JP6792179B2 - Immersion nozzle for continuous casting - Google Patents

Description

The present invention relates to a dipping nozzle used for continuous casting of steel.

In continuous steel casting, a step of injecting molten steel from a ladle into a tundish and a step of injecting molten steel from a tundish into a mold are performed. At that time, a dipping nozzle (hereinafter, also referred to as a “diving nozzle for continuous casting”) is used to inject molten steel from the tundish into the mold. The immersion nozzle is a refractory material having a function of preventing the molten steel from coming into contact with the atmosphere and reoxidizing. Two discharge holes are provided near the lower end of the immersion nozzle. When the molten steel is injected into the mold from the tundish, the molten steel flowing down the immersion nozzle is discharged from each discharge hole.

The immersion nozzle is required to have a function of properly injecting molten steel into the mold. However, in continuous steel casting, inclusions such as alumina may adhere to the inner pipe portion of the immersion nozzle or the peripheral portion of the discharge hole while using the immersion nozzle. The inclusions adhering to the immersion nozzle impede the flow of the molten steel when the molten steel is injected into the mold. For this reason, it has been pointed out that the molten steel cannot be properly injected due to the adhesion of inclusions.

A large amount of inclusions such as alumina adhere to the inner tube portion of the immersion nozzle, particularly to the portion where the discharge hole is not formed or to the upper part of the discharge hole. The portion where the discharge hole is not formed (hereinafter, also referred to as “non-discharge hole portion”) is 90 ° displaced from the opening center of the discharge hole in the direction around the nozzle center axis around the center axis of the immersion nozzle. Refers to a part. As the thickness of inclusions adhering to the immersion nozzle increases, the molten steel flow discharged from the discharge hole fluctuates. As a result, the flow velocity of the molten steel fluctuates in the mold and foaming of the molten metal surface is likely to occur. When the molten steel flow fluctuates greatly during casting, non-metal inclusions, bubbles, mold powder, etc. are trapped in the solidified shell in the process of forming a solidified shell in the mold, which causes quality abnormalities in the slab. It may occur.

As for the immersion nozzle for continuous casting, the techniques described in Patent Documents 1 to 4 are known.
Patent Document 1 describes a technique for forming a layer of a difficult-alumina adhering material that suppresses adhering of alumina inclusions on the inner tube portion of the immersion nozzle.
Patent Document 2 describes a technique for suppressing adhesion of alumina inclusions by blowing an inert gas such as argon into the inner tube portion of the immersion nozzle, that is, by blowing a gas.
Patent Document 3 describes a technique for suppressing adhesion of alumina inclusions to the periphery of the discharge hole by adjusting the shape and area of the discharge hole of the immersion nozzle.
Patent Document 4 describes a technique for forming the upper wall of the discharge hole of the immersion nozzle in an arc shape.

JP-A-2010-253546 Japanese Unexamined Patent Publication No. 2005-313197 Japanese Unexamined Patent Publication No. 2017-177195 International Publication No. 2005/070589

However, the techniques described in Patent Documents 1 to 4 have the following problems.
First, in the technique described in Patent Document 1, depending on the type of steel handled in continuous casting, the difficult-alumina adhering material reacts with the components in the steel, so that this technique may not be applicable. Further, in the technique described in Patent Document 2, bubble defects may occur due to gas blowing. On the other hand, although the technique described in Patent Document 3 has a certain inhibitory effect on the adhesion of alumina inclusions, there is still room for improvement. Further, in the technique described in Patent Document 4, since only the upper wall of the discharge hole is formed in an arc shape, the flow of molten steel cannot be sufficiently controlled, and the curvature of the arc that defines the shape of the upper wall of the discharge hole is defined. If is small, the nozzle thickness of the upper wall portion of the discharge hole becomes thin and the durability is lowered.

The present invention has been made to solve the above problems, and an object of the present invention is to suppress adhesion of alumina inclusions without using a difficult alumina adhering material or blowing gas. At the same time, it is an object of the present invention to provide a dipping nozzle for continuous casting, which is more durable than the conventional one.

