Immersion nozzle Technical field [0001] 　The present invention relates to a dipping nozzle for continuous casting in which molten steel is poured into a mold from a tundish, and in particular, in the lateral direction (vertical) near the discharge hole of the dipping nozzle, which is used for thin slabs, medium-thick slabs, and the like. (Direction perpendicular to the direction) The cross section relates to a flat dipping nozzle. Background technology [0002] 　In the continuous casting process in which molten steel is continuously cooled and solidified to form a slab having a predetermined shape, a dipping nozzle for continuous casting (hereinafter, also simply referred to as “immersion nozzle”) installed at the bottom of the tundish is used. The molten steel is poured into the mold. [0003] 　Generally, the immersion nozzle consists of a pipe body having a bottom portion in which the upper end is a molten steel introduction port and a molten steel flow path (inner hole) extending downward from the molten steel introduction port is formed inside, and the lower part of the pipe body. A pair of discharge holes communicating with the molten steel flow path (inner hole) are formed on the side surface so as to face each other. The immersion nozzle is used with its lower part immersed in the molten steel in the mold. As a result, the molten steel poured into the water is prevented from scattering, and the contact between the molten steel and the atmosphere is blocked to prevent oxidation. In addition, by using a dipping nozzle, the molten steel in the mold is rectified to prevent impurities such as slag and non-metal inclusions floating on the molten metal surface from being caught in the molten steel. [0004] 　In recent years, there has been an increase in the production of thin slabs such as thin slabs and medium-thick slabs during continuous casting. The immersion nozzle for dealing with such a thin mold for continuous casting needs to be flat. For example, Patent Document 1 shows a flat dipping nozzle having a discharge hole on the side wall on the short side, and Patent Document 2 shows a flat dipping nozzle having a discharge hole on the lower end surface. In these flat immersion nozzles, the width of the inner hole is generally increased between the molten steel introduction port and the discharge hole to the mold. [0005] 　However, in the case of such a shape in which the width of the inner hole is expanded and a flat shape, the molten steel flow in the immersion nozzle is likely to be turbulent, and the discharge flow to the mold is also turbulent. This turbulence in the molten steel flow may cause increased fluctuations in the molten metal surface (molten steel surface) in the mold, powder entrainment in the slab, temperature inhomogeneity, etc., resulting in poor slab quality and increased operational risk. Become. Therefore, it is necessary to stabilize the molten steel flow in the immersion nozzle and discharged. [0006] 　In order to stabilize these molten steel flows, for example, Patent Document 3 discloses a dipping nozzle in which at least two bending facets are formed from a point (center) on a plane below the inner hole toward the lower edge of the discharge hole. Has been done. Further, Patent Document 3 discloses an immersion nozzle including a shunt that divides a molten steel stream into two streams. The flat immersion nozzle shown in Patent Document 3 has a molten steel flow in the immersion nozzle as compared with the immersion nozzle which does not have a means for changing the flow direction and form in the internal space as in Patent Document 1 and Patent Document 2. Is more stable. [0007] 　However, in the case of such a means for dividing the molten steel flow in the left-right direction, the fluctuation of the molten steel discharge flow between the left and right discharge holes is still large, and the fluctuation of the molten metal surface in the mold due to this may be large. be. [0008] 　Against the background described above, the present inventors have invented the flat dipping nozzle shown in Patent Document 4, and have contributed to stabilizing the surface of the molten metal in the mold. Prior art literature Patent documents [0009] Patent Document 1: Japanese Patent Application Laid-Open No. 11-5145 Patent Document 2: Japanese Patent Application Laid-Open No. 11-47897 Patent Document 3: Japanese Patent Application Laid-Open No. 2001-501132 Patent Document 4: International Publication No. 2017/81934 Outline of the invention Problems to be solved by the invention [0010] 　However, even with the flat dipping nozzle of Patent Document 4, the molten steel flow rate is approximately 0, based on the operating conditions, particularly the minimum cross-sectional area position in the region where the cross-sectional shape of the inner hole in the lateral direction near the upper end of the dipping nozzle is circular. The present inventors have found that in continuous casting performed under conditions such as 04 (t / (min. · cm 2 )) or higher, the effect of stabilizing the molten metal surface in the mold may still be insufficient. [0011] 　Therefore, an object to be solved by the present invention is to provide a dipping nozzle that stabilizes the surface of the molten metal in the mold, that is, reduces the fluctuation of the flat dipping nozzle. Means to solve problems [0012] 　In the flat immersion nozzle of Patent Document 4, a protrusion is mainly provided in the center of the inner hole, and based on this, the same or protrusion as the center is provided on the side thereof for fine adjustment of discharge flow, form, etc. Install a small protrusion. 　