JP6963192B2 - Immersion nozzle for continuous casting - Google Patents

Description

The present invention relates to a dipping nozzle for continuous casting used for continuous casting of steel.

Immersion nozzles for continuous casting used for continuous casting of steel, particularly slab continuous casting, generally have a pair of discharge holes on the side surface of the nozzle. In the casting of steel using a dipping nozzle for continuous casting, it is known that the molten steel flow (hereinafter referred to as discharge flow) supplied into the mold through the discharge hole is not constant but constantly fluctuates. Therefore, the entire discharge flow is a flow from the inner tube side of the immersion nozzle to the outer peripheral side (flow in the positive direction), whereas a partial suction flow from the outer peripheral side to the inner tube side of the nozzle (flow in the negative direction). It is known that a phenomenon in which a suction phenomenon occurs, that is, a suction phenomenon may occur.

When the suction phenomenon of the discharge flow occurs, the mold powder slag that normally does not reach the inside of the immersion nozzle is also sucked, which may lead to damage to the inner pipe of the nozzle and hinder the operation. In addition, since the discharge flow condition is different from the usual one, there is a possibility that the slab quality defect rate may increase due to inclusions and the like. Further, once sucked mold powder slag is carried to a deeper part of the mold by the discharge flow, it may not be able to float and is taken into the slab, which may cause an increase in the slab quality defect rate. The cause of this suction phenomenon is that the molten steel flow flowing into the immersion nozzle is uneven, and that inclusions block the inner tube of the immersion nozzle.

The shape of the discharge hole and the structure of the immersion nozzle inner pipe for solving the bias of the molten steel flow in the immersion nozzle (hereinafter referred to as the drift) and the blockage of the immersion nozzle inner pipe are described in, for example, the following patent documents. Can be mentioned.
Patent Document 1 describes a dipping nozzle in which the dimensional shape of the discharge hole is a horizontally long shape and the ratio of the total cross-sectional area of the discharge hole to the cross-sectional area of the inner hole is 1.2 or more and 2.6 or less.
Patent Document 2 describes a dipping nozzle having a circular reduced diameter portion in the dipping nozzle inner tube.
Patent Document 3 describes a dipping nozzle having a stepped diameter-reduced portion in the dipping nozzle inner tube.
Patent Document 4 describes a dipping nozzle having a plurality of spherical protrusions on the dipping nozzle inner tube.
Patent Document 5 describes a dipping nozzle having a plurality of droplet-shaped protrusions on the inner tube of the dipping nozzle.
Patent Document 6 describes a dipping nozzle having a plurality of stepped protrusions on the dipping nozzle inner tube.

Japanese Unexamined Patent Publication No. 2001-129645 Japanese Unexamined Patent Publication No. 4-220148 Japanese Unexamined Patent Publication No. 11-123509 Japanese Unexamined Patent Publication No. 2004-255407 Japanese Unexamined Patent Publication No. 2005-297022 Japanese Unexamined Patent Publication No. 2004-283057

By using the immersion nozzles described in Patent Documents 1 to 6, it is possible to obtain a certain effect on eliminating the drift in the immersion nozzle and preventing the inner tube of the immersion nozzle from being blocked. However, even if the immersion nozzles described in Patent Documents 1 to 6 are used, the suction of the discharge flow may occur depending on various conditions such as the casting speed and the mold size, and the suction of the mold powder slag may occur. Therefore, there is a problem that the operation is hindered and the slab quality defect rate increases.

The present invention has been made to solve the above problems, and is for continuous casting that suppresses the occurrence of the suction phenomenon of the discharge flow, hinders the operation due to the suction of the mold powder slag, and suppresses the occurrence of slab quality defects. It is an object of the present invention to provide an immersion nozzle.

The immersion nozzle for continuous casting according to the present invention includes a cylindrical nozzle body having an inner tube extending along the central axis of the nozzle, and the nozzle body is formed with a discharge hole communicating with the inner tube. At least two of them are immersion nozzles for continuous casting formed on the side wall of the nozzle body, and the upper end of the inner pipe is opened at the upper end of the nozzle body, and the inner pipe has at least two contractions having a similar shape. The nozzle body is provided with a diameter portion and is formed when the nozzle body is cut along a plane including a discharge shaft passing through the opening centers of two discharge holes and a nozzle center shaft among the discharge holes formed on the side wall portion of the nozzle body. Of the cross-sectional shapes, the cross-sectional shape of the lowest reduced diameter portion located on the lowermost side of the reduced diameter portion is the upper end point of the cross-sectional shape of the lowest reduced diameter portion and the lower end point of the cross-sectional shape of the lowest reduced diameter portion. The distance from the upper end point to the lowest diameter point is the lower end point. The cross-sectional shape of the adjacent diameter-reduced portion, which has a shape larger than the distance from the diameter-to-maximum diameter-reduced portion and is adjacent to the upper side of the bottom-reduced diameter portion, and the cross-sectional shape of the bottom-reduced diameter portion are the adjacent diameter-reduced portions. and Ri mirror symmetry der respect to a plane perpendicular to the nozzle central axis in the middle of the lowermost reduced diameter portion, the straight line passing through the upper point and lower point of the cross-sectional shape of the bottom reduced-diameter portion to the outermost contraction径点The value of the ratio of the distance to the inner diameter, which is the diameter of the inner pipe at a position other than the reduced diameter portion, is 0.09 or more and less than 0.12. The distance from the upper end of the cross-sectional shape of the discharge hole is 50 mm or more and 200 mm or less, and the distance between the most contracted diameter point of the cross-sectional shape of the lowest diameter-reduced portion and the most contracted diameter point of the cross-sectional shape of the adjacent diameter-reduced portion is , 50 mm or more and 150 mm or less.