The present invention includes a cylindrical nozzle body having an inner hole extending along the central axis of the nozzle, and two discharge holes communicating with the inner hole are formed on the side wall of the nozzle body, and the upper end of the inner hole is formed. In the immersion nozzle for continuous casting, which is opened at the upper end of the nozzle body, the size of the inner hole gradually expands toward the upper wall of the discharge hole in the molten steel immersion portion of the nozzle body on the lower end side of the inner hole. Of the lines representing the cross-sectional shape of the nozzle when the nozzle body is cross-sectionald along a plane parallel to the discharge shaft passing through the opening centers of the two discharge holes and the nozzle center axis, the size of the inner holes gradually expands. The line representing the cross-sectional shape on the lower end side of the hole is a curved line, and the line representing the cross-sectional shape of the upper wall of the discharge hole is a straight line.

In the immersion nozzle for continuous casting according to the present invention, the curvature of the curve representing the cross-sectional shape on the lower end side of the inner hole may increase as it approaches the discharge hole.

In the immersion nozzle for continuous casting according to the present invention, the angle formed by the straight line representing the cross-sectional shape of the upper wall of the discharge hole and the virtual horizontal plane orthogonal to the central axis of the nozzle may be 7 ° or more and 65 ° or less.

In the immersion nozzle for continuous casting according to the present invention, the cross-sectional shape of the inner hole is flat when the nozzle body is cross-sectionald directly above the discharge hole in a direction orthogonal to the central axis of the nozzle, and the major axis of the cross-sectional shape of the inner hole. 2a, the minor axis of the cross-sectional shape of the inner hole is 2b, and the flatness of the cross-sectional shape of the inner hole is f = 1- (b / a), the flatness f may be 0.17 or more. ..

In the immersion nozzle for continuous casting according to the present invention, the opening size of the discharge hole in the horizontal direction may be larger than the minor diameter of the cross-sectional shape of the inner hole directly above the discharge hole.

According to the present invention, it is possible to suppress the adhesion of alumina inclusions without using a difficult alumina adhering material or blowing gas, and the immersion nozzle for continuous casting has higher durability than before. Can be provided.

It is a schematic perspective view of the immersion nozzle for continuous casting which concerns on 1st Embodiment of this invention. It is a vertical cross-sectional view of the immersion nozzle for continuous casting of FIG. It is an enlarged view of a part of FIG. It is a figure which shows the cross-sectional shape of the inner hole when the nozzle body is cross-section at the position AA of FIG. It is a figure which shows the deformation example of the cross-sectional shape of the inner hole when the nozzle body is cross-sectioned at the position AA of FIG. It is a figure which shows the cross-sectional shape of the inner hole when the nozzle body is cross-sectionald in the direction orthogonal to the nozzle central axis direction just above the discharge hole in the immersion nozzle for continuous casting which concerns on 2nd Embodiment of this invention. It is a molten steel flow vector diagram at the time of using the immersion nozzle for continuous casting which concerns on embodiment of this invention. It is a molten steel flow vector diagram when the conventional immersion nozzle for continuous casting shown in FIG. 9 is used. It is a vertical sectional view of the conventional immersion nozzle for continuous casting. It is a turbulent energy distribution diagram when the immersion nozzle for continuous casting which concerns on embodiment of this invention is used. It is a turbulent energy distribution diagram when the conventional immersion nozzle for continuous casting shown in FIG. 9 is used.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
First, the present inventor conducted a fluid analysis on the immersion nozzle in which a large amount of adhesion of alumina or the like was observed, and found that the turbulent energy of the part having a large amount of adhesion was larger than that of the other parts. The reason is that the molten steel flowing down the inner pipe of the immersion nozzle collides with the molten steel that has collided with the bottom of the immersion nozzle and is inverted, and the flow of the molten steel stagnates, where the turbulent energy increases and alumina etc. adhere. This is thought to be easier to do. Further, a suction flow from the outside to the inside of the immersion nozzle is generated in the upper part of the discharge hole, and a decrease in the discharge flow velocity due to the coexistence of the suction flow and the discharge flow is also considered to be a cause of adhesion of alumina and the like.

Therefore, the present inventor has studied the shapes of the inner hole and the discharge hole of the immersion nozzle in order to reduce the turbulent energy. Then, the computational fluid dynamics calculation was repeatedly performed while changing various parameters that determine the shape of the inner hole and the discharge hole of the immersion nozzle. As a result, we have come up with a configuration of a dipping nozzle that is effective in reducing turbulent energy, suppressing suction flow, suppressing melting damage in discharge holes, and optimizing molten steel flow.

