JPH0994643A - Continuous casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily detach mold powder stuck to a mold without flawing on the mold by forming a magnetic field. SOLUTION: The mold 1 is constituted with one pair of long side mold walls 2 and one pair of short side mold walls 5. On the back surface sides of the long side mold walls 2, electromagnets 7 are arranged and coils 8 for the electromagnets 7 are connected with an electric supplying device 10. The electric supplying device 10 is energized to the coils 8 through a command from an operating disk 11. This electric supply energizes DC current having a prescribed current value through an energize starting command and the DC current with the current value till supplying a stopping command. Further, at the time of supplying the stopping command, the current value is gradually lowered while periodically changing the current direction and made to zero.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method for performing continuous casting while braking the flow of molten steel in a mold by electromagnetic force.

[0002]

2. Description of the Related Art An example of the structure of a device around a mold in continuous casting is shown in FIG. 5, for example. That is, the mold 1 is composed of a pair of long side molds 2 forming the long side surface and a pair of short side molds 5 forming the short side surface so that the mold 1 has a rectangular cross section. It is configured. A width changing device 6 composed of an actuator such as a cylinder for adjusting the slab width is attached to each of the short side molds 5, and the distance between the facing short side molds 5 can be changed. Has become. The mold 1 is water-cooled.

Molten steel 18 is supplied from the upper side of the mold 1 through the nozzle 12 into the mold 1. The supplied molten steel 18 is indirectly cooled by the water-cooled mold 1 to start solidification and solidify shell 1
It grows as 5, and moves downward. In addition, as shown in FIG. 6, the molten metal surface of the mold 1 is used for preventing oxidation and heat retention of the molten steel 18, lubrication for preventing baking between the solidified shell 15 and the mold 1, adsorption of non-metallic inclusions, and the like. Mold powder 17 having a role is supplied.

The molten metal 18 is melted on the molten metal 18 side by the heat of the molten powder 18, but on the atmosphere side is a powdery mold powder 17 covering the molten steel 18 surface. Further, the mold powder 17 in the molten state
Also flows between the solidified shell 15 and the mold 1 and plays a role of a lubricant. Therefore, since the molten mold powder is consumed, the mold powder 17 is appropriately replenished.

Here, since the discharge port 12a provided at the tip of the nozzle 12 is open facing the short side direction of the mold 1, the molten steel 18 supplied into the mold 1 from the nozzle 12 is discharged. The flow has a V shape in the short side direction of the mold 1 and is directed to the short side mold 5, and as a result, is divided into an upward flow and a downward flow. At this time, some non-metallic inclusions and bubbles 16 are mixed in the molten steel 18, and the inclusions 1
Part of the material 6 is floated on the way while entering the lower side of the mold 1 by the downward flow, but part of the material 6 is captured by the solidified shell 15. This trapping occurs as the molten steel 18 supplied from the nozzle 12 flows faster. Then, the inclusions 16 captured by the solidified shell 15 may become surface defects in the rolling line in the lower step.

In order to prevent this, the casting speed is reduced to prevent the solidified shell 15 from growing, and inclusions and bubbles 16 are formed.
There is also a method of promoting the floating of the steel, but in this method, since the casting speed is decreased, high productivity cannot be expected. Particularly, in recent continuous casting, inclusions and bubbles 16 caused by molten steel flow in the mold 1 are easily trapped at the solidification interface in order to speed up casting.

As one of the methods for preventing defects due to non-metallic inclusions as described above, in the conventional continuous casting method,
For example, JP 61-129261 A and JP 1-2
As described in Japanese Patent No. 66949 etc., a magnetic field is applied to the molten steel 18 in the mold 1 to decelerate the flow of the molten steel 18 discharged from the nozzle 12, thereby causing inclusions and bubbles 16 downward in the mold 1. Of the inclusions and the inclusions are prevented from being trapped in the solidified shell 15.

As shown in FIG. 5, a pair of direct current electromagnets 7 are arranged so as to sandwich the long side mold 2 so that a direct current is supplied to a coil 8 of the electromagnet 7 to discharge a nozzle 12 A magnetic field is formed in the mold 1 near 12a. Then, the molten steel flow discharged from the nozzle 12 is braked by the action of the magnetic field. Next, the principle of braking the molten steel flow discharged from the nozzle 12 will be described with reference to FIG. The molten steel 18 exiting from the nozzle 12 interlinks with the velocity V _IN as a conductor in the region where the magnetic field is acting. At this time, the induced current i flows upward in the plane of the drawing according to Fleming's right-hand rule. Due to the induced current i and the magnetic flux density B in the magnetic field, a force (braking force) F opposite to the flow velocity V _IN is generated in the molten steel 18. As a result, the flow velocity of the molten steel 18 is reduced to the velocity V _OUT .

