JPH06134561A - Method for supplying molten steel into mold in slab continuous casting - Google Patents

Abstract

PURPOSE:To balance molten steel quantities poured from immersion nozzles by arranging the immersion nozzles symmetrically to the center axis of a mold, controlling each sliding nozzle and adjusting the molten steel supplying quantity of the immersion nozzle discharged toward the short side in a cast slab from the discharging hole at the lower end part of the immersion nozzle. CONSTITUTION:This method for supplying the molten steel into the mold 4 in a slab continuous casting is one which the molten steel in a tundish 1 is poured into the mold 4 from the discharging holes 8 of the immersion nozzles 3 while controlling the sliding nozzles 2. Two pieces of the immersion nozzles 3 providing the discharging hole 8 on the one side surface to flow toward the short side direction in symmetric with respect to the center axis of the mold 4 are arranged, and while controlling the sliding nozzle 2 arranged in each immersion nozzle 3, the molten steel supplying quantity discharged in the short side direction of the mold from the discharging hole is independently adjusted to prevent the molten steel drift flow. By this method, the molten steel drift flow can easily be restrained and as a result, the internal defect and the surface defect in a steel plate rolled from this slab are reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten steel for casting in a slab continuous casting suitable for preventing drift of molten steel injected from a dipping nozzle into a casting mold while controlling a sliding nozzle attached to a tundish. It relates to the supply method.

[0002]

2. Description of the Related Art Conventionally, molten steel is poured from a tundish into a mold in continuous casting, as shown in FIG. 5, the tip of a dipping nozzle 30 located below a sliding nozzle 2 provided at the bottom of a tundish 1 is used as a mold. It is performed while being immersed in the molten steel 5 of No. 4 in FIG. An upper nozzle 6 is provided in the tundish 1, and a sliding nozzle composed of a three-layer plate including a fixed plate 2a, a slide plate 2b, and a lower plate 2c each having an opening with the same inner diameter at a lower portion of the upper nozzle 6. 2 is attached to the slide plate 2 between the fixed plate 2a and the lower plate 2c.
b is slid using the hydraulic cylinder 7 to control the aperture restriction position to control the molten steel flow rate from within the tundish 1.

An immersion nozzle 30 connected to the lower part of the sliding nozzle 2 is arranged at the center of the slab continuous casting mold 4 having short sides and long sides, and the molten steel in the tundish 1 is opened by the sliding nozzle 2. It is made to flow down through the immersion nozzle 30 while controlling the hole throttle position, and is injected into the continuous casting mold 4 from the left and right discharge holes 8. Molten steel 5 injected from discharge hole 8
After colliding with the solidified shell 9 on the short side, it is divided into an upflow and a downflow, but in a steady state, the amount of molten steel injected from the left and right discharge holes 8 is equal, so the upflow and the downflow are As a result of being decelerated while flowing, troubles due to upflow and downflow do not occur.

As described above, in continuous casting, the molten steel injection amount from the tundish 1 into the continuous casting mold 4 is controlled by the sliding nozzle 2, but the immersion nozzle 3 is used.
The flow rate of the molten steel 5 injected into the continuous casting mold 4 from the pair of left and right discharge holes 8 provided in the lower part of the right and left may be different from each other on the left and right, and uneven molten steel flow may occur. One of the causes of such molten steel drift is that when the immersion nozzle 30 is used as shown in FIG. 3, the deoxidation product such as alumina present in the molten steel is caused by the inner hole 14 of the immersion nozzle 30. Deposits on the inner surface of the discharge hole 8
10, the discharge hole refractory is melted by the molten steel flow, and the shapes of the left and right discharge holes 8 become uneven. as a result,
This is because the passage cross-sectional area of the discharge hole 8 becomes large and small, and the injection amount into the continuous casting mold 4 becomes large when the passage cross-sectional area is large and becomes small when it is small.

Another cause of drift of molten steel is that it is usually injected with the opening of the sliding nozzle 2 narrowed in order to control the injection amount of molten steel as shown in FIG. Main flow of molten steel flowing down through the immersion nozzle 3 11
Does not pass through the center of the inner hole 14 and is biased to either left or right. This is because the amount of molten steel injected from the pair of left and right discharge holes 8 into the continuous casting mold 4 under the influence of this is large in one and small in the other.

