IMMERSION NOZZLE

Abstract

An immersion nozzle for discharging molten steel supplied from a tundish into a mold for continuous casting of a slab includes a discharge portion that supplies the molten steel to the mold, wherein the immersion nozzle includes two regions divided by a plane in a thickness direction, the plane passing through an axial center, the discharge portion includes: a bottom portion; and a side wall that extends in a height direction from an outer edge of the bottom portion, four discharge holes are formed in the discharge portion, two discharge hole are arranged side by side in a width direction in each of the regions in the bottom portion of the discharge portion.

Description

TECHNICAL FIELD OF THE INVENTION

The present application relates to an immersion nozzle used for supplying molten steel from a tundish to a mold in continuous casting of molten steel.

The present application particularly relates to an immersion nozzle for distributing and supplying a discharge flow into a mold in high-speed casting.

The present application claims priority based on Japanese Patent Application No. 2022-047181 filed in Japan on Mar. 23, 2022, the contents of which are incorporated herein by reference.

In an immersion nozzle used for supplying the molten steel from a tundish to a mold, a high-speed casting condition in which a casting speed exceeds 3 m/min and reaches 5 to 8 m/min at the maximum is used in continuous casting of thin slabs or the like.

In a case where such a high-speed casting condition is applied, there is a demand for injecting the molten steel into the mold downward along the vertical direction, from the viewpoint of preventing disturbance on the molten steel surface in the mold.

In addition, from the viewpoint of dispersing kinetic energy of the discharge flow in the mold (in other words, reducing the discharge flow velocity), there is a demand for enlarging a discharge hole area by using multiple discharge holes or the like.

In response to these demands, immersion nozzles having various shapes have been conventionally proposed.

For example, as disclosed in Patent Documents 1 to 4, a multi-hole nozzle in which four or more discharge holes are disposed in a bottom part of an immersion nozzle has been proposed.

Alternatively, as disclosed in Patent Documents 5 to 7, a device is known in which a barrier is provided in the inside to reduce the flow velocity of a downward flow in the immersion nozzle or to smoothly distribute the downward flow to a plurality of discharge holes.

CITATION LIST

Patent Document

[Patent Document 1]

• • Published Japanese Translation No. 2004-514562 of the PCT International Publication

[Patent Document 2]

• • Japanese Unexamined Patent Application, First Publication No. H08-39208

[Patent Document 3]

• • Japanese Patent No. 3186068

[Patent Document 4]

• • Japanese Patent No. 4580135

[Patent Document 5]

• • Japanese Patent No. 4542631

[Patent Document 6]

• • Japanese Patent No. 3408884

[Patent Document 7]

• • Japanese Patent No. 6666908

SUMMARY OF INVENTION

Problems to be Solved by the Invention

The present inventors pursued studies by using a water model experiment.

As a result, it has been found out that the conventional technique has the following problem.

The downward flow inside the immersion nozzle is affected by a flow passage area-reduction mechanism such as a stopper or a slide gate for controlling the amount of molten steel to be supplied from the tundish to the immersion nozzle, and unstable fluctuation occurs (unevenness in flow or an uneven state changes).

As being affected by the fluctuation of the downward flow, the flow rate distribution to the multiple discharge holes changes.

As a result, the flowing movement inside the mold fluctuates unstably (that is, drift flows to the left and right or changes of the state occur).

This may cause defects on the surfaces of slabs to be manufactured.

In order to stabilize the flow rate distribution to the multiple discharge holes, it is sufficient to reduce the discharge hole area and increase internal pressure of the immersion nozzle.

However, in such a case, the effect of reducing the discharge flow velocity, which is the original object of providing multiple holes, is impaired.

As described above, a problem of the conventional technique is that it is difficult to achieve both distribution of the flow rate to multiple discharge holes and reduction in the discharge flow velocity.

The present disclosure has been made in order to overcome such a technical problem, and it is an object of the present disclosure to provide an immersion nozzle in which a self-stabilizing function for discharge flow distribution is fulfilled by devising an internal structure of the immersion nozzle so as to be capable of suppressing unevenness in the flowing movement of molten steel in a mold.

