JP2013184199A - Nozzle with gas injection function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a through-hole type nozzle that keeps integrity as a structure adjacent to at least a gas discharge port of a nozzle body formed of refractory and has a gas injection function difficult to break.SOLUTION: In a nozzle 20 that has a function of discharging molten steel in a vessel and injects an inert gas into the molten steel, a through hole 5 as a gas passage route is provided in three-dimensional and nonlinear manner so that the entire through hole may not be included within the same plane in any virtual directions including a virtual straight line connecting an end 5a on the side of a gas pool 2 with a gas discharge port 4.

Description

  The present invention is a nozzle that discharges molten steel in a container such as a tundish from an inner hole in continuous casting of steel, and has a function of injecting an inert gas from the inner hole surface, particularly a through-hole type nozzle. The present invention relates to a refractory nozzle having a gas passage.

  Nozzles for continuous casting of steel, especially nozzles installed at the bottom of the tundish to discharge molten steel from the tundish to the mold, the nozzles due to inclusion of inclusions such as alumina derived from the molten steel on the inner hole surface Obstruction is likely to occur. Therefore, in many cases, an inert gas is injected into the molten steel from the inner hole surface of the nozzle for the purpose of preventing inclusions from adhering to the inner hole surface and stirring the molten steel.

  As such a nozzle, there is a porous nozzle in which the main body is composed of a porous refractory, and the pores in the refractory are used as gas passages to inject gas into the molten steel from almost the entire inner surface. is there.

  In addition to a porous nozzle, a so-called through-hole nozzle may be used. In this through-hole type nozzle, for the purpose of improving the corrosion resistance, wear resistance, etc. of the nozzle, the nozzle body is composed of a dense refractory material and a through-hole is formed in the refractory structure. This through-hole is a tunnel-like space with a cross-sectional area that is small enough to prevent molten steel from entering, and is a gas provided inside the refractory of the nozzle body or between the nozzle body and the metal case disposed on the outer peripheral surface side. This is a gas passage route passing between the pool and a gas discharge port provided on the inner hole surface.

  Such a through-hole type nozzle is composed of a refractory with a dense structure in the nozzle body, so it has better corrosion resistance and wear resistance than a porous type nozzle, but tends to be inferior in thermal shock resistance. There is. Furthermore, the through-hole portion is also a “defect” in the structure, and has a drawback that thermal or mechanical stress is concentrated and tends to be a starting point of fracture. In particular, when the molten steel discharge is started or stopped or the flow rate is controlled by fitting a stopper to the upper end of the inner hole, the operation of the stopper itself becomes a mechanical external force that directly applies an impact or compression to the nozzle. The risk of destroying the through-hole type nozzle is increased. The destruction of the nozzle due to these thermal or mechanical stresses is mainly caused by the direction parallel to the longitudinal direction and the direction perpendicular to the longitudinal direction (lateral direction), where the molten steel passage direction of the inner hole is the longitudinal direction. ) And the like (symbols 11 and 12 in FIG. 4B).

  Conventionally, with regard to the arrangement structure of through-holes in a through-hole type nozzle, for example, as in Patent Documents 1 and 2, the nozzles are grouped into a plurality of stages in the vertical direction (up / down direction), and a plurality of nozzles are arranged for each group Through holes are arranged, the through holes themselves are linear paths, and almost all of the through holes of the plurality of through holes in each group exist on the same plane in the lateral direction of the nozzle, and further Thus, when there are a plurality of through holes that exist in a straight line, each of a certain cross section in the vertical direction and a certain cross section in the horizontal direction of the nozzle may be arranged so as to exist in the same plane. It is general (refer FIG. 4 (a) and FIG. 5). Specifically, in an arbitrary cross section (plane) in the lateral direction of the nozzle including the through hole, a plurality of through holes exist in the same cross section (plane). Further, in any cross section in the nozzle vertical direction, they are often arranged in the same plane as described above. In addition, even when it has an inclination (angle) in either direction from the outer peripheral side of the nozzle toward the inner hole side, for example, as in Patent Document 3, each through-hole is substantially the entire and a plurality of through-holes, In any direction, at least in any cross section (plane) in the nozzle longitudinal direction, the same cross section (plane) is often present.

