JPH1147896A - Immersion nozzle for continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the channeling in a mold, to reduce the inclusion in a nozzle and to prevent the clogging of a nozzle by arranging a spiral projection on the inner wall of the nozzle to circularly stir molten steel in the nozzle. SOLUTION: Double spirals A, B are arranged in the nozzle between a tundish and a mold. Number of spirals are desirable to be two or three. The starting point and end point of the spiral are a factor largely affected to the prevention of drift and the reduction of inclusion, etc. Then, related to the starting point of the spiral, it is desirable to control to the position having mutually 170-190 deg. angle in the same height in the case of being the double spirals and to the position having mutually 110-130 deg. angle at the same height in the case of being triple spirals. Further, related to the end point of the spiral, it is desirable to set to the position having at least 100 mm from the upper end of inner diameter part in a nozzle spouting hole. As the other, it is desirable to control the descending angle of the spiral to 20-70 deg. and the height in the spiral cross section to 5-25% to the nozzle inner diameter and the length of the bottom surface in the spiral cross section to 10-30 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting immersion nozzle used for injecting molten steel from a ladle to a tundish or from a tundish to a mold. INDUSTRIAL APPLICABILITY The immersion nozzle for continuous casting of the present invention is very useful in continuous casting of steel because it can prevent drift in the mold and blockage of the nozzle during casting and can efficiently separate inclusions in molten steel.

[0002]

2. Description of the Related Art In the continuous casting method, one of the important issues is how to prevent clogging in an immersion nozzle during casting. If clogging occurs in the nozzle, the desired molten steel discharge rate cannot be secured, not only hindering the actual operation, but also the generated clogging remains in the mold, which is a factor of deteriorating the quality of the slab. Because.

[0003] Regarding the above-described prevention of nozzle blockage, various modes in which the nozzle shape is controlled have been proposed from the viewpoint that it is effective to swirl and stir in the nozzle.

For example, Japanese Patent Application Laid-Open No. 57-130745 discloses a continuous casting nozzle provided with a spiral groove or projection on the inner wall. Specifically, a two-hole nozzle has a discharge hole from its upper end in the longitudinal direction. A spiral groove is shown up to the top. JP-A-2-41747 discloses a continuous casting nozzle in which one or more spiral steps are provided on an inner wall, and a cross-sectional area of a molten metal flow path is gradually reduced from an inlet side to an outlet side. I have.

However, in any of the above nozzles, the molten steel swirled along the spiral is not uniformly discharged from the two discharge holes, but is preferentially discharged from one of the discharge holes. There is a risk of causing an adverse effect such as the occurrence of a drift in the powder, the entrainment of the powder, and the uneven solidification.

Japanese Patent Application Laid-Open No. 7-303949 discloses a method in which an intermediate nozzle is provided at the upper end of an immersion nozzle to swirl and agitate molten steel. Specifically, fins are provided in the intermediate nozzle and the immersion nozzle as a turning force applying means for turning the molten metal, and the jet flow of the molten metal is controlled by applying a static magnetic field in the immersion nozzle. However, according to this method, since the swirling is performed by the intermediate nozzle at the upper part of the immersion nozzle, it is difficult to continue the swirling to the discharge hole of the immersion nozzle located thereunder, and the desired swirling and stirring effect is sufficiently obtained. I can't. In addition, since the swirl force applying means is provided in the intermediate nozzle from which molten steel is discharged at a high flow rate, it is extremely difficult to maintain the shape during continuous casting even if the shape is specially made of a refractory or the like. Difficult.

Further, Japanese Patent Application Laid-Open No. Hei 8-215809 discloses a continuous casting nozzle in which the shape of a spiral groove is specified.
Specifically, by forming a predetermined spiral groove composed of a plurality of strips, the molten steel flow in the nozzle is swirled, the drift of the molten steel flow is prevented by the gyro effect, and inclusions in the molten steel in the spiral groove are formed. Is preferentially adsorbed to increase the effect of removing inclusions. However, it is difficult to expect molten steel to flow along the spiral groove,
Even if swirling is obtained, the spiral groove is provided immediately above the discharge hole, so that the discharge is preferentially discharged from one of the two discharge holes, a drift occurs in the mold, and the powder is caught, There is a possibility that adverse effects such as uneven coagulation may be caused.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to swirl and agitate molten steel in a nozzle and prevent drift in a mold.
Moreover, it is an object of the present invention to provide a continuous casting immersion nozzle capable of reducing inclusions in the nozzle and preventing clogging in the nozzle.