On the other hand, in the present invention, symmetrical protrusions are provided on the sides, and the space between the side protrusions is basically a space without protrusions or the side protrusions, and the protrusion length is longer than the side protrusions. Install a small protrusion. [0013] 　In the structure of the flat immersion nozzle of Patent Document 4, the flow rate of the molten steel in the inner hole is increased from the direction directly below the center to the side (pointing to the width direction of the flat portion of the nozzle; the same applies hereinafter). Guide. In this case, the flow rate of molten steel from the discharge hole tends to increase, and the fluctuation of the molten metal surface in the mold may increase under conditions such as a large flow rate of molten steel per unit time and unit area. 　On the other hand, in the structure of the immersion nozzle of the present invention, the molten steel flow in the inner hole is adjusted so as to increase the flow rate in the direction directly below the center so that the flow rate in the lateral direction is relatively reduced. In other words, in the present invention, the ratio of the flow rate in the direction directly below the center / the flow rate in the lateral direction is relatively larger than that in the case of the structure of the immersion nozzle of Patent Document 4. 　Note that the above basically adjusts the ratio in the relationship of the flow rate in the direction directly below the center / the flow rate in the side, and does not necessarily make the relationship of the flow rate in the direction directly below the center> the flow rate in the side. do not have. [0014] 　The present invention for obtaining the above-mentioned flow form is the following flat immersion nozzles 1 to 8. 1. 1. 　In a dipping nozzle having an inner hole width Wn larger than the inner hole thickness Tn and having a pair of discharge holes at the lower part of the side wall on the short side, 　the width direction is on the wall surface in the width direction of the flat portion. The portions (hereinafter referred to as "lateral protrusions") that are inclined downward in the width direction and protrude in the thickness direction are arranged in pairs at positions symmetrical with respect to the vertical central axis of the wall surface. The 　lateral protrusions are arranged so as to face each other on both wall surfaces in the width direction, and the 　lateral protrusions have a thickness of an inner hole of 1 at the position where the lateral protrusions are arranged. The immersion nozzle, wherein the total protrusion length Ts of the portion in the thickness direction is the same at 0.18 or more and 0.90 or less for each of the two paired lateral protrusions. 2. 　On the widthwise wall surface between the two paired lateral protrusions, the protrusion length in the thickness direction is smaller than the protrusion length in the thickness direction of the lateral protrusions, and the lateral protrusions are lateral. A protrusion (hereinafter referred to as a "center protrusion") having a total protrusion length Tp of 0.40 or less (not including zero) in the thickness direction, where the thickness of the inner hole at the position where the protrusion is arranged is 1. .) Is installed, the immersion nozzle according to 1 above. 3. 3. 　2. The immersion nozzle according to 2 above, wherein the upper end surface of the central protrusion has a horizontal shape in the width direction or a curved surface having the apex at the center or a shape protruding upward including a bending point. 4. 　The immersion nozzle according to any one of 1 to 3 above, wherein the lateral protrusion and the upper end surface of the central protrusion have a horizontal shape or a shape that is inclined downward with a flat surface or a curved surface in the direction of the center of the inner hole. .. 5. 　The individual protrusion lengths of either one or both of the lateral protrusions and the central protrusions are the same or in a straight line, a curved line, or a stepped shape toward the center of the wall surface in the width direction. The immersion nozzle according to any one of the above 1 to 4 above. 6. 　