JP4669367B2 - Molten steel flow control device - Google Patents

Description

  The present invention relates to a molten steel flow control device, and more particularly, to a molten steel flow control device that controls molten steel flow in a mold in continuous casting of steel.

  For example, when steel slabs are continuously cast, a so-called electromagnetic stirring technique is used in the mold. In such electromagnetic stirring, a moving magnetic field generating coil is arranged along the long side of a rectangular casting mold, an alternating current is passed through the moving magnetic field generating coil, and the moving magnetic field generated by the moving magnetic field generating coil and the alternating current is supplied to the molten steel. To form a swirling stirring flow in the horizontal plane of the molten steel. By this electromagnetic stirring, it is possible to prevent segregation of molten steel and adhesion of oxides to the solidified shell, and to cast a slab with few defects.

  An electromagnetic stirring device for continuous casting utilizing such electromagnetic stirring is already well known. Moreover, the effect by the electromagnetic induction of such an alternating magnetic field, electromagnetic stirring technology, etc. are also disclosed (for example, patent document 1, nonpatent literature 1).

  In the electromagnetic stirring in the mold as described above, a flow in which the molten steel is swirled horizontally is formed in the casting space, and a constant flow velocity is applied to the surface of the solidified shell corresponding to the slab surface layer. In this way, it becomes possible to wash away the alumina and slag inclusions mixed in the molten steel and improve the quality of the surface layer of the slab.

  According to Patent Document 1, when an alternating current is passed through a solenoid installed around the mold, the force that separates the molten steel in the mold from the mold is caused by the interaction between the magnetic field generated in the mold and the induced current. It is known that so-called soft contact casting can be performed by electromagnetic casting.

JP 52-32824 A “(129th and 130th Nishiyama Memorial Technology Course) Material Processing Using Electromagnetic Force”, Japan Iron and Steel Institute, April 28, 1989, P21-48 “Handling of Molten Metal Based on Magnetohydrodynamics”

  However, when the above-mentioned electromagnetic stirring and electromagnetic casting are used for continuous casting of steel, it is necessary to prepare equipment such as coils, which causes a problem of increasing costs and increasing the occupied space.

  The present invention has been made in view of the above-mentioned problems of the conventional molten steel flow control device, and an object of the present invention is to provide a compact configuration in which the configuration of electromagnetic stirring and the configuration of electromagnetic casting are integrally formed. By providing a new and improved molten steel flow control device capable of improving the lubrication of molten steel in the mold while ensuring a constant flow velocity on the surface of the solidified shell and improving the quality of the slab surface layer. is there.

In order to solve the above-mentioned problems, according to the present invention, there is provided a molten steel flow control device for controlling the flow of molten steel in a mold in a continuous casting equipment for steel, which is arranged in the long side direction along the long side surface of the mold. A magnetic field generating electromagnetic coil wound around the longitudinal direction of the iron core, an AC power supply for electromagnetic stirring for supplying an alternating current to the moving magnetic field generating electromagnetic coil, and a short horizontal plane of the mold A solenoid coil that is wound around the iron core around the direction along the axis and generates an electromagnetic force inwardly in the horizontal plane in the molten steel, and an AC power source for electromagnetic casting that supplies an alternating current to the solenoid coil. A molten steel flow control device is provided.

  Such an integrally formed molten steel flow control device has both functions of electromagnetic stirring (moving magnetic field) and electromagnetic casting (fixed alternating magnetic field).

Here, the iron core may be disposed along each long side surface of the mold, and the solenoid coil may be two solenoid coils wound around the iron core.
The iron core may have a length equal to the length of the long side surface.
Incidentally, the long Henmen is that side which corresponds to the long side of the mold.

  As described above, according to the present invention, the structure of electromagnetic stirring (moving magnetic field) and the structure of electromagnetic casting (fixed alternating magnetic field) are integrally formed to improve the quality of both the surface and the surface layer in the production of slabs. It becomes possible. Accordingly, it is possible to obtain a high quality slab in which the center segregation is reduced, the thickness of the solidified shell is made uniform, and surface defects and vertical crack defects are hardly generated.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

  The embodiment of the present invention is characterized in that a configuration of electromagnetic stirring (EMS) and a configuration of electromagnetic casting (EMC) are integrally formed. The electromagnetic stirring can be distinguished as a moving magnetic field and electromagnetic casting as a fixed alternating magnetic field. In order to facilitate understanding, first, the above two configurations will be described separately, and the advantages of this embodiment will be described later.

