JP2010188402A - Immersion nozzle for curved type continuous casting machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a completely new technique capable of largely setting the cross-sectional area of the flow passage of a discharge hole while realizing the flowing pattern of a discharge flow becoming a downward flow at the inside of a curve and becoming an upward flow at the outside of the curve. <P>SOLUTION: The inner circumferential face 4 at the outside of the curve of the immersion nozzle 1, also being a position held between a pair of discharge holes 2 in a planar view is provided with a rectifying projection 5 with a specified shape so as to satisfy the following conditions (1) to (4); wherein, B denotes the horizontal length [mm] of the projection in the width direction of a mold in the planar view of the projection; d1 denotes the distance [mm] in a vertical direction between the lower edge of the rectifying projection and the bottom face at the inside of the immersion nozzle; and d2 denotes the distance [mm] in a vertical direction between the upper edge of the rectifying projection and the lower edge of the rectifying projection: 0.05≤A/ϕ≤0.15 (1), 0.4≤B/ϕ≤0.8 (2), 0.75≤d1/ϕ≤1.25 (3), and 2≤d2/A≤6 (4). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an immersion nozzle for a curved continuous casting machine.

  For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 51-138526) and Patent Document are known as techniques for suppressing the trapping and accumulation of inclusions inside the curved shell of the solidified shell during continuous casting using a curved continuous casting machine. 2 (Japanese Utility Model Laid-Open No. 3-47645) discloses a configuration in which the direction of the discharge hole of the immersion nozzle is directed inwardly in a plan view. According to such orientation, the discharge flow is directed to the inside of the curve. For example, as shown in FIG. 5 of Patent Document 1 and FIG. 2 of Patent Document 2, the flow pattern of the discharge flow is a downward flow inside the curve. Thus, an upward flow is generated on the outside of the curve, so that trapping and accumulation of inclusions inside the curve of the solidified shell can be suppressed.

  However, in order to employ the technique disclosed in Patent Document 1 and the like, the flow passage cross-sectional area of the discharge hole must be set small. This is because if the flow passage cross-sectional area of the discharge hole is increased when using the above technique, the swirling direction of a single large-diameter vortex formed near the inner bottom surface of the immersion nozzle is more than the direction of the discharge hole. Since it becomes dominant to the direction of the discharge flow, and the swirling direction of this large-sized vortex flow is switched randomly, it is not certain whether the discharge flow faces the inside of the curve or the outside of the curve after all. It is.

  As described above, the technique disclosed in Patent Document 1 and the like has a technical restriction that the flow passage cross-sectional area of the discharge hole must be set small, so that the throughput (flow rate per unit time of the discharge flow) is relatively high. Although there was no problem in carrying out continuous casting set at a low level, it becomes a big problem in the recent operations in which continuous casting is set at a relatively high throughput. This is because if the flow passage cross-sectional area of the discharge hole is small and the throughput is high, the flow rate of the discharge flow is inevitably high, the heat input to the corner of the solidified shell that is difficult to remove heat is excessive, and breakout occurs. This is because there is a risk of causing a significant coagulation delay that may cause the occurrence of the problem. Further, when the flow passage cross-sectional area of the discharge hole is small, clogging is likely to occur.

  The present invention has been made in view of the above points, and its main purpose is to break through the above technical constraints, that is, the downward flow is inside the curve and the upward flow is outside the curve. An object of the present invention is to provide a completely new technique capable of setting the flow passage cross-sectional area of the discharge hole to be large while realizing such a flow pattern of the discharge flow.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above, and the inventors of the present invention have fixed the swirling direction of a single large-diameter vortex formed near the inner bottom surface of the submerged nozzle after extensive research. The technology was found and the following invention was completed.