Further, the cross-sectional shape of the nozzle body is a cross-sectional shape when the nozzle body is cut along a plane including a discharge shaft passing through the opening centers of the two discharge holes and the nozzle center shaft, and is a cross section of the lowest diameter-reduced portion. The value of the ratio of the distance from the straight line passing through the upper end point and the lower end point of the shape to the most reduced diameter point and the inner diameter of the inner pipe at a position other than the reduced diameter portion is 0.09 or more and 0.12. It may be less than.
Further, the distance between the lower end point of the cross-sectional shape of the lowermost reduced diameter portion and the upper end of the cross-sectional shape of the discharge hole may be 50 mm or more and 200 mm or less.
Further, the distance between the most reduced diameter point of the cross-sectional shape of the lowest reduced diameter portion and the most reduced diameter point of the cross-sectional shape of the adjacent reduced diameter portion may be 50 mm or more and 150 mm or less.

According to the present invention, the inner pipe of the nozzle body of the immersion nozzle is formed with a bottom reduced diameter portion having an appropriate shape and an adjacent reduced diameter portion adjacent to the lowest reduced diameter portion, and a cross section of the adjacent reduced diameter portion. Since the shape and the cross-sectional shape of the lowest reduced diameter portion are formed symmetrically with respect to the horizontal plane orthogonal to the nozzle center axis between the adjacent reduced diameter portion and the lowest reduced diameter portion, the suction of the discharge flow is absorbed. It is possible to suppress the occurrence of the phenomenon, and it is possible to suppress the hindrance of operation and the occurrence of slab quality defects due to the suction of the mold powder slag.

It is sectional drawing of the immersion nozzle for continuous casting which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the downstream diameter-reducing part, the upstream-diameter part and the discharge hole which are shown in FIG. It is sectional drawing which shows the downstream diameter reduction part described in FIG. It is sectional drawing which shows the upstream diameter reduction part described in FIG. It is a vector diagram of the discharge flow of the conventional immersion nozzle. It is a figure which shows the flow velocity distribution of molten steel in the vicinity of the discharge flow of the conventional immersion nozzle. It is a vector figure of the discharge flow of the immersion nozzle for continuous casting which is shown in FIG. It is a figure which shows the flow velocity distribution of molten steel in the vicinity of the discharge flow of the immersion nozzle for continuous casting described in FIG. It is sectional drawing of the immersion nozzle for continuous casting which concerns on Embodiment 2 of this invention.

Embodiment 1.
Hereinafter, the first embodiment will be described in detail with reference to the drawings.
As shown in FIG. 1, the continuous casting immersion nozzle 1 is an immersion nozzle for continuously casting steel, and has a columnar nozzle body 10 extending in the vertical direction. The nozzle body 10 is made of a refractory material. As the refractory, for example, alumina-graphite, magnesia-graphite, spinel-graphite, zirconia-graphite, alumina, clay, spinel, molten quartz and the like can be appropriately used. Since the detailed configuration of the surface material and the like of each part of the nozzle body 10 and the inner tube 11 described later is known, the description thereof will be omitted.

An inner tube 11 is formed inside the nozzle body 10. The inner pipe 11 forms a flow path for the molten steel when the molten steel is injected into the mold from the tundish during continuous casting of the steel. The inner tube 11 extends from the upper end 10a of the nozzle to the lower end 10b of the nozzle along the central axis 12 of the nozzle body 10 which is the central axis of the nozzle body 10 and extends in the vertical direction. The molten steel flows through the inner pipe 11 from the upstream nozzle upper end 10a side to the downstream nozzle lower end 10b side. In the following description, the "upper side" means the upper side in the vertical direction along the nozzle central axis 12 in the nozzle body 10, and the "lower side" means the lower side in the vertical direction along the nozzle central axis 12 in the nozzle body 10. Refers to the side.

Two discharge holes 14 are formed in the side wall portion 13 of the nozzle body 10. Each discharge hole 14 is provided above the lower end 10b of the nozzle. Each discharge hole 14 is connected to an inner pipe 11 and communicates the inner pipe 11 with the space around the nozzle body 10. Further, the discharge holes 14 are formed at positions facing each other, and the discharge shaft 21 which is an axis passing through the opening center 20 of each discharge hole 14 is orthogonal to the nozzle center axis 12. That is, FIG. 1 is a cross-sectional view of the nozzle body 10 cut along a plane including the orthogonal nozzle central shaft 12 and the discharge shaft 21. In the following description, the cross-sectional shape of each part included in the nozzle body 10 means the cross-sectional shape shown in FIG.