(Electromagnetic stirring)
In a continuous casting facility for molten steel, molten metal (molten steel) is injected into a mold from an immersion nozzle, and the solidified metal is drawn out from the mold to obtain a slab. At this time, an electromagnetic stirrer is installed outside the side wall of the mold, and a swirling motion can be electromagnetically applied to the molten steel in the mold. Due to this stirring flow, the center segregation of the slab is reduced, and the thickness of the solidified shell is promoted to improve the quality of the slab.

  There are two types of electromagnetic stirrer, a linear moving magnetic field type and a rotary moving magnetic field type, depending on the form of the generated moving magnetic field. The former electromagnetic stirrer using the linear moving magnetic field type mainly performs electromagnetic stirring of the slab, and the latter electromagnetic stirrer based on the rotating magnetic field type is mainly used when casting a square slab such as billet or bloom. Used. Here, the electromagnetic stirrer using the linear moving magnetic field type used in this embodiment will be briefly described.

  FIG. 3 is a cross-sectional view showing the positional relationship between the mold 100 and the electromagnetic stirring device 110. Referring to FIG. 3, the electromagnetic stirring device 110 is configured to include a pair of iron cores 150 arranged to face each other with a slab mold 100 interposed therebetween, and a plurality of coils 152 respectively wound around the iron core 150.

  Each coil 152 is supplied with U, V, and W phase currents that are 120 degrees out of phase from a three-phase AC power source (not shown). “+” And “−” in FIG. 3 define the directions of the U, V, and W phase currents. As a result, a moving magnetic field is generated in the direction indicated by the arrow in the mold 100 in accordance with the phase change of the current flowing through each coil. This moving magnetic field generates an electromagnetic force in the moving direction of the magnetic field, that is, the arrow direction, with respect to the molten steel 160 in the mold 100. Thus, the magnetic fields generated by the coils 152 generate electromagnetic forces in opposite directions along the side surface (hereinafter referred to as the long side surface) that corresponds to the long side of the mold 100 in the molten steel 160, and the molten steel 160 is stirred. Is done.

  As described above, the magnetic stirrer 110 moves the magnetic field to create a flow of molten steel in the mold cross section, acts so that inclusions do not remain on the surface layer that hardens relatively quickly, and cleans the steel slab surface. .

(Electromagnetic casting)
In addition, an electromagnetic casting device is installed outside the mold side wall, and an electromagnetic force is applied to the molten steel in the mold toward the center of the horizontal plane, that is, the mold side wall and the molten steel are separated from each other. The slab quality can be improved by weakening the contact (soft contact).

  FIG. 4 is a perspective view showing the positional relationship between the mold 100 and the electromagnetic casting apparatus 200. Referring to FIG. 4, the electromagnetic casting apparatus 200 is formed by winding a coil around a slab mold 100. Here, several coils are shown for simplicity, but the number and thickness of the coils can be arbitrarily selected.

  For example, when an alternating current is passed through the coil of the electromagnetic casting apparatus 200 and a current is flowing in the direction of the solid arrow 210, an induced current in the direction of the wavy arrow 212 is generated in the molten steel. Further, the coil of the electromagnetic casting apparatus 200 generates an upward magnetic field represented by an arrow 214. Since the induced current and the magnetic field are orthogonal to each other, an electromagnetic force directed toward the inner side of the horizontal plane as indicated by an arrow 220 is generated according to the Fleming left-hand rule. Such an electromagnetic force is also called a pinch force.

  The above inward force does not depend on the direction of the current flowing in the coil. This is because even if the current flowing through the coil is reversed, the induced current and the magnetic field are simultaneously reversed, so the direction of the electromagnetic force is not affected. Therefore, for example, a single-phase AC power source can be applied to the coil of the electromagnetic casting apparatus 200.

  If such an electromagnetic casting apparatus 200 is not installed in the mold, the surface of the molten steel, which tends to decrease in temperature, quickly solidifies in the casting of steel having a low carbon content and a high melting point, such as ultra-low carbon steel. Causes defects.

  FIG. 5 is a longitudinal sectional view for explaining the operation of the electromagnetic casting apparatus 200. Here, as in FIG. 4, the coil of the electromagnetic casting apparatus 200 is wound around the mold 100 around the moving direction of the molten steel. For example, if a current in the direction shown in the drawing flows through the coil of the electromagnetic casting apparatus 200, an induced current is generated in the opposite direction to the current in the molten steel. The molten steel is pulled away from the inner wall (inner surface) of the mold 100 by the pinch force 252 directed toward the inner side of the molten steel generated by the induced current and the electromagnetic force 250.