  According to an aspect of the present invention, there is a bottomed cylindrical immersion nozzle used for pouring molten steel held in a tundish into a mold, which is for a curved continuous casting machine, and the immersion The immersion nozzle having a pair of opposed discharge holes formed in the peripheral wall of the nozzle is configured as follows. That is, the rectifying protrusion is provided on the inner peripheral surface on the curved outer side of the immersion nozzle and at a position sandwiched between the pair of discharge holes in a plan view. A projection horizontal thickness A [mm] specified in the mold thickness direction in plan view of the rectifying projection, and a projection horizontal length B [mm] specified in the mold width direction in plan view of the rectification projection, A rectifying protrusion lower end distance d1 [mm] which is a vertical distance between the lower end of the rectifying protrusion and the inner bottom surface of the immersion nozzle; and an upper end of the rectifying protrusion which is an upper end of the rectifying protrusion; The protrusion vertical thickness d2 [mm], which is the distance in the vertical direction between the lower end of the rectifying protrusions, satisfies the conditions of the following formulas (1) to (4).

  Hereinafter, the effect of the immersion nozzle according to the present invention will be described in comparison with the immersion nozzle of Patent Document 1 and the like.

<Immersion nozzle of Patent Document 1> FIG. 1A is a perspective view of the immersion nozzle disclosed in Patent Document 1, in which the flow passage cross-sectional area of the discharge hole is set to be relatively large. FIG. 1B is a partially cutaway perspective view of FIG. 1A, and FIGS. 1C to 1D are views similar to FIG. 1B, illustrating the flow of molten steel. . In the immersion nozzle shown in FIG. 1, the molten steel that has collided with the inner bottom surface is a large pool centered on the mold width direction as shown in FIG. A single vortex is formed. When the flow passage cross-sectional area of the discharge hole is set to be relatively large, this vortex flow continues to the outside of the discharge hole without losing its shape, so that a discharge flow having a bias in the mold thickness direction is formed. . By the way, the swirl direction of this large single vortex flows as shown in FIG. 1 (c2), when it is counterclockwise rising from the inner bottom surface toward the curved inner side, and as shown in FIG. 1 (d2). There are two cases: a clockwise direction rising from the inner bottom surface toward the curved outer side, and the turning direction is randomly switched. Therefore, if the flow passage cross-sectional area of the discharge hole is set to be relatively large as shown in FIG. 1 (a2), even if the direction of the discharge hole is greatly oriented to the inside of the curve as shown in FIG. 1 (a1), As shown in FIGS. 1 (c1) and (d1), it is not certain whether the discharge flow faces the curved outer side (see FIG. 12 (a)) or the curved inner side (see FIG. 12 (b)).

<Immersion nozzle according to the present invention> FIG. 2 (a) is a perspective view of the immersion nozzle according to the present invention, FIG. 2 (b) is a partially cutaway perspective view of FIG. 2 (a), and FIG. c) is a view similar to FIG. 2 (b), and is an image of the flow of molten steel. In the immersion nozzle of the present invention shown in FIG. 2, the molten steel collides with the rectifying protrusion provided on the curved outer side before colliding with the inner bottom surface. And by this collision, the flow of the molten steel in the immersion nozzle is once concentrated near the curved inner side. At this time, a large negative pressure region is formed between the flow straightening protrusion and the inner bottom surface, and the flow of the molten steel is attracted to the negative pressure region. As shown in FIG. And a single clockwise large eddy current rising from the inner bottom surface toward the curved outer side is formed. Thus, in the immersion nozzle according to the present invention, the swirling direction of the single large-diameter vortex is fixed by the rectifying protrusion, so the direction of the discharge flow is fixed inside the curve, and FIG. The flow pattern of the discharge flow as shown in FIG. 6 is stably realized such that the flow is a downward flow inside the curve and an upward flow outside the curve. In addition, since the immersion nozzle disclosed in FIG. 2 actively uses the single large-diameter vortex, the flow passage cross-sectional area of the discharge hole must be set small to realize the above flow pattern. Therefore, it is possible to set the flow passage cross-sectional area of the discharge hole large while realizing the above flow pattern as shown in FIG. 12B.

  If the immersion nozzle according to the present invention described above is employed, the trapping and accumulation of inclusions inside the curve of the solidified shell can be suppressed, and of course, heat input to the corner of the solidified shell can be achieved in a high-throughput operation. It becomes possible to avoid becoming excessive.

  The immersion nozzle disclosed in FIG. 2 is an example that embodies the present invention, and the technical scope of the present invention is not limited in any way by FIG.

