JP6892129B2 - Long nozzle for continuous casting - Google Patents

Description

The present invention relates to a long nozzle for continuous casting.

The long nozzle for continuous casting is formed in a substantially cylindrical shape, and has a nozzle inner hole whose upper and lower ends are opened and a peripheral wall surrounding the nozzle inner hole.
When the molten steel passes through the nozzle inner hole, the temperature of the inner peripheral wall surface side of the peripheral wall becomes relatively higher than that of the outer peripheral wall surface side, and a large temperature difference occurs between the inner and outer walls. In addition, the inner peripheral wall surface side exposed to high-temperature molten steel undergoes thermal expansion. As a result, a compressive stress is generated so as to compress the outer peripheral wall surface side having a relatively small thermal expansion from the inner peripheral wall surface side having a large thermal expansion to the outer side in the radial direction. The compressive stress may cause cracks or damage to the peripheral wall. Further, when the long nozzle injects molten steel from the ladle into the tundish, the vicinity of the lower end opening of the nozzle inner hole may be immersed in the molten steel filled with the tundish. Therefore, not only the compressive stress due to the temperature difference between the inner and outer walls but also the high heat of the immersed portion is applied, the stress is likely to be distorted, and the peripheral wall may be further cracked or damaged.

On the other hand, in the nozzle for continuous casting disclosed in Japanese Patent Application Laid-Open No. 2012-091235, the outer circumference of the lower end portion of the nozzle is cut into a quadratic curve with an arbitrary vertical cross-sectional shape as a base point. Is chamfered. In this way, by thinning the peripheral wall near the lower end opening of the nozzle inner hole, the thermal stress concentration when immersed in molten steel is dispersed, and cracks and cracks on the outer periphery of the lower end portion are prevented.

Japanese Unexamined Patent Publication No. 2012-091235

However, with the shape described in the above document, the thermal shock resistance or stress dispersion is not sufficient, and the durability remains uncertain. Therefore, when the long nozzle for continuous casting is used repeatedly a plurality of times or during use, cracks or cracks may occur in the vicinity of the lower end opening of the nozzle, and the long nozzle for continuous casting may be damaged.

Therefore, the problem to be solved by the present invention is to provide a long nozzle for continuous casting that disperses the stress on the peripheral wall due to the thermal shock when the molten steel is injected or the pressure when the molten steel is immersed in the molten steel. is there.

The long nozzle for continuous casting according to claim 1 includes a peripheral wall portion formed in a substantially cylindrical body and a peripheral wall portion.
Surrounded by the peripheral wall portion, it has a nozzle inner hole provided for an upper end opening and a lower end opening.
At the lower part of the peripheral wall portion, a skirt having a divergent shape is provided so that the inner and outer diameters of the peripheral wall portion gradually increase as it approaches the lower end opening end surface.
The vertical cross-sectional view shape of the hem portion curved in an arc shape so as to project toward the inner peripheral wall surface is formed so that the radius of curvature on the outer peripheral wall surface side is larger than that on the inner peripheral wall surface side.
The wall thickness, which is the difference between the outer diameter and the inner diameter of the hem, gradually decreases as it approaches the lower end opening end surface .

According to the long nozzle for continuous casting according to the present invention, the lower portion of the peripheral wall portion is formed so as to have a divergent shape in which the inner and outer diameters of the peripheral wall portion gradually increase as it approaches the lower end opening end surface, that is, a so-called trumpet shape. As a result, the stress concentration on the peripheral wall can be relaxed, and the flow velocity of the molten steel flow along the inner peripheral wall surface can be reduced in the vicinity of the lower end opening of the nozzle inner hole.

It is a cross-sectional view shape along the axial direction of the long nozzle for continuous casting according to the first embodiment, and is a vertical cross-sectional view showing an outline of the configuration. It is a vertical cross-sectional view which shows the cross-sectional view shape of the hem part along the axial direction of the long nozzle for continuous casting which concerns on 1st Example. It is a vertical cross-sectional view which shows the cross-sectional view shape of the hem part along the axial direction of the long nozzle for continuous casting which concerns on 2nd Example. It is a pressure distribution diagram which shows the experimental result which compared the long nozzle for continuous casting which concerns on this Example, and the conventional example. It is explanatory drawing which shows the experimental result which compared the long nozzle for continuous casting which concerns on this Example, and the conventional example.