[0009]

The immersion nozzle for continuous casting of the present invention, which has achieved the above object, has a gist in that a spiral projection is provided on the inner wall. From the viewpoint of preventing drift, the number of spirals is preferably two or three. The starting point and the end point of the helix are also factors that greatly affect the prevention of drift and the reduction of inclusions. In the case of a double helix, the starting point of the helix is 170 to 1 at the same height.
In the case of a triple helix at a position of 90 °, it is preferable to control the positions at 110 to 130 ° with each other at the same height,
The end point of the spiral is preferably set at a position at least 100 mm from the upper end of the inner diameter of the nozzle discharge hole. In addition, the descending angle of the spiral is controlled to 20-70 °, and the height of the spiral cross section is 5-25
%, Controlling the length of the bottom surface of the spiral cross section to 10 to 30 mm is a preferable embodiment for obtaining more excellent characteristics.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic explanatory view of the present invention in which a double spiral A and B are provided on a nozzle between a tundish and a mold. A spiral projection is provided on the inner wall of the nozzle in the longitudinal direction of the nozzle. From the upper end to a predetermined portion of the discharge hole. In order to clarify this configuration, FIG. 2 is a diagram illustrating a spiral state on the back side when the plane is halved in a plane parallel to the paper surface.
FIGS. 2A and 2B show the spiral state on the near side in FIG.

As described above, the nozzle of the present invention is most characterized in that a spiral projection is provided on the inner wall. At most, conventional spiral nozzles only disclose spiral grooves or steps, and it has been found that this cannot effectively prevent the immersion nozzle from being blocked. For example, Japanese Patent Application Laid-Open No. Hei 8-215809 attempts to preferentially adsorb inclusions in a spiral groove, which may improve the efficiency of removing fine inclusions.
Blockage in the nozzle cannot be effectively prevented. Japanese Patent Application Laid-Open No. 57-130745 discloses a nozzle provided with a substantially spiral groove. The spiral protrusion is described in a word, and the spiral protrusion is formed at the same level as the groove. I only recognize it. On the other hand, the present invention has been intensively studied by limiting the present invention to a spiral projection. As a result, as shown in an embodiment described later, by providing a projection instead of a groove, a significantly excellent nozzle blockage is achieved. The present inventors have found that the prevention effect can be obtained and the defect defect of the inclusion can be significantly reduced, and the present invention has been completed.

The basic structure of the present invention is as described above.
Furthermore, it is recommended that the number of spirals, the starting point, and the end point be appropriately controlled. In conventional nozzles, spirals were provided over a wide area to maximize the effect of swirling and stirring in the nozzles.
According to the study of the present inventors, it has been found that providing the nozzle from the upper end of the immersion nozzle to immediately above the discharge hole rather promotes the drift in the mold. Therefore, as a result of further study on the shape of the nozzle which can prevent the nozzle from clogging while securing the appropriate swirling and stirring effect while preventing the drift in the mold, the spiral shape was changed to a projection instead of the conventional groove. And found that the number of spirals, the starting point, and the ending point should be specified as follows.

In the following description, the reasons for setting each requirement will be described in detail with reference to FIGS. These figures are
[C] = with continuous slab caster of 240mm × 1230mm
This shows the results obtained when the spiral conditions were variously changed in a case where the casting was performed at a casting speed of 1.6 m / min using a steel type of 0.05%. The inner diameter of the immersion nozzle is 80m
mφ, the total length is 670 mm.

Number of spirals: 2 or 3 FIG. 3A shows the relationship between the number of spirals and the degree of drift. The helix conditions other than the numbers are as follows: the descent angle of the helix is 45 °, the height of the helix cross section is 10 mm (12.5% of the inner diameter), the length of the helix cross section bottom is 20 mm, the installation range of the helix is the starting point, When the number is two, the temperature is 180 ° C. at the same height, and when the number is two, the temperature is 120 ° C. at the same height. When the number is three, the end point is 120 mm from the upper end of the discharge hole. In addition, the degree of drift is shown in FIG.
As shown in the figure, the ratio of the height of the molten steel surface rising (H ₂ / H ₁ ) on the narrow surfaces at both ends of the discharge hole is expressed as “H ₂ / H _1”. Means not to occur.

From FIG. 3 (a), when the number of spirals is one, the degree of drift is worse than when no spiral is provided. This is because molten steel flows out preferentially in the direction of the spiral outlet. On the other hand, when the number of spirals was set to two or more, drift did not occur. Thus, based only on the viewpoint of preventing drifting, it is recommended that the number of spirals be two or more.
Even if more than two nozzles are formed, it is difficult to manufacture the nozzles and the cost is high, which is wasteful economically. Therefore, in the present invention, two or three nozzles are used.

The end point of the spiral: at least 100 mm or more from the upper end of the inner diameter of the immersion nozzle discharge hole. FIG. 4A shows the distance [s in FIG. It is a graph which shows a relationship. The experimental conditions were the same as in FIG. 3 except that the number of spirals was 2, the descending angle was 45 °, and the starting points of the spirals were 180 ° with each other at the same height.