  However, when the through holes are arranged linearly as in Patent Documents 1 to 3, cracks or breakage often occurs starting from the through holes. In addition, if such a linear through hole is arranged so as to be included in the same plane, cracks or breakage is further concentrated in the plane, and the refractory material of the nozzle body is spread over a wide range from the through hole or plane. Destruction often progresses. Even if the fracture is about a crack, the fractured portion including the crack becomes a new gas passage, and further, the stress due to the gas increases around the fracture path, thereby promoting the fracture.

  On the other hand, when such a broken portion such as a crack becomes a new gas passage, the number of gas discharge locations, the opening area of the gas discharge port at the end of the through hole, etc. increase without regularity. As a result, the gas discharge amount, discharge speed, discharge direction / state, etc. of each gas discharge port greatly fluctuate, and the total gas discharge amount also fluctuates beyond prediction. As a result, uniform gas discharge from the inner hole surface as intended (initial specification) cannot be performed, causing inclusions to adhere to the inner hole surface, stirring of molten steel, and floating of inclusions. Such effects will also be reduced or become unstable.

  As described above, in the prior art, the through hole of the nozzle having the gas injection function is often arranged with an emphasis on the gas outflow function / characteristic, and the refractory component of the nozzle body and Although attempts were made to improve it by optimizing the physical properties by changing the composition, the arrangement structure of the through holes was not studied from the viewpoint of preventing breakage. That is, measures for preventing breakage of the through-hole nozzle and stable gas supply are still insufficient.

JP-A-11-314142 Japanese Utility Model Publication No. 60-160965 JP 2005-279729 A

  The problem to be solved by the present invention is to provide a through-hole type nozzle having a gas injection function that is difficult to break while maintaining the integrity as a structure at least in the vicinity of a gas discharge port of a nozzle body made of a refractory. There is to do. As a result, it aims at contributing to the stable supply of gas and the prevention of nozzle blockage due to the inclusion or the increase of inclusions derived from molten steel on the inner surface of the nozzle.

The nozzle having the gas injection function of the present invention is a nozzle having the following features (1) to (4).
(1) A nozzle having a function of discharging molten steel in a container and injecting an inert gas into the molten steel,
One or more gas outlets are provided on the inner hole surface through which the molten steel passes,
The gas discharge port communicates with the gas pool through a through-hole penetrating the nozzle body.
The nozzle is characterized in that the through-hole is provided in a three-dimensional non-linear shape.
(2) The nozzle according to (1), wherein the three-dimensional non-linear shape is an uneven shape or a spiral shape.
(3) A plurality of the through holes are provided, and either or both of the end portions of the plurality of through holes on the gas pool side and the gas discharge ports communicating with the plurality of through holes are respectively The nozzle according to (1) or (2), which is not located on the same virtual plane including the central axis in the longitudinal direction of the inner hole.
(4) A plurality of the through holes are provided, and either or both of the end portions of the plurality of through holes on the gas pool side and the gas discharge ports respectively communicating with the plurality of through holes are The nozzle according to any one of (1) to (3), which is not located on the same virtual plane perpendicular to the longitudinal center axis of the inner hole.

  This will be described in detail below.

  The through hole is continuously formed with a predetermined size so that gas can pass from the gas pool to the gas discharge port on the inner hole surface at a predetermined pressure and flow rate. Since such a through hole is a space, it is a defective part of the tissue in the structure and also a part where stress tends to concentrate.

  As shown in Patent Documents 1 to 3, the conventional through-hole is a straight line with no irregularities, but in other words in terms of the length between the vertices of the irregularities, the length is one time the diameter of the through-hole. That's what it means. When the through hole is formed in a straight line as the gas passage path in this way, the entire path of the through hole is included in one virtual plane regardless of which direction it is. In this way, if the space, that is, the defective part as a structure is concentrated in one plane and penetrates the nozzle body, the nozzle body is continuously divided over the entire length in the thickness direction. Therefore, stress concentrates on the plane and it becomes easy to break. Furthermore, when a plurality of such linear through holes are arranged, if the plurality of through holes are arranged so as to be included in the same virtual plane, stress is more likely to concentrate on the plane, and the plane Since the space portion is relatively large in the inside, the bonding force of the refractory structure is also relatively fragile, and breakage is more likely to occur, and breakage is likely to expand.