By adopting the method as described above, the floating of inclusions and bubbles 16 is promoted even if the casting speed is high, and it becomes possible to obtain a slab of good quality. Then, in the conventional case, as shown in FIG. 8, when a predetermined direct current is applied to the coil 8 of the electromagnet 7 at the start of the operation for braking the flow of the molten steel 18, the width of the slab is changed. When the braking is no longer required, the energization of the DC current is stopped.

On the other hand, when the width of the slab is changed, the short side mold 5 is moved to change the width of the slab. However, in order to stop the flow of the molten steel 18 as described above, once the long side is moved. When a magnetic field is applied to the core 9, the iron core 9 of the electromagnet 7 and the mold powder 17, which is a magnetic material, are magnetized, so that residual magnetism remains in the core 9 and the mold powder 17 even if the magnetic field disappears. Therefore, even if the formation of the magnetic field by the electromagnet 7 is stopped in order to change the slab width, the residual powder magnetism causes the mold powder 17 on the surface of the mold 2 on the long side of the mold 1.
Is attached.

The reason why the remanence is generated will now be described. As shown in FIG. 4, the iron core 9 is magnetized by the magnetizing force H of the magnetic field generated by energizing the electromagnet 7.
The mold powder 17 is magnetized along the path of oab in FIG. 4 and has a magnetic flux density Bm. From this state, when the energization is stopped, the magnetization curve changes along the path bc in FIG. 4, and the residual magnetism of Br remains in the iron core 9 and the mold powder 17 even if the magnetizing force H becomes zero. Is. The residual magnetism remains even if the magnetizing force H becomes zero because of the coercive force of the iron core 9 and the like.

When the mold powder 17 is attached to the long side mold 2 as described above, the short side mold 5 is moved so that the short side molds 5 are relatively close to each other. The end surface of the short-side mold 5 rubs the mold powder 17 attached to the long-side mold 2, and the surfaces of the short-side mold 5 and the long-side mold 2 are scratched to reduce the life of the mold 1. There is a problem to let. Alternatively, when the short side mold 5 is moved, a mold powder 17 is formed between the short side mold 5 and the long side mold 2.
There is a case where the short side mold 5 cannot be moved due to the insertion of the mold.

In order to prevent this, conventionally, an operator uses an aluminum rod to remove the mold powder 17 adhering to the long side mold 2.

[0014]

However, even if the operator tries to peel off the mold powder 17 adhering to the long side mold 2 using the aluminum rod as described above, the mold powder 17 and the iron core are removed. The amount peeled off by the attraction force due to the residual magnetism with 9 is very small,
If it is attempted to peel it off forcibly, there is a problem that the surface of the long-side mold 2 may be scratched when it is rubbed with a stick.

The present invention has been made by paying attention to the above problems, and an object thereof is to easily separate the mold powder adhered to the mold by forming a magnetic field without causing a scratch on the mold. I am trying.

[0016]

In order to achieve the above object, in the continuous casting method of the present invention, a current is supplied to a coil of an electromagnet arranged on the outer periphery of the mold to provide a predetermined magnetic field in the mold. In the continuous casting method in which the continuous casting is performed while applying the braking to the molten steel, the current to the coil is set to zero in order to release the braking to the molten steel, the current is alternately changed while changing the direction of the current. The feature is that the magnitude of is gradually reduced to zero.

In this continuous casting method, a magnetic field for damping the flow of molten steel is formed in the mold so that the magnetic field is not required even if the mold powder in the mold or the iron core of the electromagnet is magnetized. When the current to the coil is set to zero in order to release the braking, the magnitude of the current is gradually reduced by alternately changing the direction of the current, and the hysteresis loop of the residual magnetism of the mold powder and the iron core As the current becomes zero, the residual magnetism of the iron core and the mold powder becomes zero.

That is, when the direction of the current is alternately changed without changing the magnitude of the current, the residual magnetism of the iron core or the like draws a hysteresis loop that draws the path of bcdefb as shown in FIG. Then, by gradually reducing the magnitude of the current, the hysteresis loop is gradually reduced, and the residual magnetism becomes zero when the current becomes zero.