As shown in FIG. 4, up to the position just above the discharge hole (ie, s =
0) It can be seen that when the spiral is provided, the drift easily occurs. Therefore, in order to effectively prevent the occurrence of drift, it is recommended that the end point of the spiral be set to at least 100 mm or more from the upper end of the inner diameter of the immersion nozzle discharge hole. It is preferably at least 110 mm, more preferably at least 120 mm. Although the upper limit is not particularly limited, it is recommended that the upper limit be 200 mm or less (more preferably 150 mm or less) in consideration of the position of the nozzle discharge hole and the level of the molten metal.

In the case of a double helix, the starting point of the helix is at the same height and 170 to 190 ° from each other.
In the case of a triple helix, 110 to 1 at the same height
It is recommended to set the position at 30 °. Above all,
The spiral is symmetrical at the same height about the axis of the nozzle (ie, 180 ° for a double spiral, 12 ° for a triple spiral).
0 °) is the most recommended mode because it can more effectively prevent the drift of the molten steel, but is not limited to this, and each is within the range of ± 10 ° as an allowable level of the present invention. May be included within the scope. Therefore, in the case of a double helix, it can be installed at a minimum of 170 ° and a maximum of 190 °, while in the case of a triple helix, it can be installed at a minimum of 110 °,
It can be installed at a maximum of 130 °.

By specifying the above requirements, a better effect can be obtained. However, it is recommended to control the shape of the spiral as follows for further improvement.

Spiral descending angle: 20-70 ° FIG. 5A is a graph showing the relationship between the spiral descending angle and the rotation index. This is a single hole in the immersion nozzle, and the rotation status (swirl stirring) immediately below the immersion nozzle was evaluated using a water model [x in FIG. 3 (b) is a measurement point]. The rotation speed is represented by a ratio of the rotation speed under each condition to the rotation speed when the descent angle of the spiral is set to 20 °. The experimental conditions were as follows: the number of spirals: 2, the starting points of the spirals were 180 ° from each other at the same height.
Was set in the same way as in the case of.

FIG. 5 shows that when the spiral descending angle is 20 to 70 °, the rotation index becomes 1 or more and good results are obtained. A more preferred lower limit is 30 ° and a more preferred upper limit is 60 °.

Spiral section height: 5 to 2 with respect to inner diameter
5% Bottom length of spiral cross section: 10 to 30 mm Fig. 6 (a) shows good swirling agitation (rotation index 1.0 or more)
5 is a graph showing the relationship between the height of the spiral cross section and the length of the bottom surface of the cross section for obtaining the following formula. The experimental conditions were set in the same manner as in FIG. 3 except that the number of spirals was two. In the present invention, the “bottom length of the spiral cross section” and the “height of the spiral cross section” are:
These correspond to w and h in FIG.

FIG. 6 shows that in order to obtain a good rotation index,
The height of the spiral cross section is 4 to 20 mm (5 to 25 mm
%), It is recommended that the bottom length of the spiral cross section be 10 to 30 mm. Among them, the height of the spiral cross section is determined according to the inner diameter of the immersion nozzle used, and therefore, in the present invention,
It is preferable to specify the height of the spiral cross section to be 5 to 25% of the inner diameter. A more preferred lower limit is 8 mm (10% of the inner diameter), while a more preferred upper limit is 16 mm.
mm (20% of the inner diameter). Further, the lower limit (10 mm) of the bottom length of the spiral cross section is specified from the viewpoint of securing strength enough to withstand the collision force of molten steel. More preferably, the bottom length of the spiral cross section is 20 mm. The upper limit of the bottom length of the spiral cross section is determined by the number of spirals provided in the nozzle. As the length of the bottom increases, the number of spirals decreases.
mm is sufficient. The shape of the spiral cross section is not limited to a trapezoidal shape as shown in the figure, but may be elliptical, circular, etc.
Various shapes can be appropriately adopted.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples do not limit the present invention, and all changes and implementations without departing from the spirit of the present invention will be described. Within the technical scope of

[0025]

【Example】

Example 1 In this example, the effect of preventing the nozzle from being blocked and the effect of preventing the inclusion of inclusions from being formed by the spiral projection were examined. In particular,
The number of spirals: 2, the descending angle of the spiral: 45 °, the height of the spiral cross section: 10 mm, the bottom length: 20 mm, the end point of the spiral: 120 mm from the upper end of the discharge hole, and the nozzle of the present invention.
Using the nozzle of the comparative example having no spiral, the above effects were compared and studied. The effect of preventing nozzle blockage was evaluated using a “nozzle blockage index,” which indicates the amount of alumina or the like deposited on the inner wall of the nozzle. The effect of preventing inclusions from inclusions was evaluated using an “inclusion defect index,” which indicates an index of the number of defects by ultrasonic flaw detection.