  In the present invention, by forming the through-hole in a three-dimensional non-linear shape, without concentrating the space that is also a defective portion that may be a starting point of destruction in the structure in a narrow range, particularly in the same plane, Dispersed over a wide range. By dispersing the space that is a defect in a three-dimensionally wide range, the stress is also three-dimensionally dispersed so as not to be concentrated. In the present invention, a three-dimensional non-linear shape means that a space, that is, a through-hole exists continuously in the same wide plane, particularly in the same plane where stress concentration is likely to cause continuous destruction. In other words, it means that a three-dimensional path is also provided in the direction perpendicular to the plane.

  If the through hole changes two-dimensionally non-linearly in any particular plane and does not change in the three-dimensional direction perpendicular to the two-dimensional plane, it is linear on that plane. On the contrary, there are more (longer) defects in the space than in the case described above, and stress tends to concentrate on the plane, so the effect of stress distribution or prevention of destruction is not sufficient. In other words, it is necessary to arrange them non-linearly in any direction in three dimensions. In the present invention, the plane is a virtual plane inside the nozzle structure, and does not actually divide the tissue.

  In the present invention, the “three-dimensional non-linear shape” is preferably an uneven shape or a spiral shape. The unevenness may be a continuation of the bent portion, but it is preferable that the vicinity of the apex is not an acute angle but a curved shape in order to avoid stress concentration at the apex. Also, it is not necessary to have an orderly and regularity.

  Further, in order to disperse stress in a three-dimensional manner with higher uniformity, the through hole is spirally wound around a virtual straight line connecting the gas pool side end and the gas discharge port on the inner hole surface. The diameter of the spiral circle viewed from a direction perpendicular to the virtual straight line is more preferably not constant.

  The nozzle targeted by the present invention has a cylindrical structure through which molten steel passes through an inner hole, and receives heat from the inner hole, and a temperature gradient is generated from the inner hole side to the outer peripheral side. Then, a strong compressive stress is generated in the radial direction of the inner hole side of the nozzle, and a strong tensile stress is generated on the outer peripheral side, so that cracks or breakage tends to occur in the vertical direction of the nozzle. Also in the vertical direction, a strong compressive stress is generated in the longitudinal direction on the inner hole side and a strong tensile stress is generated in the vertical direction on the outer peripheral side, which is liable to cause cracks or breaks in the lateral direction.

  From the viewpoint of a structure having such characteristics, in a virtual vertical coplanar plane (reference numeral 7 in FIG. 2) including the vertical central axis of a nozzle (inner hole) where stress is concentrated and easily cracks or breaks. In addition, it is preferable to disperse without concentrating defects or fragile portions in the refractory structure in a virtual imaginary plane (reference numeral 8 in FIG. 2) in the lateral direction perpendicular to the longitudinal central axis. The through hole is a space, and is also a defective portion or a fragile portion of the structure. Therefore, it is preferable that the entire path of the through hole does not overlap in the same vertical plane including the vertical central axis and in the same horizontal plane perpendicular to the vertical central axis.

  More specifically, a three-dimensional non-linear shape and degree that are more preferable from such a viewpoint are illustrated. The gas discharge port is connected from the end of the through hole on the gas pool side by a straight line, and the radial direction with the straight line as an axis. Variation length, that is, the difference in radial length in the longitudinal direction or the lateral direction between adjacent apexes of bending or unevenness (reference numeral 10 in FIG. 2B) (Lv or Lh in FIG. 2A) ) Is preferably more than twice the diameter of the through hole (d in FIG. 2 (a)) in order to ensure that the space does not exist in the same virtual plane and to increase the degree of stress dispersion. Is more preferably 3 times or more of the through-hole diameter.

  Further, in order to minimize the probability that the through-hole path exists in the same plane at the same time in the vertical direction and the horizontal direction, the direction of the virtual plane (reference numeral 9 in FIG. 2) connecting the concave and convex adjacent to the concave and convex is the nozzle. The plane including the vertical axis direction is 45 °, and the length between the vertices (L in FIG. 2) is about 2 times the diameter of the through hole, which is a value obtained by multiplying the diameter of the through hole by twice √2. It is preferable to exceed .9 times, and it is more preferable to exceed about 4.3 times the diameter of the through hole, which is a value obtained by multiplying the diameter of the through hole by 3 times √2. That is, when the length is as described above, through-holes continuously exist in the entire path in the same vertical plane including the central axis in the nozzle vertical direction and in the horizontal plane perpendicular to the vertical direction. In addition, since the concavo-convex vertices are separated from each other, the stress dispersion effect can be enhanced. This will be explained with reference to the figure. By increasing the length between the concave and convex vertices centered on the line 8 in FIG. 2, there is no possibility that the through-holes continue in the direction of the line 8 in FIG. become.

