KR20100078815A - Stopper and stopper assembly - Google Patents

Abstract

PURPOSE: A stopper and a stopper assembly are provided to prevent inclusion from being attached to the inner wall of the submerged nozzle and a stopper head unit and the side of the stopper head by reducing pressure around the stopper head unit. CONSTITUTION: A stopper(200) comprises the molten steel outlet of a tundish(100) and includes an inner hollow(210). The stopper is extended in the longitudinal direction, wherein a head unit larger than the size of a molten steel outlet is formed at the end of the stopper. Multi-stage argon outlets are vertically formed on the head unit. The multi-stage argon outlets are formed to cross each other. The stopper assembly comprises a stopper and a bubble activator(120). The bubble activator surrounds the molten steel outlet and is projected upward.

Description

Stopper and stopper assembly

The present invention relates to a stopper and a stopper assembly, and more particularly, to supply argon bubbles continuously and uniformly to the stopper head to minimize the attachment of alumina inclusions or other foreign substances to the stopper head and the inner wall of the immersion nozzle. Relates to a stopper and a stopper assembly.

In general, the tundish used in the continuous casting device serves to discharge the molten steel into the mold through the molten steel outlet formed in the bottom and the immersion nozzle connected to the molten steel outlet.

As shown in FIG. 1, the molten steel is supplied from the tundish 10 to the mold through the immersion nozzle 11, and the flow rate of the molten steel supplied through the immersion nozzle is increased in the up and down motion of the stopper 20a. Are controlled accordingly. At this time, the head portion 25a is formed at the end of the stopper.

In aluminum deoxidized steel, which uses aluminum as a deoxidizer to remove oxygen in molten steel during continuous casting of steel, alumina inclusions of several μm to several tens of μm remain in the molten steel, which acts as a factor to deteriorate product quality. The alumina inclusions are attached to the head of the stopper and the inner wall of the immersion nozzle during continuous casting to reduce the effective cross-sectional area of the molten steel to increase the opening degree of the stopper, thereby preventing the normal casting operation. .

In addition, the cumulatively produced alumina inclusions are separated from the inner wall of the head portion of the stopper and the immersion nozzle and mixed into the mold, which adversely affects the quality of the cast steel. When molten steel with a large flow rate flows into the mold instantaneously while the coarse alumina inclusions are separated, a large fluctuation occurs in the mold bath surface, and slag is mixed into the molten steel.

In addition, if the alumina inclusions are unevenly attached to the head portion of the stopper, the occurrence of drift is promoted. The molten steel drift causes an asymmetric flow of molten steel in the discharge hole symmetrically formed under the immersion nozzle, which adversely affects the quality of the cast steel.

Therefore, in recent years, a stopper has been developed to solve the problem that the above-described alumina inclusions adhere to the head of the stopper or the inner wall of the immersion nozzle and grow. This will be described with reference to FIGS. 2 and 3.

The stopper 20b shown in FIG. 2 has an inner cavity 21 through which argon is introduced, and a porous body 22 having porous pores formed therein at the lower end of the head. When argon is injected through the stopper inner hole, argon bubbles are discharged to the outside of the stopper through the porous body 22 having porous pores formed at the bottom of the stopper head part 25b, and soaked with the head part 25b of the stopper. Inclusions may be prevented from being attached to the inner wall of the nozzle (11 'in FIG. 1).

However, the stopper 20b having a porous body having porous pores as described above can prevent the inclusions from adhering to the inner wall of the immersion nozzle, but because the argon bubble is discharged only to the lower end of the stopper, the stopper head part Inclusion of inclusions on the side surface cannot be prevented. Thus, inclusions are partially attached to the head portion of the stopper, and the flow of the argon bubble is unstable as the flow of molten steel is formed abnormally due to the inclusions.