(First Embodiment)
FIG. 1 is a schematic perspective view of a dipping nozzle for continuous casting according to the first embodiment of the present invention.
As shown in FIG. 1, the continuous casting immersion nozzle 1 includes a columnar nozzle body 10. An inner hole 12 is formed inside the nozzle body 10. The inner tube portion of the immersion nozzle 1 for continuous casting is formed by the inner hole 12. The inner hole 12 forms a flow path through which the molten steel flows down when the molten steel is injected into the mold from the tundish in continuous casting of steel. The inner hole 12 extends along the nozzle central axis 14 of the continuous casting immersion nozzle 1. In the present embodiment, one of the nozzle central axial directions J is set with reference to the posture of the continuous casting immersion nozzle 1 when the nozzle body 10 of the continuous casting immersion nozzle 1 is vertically erected to continuously cast steel. The upper side (upper side) and the other side are lower side (lower side). The nozzle central axis direction J is a direction parallel to the nozzle central axis 14.

The material of the nozzle body 10 is not particularly limited, and for example, alumina-graphite, magnesia-graphite, spinel-graphite, zirconia-graphite, alumina, clay, spinel, molten quartz, etc. can be used. Can be used.

Two discharge holes 18 are formed in the side wall portion 16 of the nozzle body 10. The two discharge holes 18 are formed at positions facing each other in a direction orthogonal to the nozzle central axis 14. The two discharge holes 18 are opened outward on the outer peripheral surface of the side wall portion 16, respectively. Each discharge hole 18 communicates with the inner hole 12 of the nozzle body 10 in the vicinity of the lower end 10b of the nozzle body 10. Each discharge hole 18 is a hole for discharging molten steel that flows down along the inner hole 12 of the nozzle body 10. The discharge direction M of the discharge hole 18 is diagonally downward with respect to the discharge shaft 22. The discharge shaft 22 is a shaft that passes through the opening centers 20 and 20 of the two discharge holes 18. The discharge shaft 22 is orthogonal to the nozzle central shaft 14.

In the nozzle central axis direction J, the portion from the lower end 10b of the nozzle body 10 to a predetermined height is the molten steel immersion portion 24. The molten steel immersion portion 24 is a portion that is immersed in the molten steel when a part of the nozzle body 10 is arranged in the mold and the molten steel is injected. The upper end position of the molten steel immersion portion 24 can be specified by the position of the powder line 26. The powder line 26 refers to a portion where the mold powder added into the mold becomes a slag and comes into contact with the outer peripheral surface of the nozzle body 10. Since the outer peripheral surface of the nozzle body 10 is eroded by contact with the mold powder, the portion of the nozzle body 10 corresponding to the powder line 26 is made of a highly corrosion-resistant material, for example, a zirconia-graphitic material, and the other parts. Is composed of, for example, an alumina-graphitic material. Therefore, the position slightly below the upper end position of the portion made of a material having high corrosion resistance with respect to the mold powder is the position of the powder line 26, and the position of the powder line 26 is the upper end position of the molten steel immersion portion 24.

The upper end 12a of the inner hole 12 is circularly opened at the upper end 10a of the nozzle body 10, and the lower end 12b of the inner hole 12 is closed above the lower end 10b of the nozzle body 10. Further, in the lower end side 12c of the inner hole 12, the size of the inner hole 12 gradually expands toward the upper wall 18a of the discharge hole 18 in the molten steel immersion portion 24 of the nozzle body 10. The size of the inner hole 12 described here means the size of the inner hole 12 when the nozzle body 10 is cross-sectioned along a virtual horizontal plane orthogonal to the nozzle central axis 14. The position where the size of the inner hole 12 starts to expand in the nozzle central axis direction J corresponds to the position of the powder line 26.

FIG. 2 is a vertical cross-sectional view of the immersion nozzle for continuous casting of FIG. 1, and FIG. 3 is an enlarged view of a part of FIG.
2 and 3 show the nozzle cross-sectional shape when the nozzle body 10 is cross-sectionald along a plane parallel to the nozzle central shaft 14 and the discharge shaft 22. Of the lines representing the cross-sectional shape of the nozzle, the line representing the cross-sectional shape of the lower end side 12c of the inner hole 12 in which the size of the inner hole 12 gradually expands is a curve L1, and the cross-sectional shape of the upper wall 18a of the discharge hole 18 The line representing is a straight line L2. As shown in FIG. 1, the curve L1 representing the cross-sectional shape of the lower end side 12c of the inner hole 12 is curved in an arc shape toward the upper wall 18a of the discharge hole 18. The curvature of the curve L1 increases as it approaches the discharge hole 18.