FIG. 3 is a perspective view of an immersion nozzle disclosed in Patent Document 1 in which a flow passage cross-sectional area of a discharge hole is set to be relatively large Perspective view of immersion nozzle according to the present invention FIG. 6 is a cross-sectional view taken along line 3-3 in FIG. 5, and is an elevational cross-sectional view of an immersion nozzle according to an embodiment of the present invention. Fig. 4 is a cross-sectional view taken along line 4-4 in Fig. 5, and is an elevational cross-sectional view of an immersion nozzle according to an embodiment of the present invention. FIG. 5 is a cross-sectional view taken along line 5-5 in FIG. 4 and is a horizontal cross-sectional view of an immersion nozzle according to an embodiment of the present invention. The figure which imaged the flow of the molten steel implement | achieved by the immersion nozzle which concerns on one Embodiment of this invention The figure which shows the modification of a baffle protrusion The figure which shows the modification of an ejection hole Explanatory drawing on test method for technical effect confirmation test A diagram for explaining the phenomenon of fluid separation by the rectifying protrusion and the possibility of reattachment Graph showing the relationship between the discharge angle to the inside of the curve and the amount of inclusions Overall view of curved continuous casting machine

  As is well known, focusing on the casting path of a continuous casting machine, there are a curved continuous casting machine and a vertical bending continuous casting machine. The former has an arc path portion, a correction path portion, and a horizontal path portion along the casting path from the mold, and the latter has a vertical path portion upstream of the arc path portion, and floats inclusions in the molten steel. Is intended. Focusing on the cross-sectional shape of a slab cast by a continuous casting machine, there are a slab having a cross-sectional aspect ratio of 2 or more, a bloom of 2 or less, and a billet having a square cross-sectional shape. The application object of the present invention is limited to an immersion nozzle used in continuous casting of slabs or blooms in a curved continuous casting machine. Hereinafter, in this specification, the example which applied this invention to the immersion nozzle used by the continuous casting of the slab in a curved type continuous casting machine is demonstrated as an example.

  Hereinafter, the configuration of an immersion nozzle according to an embodiment of the present invention will be described with reference to the drawings. The immersion nozzle 1 shown in FIG. 2 is used for pouring molten steel held in a tundish into a mold, and is formed in a bottomed cylindrical shape. A pair of opposed discharge holes 2 are formed in the peripheral wall of the immersion nozzle 1 at a position slightly away from the inner bottom surface 3 of the immersion nozzle 1. And the rectification | projection protrusion 5 is provided in the inner peripheral surface 4 of the curved outer side of the immersion nozzle 1 which concerns on this embodiment, and the position pinched | interposed between the said pair of discharge holes 2 by planar view. Here, since the direction of the discharge flow of the molten steel discharged from the discharge hole 2 of the immersion nozzle 1, the mold width direction and the mold thickness direction are closely related technically, each figure shows the mold width direction and the mold as much as possible. The thickness direction is illustrated. As shown in FIG. 2, the immersion nozzle 1 is arranged in the mold so that the forming direction 6 of the discharge holes 2 coincides with the mold width direction. Each figure also shows the axial direction of the immersion nozzle 1 that is orthogonal to the mold width direction and the mold thickness direction as much as possible. Hereinafter, the configuration of the immersion nozzle 1 will be described in detail.

(Immersion nozzle 1)
As shown in FIG. 3, the immersion nozzle 1 has a bottomed cylindrical shape having an inner diameter φ [mm], and is integrally formed with a rectifying protrusion 5 and a refractory. The inner diameter φ [mm] of the immersion nozzle 1 is 60 to 100, for example.

(Discharge hole 2)
The discharge holes 2 are formed in the peripheral wall of the immersion nozzle 1 so as to face each other as shown in FIG. 5, and are slightly inclined downward from the inner peripheral surface 4 to the outer peripheral surface 7 of the immersion nozzle 1 as shown in FIG. As shown in FIG. 3, the inner peripheral surface 4 of the immersion nozzle 1 has a rounded rectangular edge 8, and the outer peripheral surface 7 of the immersion nozzle 1 similarly has a rounded rectangular edge. 9 (see also FIG. 4). Further, the forming direction 6 of the discharge holes 2 is parallel to the mold width direction in a plan view of FIG. Further, as shown in FIG. 5, the discharge hole 2 is formed so as to be gradually widened from the inner peripheral surface 4 to the outer peripheral surface 7 of the immersion nozzle 1.