The stopper 20c illustrated in FIG. 3 is to solve the problem of the stopper illustrated in FIG. 2, and an inner cavity 21 through which argon is introduced is formed therein, and at least one argon outlet on the side of the head. 23 is formed. The stopper 20c may have one or more argon outlets on the side of the stopper head to prevent the inclusions from being attached to the head portion 25c of the stopper and the inner wall of the immersion nozzle ('11' in FIG. 1). As described above, the stopper 20c having the argon outlet on the side of the stopper head has an argon bubble uniformly formed when the flow of molten steel around the stopper is steady, and flows into the immersion nozzle, thereby immersing the head and the head of the stopper. It is possible to prevent the inclusions from adhering to the inner wall of the nozzle. However, due to the asymmetrical shape of the tundish and fluctuations in various operating conditions, the flow of molten steel around the stopper appears unsteady, and the argon bubbles do not flow into the immersion nozzle and rise, causing the inclusions to be attached to the stopper head. do. Inclusions attached to the head portion of the stopper cause drift or coarse generated inclusions leave the mold and adversely affect the quality of the cast. As the inclusions are attached, the opening of the stopper increases, and the flow rate of the molten steel around the argon outlet is slowed down, so that a large amount of argon bubbles do not flow into the immersion nozzle and rise, thereby preventing the attachment of the inclusions to the stopper head and the inner wall of the immersion nozzle. There is a problem that can not be.

In order to solve the above problems, the flow around the stopper head portion is uniform and the argon bubble is activated to prevent alumina inclusions or other foreign substances from adhering to the stopper head portion and the inner wall of the immersion nozzle. Steady) Provides a stopper and a stopper assembly to enable a continuous casting process.

The stopper according to the present invention for achieving the above object,

A stopper having an inner cavity through which argon is injected and opening and closing a molten steel outlet of a tundish, the head portion extending in a length direction and larger than the size of the molten steel outlet is formed at an end thereof, and the head portion has a plurality of argon outlets in a vertical direction. Is formed.

The argon outlet of each stage in the argon outlet of the plurality of stages is preferably formed in the radial direction.

Argon outlets of each stage in the argon outlet of the plurality of stages is preferably formed to cross each other.

In addition, the stopper assembly according to the present invention,

A stopper assembly for opening and closing a molten steel outlet of a tundish, the stopper assembly comprising: a stopper extending in a longitudinal direction and having a head portion greater than the size of the molten steel outlet at an end thereof; And a bubble activator surrounding the molten steel outlet and protruding upward.

It is preferable that the bubble activator has a rod-shaped, triangular, or triangular trapezoidal trapezoid, or an annular annular shape that forms a curved surface whose width becomes wider toward the bottom.

The bottom of the bubble activator is preferably connected to the top of the nozzle.

The height of the bubble activator is preferably greater than the height of the head portion of the stopper.

The stopper may be formed in the inner cavity for argon is injected, the porous body is formed at the bottom of the head portion.

The stopper may be formed with an inner cavity portion into which argon is injected, and at least one argon outlet may be formed at a side of the head portion.

The stopper may be formed with an inner cavity portion into which argon is injected, and a plurality of argon outlets may be formed in the head portion in the vertical direction.

According to the present invention as described above, since the bubble activator is wrapped around the stopper head portion at a predetermined interval, the molten steel flow rate around the head portion is accelerated by the bubble activator, and thus the pressure around the head portion is decompressed, so unlike the conventional There is an effect that can prevent the inclusion of the inclusions on the head portion, the inner wall of the immersion nozzle, and the side of the stopper head portion.

In addition, by preventing the rise of argon bubbles to prevent inclusions on the inner wall of the stopper head and the immersion nozzle, it enables a steady continuous casting process and increases the number of continuous castings and improves the quality of the castings. There is an effect that can be improved.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention; First, it should be noted that the same components or parts in the drawings represent the same reference numerals as much as possible. In describing the present invention, detailed descriptions of related well-known functions or configurations are omitted in order not to obscure the gist of the present invention.

Figure 4 is a side cross-sectional view showing a stopper assembly according to an embodiment of the present invention, Figure 5 is a cross-sectional view showing various shapes of the bubble activator according to an embodiment of the present invention, Figure 6 is an embodiment of the present invention In the case of using the stopper assembly according to the related art and the conventional stopper, FIG. 7 illustrates a comparison between the velocity field and the pressure field around the stopper head, and FIG. When a stopper is used, FIG. 8 illustrates a comparison of turbulent kinetic energy around the stopper head, FIG. 8 is a side cross-sectional view and a planar cross-sectional view of the stopper according to an embodiment of the present invention, and FIG. 9 is an embodiment of the present invention. This graph shows the number of argon bubble generations per second and the minimum critical argon flow rate for argon bubble generation.

