JPH0671401A - Controller for fluid of molten steel in continuous casting mold - Google Patents

Abstract

PURPOSE:To provide a controller for the fluidity of a molten steel in a continuous casting mold, by which a cast slab excellent in surface property is obtd. by controlling flowing speed at the front surface of the solidification in the mold. CONSTITUTION:In the controller for the fluid of the molten steel in the continuous casting mold, electromagnetic coils 7-1, 7-2 divided into two or more in the width direction of the continuous casting mold are arranged so as to position in the vicinity of a meniscus and a control part 10 for independently controlling magnetic field impressing directions of each electromagnetic coil in the reverse direction to the faced coils in the thickness direction, is connected with the electromagnetic coils. Further, the other electromagnetic coils 8-1, 8-2 are arranged at the lower position than the coil in the casting direction and a control part 11 for independently controlling magnetic field impressing directions of the electromagnetic coil is connected with the electromagnetic coils. The meniscus flowing speed of the molten steel in the mold is controlled and the descending flow is controlled at the same time, and the entrapment of the inclusion into the solidified shell is prevented and the cast slab having excellent surface property can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow control device for molten steel in a continuous casting mold.

[0002]

2. Description of the Related Art In continuous casting, the flow of molten steel in a continuous casting mold is an important factor that affects the quality of the slab. Therefore, it is generally practiced to electromagnetically stir the unsolidified portion of the slab to reduce segregation inside the slab and obtain a good slab.

For example, in Japanese Examined Patent Publication No. 64-10305, two electromagnetic stirrers are installed facing each other near the meniscus on the long side of at least one of the molds, and the electromagnetic stirrer installed on the long side is used to mold the mold. It is disclosed that a flow toward the center in the width direction is applied to the inner molten steel so that the depth of penetration of the molten steel flow from the immersion nozzle into the molten steel in the mold is made shallow to produce a slab of good quality.

In Japanese Patent Laid-Open No. 64-2771, a moving magnetic field is applied according to the strength of the molten steel discharge flow from the left and right discharge ports of the immersion nozzle to realize an appropriate level fluctuation of the molten metal surface. It is disclosed to prevent surface defects due to mold powder entrainment and surface cracking of a slab due to abnormal fluctuations in the molten metal surface.

[0005]

The present invention further provides a molten steel flow control device in a continuous casting mold for controlling a solidification front flow velocity in the mold to obtain a slab having excellent surface properties.

[0006]

According to the present invention, an electromagnetic coil divided into two or more parts in the width direction of a continuous casting mold is provided such that the center of the electromagnetic coil in the casting direction is located near the meniscus, and the magnetic field of each electromagnetic coil is increased. A control unit for independently controlling the application direction in the opposite direction to the opposing coil in the thickness direction is connected to the electromagnetic coil, and another electromagnetic coil is arranged so that the coil center is located below the coil in the casting direction. And a control unit for independently controlling the magnetic field application direction of the electromagnetic coil is connected to the electromagnetic coil, the apparatus for controlling the flow of molten steel in a continuous casting mold.

[0007]

The operation of the present invention will be described in detail below. FIG. 2 is a perspective view showing a main part of a mold for continuous casting according to the present invention with a part thereof cut away.

The mold is composed of long-side mold copper plates 1-1 and 1-2 and short-side mold copper plates 1-3 and 1-4, and the lower part of the immersion nozzle 2 attached to the tundish provided above is inserted. There is. The discharge holes provided in the lower portion of the immersion nozzle 2 are open one by one on both sides of the immersion nozzle 2 so as to face each other in the direction of the shorter side of the mold, but are not particularly limited.

Molten steel 3 is injected from the tundish into the mold through the immersion nozzle 2. The discharge flow 5 discharged from the immersion nozzle 2 is directed toward the short side mold copper plate 1-3 and hits the short side. , The molten steel flow that splits downward and goes upward becomes a discharge reversal flow 8 and forms a solidification front flow 6. On the other hand, the molten steel flow directed downward becomes the downflow 7.

According to the present invention, as shown in FIG. 1, 2 in the width direction of the mold is provided outside the long side surfaces 1-1 and 1-2 of the mold which face each other.
Agitating electromagnetic coils 7-1 and 7-2 divided into more than two parts
Is provided, and a switching unit that changes the direction of the moving magnetic field and a current controller are provided in the control unit 10 that generates the moving magnetic field and is separated from the mold, and is connected to the AC power supply.

The number of coils in the width direction of the electromagnetic coils 8-1 and 8-2 is not limited to the respective ones, but a switching that changes the direction of the static magnetic field is generated by the control unit 11 which generates a static magnetic field and is separated from the mold. And a current controller are provided and are connected to the DC power supply.

