Submerged nozzle

Abstract

The present invention provides a submerged nozzle that can increase the molten steel flow velocity in a mold width direction, without increasing size, in order to allow a molten steel flow to reach near ends in the mold width direction while homogenizing the molten steel flow, which was discharged from a discharge hole. In the present invention, the submerged entry nozzle is such that the shape of a region from an arbitrary position, above a branching section 5 where a discharge hole 4 branches off from an inner hole 3, to the branching section 5 is such that the horizontal cross-sectional area of ​​the inner hole 3 gradually decreases downwards, and the B / A ratio, which is a ratio of the width B of the inner hole 3 at the branching section 5 to the maximum width A of the discharge hole 4, is set within a range of 0.2 to 0.95.

Description

Immersion nozzle

[0001] The present invention relates to an immersion nozzle used for injecting molten steel discharged from the bottom of a tundish into a mold in the continuous casting of steel.

[0002] In the continuous casting of steel, the flow characteristics of molten steel in the mold not only have a great influence on the continuous casting process and the quality of the slab, but also affect the operational safety regarding the formation of the shell in the mold. Therefore, conventionally, regarding the flow pattern of molten steel from the immersion nozzle into the mold, many immersion nozzle structures have been disclosed in order to optimize the uniformity, dispersibility, etc. according to individual casting conditions.

[0003] For example, in Patent Document 1, the shape of the inner hole of the discharge hole in the longitudinal cross-section of the immersion nozzle passing through the center of the immersion nozzle and the center of the discharge hole is such that the inner hole of the discharge hole gradually decreases in diameter in a curve from the starting point of the discharge hole towards the end, and the gradually decreasing diameter curve has the inner shape of the discharge hole represented by the diameter of the longitudinal cross-section of the immersion nozzle in at least a part or all of the discharge hole. An immersion nozzle is disclosed. By using this immersion nozzle, it is said that the molten steel flow discharged from the discharge hole can be made uniform.

[0004] Further, in Patent Document 2, an immersion nozzle is disclosed in which the inner wall surfaces of a pair of symmetric discharge holes that discharge molten steel laterally from the side surface of the straight body part are parallel to the longitudinal direction of the central axis of the discharge hole and have a length of 45 mm or more. By using this immersion nozzle, it is possible to stably form the molten steel flow required near the molten steel surface (upper surface of molten steel) at the end of the mold and near the molten steel surface (upper surface of molten steel) of the entire mold. Particularly, in continuous casting in which molten steel is injected into a wide mold with a width dimension of 2000 mm or more, it is said that the molten steel flow required near the molten steel surface (upper surface of molten steel) at the end of the mold and near the molten steel surface of the entire mold can be stably formed.

[0005] Japanese Patent No. 4665056 Japanese Unexamined Patent Application Publication No. 2007 - 326144

[0006] In continuous casting of steel, in addition to homogenizing the molten steel flow as described above, it is necessary to stably form an appropriate molten steel flow at each location within the mold in order to improve or maintain high quality steel and to avoid risks such as breakout. However, especially with wide molds, it can be difficult to form a sufficient molten steel flow that reaches the ends in the width direction. For example, in the case of a structure whose main purpose is to homogenize the molten steel flow discharged from the discharge hole, as in Patent Document 1, although the velocity distribution of the molten steel at the cross-section of the discharge hole is homogenized, the straight-line velocity of the molten steel often decreases along with the homogenization of the molten steel flow velocity at such a cross-section of the discharge hole. Therefore, it may not be possible to reach the vicinity of the mold ends in the width direction within the mold in sufficient or necessary amounts of molten steel flow.

[0007] On the other hand, according to the structure of Patent Document 2, it is possible to make the molten steel flow discharged from the discharge hole of the immersion nozzle reach near the mold edge in the width direction within the mold. However, the structure of Patent Document 2 requires both lengthening the discharge hole portion of the immersion nozzle and enlarging the area around the discharge hole, which can lead to problems such as increased weight of the immersion nozzle, increased risk of nozzle breakage, increased cost of the immersion nozzle, and obstruction of reverse flow formation within the mold.

[0008] Therefore, the problem that the present invention aims to solve is to provide an immersion nozzle that can increase the molten steel flow velocity in the mold width direction without increasing the size, in order to homogenize the molten steel flow discharged from the discharge hole and allow the molten steel flow to reach near the end of the mold width direction.