Each discharge hole 14 forms a flow path through which the molten steel flowing through the inner pipe 11 flows out to the outside of the nozzle body 10. The molten steel flowing through the inner pipe 11 flows out from each discharge hole 14, so that the molten steel is injected into the mold.

The cross-sectional shape of the discharge hole upper portion 14a connecting the uppermost side of the opening of each discharge hole 14 and the upper inner pipe 11 is formed as a two-step taper in which straight lines are combined so that the lower side expands radially outward. There is. The cross-sectional shape of the discharge hole lower portion 14b connecting the lowermost side of the opening of each discharge hole 14 and the inner pipe 11 is formed so that the lower side expands radially outward. A downstream diameter reduction portion 15 is formed on the upper side of each discharge hole 14. An upstream reduced diameter portion 16 is formed on the upper side of the downstream reduced diameter portion 15. The downstream reduced diameter portion 15 constitutes a reduced diameter portion located at the lowermost side in the inner pipe 11, that is, a lowest reduced diameter portion. Further, the upstream reduced diameter portion 16 constitutes a reduced diameter portion adjacent to the upper side of the downstream reduced diameter portion 15, which is the lowermost reduced diameter portion in the inner pipe 11, that is, an adjacent reduced diameter portion.

As shown in FIG. 2, the cross-sectional shape of the discharge hole 14, the downstream reduced diameter portion 15 and the upstream reduced diameter portion 16 shown in FIG. 1 will be described in an enlarged manner on the left side. The right discharge hole 14, the downstream reduced diameter portion 15 and the upstream reduced diameter portion 16 in FIG. 1 are mirror images of the left discharge hole 14, the downstream reduced diameter portion 15 and the upstream reduced diameter portion 16 with respect to the nozzle central axis 12. Since it is symmetric, the description is omitted.

The cross-sectional shape of the downstream reduced diameter portion 15 projects most in the radial direction of the inner pipe 11 at a position between the upper end point 15a in the vertical direction, the lower end point 15b in the vertical direction, and the upper end point 15a and the lower end point 15b. It has a maximum contraction point of 15c. The upper end point 15a, the outermost diameter point 15c, and the lower end point 15b are connected by a curve 15d. The distance F between the lower end point 15b and the uppermost side 14c of the discharge hole 14 is formed so as to be 50 mm or more and 200 mm or less.

The cross section of the upstream reduced diameter portion 16 projects most in the radial direction of the inner pipe 11 at a position between the upper end point 16b in the vertical direction, the lower end point 16a in the vertical direction, and the upper end point 16b and the lower end point 16a. It has a maximum contraction point 16c. The upper end point 16b, the outermost diameter point 16c, and the lower end point 16a are connected by a curve 16d.

At this time, considering the horizontal plane 17 forming a plane orthogonal to the nozzle central axis 12 between the upper end point 15a of the downstream reduced diameter portion 15 and the lower end point 16a of the upstream reduced diameter portion 16, the downstream reduced diameter portion 15 The cross section and the cross section of the upstream reduced diameter portion 16 are formed symmetrically with respect to the horizontal plane 17. Further, the distance G between the maximum reduction point 15c of the downstream reduction portion 15 and the maximum reduction point 16c of the upstream reduction portion 16 is formed to be 50 mm or more and 150 mm or less.

As shown in FIG. 3, in the cross section of the downstream reduced diameter portion 15, considering the unequal side triangle 15e shown by the broken line having the upper end point 15a, the lower end point 15b, and the maximum reduced diameter point 15c as vertices, the upper end point 15a and A closed curve composed of a line segment 15f connecting the lower end point 15b and a curve 15d circumscribes the triangle 15e. That is, the cross section of the downstream reduced diameter portion 15 forming the closed curve circumscribes the triangle 15e. Further, the line segment 15f is a part of a straight line passing through the upper end point 15a and the lower end point 15b, and extends on the wall surface of the inner pipe 11.

The distance L1 between the upper end point 15a and the maximum reduction point 15c and the distance L3 between the lower end point 15b and the maximum reduction point 15c are such that the downstream reduction portion 15 is formed so that L1 is larger than L3. .. Further, the inner diameter D (FIG. 2), which is the diameter of the inner pipe 11 at positions other than the distance H1 between the line segment 15f and the maximum diameter reduction point 15c and the downstream reduction portion 15 and the upstream reduction portion 16 (see FIG. 2). The downstream diameter reduction portion 15 is formed so that the value H1 / D of the ratio to 1 and FIG. 2) is 0.09 or more and 0.12 or less.

Since the cross section of the downstream reduced diameter portion 15 and the cross section of the upstream reduced diameter portion 16 are formed symmetrically with respect to the horizontal plane 17, the upper end point 16b is formed in the cross section of the upstream reduced diameter portion 16 as shown in FIG. Considering an unequal-sided triangle 16e indicated by a broken line with the apex of the lower end point 16a and the outermost diameter point 16c, a closed curve composed of a line segment 16f and a curve 16d connecting the upper end point 16b and the lower end point 16a. Is circumscribing the triangle 16e. That is, the cross section of the upstream reduced diameter portion 16 forming the closed curve circumscribes the triangle 16e. Further, the line segment 16f is a part of a straight line passing through the upper end point 16b and the lower end point 16a, and extends on the wall surface of the inner pipe 11.