FIG. 7 shows the result of the nozzle blockage index, and FIG. 8 shows the result of the inclusion defect index. As is apparent from these figures, the use of the nozzle of the present invention makes it difficult for inclusions to adhere to the inner surface of the nozzle, so that blockage in the nozzle can be effectively prevented. This is considered to be based on the fact that the nozzle of the present invention was able to sufficiently rotate molten steel in the nozzle. In addition, the inclusion having a small specific gravity increases the swirling speed and concentrates the inclusion at the center of the nozzle, and increases the frequency of being caught by the inert gas blown into the nozzle in order to prevent nozzle clogging. By doing so, adverse effects due to inclusions can be reduced.

Embodiment 2 In this embodiment, the effect of the formation of the spiral projection which characterizes the present invention most was compared with the case of the spiral groove.
More specifically, as shown in Table 1, a nozzle formed of a double helix or a triple helix has the same shape except that a distinction between a groove and a projection is provided. The inclusion defect index was investigated. The results are also shown in Table 1.

[0028]

[Table 1]

As is evident from Table 1, No. 1 to No. 6 having spiral projections (Examples of the present invention) have a nozzle blockage index of 0.1 in any of the double spiral and triple spiral modes. 2-0.
3, the inclusion defect defect index is extremely small, 0.05 to 0.1, but is not satisfied with the requirements of the present invention.
In all of 7 to 12 (Comparative Examples), the above evaluation criteria were the smallest, 2.5 (nozzle clogging index) and 1.4 (inclusion defect defect index), which were much larger than those of the present invention. became. Thus, it can be understood that the provision of the spiral projection instead of the conventional spiral groove can extremely effectively prevent defects due to nozzle blockage and inclusion of inclusions.

Example 3 In this example, the effects of various desirable requirements defined in the present invention on the evaluation index were examined. Specifically, as shown in Table 2, the shapes of various nozzles provided with spiral projections were variously changed, and the nozzle blockage index and the inclusion defect index were examined in the same manner as in Example 1. The results are also shown in Table 2.

[0031]

[Table 2]

First, Nos. 1 and 2 are examples in which the number of spirals is one or four, respectively, but the number of spirals is two or three.
The evaluation index is larger than that of the present invention examples (Nos. 1 to 6 in Table 1).

Nos. 3 to 6 / Nos. 7 to 10 are examples in which the starting point / ending point of the helix does not satisfy the preferred requirements of the present invention, but examples satisfying the requirements of the present invention (for example, No. 1 in Table 1). .
1, 2, 6, etc.), the evaluation index becomes large, and the desired effect cannot be obtained.

Nos. 11 to 14 are examples in which the descending angle of the spiral is not preferable, and Nos. 15 to 18 are examples in which the shape of the spiral cross section is not preferable. No. 1 of No. 2) and the like, the effect of blocking nozzles and the effect of reducing inclusion failure are poor.

[0035]

Since the present invention is configured as described above, the molten steel in the nozzle can be swirled and agitated, and the drift in the mold can be prevented. In addition, the inclusion in the nozzle can be reduced, and the nozzle can be blocked. Thus, it is possible to provide a continuous casting immersion nozzle capable of preventing the occurrence of the problem.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a basic configuration of the present invention.

FIG. 2 is a sectional view showing a configuration of a spiral in FIG. 1;

FIG. 3 is a graph showing the relationship between the number of spirals and the degree of drift.

FIG. 4 is a graph showing the relationship between the distance from the upper end of the inner diameter portion of the immersion nozzle discharge hole and the degree of drift.

FIG. 5 is a graph showing a relationship between a descending angle of a spiral and a rotation index.

FIG. 6 is a graph showing the relationship between the height of the spiral cross section and the bottom length of the cross section.

FIG. 7 is a graph showing a result of a nozzle blockage index in Example 1.

FIG. 8 is a graph showing the results of inclusion defect index in Example 1.

Claims (6)

[Claims] 1. An immersion nozzle for continuous casting, wherein a spiral projection is provided on an inner wall. 2. The nozzle according to claim 1, wherein the number of the spirals is two or three. 3. When the starting point of the helix is a double helix, the starting point of the helix is 170 to 190 at the same height.
In the case of a triple helix, it is 110-130 with each other at the same height.
The nozzle according to claim 1, wherein the nozzle is located at a position ゜. 4. The end point of the spiral is at least 100 mm from the upper end of the inner diameter of the nozzle discharge hole.
4. The nozzle according to any one of items 1 to 3, 5. The nozzle according to claim 1, wherein a descending angle of the spiral is 20 to 70 °. 6. The height of the spiral cross section is 5 to 25% with respect to the inner diameter of the nozzle, and the bottom length of the spiral cross section is 10 to 30%.
The nozzle according to any one of claims 1 to 5, wherein the diameter is in mm.