As shown in FIG. 3, the discharge hole 8 of the immersion nozzle 30.
If the deposit 10 such as alumina adheres to the molten steel, it impedes the injection of the molten steel, so in order to ensure the required amount of molten steel, for example, when the sliding nozzle 2 is fully opened, the molten steel main flow that flows down in the immersion nozzle 30 is used. 11 is located in the center of the inner hole 14. At this time, if there are no deposits such as alumina, the amount of molten steel injected from the left and right discharge holes 8 will be uniform, but
If the deposits 10 formed inside are different on the left and right, the cross-sectional area of the passage becomes uneven on the left and right. That is, when the amount of the deposit 10 on the right side is small and the amount of the deposit 10 on the left side is large, the molten steel passage cross-sectional area of the discharge hole 8 is large on the right side and small on the left side. For this reason, the equal relationship of the amount of molten steel injected from the left and right discharge holes 8 is broken, so that the right side is large and the left side is small, and so-called molten steel drift occurs.

On the right side where the amount of molten steel injected from the discharge hole 8 of the dipping nozzle 30 is large, the collision force against the solidified shell 9 formed in the short side 4a is large, and the molten steel moves upward along the inner surface of the solidified shell 9 and The flow will be split down vigorously. In this way, the strong upward flow causes rise of the molten metal surface 12 and prevents the flux 13 on the molten metal surface from being supplied between the inner wall surface of the mold 4 and the solidification shell 9, resulting in insufficient supply. The formation of the solidified shell 9 becomes non-uniform and causes not only wrinkles and cracks in the cast slab but also non-metallic inclusion physical defects in the slab by entraining the flux 13. Further, the rightward descending flow, which has a strong influence, reaches deep into the molten steel 5 and hinders the floating of the non-metallic inclusions, and is trapped by the solidified shell 9 and causes defects in the non-metallic inclusions of the slab.

On the other hand, on the left side where the amount of molten steel injected from the discharge hole 8 is small, the impact force on the solidified shell 9 formed in the short side 4a is small, and the molten steel is moved upward and downward along the inner surface of the solidified shell 9. The shunting power is weak. For this reason, the trouble as shown on the right side does not occur, but since the molten steel flow rate is small, stagnation is likely to occur in the molten steel flow in the discharge hole 8 and nozzle clogging is likely to occur due to adhesion of alumina etc. Not only is it difficult to impair the productivity, but also the refractory cost increases due to the replacement of the immersion nozzle.

In this way, once the uneven flow occurs, it is difficult to eliminate it, and when the uneven flow becomes severe, operational trouble such as breakout due to remelting of the solidified shell 9 formed in the mold 4 is caused. In addition, slab surface defects are likely to occur due to fluctuations in the molten metal level in the mold 4, and in the worst case, casting must be stopped. As described above, when the difference in the amount of molten steel discharged from the left and right discharge holes 8 is caused by the uneven flow generated in the immersion nozzle 3, not only the operation of the continuous casting mold is hindered but also the quality of the cast piece is deteriorated, which is not preferable. .

Therefore, in order to suppress the uneven flow of molten steel from the discharge holes of the immersion nozzle into the continuous casting mold, uneven distribution of molten steel is disclosed in JP-A-62-197258. It is disclosed that the difference is detected by using a level gauge and the casting speed is controlled to be low so as to suppress the level difference due to the molten steel swelling, thereby eliminating the drift. However, if the casting speed is slowed down, the adherence of alumina is likely to occur due to the stagnation of the molten steel flow in the discharge holes 8 of the immersion nozzle, and there is a risk of promoting molten steel uneven flow, and it is difficult to reliably prevent uneven flow. .

Further, as shown in FIG. 6, the molten steel discharged from the discharge hole of the immersion nozzle 30 is electromagnetically stirred by using an electromagnetic stirrer 31 installed on the back surface of the long side of the mold 4, or FIG.
Install the electromagnetic brake device 32 as shown in
It is known that an electromagnetic brake is applied to the molten steel flow discharged from the 30 discharge holes 8 to reduce the flow velocity. However, the device provided with the electromagnetic stirrer 31 or the electromagnetic brake device 32 can reduce the molten steel drift, but is not sufficient, and has a weak point that it cannot essentially prevent the molten steel drift.