The present invention relates to a long nozzle for continuous casting. As shown in FIG. 1, the continuous casting long nozzle 10 is surrounded by a nozzle body 10a formed in a substantially cylindrical body and a peripheral wall portion 11 of the nozzle body 10a, and has an upper end opening 12a and a lower end opening 12b. It has an inner hole 12. A mortar-shaped mounting portion 13 is connected to the upper end of the peripheral wall portion 11 of the nozzle body 10a, and the bottom opening of the mounting portion 13 communicates with the upper end opening 12a of the nozzle inner hole 12.
Then, as shown in FIG. 2 or 3, the portion where the present invention is implemented is the lower portion of the peripheral wall portion 11 of the nozzle body 10a, particularly near the lower end opening 12b of the nozzle inner hole 12. Examples of the present invention are shown below.

The long nozzle 10 for continuous casting according to this embodiment will be described with reference to the attached drawings. FIG. 2 is a partial vertical cross-sectional view showing a vertical cross-sectional view shape of the long nozzle 10 for continuous casting according to the present embodiment along the vertical direction.

As shown in FIG. 1, the long nozzle 10 for continuous casting has a nozzle body 10a having a substantially cylindrical shape. The peripheral wall portion 11 of the nozzle body 10a surrounds a nozzle inner hole 12 having an upper end opening 12a and a lower end opening 12b. The upper part of the peripheral wall 11a and the upper part of the nozzle inner hole 12 are formed in a substantially straight tubular shape. As shown in FIG. 2, the peripheral wall lower portion 11b is formed in a divergent shape by gradually increasing the inner and outer diameters of the peripheral wall portion 11 as it approaches the end surface of the lower end opening 12b of the nozzle inner hole 12 from a predetermined height. There is. The portion formed in the divergent shape is referred to as a hem portion 20. In accordance with the degree of expansion of the hem portion 20, the diameter of the nozzle inner hole 12 also gradually increases as it approaches the end surface of the lower end opening 12b, and exhibits a divergent shape.

As shown in FIG. 2, the hem portion 20 is formed in an arc shape in which the vertical cross-sectional view shape is curved toward the inner peripheral wall surface 21 side and protrudes. That is, the peripheral wall lower portion 11b including the hem portion 20 is formed so as to have a so-called "trumpet shape" that gently spreads from a predetermined height toward the end surface of the lower end opening 12b. By increasing the radius of curvature of the hem portion 20 and gently curving it in this way, the molten steel flow can flow along the inner peripheral wall surface, and is shown in FIGS. 4 (b) to 4 (d), for example. As will be described later, stress concentration due to heat can be relaxed rather than chamfering the corner portion of the lower end opening 12b on the inner peripheral wall surface 21 side.
The vertical cross-sectional view shape of the hem portion 20 is not limited to the trumpet shape curved in an arc shape, and may be a tapered shape in which the gradient becomes linear toward the end surface of the lower end opening 12b.

The wall thickness, which is the difference between the outer diameter and the inner diameter of the peripheral wall portion 11 and the hem portion 20, is kept constant at a predetermined thickness from the upper portion 11a of the peripheral wall portion to the end surface of the lower end opening 12b. Thereby, the structural strength of the peripheral wall lower portion 11b including the hem portion 20 can be improved.

The long nozzle 10A for continuous casting according to this embodiment will be described with reference to FIG. 3 attached. FIG. 3 is a partial vertical cross-sectional view showing a vertical cross-sectional view shape of the long nozzle 10A for continuous casting according to the present embodiment along the vertical direction.

The long nozzle 10A for continuous casting according to this embodiment and the long nozzle 10 for continuous casting described in the first embodiment have different wall thicknesses at the hem portion 20A. That is, the wall thickness of the hem portion 20 according to the first embodiment is kept constant at a predetermined thickness, whereas the wall thickness of the hem portion 20A according to the present embodiment is reduced to the end surface of the lower end opening 12b. It is formed so that it becomes thinner and thinner as it approaches.

As shown in FIG. 3, in the vertical cross-sectional view shape of the hem portion 20A, the radius of curvature on the outer peripheral wall surface 22 side is larger and gentler than that on the inner peripheral wall surface 21 side of the hem portion, so that the outer peripheral wall surface 22 side, that is, While suppressing the change in the outer diameter of the hem portion 20, the expansion degree of the inner peripheral wall surface 21 side, that is, the nozzle inner hole 12 can be increased, and the diameter of the lower end opening 12b can be increased. Therefore, the flow velocity concentration in the vertical direction of the molten steel flow can be relaxed as compared with the hem portion 20 described in the first embodiment.