[0009] According to one aspect of the present invention, the following immersion nozzle is provided: An immersion nozzle having a molten steel inlet at its upper end, and having discharge holes symmetrically on both sides that branch off from near the lower end of an inner bore which is a molten steel passage path extending downward from the molten steel inlet, wherein the region from an arbitrary position above the branching point where the discharge holes branch off to the branching point has a shape in which the horizontal cross-sectional area of ​​the inner bore gradually decreases downward, and in a cross-sectional view taken by a plane perpendicular to the central axis of the molten steel passage direction of the inner bore and the central axis of the molten steel discharge direction of the discharge holes, and including the central axis of the molten steel passage direction of the inner bore, the B / A ratio, which is the ratio of the width B of the inner bore at the branching point to the maximum width A of the discharge hole, is 0.2 or more and 0.95 or less.

[0010] According to the immersion nozzle of the present invention, the molten steel flow velocity in the mold width direction can be increased without increasing the size, in order to homogenize the molten steel flow discharged from the discharge hole and to allow the molten steel flow to reach near the end in the mold width direction.

[0011] A cross-sectional view of an immersion nozzle, which is one embodiment of the present invention (cross-sectional view by a plane including the central axis of the molten steel passage direction of the inner bore and the central axis of the molten steel discharge direction of the discharge hole). Conceptual diagram showing examples of single and double vortex shapes formed in the immersion nozzle. Conceptual diagram showing backstep flow. Cross-sectional view of I-I in Figure 1 (cross-sectional view by a plane perpendicular to the plane including the central axis of the molten steel passage direction of the inner bore and the central axis of the molten steel discharge direction of the discharge hole, and also including the central axis of the molten steel passage direction of the inner bore). Simulation results by two-dimensional CFD (Computational Fluid Dynamics) (velocity contour plot). Perspective view of the cross-sectional view of Figure 1. Simulation results of molten steel flow when the B / A ratio is changed. Observation plane of the simulation results in Figure 7A. Experimental results of a water experiment (discharge hole angle: downward 15 degrees). Experimental results of another water experiment (discharge hole angle: downward 15 degrees). Measurement results of water surface flow velocity at each observation point in the water experiment in Figure 8B (discharge hole angle: downward 15 degrees). Experimental results of another water experiment (discharge hole angle: upward 15 degrees). Figure 8D shows the measurement results of the water surface flow velocity at each observation point in the water experiment (discharge hole angle: 15 degrees upward). Diagram showing the observation position when the mold flow was calculated using CFD. Results of calculating the mold flow using CFD in a planar tapered shape (velocity contour plot). Results of calculating the mold flow using CFD in a planar tapered shape (graph of values ​​at the observation position shown in Figure 9). Graph showing the relationship between the B / A ratio and the area ratio of the flow channel cross-sectional area. Results of calculating the mold flow using CFD in an inverted frustoconical shape (graph of values ​​at the observation position shown in Figure 9). Results of calculating the mold flow using CFD with varying height h in a planar tapered shape (graph of values ​​at the observation position shown in Figure 9). Results of calculating the mold flow using CFD with varying well depth d in a planar tapered shape (graph of values ​​at the observation position shown in Figure 9).

[0012] Figure 1 shows a cross-sectional view of the overall configuration of an immersion nozzle, which is one embodiment of the present invention. The immersion nozzle 1 has a molten steel inlet 2 at its upper end for introducing molten steel discharged from the bottom of a tundish (not shown), and discharge holes 4 are symmetrically provided on both sides, branching off from near the lower end of an inner hole 3, which is a molten steel passage path extending downward from the molten steel inlet 2. Here, the body 11 of the immersion nozzle 1 is composed of an upper flange portion 111 that is joined to a lower nozzle, etc. (not shown) attached to the bottom of the tundish, and a cylindrical straight body portion 112 that extends downward from the upper flange portion 111, with the discharge holes 4 formed in this cylindrical straight body portion 112.

[0013] In conventional immersion nozzles, which have a discharge hole 4 formed in a cylindrical straight section 112, it has been difficult to increase the molten steel flow velocity in the mold width direction while homogenizing the molten steel flow using conventional techniques. In contrast, the inventors have found that by forming a twin vortex at the branching section 5 where the discharge hole 4 branches off from the inner hole 3, it is possible to increase the molten steel flow velocity in the mold width direction while homogenizing the molten steel flow compared to a single vortex.

