JPH04197554A - Apparatus for continuously casting cast slab - Google Patents

Abstract

PURPOSE:To enable casting of a steel sheet having good surface characteristic even without providing large capacity of high frequency power source by inserting magnetic field convergent plate at connecting part between a refractory nozzle and a mold and providing a high frequency coil at neighborhood along this magnetic field convergent plate. CONSTITUTION:At the time of setting the magnetic field convergent plate 4 at near the high frequency coil 5, the magnetic field generated with the high frequency coil 5 is converged after passing in the magnetic field convergent plate 4 without dispersing. Then, by inserting the magnetic field convergent plate 4 at the connecting part between the refractory nozzle 2 and the mold 3, the magnetic field is converged at near the connecting part and in there, high magnetic pressure can be efficiently acted. By this method, space 8 is formed in there, and the connecting part and the molten steel 6 are made to under noncontacting condition. Therefore, the development of solidified shell 7 is not developed in the zone before the mold 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a continuous slab casting apparatus of a type in which a refractory nozzle for supplying molten steel and a mold are connected.

[Prior Art] In continuous casting equipment for slabs, a type in which a refractory nozzle and a mold are connected is mainly applied to horizontal continuous casting equipment. FIG. 5 is a diagram showing the general structure of a conventional horizontal continuous casting apparatus. 1 is a tundish, 2 is a refractory nozzle, and 3 is a water-cooled mold, and the refractory nozzle 2 and mold 3 are connected via a break ring (connection refractory) 20.
2 and 5, the slab is intermittently pulled out from the mold 3. 6 indicates molten steel, and 7 indicates solidified shell.

In the above horizontal continuous casting apparatus, 2. play chest leg 2
Around 0, the break ring 20 is not damaged because the state changes repeatedly, such as direct contact with the flowing molten steel 6 or the formation of a solidified shelf, every time the slab is drawn intermittently. However, it cannot withstand long-term casting.

In addition, there is a pull-out mark called koltnoyat on the slab (
surface defects), and these marks cause defects on rolled products in subsequent processes. Furthermore, when molten steel is inserted between the brush ring 20 and the mold 3, the solidified shell is forced to adhere and peel off, resulting in poor surface quality of the slab and sometimes causing blowout. Become.

As a technique for solving such problems, there is a technique proposed in Japanese Patent Application Laid-Open No. 1-284469 shown in FIG.

In this device, the refractory nozzle 2 and the mold 3 are directly connected, and the refractory nozzle 2 at this connection part (just before the entrance of the mold 3)
A high frequency coil 5 is embedded inside.

When a high-frequency current is applied during casting, this high-frequency coil 5 pushes away the molten steel 6 at the connecting portion inward by the generated magnetic pressure, forming a space 8 there, and forming a space 8 between the connecting portion and the molten steel w46. or to prevent contact. As a result, no solidification shelf is formed at the connection portion, and solidification of the molten steel 6 starts from the mold 3 portion. In this way, the surface quality of the slab is improved.

[Problems to be Solved by the Invention] However, since the above-mentioned conventional device is configured to simply generate a magnetic field by energizing a high-frequency coil, the generated magnetic field diffuses and the connection between the refractory nozzle and the mold is interrupted. The efficiency of generating effective magnetic pressure acting on the area is very low. Therefore, in order to generate magnetic pressure that can make the connection part and molten steel non-contact, a large high-frequency current must be passed through the high-frequency coil, and a steel plate with good surface texture or Casting requires a large-capacity, high-frequency power source.

In addition, a high frequency coil is embedded inside the fireproof nozzle,
If the high-frequency coil is arranged in this way, there is a risk that the refractory nozzle may be damaged by the heat load, making maintenance and management of the refractory nozzle and the high-frequency coil very difficult.

SUMMARY OF THE INVENTION An object of the present invention is to provide a continuous slab casting apparatus that is capable of casting steel plates with good surface properties without being equipped with a large-capacity high-frequency power source.

[Means and effects for solving the problem] In order to achieve the above object, in the present invention, a magnetic field convergence plate is interposed in the connecting part between the refractory nozzle and the mold, and a magnetic field convergence plate is provided in the vicinity along the magnetic field convergence plate. Equipped with a high frequency coil.

When a magnetic field convergence plate is placed near the high-frequency coil, the magnetic field generated by the high-frequency coil passes through the magnetic field convergence plate and is focused without being diffused. Therefore, if a magnetic field convergence plate is interposed at the connecting part between the refractory nozzle and the mold, the magnetic field will be converged near the connecting part, and high magnetic pressure can be efficiently applied there.

As the material for the magnetic field convergence plate, a soft magnetic material having high magnetic permeability and high saturation magnetic flux density is used, and for example, a silicon steel plate is suitable.

Note that the thickness of the magnetic field convergence plate is preferably thinner than the skin depth δ expressed by the following equation.

δ=(2/Cωσμ) ) ”' However, ω: Angular frequency of high-frequency current σ: Electrical conductivity μ of the magnetic field convergence plate, magnetic permeability of the magnetic field convergence plate This means that the magnetic field moves from the skin toward the thickness direction. This is because the magnetic field convergence plate is exponentially attenuated, so if the plate thickness is greater than δ, even if the magnetic field convergence plate is brought close to the connection portion, the effect will be reduced.

[Example 1] Fig. 1 shows an embodiment of the present invention, and is a partial sectional view of a continuous casting apparatus for casting slabs that is wider than the opening cross section of the mold or the refractory nozzle, and Fig. WF and Fig. 2 show an embodiment of the present invention. FIG. 7 is a partial cross-sectional view of a continuous slab casting apparatus showing another embodiment in which the opening cross-sections of the mold and the refractory nozzle are the same. In FIGS. 1 and 2, reference numeral 2 indicates a refractory nozzle connected to introduce molten steel from the tandem mold, and 3 indicates a mold made of copper and having a water-cooled structure.

