JP2607334B2 - 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 THE INVENTION are 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) a mold Direction from center to one short side only
Stirring pattern and (b) center from only one short side of mold
Of each electromagnetic coil can be selected
And wherein the controllable movement direction of the moving magnetic field independently and by applying a traveling magnetic field which satisfies the control system to obtain the meniscus flow velocity of 10~60cm / sec in molten steel the formula, connected to said electromagnetic coil It is a flow control device for molten steel in a continuous casting mold.

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 experiments by 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. We have obtained knowledge that is extremely effective in improving the surface properties of cast slabs. That is, in the present invention, the center of the electromagnetic coil in the casting direction is provided so as to be located near the meniscus, but preferably within 300 mm immediately below the meniscus.

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 in a range up to 300 mm 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. Here, the relationship between the meniscus flow velocity and the magnetic field moving velocity will be described. That is, the magnetic field moving speed V is expressed by equation (1). V = C ₁ × L × f + C ₂ (1) (L: pole pitch of coil, f: magnetic field frequency, C ₁ ,
(C ₂ : adjustment coefficient) Further, since the magnetic field moving speed is determined by the meniscus flow velocity Vp, the magnetic field moving speed V is a function of Vp. At this time, the function is considered by a linear expression (2) or a quadratic expression (3). V = f (Vp) = C ₃ × Vp + C ₄ (2) = C ₃ × Vp ² + C ₄ × Vp + C ₅ (3) Equations (1) and (2) Equation (4) or Equation (5) is obtained by simultaneously solving Equation (3) or Equation (3) and solving for Vp. Vp = C ₆ × L × f + C ₇ (4) = C ₆ × L ^0.5 × f ^0.5 + C ₇ (5) Also, V = f (Vp) is increased. When expressed by the following equation, Vp is expressed by the equation (6) (C ₇ = 1 / order). Vp = C ₆ × L ^C7 × f ^C7 + C ₈ (6)

At this time, the variation of the coil current I which affects Vp like L and f is included in the variation range of C ₆ and C ₈ . Actually, the operation was performed in the range of 0 to 2500 mA. Here, the proper value range of the meniscus flow velocity Vp (Vp
_min , Vp _max ) and equation (6) yields equation (7). Vp _min ≦ C ₆ × L ^C7 × f ^C7 + C ₈ ≦ Vp _max (7) By transforming this, the equation (8) is obtained. C ₉ ≦ L × f ≦ C ₁₀ (8)

From the above derivation, equation (8) is obtained regardless of the order of V = f (Vp). FIG. 5 is based on the linear equation of L × f on the horizontal axis and Vp on the vertical axis.
0 ≦ L × f ≦ 40000 (L: coil pitch (mm),
f: magnetic field frequency (Hz)), it is possible to appropriately control the meniscus flow velocity.

The meniscus flow velocity is measured by, for example, 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,... To select the stirring pattern shown in FIG.

[0016]

【Example】

Example 1 Continuous casting was performed using the stirring pattern shown in FIG. 6 under the mold conditions and electromagnetic stirring conditions shown in Table 1, and the incidence of surface defects was examined. FIG. 7 shows the result. (A) is a conventional example,
(B) shows an example of the present invention.

[0017]

[Table 1]

[0018]

[Table 2]

The meniscus flow rate was controlled within the range of 10 to 30 cm / sec by the stirring pattern for reducing the discharge reversal flow, and the incidence of surface defects was reduced.

Example 2 Continuous casting was performed using the stirring pattern shown in FIG. 8 under the mold conditions and coil specifications shown in Example 1, and the incidence of surface defects was examined. FIG. 9 shows the result. (A) is a conventional example,
(B) shows an example of the present invention. The meniscus flow velocity was controlled in the range of 40 to 60 cm / sec by the stirring pattern for accelerating the discharge reversal flow, and the incidence of surface defects was reduced.

[0021]

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 graph of the presence of a molten steel discharge flow per unit volume and meniscus.

FIG. 5 is a graph of a magnetic field moving speed and L × f.

FIG. 6 is a stirring pattern of the present invention.

FIGS. 7A and 7B are graphs of the incidence rate of surface defects and the meniscus flow velocity.

FIG. 8 is another stirring pattern of the present invention.

FIGS. 9A and 9B are graphs of a surface defect occurrence rate and a meniscus flow velocity.

 ──────────────────────────────────────────────────続 き 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) 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
A stirring pattern directed only to one short side;
The moving direction of the moving magnetic field of each electromagnetic coil can be controlled independently , and a moving magnetic field that satisfies the following formula can be applied by selecting the stirring pattern directed to the center only from the short side of the mold. A flow control device for molten steel in a continuous casting mold, wherein a control system for obtaining a meniscus flow rate of 10 to 60 cm / sec in molten steel is connected to the electromagnetic coil.