Next, the experiment of the first experiment according to this example will be described. In the first experiment, a model of long nozzles 10 and 10A for continuous casting was prepared in which the hem portions 20 and 20A were formed so as to have the same configuration as that of the above embodiment, respectively, and as a comparative example, the peripheral wall portion 11 was prepared as before. Is formed straight up to the end face of the lower end opening 12b, and further, the corner portion on the inner peripheral wall surface 21 side of the lower end opening 12b is chamfered to form an arc shape having a radius of curvature smaller than that of the hem portions 20 and 20A described in the examples. Three examples formed in the above were prepared, and the thermal stress distribution when molten steel was poured into the nozzle inner hole 12 was simulated. FIG. 4 shows a pressure distribution diagram showing an outline of the simulation results.

The simulation conditions shall indicate the state when the long nozzles 10, 10A for continuous casting, etc. are preheated at 700 ° C. and molten steel at 1550 ° C. is injected into the nozzle inner hole 12 for 1 minute.
FIG. 4 shows the thermal stress distribution on the vertical cross-sectional view in which the simulation area 30 shown by the dotted line in FIG. 1 is partially enlarged. The thick line in the figure shown in FIG. 4 is the inner peripheral wall surface which is the boundary between the cross section of the hem peripheral wall and the nozzle inner hole 12.
Further, in the thermal stress distribution, the portion where the hatching interval is narrow is the portion where the pressure related to the thermal stress is higher. The portion indicated by the dense line descending to the right is referred to as the high-pressure portion 31, the portion indicated by the downward-sloping straight line is referred to as the medium-pressure portion 32, and the portion indicated by the downward-sloping straight line is referred to as the low-pressure portion 33.
Based on these conditions and the legend of the figure, FIGS. 4 (a) to 4 (f) will be described below.

FIG. 4A shows the hem portion of a conventional long nozzle for continuous casting, in which the corner portion on the inner peripheral wall surface side of the lower end opening is at a right angle.
FIG. 4B is a hem portion in which the corner portion on the inner peripheral wall surface 21 side of the lower end opening 12b is chamfered so that the radius of curvature is 5 mm.
FIG. 4C is a hem portion in which the corner portion on the inner peripheral wall surface 21 side of the lower end opening 12b is chamfered so that the radius of curvature is 20 mm.
FIG. 4D is a hem portion in which the corner portion on the inner peripheral wall surface 21 side of the lower end opening 12b is chamfered so that the radius of curvature is 40 mm.
FIG. 4 (e) is the hem portion 20 shown in the first embodiment.
FIG. 4 (f) is the hem portion 20A shown in the second embodiment.

In each of the pressure distribution conditions related to the thermal stress inside the wall of the hem portion shown in FIGS. 4 (a) to 4 (d), the high-pressure portion 31 is distributed along the inner peripheral wall surface 21, and the medium-pressure portion 31 is distributed. 32, a large high-pressure portion 31 is distributed on the outer peripheral wall surface side with the low-pressure portion 33 interposed therebetween. In particular, the high-pressure portion 31 distributed to the outer peripheral wall surface side corner portion as shown in FIG. 4C is a major cause of the outer peripheral wall surface side corner portion being chipped.

On the other hand, in the pressure distribution state related to the thermal stress inside the wall of the hem portion 20 shown in FIG. 4 (e), the elongated high-pressure portion 31 is distributed along the inner peripheral wall surface 21 and is distributed in a substantially J shape. The high-pressure portion 31 is distributed on the outer peripheral wall surface 22 side of the low-pressure portion 33 and the medium-pressure portion 32 surrounding the low-pressure portion 33.
Here, it is noted that the area of the high-voltage portion 31 on the outer peripheral wall surface 22 side is very small as compared with FIGS. 4A to 4D.
The high-pressure portion 31 on the inner peripheral wall surface 21 side can be inferred to be the pressure caused by the molten steel flow compressing the inner peripheral wall surface 21. It can be inferred that the portion where the stress is concentrated on the outer peripheral wall surface 22 side is the high pressure portion 31 on the outer peripheral wall surface 22 side due to the reaction to the compression pressure on the inner peripheral wall surface 21 side. If molten steel is further poured in this state, cracks may occur or damage may occur centering on the high-pressure portion 31 on the outer peripheral wall surface 22 side, but the outer peripheral wall surface is compared with FIGS. 4 (a) to 4 (d). The area of the high-pressure portion 31 on the 22 side is very small, and the medium-pressure portion 32 is widely distributed so as to surround the high-pressure portion 31. Therefore, the stress of the hem portion 20 according to the first embodiment shown in FIG. 4 (e) is relaxed as compared with the experimental examples of FIGS. 4 (a) to 4 (d).
As a result, it can be inferred that the hem portion 20 is less likely to be damaged and has improved durability. The improvement in durability has been confirmed in the second experiment described later.
Further, in the hem portion 20A shown in FIG. 4 (f), the area of the high-pressure portion 31 on the outer peripheral wall surface 22 side is larger than that in FIGS. 4 (a) to 4 (e) as in the case of FIG. 4 (e). It is very narrow, and the medium pressure portion 32 and the low pressure portion 33 are widely distributed so as to surround the high pressure portion 31. Therefore, the stress of the hem portion 20A according to the second embodiment shown in FIG. 4 (f) is relaxed as compared with the experimental examples of FIGS. 4 (a) to 4 (e).
As a result, it can be inferred that the hem portion 20A has a low risk of breakage and has improved durability. The improvement in durability has been confirmed in the second experiment described later.