In Japanese Patent Laid-Open No. 63-33171, a bar-shaped core material extending along the molten steel passage of the immersion nozzle is provided, and in Japanese Patent Laid-Open No. 63-295056, the center of the molten steel flow path of the immersion nozzle is provided. It is disclosed that a plate-shaped member that passes through and is parallel to the sliding direction of the sliding nozzle is provided. However, even if the rod-shaped core material or the plate-shaped member is provided in the molten steel passage of the immersion nozzle, there is a deviation of the molten steel that falls due to the adjustment of the opening of the sliding nozzle. It is difficult to sufficiently prevent the molten steel drift that is caused. Should a nonuniform flow occur, the rod-shaped core material or plate-shaped member present in the molten steel flow channel becomes an alumina adhering medium, and the adhering matter grows to promote the nonuniform flow, so that there is a great danger of having an adverse effect.

[0013]

DISCLOSURE OF THE INVENTION The present invention solves the problems of the prior art described above, and the immersion is performed without adjusting large-scale equipment simply by adjusting the aperture throttle position of the sliding nozzle provided in the lower part of the tundish. It is an object of the present invention to provide a method for supplying molten steel to a mold in continuous slab casting, which can balance the amount of molten steel injected from a discharge hole of a nozzle.

[0014]

Means for Solving the Problems The present invention for achieving the above-mentioned object is to provide a casting mold in slab continuous casting in which molten steel in a tundish is injected into a casting mold from a discharge hole of a dipping nozzle while controlling a sliding nozzle. In the molten steel supply method, two immersion nozzles each having a discharge hole on one side that flows symmetrically with respect to the center axis of the mold and flows out in the short side direction are arranged.
While controlling the sliding nozzles installed in each dipping nozzle, the amount of molten steel discharged from each discharge hole in the short side direction of the mold is adjusted independently to prevent molten steel drift in the mold. It is a method of supplying molten steel to a mold in casting.

[0015]

As described above, according to the present invention, two immersion nozzles each having a discharge hole on one side that flows out in the short side direction symmetrically with respect to the center axis of the mold are arranged, and each immersion nozzle is arranged. Since the molten steel supply amount to each discharge hole is adjusted independently while controlling the opening of the sliding nozzle, it is possible to easily prevent the molten steel drift from being discharged into the mold from the discharge holes of the two immersion nozzles.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an apparatus for supplying molten steel to a continuous slab mold 4 according to an embodiment of the present invention. The tundish 1 is lined with a refractory material and the outside is covered with an iron skin, and the tundish 1 has a ladle. Molten steel (not shown) is injected from here. Two injection nozzles 6 are arranged in close proximity to the bottom of the tundish 1, and are connected below the two injection nozzles 6, respectively, with a fixed plate 2a, a slide plate 2b, and a lower plate 2c. A configured sliding nozzle 2 is installed.

To each sliding nozzle 2, two immersion nozzles 3 each having a discharge hole 8 on one side are connected and supported. In the steady state, the lower part of the immersion nozzle 3 is immersed in the molten steel 5 in the mold 4, and the discharge holes 8 of the two immersion nozzles 3 face the short side of the mold 4. Mold 4
The inner molten metal surface is covered with the flux 13 to prevent the molten steel in the mold 4 from being oxidized and to improve the lubricity between the mold 4 and the solidified shell 9.

Next, the operation of the embodiment of the present invention will be described. Molten steel is poured into a tundish 1 from a ladle (not shown), and the molten steel is connected to two upper nozzles 6 provided near the bottom of the tundish 1, two sliding nozzles 2 and two Mold 4 through immersion nozzle 3
Inject. Then, the slide plate 2b of each sliding nozzle 2 is slid to adjust the opening area to independently control the molten steel supply amount.

In this way, the molten steel 5 supplied from the two upper nozzles 6 arranged at the bottom of the tundish 1 is independently adjusted by using the respective sliding nozzles 2, so that the two immersions are performed. Using the inner hole 14 of the nozzle 3 as a flow path, the molten steel discharge flow discharged from the discharge hole 8 into the mold 4 is made uniform on the left and right sides, thereby preventing molten steel drift. The molten steel 5 injected from the discharge holes 8 collides with the solidified shell 9 on the short side and is then divided into an upflow and a downflow, but the amount of molten steel injected from the left and right discharge holes 8 is equal. As a result of the upflow and the downflow being decelerated while flowing, troubles such as the entrainment of the flux 13 due to the upflow and the downflow and the trapping of non-metallic inclusions in the solidified shell 9 can be suppressed.