On the other hand, as shown in FIG. 3, the angle θ formed by the straight line L2 representing the cross-sectional shape of the upper wall 18a of the discharge hole 18 and the virtual horizontal plane 30 orthogonal to the nozzle central axis 14 is preferably 7 ° or more and 65 ° or less. Yes, more preferably 10 ° or more and 60 ° or less. If the angle θ is less than 7 °, the flow of molten steel may peel off from the upper wall 18a without following the upper wall 18a of the discharge hole 18. Further, if the above angle θ exceeds 65 °, the flow velocity when the molten steel is injected into the mold from the continuous casting immersion nozzle 1 increases, and the flow of the molten steel in the mold may become improper. The case where the flow of molten steel becomes improper in the mold is, for example, the following cases. That is, since the molten steel inflow angle into the mold becomes deeper downward, reverse flow due to the discharge flow is less likely to occur in the mold. As a result, the heat supply on the molten metal surface is reduced, which may affect the abnormal solidification of the molten metal surface and the abnormal melting of the mold powder.

FIG. 4 is a diagram showing a cross-sectional shape of an inner hole when the nozzle body is cross-sectionald at the positions AA of FIG. The cross-sectional shape of the inner hole at the position AA in FIG. 3 represents the cross-sectional shape of the inner hole when the nozzle body is cross-sectionald directly above the discharge hole in a direction orthogonal to the nozzle center axis.
As shown in FIG. 4, the cross-sectional shape of the inner hole 12 immediately above the discharge hole 18 is a flat shape, that is, an elliptical shape. Here, the major axis of the cross-sectional shape of the inner hole 12 is 2a, the minor axis of the cross-sectional shape of the inner hole 12 is 2b, and the flatness of the cross-sectional shape of the inner hole 12 is f = 1- (b / a). In such a case, the flatness f of the cross-sectional shape of the inner hole 12 is preferably 0.17 or more, more preferably 0.28 or more. When the flatness f is less than 0.17, it is difficult to obtain a discharge flow along the upper wall 18a of the discharge hole 18 when the molten steel is discharged from the discharge hole 18, and a suction flow is generated in the upper part of the discharge hole 18. In some cases.

In the first embodiment, the cross-sectional shape of the inner hole 12 immediately above the discharge hole 18 is an elliptical shape, but the cross-sectional shape is not limited to this, and if the condition of the above-mentioned flatness f is satisfied, it is not an ellipse. It may have a flat shape. As a flat shape other than the ellipse, for example, as shown in FIG. 5, among the line segments representing the cross-sectional shape of the inner hole 12, the two line segments 31 facing each other in the major axis direction are arcs, respectively, in the minor axis direction. It can be mentioned that the two line segments 32 facing each other are straight lines. In addition to this, although not shown, a rectangle or a rectangle with rounded corners can be mentioned.

In the first embodiment, the hole shape of the lower end side 12c of the inner hole 12 in the molten steel dipping portion 24 is characteristic, and the hole shape of the inner hole 12 located above the molten steel dipping portion 24 is not limited. .. Therefore, in order to make the flow velocity distribution of the molten steel discharged from the discharge hole 18 uniform, an uneven step may be provided on the inner surface of the inner hole 12 located above the molten steel immersion portion 24, or a plurality of uneven steps may be provided. A mogul shape having spherical protrusions may be provided. Further, in the first embodiment, the cross-sectional shape of the upper wall 18a of the discharge hole 18 is specified, but the cross-sectional shape of the lower wall 18b of the discharge hole 18 is not limited. That is, the cross-sectional shape of the lower wall 18b of the discharge hole 18 may be an upward shape, a horizontal shape, a downward shape, or the like.

