JP2002120052A - Device and method for controlling fluidity of molten steel in mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfy both the need for improving the quality of surface layer in a cast slab by securing a fixed flowing speed to the front surface of solidified shell and the contradicting need for improving the internal quality by restraining the deterioration of the internal quality caused by the entrapment of fused flux as a lubricant with the fluidity. SOLUTION: A device for controlling the fluidity of molten steel in a mold, is peculiarly composed of a linear motor electromagnetic coil having an iron core for giving the electromagnetic force in the direction along the long sides to the molten steel in a mold, in the casting space constituted of one pair of the long sides and the short sides in the mold for continuously casting the molten steel. This control device is peculiarly disposed with a coil which gives the direct current generating the uniform static magnetic field to the breadthwise direction of the long sides in the direction crossing at the right angle to the linear motor electromagnetic coil and at the vertical direction to the long sides of this casting space, so as to surround this iron core.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an apparatus and a method for controlling molten steel flow in a mold in continuous casting of steel.

[0002]

2. Description of the Related Art For example, when continuously casting a steel slab,
A moving magnetic field generating coil is arranged along the long side of the rectangular casting mold, an alternating current is applied to the coil, and the moving magnetic field generated by the coil is applied to the molten steel to form a swirling agitating flow in the molten steel cross-sectional direction. As a result, a technique of casting a slab with few defects while preventing segregation of molten steel and adhesion of an oxide to a solidified shell and the like, that is, a so-called electromagnetic stirring is well known. A typical document is "Material processing using electromagnetic force (129.130th Nishiyama Memorial Technical Lecture 1989)
(April 1975), which describes the electromagnetic induction and agitation techniques and effects of an alternating magnetic field. As an example of a mold structure, Japanese Patent Publication No. 58-49172 discloses an "electromagnetic stirrer for continuous casting".
Is disclosed.

[0003] In the electromagnetic stirring in a mold, impurity particles present in steel are formed by forming a horizontally swirling flow in a casting space and applying a constant flow velocity to the front surface of a solidified shell corresponding to the surface layer of a slab. It has been shown that alumina and slag-based inclusions mixed in molten steel can be washed away by deoxidation to improve the quality of the surface layer of a slab. However, in the meniscus in the mold, a liquid mainly composed of molten oxide called powder or flux exists as a casting lubricant at the upper part of the molten steel, which is caught in the molten steel due to the flow and turbulence of the meniscus, and is washed away on the surface layer. Even if it does not cause any problem, it has been a problem that it is transported into the molten steel pool and finally captured in the slab, and appears as a defect particularly when processing involving large deformation is performed. For this reason, conventionally, measures have been taken to make the flux hard to be entrained by adjusting the viscosity of the flux. However, also in this case, there is a contradictory problem that an increase in viscosity leads to deterioration of lubrication.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a demand for improving the quality of the surface layer of a slab by securing a constant flow velocity in front of a solidified shell, a method of calming a meniscus, and allowing a molten flux as a lubricant to flow. An object of the present invention is to satisfy conflicting demands for improving the internal quality to prevent the internal quality from being caught and deteriorating.

[0005]

SUMMARY OF THE INVENTION The present invention has solved the above-mentioned problems, and the gist of the present invention is to provide a continuous casting mold for molten steel in a casting space composed of a pair of long sides and short sides. In a device consisting of a linear motor electromagnetic coil having an iron core for applying an electromagnetic force in a direction along the long side to the molten metal in the mold on a pair of long side surfaces, the device is orthogonal to the linear motor electromagnetic coil, and The flow control of molten steel in a mold, characterized in that a coil for applying a direct current for generating a uniform static magnetic field in a long side width direction in a direction perpendicular to a long side of the casting space is arranged so as to surround the iron core. A moving magnetic field that satisfies the condition of the following equation (1) is applied by using the molten steel flow device in the mold so as to turn counterclockwise on a pair of long sides in the casting space; and Simultaneous application of a static magnetic field under the condition of the following equation (2) In the mold molten steel flow control method according to claim bets it is.