Means for Solving the Problem

The gist of the present disclosure is as follows.

• • (1) According to one aspect of the present invention is an immersion nozzle for discharging molten steel supplied from a tundish into a mold for continuous casting of a slab, the immersion nozzle including a discharge portion that supplies the molten steel to the mold, in which the immersion nozzle includes two regions divided by a plane in a thickness direction, the plane passing through an axial center, the discharge portion includes: a bottom portion; and a side wall that extends in a height direction from an outer edge of the bottom portion, four discharge holes are formed in the discharge portion, two discharge holes are arranged side by side in a width direction in each of the regions in the bottom portion of the discharge portion, the discharge portion includes: an internal barrier that is disposed at the center in the width direction and that distributes the molten steel supplied from the tundish to each of the regions; a branch flow passage through which a branch flow, which is the molten steel that has been distributed by the internal barrier, flows between the side wall of each of the regions and the internal barrier; and a distribution block, on a bottom portion side relative to the internal barrier, that further distributes the branch flow that has passed through the branch flow passage to a distribution flow passage in each of the regions to supply the branch flow to each of the discharge holes, in a case where out of the two discharge holes disposed in each of the regions, the discharge hole disposed on an outer side in the width direction is defined as an outer discharge hole, the discharge hole disposed on an inner side in the width direction is defined as an inner discharge hole, and when either one of the branch flow passages is closed, a relationship between a flow rate Qa of the molten steel to be discharged from the inner discharge hole disposed in a region where the branch flow passage is closed and a flow rate Qb of the molten steel to be discharged from the inner discharge hole disposed in a region in which the branch flow passage is not closed satisfies an equation (1), and a relationship between a discharge flow rate Q_out of the molten steel to be discharged from the outer discharge hole and a discharge flow rate Q_IN of the molten steel to be discharged from the inner discharge hole satisfies an equation (2).

$\begin{array}{cc}\mathrm{Qa}/\mathrm{Qb}>1.& \left(1\right)\end{array}$ $\begin{array}{cc}0.1\le Q_{\mathrm{IN}}/Q_{\mathrm{out}}\le 1.& \left(2\right)\end{array}$

• • (2) In the immersion nozzle described in the above (1), the immersion nozzle may include a straight body portion that receives the molten steel supplied from the tundish, the discharge portion, and a connection portion that connects the straight body portion with the discharge portion, and a projection area of the internal barrier, when the immersion nozzle is projected on a horizontal plane, may be equal to or larger than a flow passage area of the straight body portion.
  • (3) In the immersion nozzle described in the above (1) or (2), a surface of the internal barrier on a side that receives the molten steel supplied from the tundish may include a recessed portion.
  • (4) In the immersion nozzle described in one of the above (1) to (3), in each of the regions, an outer discharge angle α1, which is defined by an angle of a wall surface that forms the outer discharge hole, may be between equal to or larger than downward 40 degrees and equal to or smaller than downward 75 degrees, and a relationship between α1 and an inner discharge angle α2, which is defined by an angle of a wall surface that forms the inner discharge hole, may satisfy an equation (3).

$\begin{array}{cc}-5\mathrm{degrees}\le ❘\mathrm{\alpha 2}❘-❘\mathrm{\alpha 1}❘\le 15\mathrm{degrees}& \left(3\right)\end{array}$

• • (5) In the immersion nozzle described in one of the above (2) to (4), a value obtained by dividing a flow passage area of the branch flow passage by a flow passage area of the straight body portion may be equal to or larger than 0.4 and equal to or smaller than 1.5.
  • (6) In the immersion nozzle described in one of the above (2) to (5), a value obtained by dividing a flow passage area of the distribution flow passage by a flow passage area of the straight body portion may be equal to or larger than 0.3 and equal to or smaller than 1.5.

Effects of the Invention

According to the immersion nozzle in the present disclosure, unevenness in the flowing movement of the molten steel in the mold can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a typical continuous casting apparatus for slabs.

FIG. 2 is a schematic view illustrating a state in which flowing movements of molten steel are uneven in a mold.

FIG. 3 is a cross-sectional view, in a width direction, that passes through an axial center C of an immersion nozzle 100.