According to the experiments conducted by the present inventors, the immersion nozzle 2
The collision strength of the molten steel poured from the
It has been found that controlling the solidification front flow velocity formed by the discharge flow 5 within a certain range while suppressing the above is extremely effective in improving the surface quality of the cast slab. That is, the present invention is provided so that the centers of the electromagnetic coils 7-1 and 7-2 in the casting direction are located near the meniscus.

In order to wash away the surface layer of the solidified shell 4 and remove inclusions and segregation, a certain molten steel discharge flow rate is necessary. Further, it is necessary to suppress the downward flow 7 in order to remove inclusions and the like flowing downward together with the downward flow 7 discharged together with the discharge flow 5. Furthermore, in order to prevent inclusions from being trapped by the meniscus, it is necessary to control the solidification front flow 6.

The present inventors have found that the coagulation front flow velocity is 10-60.
It has been found that the surface defects of the cast slab are reduced by setting it to be cm / sec. However, it has been found that even with this, it is not possible to suppress defects caused by inclusions and the like on the downflow 7. Therefore, the inventors of the present invention have made intensive studies, and have simultaneously controlled the downflow velocity such as the downflow 7a together with the solidification front velocity.

The solidification front flow velocity is measured, for example, by inserting a thermorey cylinder into the molten steel flow and measuring the resistance force F due to the flow with a strain gauge. The strain and resistance can be determined by a regression equation by drawing a calibration curve using a weight in advance.

The control unit 10 shown in FIG.
The directions and strengths of the moving magnetic fields can be controlled separately for -1, 7-2 ,.

Further, the control section 11 includes the respective electromagnetic coils 8-1,
8-2 can control the strength and direction of the static magnetic field separately.

[0018]

[Examples] Under the mold conditions and electromagnetic stirring conditions shown in Table 1, continuous casting was performed using the stirring pattern shown in FIG. 3, and the occurrence rate of surface defects was investigated. Table 2 shows the coil specifications and capabilities in this case.

FIG. 3 shows a stirring pattern of molten steel,
Figures (a) and (b) show a pattern in which the discharge reversal flow is agitated, and figure (c) shows a pattern that suppresses the downward flow.

[0020]

[Table 1]

[0021]

[Table 2]

FIG. 4A shows the surface defect occurrence rate of the conventional example when only electromagnetic stirring is performed. 10-60 cm / s
Although it is about 5% at maximum, it is not yet perfect. According to the example of the present invention, as shown in FIG.
The surface defect occurrence rate was 1% or less in the range of 0 to 60 cm / s. Further, the downward flow suppressing effect of the present invention is 7a in FIG.
As shown in.

[0023]

According to the molten steel flow control device of the present invention, an electromagnetic coil for controlling the direction and strength of the moving magnetic field near the meniscus, and another static magnetic field strength and direction below the coil are controlled. By providing the electromagnetic coil to control the solidification front flow velocity of the molten steel in the mold of continuous casting, it is possible to prevent the inclusion of inclusions and the like due to the downward flow, it is possible to obtain a slab with excellent surface properties .

[Brief description of drawings]

FIG. 1 is a perspective view showing a main part of the present invention and showing an arrangement of electromagnetic coils.

FIG. 2 is a partially cutaway perspective view of a main part of a mold for continuous casting according to the present invention.

FIG. 3 shows various aspects of the stirring pattern of molten steel,
(A), (b) is a figure which shows the stirring pattern of the Example of this invention.

4A and 4B show the relationship between the solidification front flow velocity and the surface defect occurrence rate, FIG. 4A is a conventional example, and FIG. 4B is a drawing showing the present invention example.

[Explanation of symbols]

 1-1, 1-2 Long-sided mold copper plate 1-3, 1-4 Short-sided mold copper plate 2 Immersion nozzle 3 Molten metal (molten steel) 4 Solidification shell 5 Molten metal discharge flow 6 Solidification front flow 7 Downflow (conventional example) 7a Descent Flow (Example of the present invention) 8 Upflow 7-1, 7-2 Stirring coil 8-1, 8-2 Static magnetic field coil 10 Control unit (AC magnetic field) 11 Control unit (DC magnetic field)

Front Page Continuation (72) Inventor Jun Fukuda 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corporation Kimitsu Works

Claims (1)

[Claims] 1. An electromagnetic coil divided into two or more parts in the width direction of a continuous casting mold is provided such that the center of the electromagnetic coil in the casting direction is located near the meniscus, and the magnetic field application directions of the electromagnetic coils are opposed to each other in the thickness direction. A control unit that independently controls the coil in the opposite direction is connected to the electromagnetic coil, and another electromagnetic coil is provided so that the coil center is located below the coil in the casting direction. A flow control device for molten steel in a continuous casting mold, characterized in that a control unit for independently controlling the application direction is connected to the electromagnetic coil.