The distance L2 between the lower end point 16a and the maximum reduction point 16c and the distance L4 between the upper end point 16b and the maximum reduction point 16c are such that the upstream reduction portion 16 is formed so that L2 is larger than L4. .. Further, the distance H1 between 16f, which is a line segment connecting the upper end point 16b and the lower end point 16a, and the maximum diameter reduction point 16c, and the diameter of the inner pipe 11 at a position other than the downstream reduction portion 15 and the upstream reduction portion 16. The upstream diameter reduction portion 16 is formed so that the value H2 / D of the ratio to the inner diameter D is 0.09 or more and 0.12 or less.

Next, the state of the discharge flow in the vicinity of the discharge hole at the time of casting in the conventional immersion nozzle will be described. During continuous casting with a conventional immersion nozzle, a suction flow (negative direction flow) of a discharge flow that leads to the generation of suction of mold powder slag may occur. By using a casting nozzle shape that has the same shape as the casting nozzle that generated the suction flow during casting and conducting a water model test that was carried out in response to the casting conditions at the time of generation, the position where the suction flow is frequently generated is located. It is known to be above the discharge hole.

When fluid analysis was performed by computer under the same conditions as the above water model test, in the model in which the suction flow was generated, the molten steel flow flowing down from the upper side in the vertical direction was slow on the wall surface of the inner pipe of the immersion nozzle. It is known to be in a state. Further, in the discharge hole portion, it has been found that the molten steel flow, which had been flowing downward in the substantially vertical direction until then, suddenly changes the direction of flow, but at that time, the discharge flow is separated from the upper surface of the discharge hole.

It is known that when the discharge flow is peeled off, the pressure of the molten steel flow is reduced in the region where the peeling occurs, and the discharge flow is backflowed. In the discharge hole of the immersion nozzle, the discharge flow is likely to peel off at the point where the molten steel flow flows from the inner pipe to the discharge hole, so there is a possibility that backflow will occur in the area above the discharge hole on the downstream side of the peeling point. Is high. It has been found that when the peeling region of the discharge flow expands and the backflow affects the outside of the discharge hole, it becomes a suction flow.

By forming a reduced diameter region in a part of the inner pipe in the immersion nozzle, the molten steel flow is concentrated in the reduced diameter region and diffuses again after passing through the reduced diameter region. At this time, it is generally known that the molten steel flow is rectified and the drift is eliminated. However, the rectified molten steel flow has a large flow velocity in the central portion and a relatively small flow velocity in the inner pipe wall surface portion. Therefore, if the molten steel flow flows into the discharge hole as it is, a large peeling region of the discharge flow is generated.

On the other hand, by providing a plurality of diameter-reduced portions in the inner pipe of the immersion nozzle along the vertical direction, the molten steel flow is once concentrated at the diameter-reduced portion one step above the bottom stage to eliminate the drift, and then downstream thereof. It is possible to use a configuration in which the inner pipe diameter is gradually expanded or contracted, and the inner diameter portion is expanded again downstream of the diameter-reduced portion in the lowermost stage. By using this configuration, a strong peeling region is generated downstream of the reduced diameter portion after the molten steel has passed through the lowermost stage of such an inner pipe shape, and the peeling region downstream of the reduced diameter portion and the other region Due to the pressure difference, the molten steel flow after passing through the reduced diameter portion is strongly attracted to the inner pipe wall surface. As a result, the flow velocity of the molten steel flow in the vicinity of the inner pipe wall surface increases. Then, it is known that the development of the peeled region of the discharge flow discharged from the discharge hole can be suppressed by the molten steel flowing into the discharge hole in a state where the flow velocity in the vicinity of the inner pipe wall surface is high.

It is known that even in the conventional immersion nozzle, a plurality of steps of reduced diameter portions are formed. For example, Patent Document 3 describes a dipping nozzle having a plurality of stages of reduced diameter portions formed in an inner tube over a specific range along a vertical direction. In this immersion nozzle, if the inner pipe diameter in the reduced diameter portion is reduced, the flow rate per unit time of molten steel that can pass through the inner pipe of the immersion nozzle, that is, the throughput, is reduced. It is known that it is difficult to change.

Further, for example, Patent Document 5 describes a configuration in which a plurality of discontinuous protrusions are formed in the horizontal direction of the immersion nozzle to form a reduced diameter portion. It is known that this immersion nozzle has little effect of attracting the flowing molten steel flow to the inner pipe wall surface, and it is difficult to suppress the peeling of the molten steel flow discharged from the discharge hole.

