore, electromagnetic braking has been used for a long time as a method for quickly floating and absorbing these inclusions and fluxes into the absorption flux above the molten steel in the mold.

Such an electromagnetic braking method uses permanent magnets or electromagnets placed between the molten steel injected into the mold to apply a static magnetic field to the molten steel flow being injected into the mold, thereby actively controlling the injection flow rate. By slowing down the speed, it is possible to prevent accompanying minute inclusions and entangled flux from penetrating deep into the molten steel, and also to encourage them to rise to the surface due to buoyancy (Japanese Patent Laid-Open No. 1983-1993). −17356
(See Japanese Patent Application Laid-Open No. 188555, etc.).

[Problem that the invention seeks to solve]

The electromagnetic stirring method and electromagnetic braking method mentioned above are as follows:
Using independent electromagnetic stirring devices and electromagnetic braking devices, they have different effects and solve different problems.

However, in actual operations, when manufacturing general materials, there are steel types to which the electromagnetic stirring method is applied and steel types to which the electromagnetic braking method is applied, and these steel types are usually not the same. Furthermore, in the production of high-grade steel grades, it may be desirable to use both electromagnetic stirring and electromagnetic braking in combination.

However, having a dedicated continuous casting machine for each type of steel not only requires a large amount of equipment cost, but also does not necessarily allow for a high operating rate of the equipment. Therefore, this dedicated continuous casting machine for each type of steel cannot be called an industrial solution. Therefore, an electromagnetic stirring mold and an electromagnetic braking mold are prepared together with respective control devices, and these electromagnetic stirring mold and electromagnetic braking mold are rearranged and used depending on the steel type. However, this recombination requires the removal and
Installation requires a great deal of time and effort, and continuous casting must be suspended during that time. As a result, the productivity of continuous casting equipment decreases. In addition, the number of deceleration-stops and start-up accelerations increases in response to this rearrangement, which causes changes in the cooling rate, solidification coefficient, etc., resulting in variations in the quality of the slabs and problems such as a decrease in yield. Furthermore, since the electromagnetic stirring mold and the electromagnetic braking mold cannot be used at the same time, it is not suitable for manufacturing high-grade steel. In other words, recombining and using electromagnetic stirring molds and electromagnetic braking molds poses economic and effectiveness problems when trying to improve the quality of slabs and the quality yield of products to be manufactured. It includes.

Therefore, an object of the present invention is to solve these problems and to economically and efficiently manufacture slabs of excellent quality.

[Means for solving problems]

In order to achieve the object, the present invention disposes at least three independent electromagnetic coils outside a circumferential copper plate for continuous casting along the width direction of the mold, and electromagnetically stirs the molten steel in the mold. Each of the electromagnetic coils is connected to a power source that can selectively supply a multiphase alternating current, a series current, or an AC/DC superimposed current for selectively applying force, electromagnetic braking force, or a combination of both. shall be.

The three or three pairs of electromagnetic coils can be used in Y-connection or Δ-connection with respect to the power source.

[Effect]

According to experiments and studies conducted by the present inventor using a known electromagnetic stirring device shown in FIG. 1, multiphase alternating current is passed through each coil as shown in FIG.
A magnetic field with a magnetic flux distribution as shown in the figure was generated to perform an electromagnetic stirring operation on weakly deoxidized, non-sedated molten steel poured into a mold. As a result, it was confirmed that the bubble generation prevention results were comparable to those of the prior art. In the electromagnetic device having such a configuration, a direct current is passed through each coil as shown in Fig. 3b, and a magnetic field with a magnetic flux distribution as shown in Fig. 4b is generated. An electromagnetic braking operation was performed. As a result, as shown in Figure 5a, inclusions of about 100 μm/piece were reduced to 1/1
decreased to 0.

Furthermore, when an alternating current with a DC bias as shown in Fig. 3c is applied to generate a magnetic field with a magnetic flux distribution as shown in Fig. 4c, electromagnetic stirring and electromagnetic braking are performed simultaneously. As shown in FIG. 5b, the inclusions of about 100 μm/piece were reduced to less than 1/100.

In addition, when an electromagnetic braking force is applied to each discharge part of the immersion nozzle to control the discharge amount, that is, the amount of injection into the mold, it is possible to
It became virtually impossible to detect inclusions of the order of m/m and 40 μm/m.