FIG. 4 is a plan view of the immersion nozzle 100.

FIG. 5 is a bottom view of the immersion nozzle 100.

FIG. 6 is a projection view of the immersion nozzle 100, which is projected on a horizontal plane, and is a view when attention is focused on a flow passage 11 and an internal barrier 34.

FIG. 7 is an enlarged view of the internal barrier 34.

FIG. 8 is an enlarged view of a bottom portion 31 side of a discharge portion 30.

FIG. 9 is a cross-sectional view, in the width direction, that passes through the axial center C of an immersion nozzle 200.

FIG. 10 is an enlarged view of a bottom portion 131 side of a discharge portion 130.

FIG. 11A is a schematic view illustrating a mode of a discharge portion of an immersion nozzle of Experimental Example A.

FIG. 11B is a schematic view illustrating a mode of a discharge portion of an immersion nozzle of Experimental Example B.

FIG. 11C is a schematic view illustrating a mode of a discharge portion of an immersion nozzle of Experimental Example C.

FIG. 11D is a schematic view illustrating a mode of a discharge portion of an immersion nozzle of Experimental Example D.

FIG. 11E is a schematic view illustrating a mode of a discharge portion of an immersion nozzle of Experimental Example E.

FIG. 11F is a schematic view illustrating a mode of a discharge portion of an immersion nozzle of Experimental Example F.

FIG. 11G is a schematic view illustrating a mode of a discharge portion of an immersion nozzle of Experimental Example G.

FIG. 11H is a schematic view illustrating a mode of a discharge portion of an immersion nozzle of Experimental Example H.

FIG. 11I is a schematic view illustrating a mode of a discharge portion of an immersion nozzle of Experimental Example I.

FIG. 11J is a schematic view illustrating a mode of a discharge portion of an immersion nozzle of Experimental Example J.

FIG. 11K is a schematic view illustrating a mode of a discharge portion of an immersion nozzle of Experimental Example K.

FIG. 11L is a schematic view illustrating a mode of a discharge portion of an immersion nozzle of Experimental Example L.

FIG. 11M is a schematic view illustrating a mode of a discharge portion of an immersion nozzle of Experimental Example M.

FIG. 12 is a schematic diagram of a full-scale water model experiment.

EMBODIMENT(S) OF THE INVENTION

FIG. 1 illustrates a schematic view of a typical continuous casting apparatus for slabs.

As illustrated in FIG. 1, molten steel S stored in a tundish T is supplied to a mold M through an immersion nozzle N.

Then, the molten steel S that has been supplied is drawn out while being gradually cooled in the mold M, and continuous casting of slabs is conducted.

The flow rate of the molten steel S to be supplied from the tundish T to the immersion nozzle N is adjusted by a flow passage area-reduction mechanism such as a slide gate or a stopper.

On the other hand, the adjustment of the flow rate causes fluctuation or unevenness in the downward flow in the immersion nozzle N.

In a case where the immersion nozzle N includes multiple discharge holes, the flow rate distribution to multiple discharge holes changes due to fluctuation or unevenness in the downward flow, and unevenness also occurs in the flowing movement of the molten steel in the mold.

FIG. 2 is a schematic view illustrating a state in which unevenness occurs in the flowing movement of the molten steel in the mold.

As illustrated in FIG. 2, when the flow passage of the molten steel is adjusted by the flow passage area-reduction mechanism, drift flows are generated in the immersion nozzle.

Then, when the molten steel in which the drift flows are generated is discharged into the mold, drift flows are also generated in the flowing movement of the molten steel in the mold.

When the drift flows are generated in the mold, problems such as molten steel surface disturbance and stagnation occur.

If the slabs are cast in such a flowing movement state, the formation of the solidified shell will be affected, and surface defects may occur in the slabs to be manufactured.

In addition, it can also be said that it is important to suppress the unevenness in the flowing movement of the molten steel in the mold, from the viewpoint of stabilizing the casting operation.

Hence, there is a demand for a technique of suppressing the unevenness in the flowing movement of the molten steel in the mold.

The present inventors conducted experimental studies on such problems.