[0014] Single vortex and double vortex refer to the shape of the vortex formed at the branching section 5, and conceptual examples of these vortex shapes are shown in Figure 2. Here, Figure 2 is a vertical cross-section of the inner bore when the discharge hole is viewed from the outside of the immersion nozzle, and corresponds to the I-I cross-section in Figure 1. In other words, Figure 1 shows a cross-sectional view by a plane that includes the central axis of the molten steel passage direction of the inner bore and the central axis of the molten steel discharge direction of the discharge hole, and Figure 2 (the I-I cross-section in Figure 1) shows a cross-sectional view by a plane that is perpendicular to the above plane and includes the central axis of the molten steel passage direction of the inner bore. Among the vortex shapes shown in Figure 2, the vortex shape shown in Figure (a) is called a single vortex, and the vortex shape shown in Figure (b) is called a double vortex. As will be described in detail later, the immersion nozzle according to the present invention can guarantee the formation of double vortices as shown in Figures (c) and (d).

[0015] The inventors focused on a phenomenon called backstep flow as a means of forming such twin vortices. In general fluid dynamics, backstep flow is a turbulent flow phenomenon in which vortices are generated in the opposite direction to the original flow direction at locations where there is a step in the flow path, that is, where the cross-sectional area of ​​the flow path rapidly expands, as conceptually shown in Figure 3.

[0016] In this invention, in order to form such a backstep flow, as illustrated in Figure 4, the width B of the inner bore 3 at the branching section 5 where the discharge hole 4 branches off from the inner bore 3 is made smaller than the maximum width A of the discharge hole 4, thereby creating a narrowed portion in the molten steel flow path. Here, Figure 4 is a cross-sectional view taken along line I-I in Figure 1. That is, Figure 4 shows a cross-sectional view taken along a plane that is perpendicular to the plane containing the central axis of the molten steel passage direction of the inner bore 3 and the central axis of the molten steel discharge direction of the discharge hole 4, and also contains the central axis of the molten steel passage direction of the inner bore 3 (hereinafter, this cross-sectional view is referred to as the "specific cross-sectional view"). The maximum width B of the discharge hole 4 and the width B of the inner bore at the branching section are the width dimensions (horizontal length) in this specific cross-sectional view.

[0017] As shown in Figure 4, the cross-sectional area of ​​the inner bore 3 decreases in the constricted portion, so the flow velocity of the molten steel increases in the constricted portion. Then, the moment the molten steel flow with increased velocity enters the discharge hole 4, a rapid expansion of the flow path occurs, causing a backstep flow and forming a twin vortex. In other words, in this embodiment, in the specific cross-sectional view shown in Figure 4, the B / A ratio, which is the ratio of the width B of the inner bore at the branching portion 5 to the maximum width A of the discharge hole, is made less than 1, thereby forming a twin vortex at the branching portion 5.

[0018] Figure 5 shows the simulation results of observing a backstep flow (double vortex) using two-dimensional CFD (Computational Fluid Dynamics). In this simulation, a steady-state calculation was performed using a standard k-ε model with a flow path width of 70 mm from inlet to outlet, a molten steel velocity of 1.8 m / s at the inlet, a B / A ratio of 0.6 (i.e., a narrowing section width of 42 mm). As shown in the velocity contour plots of Figure 5(a) (constant flow path shape) and Figure 5(b) (gradually narrowing flow path shape), the flow velocity increased in the narrowing section in both shapes. However, after that, as shown in Figures 5(c) and 5(d), the velocity vectors differed in the section where the flow path rapidly expanded after the narrowing section. As a result, as shown in Figure 5(e), the size of the vortices in the backstep flow differed. That is, larger vortices were generated in the shape of Figure 5(b), where the flow path gradually narrows.

[0019] As described above, the condition for forming a backstep flow is the presence of a rapidly expanding section. Applying this to this embodiment, by making the B / A ratio less than 1, a rapidly expanding section is formed below the branching section 5, with the branching section 5 as the boundary. The shape of the inner bore above the branching section 5 is not a condition for forming a backstep flow. However, from the simulation results shown in Figure 5, it was found that the shape of the region from any position above the branching section 5 to the branching section 5 is preferably such that the horizontal cross-sectional area of ​​the inner bore gradually decreases downwards. That is, as illustrated in Figure 5(a), if the horizontal cross-sectional area of ​​the inner bore, which is the flow path, is constant, the velocity distribution in the rapidly expanding section of the flow path tends to be low and flat. In contrast, as illustrated in Figure 5(b), if the horizontal cross-sectional area of ​​the inner bore, which is the flow path, gradually decreases downwards, the velocity distribution in the rapidly expanding section of the flow path tends to be bell-shaped and faster. Furthermore, a shape in which the horizontal cross-sectional area of ​​the inner bore gradually decreases downwards is effective for reasons such as being able to further increase the flow velocity in the branching section 5, widening the region where backstep flow occurs, and lengthening the reattachment distance of the backstep flow.