  As shown in FIG. 3, the discharge hole lower end distance hd [that is the distance in the vertical direction between the discharge hole lower end 8 d that is the lower end of the edge 8 of the discharge hole 2 on the inner peripheral surface 4 of the immersion nozzle 1 and the inner bottom surface 3. mm] is, for example, 20-40. Similarly, the discharge hole upper end distance hu [mm], which is the distance in the vertical direction between the discharge hole upper end 8 u which is the upper end of the edge 8 and the inner bottom surface 3, is 50 to 120, for example. In addition, in the elevation view shown in FIG. 3, the flow passage cross-sectional area of the discharge hole 2 that can be specified two-dimensionally by projecting the edge 8 of the discharge hole 2 on the inner peripheral surface 4 of the immersion nozzle 1 is high throughput. Therefore, the diameter corresponds to the area of a circle having a diameter of 70 to 110 [mm]. Specifically, in the elevation view shown in FIG. 3, the flow path width Wi [of the discharge hole 2 that can be specified two-dimensionally by projecting the edge 8 of the discharge hole 2 on the inner peripheral surface 4 of the immersion nozzle 1. mm] and the flow path height Hi [mm] are 50 to 95 and 80 to 100, respectively. In FIG. 3, the space surrounded by the inner bottom surface 3, the discharge hole lower end 8 d and the inner peripheral surface 4 is generally referred to as a hot water reservoir 10, and this hot water reservoir 10 mainly prevents splashing of molten steel at the start of casting. The function to perform is demonstrated. A downward discharge angle θ [deg.], Which is an angle θ between the inner bottom surface 2a of the discharge hole 2 and the horizontal in an elevational view shown in FIG. ] Is approximately 10-55.

(Rectifying protrusion 5)
<Cross-sectional shape> As shown in FIG. 3, in the cross section perpendicular to the mold width direction, the rectifying protrusion 5 is substantially trapezoidal and gradually narrows from the inner peripheral surface 4 toward the axis C of the immersion nozzle 1. It is a round shape. That is, the rectifying protrusion 5 includes a protrusion upper surface 11 as a plane inclined downward on the axis C side, a protrusion lower surface 12 as a plane inclined upward on the axis C side, and the protrusion upper surface 11 and the protrusion lower surface 12. A protrusion inner peripheral surface 13 for connecting the two. In the cross-sectional view shown in FIG. 3, the upper surface 11 and the lower surface 12 of the protrusion are inclined at approximately 30 to 60 degrees with respect to the horizontal. The protrusion inner peripheral surface 13 is a flat surface and is orthogonal to the mold thickness direction. The protrusion inner peripheral surface 13 extends in the mold width direction in the cross-sectional view shown in FIG. 4, and in particular, the lower end line 13d of the protrusion inner peripheral surface 13 (the lower end portion 5d of the rectifying protrusion 5) is seen in the elevation view of FIG. Parallel to the mold width direction. Similarly, the upper end line 13u of the protrusion inner peripheral surface 13 (the upper end portion 5u of the rectifying protrusion 5) is also parallel to the mold width direction in the elevational view of FIG. In short, in the present embodiment, the rectifying protrusion 5 is formed so as to extend in the mold width direction.

<Protrusion Vertical Thickness> The symbol d2 shown in FIG. 4 is the protrusion vertical thickness d2 [mm] which is the distance in the vertical direction between the upper end line 13u (the upper end of the rectifying protrusion) and the lower end line 13d (the lower end of the rectifying protrusion). is there. That is, the protrusion vertical thickness d2 [mm] of the rectifying protrusion 5 is specified by paying attention to the protrusion inner peripheral surface 13.