The item according to any one of 1 to 5 above, wherein any one or both of the lateral protrusion and the lateral protrusion provided with the central protrusion are installed at a plurality of locations in the vertical direction. Immersion nozzle. 7. 　The immersion nozzle according to any one of 1 to 6 above, which has an upward protrusion near the center of the bottom of the inner hole. 8. 　The immersion nozzle has a molten steel flow rate of 0.04 (t / (min. · Cm 2 )) based on the minimum cross-sectional area position in the region where the cross-sectional shape of the inner hole in the lateral direction near the upper end of the immersion nozzle is circular. The immersion nozzle according to any one of 1 to 7 above, which is for continuous casting. [0015] 　In the present invention, the width Wn and the thickness Tn of the inner hole are the width (length in the long side direction) of the inner hole at the upper end position of the pair of discharge holes provided on the short side side wall portion of the immersion nozzle. ， Thickness (length in the short side direction). Effect of the invention [0016] 　The flat immersion nozzle of the present invention controls the molten steel flow in a continuous state in which the molten steel flow is gradually increased or decreased without being fixedly or completely separated from the central portion to the lateral portion. It is possible to secure an appropriate balance of the molten steel flow in the immersion nozzle. As a result, the molten steel flow rate is approximately 0.04 (t / (min. · Cm 2 )) based on the operating conditions, especially the minimum cross-sectional area position in the region where the lateral cross-sectional shape near the upper end of the immersion nozzle is circular. Even in continuous casting, which tends to generate a high-speed or large amount of molten steel flow on the side discharge hole side under the above conditions, the flow velocity or flow rate of the molten steel flowing out of the discharge hole is appropriately suppressed, and the hot water in the mold is used. The surface etc. can be stabilized, that is, the fluctuation can be reduced. 　As a result, the quality of the slab can be improved by suppressing the fluctuation of the molten metal level in the mold, reducing the entrainment of powder and the like in the mold, and promoting the floating of inclusions in the molten steel. In addition, since excessive molten steel flow to the side wall of the mold is suppressed, the risk of accidents such as breakout can be reduced. A brief description of the drawing [0017] FIG. 1 is an image diagram showing an example (first embodiment of the present invention) of the immersion nozzle of the present invention in which a lateral protrusion is installed. FIG. 1A is a cross-sectional view passing through the center on the short side, and FIG. 1B is a length. There is a cross-sectional view (view AA) passing through the center of the side. FIG. 2 is an image diagram showing an example (second embodiment of the present invention) of the immersion nozzle of the present invention in which a pair of lateral protrusions are installed above in addition to the lateral protrusions of FIG. 1, and FIG. 2A is a short side. A cross-sectional view passing through the center of the side, (b) is a cross-sectional view (viewing AA) passing through the center of the long side. FIG. 3 is an image diagram showing an example of an immersion nozzle of the present invention in which a central protrusion is provided between the lateral protrusions of FIG. 1 (third embodiment of the present invention), in which FIG. 1A passes through the center on the short side. The cross-sectional view, (b) is a cross-sectional view (view AA) passing through the center on the long side. FIG. 4 is an image diagram showing an example (fourth embodiment of the present invention) of the immersion nozzle of the present invention in which a pair of lateral protrusions are installed above in addition to the lateral protrusions of FIG. 3 and the central protrusions between them. , (A) is a cross-sectional view passing through the center on the short side, and (b) is a cross-sectional view passing through the center on the long side (view AA). FIG. 5 is an enlarged view of the vicinity of the portion where the central protrusion is installed between the lateral protrusions in FIG. 3 or 4, and the central portion of the central protrusion is a straight line in the upward direction and has a chevron shape. Furthermore, it is a cross-sectional view passing through the center on the short side of an example in which the central portion of the bottom protruding portion is a straight line in the upward direction and forms a chevron shape. 