  When the molten steel and the mold are separated from each other in this way, the powder 260 as a lubricant easily flows into the mold and the flow of the molten steel is improved, so that the solidification speed of the molten steel becomes slow and the electromagnetic casting apparatus 200 is used. Compared to the case where the molten steel is not formed, the molten steel starts to solidify (solidified shell 264) from a deeper position of the mold, so that surface defects and vertical crack defects are less likely to occur. Further, the mold 100 may be longitudinally vibrated, and the powder 260 is more likely to flow in by the longitudinal vibration.

  FIG. 6 is a perspective view showing another embodiment of the electromagnetic casting apparatus. Referring to FIG. 6, in the electromagnetic casting apparatus 400, a coil wound around a direction along the short horizontal side of the mold 100 is arranged on each long side surface along the side surface of the mold 100. In these two coils, a current flows in a direction facing each other. Here, for the sake of simplicity, the coil is represented only by an arrow, but the thickness and number of windings can be arbitrarily selected.

  For example, when an alternating current is passed through the coil of the electromagnetic casting apparatus 400 and a current in the direction of the solid arrow 410 flows, an induced current in the direction of the wavy arrow 412 is generated in the molten steel. In addition, due to the interaction between the two coils of the electromagnetic casting apparatus 400, a magnetic field upward indicated by the arrow 414 is generated. Since the induced current and the magnetic field are orthogonal to each other, an electromagnetic force (pinch force) inward of the horizontal plane as represented by an arrow 420 is generated according to the Fleming left-hand rule.

  The above inward force does not depend on the direction of the current flowing in the coil, as described with reference to FIG. Therefore, for example, a single-phase AC power supply can be applied to the coil of the electromagnetic casting apparatus 400. Note that the current directions (phases) of the two coils may be equal, or one of them may be delayed. This is because, in general, a high-frequency current can enhance the skin effect and concentrate electromagnetic force on the steel surface.

(Molten steel flow control device)
The molten steel flow control device according to the embodiment of the present invention is formed integrally by combining the above-described electromagnetic stirring configuration and the electromagnetic casting configuration.

  FIG. 1A is a perspective view showing a configuration of a continuous casting mold 500 of a steel slab and a molten steel flow control device 510 in the present embodiment, FIG. 1B is a plan view of FIG. 1A, and FIG. It is a front view of FIG. 1A.

  The mold 500 includes a long side back plate 520, a short side back plate 522, and an injection nozzle 524. The molten steel flow control device 510 includes an iron core 526, a moving magnetic field generating electromagnetic coil 528, an electromagnetic stirring AC power supply 530, a solenoid coil 532, and an electromagnetic casting AC power supply 534.

  The long side back plate 520 covers the long side surface of the mold 500 having a rectangular cross section. Further, the long side back plate 520 is formed of a plate such as a copper plate and stainless steel, and includes a cooling water flow path.

  The short side back plate 522 covers a side surface (hereinafter referred to as a short side surface) corresponding to the short side of the mold 500 having a rectangular cross section. Similarly to the long side back plate 520, the short side back plate 522 is formed of a plate such as a copper plate and stainless steel, and includes a cooling water flow path. The short side back plate 522 and the long side back plate 520 described above form a casting space.

  The injection nozzle 524 is formed of an inflow port and a discharge port, and in the case of a mold having a rectangular cross section, discharge is performed so that the molten steel collides with the short side surface. In the molten steel pool 550, the discharged molten steel is divided into two flows, a flow toward the meniscus and a flow toward the lower side of the molten steel pool 550, and four large vortices are formed when viewed from the long side surface. As the molten steel moving toward the lower side of the molten steel pool 550 descends the molten steel pool 550, the surface is cooled to become a solidified shell 264.

  The iron core 526 is formed of a magnetic material such as a silicon steel plate, and is arranged along the long side surface in the long side direction. Further, the length of the iron core 526 may be substantially equal to the length of the long side.

  The moving magnetic field generating electromagnetic coil (linear motor) 528 is wound around the longitudinal direction of the iron core 526, and obtains electric power from the AC power source 530 for electromagnetic stirring, and horizontally turns the molten steel on the transverse section (horizontal plane) of the mold. Supply the moving electromagnetic force. The detailed configuration is substantially the same as that of the electromagnetic stirring device shown in FIG.

