JPS6325001Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an immersion nozzle used between a tundish and a mold in continuous casting.

In continuous casting, a submerged nozzle is used to prevent the molten steel from coming into contact with air and becoming oxidized and contaminated when the molten steel in the tundish is injected into the mold. This immersion nozzle is usually provided with a plurality of discharge holes in the horizontal direction at its bottom, and is designed to prevent the molten steel flow from penetrating deeply downward when the molten steel is injected into the mold. This promotes the floating of inclusions in the molten steel injected into the mold.

However, when such a submerged nozzle is used, drift may occur in the molten steel flow discharged from each discharge hole. This point will be explained with reference to FIG. This figure shows the molten steel injection situation when a two-layer sliding nozzle 5 consisting of an upper plate 5' and a lower plate 5'' having molten steel passage holes is used between the immersion nozzle 1 and the tundish 6. In this case, the flow center of the molten steel flowing inside the immersion nozzle 1 is biased toward the narrowing side of the two-layer sliding nozzle 5 (left side in the figure), so it flows from the discharge hole 8' rather than from the discharge hole 8''. The flow rate of discharged molten steel increases. Therefore, the penetration depth of the molten steel flow is large, and
Since the upward flow is also strong, it disturbs the molten metal surface and causes the mold flux 3 to be drawn into the steel, causing inclusion defects, and the mold flux 3 flows between the mold 2 and the solidified shell 4. This can cause the solidified shell to stick to the mold, which can also cause breakouts.

Defects caused by these phenomena occur exclusively because there is a drift in the molten steel flow discharged from the immersion nozzle 1. It is something that occurs. Therefore, conventionally, the following measures have been taken.

That is, one is a "stopper system" in which a stopper 7 is disposed at the outlet of the tundish 6, as shown in FIG. However, this method has drawbacks such as difficulty in controlling the amount of molten steel injected, a great deal of effort required for setting up the stopper 7, and the cost of the stopper itself being high. As another method, as shown in FIG. 3, there is a method in which the sliding nozzle is of a three-layer type 9 and the flow is narrowed in a direction perpendicular to the discharge flow from the discharge hole 8 of the submerged nozzle 1. but,
This method is also expensive due to the increased number of plates, and since the drive mechanism is provided in a direction perpendicular to the longitudinal direction of the tundish tray 6, it protrudes significantly outward from the tundish tray 6, causing handling problems. There are drawbacks.

Therefore, the inventor of the present invention has conducted intensive research to enable even more effective prevention of drifting without relying on the conventional drifting prevention method described above. It was discovered that by changing the shape of the discharge part, it is possible to equalize the flow rate of molten steel flowing out from each discharge hole.The gist of this invention is that the molten steel flows down. It has a bottomed hole and two or four discharge holes arranged at equal intervals on the side wall of the bottom, and the vertical cross-sectional shape of the bottom of the bottomed hole when cut along a vertical plane including a straight line connecting the opposing discharge holes is chevron-shaped. , in an immersion nozzle that is an inverted mountain type or a stepped concave type,
Mold immersion that does not cause drifting, characterized in that the apex of the chevron-shaped cross section, the lowest point of the valley of the reverse chevron-shaped cross section, or the center point of the stepped concave cross-section is changed with respect to the axis of the bottomed hole. It's in the nozzle.

In normal continuous casting, an immersion nozzle with two discharge holes arranged oppositely is used in the case of continuous slab casting, and a submerged nozzle with four discharge holes arranged evenly in the circumferential direction in the case of continuous bloom casting. Since a immersion nozzle with a plurality of discharge holes is used, this invention also targets a device with two or four discharge holes arranged at equal intervals.

Hereinafter, the present invention will be explained in detail based on examples.

As described above, when a two-layer sliding nozzle is used (FIG. 1), the injection flow causes a drift in the injection flow within the submerged nozzle due to the throttle injection. The drifted flow form is such that a flow core of molten steel is formed along the inner wall of the lower plate 5'' on the throttle side. As shown in Fig. 4, the vertical cross-sectional shape can be a chevron shape, an inverted chevron shape, or a stepped concave shape. point, and in the case of a stepped concave cross section, the center point coincides with the axis of the submerged nozzle (i.e., the axis of the bottomed hole), and the cross-sectional shape is also symmetrical with respect to the axis, so it is a bottomed hole. The flow rate of molten steel flowing down the holes is not evenly distributed to each discharge hole at the bottom of the nozzle.

In other words, as shown in the same figure, when the flow center (arrow) of the injection flow is from the left and the cross-sectional shape of the bottom is chevron-shaped a, the discharge flow rate from the left discharge hole is higher than that from the right side. On the other hand, in the case of an inverted mountain shape b, the discharge flow rate from the right side discharge hole is higher than that of the discharge hole. Further, when the stepped concave type c is used, the discharge amount from the right discharge hole is larger.