As a result, the present inventors have found out that by combining the following two elements, it becomes possible to fulfill a self-stabilizing function for the discharge flow distribution effective to an immersion nozzle having multiple discharge holes.

The first element is to provide an internal barrier capable of distributing the downward flow, which has passed through the flow passage area-reduction mechanism from the tundish, to the left and right.

The second element is to provide, under the internal barrier, as a mechanism for correcting unevenness between the left and right caused by the flow rate distribution in a first stage, a distribution block capable of distributing the flow rate to increase the distribution on the side where the flow rate distribution has been reduced by the first distribution.

Hereinafter, description will be made in detail with regard to the immersion nozzle in the present disclosure that has been made on the basis of the above findings.

First Embodiment

FIG. 3 is a cross-sectional view, in a width direction, that passes through an axial center C of the immersion nozzle 100 according to a first embodiment.

Note that in the present disclosure, in FIG. 3, a left-right direction will be referred to as a width direction, an up-down direction will be referred to as a height direction, and a depth direction will be referred to as a thickness direction.

An immersion nozzle 100 according to the first embodiment is used for discharging the molten steel, which has been supplied from a tundish, to a mold for continuous casting of slabs.

The immersion nozzle 100 has a hollow shape, and a flow passage for the molten steel is formed in the inside.

As illustrated in FIG. 3, the immersion nozzle 100 includes a straight body portion 10, which receives the molten steel that has been supplied from the tundish, a discharge portion 30, which supplies the molten steel to the mold, and a connection portion 20, which connects the straight body portion 10 with the discharge portion 30.

The straight body portion 10 and the connection portion 20 are optional parts, but are usually provided in the immersion nozzle.

In addition, the immersion nozzle 100 includes two regions R1 and R2, which are divided by a plane in the thickness direction (that is, a plane parallel to the extending direction of the axial center C and the thickness direction) that passes through the axial center C.

The region R1 and the region R2 are regions determined for the sake of description of the immersion nozzle 100.

In the immersion nozzle 100, the region R1 and the region R2 are typically in a plane-symmetrical shape.

The “axial center C” is an intersection line of planes that respectively divide the length in the width direction and the length in the thickness direction of the immersion nozzle 100 into two equal parts.

The axial center C usually passes through the centers of the straight body portion 10, the connection portion 20, and the discharge portion 30.

The center of each member is an intersection line of planes that divide the length in the width direction and the length in the thickness direction of each member into two equal parts.

In addition, the immersion nozzle 100 includes two regions R3 and R4, which are divided by a plane in the width direction (that is, a plane parallel to the extending direction of the axial center C and the width direction) that passes through the axial center C (see FIG. 4).

In the immersion nozzle 100, the region R3 and the region R4 may be in a plane-symmetrical shape.

In the immersion nozzle 100, typically, the region R1 and the region R2 are in a plane-symmetrical shape, and the region R3 and the region R4 are in a plane-symmetrical shape.

The straight body portion 10 is a tubular part that receives the molten steel that has been supplied from the tundish.

FIG. 4 is a plan view of the immersion nozzle 100.

As illustrated in FIG. 4, a flow passage 11 having a constant shape, through which a downward flow of the molten steel flows, is formed inside the straight body portion 10.

The sizes of the straight body portion 10 and the flow passage 11 can be appropriately set in accordance with an object.

As illustrated in FIG. 4, usually, the length in the thickness direction of each member (the straight body portion 10, the connection portion 20, and the discharge portion 30) of the immersion nozzle 100 is substantially constant, and the length in the thickness direction of the internal flow passage is also substantially constant.

“Substantially constant” means that manufacturing errors and circumstances (for example, within a prescribed length of ±1%) are included.

For example, for manufacturing circumstances, slight tapering is given from an upper end to a lower end, in some cases.

Here, W11 is defined as a length in the width direction of the flow passage 11 of the straight body portion 10, and S11 is defined as a flow passage area of the straight body portion 10.

In the present application, the “flow passage area” means an area of a cross-section perpendicular to a central axis of the flow passage.