As described above, in the present invention, when the magnetic field is extinguished by stopping the energization of the coil in order to change the slab width and the like, the residual magnetism of the iron core of the electromagnet and the mold powder becomes zero and adheres to the mold. The mold powder that has been used falls naturally without being magnetically attached to the mold surface.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the mold 1 of the present embodiment includes a pair of long side molds 2 and a pair of short side molds 5.
It is composed of The pair of long side molds 2 are arranged laterally opposite to each other with a predetermined space therebetween. Each of the long-side molds 2 is composed of a mold body 3 made of a copper plate or the like constituting the mold surface, and a holding plate 4 attached to the back surface of the mold body 3. A plurality of vertically extending cooling passages 3a are formed on the back surface side of the mold body 3, and cooling water is supplied from the lower side to the upper side of the cooling passages 3a, respectively. The body 3 is designed to be cooled.

The pair of short side molds 5 are arranged so as to face each other at a predetermined interval, and are arranged between the long side molds 2 in a state of being oriented in a direction orthogonal to the long side molds 2. To be done. Thereby, the long side mold 2 and the short side mold 5 are
And form a mold space having a rectangular cross section.
Further, each of the short side molds 5 can be moved in the thickness direction by a width changing device 6, and the distance between the pair of short side molds 5 can be changed. In the present embodiment, the width changing device 6 is composed of a cylinder device.

Electromagnets 7 are arranged on the back side of the long side mold 2, and a coil 8 of the electromagnet 7 is arranged.
Is connected to the current supply device 10. Although FIG. 1 illustrates the state in which the current supply device 10 is connected to only one coil 8, other coils 8 are also connected to the current supply device 10. The current supply device 10 can energize the coil 8 according to a command from the operation panel 11.

The power is supplied to the operation panel 1 as shown in FIG.
According to the energization start command P1 from 1, a DC current of a predetermined current value, for example, 500 amperes is energized, and the DC current is energized with the above current value until the stop designation P2 is supplied. Further, when the stop designation P2 is supplied from the operation panel 11 to release the braking to the molten steel, the current value is gradually reduced while the direction of the current is periodically changed so that the current value is controlled to zero. It is set. In the present embodiment, for example, the magnitude of the current is controlled so as to be zero from about 100 amperes to about 3 cycles.

In the center of the mold 1, a molten steel supply nozzle 12 whose axis is oriented vertically is arranged from the upper side, and a discharge port 12a provided at the lower end of the nozzle 12 has a short side of the mold 1. Facing the direction. Here, as shown in FIG. 2, the electromagnet 7 is set so as to form a magnetic field at a position 19 in the vicinity of the discharge port 12a of the nozzle 12 in the mold 1 by being supplied with a direct current as in the conventional case. The flow of the molten steel is damped by the electromagnetic force of the magnetic field.

Next, the operation and the like of the above construction will be described with reference to FIGS. At the time of casting, the current supply device 10
When the energization start command P1 is supplied to the current supply device 1
0 energizes the coil 8 of the electromagnet 7 with a direct current until the stop designation P2 is supplied. As a result, the electromagnet 7 forms a predetermined magnetic field in the mold 1. In that state, the molten steel is supplied from the molten steel supply nozzle 12 into the mold 1, and continuous casting is performed.

At this time, as in the conventional case, the magnetic field damps the flow velocity of the molten steel discharged from the nozzle 12, whereby inclusions and bubbles 16 trapped in the solidification shell 15 are generated.
Can be reduced and a good slab can be obtained. In this state, the electromagnet 7 has a magnetic flux density corresponding to the magnetic field.
The iron core 9 and the mold powder 17 are magnetized.

In order to change the slab width from this state,
That is, in order to release the braking on the molten steel, the operation panel 11
When the stop designation P2 is supplied to the current supply device 10 by operating, the current supply device 10 gradually reduces the current passing through the coil 8 to zero while changing its direction periodically. As a result, a gradually decreasing magnetizing force acts on the iron core 9 and the mold powder 17 in an alternating manner, and the hysteresis loop of the residual magnetism of the iron core 9 and the like gradually decreases, and when the current becomes zero, The residual magnetism of the iron core 9 and the like becomes zero.

