WO2020153195A1

WO2020153195A1 - Immersion nozzle

Info

Publication number: WO2020153195A1
Application number: PCT/JP2020/001078
Authority: WO
Inventors: 福永　新一; 和久香月; 順也矢野; 大樹古川
Original assignee: 黒崎播磨株式会社
Priority date: 2019-01-21
Filing date: 2020-01-15
Publication date: 2020-07-30
Also published as: CN113226594A; JP7134105B2; JP2020116591A; TW202035036A; BR112021010225A2; US20220134420A1; TWI731561B; EP3915696A4; CA3121954A1; EP3915696A1; CN113226594B; ZA202103504B

Abstract

The objective of the present invention is to stabilize a discharge flow of molten steel and stabilize the melt surface inside a mold, that is, to reduce fluctuation thereof, in a flat immersion nozzle. In the present invention, lateral protrusion parts 1 protruding in the thickness direction are provided in the wall surface in the width direction of a flat portion in an immersion nozzle, which has a flat shape in which the width Wn of an inner hole is greater than the thickness Tn of the inner hole. These lateral protrusion parts 1 are arranged so as to form a pair slanting in the width direction and downward, at axisymmetric positions with respect to center axis in the vertical direction of the wall surface in the width direction, and the lateral protrusion parts 1 are arranged facing each other in both wall surfaces in the width direction.

Description

Immersion nozzle

The present invention relates to a dipping nozzle for continuous casting in which molten steel is poured from a tundish into a mold, and particularly in a lateral direction (vertical direction) near a discharge hole of a dipping nozzle such as used for thin slabs and medium-thickness slabs. Perpendicular to the direction) The section relates to a flat immersion nozzle.

In a continuous casting process in which molten steel is continuously cooled and solidified to form a slab having a predetermined shape, a continuous casting immersion nozzle (hereinafter, simply referred to as “immersion nozzle”) installed at the bottom of a tundish is used. Molten steel is poured into the mold.

In general, an immersion nozzle is composed of a pipe body having a bottom portion, the upper end portion of which is a molten steel introduction port, and a molten steel flow passage (inner hole) extending downward from the molten steel introduction port is formed inside thereof. On the side surface, a pair of discharge holes communicating with the molten steel flow path (inner hole) are formed facing 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 is prevented from scattering, and the contact between the molten steel and the atmosphere is blocked to prevent oxidation. In addition, by using the immersion nozzle, the molten steel in the mold is rectified so that impurities such as slag and non-metallic inclusions floating on the molten metal surface are prevented from being caught in the molten steel.

In recent years, there has been an increase in the production of thin slabs such as thin slabs and medium-thickness slabs during continuous casting. The dipping nozzle for accommodating such a thin mold for continuous casting needs to be flat. For example, Patent Document 1 discloses a flat immersion nozzle in which a discharge hole is provided on a short side wall, and Patent Document 2 discloses a flat immersion nozzle in which a discharge hole is further provided on a lower end surface. In these flat dipping nozzles, generally, the width of the inner hole is enlarged between the molten steel introduction port and the discharge hole to the mold.

However, in the case of such a shape that the width of the inner hole expands and the shape is flat, the molten steel flow in the immersion nozzle is likely to be disturbed, and the discharge flow to the mold is also disturbed. This turbulence of the molten steel flow is also a cause of increased fluctuations of the molten metal surface (molten steel surface) in the mold, entrainment of powder in the slab, temperature non-uniformity, and other factors causing poor slab quality and increased operational risk. Become. Therefore, it is necessary to stabilize the molten steel flow in the immersion nozzle and discharged.

In order to stabilize these molten steel flows, for example, Patent Document 3 discloses an immersion nozzle in which at least two bending facets are formed from a point (center) on the plane below the inner hole toward the lower edge of the discharge hole. Has been done. Further, Patent Document 3 discloses an immersion nozzle equipped with a flow divider that divides the molten steel flow 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 shape in the internal space as in

Patent Documents

1 and 2. Will be more stable.

However, in the case of such a means for diverting the molten steel flow in the left-right direction, the variation of the molten steel discharge flow between the left and right discharge holes is still large, and the variation of the molten metal level in the mold may be increased accordingly. is there.