The central axis of the flow passage of the straight body portion 10 extends like a straight line. Therefore, the flow passage area S11 of the straight body portion 10 is equal to a projection area, which is projected on a horizontal plane, of the flow passage 11 of the straight body portion 10.

The length W11 in the width direction of the flow passage 11 and dimensions of the flow passage area S11 will be described later.

A cross-section of the straight body portion 10 that is perpendicular to the axial center C has a rectangular shape.

However, in the immersion nozzle in the present disclosure, the cross-sectional shape of the straight body portion is not particularly limited, and may be circular, elliptical, or polygonal.

The connection portion 20 is a part that connects the straight body portion 10 with the discharge portion 30, and includes a flow passage through which the molten steel flows from the straight body portion 10 to the discharge portion 30.

The shape of the connection portion 20 is not particularly limited.

In FIG. 3, the connection portion 20 is gently inclined from the straight body portion 10 to the discharge portion 30.

The discharge portion 30 is a part that supplies the molten steel to the mold, and has a substantially fan shape in which the width increases from the straight body portion 10 side toward the bottom portion 31 side, when viewed in the thickness direction.

In addition, the discharge portion 30 has a flat shape in which a length in the thickness direction is shorter than a length in the width direction.

The discharge portion 30 includes a bottom portion 31 and a side wall 32, which extends from an outer edge of the bottom portion 31.

As illustrated in FIG. 3, the bottom portion 31 is a part that forms a region corresponding to an arc of the substantially fan shape.

A lower end of the side wall 32 is connected with the outer edge of the bottom portion 31, and an upper end is connected with an outer edge of the connection portion 20.

The side wall 32 is a member that forms the outside of the discharge portion 30, and also contributes to formation of the flow passages of the molten steel, for example, outer discharge holes 33aa and 33ba and a branch flow passage 35 to be described later.

The substantially fan shape of the discharge portion 30 may be appropriately set in accordance with the constitution of the internal flow passage and the angles of the discharge holes 33 with respect to the horizontal direction.

FIG. 5 illustrates a bottom view of the immersion nozzle 100.

As illustrated in FIG. 5, the discharge portion 30 includes four discharge holes 33.

As the number of the discharge holes 33 increases, the discharge hole area is increased, so that the discharge flow velocity can be reduced.

On the other hand, if there are too many discharge holes 33, the outer dimension of the immersion nozzle will be enlarged, thereby leading to problems in cost and operational handling.

In addition, if there are an odd number of discharge holes, the discharge hole at the center portion in width will be directed immediately downward, from the viewpoint of maintaining the left-right symmetry.

The discharge flow directed immediately downward from the center portion in width will interfere with the discharge flows from other discharge holes, thereby causing instability of the flowing movements in the mold, in some cases.

Hence, in the immersion nozzle 100 in the present disclosure, the number of the discharge holes is four, so that the unevenness in the flowing movement of the molten steel in the mold can be suppressed.

In addition, the discharge holes 33 are disposed in the bottom portion 31 of the discharge portion 30.

More specifically, two discharge holes 33 are disposed side by side in the width direction in each of the region R1 and the region R2.

As illustrated in FIG. 5, the discharge holes 33 may be disposed on a straight line in the width direction.

In FIG. 5, the shape of the discharge hole 33 is rectangular in a bottom view.

However, in the immersion nozzle in the present disclosure, the shape of the discharge hole is not limited to this, and may be a circle, an ellipse, or a polygon.

Here, out of two discharge holes 33, which are disposed in each of the region R1 and region R2, the discharge holes 33 disposed on the outer sides in the width direction are respectively defined as outer discharge holes 33aa and 33ba, and the discharge holes 33 disposed on the inner sides in the width direction are respectively defined as inner discharge holes 33ab and 33bb.

Returning to FIG. 3, the constitution of the discharge portion 30 will be further described.

The discharge portion 30 includes an internal barrier 34, branch flow passages 35, and distribution blocks 36.

The internal barrier 34 is disposed at the center in the width direction, and distributes the molten steel (the downward flow) that has been supplied from the tundish to each of the regions R1 and R2.

