Immersion nozzle

Abstract

The present invention is a flat immersion nozzle that stabilizes a molten metal surface or the like in a mold. The present invention is an immersion nozzle X in the interior of which is formed a molten steel flow passage 15 having upper end part that is an introduction port 11 and extending downward from the introduction part, the molten steel flow passage 15 and the outer shape of at least a lower part 13 of a pipe body 1 having a bottom part 2 each have a rectangular flat cross section, both side walls 131 on the short sides of the lower part 13 being formed parallel to the up-down direction direction center axis 151 of the molten steel flow passage 15, and a pair of discharge holes 16 communicating with the molten steel flow passage 15 being formed in the lower end parts of both side walls 131 on the short sides of the lower part 13 so as to face each other. The immersion nozzle X has a pair of guide plates 3 in the vicinity of the pair of discharge holes 16. The pair of guide plates 3 are formed so as to connect both side walls 132 on the long sides of the lower part 13 and guide, toward the pair of discharge holes 16, the molten steel flowing in the molten steel flow passage 15. When A is defined as the shortest interval between the pair of guide plates 3 in the long side direction and B is defined as the length of the molten steel flow passage 15 in the lower part 13 in the long side direction, A / B is 0.25 to 0.9.

Description

Submerged Entry Nozzle

[0001] The present invention relates to an immersion nozzle for continuous casting that pours molten steel from a tundish into a mold, and in particular to an immersion nozzle that has a flat horizontal cross section near its discharge hole and is used for thin slabs, medium thickness slabs, etc.

[0002] In a continuous casting process in which molten steel is continuously cooled and solidified to form a cast piece of a predetermined shape, molten steel is poured into a mold through an immersion nozzle (IEN) installed at the bottom of a tundish. Generally, an IEN consists of a tubular body with a bottom, an upper end serving as a molten steel inlet, and an internal molten steel flow path extending downward from the molten steel inlet. A pair of opposing discharge holes communicating with the molten steel flow path are formed on the lower side of the tubular body. The IEN is used with its lower part immersed in the molten steel in the mold. This prevents the poured molten steel from splashing and also prevents oxidation by blocking contact between the molten steel and the atmosphere. Furthermore, the IEN rectifies the flow of molten steel in the mold, preventing impurities such as slag and nonmetallic inclusions floating on the surface of the molten steel from being entrained in the molten steel.

[0003] In recent years, there has been an increase in the production of thin cast pieces, such as thin slabs and medium-thick slabs, during continuous casting. Submerged entry nozzles that can accommodate such thin molds for continuous casting must be flattened. For example, Patent Document 1 discloses a flat submerged entry nozzle with discharge holes provided in the narrow side walls, and Patent Document 2 discloses a flat submerged entry nozzle that also has discharge holes provided in the lower end surface. These flat submerged entry nozzles generally require an increased width (synonymous with the length in the long side direction; the same applies hereinafter) of the molten steel flow path between the molten steel inlet and the discharge holes into the mold.

[0004] However, when the width of the molten steel flow path is increased and the shape is flat, the molten steel flow inside the immersion nozzle is easily disturbed, and the discharge flow into the mold is also disturbed. These disturbances in the molten steel flow and discharge flow can cause increased fluctuations in the melt surface (molten steel surface) in the mold, powder entrainment in the cast slab, temperature non-uniformity, etc., which can lead to poor cast slab quality and increased operational hazards. Therefore, it is necessary to stabilize the molten steel flow inside the immersion nozzle and the discharge flow into the mold.

[0005] In order to stabilize the molten steel flow and discharge flow, Patent Document 3 discloses an immersion nozzle in which at least two bending facets are formed from a point (center) on a plane below the elongated hole, which serves as the molten steel flow path, toward the lower edge of the discharge hole. Patent Document 3 also discloses an immersion nozzle equipped with a pair of deflector plates that split the molten steel flow into two separate streams ( Figures 23 and 28 ). The flat immersion nozzle disclosed in Patent Document 3 provides a more stable molten steel flow within the immersion nozzle than the immersion nozzles disclosed in Patent Documents 1 and 2 that do not have a means for changing the flow direction or shape within the internal space of the molten steel flow path.