On the other hand, as described above, the immersion nozzle 1 for continuous casting according to the first embodiment of the present invention has a downstream reduced diameter portion 15 and an upstream reduced diameter portion 16 in the inner pipe 11 of the nozzle body 10 as shown in FIG. It has two reduced diameter portions. Further, as shown in FIG. 3, the cross section of the downstream reduced diameter portion 15 circumscribes the isosceles triangle 15e, and as shown in FIG. 4, the cross section of the upstream reduced diameter portion 16 is inscribed in the isosceles triangle 16e. ing. Further, regarding the cross-sectional shape of the downstream reduced diameter portion 15 (see FIG. 3), the distance L1 between the upper end point 15a and the maximum reduced diameter point 15c is larger than the distance L3 between the lower end point 15b and the maximum reduced diameter point 15c. The upstream diameter reduction portion 16 (see FIG. 4) has a cross-sectional shape in which the distance L2 between the lower end point 16a and the maximum diameter reduction point 16c is the upper end point 16b and the maximum diameter reduction point 16c. It is formed so as to be larger than the distance L4 of. Then, as shown in FIG. 2, the downstream reduced diameter portion 15 and the upstream reduced diameter portion 15 and the upstream reduced diameter portion so that the cross-sectional shape of the downstream reduced diameter portion 15 and the cross-sectional shape of the upstream reduced diameter portion 16 are mirror image symmetric with respect to the horizontal plane 17. 16 is formed.

In the continuous casting immersion nozzle 1, the downstream diameter-reduced portion 15 of the inner pipe 11 has the above-mentioned shape, so that the lowermost stage of the immersion nozzle 1 does not significantly affect the throughput of molten steel that can pass through the inner pipe 11. The inner pipe diameter of the downstream reduced diameter portion 15 which is the reduced diameter portion can be made smaller than that of the conventional immersion nozzle. Therefore, the diameter of the inner pipe 11 in the downstream can be made larger than the maximum diameter point 16c which is the minimum diameter of the inner pipe 11 in the downstream reduced diameter portion 15. As a result, a strong peeling region of the molten steel flow is generated downstream after passing through the downstream reduced diameter portion 15, and due to the pressure difference between the peeled portion and the other region, the molten steel flow after passing through the downstream reduced diameter portion 15 is passed through the inner pipe 11. It is possible to increase the effect of being strongly attracted to the wall surface of.

Further, the downstream reduced diameter portion 15 is such that the cross-sectional shape of the downstream reduced diameter portion 15 which is the lowermost reduced diameter portion and the cross-sectional shape of the upstream reduced diameter portion 16 one step above the reduced diameter portion are mirror image symmetric with respect to the horizontal plane 17. After passing through the downstream reduced diameter portion 15 by forming the upstream reduced diameter portion 16 and making the change in the inner pipe diameter between the upstream reduced diameter portion 16 and the downstream reduced diameter portion 15 a gradual change. By expanding the inner pipe diameter D, it is possible to maximize the effect of attracting the molten steel flow to the wall surface of the inner pipe 11.

The distance H1 between the maximum reduced diameter point 15c, which is the maximum reduced diameter portion of the downstream reduced diameter portion 15, and the line segment 15f extending on the wall surface of the inner pipe 11, and the maximum reduced diameter portion, which is the maximum reduced diameter portion of the upstream reduced diameter portion 16. The distance H2 between the point 16c and the line segment 16f extending on the wall surface of the inner pipe 11 is the rectification of the molten steel flow flowing down and the inner pipe 11 of the molten steel flow passing through the upstream diameter reduction portion 16 and the downstream diameter reduction portion 15. It is known to have a significant effect on the pulling effect on the wall surface. H1 / D, which is the value of the ratio of the distance H1 to the inner pipe diameter D of the inner pipe 11, is 0.09 or more and 0.12 or less, and H2 /, which is the value of the ratio of the distance H2 to the inner pipe diameter D. It is known from the study of the present invention that when D is 0.09 or more and 0.12 or less, it is the most preferable value for obtaining the rectifying effect and the attracting effect of the molten steel flow. When H1 / D or H2 / D is less than 0.09, there arises a problem that the rectifying effect and the attracting effect are lowered. Further, when H1 / D or H2 / D is larger than 0.12, there arises a problem that the throughput of molten steel in the inner pipe 11 decreases.

The distance F between the uppermost side 14c of the discharge hole 14 and the lower end point 15b of the downstream reduced diameter portion 15 which is the lowermost reduced diameter portion is preferably in the range of 50 mm or more and 200 mm or less, more preferably. It is desirable that it is within the range of 75 mm or more and 150 mm or less.

When the distance F is larger than the above-mentioned preferable range, the velocity of the molten steel flow in the vicinity of the wall surface of the inner pipe 11 is too low until it reaches the discharge hole 14. Therefore, when the molten steel flows into the discharge hole 14 in a state where the flow velocity near the wall surface of the inner pipe 11 is large, there arises a problem that the effect of the downstream diameter-reduced portion 15 of suppressing the development of the peeled region of the discharge flow is impaired. .. Further, when the distance F is smaller than the above-mentioned preferable range, the peeling region of the molten steel formed immediately below the downstream diameter-reduced portion 15 also affects the discharge flow discharged from the discharge hole 14, so that the discharge flow Causes the problem of instability.

