JPH0724559A - Method and device for controlling flow of molten metal in mold in continuous casting - Google Patents

Abstract

PURPOSE:To obtain a metal slab having excellent surface characteristic by giving various shapes of flow to molten metal in a mold, continuously varying electromagnetic stirring thrust even in the case the molten metal flow continuously varies to execute the flow control and solving a problem caused by an eddy of the stirring thrust. CONSTITUTION:Circuits for connecting each coil of electromagnetic stirring coil 6 arranged along two mold long sides in a meniscus surface 5 and electric sources 8, 9 are divided into two, respectively. The combination of the optional two circuits of each circuit of the total four divided circuits is connected to the separated electric source, respectively or each circuit of the four circuits is individually connected to the separated electric source to control the electromagnetic stirring thrust with the coil 19 of each circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten metal flow control method and apparatus for obtaining a slab free from surface defects such as vertical cracks in continuous casting of a metal slab such as steel.

[0002]

2. Description of the Related Art In continuous casting of metal slab, FIG.
As shown in FIG. 1, the molten metal 1 is injected into the mold 3 from the dipping nozzle 2 and is cooled along with the mold 3 to solidify the shell 4
Is formed and pulled out to form a slab. As shown in FIG. 14 (see FIG. 13A-A), the immersion nozzle 2 is provided at the center of the cross section of the mold, and the molten metal 1 in the mold is discharged from the nozzle port and flows as shown by the arrow in FIG. Surface 5
Inside, a reverse flow from the mold short side 16 toward the immersion nozzle 2 is generated as shown by the solid arrow in FIGS. 13 and 14.

In continuous casting of such metal slabs, as a countermeasure against the occurrence of slab surface defects such as vertical cracks in the solidified shell 4, surface defects caused by non-metallic inclusions in the molten metal, powder on the meniscus, etc. The fluidization of the molten metal in the No. 5 is proposed by Japanese Patent Laid-Open No. 1-22845, and it is described that the electromagnetic stirring method is used as a means for flowing the molten metal.

A conventional electromagnetic stirrer for molten metal in a mold is
As shown in FIG. 15, mold long sides 15a and 15b
The electromagnetic stirring coils 6a and 6b provided along the ridges apply uniform electromagnetic stirring thrust to the molten metal in the mold 3. That is, in the electromagnetic stirring coil 6a, a plurality of magnetic poles 17a are arranged along the long side 15a of the mold,
The coil 19a is wound around the slot 18a between the magnetic poles 17a, and the electromagnetic stirring coil 6b is similarly constructed. Each coil 19a and 19b is a connection box 7a.
A typical example of the connection is as shown in FIG. 14, in which the electromagnetic stirring thrust of the moving magnetic field system uniformly applies to the molten metal in the meniscus surface 5 as indicated by the arrow. It was being done.

FIG. 16 shows the thrust distribution in the plane of the meniscus when the frequency of the three-phase power source 8 is 2 Hz and the current is 400 A by the conventional device of FIG. The figure is illustrated by "general-purpose electromagnetic field numerical analysis software", and the arrow indicates the direction of the thrust in the area of each square in the direction of the arrow and the magnitude of the thrust in the length of the arrow. As can be seen from FIG. 16, the component in the long side direction of the thrust force along the long side 15 of the mold is substantially constant at each position of the long side.

[0006]

As described above, in the conventional electromagnetic stirring device in the mold in the continuous casting of the metal slab, the electromagnetic stirring thrust is evenly applied to the molten metal along the long side of the mold. The resulting rotating flow of the molten metal in the meniscus plane overlaps with the reversing flow and the electromagnetic stirring thrust, and is strong when going from the mold short side 16 to the dipping nozzle 2 as shown by the broken line arrow in FIG. The flow was weak when heading for the short side 16. For this reason, stagnation occurs in the molten metal flow in the meniscus surface 5, non-metallic inclusions in the molten metal accumulate in the stagnation portion, and powder is entrapped, so that measures against defects such as vertical cracks on the slab surface are sufficient. It wasn't something.