[0006] JP-A-11-5145 JP-A-11-47897 Patent No. 4583508

[0007] However, as will be described in detail later, when the present inventors evaluated the fluctuations in the molten metal level in the mold using a water model test with the immersion nozzle disclosed in Patent Document 3, they found that the fluctuations were large. Therefore, the problem that the present invention aims to solve is to provide a flat immersion nozzle that can stabilize the molten metal level and the like in the mold, that is, can reduce the fluctuations.

[0008] The present inventors conducted a detailed analysis of the cause of the large fluctuations in the molten steel level in the mold when using the submerged entry nozzle disclosed in Patent Document 3. As a result, they discovered that the two bending facets in the submerged entry nozzle disclosed in Patent Document 3 are divergent, i.e., the outer shape of the lower part of the tubular body, which is the main body of the submerged entry nozzle, and the molten steel flow path are both divergent, which causes the approximately horizontal discharge flow discharged from the pair of discharge holes to become stronger, particularly under high throughput conditions, resulting in an increase in the reverse flow in the mold and large fluctuations in the molten steel level. Based on this discovery, the present inventors decided to adopt a so-called straight shape for the shape of the tubular body, which is the main body of the submerged entry nozzle, in which both side walls on the shorter sides of the lower part of the tubular body having the pair of discharge holes are formed parallel to the vertical central axis of the molten steel flow path. They conducted extensive testing and research with this straight shape to stabilize the molten steel flow in the molten steel flow path of the submerged entry nozzle and optimize the discharge flow into the mold. As a result, the inventors discovered that it is effective to provide a pair of guide plates near a pair of discharge holes to guide the molten steel flowing through the molten steel flow path of the immersed nozzle toward the pair of discharge holes. They also discovered that by providing a pair of guide plates so as to connect both side walls on the longer sides of the lower part of the tubular body and by setting the shortest distance between the pair of guide plates in the direction of the longer side within an appropriate range, it is possible to stabilize the flow of molten steel within the molten steel flow path of the immersed nozzle and optimize the discharge flow into the mold, which led to the completion of the present invention.

[0009] That is, one aspect of the present invention provides the following submerged entry nozzle: A submerged entry nozzle comprising a tube having a bottom, an upper end of which serves as an inlet for molten steel, and an internal molten steel flow path extending downward from the inlet, wherein at least the outer shape of the lower part of the tube and the molten steel flow path have a rectangular flat cross section, both side walls on shorter sides of the lower part are formed parallel to the vertical central axis of the molten steel flow path, and a pair of discharge holes communicating with the molten steel flow path are formed in opposing lower ends on both side walls on the shorter sides of the lower part, wherein the submerged entry nozzle further comprises a pair of guide plates near the pair of discharge holes, the pair of guide plates connecting the both side walls on longer sides of the lower part and being formed so as to guide molten steel flowing through the molten steel flow path toward the pair of discharge holes, wherein A is the shortest distance between the pair of guide plates in the long side direction and B is the length of the molten steel flow path in the long side direction at the lower part, and wherein A / B is 0.25 or more and 0.9 or less.

[0010] According to the present invention, in a flat submerged entry nozzle, it is possible to stabilize the flow of molten steel in the molten steel flow path and optimize the flow discharged into the mold, thereby reducing fluctuations in the molten steel level and the like in the mold.