<Directing protrusion lower end distance> Reference sign d1 shown in FIG. 4 is a rectifying protrusion lower end distance d1 [mm], which is a distance in the vertical direction between the lower end line 13d and the inner bottom surface 3 described above. That is, the rectifying protrusion lower end distance d1 [mm] of the rectifying protrusion 5 is specified by paying attention to the protrusion inner peripheral surface 13 and the inner bottom surface 3.

<Protrusion Horizontal Thickness> The symbol A shown in FIG. 5 indicates the protrusion horizontal thickness A [specification of the rectifying protrusion 5 in the mold thickness direction (direction perpendicular to the forming direction 6 of the discharge holes 2) in the plan view of FIG. mm]. Specifically, the protrusion horizontal thickness A [mm] is perpendicular to the mold width direction in a plan view of FIG. 5, and is an overlap distance between the straight line E passing through the axis C of the immersion nozzle 1 and the rectifying protrusion 5. Identified.

<Protrusion Horizontal Length> The symbol B shown in FIG. 5 indicates the protrusion horizontal length specified in the mold width direction (direction parallel to the formation direction 6 of the discharge holes 2) of the flow straightening protrusion 5 in plan view of FIG. B [mm]. Specifically, the protrusion horizontal length B [mm] is specified as the maximum length itself in the mold width direction of the rectifying protrusion 5 specified by the broken line and the solid line in FIG.

  The rectifying protrusion 5 having the above shape further satisfies the conditions of the following formulas (1) to (4).

  The configuration of the immersion nozzle 1 according to this embodiment has been described above. From the viewpoint of strength, melting damage, etc., it is preferable that the surface and the surface intersect at an obtuse angle, and the portion where the surface and the surface intersect with each other is appropriately rounded. However, when each of the above dimensions becomes unclear due to rounding, dimensions that can be specified when assuming no rounding shall be adopted instead.

  Next, the operation of the immersion nozzle 1 according to the present embodiment will be described based on FIG. In the immersion nozzle 1 according to the present embodiment, as shown in FIG. 6A, the molten steel that has flowed from the upper end to the lower end of the immersion nozzle 1 is provided outside the curve before colliding with the inner bottom surface 3. Collides with rectifying protrusion 5. And by this collision, the flow of the molten steel in the immersion nozzle 1 is once concentrated near the curved inner side. At this time, a large negative pressure region F is formed between the rectifying protrusion 5 and the inner bottom surface 3, and the flow of the molten steel is attracted to the negative pressure region F. As shown in FIG. A single large-diameter vortex P that is clockwise and rises from the inner bottom surface 3 toward the curved outer side with the direction as an axis is formed. Thus, in the immersion nozzle 1 according to the present embodiment, the swirling direction of the single large-diameter vortex P is fixed by the rectifying protrusion 5, so the direction of the discharge flow is fixed inside the curve, As shown in FIG. 12B, the flow pattern of the discharge flow that is a downward flow inside the curve and an upward flow outside the curve is stably realized. Further, since the immersion nozzle 1 disclosed in FIG. 2 actively uses the single large-diameter vortex P, the flow passage cross-sectional area of the discharge hole 2 is no longer reduced in order to realize the flow pattern. Therefore, it is possible to set the flow passage cross-sectional area of the discharge hole 2 large while realizing the above flow pattern as shown in FIG. 12B. .

  Therefore, if the above immersion nozzle 1 is employed, the trapping and accumulation of inclusions inside the curve of the solidified shell can be suppressed, and the heat input to the corner of the solidified shell becomes excessive in high-throughput operation. Can be avoided.

  Although the preferred embodiment of the present invention has been described above, the rectifying protrusions 5 and the discharge holes 2 can be changed as follows.

  That is, the projection inner peripheral surface 13 of the rectifying projection 5 may be formed to draw an arc in the same manner as the inner peripheral surface 4 in a plan view shown in FIG. The measurement standards of the protrusion horizontal thickness A [mm], the protrusion horizontal length B [mm], the straightening protrusion lower end distance d1 [mm], and the protrusion vertical thickness d2 [mm] are shown in FIGS. 7 (a1) and (a2). As described above, this is exactly the same as the above embodiment.