This is considered to be due to the synergistic effect of the effect of reducing the injection flow rate and the effect of completely blocking outside air from entering the molten steel in controlling the discharge amount.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples.

In this example, first, a power supply device capable of supplying each of multiphase alternating current, direct current, and a superimposed current of both was prepared.

FIGS. 1a and 1b show a state in which an electromagnetic coil, which is operated by being connected to this power supply device, is placed in a continuous casting mold.

The inside of the continuous casting mold is provided with a long piece copper plate 1 and a short side copper plate 2. A box 3 for storing an electromagnetic coil is arranged on the side of the long side copper plate 1. Each electromagnetic coil is equally divided into 2n pieces (n is 1 or 2). In the example in Figure 2, n=
1, which is divided into distances τ ₁ and τ ₂ along the long side direction. The distances τ ₁ and τ ₂ are assumed to have the same length and are set in a range of approximately 200 to 1000 mm.
Within these distances τ ₁ and τ ₂ , the magnetic paths of m (m is an integral multiple of 3) independent excitation coils are connected by a core 5 made of a silicon steel plate. FIG. 1a shows three (m=3) excitation coils 40a ₁ and 40 with lengths τ ₁ and τ ₂ , respectively.
b ₁ , 40c ₁ , 40a ₂ , 40b ₂ , 40c ₂ , 41a ₁ ,
An example is shown in which 41b ₁ , 41c ₁ , 41a ₂ , 41b ₂ , 41c ₂ are wound and arranged in a direction perpendicular to the long copper plate 1. Fig. 1b shows another example of the arrangement of excitation coils, with lengths of τ ₁ and τ ₂ each having three pieces (m=3).
excitation coils 40a ₀ , 40b ₀ , 40c ₀ , 41a ₀ ,
41b ₀ and 41c ₀ are wound and arranged in a direction parallel to the long copper plate 1.

FIG. 2 a1, a2, b shows each of the coils 40a ₁ , 40b ₁ , 40c ₁ , 40a ₂ , 4 in the storage box 3.
0b ₂ , 40c ₂ , 41a ₁ , 41b ₁ , 41c ₁ , 41
A wiring diagram of a ₂ , 41b ₂ , and 41c ₂ is shown.

In the connection diagram, 40a ₁ and 40a ₂ , 40b ₁ and 40b ₂ , and 40c ₁ and 40c ₂ are connected in series, a1 is further connected in a star shape with the center point O, and b is connected in series. It is assumed that the terminals 40a, 40b, and 40c can be separated from the point O and connected to the terminals S, R, and T to perform a Δ connection. Here, the method of connecting or winding the coils 40a ₁ and 40a ₂ can be done by winding the coils in the same direction and reversing the connection direction, as shown in FIG. 2 a1, so that the excitation current flows in opposite directions, or Assume that the coil is wound in the opposite direction as shown in Figure 2 a2. 40b ₁ and 40b ₂ , 40c ₁ and 4
The same goes for _0c2 . Points R, S, and T indicate the coil terminals after connection at the point O. I _R , I _S , I _T
represents the three-phase AC excitation current that excites each coil. 41a ₁ , 41b ₁ , 41c ₁ , 41a ₂ , 41
Similar connections are made for b ₂ and 41c ₂ .

FIG. 3a shows the excitation current that excited the coil with three-phase alternating current.

By exciting each coil with time-varying three-phase currents I _R , _IS , and I _T using terminals R, S, and T in Figure 2, a magnetic field whose magnetic flux density changes over time is created in the mold. Occur. FIG. 4a shows the magnetic flux density distribution in the long side direction of the magnetic field within the mold generated at this time. The magnetic flux density distribution curve of the magnetic field moves in the long side direction a (or in the opposite direction to a) over time.
An induced current is generated in the molten steel due to the movement of the magnetic flux density distribution, and the electromagnetic force generated by this induced current and the magnetic field causes the molten steel in the mold to be electromagnetically driven in the same direction as the movement direction of the magnetic flux density distribution. The force causes the molten steel to flow.

The generation of molten steel flow suppresses the generation of CO bubbles during the solidification process during casting of unoxidized steel, and prevents the generation of pinholes beneath the slag surface.