The distance G between the maximum reduction point 15c of the downstream reduction portion 15 and the maximum reduction point 16c of the upstream reduction portion 16 is preferably 50 mm or more and 150 mm or less. When the distance G is less than 50 mm or more than 150 mm, there arises a problem that the rectifying effect and the pulling effect of the downstream reduced diameter portion 15 and the upstream reduced diameter portion 16 are lowered.

Next, an example of a discharge flow in the conventional immersion nozzle for continuous casting and a discharge flow in the immersion nozzle 1 for continuous casting according to the first embodiment of the present invention will be described.
FIG. 5 shows as a vector diagram the results of calculation by computational fluid dynamics (CFD) for the discharge flow around one discharge hole in the mold of a conventional immersion nozzle having an inner pipe diameter and an inner pipe shape. Here, the conventional inner pipe diameter and inner pipe shape are an inner pipe diameter and an inner pipe shape having a stepped reduced diameter portion as described in Patent Document 3. Further, in FIG. 5 and FIG. 6 described later, elements equivalent to or similar to the immersion nozzle according to the first embodiment of the present application are indicated by the same reference numerals as those in FIGS. 1 to 4.

The CFD calculation conditions at this time are as follows.
-Mold size: 240 mm x 1400 mm
-Casting speed: 2.6 m / min (throughput: 6.3 t / min)
・ Immersion depth: 235 mm from the top of the discharge hole, no deflection

In this conventional inner tube shape, the discharge hole lower portion 14b is formed so that the lower side of the cross-sectional shape extends outward in the radial direction. In FIG. 5 and FIG. 7 of the vector diagram described later, the flow velocity of the molten steel is represented by the length of the vector indicated by the arrow in each diagram.

As shown in FIG. 5, depending on the inner pipe diameter, the inner pipe shape, and the shape of the discharge hole of the conventional immersion nozzle, the discharge flow below the discharge hole 14 among the discharge flows has a high downward flow velocity. It becomes 30.

FIG. 6 is a diagram showing a flow velocity distribution of molten steel in a mold in the vicinity of one discharge hole 14 of a dipping nozzle having a conventional inner pipe diameter and inner pipe shape. Since the discharge flow 30 having a high descending flow velocity is generated, there is a high possibility that the suction flow 30a, which leads to the generation of suction of the mold powder slag, is generated above the discharge hole 14. In FIG. 6 and FIG. 8 showing the flow velocity distribution described later, the portion where the flow velocity of the molten steel is high is represented by a bright color.

FIG. 7 shows a vector diagram showing a discharge flow 31 from one discharge hole 14 in the mold of the continuous casting immersion nozzle 1 according to the first embodiment of the present invention. Since the downstream reduced diameter portion 15 and the upstream reduced diameter portion 16 (see FIG. 2) are formed in the inner pipe 11, the discharge flow 30 (see FIG. 5) of the conventional immersion nozzle is more than that of the first embodiment. The descending flow velocity of the discharge flow 31 becomes low.

FIG. 8 is a diagram showing a flow velocity distribution in the mold in the vicinity of one discharge hole 14 of the continuous casting immersion nozzle 1 according to the first embodiment of the present invention. Since the descending flow velocity of the discharge flow 31 is slower than that of the conventional immersion nozzle, the continuous casting immersion nozzle 1 according to the present invention has a suction flow that leads to the generation of suction of the mold powder slag as compared with the conventional immersion nozzle. The possibility of occurrence above the discharge hole 14 is reduced.

Next, as shown in Table 1, a comparative example in which the frequency of suction flow of the discharge flow and the stability of the molten metal surface were evaluated for a plurality of immersion nozzles having different inner pipe diameters, inner pipe shapes, and discharge hole shapes. And an embodiment will be described. Elements equivalent to or similar to the immersion nozzle according to the first embodiment of the present application are indicated by the same reference numerals as those in FIGS. 1 to 4. The immersion nozzles of Comparative Examples 1 to 9 and Examples 1 to 8 are characterized by the nozzle shape, the number of diameter-reduced portions (upstream-reduced portion 16 and downstream-reduced portion 15), the upper end point 15a and the maximum diameter-reduced point 15c. L1 which is the value of the ratio of the distance L1 to and the distance L3 between the lower end point 15b and the maximum diameter reduction point 15c, the distance H1 between the line segment 15f and the maximum reduction diameter point 15c, and the inner diameter D. H1 / D, which is the value of the ratio of The distance G is formed as a parameter.

For each of Comparative Examples 1 to 9 and Examples 1 to 8 , the total value of each evaluation point is totaled with the frequency of suction flow in the left discharge hole and the right discharge hole and the stability of the molten metal as evaluation points. It is evaluated. The mold size at this time is 220 × 1600 mm, and the throughput is 6 t / min. Further, as shown in FIG. 2, the upstream reduced diameter portion 16 and the downstream reduced diameter portion 15 are formed symmetrically with respect to the horizontal plane 17 as in the first embodiment.