The branch flow passage 35 is present between the side wall 32 of each of the region R1 and the region R2 and the internal barrier 34, and is a flow passage for causing the molten steel (a branch flow) that has been distributed by the internal barrier 34 to flow.

The distribution block 36 is disposed on the bottom portion 31 side relative to the internal barrier 34, further distributes the branch flow that has passed through the branch flow passage 35 in each of the region R1 and the region R2, and supplies the branch flow to at least three discharge holes 33.

The internal barrier 34 is disposed on the straight body portion 10 side relative to the distribution blocks 36, and is disposed on a lower side than the lower end of the straight body portion 10.

The internal barrier 34 has a role of distributing the downward flow (the molten steel) supplied from the straight body portion 10 to each of the region R1 and the region R2 (one side and the other side in the width direction).

That is, the internal barrier 34 is a member for distributing the molten steel in a first stage.

The branch flow passage 35 is formed between a side surface 34c of the internal barrier 34 and the side wall 32, and causes the branch flow that has been distributed by the internal barrier 34 to flow.

After passing through the branch flow passage 35, the branch flow is discharged from the discharge holes 33 into the mold.

The branch flow is partially discharged directly from the outer discharge holes 33aa and 33ba, but the branch flow partially collides with the distribution block 36, and is distributed to at least three discharge holes 33.

The distribution block. 36 is disposed on the bottom portion 31 side relative to the internal barrier 34.

The distribution block 36 is a member that further distributes the branch flow that has passed through the branch flow passage 35 in each of the region R1 and the region R2, and that supplies the branch flow to at least three discharge holes 33.

That is, the distribution block 36 is a member for distributing the molten steel in a second stage.

“At least three discharge holes 33” means at least the inner discharge holes 33ab and 33bb and the outer discharge hole in the region where the aforementioned distribution block 36 is disposed.

For example, when attention is focused on the distribution block 36 disposed in the region R1, the outer discharge hole 33aa corresponds to the outer discharge hole in the region R1 where the aforementioned distribution block 36 is disposed.

In this manner, in the discharge portion 30, the molten steel supplied from the tundish is distributed in two stages, the flow rates of the molten steel to be discharged from the respective discharge holes 33 are averaged, and the unevenness is suppressed.

That is, in the discharge portion 30, even though unevenness occurs in the flow rate due to the flow rate distribution in the first-stage with use of the internal barrier 34, such unevenness in the flow rate distribution can be corrected in the flow rate distribution in the second stage with use of the distribution block 36.

However, by simply providing the internal barrier 34 and the distribution blocks 36, the flow rate distribution function cannot be sufficiently fulfilled, in some cases.

Hence, in the immersion nozzle 100, the internal barrier 34 and the distribution blocks 36 are provided so that the following characteristics 1 and 2 can be achieved.

Characteristic 1

In a case where either one of the branch flow passages 35 is closed, the flow rate of the molten steel to be discharged from the inner discharge hole disposed in the region where the branch flow passage 35 is closed is larger than the flow rate of the molten steel to be discharged from the inner discharge hole disposed in the region where the branch flow passage 35 is not closed.

That is, for example, when the branch flow passage 35 (an elliptical part surrounded by a broken line in FIG. 3) in the region R1 is closed, the flow rate of the molten steel to be discharged from the inner discharge hole 33ab, which is disposed in the region R1, is larger than the flow rate of the molten steel to be discharged from the inner discharge hole 33bb, which is disposed in the region R2.

This means that the branch flow that collides with the distribution block 36 in the region R2 is mainly supplied to the inner discharge hole 33ab in the region R1 rather than the inner discharge hole 33bb in the region R2.

The immersion nozzle 100 has such a characteristic 1. Therefore, in the immersion nozzle 100, even though unevenness occurs between the flow rates by the flow rate distribution in the first stage with the use of the internal barrier 34, such unevenness in the flow rate distribution is correctable with the flow rate distribution in the second stage with the use of the distribution blocks 36.

That is, it can be said that the immersion nozzle 100 fulfills a self-stabilizing function for the discharge flow distribution.

According to the immersion nozzle having such a characteristic, the unevenness in the flowing movement of the molten steel in the mold can be suppressed.