  In addition, in the plan view shown in FIG. 7B1, the rectifying protrusion 5 according to the above embodiment may be formed by obliquely cutting an end in the mold width direction. The measurement standards of the protrusion horizontal thickness A [mm], the protrusion horizontal length B [mm], the straightening protrusion lower end distance d1 [mm], and the protrusion vertical thickness d2 [mm] are shown in FIGS. 7B1 and 7B2. As described above, this is exactly the same as the above embodiment.

  8 (c1), the discharge hole 2 according to the above embodiment may be formed with a constant flow path width from the inner peripheral surface 4 to the outer peripheral surface 7.

  Hereinafter, the test for confirming the technical effect of the immersion nozzle 1 which concerns on the said embodiment is demonstrated. Each numerical range mentioned above is reasonably supported by the following test.

≪Examination: Outline of examination≫
Each test is a so-called water model test that employs a water tank and water instead of the mold and molten steel. Each test was performed while making minor changes to the structure of the immersion nozzle 1 and the size of the water tank.

≪Test: Test method: Fig. 9≫
In this test, the state of the discharge flow from the immersion nozzle 1 for 100 seconds in a steady state where water is supplied to the immersion nozzle 1 at a predetermined water flow rate Wat [L / min] is shown in FIG. Visually photographed and recorded using a commercially available video camera. At this time, the state of the discharge flow was visualized by including air in the water flowing through the immersion nozzle 1. Then, by analyzing the video at this time based on appropriate image processing, it was investigated how long in 100 seconds the direction of the discharge flow was sufficiently directed toward the inside of the curve. As a result of this investigation, the time during which the direction of the discharge flow is sufficiently directed toward the inside of the curve, specifically, the discharge angle α [deg. ] Was 5 or more, and the inner discharge time rate R as a value obtained by dividing the time by 100 seconds was obtained. When the inner discharge time rate R is approximately 100%, the immersion nozzle 1 evaluates as “◯” because the direction of the discharge flow can be sufficiently directed toward the inside of the curve, and otherwise indicates “× ". In FIG. 9, the unit of numerical values is mm, the symbol W indicates the width of the water tank (corresponding to the mold width), and the symbol D indicates the thickness of the water tank (corresponding to the mold thickness). Further, the discharge angle α [deg. The reason for adopting 5 as the threshold value is described at the end of the present specification.

≪Test: Individual test conditions and test results≫
Next, individual test conditions and test results of each test are shown in Table 1 below. In Table 1 below, the column title “W mm” is the size of the water tank and corresponds to the mold width in the actual machine. The column title “D mm” is also the size of the water tank and corresponds to the mold thickness in the actual machine. The size of the water tank in Table 1 below assumes a mold for a general slab. The column title “Air NL / min” means the flow rate of air introduced into the immersion nozzle during the test. This air was blown from the vicinity of the upper end of the immersion nozzle shown in FIG. The column title “SV open / close direction” means the open / close direction of the slide valve. That is, generally, a slide valve for adjusting the flow rate of the molten steel to the mold is provided at the upper end of the immersion nozzle 1, and this slide valve slides the valve in a specific direction and opens the slide. The flow rate can be adjusted by adjusting the degree. If the slide direction of this valve matches the mold thickness direction, “mold thickness direction” is described in the corresponding place in the column title “SV opening / closing direction”, and if the slide direction of this valve matches the mold width direction, the same Is described as “mold width direction”. In the column title “ejection hole shape”, “trumpet” corresponds to FIG. 5, and “parallel” corresponds to FIG. 8 (c1). The column title “S mm” refers to the discharge hole 2 that can be identified two-dimensionally by projecting the edge 8 of the discharge hole 2 on the inner peripheral surface 4 of the immersion nozzle 1 in an elevational view shown in FIG. The channel cross-sectional area is meant, and the diameter [mm] when the channel cross-sectional area is expressed by the diameter of a circle having the same area is described. In the column title “rectifying step position”, “outside” means that the rectifying protrusions 5 are arranged on the curved outer side in a plan view of FIG. 5, and “inside” means that the plane in FIG. This means that the straightening protrusions 5 are arranged on the curved inner side. For the column title “Formula (1)” and the like, refer to each formula. In addition, the case where the corresponding mathematical formula is satisfied was set as “◯”, and the case where it was not satisfied was set as “X”. The column title “R%” means the inner discharge time rate R [%]. For reference, the column title “Ave (α) deg.” Has a discharge angle α [deg. The average value of] was described. The column title “overall evaluation” describes the result of evaluation based on the inner discharge time rate R. In addition, Test No. In 6, 11, 25, 30, 44, and 49, this comprehensive evaluation column is “X” for other special reasons.