As shown in Figure 4, the stopper assembly according to an embodiment of the present invention, the stopper 200 and the molten steel outlet that extends in the longitudinal direction and the head portion 220 is formed at the end larger than the size of the molten steel outlet It includes a bubble activator 120 surrounding the protruding upward.

The immersion nozzle 110 is formed of a hollow cylinder extending downwardly in connection with a molten steel outlet formed in a predetermined portion of the tundish bottom, and the bubble activator 120 has a tundish bottom around the portion where the immersion nozzle 110 is formed. It is formed so as to protrude upwardly surrounding the molten steel outlet.

The molten steel is discharged into the mold through the immersion nozzle 110, and the bubble activator 120 forms a rapid flow rate around the head portion 220 of the stopper 200 to lower the pressure around the head portion, thereby argon bubbles are formed. To be easily formed. And, the argon bubble does not rise due to the high flow rate. Therefore, the position of the argon outlet can be increased to the upper side than before, and thus the inclusion of the inclusions to the stopper head can be prevented with a larger area even with argon of the same flow rate. In addition, since the rising argon bubble does not occur, the efficiency of preventing the inclusion of the inclusions of the argon bubble is increased, thereby reducing the amount of argon that causes the cast pin hole defect. In addition, the bubble activator 120 prevents inflow of molten steel flowing along the bottom of the tundish 100 to uniform the flow field around the stopper head 220 to prevent the occurrence of drift and turbulence.

5, the shape of the bubble activator 120 will be described in more detail. Since the bubble activator is for increasing the flow rate around the head portion 220 of the stopper by forcing the flow (A) of the molten steel in the tundish as shown by the arrow of Figure 4, the flow of the molten steel near the bottom of the tundish Any shape that can raise the force is possible.

For example, the bubble activator 120 has an annular annular shape 121 having a rod-shaped cross section, an annular annular shape 122 having a triangular cross section thereof, or an annular annular shape 123 having an upper and lower ray trapezoidal shape, Alternatively, the width of the cross section may be increased toward the lower portion, and may be formed as an annular ring shape 124 forming a smooth curved surface. Alternatively, the triangular, trapezoidal, or curved shape may be formed in symmetrical shapes 125, 126, and 127.

In order to further increase the flow velocity of the molten steel, it is preferable that the annular ring shape (122 to 127) that the width of the cross-section is wider toward the lower portion of the shapes (121 to 127). In addition, it is more preferable to form a rigid shape against the fluid pressure generated by forcibly increasing the flow of molten steel, which is a shape (125, 126, 127) symmetrical triangular, trapezoidal, curved surface shape.

In addition, it is desirable to be connected to the bottom of the bubble activator and the top 111 of the immersion nozzle, so that the molten steel accelerated by the bubble activator is discharged through the immersion nozzle while maintaining its acceleration, and the inclusions are not deposited. Because.

In addition, the height of the bubble activator is preferably larger than the height of the stopper head 220, which will be described later. Here, the height of the stopper head portion refers to the height from the bottom of the tundish 100 when the stopper 200 seals the nozzle. If the height of the head portion is higher, the decompression effect around the head portion by the bubble activator will not be affected, and bubble formation of argon flowing through the argon outlet will not be easy.

The stopper 200 controls the discharge of molten steel by opening and closing the immersion nozzle 110 by vertical movement. In more detail, it is formed of a cylindrical refractory having an outer diameter larger than the diameter of the immersion nozzle 110, the lower end of the hemispherical head portion 220 may be formed.

That is, a stopper as shown in FIG. 1 may be used. In the present invention, since the bubble activator 120 is wrapped around the stopper head 220 at a predetermined interval, the molten steel flow rate around the head by the bubble activator is increased. Since it is faster and thus the pressure around the head is reduced, the phenomenon in which the inclusions are attached to the inner wall of the stopper head 220 and the immersion nozzle 110 can be remarkably reduced.

In addition, the stopper may be formed in the inner cavity is injected gas, the lower end of the head portion may be a porous body is formed.