Further, the discharge flow velocity of the molten metal may vary from discharge port to discharge port due to the non-metallic inclusions in the melt adhering to the discharge port of the immersion nozzle 2. In this case, the molten metal flow in the plane of the meniscus fluctuates continuously and variously. Therefore, if a uniform electromagnetic stirring thrust is applied as in the conventional case, a uniform rotating flow cannot be stably obtained. Further, in addition to rotation, it is also desired to apply various forms of thrust such as braking and acceleration to the reverse flow to the molten metal flow in the meniscus plane. However, the conventional electromagnetic stirring is performed by using a three-phase one power source, and a method of changing the thrust by changing the wiring of the electromagnetic stirring coil may be considered, but the thrust is continuously applied to the continuously changing molten metal flow. It was difficult to change. Further, there is a problem that the electromagnetic stirring thrusts along the long sides of both molds interfere with each other to generate thrust vortices, and surface defects such as vertical cracks are likely to occur in the stagnation shell.

According to the present invention, in continuous casting of a metal slab such as steel, the molten metal in the mold is uniformly rotated in the meniscus plane, or a proper thrust distribution for braking or accelerating the reverse flow is imparted. In addition, even when the molten metal flow fluctuates continuously, the electromagnetic stirring thrust is continuously changed, and the problem caused by the vortex of the stirring thrust is solved to obtain a metal slab with excellent surface properties. To do.

[0009]

According to the method of the present invention, in continuous casting of a metal slab, an electromagnetic stirring coil is provided along two long sides of a mold in a meniscus plane while pouring a molten metal into a mold from an immersion nozzle. Is a method of controlling the flow of the molten metal in the meniscus plane by dividing the circuit connecting each coil of the two electromagnetic stirring coils and the power source into two, and dividing each circuit into a total of four divided circuits. Each of the two combinations is connected to a different power source, or each of the four circuits is connected to a different power source to control the electromagnetic stirring thrust by the coil of each circuit.

Further, in the continuous casting of metal slabs, the apparatus of the present invention, while pouring the molten metal into the mold from the dipping nozzle, uses a magnetic stirring coil provided along the two long sides of the mold in the meniscus plane to form the meniscus of the molten metal. A device for controlling in-plane flow, comprising: the two electromagnetic stirring coils, two or four power sources, a connection box that connects each electromagnetic stirring coil to each power source, and control of each power source condition. Each electromagnetic stirring coil is a moving magnetic field system in which a plurality of magnetic poles are arranged along the long side of the mold, and each magnetic pole has a coil wound around it. Each of the divided circuits is divided into two, and any two combinations of the divided four circuits are connected to different power sources, or the four circuits are different from each other. Characterized in that it is connected to the source.

[0011]

The present invention will be described with reference to the drawings. FIG. 1 is an explanatory view showing a cross section of continuous casting of a metal slab, which is a target of the present invention, as seen from a meniscus surface, and an example of wire connection of an electromagnetic stirring coil in the present invention example. A molten metal is injected from a dipping nozzle 2 provided at the center of the cross section of a mold 3 having a substantially rectangular cross section, and electromagnetic stirring coils 6 are provided along the two long sides 15a and 15b of the mold, respectively. The electromagnetic stirring thrust controls the flow of the molten metal within the meniscus surface 5.

The method of claim 1 and the apparatus of claim 3 of the present invention use two power supplies, a first power supply 8 and a second power supply 9, as illustrated in FIG. The circuit connecting each coil 19 of each of the two electromagnetic stirring coils 6 and each power source is divided into two, and a total of four divided circuits A, B, C,
Any two arbitrary combinations of D are respectively connected to different power supplies 8 and 9 to control the electromagnetic stirring thrust by the coils of each circuit. Specifically, the circuit A and the circuit C are used as the first power source 8, and the circuit B and the circuit D are
Connected to the second power supply 9, circuit A and circuit B to the first power supply 8, circuit C and circuit D
To the second power supply 9, circuit A and circuit D to the first power supply 8, circuit B and circuit C
Is connected to the second power supply 9, and there are three combinations. These three combinations may be appropriately selected during operation by switching the switch box 14, or may be set in advance without using the switch box 14.