(Summary)
(Claim 1)
As described above, in the above embodiment, the immersion nozzle 1 is configured as follows. That is, the rectifying protrusion 5 is provided on the inner peripheral surface 4 on the curved outer side of the immersion nozzle 1 and at a position sandwiched between the pair of discharge holes 2 in a plan view. The conditions of the following formulas (1) to (4) are satisfied.

  According to the above configuration, since the swirling direction of the single large-diameter vortex P is fixed by the rectifying protrusion 5, the direction of the discharge flow is fixed inside the curve, as shown in FIG. As described above, the flow pattern of the discharge flow that is a downward flow inside the curve and an up flow outside the curve is stably realized. Further, since the immersion nozzle 1 disclosed in FIG. 2 actively uses the single large-diameter vortex P, the flow passage cross-sectional area of the discharge hole 2 is no longer reduced in order to realize the flow pattern. Therefore, it is possible to set the flow passage cross-sectional area of the discharge hole 2 large while realizing the above flow pattern as shown in FIG. 12B. .

  If the immersion nozzle 1 according to the above embodiment is employed, the trapping and accumulation of inclusions inside the curve of the solidified shell can be suppressed, and of course, heat input to the corner of the solidified shell is excessive in high-throughput operation. It becomes possible to avoid becoming.

(Discussion)
Hereinafter, the results of Table 1 will be discussed in detail.

(Discharge hole shape)
Test No. According to Nos. 1 to 57, it was proved that the parallel type shown in FIG. 8C1 is sufficiently effective as a variation of the discharge hole shape in addition to the trumpet type shown in FIG.

(Cross-sectional area of discharge hole)
Test No. 1 to 57 show that the flow passage cross-sectional area of the discharge hole 2 can be set to be larger than that of Patent Document 1 or the like while the direction of the discharge flow is directed to the inside of the curve. .

(Rectification step position)
Test No. According to the comparison between 1, 20, 39 and other tests, whether the rectifying protrusion 5 is arranged inside the curve or the curve outside, and the direction of the discharge flow is directed inside the curve. It can be seen that there is a close one-to-one correspondence between being directed to the outside of the curve. Although not actually tested, if the rectifying protrusion 5 is arranged at another position that is neither the curved outer side nor the curved inner side, the vortex P as shown in FIG. 6 will not be formed in theory. In addition, Test No. In 2, 21, and 40, the rectifying protrusion 5 was not provided. At this time, the flow of molten steel was exactly as shown in FIGS. 1 (c2) and (d2).

(Formula 1, Formula 2)
Test No. According to 2 to 11, 21 to 30, and 40 to 49, it can be seen that when the rectifying protrusion 5 is too small in the plan view of FIG. The flow of molten steel at this time would have been exactly the flow of FIG. 1 (c2) and (d2). That is, it is considered that the negative pressure region F shown in FIG.

  In addition, Test No. If the thickness of the rectifying protrusion 5 is excessively large in the plan view of FIG. 5 as in FIGS. 6, 25, and 44, the evaluation regarding the inner discharge time rate R is good, but it becomes weak against thermal shock and is sufficient for actual use. It is difficult to ensure a sufficient strength. Therefore, these test Nos. The overall evaluation was “×”.