The method of evaluating the frequency of suction flow generation for each immersion nozzle at this time is to measure the average flow velocity of the discharge flow 12 times every 5 seconds during casting, and for each measurement, the left and right discharges are based on the value of the average flow velocity. It is determined whether or not a suction flow is generated in the hole 14, and the number of times the suction flow is generated in 12 times is evaluated as the following evaluation points.
・ The number of times the suction flow occurred is 0 ... Evaluation point 0
・ The number of times suction flow has occurred is 1 or more and 2 or less ... Evaluation point 1
・ The number of times suction flow has occurred is 3 or more and 6 or less ... Evaluation point 3
・ The number of times the suction flow occurred was 7 or more and 12 or less ... Evaluation point 5

Further, in the method of evaluating the stability of the molten metal surface with respect to each immersion nozzle at this time, the stable state of the molten metal surface is evaluated as the following evaluation points.
・ When the surface of the water is stable ... Evaluation point 0
・ When the surface of the water is unstable ... Evaluation score 5

Further, the comprehensive evaluation for each immersion nozzle at this time is determined as follows based on the total value of the evaluation points.
・ The total value of evaluation points is 1 point or less ... ◎
・ The total value of evaluation points is 2 points or more and 5 points or less ... △
・ The total value of evaluation points is 6 points or more ... ×
That is, it is evaluated that the immersion nozzle having a lower total evaluation point has less suction flow of the discharge flow during casting, the molten metal surface is stable, and has a good immersion nozzle shape suitable for casting. ..

Of the examples of Comparative Examples 1 to 9 and Examples 1 to 8 , Examples 1 to 3, Examples 4 and 5, and Examples 6 to 8 have a comprehensive evaluation of ⊚ and a good immersion nozzle shape for casting. Is evaluated as having.

As described above, the cylindrical nozzle body 10 having the inner tube 11 extending along the central axis 12 of the nozzle is provided, and the nozzle body 10 is formed with a discharge hole 14 communicating with the inner tube 11, and the discharge hole 14 is formed. At least two of them are formed in the side wall portion 13 of the nozzle body 10, and the upper end of the inner tube 11 is an immersion nozzle for continuous casting which is opened at the upper end of the nozzle body 10, and the inner tube 11 has a similar shape. The discharge shaft 21 and the nozzle center are provided with the two downstream reduced diameter portions 15 and the upstream reduced diameter portion 16 and pass through the opening center 20 of the two discharge holes 14 among the discharge holes 14 formed in the side wall portion 13 of the nozzle body 10. Of the cross-sectional shapes of the nozzle body 10 when the nozzle body 10 is cut along a plane parallel to the shaft 12, the cross-sectional shape of the downstream reduced diameter portion 15 located at the lowermost side of the reduced diameter portion is the downstream. The upper end point 15a of the reduced diameter portion 15 in the vertical direction, the lower end point 15b of the downstream reduced diameter portion 15 in the vertical direction, and the most protruding maximum reduced diameter of the downstream reduced diameter portion 15 with respect to the radial direction of the inner pipe 11. It is circumscribed to a triangle 15e having a point 15c as an apex, and the distance L1 from the upper end point 15a to the maximum reduction point 15c has a shape larger than the distance L3 from the lower end point 15b to the maximum reduction point 15c, and is downstream. The cross-sectional shape of the upstream reduced diameter portion 16 adjacent to the upper side of the reduced diameter portion 15 and the cross-sectional shape of the downstream reduced diameter portion 15 are orthogonal to the nozzle central axis 12 between the upstream reduced diameter portion 16 and the downstream reduced diameter portion 15. Since it is mirror image symmetric with respect to the horizontal plane 17 to be formed, it is possible to suppress the occurrence of the suction phenomenon of the discharge flow, and it is possible to suppress the hindrance of operation and the occurrence of slab quality defects due to the suction of the mold powder slag.

The cross-sectional shape of the nozzle body 10 is a cross-sectional shape when the nozzle body 10 is cut along a plane including the discharge shaft 21 passing through the opening centers 20 of the two discharge holes 14 and the nozzle center shaft 12, and is downstream. The distance H from the line segment 15f passing through the upper end point 15a and the lower end point 15b of the cross-sectional shape of the reduced diameter portion 15 to the maximum reduced diameter point 15c, and the inner diameter D which is the diameter of the inner pipe 11 at a position other than the reduced diameter portion. Since the value of the ratio to and is 0.09 or more and less than 0.12, the molten steel flow due to the expansion of the inner diameter D after passing through the downstream diameter reduction portion 15 while ensuring the throughput of the molten steel in the inner pipe 11. The effect of attracting the inner pipe 11 to the wall surface can be maximized.

Further, since the distance F between the lower end point 15b of the downstream diameter reduction portion 15 and the uppermost side 14c of the discharge hole 14 is 50 mm or more and 200 mm or less, the flow velocity near the wall surface of the inner pipe 11 is large and the discharge hole 14 is reached. The effect of the downstream reduced diameter portion 15 that the molten steel does not flow in and suppresses the development of the peeled region of the discharge flow is not impaired, and the peeled region of the molten steel formed directly below the downstream reduced diameter portion 15 is the discharge hole. Since it does not affect the discharge flow discharged from 14, the discharge flow can be stabilized.