The method of claim 2 and the apparatus of claim 4 of the present invention are, as illustrated in FIG. 2, four power sources, namely, a first power source 8, a second power source 9, a third power source 10 and a fourth power source 1.
Use 1. Each coil 19 of the two electromagnetic stirring coils 6
And the circuit connecting each power supply is respectively divided into two, and a total of four divided circuits A, B, C, D are connected to different power supplies 8, 9, 10, 11 respectively, and electromagnetic stirring is performed by the coils of each circuit. Thrust is controlled.

In the present invention, the control of the electromagnetic stirring thrust distribution is controlled by two power sources 8, 9 or four power sources 8, 9, 1 based on the observation result of the molten metal flow state on the meniscus surface 5.
It is performed by adjusting conditions such as frequency, phase difference and current of 0 and 11. The molten metal flow state may be observed by a person directly looking at the meniscus surface, or by a sensor 13 such as a television camera that outputs an image processing result. In addition, each circuit A,
The connection of B, C, and D is a circuit according to the purpose, such as one in which the coils 19 are connected in series, one in parallel, or one in which series and parallel are mixed. It may be fixed to a certain circuit during operation, or may be switched appropriately. Each power source 8, 9,
In addition to those shown in FIGS. 1 and 2, 10 and 11 can be configured as shown in FIG. In addition to such an inverter system, a cycloconverter system may be used.

According to the present invention as described above, the electromagnetic stirring thrust is controlled by using the two or four power sources by the divided four circuits A, B, C and D, so that the in-plane of the meniscus is controlled. Various forms of thrust distribution can be applied to the molten metal, and appropriate flow control can be performed according to the continuously changing state of continuous casting. FIG. 4 shows thrust distributions for various forms of electromagnetic stirring thrust by the conventional one power supply system, the two power supply system and the four power supply system of the present invention. The rectangle in the figure indicates the meniscus surface surrounded by the mold, the direction of the arrow indicates the direction of thrust, and the length of the arrow indicates the magnitude of thrust. Rotation has a rotating effect on the molten metal in the plane of the meniscus, braking has a braking effect on the reverse flow, acceleration has an acceleration effect on the reverse flow, and translation is one mold short side to the other mold short. It exerts a flow action toward the side. In FIG. 4, the impedances of the circuits A, B, C and D are the same, and the thrust pattern is changed by the connection of the circuits. In the conventional one power supply system, the magnitude of thrust by each circuit is the same, but when using the two power supplies of the present invention, the magnitude of the two sets of thrust can be arbitrarily changed by changing the current value of both power supplies. Can be changed. When the four power supplies of the present invention are used, the magnitude of thrust of each circuit can be changed for each circuit.

Therefore, even when the molten metal flow in the mold changes during the continuous casting operation due to the condition of the discharge port of the immersion nozzle, etc., the desired molten metal flow can be obtained by continuously controlling the flow according to the present invention. Obtainable. For example, when inclusions adhere to the discharge port of the immersion nozzle provided at the center of the cross section of the mold and the molten metal flow in the mold changes,
FIG. 5 shows a case where the molten metal is controlled so as to have a uniform rotating flow in the meniscus plane. (1) is a case in which the discharge ports of the immersion nozzle are clean with no deposits on the left and right, and the molten metal flow in the meniscus surface when electromagnetic stirring is not performed is a symmetrical reverse flow. In this case, in order to obtain a uniform rotating flow by electromagnetic stirring, the electromagnetic stirring thrust should be strengthened in the direction opposite to the reversing flow, that is, in the direction from the center of the mold to the short side of the mold. That is, it is weakened in the direction from the short side of the mold to the center of the mold. Such a thrust distribution is obtained by setting the current value supplied to each circuit to A = C <B = D in FIG. 1 or FIG. 2, and is achieved by the 2-power supply or 4-power supply system of the present invention. . (2) is a case where inclusions and the like adhere to one side of one of the discharge ports, and the molten metal flow without electromagnetic stirring is weakened on the side with the adhered substances, so that it is supplied to each circuit by the four-power supply method of the present invention. Current value,
By setting A <C <B <D, the thrust can be distributed as shown in the figure, and a uniform rotating flow can be obtained. (3) is a case where there is a deposit on both sides of one discharge port, and in this case also, the thrust is distributed as shown by setting A <C <B <D in the four power supply system of the present invention. , A uniform rotating flow can be obtained. (4) is the case where one discharge port is blocked by adherents, and the molten metal flow without electromagnetic stirring is a translational flow from one mold short side to the other mold short side, so electromagnetic stirring thrust is , The current value supplied to each circuit,
By setting A = B <C = D and distributing as shown in the figure, a uniform rotating flow can be obtained.
Achieved with a power system. The control for obtaining these thrust distributions is performed by observing the molten metal flow on the meniscus surface and appropriately changing the power supply conditions or connection. In the case of (2) and (3) in FIG. 5, although it is incomplete, it is possible to obtain a substantially uniform rotating flow even in the dual power supply system.