The immersion nozzle for continuous casting according to the first embodiment of the present invention has the following effects.
First, in the first embodiment, the size of the inner hole 12 of the continuous casting immersion nozzle 1 is gradually enlarged toward the upper wall 18a of the discharge hole 18. As a result, when the molten steel flows down the inner hole 12 of the nozzle body 10, the flow velocity of the molten steel is reduced. Therefore, the flow velocity of the molten steel colliding with the lower end 12b of the inner hole 12 can be reduced, and the turbulent energy generated in the vicinity of the discharge hole 18 can be reduced. As a result, it is possible to prevent inclusions such as alumina from adhering to the vicinity of the discharge hole 18.
Further, in the first embodiment, the curve L1 is a line representing the cross-sectional shape of the lower end side 12c of the inner hole 12 in which the size of the inner hole 12 gradually expands. As a result, the flow of molten steel in the inner hole 12 of the nozzle body 10 is guided to the upper wall 18a of the discharge hole 18 along the shape of the lower end side 12c of the inner hole 12. Therefore, when the molten steel is discharged from the discharge hole 18, the molten steel flows along the upper wall 18a of the discharge hole 18. As a result, the generation of the suction flow is suppressed in the upper part of the discharge hole 18, so that the molten steel can be discharged from the entire opening of the discharge hole 18 at a stable flow velocity. On the other hand, the line representing the cross-sectional shape of the upper wall 18a of the discharge hole 18 is a straight line L2. As a result, the nozzle thickness of the upper wall 18a portion of the discharge hole 18 can be increased, and melting damage can be suppressed. Therefore, the fluidity of the molten steel can be well maintained for a long period of time.
Therefore, according to the first embodiment, it is possible to suppress the adhesion of alumina inclusions without using a difficult alumina adhering material or blowing gas, and the durability is higher than before. A dipping nozzle for continuous casting can be provided. As a result, it becomes possible to optimize the flow of molten steel, and eventually to improve the quality and productivity of slabs.

Further, in the first embodiment, the curvature of the curve L1 representing the cross-sectional shape of the lower end side 12c of the inner hole 12 increases as it approaches the discharge hole 18. As a result, the flow of molten steel in the inner hole 12 of the nozzle body 10 can be more reliably guided to the upper wall 18a of the discharge hole 18.

Further, in the first embodiment, the angle θ formed by the straight line L2 representing the cross-sectional shape of the upper wall 18a of the discharge hole 18 and the virtual horizontal plane 30 orthogonal to the nozzle central axis 14 is 7 ° or more and 65 ° or less. .. When the angle θ is 7 ° or more, it is possible to prevent the molten steel that has flowed down the inner hole 12 from peeling from the upper wall 18a of the discharge hole 18. Further, when the angle θ is 65 ° or less, the flow velocity of the molten steel falling when the molten steel is injected into the mold from the immersion nozzle 1 for continuous casting can be suppressed, and the flow of the molten steel can be appropriately maintained in the mold.

Further, in the first embodiment, the cross-sectional shape of the inner hole 12 immediately above the discharge hole 18 is a flat shape, and the flatness is 0.17 or more. Thereby, the generation of the suction flow in the upper part of the discharge hole 18 can be suppressed more effectively.

(Second Embodiment)
Subsequently, the immersion nozzle for continuous casting according to the second embodiment of the present invention will be described. In the second embodiment of the present invention, the same parts or corresponding parts as in the case of the first embodiment are designated by the same reference numerals, and duplicate description will be omitted.

FIG. 6 is a diagram showing a cross-sectional shape of an inner hole when the nozzle body is cross-sectionald at the position AA of FIG. 3 in the immersion nozzle for continuous casting according to the second embodiment of the present invention.
As shown in FIG. 6, the two discharge holes 18 provided in the nozzle body 10 are opened outward on the outer peripheral surface of the side wall portion 16 of the nozzle body 10, respectively. The horizontal dimension of the discharge hole 18 gradually increases from the inner peripheral surface of the side wall portion 16 toward the outer peripheral surface. The horizontal opening dimension W of the discharge hole 18 on the outer peripheral surface of the side wall portion 16 is larger than the minor axis 2b of the cross-sectional shape of the inner hole 12 directly above the discharge hole 18. When such a configuration is adopted, when the molten steel flowing down the inner hole 12 of the nozzle body 10 is discharged from the discharge hole 18, the effect that the flow of the molten steel is more stable can be expected.

FIG. 7 is a flow vector diagram of the molten steel when the immersion nozzle for continuous casting according to the embodiment of the present invention is used, and FIG. 8 is a molten steel when the conventional immersion nozzle for continuous casting shown in FIG. 9 is used. It is a flow vector diagram.
As shown in FIG. 9, in the conventional immersion nozzle for continuous casting, the size of the inner hole 12 of the nozzle body 10 is the same over the entire nozzle central axis direction J.