[0020] Examples of shapes in which the horizontal cross-sectional area of ​​the inner bore gradually decreases downwards include a planar tapered shape having a pair of opposing planar tapers 6 formed so that the width of the inner bore 3 gradually decreases in a specific cross-sectional view as shown in Figure 4, as well as an inverted frustoconical shape (hereinafter referred to as "inverted frustoconical shape"). In particular, in the case of the planar tapered shape, the flow velocity distribution tends to become bell-shaped and increase in speed. Furthermore, regarding the degree of reduction in the horizontal cross-sectional area that changes as the inner bore moves downwards, in the case of the inverted frustoconical shape, the shape specified from the viewpoint of the need to secure the total molten steel discharge capacity of the immersion nozzle and ease of manufacture tends to increase the degree of reduction, and the allowable range of the B / A ratio tends to narrow. Therefore, a planar tapered shape with fewer such restrictions is preferable. Note that while the planar tapered shape is shown in two dimensions in Figures 1 and 4, its three-dimensional shape is shown in Figure 6. That is, Figure 6 is a perspective view of the cross-sectional view of Figure 1, and Figure 6 shows one of the pair of planar tapers 6. Furthermore, as shown in Figures 1 and 6, in the illustrated immersion nozzle 1, the vertical position of the lower end surface 31 of the inner bore 3 is lower than the vertical position of the lower end 41 of the discharge hole 4 on the inner bore 3 side. As a result, a well (recess) 7 is formed with the lower end surface 31 of the inner bore as its bottom surface. In the following explanation, well depth refers to the vertical length from the lower end surface 31 of the inner bore to the lower end 41 of the discharge hole. A through hole can also be provided at the bottom of the well 7, but in this case as well, the well depth is defined as the vertical length from the lower end surface 31 of the inner bore to the lower end 41 of the discharge hole.

[0021] Figure 7A shows the simulation results for a well with an inner bore diameter and discharge port diameter of 70 mm, a well depth of 20 mm, a molten steel flow velocity of 1 T / min, a B / A ratio of 1 to 0.5, and discharge port angles of 15 degrees downward, horizontal, and 15 degrees upward. The observation plane for the simulation results shown in Figure 7A is the same as shown in Figure 7B and corresponds to the specific cross-sectional view described above. Figure 7A shows the trajectory of the molten steel flow on this observation plane. From the simulation results in Figure 7A, it can be confirmed that twin vortices develop as the B / A ratio decreases.

[0022] Figure 8A shows the experimental results of a water experiment with an inner bore diameter and discharge hole diameter of 50 mm, a well depth of 20 mm, and a discharge hole angle of 15 degrees downward. When observing the trajectory of the water discharged from the discharge hole in the water experiment, as shown in Figure 8A, the conventional product (B / A ratio = 1) showed a lot of splashing as a result of forming a single vortex. In contrast, the product of the present invention (B / A ratio = 0.6) showed less splashing as a result of forming a double vortex, and it was confirmed that it drew a single parabolic trajectory. The lower part of Figure 8A shows perspective views corresponding to the cross-sectional view in Figure 1 for the conventional product and the product of the present invention, respectively.

[0023] Figure 8A shows the results of a water experiment conducted after the initial water experiment, where the immersion nozzle was submerged and the water flow rate was set to an equivalent of 1.6 T / min for molten steel. Figure 8C shows the results of measuring the water surface velocity using a propeller flow meter in this experiment. The cross-sectional size of the water tank, which simulates a mold, is 1650 mm wide and 200 mm thick. The observation points on the water surface were eight points (four on each side) divided into four sections relative to the discharge direction when viewed from the central axis of the immersion nozzle located in the center of the water tank simulating a mold, and two points in the center of the gap between the immersion nozzle and the mold thickness. Compared to the conventional product, an increase in water surface velocity was observed at all observation points with the present invention. Figures 8D and 8E show the results of the same water experiment conducted with the discharge hole angle set upward to 15 degrees. Even when the discharge hole angle was changed to an upward direction, an increase in water surface velocity was observed with the present invention compared to the conventional product, and the vertical fluctuations of the water surface were also gentler.