Under the background described above, the present inventors have invented the flat immersion nozzle shown in Patent Document 4 and have contributed to stabilizing the molten metal surface in the mold.

Japanese Patent Laid-Open No. 11-5145 JP-A-11-47897 Japanese Patent Publication No. 2001-501132 International Publication No. 2017/81934

However, even with the flattened submerged 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 transverse cross sectional shape of the inner hole near the top of the submerged nozzle is circular. The present inventors have found that in continuous casting performed under conditions such as 04 (t/(min.·cm ² )) or more, the effects such as stabilization of the molten metal surface in the mold may still be insufficient.

Therefore, the problem to be solved by the present invention is to provide a flat immersion nozzle that stabilizes the molten metal surface in the mold, that is, reduces the fluctuation.

In the flat dipping nozzle of Patent Document 4, a protruding portion is installed mainly in the center of the inner hole, and based on that, for fine adjustment adjustment of the discharge flow, shape, etc., the same or protruding to the center also on the side thereof. Install a protrusion with a small thickness.
On the other hand, in the present invention, symmetrical projecting portions are installed laterally, and the space between the projecting portions is based on the space without the projecting portion or the lateral projecting portion, and the projecting length is longer than that of the lateral projecting portion. Install a small protrusion.

In the structure of the flat-shaped immersion nozzle of Patent Document 4, the molten steel flow in the inner hole is set to have a larger flow amount to the side (in the width direction of the flat portion of the nozzle; the same applies hereinafter) than the direction directly below the center. Lead. In this case, the molten steel flow rate from the discharge hole tends to increase, and the fluctuation of the molten metal level in the mold may increase under conditions such as a large molten steel flow rate per unit time or 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 directly below the center, and the flow rate to the side 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 made relatively larger than in the case of the structure of the immersion nozzle of Patent Document 4.
In the above, basically, the ratio is adjusted in the relationship of the flow rate in the direction directly below the center/the flow rate in the lateral direction. Absent.

The present invention for obtaining the above-mentioned flow form is the following flat nozzles 1 to 8.
1.
An immersion nozzle having a flat shape in which the width Wn of the inner hole is larger than the thickness Tn of the inner hole and having a pair of discharge holes in the lower part of the short side wall,
On the wall surface in the width direction of the flat portion, at a position axially symmetric with respect to the longitudinal center axis of the wall surface in the width direction, a portion that inclines downward in the width direction and protrudes in the thickness direction (hereinafter referred to as “side”). "Protrusions") are arranged in pairs,
The lateral protrusions are arranged on both side walls in the width direction so as to face each other,
The total protrusion length Ts in the thickness direction of the lateral protrusions, where the thickness of the inner hole at the position where the lateral protrusions are arranged is 1, is 0 for each of the two lateral protrusions forming the pair. Immersion nozzle that is the same between 18 and 0.90.
2.
On the wall surface in the width direction between the two lateral projections forming the pair, the projection length in the thickness direction is smaller than the projection length in the thickness direction of the lateral projections, and A protrusion having a total protrusion length Tp in the thickness direction of which the thickness of the inner hole at the position where the protrusion is arranged is 1 is 0.40 or less (not including zero) (hereinafter referred to as "central protrusion"). .) is installed, The immersion nozzle as described in 1 above.
3.
3. The immersion nozzle according to 2 above, wherein the upper end surface of the central protruding portion has a horizontal shape in the width direction or a curved shape having a vertex at the center or a shape protruding upward including a bending point.
4.
4. The immersion nozzle according to any one of 1 to 3 above, wherein the upper end surfaces of the side protruding portion and the central protruding portion have a horizontal shape in a central direction of the inner hole or a shape inclined downward with a flat surface or a curved surface. ..
5.
One or both of the side protruding portion and the central protruding portion may have the same protruding length, or may be a straight line, a curved line, or a stepped shape that is shortened toward the center of the widthwise wall surface. The immersion nozzle according to any one of 1 to 4 above.
6.
Either one or both of the side protrusions provided with the side protrusions and the central protrusions are installed at a plurality of positions in the vertical direction, according to any one of 1 to 5 above. Immersion nozzle.
7.
7. The immersion nozzle according to any one of 1 to 6 above, which has an upward protruding portion 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 )) with reference to the minimum cross-sectional area position in a region where the transverse cross-sectional shape of the inner hole 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.