Next, when the thrusts of the opposing electromagnetic stirring coils interfere with each other to generate a swirl of the thrust, the position of the swirl can be changed by adjusting the phase difference of each power source according to the present invention. Therefore, nonmetallic inclusions in the molten metal do not accumulate in the stagnation portion between the vortices, and a slab without surface defects such as vertical cracks can be obtained. Further, even if a plurality of power supplies are used in the present invention, the total power supply capacity is the same as in the case of one power supply, and the total equipment cost is rather low.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 6, according to the device of the present invention, which uses two power supplies 8 and 9, circuits A and C are connected to a first power supply 8 and circuits B and D are connected to a second power supply 9, The molten steel was rotationally fluidized in the meniscus surface 5. Both the first power source 8 and the second power source 9 have a frequency of 1.8 Hz. First
When the current density I ₁ of the power source 8 is set to 8.319 × 10 ⁶ AT / m ² (peak value) and the current density I ₂ of the second power source 9 is changed, the electromagnetic stirring thrust distribution in the meniscus plane is expressed as Figure 7-
11 shows. Each of these figures has the same display as in FIG. 15, and α in the figure is I ₁ / I ₂ . Also in FIG.
7 to 11 show the components of the thrust force in the direction of the long side 15a of the mold in a ratio with the maximum thrust force being 1.0.

As can be seen from FIGS. 7 to 12, the electromagnetic stirring thrust distribution in the meniscus plane can be changed by changing the currents of the two power supplies. By observing the molten steel flow from above the meniscus surface and adjusting the value of α, a uniform rotating flow was given to the molten steel within the meniscus surface, and as a result, a steel slab without surface defects was obtained.

Next, in the device of the present invention shown in FIG. 6, the position of the thrust vortex in the meniscus plane is changed by changing the phase difference between the power supplies 8 and 9, and as a result, a slab having a more excellent surface texture is obtained. Was obtained.

Further, in the device of the present invention shown in FIG.
While observing the molten steel flow from the meniscus surface, each power source 8,
Adjust the current of 9, 10 and 11 and melt the molten steel to the meniscus surface 5
It was made to rotate and flow inside. One of the immersion nozzles 2 after casting was closed as shown in FIG. 5 (4), but a uniform rotating flow was always obtained during casting, and a slab having a good surface quality was obtained.

[0022]

According to the present invention, in the continuous casting of a metal slab such as steel, the molten metal in the mold can be uniformly rotated in the meniscus plane, or the reverse flow can be braked or accelerated. Even when the molten metal flow fluctuates continuously, the electromagnetic stirring thrust is continuously changed, and the problem caused by the vortex of the stirring thrust can be solved to obtain a metal slab having excellent surface properties. Besides,
Even if two or four power sources are used, the total power capacity does not change, and the facility cost is rather low.

[Brief description of drawings]

1 is an illustration of the method and apparatus of the present invention.

FIG. 2 is an explanatory diagram of the method and apparatus of the present invention.

FIG. 3 is an explanatory diagram of a power source used in the method and apparatus of the present invention.

FIG. 4 is an explanatory view of the operation of the present invention.

FIG. 5 is an explanatory view of the operation of the present invention.