6 is a top view of the inner hole of the immersion nozzle of FIG. 5, and is an image diagram showing the relationship between the lateral protrusion and the central protrusion. FIG. 7 is an image diagram showing a cross section passing through the center on the short side side of the immersion nozzle in an example in which the upper end portion of the central protrusion portion in FIG. 5 is a curved surface. FIG. 8 is an image diagram showing a cross section passing through the center on the short side side of the immersion nozzle in an example in which the upper end portion of the central protrusion portion in FIG. 5 is a flat surface. [Fig. 9] Fig. 9 is an image diagram showing a cross section passing through the center of the long side of the immersion nozzle in an example of a shape in which the upper surface of the lateral protrusion or the central protrusion is inclined toward the center of the inner hole. FIG. 10 is an image view of a top view showing an example in which the protrusion lengths of the upper surfaces of the lateral protrusion and the central protrusion of FIG. 5 are constant (the end on the inner hole side is parallel to the wall surface in the width direction). FIG. 11 is an image diagram of a top view showing an example in which the protrusion length of the upper surface of the central protrusion in FIG. 5 is reduced or contracted in a straight line in the central direction. [Fig. 12] Fig. 12 is an image of a top view showing an example in which the protrusion length of the upper surface of the central protrusion in FIG. 5 is reduced or contracted in a curved line in the central direction. [Fig. 13] Fig. 13 is an image of a top view showing an example in which the protrusion lengths of the upper surfaces of the lateral protrusion and the central protrusion in FIG. 5 are straight and integrated and continuously reduced. FIG. 14 is an image diagram showing a cross section passing through the center on the short side in an example in which the upper surface of the bottom protruding portion of the immersion nozzle of FIG. 5 is a flat surface. FIG. 15 is an image diagram showing a cross section passing through the center on the short side in an example in which the upper surface of the bottom protruding portion of the immersion nozzle of FIG. 5 is a curved surface. FIG. 16 is an image diagram showing a cross section passing through the center on the short side in an example in which the upper surface of the bottom protruding portion of the immersion nozzle of FIG. 5 is provided with a convex portion in the center and the diameter is expanded toward the bottom. FIG. 17 is an image diagram showing a cross section passing through the center on the short side side in an example in which a hole for discharging molten steel is also provided in the bottom protruding portion of the immersion nozzle of FIG. [Fig. 18] Fig. 18 is an image diagram showing changes in the mold and the molten metal surface (molten steel surface) in the mold. FIG. 18A is an image diagram of a top view of the vicinity of the mold molten metal surface (inner surface), and FIG. It is an image diagram of the cross-sectional view (half in the vertical direction) passing through the center on the short side side of. FIG. 19 is a diagram showing fluctuations (maximum value, left-right average) of the molten metal surface (molten steel surface) in the mold of Example 3 in Table 1. Mode for carrying out the invention [0018] 　It is possible to form a molten steel flow toward the end side in the width direction to some extent by installing a flow diversion means as described in Patent Document 3. However, when such a fixed or complete diversion is performed, a part of the inner hole, that is, a molten steel flow separated by a single narrow range is generated, and the part where the flow direction and the flow velocity are different depending on the location of the inner hole. It is easy to occur. In particular, when the flow rate or direction fluctuates due to the flow rate control of molten steel, the molten steel flow is biased to either side, and the discharge flow from the immersion nozzle into the mold and the molten metal surface may be significantly disturbed. [0019] 　Therefore, in the present invention, for example, as shown in the first embodiment of FIG. 1, first, on the side surface of the wall surface in the width direction (long side side) of the flat portion of the immersion nozzle 10, with respect to the central axis of the wall surface in the width direction. A pair of axisymmetric lateral protrusions 1 (see FIG. 1 (a) and the like; hereinafter, also simply referred to as “axially symmetric lateral protrusions”) are installed. 　