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 wall of the immersion nozzle. , Thickness (length in the short side direction).

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 portions. Therefore, 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 area where the horizontal cross-sectional shape near the top of the immersion nozzle is circular. Even in continuous casting, which is performed under the above conditions and tends to generate a high velocity or a large amount of molten steel flow on the side of the discharge holes, the flow velocity or flow rate of the molten steel flowing out from the discharge holes is suppressed appropriately, The surface can be stabilized, that is, its fluctuation can be reduced.
As a result, the fluctuation of the molten metal level in the mold is suppressed, so that the inclusion of powder and the like in the mold is reduced, and the floating of the inclusions in the molten steel is promoted, so that the quality of the slab can be improved. Further, since the excessive molten steel flow to the side wall of the mold is suppressed, the risk of accident such as breakout can be reduced.

It is an image figure which shows the example (1st form of this invention) of the immersion nozzle of this invention which installed the side protrusion, (a) is sectional drawing which passes along the short side center, (b) shows the long side center. There is a sectional view (view AA) passing through. FIG. 1A is an image diagram showing an example of the immersion nozzle of the present invention (a second embodiment of the present invention) in which a pair of side protrusions is installed in addition to the side protrusions of FIG. 1, (a) passing through the center of the short side. Sectional view (b) is a sectional view (view AA) passing through the center of the long side. FIG. 3 is an image view showing an example of the immersion nozzle of the present invention (third embodiment of the present invention) in which a central protrusion is installed between the side protrusions of FIG. 1, (a) is a cross-sectional view passing through the center of the short side, b) is a sectional view (view AA) passing through the center of the long side. FIG. 3A is an image diagram showing an example of the immersion nozzle of the present invention (fourth embodiment of the present invention) in which, in addition to the lateral protrusions and the central protrusion between them in FIG. Is a cross-sectional view passing through the center of the short side, and (b) is a cross-sectional view (view AA) passing through the center of the long side. FIG. 5 is an enlarged view of the vicinity of the portion where the central protrusion is installed between the side protrusions of FIG. 3 or FIG. 4, the central portion of the central protrusion is a straight mountain chevron, and the bottom protrusion is further formed. FIG. 6 is a cross-sectional view of the example in which the central portion of the above has a mountain shape with a straight line in the upward direction, and passing through the center of the short side. FIG. 6 is a top view of the inner hole of the immersion nozzle shown in FIG. 5, and is an image diagram showing a relationship between a side protrusion and a central protrusion. FIG. 6 is an image diagram showing a cross section that passes through the center of the short side of the immersion nozzle in an example where the upper end of the central protruding portion of FIG. 5 is a curved surface. FIG. 6 is an image diagram showing a cross section that passes through the center of the short side of the immersion nozzle in an example in which the upper end of the central protruding portion of FIG. 5 is a flat surface. It is an image figure which shows the cross section which passes along the long side side center of an immersion nozzle in the example of the shape which the upper surface of a side protrusion part or a center protrusion part inclines toward the inner hole center direction. FIG. 6 is a top view image diagram showing an example in which the protruding lengths of the upper surfaces of the side protruding portion and the central protruding portion of FIG. 5 are constant (the inner hole side end portion is parallel to the width direction wall surface). FIG. 6 is a top view image diagram showing an example in which the projection length of the upper surface of the central protruding portion of FIG. 5 is linearly reduced in the central direction. FIG. 6 is a top view image diagram showing an example in which the protruding length of the upper surface of the central protruding portion of FIG. 5 is curvilinearly reduced in the central direction. FIG. 6 is a top view image diagram showing an example in which the protrusion lengths of the upper faces of the side protrusions and the central protrusion of FIG. 5 are linear and integrally reduced continuously. FIG. 6 is an image diagram showing a cross section passing through the center of the short side in an example in which the upper surface of the bottom protruding portion of the immersion nozzle in FIG. 5 is a plane. It is an image figure which shows the cross section which passes along the center of a short side in the example which the upper surface of the bottom protrusion part of the immersion nozzle of FIG. 5 is a curved surface. It is an image figure which shows the cross section which passes along the center of a short side in the example which the upper surface of the bottom protrusion part of the immersion nozzle of FIG. 5 equips with a convex part in the center, and expands diameter toward the bottom. It is an image figure which shows the cross section which passes along the center of a short side in the example which equips the bottom protrusion part of the immersion nozzle of FIG. 5 with the hole for molten steel discharge. FIG. 3 is an image view showing a change in the mold and the molten metal surface (molten steel surface) in the mold, (a) is a top view image diagram near the mold molten metal surface (inner surface), and (b) is a short side near the molten metal surface (inner surface) It is an image figure of the cross-sectional view (longitudinal half) which passes along the center. It is a figure which shows the fluctuation|variation (maximum value, right-and-left average) of the molten metal surface (molten steel surface) in the mold of Example 3 of Table 1.

