JP2607332B2 - Flow control device for molten steel in continuous casting mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In continuous casting, it is common practice to reduce the segregation inside a slab and obtain a good slab by electromagnetically stirring an unsolidified portion of the slab. For example, in Japanese Patent Publication No. 64-10305, two electromagnetic stirrers are installed facing each other near the meniscus on at least one long side of the mold, and the molten steel in the mold is formed by the electromagnetic stirrer installed on the long side. It is disclosed that a flow toward the center in the width direction is provided to reduce the penetration depth of the molten steel flow from the immersion nozzle into the molten steel in the mold, thereby producing a slab of good quality.

In Japanese Patent Application Laid-Open No. 64-2771, a moving magnetic field is applied in accordance with the strength of a molten steel discharge flow from the left and right discharge ports of an immersion nozzle to achieve an appropriate magnitude of level change of the molten metal. It is disclosed to prevent surface defects due to mold powder wrapping due to fluctuations in the molten metal level and surface cracks of the slab.

[0004]

The flow of molten steel in a continuous casting mold is an important factor influencing slab quality. The present invention provides an apparatus for controlling the flow of molten steel in a continuous casting mold to obtain a slab having excellent surface properties by controlling the meniscus flow rate in the mold.

[0005]

The present invention SUMMARY OF] is provided an electromagnetic coil which is divided into two or more divisions in a continuous casting mold width direction as the electromagnetic coil center of the casting direction is located in the meniscus near, (a) mold center Stirring toward the short side from (b)
Each stirring pattern with stirring directed from the short side of the mold to the center
A control system that independently controls the moving direction of the moving magnetic field of each electromagnetic coil so that the user can select a magnetic field is connected to the electromagnetic coil , and
To obtain a meniscus flow rate of 10-60 cm / sec in molten steel
A flow control device for molten steel in a continuous casting mold characterized by being made possible .

Hereinafter, the present invention will be described in detail. FIG. 1 is a partial cutaway view of a main part of a continuous casting mold according to the present invention.

The mold comprises 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 an immersion nozzle 2 attached to a tundish (not shown) is inserted. The discharge holes provided at the lower part of the immersion nozzle 2 are opened one by one on both sides of the immersion nozzle so as to face each other in the short side direction of the mold, but are not particularly limited.

[0008] The molten steel 3 is injected into the mold from the tundish through the immersion nozzle, and the discharge flow 5 discharged from the immersion nozzle is directed upward and downward on the short side toward the short side, and separated upward. The headed molten steel flow becomes a discharge reversal flow a and forms a meniscus flow 6. On the other hand, molten steel flow b
Is a downward flow.

According to the present invention, there are provided long side surfaces 1-
Stirring electromagnetic coils 7-1 and 7-2 that are divided into two or more in the width direction of the mold are provided outside the molds 1-2 and 1-2 to generate a moving magnetic field. Further, a switch and a current controller for changing the direction of the moving magnetic field are provided in the control room 10 remote from the mold, and are connected to an AC power supply. L in FIG. 3 is a pole pitch of the electromagnetic coil.

According to the experiments of the present inventors, it is impossible to control the meniscus flow formed by the discharge reversal flow within a certain range while securing the collision strength of the molten steel poured from the immersion nozzle against the solidified shell. And the knowledge which was extremely effective in improving the surface properties of the slab was obtained. That is, the present invention is provided so that the center of the electromagnetic coil in the casting direction is located near the meniscus,
Preferably, the distance from the meniscus to immediately below 300 mm is good.

In order to wash out the surface layer of the solidified shell and to remove inclusions and segregation, a certain flow rate of molten steel is required. Further, it is necessary to control the meniscus flow in order to prevent inclusions from being captured by the meniscus. That is, FIG. 4 shows the molten steel discharge flow by distance from the meniscus. That is, the critical point can be 300 mm from the meniscus. Therefore, the center of the electromagnetic coil is set within a range of 300 mm directly below the meniscus where only the meniscus flow exists, and only the meniscus flow is controlled.

When the meniscus flow rate is less than 10 cm / sec,
As the meniscus flow velocity decreases, the meniscus
The supply of heat to
A solidified mass of powder forms and gets caught in molten steel
Is trapped in the solidified shell and causes slab surface defects.
Or the molten steel in the meniscus part solidified and skinned
This will cause operation trouble. And vice versa
When the meniscus flow velocity exceeds 60 cm / sec,
As the size increases, powder is cut off,
It causes a powdery surface defect. Therefore, the present invention controls the meniscus flow rate in the range of 10 to 60 cm / sec.

The meniscus flow velocity is measured, for example, by inserting a thermo-alloy cylinder into a molten steel flow and measuring the resistance F caused by the flow with a strain gauge. The strain and the resistance can be determined in advance by drawing a calibration curve using a weight and using a regression equation. The control unit 10 shown in FIG. 2 can control the direction and strength of the moving magnetic field for each of the electromagnetic coils 7-1, 7-2,.

[0014]

EXAMPLE Continuous casting was performed using the stirring pattern shown in FIG. 5 under the molding conditions and electromagnetic stirring conditions shown in Table 1, and the incidence of surface defects was examined. FIG. 5A shows a stirring pattern in which the discharge reverse flow is decelerated, and FIG. 5B shows a stirring pattern in which the discharge reverse flow is accelerated.

[0015]

[Table 1]

Table 2 shows the coil specifications and capabilities at this time.

[0017]

[Table 2]

FIG. 6A shows the rate of occurrence of surface defects by the conventional method. According to the present invention, as shown in FIG. 6B, the rate of occurrence of surface defects was 5% or less within the range of the meniscus flow rate of 10 to 60 cm / sec.

[0019]

According to the present invention, since the meniscus flow rate of molten steel in a continuous casting mold is controlled, a cast piece having excellent surface properties can be obtained.

[Brief description of the drawings]

FIG. 1 is a partially cutaway explanatory view of the present invention.

FIG. 2 is a partial perspective view of the present invention.

FIG. 3 is a partial plan view of the present invention.

FIG. 4 is a table showing a relationship between a molten steel discharge flow per unit volume and a distance from a meniscus.

FIGS. 5 (a) and (b) are stirring patterns of an example of the present invention.

FIGS. 6A and 6B are tables showing the relationship between the meniscus flow velocity and the incidence rate of surface defects.

Continuation of the front page (56) References JP-A-57-75268 (JP, A) JP-A-1-228645 (JP, A) JP-A-63-104763 (JP, A) JP-A-63-16840 (JP) , A)

Claims (1)

(57) [Claims] The method according to claim 1 electromagnetic coil is divided into two or more split into a continuous casting mold width direction, provided as the electromagnetic coil center of the casting direction is located in the meniscus near the (a) mold center
Stirring directed to the short side and (b) directing from the short side of the mold to the center
A control system that independently controls the moving direction of the moving magnetic field of each electromagnetic coil so that each stirring pattern can be selected with stirring to be performed is connected to the electromagnetic coil , and 10 to 60 cm / sec is applied to molten steel.
A flow control device for molten steel in a continuous casting mold, wherein a meniscus flow rate can be obtained .