[0024] Figure 9 shows the observation positions used for horizontal evaluation when calculating mold flow using CFD. From the perspective of the mold thickness direction, the maximum flow velocity in the X direction was observed on the plane at the left and right 1 / 4 positions when viewing the mold width direction from left to right, and this was used as an evaluation index. Figure 10 shows the CFD calculation results as a flow velocity contour plot. The conditions were: inner bore diameter and discharge hole diameter both 70 mm, well depth 20 mm, molten steel flow velocity 1, 2, 3 T / min, B / A ratio 1 to 0.2, discharge hole angle downward 15 degrees, mold width 2000 mm, and mold thickness 260 mm. The plane on which the flow velocity contour plot was drawn was the central cross-section in the mold thickness direction. From Figure 10, it can be observed that the discharge flow velocity increases as the B / A ratio decreases, and the discharge flow reaches the edges of the mold. Figure 11 shows the values ​​at the observation positions shown in Figure 9. Figure 11 shows that as the B / A ratio decreases, an increase in flow velocity at the observation point can be observed.

[0025] Here, it was observed that when the B / A ratio falls below 0.5, the velocity contour plot in Figure 10 changes significantly, and the values ​​at the observation position in Figure 11 also change. This is because making the B / A ratio too small causes strong flow separation from the wall when the flow exits the discharge hole from the branching section, further altering the flow shape. Therefore, it is preferable to have a B / A ratio of 0.5 or higher, and more preferable to have a B / A ratio of 0.6 or higher. Also, as shown in Figure 12, when the internal bore shape (referring to the shape of the region from any position above the branching section 5 to the branching section 5; the same applies hereinafter) is a planar tapered shape, at a B / A ratio of 0.5, the area ratio becomes 0.6 compared to the flow path cross-sectional area when the original B / A ratio was 1. Therefore, from the viewpoint of considering the operating conditions in an actual furnace, it is preferable to have a B / A ratio of 0.5 or higher, and more preferable to have a B / A ratio of 0.6 or higher. This is because, in typical continuous casting equipment, flow control devices such as stoppers and sliding gates are installed upstream of the immersion nozzle, and these flow control devices are designed to operate at an area opening of around 50% to 75%. In other words, if the B / A ratio is less than 0.5, the flow path cross-sectional area will become less than 0.6 times the original B / A ratio of 1.0, and even if the area opening of the flow control device is set to 100%, it may not be possible to obtain the original flow rate. Furthermore, as shown in Figure 12, the decrease in flow path cross-sectional area when the bore shape is an inverted frustoconical shape is greater than when it is a planar tapered shape, so when the bore shape is an inverted frustoconical shape, it is preferable to set the B / A ratio to 0.8 or higher.

[0026] Figure 13 shows the results of CFD calculations at the observation position shown in Figure 9, when the bore shape is an inverted frustoconical shape. The conditions are: bore diameter and discharge hole diameter are both 70 mm, well depth 20 mm, molten steel flow velocity 1.2 T / min, B / A ratio 1 to 0.6, discharge hole angle downward 15 degrees, mold width 2000 mm, mold thickness 260 mm. It can be observed that the flow velocity at the observation position increases as the B / A ratio decreases, but for the reasons mentioned above, a planar tapered bore shape is preferable.

[0027] Figure 14 shows the results of a CFD calculation at the observation position shown in Figure 9, where the internal bore shape is a planar tapered shape, the B / A ratio is fixed at 0.9, and the height of the planar tapered shape is h. Other conditions are: internal bore diameter and discharge hole diameter are both 70 mm, well depth 20 mm, molten steel flow velocity 1, 2, 3 T / min, discharge hole angle downward 15 degrees, mold width 2000 mm, and mold thickness 260 mm. Here, the height h of the planar tapered shape is, in other words, the vertical length of the region having a planar tapered shape (a shape in which the horizontal cross-sectional area of ​​the internal bore gradually decreases downwards), as shown in Figure 1.