  In a spiral shape, the stress can be distributed in multiple directions, more uniformly and gradually continuously by spiraling, so that the gas discharge port is connected straight from the end of the through hole on the gas pool side. When the diameter inside the spiral in the radial direction with respect to the straight line as an axis is at least larger than the diameter of the through hole, the spaces do not overlap continuously in the axial direction. In the spiral shape, in order to more surely prevent the space from existing in the same virtual plane and to increase the degree of stress dispersion, it is more preferable that the inner diameter of the spiral is twice or more the diameter of the through hole.

  In addition to the arrangement method of the individual through-holes described above, when arranging a plurality of through-holes, the relative arrangement position of the through-holes in the nozzle should be a structure in which stress is less likely to concentrate, That is, the through-holes are dispersed without concentrating in a virtual longitudinal same plane including the vertical center axis of the nozzle (inner hole) and in a horizontal virtual same plane perpendicular to the vertical center axis. Is preferred.

  Therefore, first, in the arrangement of the through holes in the nozzle vertical direction, at least one of the plurality of gas discharge ports and the plurality of gas pool side ends of the through holes is on the same virtual plane including the vertical center axis. It is preferable that the arrangement structure is not included in the structure. For example, when three through holes are arranged, an arrangement in which at least one of the three gas discharge ports and the three gas pool side ends is not included on the same virtual plane including the longitudinal central axis. A structure is preferred. In addition, since the dispersive effect is increased by making the arrangement structure in which both of the plurality of gas discharge ports and the gas pool side end portions are not included on the same virtual plane including the longitudinal center axis, respectively. Further preferred.

  Similarly, in the arrangement of the through holes in the nozzle lateral direction, at least one of the plurality of gas discharge ports and the plurality of gas pool side ends is on the same virtual plane perpendicular to the longitudinal central axis. It is preferable that the arrangement structure is not included, and it is more preferable that both are not included on the same virtual plane perpendicular to the longitudinal central axis because the dispersion effect is increased.

  Whether the longitudinal direction or the lateral direction of a nozzle having a cylindrical structure is more likely to break depends on factors such as the diameter, the thickness of the refractory, and the length of the shape surface. And depends on operating conditions. Therefore, regarding the direction of unevenness of the above-described through holes, the direction not to be arranged in the same plane when arranging a plurality of through holes, etc., either the vertical direction or the horizontal direction has priority, or both Whether or not to do so may be determined according to individual design conditions and operation conditions.

  According to the present invention, a dense refractory material is applied to the nozzle body, and while maintaining the integrity as a structure, the gas injection amount is controlled, and a through-hole type nozzle that is difficult to break is obtained. be able to. And steel leakage accidents due to nozzle breakage can be prevented, gas injection can be stabilized, steel quality can be stabilized, and inclusions such as alumina on the inner surface of various nozzles for continuous casting Can also be suppressed.

In an example of the nozzle of the present invention, (a) shows a through-hole part in the nozzle longitudinal section, (b) shows a through-hole part in a vertical (lateral) direction section with respect to the nozzle longitudinal direction, (c) An example of the shape of a through hole (spiral) is shown. An example of the through hole of the nozzle of the present invention is shown, (a) conceptually shows the relative positional relationship between the concavo-convex vertices of the through hole when the through hole is viewed from the inner hole side of the nozzle, (B) conceptually shows the relative positional relationship between the concavo-convex vertices of the through hole when the through hole is viewed from above the nozzle. An example of the nozzle of the present invention having a plurality of through-holes, wherein (a) shows a case where a gas pool is provided between the refractory outer peripheral surface of the nozzle body and a metal case, and (b) shows a gas pool. The case where it is provided inside the refractory of the nozzle body is shown. An example of a conventional nozzle for gas injection is shown in a cross section in the vertical axis direction, (a) shows an array of through holes, and (b) shows a plurality of through holes in a virtual same plane in the vertical or horizontal direction of the nozzle. In this case, the state of occurrence of cracks and fractures is conceptually shown. An example of a conventional nozzle for gas injection, (a) shows a through-hole portion in the nozzle longitudinal section, (b) shows a through-hole portion in a vertical (lateral) direction cross section with respect to the nozzle longitudinal direction, c) shows an example of the shape of a through-hole (linear shape).