The molten steel flow to the widthwise end portion side can be formed to some extent by installing the flow dividing means as in the above-mentioned Patent Document 3. However, when such a fixed or complete diversion is carried out, a part of the inner hole, that is, a molten steel flow separated into a single narrow area is generated, and a part having a different flow direction and flow velocity at each position of the inner hole is generated. It is easy to occur. Especially when there is a change in the flow rate or direction due to molten steel flow rate control, etc., the molten steel flow may be biased in one direction, and the discharge flow from the dipping nozzle into the mold and the molten surface may be significantly disturbed.

Therefore, in the present invention, for example, as shown in the first embodiment of FIG. 1, first, at the side portion of the wall surface in the width direction (long side) of the flat portion of the immersion nozzle 10, with respect to the center axis of the width direction wall surface. A pair of axially symmetric side protrusions 1 (see FIG. 1A and the like. Hereinafter, also simply referred to as “axisymmetric side protrusions”) are installed.
The upper surfaces of the pair of side protrusions 1 are inclined from the center side of the side protrusions 1 in the width direction of the flat portion and downward, that is, in the direction of the discharge hole 4. With such an inclination, the flow velocity and flow form of the molten steel from the inner hole 3 or the discharge hole 4 can be gently changed while optimizing the generation of vortex and the like, and can be optimized.

The pair of axisymmetric side protrusions are installed on the other widthwise wall surface sandwiching the inner hole so as to face each other in a plane-symmetric relationship with respect to the thickness direction of the flat portion (FIG. 1(b)). Etc. Hereinafter, the side protrusions having a plane symmetry relationship are also simply referred to as “plane symmetry side protrusions.” In the present invention, for example, as shown in FIG. The total length Ts in the thickness direction of the lateral protrusions 1 with the thickness Tn of the inner hole at the specified position being 1 is set to 0.18 or more and 0.90 or less, that is, the lateral symmetry of plane symmetry. There is a space through which molten steel passes between the parts.
By providing the space with such an interval, the molten steel flow is not fixedly and completely divided in the inner hole, but the flow direction and flow velocity of the portion where the molten steel flow passes are gently controlled. As a result, the molten steel flow can be mitigated from flowing toward the discharge hole with a clear boundary.

In addition, by adjusting the installation location, length, direction, etc. of the lateral protrusion, it is possible to avoid concentrating the molten steel flow near the center or on the lateral side, and at the same time, on the width direction end side, that is, the discharge hole side and the center side. It is possible to give an appropriate balance to the molten steel flow while being dispersed. Moreover, not only is it simply dispersed, but since the space is in communication even in the area where the lateral protrusions are installed, the molten steel flow is not completely divided but forms a gentle boundary, and is gently mixed and homogenized. While becoming a dispersed flow.

Note that, as mentioned 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 protrusions of FIG. 1 (denoted by reference numeral 1a in FIG. 2 and hereinafter also referred to as “lower lateral protrusions”), they are laterally upward. A pair of protrusions (indicated by reference numeral 1b in FIG. 2 and hereinafter also referred to as "upper side protrusions") are installed.

Further, according to the present invention, between the axisymmetric side protrusions, as in the third and fourth embodiments shown in FIGS. 3 and 4, the protrusions having a smaller protrusion length than the axisymmetric side protrusions. (Center protrusion) can be installed. In the third embodiment shown in FIG. 3, the central protrusion 1p is installed between the axially

symmetrical side protrusions

1 and 1 shown in FIG. 1. In the fourth embodiment shown in FIG. 4, the central protrusion 1p is provided. A central protrusion 1p is provided between the

lower side protrusions

1a, 1a.