In this regard, in the present invention, as shown in FIG. 5, when there is a drift similar to that shown in FIG. When the shape is an inverted mountain shape b, it is the lowest point of the valley. When the shape is a stepped concave shape c or d, the center point is shifted to make the bottom shape eccentric.

In other words, the position of the center of the skewed flow varies depending on the degree of restriction of the sliding nozzle, the length and inner diameter of the immersed nozzle, etc., but the cross-sectional shape of the bottom is such that its center matches the center of the skewed flow. By adopting this shape, as shown in FIG. 5, it becomes possible to make the flow rate discharged from each discharge hole uniform.

In addition, in the case of a stepped concave shape, a cross-sectional shape c that simply aligns the center point with the flow center of the drifted flow has some effect, but as shown in d, a shape with a tapered side wall of the concave part This will further improve its effectiveness. In other words, the center of each shape is eccentric to the axis of the bottomed hole, and the center is aligned with the flow center of the uneven flow.
Furthermore, it is desirable that the bottom shape has a tapered portion that is symmetrical in the left and right directions with respect to the center of each shape.

The cross-sectional shape of the bottom of the immersion nozzle depends on the steel type,
Although it differs depending on the casting speed, etc., it goes without saying that the same effect can be achieved as long as the shape satisfies the above-mentioned conditions.

Next, the effects of the present invention will be explained.

Figure 6 shows the cross-sectional shape of the bottom of the immersion nozzle when the shape according to the present invention [a, c, d in Figure 5] is adopted and the shape according to the conventional method [a, c, d in Figure 4].
The results of examining the distribution of the amount of inclusions in the cast slab in the width direction are shown in the case where [c] is adopted. Note that in the figure, A indicates a case of a chevron-shaped shape, and B indicates a case of a stepped concave shape.

As is clear from the figure, in any case, according to the present invention, almost the same distribution of inclusions can be obtained at each position at the slab corner (center side and opposite flow center side of the drifted flow) and the center of the slab. This confirms that molten steel is evenly discharged from each discharge hole, despite the presence of uneven flow within the immersion nozzle.

On the other hand, in the conventional method, a larger amount of inclusions remains at the slab corner corresponding to the flow center side of the drift, and the influence of the drift is severe, and the influence also extends to the center of the slab, resulting in an overall amount of inclusions. The amount of residual is also considerably higher than that of the present invention.

In addition, even in the present invention, in the case of stepped concave type c,
Although the inclusion distribution condition is slightly inferior to the shape d in which a tapered portion is provided, it is clear that it still has a far superior effect compared to the conventional method.

As is clear from the above explanation, according to the present invention, it is possible to almost eliminate the influence of drifting of molten steel by simply changing the cross-sectional shape of the bottom of the immersion nozzle, which has the shape of the conventional method. Therefore, it is clear that this method has a remarkable effect compared to the conventional measures for preventing the occurrence of drifting, which are accompanied by various technical drawbacks and are expensive.

[Brief explanation of the drawing]

Fig. 1 is a diagram schematically showing the vicinity of the mold in the conventional method, and Fig. 2 is a diagram illustrating measures to prevent the occurrence of drifting by the conventional injection method using a stopper.
Figure 3 is a diagram similarly illustrating measures to prevent the occurrence of drifting by an injection method using a three-layer sliding nozzle, and Figure 4 shows the discharge flow situation in the case of a conventional method using a submerged nozzle with a bottom cross section. Figure 5 shows the discharge flow situation in the case of the immersed nozzle according to the present invention, and Figure 6 shows the distribution of the amount of inclusions in the slab width direction in the bottom cross-sectional shape of the immersed nozzle in the present invention and the conventional method. It is a figure showing the influence on. 1...Immersion nozzle, 2...Mold, 3...Mold flux, 4...Coagulation shell, 5...2
Layered sliding nozzle, 6... Tundish, 7... Stopper, 8... Discharge hole, 9... 3
Layered sliding nozzle.

Claims (1)

[Claims for Utility Model Registration] 1. Having a bottomed hole through which molten steel flows and two or four discharge holes arranged at equal intervals on the bottom side wall,
In an immersion nozzle in which the vertical cross-sectional shape of the bottom of the bottomed hole cut along a vertical plane including a straight line connecting opposing discharge holes is a chevron-shaped, an inverted chevron-shaped, or a stepped concave shape,
Mold immersion that does not cause drifting, characterized in that the apex of the chevron-shaped cross section, the lowest point of the valley of the reverse chevron-shaped cross section, or the center point of the stepped concave cross-section is eccentric to the axis of the bottomed hole. nozzle. 2. When the vertical cross-sectional shape of the bottom of a bottomed hole is a stepped concave shape, a request for utility model registration in which the stepped concave cross section has a tapered portion that is symmetrical to the left and right with respect to a vertical line passing through its center point. The immersion nozzle according to scope 1.