Next, FIG. 3b shows the exciting current when the coil is excited with direct current. That is, I _1R , I _1S , I _1T are I _1R
By exciting with a DC excitation current that does not change over time, +I _1S +I _1T = 0, a DC magnetic field whose magnetic flux density does not change over time is generated in the mold. FIG. 4b shows the magnetic flux density distribution in the long side direction of the magnetic field generated within the mold at this time.

By generating a magnetic field having such a magnetic flux density distribution, it becomes possible to apply an electromagnetic braking force to the injection flow injected into the mold from the immersion nozzle. Moreover, the values of I _1R , I _1S , and I _1T are I _1R + I _1S + I _1T =
By using a direct current with a DC current of 0 and changing its ratio arbitrarily, the magnitude and position of the peak value L _a of the magnetic flux density distribution of the magnetic field generated in the mold can be arbitrarily adjusted and controlled. The braking force can be applied to be most effective depending on the injection flow distribution and the desired braking position.

Furthermore, by passing through the coil an excitation current that is a superimposition of three-phase alternating current and direct current shown in FIGS. 3a and 3b, the electromagnetic driving force is generated simultaneously with the electromagnetic braking force, and the necessary It is also possible to perform desired stirring while applying a braking force.

FIG. 3c shows an example of the excitation current at this time. Figure 4c shows the magnetic flux density distribution in the long side direction of the magnetic field inside the mold at this time, and the magnetic flux density distribution B _DC , which is the basis of the braking force, does not move in time but moves in the long side direction a in time. magnetic flux density distribution, which is the basis of stirring force.
B Magnetic flux density distribution for braking and stirring superimposed with _AC
B _TOTAL is obtained.

In order to generate the three types of excitation currents as described above, the present invention prepares a power supply device that is known per se and is capable of supplying each of multiphase alternating current, direct current, and a superimposed current of both.

Although the above embodiment shows an example in which three-phase alternating current is applied to three excitation coils, it is also possible to have n excitation coils of three or more and to flow n-phase polyphase alternating current through them. Of course it can be done.

〔Effect of the invention〕

As described above, the present invention can selectively perform multiphase alternating current excitation, direct current excitation, or superimposed multiphase alternating current and direct current excitation on the excitation coil installed in the mold, so that one electromagnetic force can be generated. By applying electromagnetic driving force, electromagnetic braking force, or a combination thereof to the molten steel in the mold without interrupting the continuous casting operation, the internal quality can be adjusted economically according to the type of steel to be cast and the desired quality. It can be done in a specific manner. As a result, it is possible to provide a steel material that meets the desired material quality at a low cost, which brings about many effects.

[Brief explanation of drawings]

Figures 1a and 1b show electromagnetic coils placed in the mold, where a shows an example in which the coil is wound in a direction perpendicular to the copper mold plate, and Fig. 1 b shows an example in which the coil is wound in a direction parallel to the copper mold plate. Further, FIGS. 2a1, a2, and b each show a wiring diagram of the coil shown in FIG. 1. FIG. 3a shows the coil excitation current during multiphase AC excitation, and FIG. 3B shows the coil excitation during DC excitation. FIG. 3c shows the coil excitation current when multiphase alternating current and direct current are superimposed. FIG. 4a shows the magnetic excitation density distribution within the mold during multiphase AC excitation, and FIG. 4b shows the magnetic excitation density distribution within the mold during DC excitation. FIG. 4c shows the magnetic flux density distribution within the mold when excitation is performed by superimposing multiphase alternating current and direct current. FIG. 5 shows the relationship between the operating method and the amount of inclusions in molten steel in an experimental example of the apparatus of the present invention.

Claims (1)

[Claims] 1. At least m.
2n pieces (n is 1 or 2) of electromagnetic coils (m is an integral multiple of 3) are arranged along the width direction of the mold, and electromagnetic stirring force, electromagnetic braking force, or a combination of both are applied to the molten steel in the mold. An electromagnetic coil for a continuous casting mold, characterized in that each of the electromagnetic coils is connected to a power source capable of selectively supplying a multiphase alternating current, a series current, or an AC/DC superimposed current for selectively applying force. Device. 2. The electromagnetic coil device for continuous casting molds according to claim 1, characterized in that 2m electromagnetic coils are Y-connected to a power supply terminal and excited. 3. The electromagnetic coil device for a continuous casting mold according to claim 1, characterized in that the electromagnetic coil device for continuous casting molds is configured to excite the 3 m electromagnetic coils by connecting them in a delta to a power supply terminal.