  With such a configuration, the molten steel near the upper surface of the molten steel in the mold can be swung in the meniscus (interface) portion of the molten steel pool 550 in the direction indicated by the arrow 552 (see FIG. 1B) around the molten steel injection nozzle. . Here, of the molten steel in the mold, the meniscus molten steel has a strong horizontal turning motion near the mold wall surface (long side surface). The swirl velocity in such a horizontal swirl is generally defined by the product of the square of the magnetic field and the frequency.

  The solenoid coil 532 is wound around the iron core 526 with the direction along the short horizontal side of the mold as an axis, and obtains electric power from the AC power source 534 for electromagnetic casting to pull the molten steel away from the long side surface of the mold. Supply electromagnetic force. The magnetic field generated by the solenoid coil 532 generates the alternating magnetic field shown in FIG. 6 in the molten steel, and generates an electromagnetic force that pulls the molten metal away from the mold.

  In the molten steel flow control device 510 according to the present embodiment, an electromagnetic stirring unit including a moving magnetic field generating electromagnetic coil 528 and an iron core 526 and an electromagnetic casting unit including a solenoid coil 532 and an iron core 526 are integrally formed. Due to the action of the two electromagnetic forces by the electromagnetic stirring part and the electromagnetic casting part, it is possible to simultaneously enjoy the cleaning effect by stirring and the improvement of lubrication in the mold.

  In addition, the electromagnetic field generated by the solenoid coil 532 not only gives the action of pulling the molten steel away from the mold, but also causes the action of the induction current generated by the solenoid coil 532 to heat the molten steel in the mold, and in general, cooling is excessively performed. It is possible to increase the temperature in the vicinity of the molten metal surface in the mold, which tends to occur, and to make the solidification more uniform.

  Further, the iron core 526 shared with the moving magnetic field generating electromagnetic coil 528 effectively acts on the amplification of the alternating magnetic field by the solenoid coil 532, and even if the coil current of the solenoid coil 532 is reduced, a strong magnetic field can be induced. Demonstrate a synergistic effect. Therefore, operation with low power consumption is possible.

  More specifically, due to the action of electromagnetic casting (fixed alternating magnetic field), the molten metal in the mold is pushed inside and pulled away from the mold to improve the lubrication state. At the same time, the solidification is made uniform without the predetermined portion being biased and cooled. Also, the temperature rises by about 5 ° C due to Joule heating. In this state, when the molten metal is swirled horizontally by electromagnetic stirring (moving magnetic field), the front of the uniformized solidified shell is washed away uniformly, and further, the growth of the solidified shell is slowed by heating, so non-metallic inclusions are caused. Objects are not easily captured, and the number of inclusions on the surface of the slab (from the surface of the slab to 10 mm) is reduced by a synergistic action. In addition, the unevenness of the slab surface is reduced because the lubrication state is improved by the action of electromagnetic casting (fixed AC magnetic field), but the temperature distribution in the slab circumferential direction becomes uniform by further swirling the molten metal horizontally, The average unevenness is improved. Such an effect is demonstrated in the following examples.

  For example, the mold 500 shown in FIGS. 1A, 1B, and 1C has a width of 1650 mm, a height of 800 mm, and a cavity (casting space) thickness of 255 mm. For this mold, the molten steel flow control device 510 has a slot of 24 coils for flowing a three-phase alternating current through an iron core 526 having a width (1650 mm) substantially equal to the casting width (1650 mm), a height of 150 mm, and a thickness of 150 mm. A pole linear motor was installed.

  Further, a solenoid coil 532 that is wound around the iron core 526 with the direction along the short horizontal plane of the mold as an axis and generates a magnetic field in the short horizontal direction of the mold is disposed.

The molten steel was cast using the molten steel flow control device 510. At this time, the power sources for supplying power to the moving magnetic field generating electromagnetic coil 528 and the solenoid coil 532 are the electromagnetic stirring AC power source 530 and the electromagnetic casting AC power source 534, respectively. The AC power supply 530 for electromagnetic stirring is a 5-phase three-phase AC, and can supply an electromagnetic force of 5 × 10 ⁴ N / m ^{3 at} the maximum in the mold. Further, the AC power source 534 for electromagnetic casting is a single-phase AC of 50 Hz, and can supply an electromagnetic force (pinch force) of a maximum of 1 × 10 ⁵ N / m ^{3 in} the mold.