According to the above-mentioned first experiment shown in FIG. 4, the shapes of the hem portions 20 and 20A are formed into a divergent shape in which the inner and outer diameters of the peripheral wall 11 gradually increase as the lower end openings 12b end faces, that is, a so-called trumpet shape. As a result, it was confirmed that the stress concentrated on the outer peripheral wall surface 22 side was relaxed as compared with the lower end opening shape shown in FIGS. 4 (a) to 4 (d). As a result, it is possible to prevent stress from concentrating on the outer peripheral wall surface 22 side, so that it is possible to improve the durability of the long nozzle 10 and prevent it from being damaged during use.

Subsequently, the second experiment was conducted. In the second experiment, out of the above six examples, long nozzles for continuous casting corresponding to FIGS. 4 (c) to 4 (f) were prepared, and an experiment related to durability was conducted. The result of the second experiment is shown in FIG.
In the second experiment, the long nozzle is preheated at 1200 ° C. and repeatedly immersed in molten steel at 1550 ° C. to confirm the presence or absence of cracks.
As shown in FIG. 5, in the experiments a and b corresponding to FIGS. 4 (c) and 4 (d), cracks were generated in the fifth immersion.
On the other hand, in Experiment C corresponding to the first example, cracks were generated in the seventh immersion, and in Experiment D corresponding to the second example, cracks were generated in the ninth immersion.
As a result, it was confirmed that the shapes of the hem portions 20 and 20A described in the first embodiment and the second embodiment can improve the durability of the tips of the long nozzles 10 and 10A.

According to the continuous casting nozzles 10 and 10A according to the present embodiment, the hem portions 20 and 20A have a divergent shape in which the inner and outer diameters of the peripheral wall 11 gradually increase as they approach the end surface of the lower end opening 12b, that is, a so-called trumpet shape. Formed. It is preferable that the hem portions 20 and 20A have a radius of curvature as large as possible and are gently curved. By forming the curved shape in this way, it is possible to alleviate the concentration of thermal stress inside the peripheral walls of the hem portions 20 and 20A.

10, 10A ... Long nozzle for continuous casting, 10a ... Nozzle body,
11 ... Circumferential wall, 11a ... Upper peripheral wall, 11b ... Lower peripheral wall,
12 ... Nozzle inner hole, 12a ... Upper end opening, 12b ... Lower end opening,
13 ... Mounting part,
20, 20A ... hem, 21 ... inner wall surface, 22 ... outer wall surface,
30 ... Simulation area, 31 ... High pressure part, 32 ... Medium pressure part, 33 ... Low pressure part.

Claims (1)

The peripheral wall formed in a substantially cylindrical body and
Surrounded by the peripheral wall portion, it has a nozzle inner hole provided for an upper end opening and a lower end opening.
At the lower part of the peripheral wall portion, a skirt having a divergent shape is provided so that the inner and outer diameters of the peripheral wall portion gradually increase as it approaches the lower end opening end surface.
The vertical cross-sectional view shape of the hem portion curved in an arc shape so as to project toward the inner peripheral wall surface is formed so that the radius of curvature on the outer peripheral wall surface side is larger than that on the inner peripheral wall surface side.
A long nozzle for continuous casting , wherein the wall thickness, which is the difference between the outer diameter and the inner diameter of the hem portion, gradually decreases as it approaches the lower end opening end surface.

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