In this structure, in Patent Document 4, by providing a protrusion having a protrusion length larger than that of the axisymmetric side protrusion, the structure is provided to a side of the molten steel flow between the axisymmetric side protrusions. This has the opposite effect of increasing the molten steel flow, that is, the effect of increasing the ratio of the molten steel flow between the axisymmetric lateral protrusions (central portion)/the lateral molten steel flow. 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 side protrusions (central part)/the molten steel flow to the side It is often effective to reduce the ratio of.

The balance between the molten steel flow to the central part and the molten steel flow to the side is such as the magnitude of molten steel flow velocity (molten steel flow rate per unit time, per unit cross-sectional area), drawing speed, mold size/shape, immersion depth, and so on. It can be optimized depending on the nozzle structure such as the discharge hole area. Specifically, there is no central protrusion between the side protrusions that are axially symmetrical, such as the widthwise or downward angle of the side protrusions, the length in the width direction, the protrusion length, or the like. Methods such as adjusting the protruding height of the central protruding portion and adjusting the shape of the upper end surface can be adopted.
Specifically, as shown in FIG. 6, the protrusion length Tp/2 of the central protrusion is smaller than the protrusion length Ts/2 of the lateral protrusion 1, and The total protrusion length Tp with the thickness Tn of the inner hole at the position where the directional protrusion 1 is arranged being 1 is set to 0.40 or less. In other words, Tp<Ts and Tp/Tn≦0.40.

Further, the upper end surface of the central protruding portion has a horizontal shape in the width direction as shown in FIG. 8 or a shape protruding upward including a curved surface or a bending point having the center at the apex as shown in FIGS. 5 and 7. be able to. With such a shape, the flow velocity and flow form of molten steel can be further changed and optimized.

Further, as shown in FIG. 9, the upper end surface of the lateral protrusion or the central protrusion has a boundary portion with the wall surface in the width direction (long side) of the flat portion of the immersion nozzle as an apex in the thickness direction of the flat portion of the immersion nozzle. It is also possible to incline downward in the central direction, that is, in the central direction of the inner hole (space side). With such an inclination, the flow velocity and flow form of molten steel can be further changed and optimized.

Further, the protrusion length of the upper end surface of the side protrusion or the central protrusion can be the same as shown in FIG. 10, and as shown in FIGS. It is also possible to incline so that the length becomes shorter toward the center of the wall surface. With such an inclination, the flow velocity and flow form of molten steel can be further changed and optimized.

In a flat dipping nozzle, the discharge holes on the short side wall are opened long in the vertical direction, so there may be a part where the discharge flow velocity decreases at the upper side, especially near the upper end. A backflow phenomenon that draws into the submerged nozzle is also often seen. Therefore, in the present invention, as shown in FIG. 2 and FIG. 4, for example, in addition to the above-mentioned axially symmetric and plane symmetric lower side protrusions 1a, one or a plurality of axially symmetric and plane symmetric side protrusions are provided above the lower side protrusions 1a. 1b (upper side protrusion) can be installed. The upper side protruding portion 1b can have the same optimized structure as the lower side protruding portion 1a.

The upper side protruding portion 1b suppresses a decrease in flow velocity particularly above the discharge hole, or suppresses turbulence of the molten steel flow such as backflow near the upper end to uniformize the flow velocity distribution at each vertical position of the discharge hole. It also has the function of adjusting the flow balance in the upper limit direction while complementing the function of
Also between the

upper side protrusions

1b and 1b, a central protrusion can be installed in the same manner as between the

lower side protrusions

1a and 1a described above.

The bottom part 5 inside the immersion nozzle may be a wall surface as a partition wall with a mold, instead of forming a discharge hole near the center as shown in FIG. 14, or FIG. 1 to FIG. 5, FIG. 7, FIG. As shown in FIGS. 15 and 16, the structure may be such that the central portion is projected upward and the bottom projection portion is included. Further, as shown in FIG. 17, a discharge hole 6 may be provided in the bottom portion 5. Such a protruding structure of the bottom portion is useful for changing the flow direction/form, flow velocity, etc. when converting the molten steel flow to the central portion into the discharge hole direction.

Next, the present invention will be described together with examples.