[0011] 1 shows an embodiment of the submerged entry nozzle, where (a) is a vertical cross-sectional view taken along the width direction (i.e., the long side direction), (b) is a vertical cross-sectional view taken along the thickness direction (i.e., the short side direction), (c) is a cross-sectional view taken along the CC direction of (a), and (d) is a view taken along the D-D direction of (a). A perspective perspective view of the main parts of the submerged entry nozzle shown in FIG. 1. A model diagram of fluid dynamics (CFD). A diagram showing the results of an analysis of the flow state of molten steel within the submerged entry nozzle using fluid dynamics (CFD). A graph showing the relationship between the mass flow rate of the discharge flow from the discharge holes and "A / B" as determined by fluid dynamics (CFD). A graph showing the relationship between the mass flow rate difference between the discharge flows from a pair of discharge holes and "A / B" as determined by fluid dynamics (CFD). A vertical cross-sectional view taken along the width direction (i.e., the long side direction) of a conventional submerged entry nozzle disclosed in Patent Document 3. The results of a water model test are shown, with (a) being an example of the present invention and (b) being a conventional example.

[0012] FIG. 1 shows an embodiment of the submerged entry nozzle X, with FIG. 1(a) showing a vertical cross section along the width direction (i.e., the long side direction), FIG. 1(b) showing a vertical cross section along the thickness direction (i.e., the short side direction), FIG. 1(c) showing a cross section along the CC direction in FIG. 1(a), and FIG. 1(d) showing a view along the D-D direction in FIG. 1(a). FIG. 2 also shows a perspective view of the main components of the submerged entry nozzle X shown in FIG. 1. As shown in FIGS. 1(a) and 1(b), the submerged entry nozzle X is generally composed of a tubular body 1 having a bottom portion 2, a cylindrical upper portion 12 having a molten steel inlet 11 at its upper end, a lower portion 13 having a rectangular flat cross section, and an intermediate portion 14 that connects the upper portion 12 and the lower portion 13 and is flared in FIG. 1(a). A molten steel flow path 15 extending downward from the inlet 11 is formed inside the tubular body 1. In other words, the tubular body 1 is the main body of the submerged entry nozzle X.

[0013] As described above, the lower portion 13 of the tube 1 has a rectangular flat cross section. That is, as shown in Fig. 1(c), the horizontal cross section of the lower portion 13 is a rectangular flat cross section defined by a pair of opposing short side walls (both side walls on the short side) 131 and a pair of opposing long side walls (both side walls on the long side) 132. As shown in Fig. 1(a), the vertical cross section of the lower portion 13 along the width direction, i.e., the long side direction, is a so-called straight shape in which the both short side walls 131 are formed parallel to the vertical central axis 151 of the molten steel flow path 15. A pair of discharge holes 16 communicating with the molten steel flow path 15 are formed opposite to each other at the lower end portions of the both short side walls 131.

[0014] As described above, the submerged entry nozzle X has a flattened shape in which the outer shape of the lower portion 13 and the molten steel flow path 15 have a rectangular flat cross section, and the both side walls 131 on the short sides are straight and formed parallel to the vertical central axis 151 of the molten steel flow path 15. In this basic shape, the submerged entry nozzle X has a pair of guide plates 3 near the pair of discharge holes 16. The pair of guide plates 3 connect both side walls 132 on the long sides and are formed so as to guide the molten steel flowing through the molten steel flow path 15 toward the pair of discharge holes 16. Specifically, as shown in FIG. 1( a), the pair of guide plates 3 in the submerged entry nozzle X are arranged in a V-shape (inverted V-shape) in a vertical cross section taken along the long sides, and are arranged symmetrically with respect to the vertical central axis 151 of the molten steel flow path 15, i.e., the vertical central axis of the tube body 1.