That is, a stopper as shown in FIG. 2 may be used, but in the related art, it is not possible to prevent the inclusions from being attached to the side of the stopper head. However, in the present invention, the bubble activator may be spaced around the stopper head 220. Since the 120 is wrapped, the molten steel flow rate around the head portion is increased by the bubble activator, and thus the pressure around the head portion is reduced, thereby preventing the inclusion of the inclusion on the side of the stopper head unlike the conventional art.

In addition, the stopper may be formed in the inner cavities through which the gas is injected, at least one argon outlet is formed on the side of the head portion.

That is, a stopper as shown in FIG. 3 may be used. In the related art, an argon bubbling defect and a stopper caused by abnormal flow of molten steel around the stopper caused by variations in the shape of the tundish and various operating conditions are known. Although the phenomenon in which the inclusions are attached to the head portion cannot be prevented, in the present invention, since the bubble activator 120 is wrapped around the stopper head portion 220 at a predetermined interval, the molten steel flow rate around the head portion is increased by the bubble activator. Accordingly, since the head portion is reduced in pressure, unlike the conventional art, it is possible to prevent argon bubbling failure and inclusions on the stopper head portion.

In addition, the stopper may be formed in the inner cavity to be injected with argon, the head portion may be formed with a plurality of stages of argon outlet in the vertical direction (see Fig. 8).

On the other hand, the stopper shown in Figure 8 is a stopper according to an embodiment of the present invention, opening and closing the molten steel outlet of the tundish is formed with an internal cavity to be injected with argon, extending in the longitudinal direction than the size of the molten steel outlet at the end A large head portion is formed, and the head portion is formed with a plurality of stages of argon outlets in the vertical direction. At this time, the argon outlet of each end is preferably formed in the radial direction, the argon outlet of each end is preferably formed to cross each other.

Since the rapid flow rate is formed around the head portion 220 by the bubble activator 120 adopted in the present invention so that the argon bubble does not rise, the position of the argon outlet can be increased to the upper side than before, and thus the argon outlet. Since a plurality of stages may be formed in a plurality of stages, it is possible to prevent the inclusion of inclusions in the stopper head portion with a larger area even with argon of the same flow rate.

Hereinafter, numerical analysis was performed on the case of using and not using the bubble activator by applying the actual operating conditions.

6 is a diagram showing the velocity field and the pressure field around the stopper head portion, when the bubble activator is installed, the speed around the stopper head portion is high and the pressure is low. This is because, by installing the bubble activator, the flow velocity is increased around the stopper head portion, and the pressure is relatively low as a high velocity field is formed.

The flow velocity and pressure at the top of the stopper head where the argon outlet is located are 0.49 m / s, 88,000 Pa, 0.68,000 m / s, and 86,000 Pa, respectively. It is easy to generate argon bubbles under the influence of relatively low pressure, and it is effective to prevent inclusions on the stopper head and the inner wall of the immersion nozzle because the argon bubble does not rise due to the high flow rate.

FIG. 7 is a diagram showing turbulent kinetic energy around the stopper head, and when the bubble activator is installed, the turbulent kinetic energy is low, which prevents the bubble activator from flowing back from the tundish bottom to stop the flow of molten steel. This is because a uniform flow field is formed around the head to reduce the occurrence of turbulence. In general, it is known that inclusions are generated where turbulence occurs and by installing a bubble activator, it is possible to prevent inclusions inside the stopper head and the immersion nozzle.

Using the modeling device manufactured to 1/3 of the actual size, the experiment was conducted with and without the bubble actuator.

FIG. 8 illustrates a stopper having 12 argon outlets used in the experiment, in particular, an 'argon 12 outlet stopper' using argon gas, as shown in FIG. 8A, Original, 3mm upside, and 6mm upside. There are six argon outlets each in height, and the 3mm upside outlet and the 6mm upside outlet are arranged zigzag based on the original outlet as shown in (b) of FIG. 8. For 12 outlet stopper with original outlet and 3mm upside outlet, and 12 outlet stopper with original outlet and 6mm upside outlet, the discharge rate of water is kept constant at 35 l / min. And 20mm, 30mm, Experiments were carried out for the case where bubble activators of 40 mm and 50 mm height were installed, respectively.