Further, since the distance G between the maximum reduction point 15c of the downstream reduction portion 15 and the maximum reduction point 16c of the upstream reduction portion 16 adjacent to the downstream reduction portion 15 is 50 mm or more and 150 mm or less, it is downstream. The rectifying effect and the pulling effect of the reduced diameter portion 15 and the upstream reduced diameter portion 16 can be improved.

Embodiment 2.
Next, the second embodiment will be described. In the second embodiment, the same reference numerals as those in FIGS. 1 to 8 are the same or similar components as those in the first embodiment, and thus detailed description thereof will be omitted.
In the second embodiment, a discharge hole is further provided at the lower end 10b of the nozzle as compared with the first embodiment.

As shown in FIG. 9, a lower discharge hole 41 connected to the inner pipe 11 and opening in the vertical direction is formed at the lower end 10b of the nozzle of the nozzle body 10c. As a result, molten steel flowing through the inner pipe 11 is injected into the mold from the lower discharge hole 41 in addition to the discharge hole 14 formed in the side wall portion 13 of the nozzle body 10c. Other embodiments are the same as those in the first embodiment.

Therefore, in the second embodiment as well, the occurrence of the suction flow suction phenomenon can be suppressed, and the operation hindrance and the occurrence of the slab quality defect due to the suction of the mold powder slag can be suppressed as in the first embodiment.

In the first and second embodiments, the inner tube 11 of the nozzle body 10 has two reduced diameter portions, a downstream reduced diameter portion 15 and an upstream reduced diameter portion 16, but three or more reduced diameter portions are provided. You may have.

Further, in the first and second embodiments, the continuous casting dipping nozzle 1 is a continuous casting dipping nozzle for steel, but it may be a continuous casting dipping nozzle for a metal other than steel, for example, copper.

Further, in the first and second embodiments, the cross-sectional shape of the discharge hole upper portion 14a of each discharge hole 14 is formed as a two-step taper in which straight lines are combined so that the lower side expands radially outward. It may be configured as a taper. Further, the cross-sectional shape of the lower portion 14b of the discharge hole of each discharge hole 14 is formed so that the lower side expands radially outward, but the lower side may be formed so as to contract radially inward.

10 Nozzle body, 11 Inner pipe, 12 Nozzle center axis, 14 Discharge hole, 14c Top side, 15 Downstream reduced diameter part (bottom reduced diameter part), 15a Upper end point, 15b Lower end point, 15c Maximum diameter point, 15e triangle , 15f line segment, 16 upstream reduced diameter part (adjacent reduced diameter part), 16a lower end point, 16b upper end point, 16c most reduced diameter point, 16e triangle, 16f line segment, 17 horizontal plane, 20 opening center, 21 discharge shaft, D Inner pipe diameter, F distance, G distance, H1, H2 distance, L1 distance, L2 distance, L3 distance, L4 distance.

Claims (1)

A cylindrical nozzle body having an inner tube extending along the central axis of the nozzle is provided, and the nozzle body is formed with discharge holes communicating with the inner tube, and at least two of the discharge holes are the nozzle body. A dipping nozzle for continuous casting, which is formed on the side wall portion of the inner pipe and the upper end of the inner pipe is opened at the upper end of the nozzle body.
The inner tube comprises at least two reduced diameter portions having similar shapes.
Of the discharge holes formed on the side wall of the nozzle body, the nozzle body when the nozzle body is cut along a plane including the discharge shaft passing through the opening center of the discharge holes and the nozzle center axis. Of the cross-sectional shape
The cross-sectional shape of the lowest reduced diameter portion located on the lowermost side of the reduced diameter portion is the upper end point of the cross-sectional shape of the lowest reduced diameter portion and the lower end of the cross-sectional shape of the lowest reduced diameter portion. It is circumscribed in a triangle having a point and the most protruding diameter point of the bottom diameter portion of the cross-sectional shape in the radial direction of the inner pipe as the apex, and the most contraction point from the upper end point. The distance to is larger than the distance from the lower end point to the most contracted diameter point.
The cross-sectional shape of the adjacent reduced diameter portion adjacent to the upper side of the lowest reduced diameter portion and the cross-sectional shape of the lowest reduced diameter portion are in the middle between the adjacent reduced diameter portion and the lowest reduced diameter portion. Ri mirror symmetry der respect to a plane perpendicular to the nozzle central axis,
The inner pipe diameter, which is the distance from the straight line passing through the upper end point and the lower end point of the cross-sectional shape of the lowermost reduced diameter portion to the outermost reduced diameter point, and the diameter of the inner pipe at a position other than the reduced diameter portion. The value of the ratio with is 0.09 or more and less than 0.12.
The distance between the lower end point of the cross-sectional shape of the lowest diameter portion and the upper end of the cross-sectional shape of the discharge hole is 50 mm or more and 200 mm or less.
A dipping nozzle for continuous casting in which the distance between the most reduced diameter point of the cross-sectional shape of the lowest reduced diameter portion and the most reduced diameter point of the cross-sectional shape of the adjacent reduced diameter portion is 50 mm or more and 150 mm or less.

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