Then, the mold powder 17 adhering to the surface of the mold 1, particularly the surface of the long side mold 2, falls freely by its own weight without being magnetically attached to the surface of the mold 1. As a result, the mold powder 17 does not adhere to the surface of the mold 1 or only a small amount of the mold powder 17 adheres. Even if the amount of the mold powder 17 attached to the mold 1 is large, there is no attraction force due to the residual magnetism, and therefore the attached mold powder 17 can be easily peeled off without damaging the surface of the mold 1. .

When the energization of the coil 8 of the electromagnet 7 is stopped as described above, the width changing device 6 is operated to change the positions of the pair of short side molds 5, and the space between the pair of short side molds 5 is changed. Change the distance. At this time, since the mold powder 17 does not adhere to the surface of the long side mold 2, the mold powder 17 adhered to the surface of the long side mold 2 causes scratch marks on the surfaces of the short side mold 5 and the long side mold 2. Attaching is avoided. Therefore, the life of the mold 1 is improved.

In the above embodiment, an example in which the energization of the coil 8 is stopped to change the slab width has been described, but the present invention is not limited to this. For example, even when the continuous casting operation is stopped, the energization of the coil 8 is controlled as described above to form the mold powder 1 on the surface of the mold 1.
7 may not be attached. This facilitates the cleaning work of the mold 1.

Further, in the above-mentioned embodiment, the current to the coil 8 is attenuated while being changed cyclically, but it is controlled so as to reduce the magnitude of the current while changing the direction of the current aperiodically. May be.

[0032]

[Example] The width of the long side mold 2 of the mold 1 is 1500 m
Continuous casting using a continuous casting machine in which the width of the short side mold 5 is 300 mm and the length of the coil 8 is 800 mm and the pole tip area of the iron core 9 is 150 mm × 150 mm. The coil 8 is supplied with a direct current of 500 amperes during continuous casting for braking molten steel, and when the energization is stopped, the current is supplied to the coil 8 from 100 amperes in three cycles so that the magnitude of the current becomes zero. It attenuated while changing the direction of the current periodically.

As a result of controlling the energization at the time of stopping the current as described above, the residual magnetism of the mold powder 17 and the iron core 9 becomes zero and remains in the long side mold 2 and the short side mold 5 when the width of the mold 1 is changed. It was confirmed that oyster flaws due to the powder were not formed.

[0034]

As described above, in the continuous casting method of the present invention, when braking the molten steel becomes unnecessary and the current supply to the coil of the electromagnet is stopped, the current direction is alternately changed. By attenuating, the residual magnetism of the electromagnet's iron core and mold powder is erased, so the mold powder adhering to the mold surface spontaneously falls, and There is an effect that the peeling work is unnecessary or reduced.

This is especially true when changing the width of the mold.
It is possible to avoid the formation of scratches on the surface of the mold due to the mold powder remaining on the surface of the mold, and to extend the life of the mold.

[Brief description of drawings]

FIG. 1 is a plan view showing a device configuration around a mold of a continuous casting machine according to an embodiment of the present invention.

FIG. 2 is a side sectional view showing a device configuration around a mold of the continuous casting machine according to the embodiment of the present invention.

FIG. 3 is a diagram showing a transition of energization of a coil of the electromagnet according to the exemplary embodiment of the present invention.

FIG. 4 is a diagram showing a hysteresis loop of residual magnetism.

FIG. 5 is a plan view showing a device configuration around a mold according to a conventional continuous casting machine.

FIG. 6 is a side sectional view showing a device configuration around a mold according to a conventional continuous casting machine.

FIG. 7 is a diagram for explaining deceleration of the flow of molten steel by a magnetic field.

FIG. 8 is a diagram showing a transition of energization of a coil of an electromagnet according to a conventional continuous casting machine.

[Explanation of symbols]

 1 Mold 2 Long Side Mold 5 Short Side Mold 6 Width Change Device 7 Electromagnet 8 Coil 9 Iron Core 10 Current Supply Device 15 Solidification Shell 16 Inclusions and Bubbles 17 Mold Powder 18 Molten Steel

Claims (1)

[Claims] 1. A continuous casting method for continuously casting while supplying a current to a coil of an electromagnet arranged on the outer periphery of a mold to form a predetermined magnetic field in the mold and braking the molten steel, and braking the molten steel. The continuous casting method is characterized in that, when the current to the coil is set to zero in order to cancel, the magnitude of the current is gradually reduced to zero while alternately changing the direction of the current.