6 indicates the molten steel, and 7 indicates the solidified shell.

A magnetic field convergence plate 4 is interposed between the refractory nozzle 2 and the mold 3 in a circular manner, and the two are connected. The magnetic field convergence plate 4
The inner (molten steel side) end face is the same as the inner surface of the mold 3, or is installed with a size slightly outside the inner surface of the mold 3. The magnetic field convergence plate 4 is made of a magnetic material with high magnetic permeability, such as an electromagnetic steel plate.

A high frequency coil 5 is provided around the outer periphery of the refractory nozzle 2 at a position as close to the magnetic field convergence plate 4 as possible. If the high-frequency coil 5 is provided on the outer periphery of the refractory nozzle 2 as described above, the refractory nozzle 2 will not be damaged by heat load, and no problems will arise in the maintenance and management of the high-frequency coil.

In the device configured as described above, the high frequency coil 5
When energized, the generated magnetic field passes through the magnetic field convergence plate 4, converges, and acts very precisely on the connection between the refractory nozzle 2 and the mold 3. Therefore, even if a large current is not applied to the high frequency coil 5, a large magnetic pressure can be applied to the connecting portion,
A space 8 is formed there, and the connection portion and the molten steel 6 are in a non-contact state. Therefore, the solidification shelf is generated in mold 3.
No longer occurs in previous areas.

In this way, in each of the above embodiments, a large magnetic pressure can be generated without applying a large current. Since the heating accompanying the generation of eddy currents is simultaneously and efficiently carried out at the connecting portion, solidification of the molten steel 6 in the vicinity of this connecting portion is prevented, and the effect of improving the surface properties of the slab is further increased.

The magnetic field convergence plate 4 is placed between the refractory nozzle 2 and the mold 3 in direct contact with the mold 3, and is constantly cooled. If the magnetic field convergence plate 4 is not cooled and the high frequency coil 5 is energized, the magnetic field convergence plate 4 will be heated by the eddy current and reach a very high temperature, and the magnetic properties will also deteriorate. , there is no need to separately install a cooling device for cooling it.

In the above embodiments, a horizontal continuous casting apparatus has been described, but in the present invention, the angle of the refractory nozzle may be vertical, and the angle may be arbitrary.

Next, in the continuous casting apparatus for round billets with a diameter of 60 mm having the configuration of the embodiment shown in FIG.
Figure 3 shows the results obtained by simulation of the magnetic pressure generated at the connecting part of the . The conditions at this time were as follows.

Inner diameter of refractory nozzle d1 40 Inner diameter of forward mold d, 60M Material of magnetic field convergence plate Thickness of electromagnetic steel plate magnetic field convergence plate 1.5 - Relative magnetic permeability of magnetic field convergence plate 100 High frequency current 3000 A frequency
3000 ) [z Figure 3 shows the magnetic pressure (expressed in terms of molten steel column) between the position A of the inner end face of the magnetic field convergence plate 4 and the position 0 on the inner side of the magnetic field converging plate 4 at the connecting part between the refractory nozzle 2 and the mold 3. ), where the curve ■ shows the change in magnetic pressure under the above conditions according to the example, and the curve ■ shows the case where there is no magnetic field convergence plate (only the high-frequency coil is installed).
is the change in magnetic pressure.

As is clear from this figure, the magnetic pressure at the connecting portion is about 10 cm in the case without the magnetic field convergence plate (2), and about 100 cm in the case of the embodiment (2). The magnetic pressure at the joint increased approximately 10 times.

Based on the results of this simulation, casting was carried out by continuous drawing for each of the device having the configuration of the embodiment shown in FIG. 1 and the device without the magnetic field convergence plate 4. As a result, it was found that the result of applying a high frequency current of 2000 A and 3000 Hz to the device of the example was better than that of the case of applying a high frequency current of 5000 A and 3000 Hz to the device without the magnetic field convergence plate 4. It was found that the surface quality was good and that the slab could be produced stably.

[Effects of the Invention] In the present invention, a magnetic field convergence plate is interposed at the connecting portion between the refractory nozzle and the mold, and a high-frequency coil is provided near the magnetic field converging plate to direct the magnetic field to the vicinity of the connecting portion. Since it is possible to converge the magnetic flux and apply high magnetic pressure to it efficiently, slabs with good surface quality can be produced in a stable state without increasing the capacity of the high-frequency power source. This also allows casting by continuous drawing.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of a continuous slab casting apparatus showing one embodiment of the present invention, FIG. 2 is a partial cross-sectional view of a continuous slab casting apparatus showing another embodiment of the present invention, and FIG. Figure 4 shows the magnetic pressure generated at the joint between the refractory nozzle and the mold, Figure 4 is a partial cross-sectional view of a conventional slab continuous casting apparatus equipped with a high-frequency coil, and Figure 5 shows a conventional horizontal continuous casting apparatus. FIG. 1 is a diagram showing a general structure of a casting device. DESCRIPTION OF SYMBOLS 1...Tandish, 2.Refractory nozzle, 3...Mold, 4...Magnetic field convergence plate, 5...High frequency coil, 6.
- Molten steel, 7... Solidified shell, 8... Space.

Claims (1)

[Claims] In a continuous casting device for slabs in which a refractory nozzle and a mold are connected, a magnetic field converging plate is interposed in the connecting part of the refractory nozzle and the mold, and a high-frequency wave is applied near the magnetic field converging plate. A continuous slab casting device characterized by being equipped with a coil.