FIG. 6 is a cross-sectional view and circuit diagram of a device according to the present invention.

FIG. 7 is an explanatory diagram showing a distribution of electromagnetic stirring thrust in the example of the present invention.

FIG. 8 is an explanatory diagram showing a distribution of electromagnetic stirring thrust in the example of the present invention.

FIG. 9 is an explanatory diagram showing the distribution of the electromagnetic stirring thrust in the example of the present invention.

FIG. 10 is an explanatory diagram showing a distribution of electromagnetic stirring thrust in the example of the present invention.

FIG. 11 is an explanatory diagram showing the distribution of the electromagnetic stirring thrust in the example of the present invention.

FIG. 12 is a graph showing the distribution of electromagnetic stirring thrust in the example of the present invention.

FIG. 13 is an explanatory diagram showing a situation inside a mold in conventional continuous casting.

14 is a view on arrow AA of FIG.

FIG. 15 is a cross-sectional view and a circuit diagram of a conventional device example.

FIG. 16 is an explanatory diagram showing the distribution of the electromagnetic stirring thrust according to the conventional device example.

[Explanation of symbols]

 1: Molten metal 2: Immersion nozzle 3: Mold 4: Solidification shell 5: Meniscus surface 6: Electromagnetic stirring coil 7: Wiring box 8: First power supply 9: Second power supply 10: Third power supply 11: Fourth power supply 12: Control Box 13: Sensor 14: Switch box 15: Mold long side 16: Mold short side 17: Magnetic pole 18: Slot 19: Coil

Claims (4)

[Claims] 1. In continuous casting of a metal slab, while pouring molten metal into a mold from a dipping nozzle, an electromagnetic stirring coil provided along two long sides of the meniscus surface causes the molten metal to flow in the meniscus surface. A method for controlling a flow, wherein a circuit connecting each coil of the two electromagnetic stirring coils to a power source is divided into two, and any two combinations of the divided four circuits are separately separated. The method for controlling the flow of molten metal in a mold in continuous casting, characterized in that the electromagnetic stirring thrust by the coil of each circuit is controlled by connecting to the power source of the above. 2. In continuous casting of a metal slab, while pouring the molten metal into a mold from a dipping nozzle, an electromagnetic stirring coil provided along two long sides of the meniscus surface causes the molten metal to flow in the meniscus surface. A method for controlling a flow, wherein a circuit connecting each coil of the two electromagnetic stirring coils to a power source is divided into two, and each of the divided four circuits is connected to a different power source, and each circuit is connected. A method for controlling the flow of molten metal in a mold in continuous casting, characterized in that the electromagnetic stirring thrust of the coil is controlled. 3. In continuous casting of a metal slab, while pouring molten metal into a mold from a dipping nozzle, an electromagnetic stirring coil provided along two long sides of the meniscus surface causes the molten metal to flow in the meniscus surface. A device for controlling flow, comprising: the two electromagnetic stirring coils, two power sources, a connection box that connects each electromagnetic stirring coil and each power source, and a control mechanism for each power source condition. The stirring coil is of a moving magnetic field type in which a plurality of magnetic poles are arranged along the long side of the mold, and each magnetic pole is wound with a coil, and the circuit constituted by the coil and the wiring of the connection box is divided into two parts. An apparatus for controlling the flow of molten metal in a mold in continuous casting, wherein any two combinations of the divided and divided four circuits are respectively connected to different power sources. 4. In continuous casting of a metal slab, while pouring the molten metal into a mold from a dipping nozzle, an electromagnetic stirring coil provided along two long sides of the meniscus surface causes the molten metal to flow in the meniscus surface. A device for controlling a flow, comprising the two electromagnetic stirring coils, four power supplies, a connection box connecting the respective electromagnetic stirring coils and the respective power supplies, and a control mechanism for each power supply condition. The stirring coil is of a moving magnetic field type in which a plurality of magnetic poles are arranged along the long side of the mold, and each magnetic pole is wound with a coil, and the circuit constituted by the coil and the wiring of the connection box is divided into two parts. And divided into 4 circuits,
A flow control device for molten metal in a mold in continuous casting, which is connected to different power sources.