  Here, we investigated the difference in quality depending on whether or not electromagnetic stirring and electromagnetic casting were performed. Whether or not the electromagnetic stirring and the electromagnetic casting are performed is determined by whether or not the AC power source 530 for electromagnetic stirring and the AC power source 534 for electromagnetic casting are applied. Therefore, (1) the two power sources are not applied, that is, there is no electromagnetic force, (2) only the electromagnetic stirring AC power source 530 is applied, that is, the three-phase AC magnetic field exists alone, and (3) the AC for electromagnetic casting. The slab quality is compared in four states: a state where only the power source 534 is applied, that is, a state where a single-phase AC magnetic field is present alone, and (4) a state where a magnetic field is present by applying both power sources.

  In evaluating the cleaning effect of non-metallic inclusions, the quality of the slab surface layer was confirmed by cutting out a sample from the slab, removing the inclusions by electrolytic extraction, and evaluating the number of large inclusions. Such large inclusions have a sphere equivalent diameter of 100 μm or more.

  FIG. 2 is an external view showing the sampling conditions of the sample 600. FIG. The slab sample 600 has at least three locations (the total width of the slab) of a surface layer sample 610 having a width of 100 mm, a height of 20 mm, and a thickness of 250 mm, and an internal sample 612 of the surface layer sample 610 having a width of 100 mm, a height of 210 mm, and a thickness of 250 mm. 1/4 width, 2/4 width, and 3/4 width).

  The unevenness of the slab surface due to soft contact was also compared. The casting in this example was performed using an extremely low carbon aluminum killed steel at a casting speed of 1.5 m / min. The results are shown in Table 1. Here, the slab surface unevenness index is a relative index based on the maximum value of the unevenness in the height direction with respect to the slab surface when no electromagnetic force is applied. In this example, in order to improve the measurement accuracy, in the slab where no electromagnetic force is applied, with respect to the line portion divided into 1 m in the length direction of the slab and 5 parts in the width direction of the slab, The value of the unevenness in the height direction with respect to the slab surface is measured by a laser displacement meter, and the difference between the maximum value and the minimum value of each line is taken as a reference by taking the average value of the above five lines. The number index of inclusions on the slab surface is based on the number per unit volume of inclusions with a sphere equivalent diameter of 100 μm or more extracted from the slab by electrolytic extraction when no electromagnetic current is applied. Relative index. From this result, it is understood that a synergistic effect of reducing the number of inclusion defects on the surface of the slab and improving the unevenness of the surface of the slab is obtained by the effect of superposition.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  The present invention is applicable to a molten steel flow control device that controls the flow of molten steel in a mold in continuous casting of steel.

It is the perspective view which showed the structure of the casting_mold | template of a continuous casting mold of steel slab, and a molten steel flow control apparatus. It is the top view which showed the structure of the casting_mold | template of a continuous casting mold of steel slab, and a molten steel flow control apparatus. It is the front view which showed the structure of the casting mold of a steel slab, and the molten steel flow control apparatus. It is the external view which showed the collection conditions of the sample of slab. It is a cross-sectional view showing the positional relationship between a mold and an electromagnetic stirring device. It is a perspective view showing the positional relationship of a casting_mold | template and an electromagnetic casting apparatus. It is a longitudinal cross-sectional view for demonstrating the effect | action of an electromagnetic casting apparatus. It is the perspective view which showed other embodiment of the electromagnetic casting apparatus.

Explanation of symbols

100,500 Mold 150,526 Iron core 510 Molten steel flow control device 528 Moving magnetic field generating electromagnetic coil 530 Electromagnetic stirring AC power source 532 Solenoid coil 534 AC power source for electromagnetic casting

Claims (3)

A molten steel flow control device for controlling the flow of molten steel in a mold in a continuous casting facility for steel,
An iron core disposed in the long side direction along the long side surface of the mold;
A moving magnetic field generating electromagnetic coil wound around the longitudinal direction of the iron core;
An AC power supply for electromagnetic stirring for supplying an AC current to the moving magnetic field generating electromagnetic coil;
A solenoid coil that is wound around the iron core around the horizontal short side direction of the mold and generates an electromagnetic force in the horizontal plane in the molten steel ;
An AC power source for electromagnetic casting for supplying an AC current to the solenoid coil;
A molten steel flow control device comprising:   The iron core is disposed along each long side surface of the mold,
  The molten steel flow control device according to claim 1, wherein the solenoid coils are two solenoid coils wound around the iron cores.   The molten steel flow control device according to claim 1, wherein the iron core has a length equal to a length of the long side surface.

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