JPH06603A - Controller for flow of molten steel in continuous casting mold - Google Patents

Abstract

PURPOSE:To control flow velocity at a meniscus and to produce a cast slab having excellent in surface characteristic by independently the controlling magnetic field impressing direction of plural electromagnetic coils. CONSTITUTION:On the outside of longitudinal side surfaces 1-1, 1-2 in a mold, the electromagnetic coils 7-1, 7-2 for stirring divided into two or above in a lateral direction are provided and the direction and the strength of shifting magnetic field are controlled by the command of a control part 10. As for the measurement of the flow velocity at the meniscus, e.g. a thermalloy-made cylinder is inserted into the molten steel flow and by measuring the resistant force caused by the flow with a strain gage, the measured result is used for control data. In the result of investigating the relation between the surface flaw generating rate of the cast slab and the flow velocity at the meniscus, by controlling the meniscus flow velocity in the range of 10-60cm/sec, the cast slab excellent in surface characteristic is produced.

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, 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 side of the mold, and the electromagnetic stirrer installed on the long side is used to melt the molten steel in the mold. It is disclosed that a slab of good quality is produced by imparting a flow toward the center in the width direction to reduce the depth of penetration of the molten steel flow from the immersion nozzle into the molten steel in the mold.

Further, in Japanese Unexamined Patent Publication No. 64-2771, a moving magnetic field is applied in accordance with 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, which is abnormal. It is disclosed to prevent surface defects due to mold powder entrainment and surface cracking of a cast piece due to fluctuations in the molten metal surface.

[0004]

The flow of molten steel in the continuous casting mold is an important factor that affects the quality of the cast slab. The present invention provides a molten steel flow control device in a continuous casting mold for controlling the meniscus flow velocity in the mold to obtain a slab having excellent surface properties.

[0005]

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 a magnetic field is applied to each electromagnetic coil. A flow control device for molten steel in a continuous casting mold, characterized in that a control system for independently controlling directions is connected to the electromagnetic coil.

The present invention will be described in detail below. FIG. 1 is a partially cutaway view showing a main part of a mold for continuous casting according to the present invention.

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 dipping nozzle 2 attached to a tundish (not shown) is inserted. The discharge holes provided in the lower part of the immersion nozzle 2 are opposed to each other in the direction of the short side of the mold and are opened one by one on both sides of the immersion nozzle, but there is no particular limitation.

Molten steel 3 is injected into the mold from the tundish through this immersion nozzle, and the discharge flow 5 discharged from the immersion nozzle is directed in the direction of the short side, hits the short side and is divided into upper and lower parts, and upward. The heading molten steel flow becomes a discharge reversal flow a, forming a meniscus flow 6. On the other hand, molten steel flow b directed downward
Becomes a downflow.

According to the present invention, the opposite long side surfaces of the mold 1-
Agitating electromagnetic coils 7-1 and 7-2, which are divided into two or more parts in the mold width direction, are provided on the outside of the parts 1 and 1-2 to generate a moving magnetic field. In addition, a switching device for changing the direction of the moving magnetic field and a current controller are provided in the control chamber 10 away from the mold, and are connected to an AC power source. L in FIG. 3 is the pole pitch of the electromagnetic coil.

According to the experiments by the present inventors, it is possible 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 to the solidified shell. We have obtained the knowledge that it is extremely effective in improving the surface properties of cast slabs. 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, it is within 300 mm directly below the meniscus.

In order to wash away the surface layer of the solidified shell and remove inclusions and segregation, a certain molten steel discharge flow rate is necessary. Furthermore, it is necessary to control the meniscus flow in order to prevent inclusions from being trapped in the meniscus. That is, FIG. 4 shows the molten steel discharge flow for each distance from the meniscus. That is, the critical point can be 300 mm from the meniscus. Therefore, the center of the electromagnetic coil is installed in the range from the meniscus where only the meniscus flow exists to 300 mm directly below to control only the meniscus flow.

In the present invention, the meniscus flow velocity is 10 cm.
When it is less than / sec or more than 60 cm / sec, the surface defect occurrence rate of the obtained slab is high. Therefore, the present invention controls the meniscus flow velocity within the range of 10 to 60 cm / sec.

The meniscus flow velocity is measured by, for example, 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 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 under the stirring conditions shown in FIG. 5 under the molding conditions and electromagnetic stirring conditions shown in Table 1, and the occurrence rate of surface defects was examined. 5A shows a stirring pattern in which the discharge reversal flow is decelerated, and FIG. 5B shows a stirring pattern in which the discharge reversal flow is accelerated.

[0015]

[Table 1]

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

[0017]

[Table 2]

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

[0019]

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

[Brief description of 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 chart of a relationship between a molten steel discharge flow per unit volume and a distance from a meniscus.

5 (a) and 5 (b) are agitation patterns of Examples of the present invention.

6A and 6B are charts showing the relationship between the meniscus flow velocity and the surface defect occurrence rate.

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 direction of each electromagnetic coil is independently controlled. A flow control device for molten steel in a continuous casting mold, wherein a control system is connected to the electromagnetic coil.