[Example A]
Example A is the second embodiment of the present invention shown in FIG. 2, that is, axially symmetric and plane symmetrical two-

sided protrusions

1a and 1b are installed as protrusions, and the

lower side protrusions

1a and 1a are arranged between them. A mode in which the central protrusion is not installed, and a fourth mode of the present invention shown in FIG. 4, that is, axially symmetric and plane symmetric side protrusions 2

steps

1a and 1b are installed as the protrusions, and the lower side protrusion 1a is installed. , 1a between the submerged nozzles in which the central protruding portion 1p is installed between the lower side protruding portion 1a and the central protruding portion 1p in the submerged nozzle inner hole space direction (a total of a pair of plane-symmetrical protruding portions). (Length) Ts, Tp to the thickness of the inner hole of the immersion nozzle (length in the short side direction) Tn, Ts/Tn, Tp/Tn, and the level of fluctuations in the casting mold (deviation index in casting mold and fluctuations in casting mold) It is the result of a water model experiment showing the relationship of (height).

The specifications of the immersion nozzle are as follows.
・Total length: 1165 mm
・Melted steel inlet: φ86mm
・Inner hole width (Wn) at the top of the discharge hole: 255 mm
・Inner hole thickness (Tn) at the top of the discharge hole: 34 mm
・Height from the lower end surface of the nozzle at the upper end position of the discharge hole: 146.5 mm
・Height of central protruding portion (height from the lower end surface of the nozzle): 155 mm
・Wall thickness of immersion nozzle: Approx. 25 mm
・Thickness of bottom of dipping nozzle (top of central part): Height 100mm
・Upward lateral protrusion (1b): The length in the width direction of the immersion nozzle (each on the left and right) is 25 mm,
Ts/Tn ratio=0.74
The inclination angle to the discharge hole direction is 45 degrees,
The immersion nozzle on the top surface is horizontal in the width and thickness directions,
100 mm between the lateral protrusions,
No central protruding part ・Lower lateral protruding part (1a): 40 mm in length (left and right) in the width direction of the immersion nozzle
Ts/Tn ratio=0.1 to 1.0 (no space),
The inclination angle to the discharge hole direction is 45 degrees,
The immersion nozzle on the top surface is horizontal in the width and thickness directions,
60 mm between the lateral protrusions,
Central protrusion Tp/Tn ratio=0 (none) to 0.7

The conditions of the mold and fluid are as follows.
・Width of mold: 1650mm
-Thickness of mold: 65 mm (center upper end 185 mm)
・Dip depth (from top of discharge hole to water surface): 83mm
・Fluid supply rate: 0.065t/(min·cm ² )
*Value converted to molten steel

Here, the index of drift in the mold is set to be 1.0 when there is no drift, and 0.8 is the index of drift in the mold ≦1.2, and the height of fluctuation of the molten metal in the mold (mm) is ≦15 mm. It was considered that the effect was obtained, and it was used as the evaluation standard.
The drift index in the mold is measured in water model experiments by measuring the flow velocities of the left and right set molten metal surfaces (30 mm underwater from the upper end of the set water level) of the immersion nozzle in the mold, and comparing the left and right flow rates. It is the absolute value when expressed by, that is, the value of the left flow velocity/the right flow velocity (or the right flow velocity/the left flow velocity), and the level of fluctuation of the molten metal in the mold is the maximum value of Sw in FIG.

The results are shown in Table 1.

It can be seen that the drift index in the mold and the fluctuation level of the molten metal surface in the mold can satisfy the criteria when the ratio of Ts to Tn (Ts/Tn) is 0.18 or more and 0.90 or less for the lateral protrusion.
Further, in the case where the central protruding portion is installed, when the protruding length is smaller than the protruding length of the lateral protruding portion (Tp<Ts) and the Tp ratio (Tp/Tn) to Tn is 0.4 or less, It turns out that the criteria can be met.

[Example B]
In Example B, in the fourth mode of the present invention shown in FIG. 4, the upper end surfaces of the lower side protruding portion 1a and the central protruding portion 1p are inclined downward in a plane toward the center of the inner hole as shown in FIG. These are the results of water model experiments showing the degree of fluctuation in the molten metal level in the mold when the shape is changed.