-2 ≦ log ₁₀ (Ba ² f) ≦ 0 (1) 0.05 ≦ Bs ≦ 0.2 (2) Ba: Maximum magnetic flux density of alternating current [Tesla] Bs by the linear motor in the casting space : Maximum magnetic flux density of static magnetic field [Tesla] f: Frequency of three-phase current of linear motor [Hz]

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a vertical and horizontal plan view showing an example of a continuous casting mold of a steel slab according to the present invention. As shown in FIG. 1, a flow control device for molten steel in a mold according to the present invention is a casting space composed of a pair of long sides 1 and short sides 2 composed of a back plate having a cooling water flow path made of a copper plate or a plate made of stainless steel or the like. In the meniscus portion of the molten steel pool 3, a moving magnetic field generating electromagnetic coil (linear motor) 5 for rotating the molten steel near the upper surface of the molten steel in the mold around the injection nozzle in the casting space 4 is connected thereto. An AC power source 6, a solenoid coil 8 for generating a DC magnetic field wound vertically around an iron core 7 of the linear motor, and a DC power source 9 connected thereto. As a result, the molten steel of the meniscus of the molten steel in the mold is caused to make a horizontal turning motion more strongly near the mold wall surface. In addition, the swirling flow velocity is generally determined by the product of the square of the magnetic field and the frequency. However, in FIG. 2, at the same time as the horizontal swirling flow generated at this time, the disturbance of the meniscus generated by the viscosity and shearing is observed. Further, the generation of vortices becomes remarkable due to shearing.
Here, when a static magnetic field generated by the solenoid coil of FIG. 1 and strengthened by the iron core acts, an electromagnetic braking effect (for example,
"Material processing using electromagnetic force (No. 129
・ Refer to the 130th Nishiyama Memorial Technical Course, April 1989. The effect of suppressing vortex generation and turbulence can be obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG.
A 4-pole linear motor having a width of casting width, a 150 mm high and a 150 mm thick iron core and a slot of 24 coils for flowing a three-phase alternating current to a mold having a thickness of 00 mm and a cavity (casting space) of 255 mm. Placed. Further, the iron core was wound in the vertical direction, and a solenoid coil was arranged so as to generate a magnetic field in the mold thickness direction. Using this apparatus, steel was cast, the index of the moving magnetic field strength including the frequency and the static magnetic field strength (magnetic flux density) were changed as shown in Table 1, and the slab quality was compared. As shown in FIG. 3, the quality of the surface and the inside was cut out from a slab,
The inclusions were taken out by electrolytic extraction and evaluated for the number of large inclusions and their types (alumina-based and powder-based) and their influence on the surface layer and internal quality. Casting was performed using a low-carbon aluminum killed steel at a casting speed of 1.5 m / min. 4 and 5 for the surface layer and the interior, respectively.
Shown in As can be seen from the results, the moving magnetic field has a minimum value at which the cleaning effect is exhibited and a maximum value at which the disturbance is not suppressed even at the static magnetic field, and the minimum value at which the disturbance effect is similarly suppressed at the static magnetic field. It can be seen that there is a maximum value that deteriorates the surface quality due to the excessive braking effect. Therefore, from FIGS. 4 and 5, it is necessary to limit the expressions (1) and (2) defined in the present invention.

[0009]

[Table 1]

[0010]

As described above, by using the method of the present invention, it is possible to produce cast pieces having good quality in both the surface layer and the inside.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an apparatus of the present invention.

FIG. 2 is a diagram showing disturbance of molten steel due to a moving magnetic field.

FIG. 3 is a diagram showing a method of collecting a slab sample.

FIG. 4 is a diagram showing an example of the relationship between the number of surface inclusions and control conditions.

FIG. 5 is a diagram showing an example of the relationship between the number of internal inclusions and control conditions.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Mold long side 2 ... Mold short side 3 ... Casting space 4 ... Swirling flow 5 ... Linear motor electromagnetic coil 6 ... 3 phase AC power supply 7 ... Iron core 8 ... Solenoid coil for static magnetic field 9 ... DC power supply

Claims (2)

[Claims] 1. A direction along a long side of a molten metal in a mold on a pair of long sides in a casting space formed by a pair of long sides and a short side of a mold for continuous casting of molten steel. An apparatus comprising a linear motor electromagnetic coil having an iron core for applying an electromagnetic force, wherein a static magnetic field uniform in a long side width direction orthogonal to the linear motor electromagnetic coil and perpendicular to a long side of the casting space. A flow control device for molten steel in a mold, characterized in that a coil for applying a direct current for generating a flow is provided so as to surround the iron core. 2. A moving magnetic field that satisfies the condition of the following equation (1) is applied to the casting space by using the apparatus according to claim 1.
A flow control method for molten steel in a mold, characterized in that a voltage is applied to the pair of long sides so as to be opposed to each other, and a static magnetic field of the following formula (2) is simultaneously applied. -2 ≦ log ₁₀ (Ba ² f) ≦ 0 (1) 0.05 ≦ Bs ≦ 0.2 (2) Ba: Maximum magnetic flux density of AC by linear motor in casting space [Tesla] Bs: Static magnetic field Magnetic flux density [Tesla] f: Frequency of three-phase current of linear motor [Hz]