First, in the case of the immersion nozzle for continuous casting according to the embodiment of the present invention, as shown in FIG. 7, the molten steel flows after being guided to the surface of the lower end side 12c of the inner hole 12 bent in an arc shape, and then the molten steel. It can be seen that the molten steel is stably discharged from the entire discharge hole 18 without peeling from the upper wall 18a of the discharge hole 18. On the other hand, in the case of the conventional immersion nozzle for continuous casting, as shown in FIG. 8, after the molten steel flows along the inner hole 12 extending straight in the direction of the central axis of the nozzle, the flow of the molten steel flows. It can be seen that the suction flow 35 is generated in the upper part of the discharge hole 18 by peeling from the upper wall 18a of the discharge hole 18. From this, when the immersion nozzle for continuous casting according to the embodiment of the present invention is used, the generation of suction flow can be suppressed at the upper part of the discharge hole 18.

FIG. 10 is a turbulent energy distribution diagram when the immersion nozzle for continuous casting according to the embodiment of the present invention is used, and FIG. 11 is a turbulence when the conventional immersion nozzle for continuous casting shown in FIG. 9 is used. It is a flow energy distribution map.
10 and 11 are views of the internal energy in the molten steel flow in the inner hole of the nozzle body calculated by computational fluid dynamics calculation, and the turbulent energy distribution based on this calculation result viewed from the discharge hole side. The low part is the part with high turbulent energy. The low-concentration portion has a ring shape, and the central portion of this ring shape has the highest turbulent energy.
First, in the case of the immersion nozzle for continuous casting according to the embodiment of the present invention, as shown in FIG. 10, a portion having a low concentration, that is, a portion having a high turbulent flow energy can be seen in the vicinity of the lower end of the inner hole 12. On the other hand, in the case of the conventional immersion nozzle for continuous casting, as shown in FIG. 11, a portion having high turbulent energy is widely seen in the vicinity of the lower end of the inner hole 12. From this, when the immersion nozzle for continuous casting according to the embodiment of the present invention is used, the turbulent flow energy can be suppressed to a small value.

(Examples and Comparative Examples)
Next, Examples and Comparative Examples of Immersion Nozzles for Continuous Casting will be described.
First, as the immersion nozzle for continuous casting according to the embodiment of the present invention, the immersion nozzles of Examples 1 to 10 shown in Table 1 below are prepared, and as the immersion nozzle for continuous casting to be compared with the present invention, the following. The immersion nozzles of Comparative Examples 1 to 4 shown in Table 2 were prepared. In Examples 1 to 10, the flatness f of the cross-sectional shape of the inner hole 12 is 0.17 or more, and the angle θ of the upper wall 18a of the discharge hole 18 is 7 ° or more and 65 or less. Further, in Examples 1 to 10, the line representing the cross-sectional shape of the lower end side 12c of the inner hole 12 is a curved line, and the line representing the cross-sectional shape of the upper wall 18a of the discharge hole 18 is a straight line. On the other hand, in each of Comparative Examples 1 to 4, at least one of the requirements does not satisfy the requirements of the embodiment of the present invention. Specifically, in Comparative Example 1, the flatness f of the cross-sectional shape of the inner hole 12 is 0, and the line representing the cross-sectional shape of the lower end side 12c of the inner hole 12 is a straight line. Further, in Comparative Example 2, the line representing the cross-sectional shape of the lower end side 12c of the inner hole 12 is a straight line. Further, in Comparative Example 3, the angle θ of the upper wall 18a of the discharge hole 18 is 5 °, and in Comparative Example 4, the angle θ is 67 °.

The turbulent energy, the suction of the upper part of the discharge hole, and the discharge direction of the molten steel were evaluated for Examples 1 to 10 and Comparative Examples 1 to 4 having the above configurations. The evaluation method is as follows.

[Evaluation methods]
<About numerical analysis>
In the numerical analysis by the computational fluid dynamics calculation, the fluid analysis software "PHOENICS" manufactured by CHAM-Japan was used. The parameters used for the numerical analysis are as follows.
・ Number of calculated cells: Approximately 400,000 (varies depending on the model)
-Fluid: molten steel (1560 ° C, density 7.08 g / cm ³ )
-Mold size: 260 mm x 1500 mm
-Casting speed: 1.6 m / min
・ Outer diameter of immersion nozzle: 150 mm
・ Immersion nozzle inner diameter: 80 mm
・ Opening size of discharge hole: length 70 mm, width 80 mm
・ Discharge hole angle: downward 15 °

<Evaluation of turbulent energy>
Based on the turbulent energy value when the flatness of the cross-sectional shape of the inner hole 12 is f = 0, the case where it is the same as or more than the standard is "large", and the case where it is 10 or more and less than 20% less than the standard. Was defined as "medium", a decrease of 20 or more and less than 50% from the standard was defined as "small", and a decrease of 50% or more from the standard was defined as "minimal". Then, if the evaluation of the turbulent energy is "medium", "small" or "minimal", it is determined that it is more effective than the case where the flatness f = 0, and if it is "large", the flatness f = It was judged to be more inappropriate than the case of 0.