  In addition, Test No. If the width of the rectifying protrusion 5 is excessively large in the plan view of FIG. 5 as in FIGS. 11, 30, and 49, the evaluation on the inner discharge time rate R is good, but the directionality of the step position is lost (particularly FIG. 7). In the case of (a1), when B / φ = 1.0, the step is completely along the inner peripheral surface 4 and the directionality is completely lost.) The generation of the vortex P is unstable. It is considered to be. Further, since the cross-sectional area of the flow path that can be specified in plan view of the immersion nozzle 1 is reduced, the flow velocity in the immersion nozzle 1 is increased, and the discharge flow is discharged from the discharge hole 2 while the flow velocity is large. Heat input can be excessive. Therefore, these test Nos. The overall evaluation was “×”.

(Formula 3)
Test No. According to 12-15, 31-34, 50-53, it can be seen that the evaluation regarding the inner discharge time rate R is better as d1 / φ is closer to 1.0. As d1 / φ is closer to 1.0, as shown in FIG. 6A, the region surrounded by the rectifying protrusion 5, the inner bottom surface 3, and the inner peripheral surface 4 becomes closer to a square, and this region is a square. This is probably because the vortex P is more likely to be generated as it is closer to, the generated vortex P is closer to a perfect circle, and the generated vortex P is less likely to lose its shape.

(Formula 4)
Test No. With the cross-sectional shape of the rectifying protrusion 5 according to 16, 35, 54, it is not possible to ensure sufficient strength to withstand use in actual casting. In this sense, in any case, these test Nos. The overall evaluation is x. In addition, Test No. 19, 38, and 57 show that the evaluation regarding the inner discharge time rate R is not good when the cross-sectional shape of the rectifying protrusion 5 shown in FIG. 3 is a flat shape. As shown in FIG. 10, the flow of the molten steel separated by the collision with the upper surface 11 of the rectifying protrusion 5 is reattached on the inner peripheral surface 13 of the rectifying protrusion 5, and as a result, In addition, it is considered that a sufficiently large negative pressure region F was not formed. In addition, “Mechanical Engineering Handbook Basic α4 Fluid Engineering First Edition 47 ”includes:“ In a prism with a flow direction length of B and a thickness of H,..., B / H> 6.0, the shear layer peeled off from the leading edge angle is reattached on the side wall. "..." This description is reinforcing support for adopting 6.0 on the right side of Equation (4) in the above embodiment.

  In the above formulas (1) to (4), the ratio is used for the following reason. That is, in general continuous casting, the inside of the pipe of the immersion nozzle 1 and the water reservoir 10 are sufficiently turbulent, and the shape inside the immersion nozzle 1 and the flow of molten steel inside the immersion nozzle 1 This is because if the similarity rule is applied and the ratio is constant even if the sizes are different, the flow of molten steel will not change.

<Threshold basis: FIG. 11>
FIG. 11 is a graph of the data disclosed in Japanese Patent Laid-Open No. 51-138526. The downward discharge angle θ [deg. ] Is 15 in any plot. According to this graph, the discharge angle α [deg. ] Is 5 or more, the discharge angle α [deg. ], The amount of inclusions can be reduced by about 60%, and the slab quality can be improved. Therefore, the discharge angle α [deg. ] Was adopted as the threshold value.

1 Immersion nozzle 2 Discharge hole 3 Inner bottom surface 5 Rectification protrusion

Claims (1)

A bottomed cylindrical immersion nozzle that is used to pour molten steel held in a tundish into a mold, and is for a curved continuous casting machine. In an immersion nozzle in which opposed discharge holes are formed,
On the inner peripheral surface of the curved outer side of the immersion nozzle, a rectifying protrusion is provided at a position sandwiched between the pair of discharge holes in a plan view,
A protrusion horizontal thickness A [mm] specified in the mold thickness direction in plan view of the rectifying protrusion;
A protrusion horizontal length B [mm] specified in the mold width direction in plan view of the rectifying protrusion;
A straightening protrusion lower end distance d1 [mm], which is a distance in the vertical direction between the straightening protrusion lower end that is the lower end of the straightening protrusion and the inner bottom surface of the immersion nozzle;
A protrusion vertical thickness d2 [mm] which is a distance in the vertical direction between the upper end of the straightening protrusion and the lower end of the straightening protrusion;
Satisfies the conditions of the following formulas (1) to (4).

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