The discharge hole 8 of the immersion nozzle 3 is placed in the mold 4.
The drift of molten steel discharged from the mold is detected by a thermocouple (not shown) embedded in the short sides 4a on the left and right of the mold 4, or a swirl flow type is provided between the immersion nozzle 3 and the mold short sides 4a on both sides thereof. A level gauge 17 is provided, the deviation of each level value measured by both level gauges 17 is calculated, the ridge on the molten steel surface is detected, and the openings of the two sliding nozzles 2 are controlled so as to suppress this ridge. By controlling independently, it is possible to prevent drift of molten steel discharged from the discharge holes 8 of the two immersion nozzles 3. The means for detecting molten steel drift is not limited to the above.

Using the apparatus of the present invention, ultra-low carbon molten steel for bicycle outer plates was continuously cast by a curved slab continuous casting machine having a radius of curvature of 12 m by the above-mentioned procedure to form a slab having a slab thickness of 220 mm and a slab width of 1300 mm. According to the present invention, it was possible to easily eliminate the molten steel drift that is discharged into the mold from the discharge hole of the immersion nozzle. As a result, as shown in FIGS. 8 (a) and 8 (b), as compared with the conventional method, the blistering defect index and the surface defect index other than blistering of the ultra-low carbon cold-rolled steel sheet for bicycle outer plates were determined by the casting speed. Irrespective of the fact that the defect index can be significantly reduced, and a remarkable effect is obtained in reducing the defect index, especially at a high casting speed.

[0022]

As described above, according to the present invention, 2
Since the amount of molten steel supplied to each discharge hole is independently controlled by separate sliding nozzles connected to the flow paths of the immersion nozzle, the discharge holes are provided on one side of the lower end of the immersion nozzle and discharged into the mold. The molten steel drift can be easily suppressed. As a result, reduction of internal defects and surface defects of the steel sheet rolled from the slab can be achieved.

[Brief description of drawings]

1 is a side sectional view of an apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the casting speed, the blistering defect index, and the surface buffing index other than blistering in the present invention and the conventional case.

FIG. 3 is a side cross-sectional view of a conventional example showing a molten steel pouring state when deposits are present in the immersion nozzle discharge hole and the sliding nozzle is fully opened.

FIG. 4 is a side cross-sectional view of a conventional example showing a state of injection of molten steel by an aperture stop of a sliding nozzle without deposits in a discharge hole of a dipping nozzle.

FIG. 5 is a side sectional view of a conventional example showing a molten steel injection state from a sliding nozzle in a steady state.

FIG. 6 is a side sectional view of a conventional example in which an electromagnetic stirrer is installed on the back of the long side of the mold.

FIG. 7 is a side sectional view of a conventional example in which a long-side back electromagnetic brake device of a mold is installed.

[Explanation of symbols]

 1 Tundish 2 Sliding Nozzle 3 Immersion Nozzle (Invention) 4 Continuous Casting Mold 5 Molten Steel 6 Upper Nozzle 7 Hydraulic Cylinder 8 Discharge Hole 9 Solidification Shell 10 Adhered Material 11 Main Molten Steel Rise 13 Flux 14 Inner Hole 15 Eddy Current Type Level meter 30 Immersion nozzle (conventional) 31 Electromagnetic stirrer 32 Electromagnetic brake device

Claims (1)

[Claims] 1. A method for supplying molten steel to a mold in slab continuous casting in which molten steel in a tundish is injected into a mold from a discharge hole of a dipping nozzle while controlling a sliding nozzle. Two immersion nozzles with discharge holes on one side that flow out in the short side direction are arranged, and the amount of molten steel discharged from each discharge hole in the short side direction of the mold while controlling the sliding nozzles installed in each immersion nozzle. A method for supplying molten steel to a mold in continuous casting of slabs, characterized in that the uneven flow of molten steel in the mold is prevented by adjusting the above.