<Evaluation of suction at the top of the discharge hole>
In the upper part of the discharge hole, the flow of molten steel from the outside to the inside of the immersion nozzle, that is, the suction flow is marked with "x", and the flow from the inside to the outside, that is, the discharge flow is ". ◎ ”, the case where it is neither the discharge flow nor the suction flow was evaluated as“ ○ ”.

<Evaluation of the discharge direction of molten steel flow>
The molten steel that has passed through the inner hole of the nozzle body is discharged diagonally downward from the discharge hole and collides with the wall on the short side of the mold. However, if the molten steel collision position at that time is lower than the molten metal surface by a predetermined amount, for example, The formation of solidified shells in the mold may be inhibited. Therefore, regarding the discharge direction of the molten steel flow, if the molten steel collision position is within 700 mm from the molten metal surface, it is regarded as “○”, that is, appropriate, and if it is below 700 mm from the molten metal surface, it is regarded as “×”, that is, inappropriate. ..

[Evaluation results]
In all of Examples 1 to 10, the turbulent energy was "medium" or less, no suction was observed in the upper part of the discharge hole, and the discharge direction of the molten steel flow was also appropriate.
On the other hand, in Comparative Example 1, the turbulent energy was large, and suction of the upper part of the discharge hole was observed. Further, in Comparative Example 2 and Comparative Example 3, suction of the upper part of the discharge hole was observed. Further, in Comparative Example 4, the turbulent energy was "minimal" and no suction was observed in the upper part of the discharge hole, but the discharge direction of the molten steel flow was inappropriate.

1 Immersion nozzle for continuous casting, 10 nozzle body, 12 inner hole, 14 nozzle center axis, 16 side wall, 18 discharge hole, 18a upper wall, 22 discharge shaft, 30 virtual horizontal plane, f flatness, L1 curve, L2 straight line, θ angle.

Claims (4)

A cylindrical nozzle body having an inner hole extending along the central axis of the nozzle is provided, and two discharge holes communicating with the inner hole are formed on the side wall portion of the nozzle body, and the upper end of the inner hole is the said. In a continuous casting immersion nozzle that opens at the upper end of the nozzle body,
On the lower end side of the inner hole, the size of the inner hole gradually expands toward the upper wall of the discharge hole in the molten steel immersion portion of the nozzle body.
Of the lines representing the cross-sectional shape of the nozzle when the nozzle body is cross-sectionald along a plane parallel to the discharge shaft passing through the opening centers of the two discharge holes and the nozzle center axis, the size of the inner holes gradually increases. a line representing the lower end of the cross-sectional shape of the bore enlarge the curve, the line representing the upper wall of the cross-sectional shape of the discharge hole Ri linearly der,
A dipping nozzle for continuous casting , wherein the angle formed by the straight line representing the cross-sectional shape of the upper wall of the discharge hole and the virtual horizontal plane orthogonal to the nozzle center axis is 7 ° or more and 65 ° or less . The immersion nozzle for continuous casting according to claim 1, wherein the curvature of the curve representing the cross-sectional shape on the lower end side of the inner hole increases as it approaches the discharge hole. The cross-sectional shape of the inner hole is flat when the nozzle body is cross-sectionald directly above the discharge hole in a direction orthogonal to the central axis of the nozzle, and the major axis of the cross-sectional shape of the inner hole is 2a, the inner hole. The flatness f is 0.17 or more when the minor axis of the cross-sectional shape is 2b and the flatness of the cross-sectional shape of the inner hole is f = 1- (b / a) . The immersion nozzle for continuous casting according to any one of the items . The immersion nozzle for continuous casting according to any one of claims 1 to 3 , wherein the opening size of the discharge hole in the horizontal direction is larger than the minor diameter of the cross-sectional shape of the inner hole directly above the discharge hole.

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