The upper surfaces of the pair of lateral protrusions 1 are inclined from the central side of the side protrusions 1 in the width direction and downward direction of the flat portion, that is, in the direction of the discharge hole 4. Due to such an inclination, the flow velocity and flow mode of the molten steel from the inner hole 3 or the discharge hole 4 can be gently changed and optimized while suppressing the generation of eddy currents and the like. [0020] 　The pair of axially symmetric lateral protrusions are also installed on the other widthwise wall surface sandwiching the inner hole so as to face each other in a plane-symmetrical relationship with respect to the thickness direction of the flat portion (FIG. 1 (b)). Etc. Hereinafter, the lateral protrusions having a plane-symmetrical relationship are also simply referred to as “plane-symmetrical lateral protrusions”. In the present invention, for example, as shown in FIG. 6, the plane-symmetrical lateral protrusions 1 are arranged. The total length Ts in the thickness direction of the lateral protrusion 1 having the thickness Tn of the inner hole at the designated position is 0.18 or more and 0.90 or less. That is, the lateral protrusions are plane-symmetrical. There is a space through which the molten steel passes between the parts. 　By providing a space with such an interval, the molten steel flow does not divide in the inner hole in a fixed and complete manner, and the part through which the molten steel flow passes. The flow direction and flow velocity are gently controlled. This makes it possible to alleviate the flow of molten steel flow on the discharge hole side with a clear boundary. [0021] 　In addition, by adjusting the installation location, length, direction, etc. of the lateral protrusions, it is possible to avoid concentrating the molten steel flow near the center or on the side, and at the end side in the width direction, that is, on the discharge hole side and the center side. It is possible to give an appropriate balance to the molten steel flow while dispersing in. Moreover, not only is it dispersed, but the space is also connected even in the area where the lateral protrusions are installed, so the molten steel flow is not completely divided but forms a gentle boundary while being gently mixed and homogenized. However, it becomes a distributed flow. [0022] 　As described above, the installation location, length, direction, etc. of the lateral protrusion can be adjusted as appropriate. For example, in the second embodiment shown in FIG. 2, in addition to the lateral protrusion of FIG. 1 (indicated by the reference numeral 1a in FIG. 2, hereinafter also referred to as “lower lateral protrusion”), the lateral protrusion is upward. A pair of protrusions (indicated by the reference numeral 1b in FIG. 2 and hereinafter also referred to as “upper side protrusions”) are installed. [0023] 　Further, in the present invention, between the axisymmetric lateral protrusions, the protrusions having a smaller protrusion length than the axisymmetric lateral protrusions as in the third and fourth modes shown in FIGS. 3 and 4 are formed. (Central protrusion) can be installed. In the third embodiment shown in FIG. 3, a central protrusion 1p is provided between the axially symmetric lateral protrusions 1 and 1 in FIG. 1, and in the fourth embodiment shown in FIG. 4, the axial symmetry in FIG. 2 is provided. A central protrusion 1p is installed between the lower side protrusions 1a and 1a of the above. [0024] 　In this structure, by installing a protrusion having a protrusion length larger than that of the axisymmetric lateral protrusion in Patent Document 4, the lateral protrusion is laterally more than the molten steel flow between the axisymmetric lateral protrusions. It has the opposite effect of increasing the molten steel flow, that is, it has the effect of increasing the ratio of the molten steel flow / the lateral molten steel flow between the axisymmetric lateral protrusions (central portion). In continuous casting with a large flow rate of molten steel (approximately 0.04 (t / (min. · cm 2 ) or more)), the molten steel flow between the axisymmetric lateral protrusions (central portion) / lateral molten steel flow It is often effective to reduce the ratio of. [0025] 　The balance between the molten steel flow to the central part and the molten steel flow to the side is determined by the magnitude of the molten steel flow velocity (flow rate of molten steel per unit time and unit cross-section), drawing speed, mold size / shape, immersion depth, and so on. It can be optimized by the nozzle structure such as the discharge hole area. Specifically, the structure should be such that there is no central protrusion between the lateral protrusions that are axisymmetric, such as the width or downward angle of the lateral protrusion, the length in the width direction, and the protrusion length. Methods such as adjusting the protrusion height of the central protrusion and adjusting the shape of the upper end surface can be adopted. 　Specifically, regarding the protruding length of the central protruding portion, as illustrated in FIG. 6, the protruding length Tp / 2 is smaller than the protruding length Ts / 2 of the lateral protruding portion 1, and the side thereof. The total protrusion length Tp, where the thickness Tn of the inner hole at the position where the direction protrusion 1 is arranged is 1, is set to 0.40 or less. In other words, Tp