[0028] Due to geometric constraints, h=0 is not possible, so in Figure 14, the value of a B / A ratio of 1.0 is plotted at the position where h=0. This CFD calculation was performed in the range of h from 15 to 150 mm, and an increase in flow velocity at the observation position was observed. It can be expected that a similar effect will occur even if h is greater than 150 mm, but this means that even if the appearance of the immersion nozzle body 11 (brick) is the same, the volume of the internal bore flow space will decrease, which means that the unit weight of the brick will increase. In other words, the smaller the value of h, the more the increase in the unit weight of the brick will be suppressed. That is, if we consider reducing the amount of brick material used and thus reducing costs, we would like h to be greater than zero and as small as possible, but looking at the shape of h=15 mm in the lower part of Figure 14, the lower end surface of the internal bore approaches an acute angle, and if h is made even smaller, the lower end surface of the internal bore will form a corner. Physically, it is possible to make h an even smaller value, but since the shape of the inner bore is the shape of the mold used to form the brick, if h is made too small, a corner will be created at the end of the mold that forms the lower end of the inner bore, which is undesirable from the standpoint of mold maintenance. Therefore, it is preferable that h be between 15 mm and 150 mm.

[0029] Figure 15 shows the CFD results investigating the effect of well depth d, with the B / A ratio fixed at 0.8 and h at 100 mm. Other conditions were: inner bore diameter and discharge hole diameter both 70 mm, molten steel flow rate 1, 2, 3 T / min, discharge hole angle downward 15 degrees, mold width 2000 mm, and mold thickness 260 mm. From these results, it was confirmed that the presence or absence of a well does not affect the acquisition of the effects of the present invention, and that the desired effect can be obtained with a well of 50 mm or less. The bottom of the inner bore can be formed in a well shape (concave), a flat shape, or a convex shape.

[0030] From the CFD results above, an increase in discharge velocity was confirmed when the B / A ratio was between 0.2 and 0.95. Specifically, by making the bore shape such that the horizontal cross-sectional area of ​​the bore gradually decreases downwards, and setting the B / A ratio between 0.2 and 0.95, it was confirmed that the molten steel flow velocity in the mold width direction can be increased without increasing the size as in the structure of Patent Document 2, in order to homogenize the molten steel flow discharged from the discharge hole and allow the molten steel flow to reach near the end in the mold width direction. Furthermore, considering the applicability in an actual furnace from the rate of decrease in the flow path cross-sectional area, it is preferable that the lower limit of the B / A ratio be 0.6 when the bore shape is a flat tapered shape, and 0.8 when the bore shape is an inverted frustoconical shape. Also, from the viewpoint of increasing the discharge velocity, it is preferable that the upper limit of the B / A ratio be 0.9.

[0031] 1 Immersion nozzle 11 Immersion nozzle body 111 Upper flange section 112 Straight section 2 Molten steel inlet 3 Inner bore (molten steel passage path) 31 Lower end surface of inner bore 4 Discharge hole 41 Lower end of discharge hole 5 Branch section 6 Flat taper 7 Well (recess)

Claims

1. An immersion nozzle having a molten steel inlet at its upper end, and symmetrically provided on both sides discharge holes branching off from near the lower end of an inner bore which is a molten steel passage path extending downward from the molten steel inlet, wherein the region from an arbitrary position above the branching point where the discharge holes branch off to the branching point has a shape in which the horizontal cross-sectional area of ​​the inner bore gradually decreases downward, and in a cross-sectional view taken with respect to a plane perpendicular to the central axis of the molten steel passage direction of the inner bore and the central axis of the molten steel discharge direction of the discharge holes, and in respect to the central axis of the molten steel passage direction of the inner bore, the B / A ratio, which is the ratio of the width B of the inner bore at the branching point to the maximum width A of the discharge hole, is 0.2 or more and 0.95 or less.

2. The immersion nozzle according to claim 1, wherein the shape of the inner bore, in which the horizontal cross-sectional area of ​​the inner bore gradually decreases downward, is a planar tapered shape having a pair of planar tapers formed opposite each other such that the width of the inner bore gradually decreases in the cross-sectional view.

3. The immersion nozzle according to claim 1 or 2, wherein the B / A ratio is 0.6 or more and 0.9 or less.

4. The immersion nozzle according to claim 1 or 2, wherein the vertical length of the region having a shape in which the horizontal cross-sectional area of ​​the inner bore gradually decreases downward is 15 mm or more and 150 mm or less.

5. The immersion nozzle according to claim 3, wherein the vertical length of the region having a shape in which the horizontal cross-sectional area of ​​the inner bore gradually decreases downward is 15 mm or more and 150 mm or less.

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