  FIG. 1 shows an example of a nozzle according to the present invention, in which (a) shows a through-hole portion in the nozzle longitudinal section, (b) shows a through-hole portion in a vertical (lateral) direction section with respect to the nozzle longitudinal direction, (C) shows a shape example (spiral) of the through hole.

  In the nozzle 20 shown in FIG. 1, the nozzle main body 1 is made of a continuous and integral (refined) refractory, and a gas pool 2 is provided therein. The gas pool 2 communicates with a gas introduction hole (reference numeral 3 in FIG. 2) leading to an inert gas supply source. A gas discharge port 4 is provided in the inner hole surface 1 a of the nozzle body 1, and a through hole 5 is provided between the gas pool 2 and the gas discharge port 4 so as to penetrate the nozzle body 1. In the present invention, the through-hole 5 is in the same plane in any virtual direction including a virtual straight line connecting the end 5a on the gas pool 2 side and the gas discharge port 4 (end 5b on the gas discharge port 4 side). Also, the entire through-hole 5 is not included and is provided in a three-dimensional non-linear shape. In the example of FIG. 1, the through hole 5 is provided in a spiral shape as shown in FIG. The nozzle body 1 is formed with an inner hole 1b that communicates in the longitudinal direction with the upper end as a molten steel inlet and the lower end as a molten steel outlet for discharging molten steel.

  FIG. 3 shows an example having a plurality of through holes 5. FIG. 3A shows an example in which a metal case 6 is disposed on the outer peripheral side of the nozzle body 1 and a gas pool 2 is provided between the nozzle body 1 and the metal case 6. FIG. Similarly, the gas pool 2 is provided inside the nozzle body 1. In any example, both the end portions 5a on the gas pool 2 side of the plurality of through holes 5 and the gas discharge ports 4 respectively communicating with the plurality of through holes 5 are the center in the vertical direction of the inner hole 1b. They are arranged so as not to be located on the same virtual plane including the axis and on the same virtual plane perpendicular to the central axis.

  Next, the manufacturing method of the nozzle of this invention is described. The summary is as follows.

  A combustible material forms a double cylindrical body in which an inner cylinder corresponding to the inner surface of the nozzle and an outer cylinder corresponding to the gas pool inner surface are arranged concentrically, and the inner cylinder and the outer cylinder of this double cylindrical body A mold in which a combustible yarn is bridged between them and cross-linked, and a combustible material layer is installed on the entire inner surface by coating or the like is further installed outside the outer cylinder. When the flammable yarn is installed, the yarn is previously formed into an uneven shape or a spiral shape. When forming a plurality of through-holes, either the end of each through-hole on the gas discharge port side or the gas pool side, or so as not to arrange the through-holes on the same virtual plane in the nozzle vertical direction and the horizontal direction, Relatively shift both positions.

  A space such as the molding cylinder thus formed is filled with a refractory serving as a nozzle body, and then dried and fired. By this firing or the like process, the combustible material that becomes the yarn and the gas pool disappears, and a through hole and a gas pool can be formed.

  The refractory layer forming the nozzle body is formed by forming a clay such as alumina-graphite that is generally used for nozzles for continuous casting by CIP, pouring or hardening a castable refractory, etc. It can be formed by any method.

  In the above description, the cross-sectional shape of the through-hole is regarded as a circular shape for convenience of explanation, but is not necessarily limited to a circular shape. However, it is preferable to avoid a shape including a portion that bends at an acute angle because cracks and breakage may occur starting from the bent portion. The cross-sectional size of the through hole is about 0.3 mm or more and about 0.5 mm or less from the viewpoint of preventing molten steel from entering while supplying a stable gas and preventing the diameter of the discharged gas from becoming coarse. It is preferable. If it is less than 0.3 mm, the resistance during gas passage is large, and the size of the refractory is further reduced by thermal expansion, which may make it difficult to obtain a sufficient gas discharge amount. If it exceeds 5 mm, the molten steel may enter the through hole and close the through hole, although it varies depending on the composition and temperature of the molten steel.