Here, the Ts/Tn ratio of the lower side protruding portion=0.74, the Tp/Tn ratio of the central protruding portion=0.18, and the inclination angles of the lower side protruding portion and the central protruding portion toward the inner hole ( 9 is compared with the case of 0 degree (horizontal) and the case of 45 degrees. Other conditions are the same as in Example A.

The results are shown in Fig. 19. The vertical axis of FIG. 19 is a value obtained by averaging the maximum melt level fluctuation value Sw (mm) in the left and right directions of the discharge hole regardless of whether the inclination angle θ is 0 degrees or 45 degrees.

As shown in FIG. 19, when the inclination angle θ is 0 degree or 45 degrees, the value is significantly smaller than the reference value of 15 mm, but when the inclination angle θ is 45 degrees, the value is 2.0 (mm) and 0 degree. It can be seen that it is reduced to about 1/2 of 3.75 (mm).

10: Immersion nozzle 1: Side protruding part 1a: Lower side protruding part 1b: Upper side protruding part 1p: Central protruding part 2: Molten steel introducing port 3: Inner hole (molten steel flow path)
4: Discharge hole (short side wall side)
5: Bottom part 6: Discharge hole (bottom part)
7: molten metal surface 20: mold Wn: width of inner hole of immersion nozzle (length in long side direction)
Wp: Width between both ends of the lateral protrusion Wc: Width of central protrusion Tn: Thickness of inner hole of immersion nozzle (length in short side direction)
Ts: protrusion length of the lateral protrusion in the space direction (total length of a pair)
Tp: Length of protrusion of the central protrusion in the space direction (total length of a pair)
ML: Mold width (long side)
Ms: Mold thickness (short side, side)
Mc: Mold thickness (short side, central part)
Sw: Fluctuation width of molten metal in the mold (dimension between upper and lower ends)

Claims

An immersion nozzle having a flat shape in which the width Wn of the inner hole is larger than the thickness Tn of the inner hole and having a pair of discharge holes in the lower part of the short side wall,
On the wall surface in the width direction of the flat portion, at a position axially symmetric with respect to the longitudinal center axis of the wall surface in the width direction, a portion that inclines downward in the width direction and protrudes in the thickness direction (hereinafter referred to as “side”). "Protrusions") are arranged in pairs,
The lateral protrusions are arranged on both side walls in the width direction so as to face each other,
The total protrusion length Ts in the thickness direction of the lateral protrusions, where the thickness of the inner hole at the position where the lateral protrusions are arranged is 1, is 0 for each of the two lateral protrusions forming the pair. Immersion nozzle that is the same between 18 and 0.90.
On the wall surface in the width direction between the two lateral projections forming the pair, the projection length in the thickness direction is smaller than the projection length in the thickness direction of the lateral projections, and A protrusion having a total protrusion length Tp in the thickness direction of which the thickness of the inner hole at the position where the protrusion is arranged is 1 is 0.40 or less (not including zero) (hereinafter referred to as "central protrusion"). .) is installed, The immersion nozzle according to claim 1.
The immersion nozzle according to claim 2, wherein an upper end surface of the central protruding portion has a horizontal shape in the width direction or a shape protruding upward including a curved surface or a bending point having a center at the apex.
The upper end surfaces of the side protruding portion and the central protruding portion have a horizontal shape in the center direction of the inner hole or a shape inclined downward with a flat surface or a curved surface, according to any one of claims 1 to 3. Immersion nozzle.
One or both of the side protruding portion and the central protruding portion may have the same protruding length, or may be a straight line, a curved line, or a stepped shape that is shortened toward the center of the widthwise wall surface. The immersion nozzle according to any one of claims 1 to 4.
One or both of the side protrusions provided with the side protrusions and the central protrusions are installed at a plurality of positions in the vertical direction, according to any one of claims 1 to 5. Immersion nozzle described.
The immersion nozzle according to any one of claims 1 to 6, which has an upward protruding portion near the center of the bottom of the inner hole.
The immersion nozzle has a molten steel flow rate of 0.04 (t/(min.·cm 2 )) with reference to the minimum cross-sectional area position in a region where the transverse cross-sectional shape of the inner hole near the upper end of the immersion nozzle is circular. The immersion nozzle according to any one of claims 1 to 7, which is for continuous casting as described above.