[0015] 1( a), the pair of guide plates 3 are described in more detail. Here, A denotes the shortest distance between the pair of guide plates 3 in the long-side direction, and B denotes the length of the molten steel flow path 15 in the lower portion 13 in the long-side direction. A / B is 0.25 or more and 0.9 or less. As will be described in detail later, if A / B is less than 0.25, negative pressure is generated within the tubular body 1, which is the main body of the submerged nozzle X, particularly within the lower portion 13. This increases the turbulence of the molten steel flow within the tubular body 1, which causes the discharge flow from the pair of discharge holes 16 to pulsate, resulting in instability and significant fluctuations in the molten steel level within the mold. On the other hand, if A / B exceeds 0.9, the function of guiding the molten steel flowing through the molten steel flow path 15 toward the pair of discharge holes 16, in other words, the function of diverting the molten steel flow to generate a substantially horizontal discharge flow, cannot be fully achieved. It is preferable that A / B is 0.4 or more from the viewpoint of suppressing deviation of the molten steel flow in the tube 1 and the discharge flow from the pair of discharge holes 16, i.e., deviation of the flow. Therefore, it is preferable that A / B is 0.4 or more and 0.9 or less.

[0016] Here, a flow divider 4 is provided at the bottom portion 2. As shown in Figures 1(a) and 2, this flow divider 4 is formed in a triangular shape with its apex at the center and inclined toward the pair of discharge holes 16. This allows the molten steel flow within the tube 1, particularly within the lower portion 13, to be diverted toward the pair of discharge holes 16.

[0017] Although the embodiment of the present invention has been described above using the submerged entry nozzle X as an example, the present invention is not limited to this submerged entry nozzle X. For example, in the submerged entry nozzle X, the pair of guide plates 3 are shaped like a letter V (inverted V), i.e., linear, but they may also be curved or bent. Furthermore, in the submerged entry nozzle X, the pair of guide plates 3 are provided so that their lower ends extend to the pair of discharge holes 16. However, the lower ends of the pair of guide plates 3 do not need to extend to the pair of discharge holes 16 and may be located upstream of the pair of discharge holes 16. In short, the pair of guide plates 3 need only connect both side walls 132 on the long sides and guide the molten steel flowing through the molten steel flow path 15 toward the pair of discharge holes 16. Furthermore, in the submerged entry nozzle X, a triangular flow divider 4 is provided on the bottom 2. However, the shape of the flow divider 4 is not limited to a triangular shape and may be, for example, a trapezoidal, conical, or truncated conical shape. In short, the flow divider 4 need only divide the molten steel flow in the tubular body 1 toward at least a pair of discharge holes 16. The bottom portion 2 itself can function as the flow divider 4, and therefore the flow divider 4 is not an essential component in the present invention.

[0018] The influence of the "A / B" ratio was examined using fluid analysis, i.e., CFD (Computational Fluid Dynamics). In CFD, each pair of discharge holes 16 was divided into four sections as shown in FIG. 3, and the mass flow rate of the discharge flow from each of the discharge holes 16a-h was calculated. The flow state of the molten steel flow within the tube 1 was also analyzed. In FIG. 3, discharge holes 16a-d correspond to one of the pair of discharge holes 16, and one of the pair of guide plates 3, not shown in FIG. 3, is located between discharge holes 16b and 16c. In FIG. 3, discharge holes 16e-h correspond to the other of the pair of discharge holes 16, and the other of the pair of guide plates 3, not shown in FIG. 3, is located between discharge holes 16f and 16g. The discharge holes 16 a to 16 d and the discharge holes 16 e to 16 h are arranged symmetrically with respect to the vertical center axis 151 of the molten steel flow path 15 , that is, the vertical center axis of the tube body 1 .

[0019] Fig. 4 shows the results of a CFD analysis of the flow state of the molten steel flow inside the tube 1. Fig. 5 shows the relationship between the mass flow rate of the discharge flow discharged from the discharge hole 16f, as determined by CFD, and "A / B." Fig. 6 shows the relationship between the mass flow rate difference between the discharge flows discharged from the pair of discharge holes 16d, 16e, as determined by CFD ("mass flow rate of the discharge flow discharged from discharge hole 16d" - "mass flow rate of the discharge flow discharged from discharge hole 16e"), as determined by CFD, and "A / B."