  In addition, as mentioned above, it is preferable that the length (Lv and Lh in FIG. 2A) between the vertices of the concave and convex portions of the through hole is two or three times the diameter of the through hole. Moreover, when it has two or more through-holes, it is preferable that the shortest distance between adjacent through-holes is also 3 times or more of the diameter of a through-hole. Furthermore, in the present invention, it is preferable that the through hole is provided in a spiral shape with a central axis in a direction connecting the gas discharge port and the end portion on the gas pool side. As described above, the inner diameter of the spiral is preferably twice or three times the diameter of the through hole, and the direction connecting the gas discharge port and the end of the gas pool, that is, the so-called pitch (reference numeral Lp in FIG. 1). However, the distance between adjacent through holes is preferably more than twice the diameter of the through hole, more preferably three times or more.

  In order to evaluate the effect of reducing the risk of breaking the gas injection nozzle, that is, the effect of relaxing the stress concentration, a bending strength measurement was performed on the test piece.

  The test piece was 40 mm × 40 mm × 160 mm, and a 0.5 mm diameter through hole was formed in the center of the test piece so as to cross the test piece in the lateral direction. As for the shape of the through-hole, the embodiment had a spiral shape, the inner diameter was 5 mm, and the pitch was about 5 mm. The comparative example was linear.

  The bending test was performed by a three-point bending method at room temperature with the support roll length (distance between fulcrums) being 100 mm.

  As a result of this bending test, the bending strength (measured value) of the comparative example was 6.5 MPa (average value), whereas the example was 7.7 MPa (average value), and the example was compared to the comparative example. An improvement of about 18.4% was observed. From this, it can be seen that in the embodiment of the present invention in which the through holes are arranged in a spiral shape, the resistance to destruction is high, the R value is small, and the variation in strength is also small.

  In addition, a mechanical nozzle is used from the lateral direction by using a real-shaped nozzle having an inner hole diameter of 90 mm to 120 mm and a length of 310 mm, in which four through holes having a diameter of 0.5 mm are arranged evenly in three stages in the circumferential direction and in the vertical direction. An impact was applied, and the occurrence of cracks and fractures was observed. As for the shape of the through holes, the embodiment has a spiral shape with an inner diameter of 5 mm and a pitch of about 5 mm, and the entire path of the plurality of through holes is in the same virtual plane including the nozzle vertical center axis and the nozzle vertical center axis They were arranged so as not to exist in the same virtual plane in the direction perpendicular to the vertical direction, the comparative example was linear, and the vertical and horizontal directions were arranged in the same virtual plane.

  As a result, in the comparative example, cracks along the through holes occurred in the vertical direction and the horizontal direction. On the other hand, in the example, cracks were not concentrated, but only small cracks were generated in the diagonal direction, compared with the comparative example.

DESCRIPTION OF SYMBOLS 20 Nozzle 1 Nozzle body 1a Inner hole surface 1b Inner hole 2 Gas pool 3 Gas introduction hole 4 Gas discharge port 5 Through-hole 5a Gas pool side end 5b Gas discharge port side end 6 Metal case 7 Nozzle longitudinal center axis 8 Virtual vertical plane including the nozzle 8 Virtual horizontal plane perpendicular to the central axis of the nozzle vertical direction 9 Virtual plane connecting the concave and convex adjacent concave and convex 10 Vertex of adjacent concave and convex 11 Crack and break in the vertical direction of the nozzle Part (image)
12 Nozzle lateral crack and fracture (image)

Claims (4)

A nozzle having a function of discharging molten steel in a container and injecting an inert gas into the molten steel,
One or more gas outlets are provided on the inner hole surface through which the molten steel passes,
The gas discharge port communicates with the gas pool through a through-hole penetrating the nozzle body.
The nozzle is characterized in that the through-hole is provided in a three-dimensional non-linear shape.   The nozzle according to claim 1, wherein the three-dimensional non-linear shape is an uneven shape or a spiral shape.   A plurality of the through holes are provided, and either or both of the end portions of the plurality of through holes on the gas pool side and the gas discharge ports respectively communicating with the plurality of through holes are the inner holes. The nozzle according to claim 1 or 2, wherein the nozzle is not located on the same virtual plane including the central axis in the vertical direction of the hole.   A plurality of the through holes are provided, and either or both of the end portions of the plurality of through holes on the gas pool side and the gas discharge ports respectively communicating with the plurality of through holes are the inner holes. The nozzle according to any one of claims 1 to 3, wherein the nozzle is not located on the same virtual plane perpendicular to the longitudinal central axis of the hole.

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