FIG. 9A is a graph showing the number of argon bubbles generated per second obtained by photographing with a high speed camera while maintaining a constant argon flow rate at 3.5 l / min. When the bubble activator is installed, it is confirmed that bubbles are actively generated because the flow rate is increased around the stopper head and a low pressure field is formed by installing the bubble activator. And in case of 12 outlet stopper with original outlet and 6mm upside outlet, if bubble activator is not installed, argon bubble generated from 6mm upside will not flow into the immersion nozzle and rise, which is relatively slow flow rate around 6mm upside channel. This is because the buoyancy of the bubble is greater than that of the molten steel. On the other hand, when the bubble activator is installed, argon bubbles generated 6mm upside are also introduced into the immersion nozzle due to the high flow rate.

9 (b) is a graph showing the minimum critical argon flow rate for argon bubble generation, it can be seen that the argon critical flow rate is less when the bubble activator is installed than when the bubble activator is installed. It can be seen that the flow velocity is increased around the stopper head and a low pressure field can be generated to generate argon bubbles even at a low argon flow rate. It can be seen that the slab quality can be improved by reducing the

As described above with reference to the drawings illustrating the stopper and the stopper assembly according to the present invention, the present invention is not limited by the embodiments and drawings disclosed herein, those skilled in the art within the scope of the invention Of course, various modifications may be made.

1 is a side cross-sectional view showing a stopper system according to the prior art;

Figure 2 is a side cross-sectional view showing a stopper having a porous body according to the prior art,

3 is a side sectional view showing a stopper having an argon outlet according to the prior art;

Figure 4 is a side cross-sectional view showing a stopper assembly according to an embodiment of the present invention,

5 is a cross-sectional view showing various shapes of a bubble activator according to an embodiment of the present invention;

6 is a view comparing the speed and pressure fields around the stopper head when using the stopper assembly according to an embodiment of the present invention and when using the conventional stopper.

7 is a view illustrating a comparison of turbulent kinetic energy around a stopper head when using a stopper assembly according to an embodiment of the present invention and a conventional stopper.

8 is a side cross-sectional view and a planar cross-sectional view of the stopper according to an embodiment of the present invention;

9 is a graph showing the number of argon bubble generation per second and the minimum critical argon flow rate for argon bubble generation for one embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

100: tundish 200: stopper

110: immersion nozzle 120: bubble activator

210: internal portion 220: head portion

A, B: flow of molten steel P: inclusions

Claims (10)

A stopper having an inner cavity in which argon is injected and opening and closing a molten steel outlet of a tundish, A stopper extending in the longitudinal direction and formed at the end of the head portion larger than the size of the molten steel outlet, the head portion is formed with a plurality of stages of argon outlet in the vertical direction. The method according to claim 1, The argon outlet of each stage in the argon outlet of the plurality of stages is a stopper formed in the radial direction. The method according to claim 1, The argon outlet of each stage in the argon outlet of the plurality of stages is formed to be staggered with each other. A stopper assembly for opening and closing the molten steel outlet of the tundish, A stopper extending in a longitudinal direction and having a head portion formed at an end thereof larger than the size of the molten steel outlet; And Bubble activator formed to project upwardly surrounding the molten steel outlet Stopper assembly comprising a. The method according to claim 4, The bubble activator is a stopper assembly having a rod-shaped, triangular, or triangular trapezoidal trapezoid, or an annular annular shape forming a curved surface of the cross-section becomes wider toward the bottom. The method according to claim 4, A bottom of the bubble activator is connected to the top of the nozzle stopper assembly. The method according to claim 4, And a height of the bubble activator is greater than a height of the head portion of the stopper. The method according to claim 4, The stopper is a stopper assembly is formed in the inner cavity to be injected with argon, the porous body is formed at the bottom of the head portion. The method according to claim 4, The stopper is a stopper assembly is formed in the inner cavity is injected with argon, at least one argon outlet on the side of the head portion. The method according to claim 4, The stopper is a stopper assembly is formed in the inner cavity to be injected with argon, the head portion is formed with a plurality of argon outlet in the vertical direction.

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