[0020] From Figure 5, it can be seen that negative pressure occurs when A / B is 0.2. This is thought to be because, as can be seen from Figure 4(a), when A / B is 0.2, the flow state of the molten steel flow in the tube 1 becomes unstable. In contrast, when A / B is 0.25 or more, negative pressure does not occur, and the flow state of the molten steel flow in the tube 1 gradually stabilizes. Furthermore, it can be seen that when A / B is 0.4 or more, the flow state of the molten steel flow in the tube 1 becomes even more stable, and deviations in the molten steel flow and discharge flow, i.e., drift, are significantly suppressed. From these fluid analysis results, it can be said that an A / B ratio of 0.25 or more is effective, and that an A / B ratio of 0.4 or more is preferable. The upper limit of A / B is set to 0.9 for the reasons mentioned above.

[0021] Next, a water model test was conducted to evaluate the fluctuation of the molten metal level in the mold. For the water model test, a submerged entry nozzle X (see FIG. 1 ) with an A / B ratio of 0.8 was used as an example of the present invention, and a conventional submerged entry nozzle Y (see FIG. 7 ) fabricated based on the disclosure of Patent Document 3 was used as an example. In the submerged entry nozzle Y, the shortest distance A' between the pair of deflector plates 5 in the longitudinal direction was 60 mm, and the length B' of the molten steel flow path directly above the pair of deflector plates 5 in the longitudinal direction was 185 mm, resulting in an A' / B' ratio of 0.3. Figure 8 shows the results of the water model test, with (a) the example and (b) the conventional example. A comparison of (a) and (b) reveals that the present invention can reduce the fluctuation of the molten metal level in the mold. This is due to the fact that the present invention can stabilize the molten steel flow in the molten steel flow path and optimize the discharge flow into the mold. That is, according to the present invention, the tubular body, which is the main body of the submerged entry nozzle, is made straight in shape, and in order to stabilize the flow of molten steel within the molten steel flow path and optimize the flow discharged into the mold, a pair of guide plates are provided to connect both side walls on the longer sides of the lower part of the tubular body, and the shortest distance between the pair of guide plates in the direction of the longer sides is set within an appropriate range, thereby making it possible to reduce fluctuations in the molten metal level, etc. within the mold.

[0022] X, Y Submerged entry nozzle 1 Tube body (submerged entry nozzle main body) 11 Inlet for molten steel 12 Upper part 13 Lower part 131 Side wall on the short side 132 Side wall on the long side 14 Middle part 15 Molten steel flow path 16, 16a to 16h Discharge hole 2 Bottom part 3 Guide plate 4 Flow divider 5 Deflector plate

Claims

1. An immersion nozzle having an upper end serving as an inlet for molten steel, with a molten steel flow path formed therein extending downward from the inlet, with at least the lower outer shape of a lower part of a tube body having a bottom, and with the molten steel flow path formed with a rectangular flat cross section, with both side walls on the shorter sides of the lower part formed parallel to the vertical central axis of the molten steel flow path, and with a pair of discharge holes communicating with the molten steel flow path formed opposite each other at the lower ends of both side walls on the shorter sides of the lower part, wherein the immersion nozzle has a pair of guide plates near the pair of discharge holes, the pair of guide plates connecting both side walls on the longer sides of the lower part, and formed so as to guide molten steel flowing through the molten steel flow path toward the pair of discharge holes, wherein A is the shortest distance between the pair of guide plates in the long side direction, and B is the length of the molten steel flow path in the long side direction at the lower part, and A / B is 0.25 to 0.

9.

2. The submerged nozzle according to claim 1, wherein the ratio A / B is 0.4 or more and 0.9 or less.

3. The submerged nozzle according to claim 1 or 2, further comprising a flow divider at said bottom portion, said flow divider being configured to divide the molten steel flow toward at least said pair of discharge holes.

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