It is possible to determine whether the immersion nozzle has a mode of satisfying the above characteristic, by performing a water model experiment having an actual size. In the water model experiment, a flow rate “a” and a flow rate “b” in the following are measured, when either one of the branch flow passages is closed.

Flow rate “a”: a flow rate of water to be discharged from an inner discharge hole disposed in a region where the branch flow passage is closed

Flow rate “b”: a flow rate of water to be discharged from an inner discharge hole disposed in a region where the branch flow passage is not closed

In a case where the flow rate “a” is larger than the flow rate “b”, it can be determined that the characteristic 1 is satisfied.

The reason why the determination can be made with the above water model experiment is that dynamic viscosities of the molten steel and water are substantially equal to each other, and thus the way that the molten steel flows and the way that water flows in the immersion nozzle can be regarded as being similar to each other.

With regard to the experimental conditions, the flow velocity/flow rate conditions same with the actual operating conditions are adopted.

For example, the flow velocity of the downward flow that passes through the straight body portion 10 is set to the same conditions with the actual operating conditions.

In addition, the time while water is caused to flow through the immersion nozzle 100 is set to at least one minute.

Thus, it becomes possible to accurately confirm whether the characteristic 1 is achieved.

The method for closing the branch flow passage 35 in the water model experiment is not particularly limited. However, for example, it is sufficient to close the region of the elliptical part indicated by the broken line in FIG. 3 by using a rubber stopper or the like that corresponds to the cross-sectional shape of the branch flow passage 35.

The above characteristic 1 can be mentioned in other words as follows.

When either one of the branch flow passages 35 is closed, Qa is defined as a flow rate of the molten steel to be discharged from the inner discharge hole disposed in the region where the branch flow passage 35 is closed, and Qb is defined as a flow rate of the molten steel to be discharged from the inner discharge hole disposed in the region where the branch flow passage 35 is not closed, Qa/Qb satisfies an equation (1) in the following.

$\begin{array}{cc}\mathrm{Qa}/\mathrm{Qb}>1.& \left(1\right)\end{array}$

From the viewpoint of more reliably fulfilling the self-stabilizing function, the value of Qa/Qb is preferably equal to or more than 1.1 times, and is more preferably equal to or more than 1.2 times.

On the other hand, if the value of Qa/Qb exceeds three times, the flow rate re-distribution for fulfilling the self-stabilizing function will become excessive, in some cases.

In this case, conversely, a drift flow may occur toward the flow passage closed side.

Thus, the value of Qa/Qb is preferably equal to or less than three times.

The value of Qa/Qb may be equal to or less than 2.1 times, may be equal to or less than 1.9 times, or may be equal to or less than 1.5 times.

Note that the ratio of the flow rate of the molten steel to be discharged from the inner discharge hole disposed in the region where the branch flow passage 35 is closed to the flow rate of the molten steel to be discharged from the inner discharge hole disposed in the region where the branch flow passage 35 is not closed will be referred to as a distribution ratio, in some cases.

Characteristic 2

The relationship between a discharge flow rate Q_out of the molten steel to be discharged from the outer discharge holes 33aa and 33ba and a discharge flow rate Q_IN of the molten steel to be discharged from the inner discharge holes 33ab and 33bb satisfies an equation (2).

$\begin{array}{cc}0.1\le Q_{\mathrm{IN}}/Q_{\mathrm{out}}\le 1.& \left(2\right)\end{array}$

Here, the discharge flow rate Q_out denotes a sum of the flow rates to be discharged from the outer discharge holes 33aa and 33ba, and the discharge flow rate Q_IN denotes a sum of the flow rates to be discharged from the inner discharge holes 33ab and 33bb.

In the equation (2), the upper limit of Q_IN/Q_out is defined as 1.0.

That is, the discharge flow rate Q_IN from the inner discharge holes 33ab and 33bb does not exceed the discharge flow rate Q_out from the outer discharge holes 33aa and 33ba.

This is because, from the viewpoint of the stability of the flowing movements in the mold, it is necessary to form a clear collision pattern of the discharge flow with a short-side solidified shell, and thus it is desirable that the main flows are the discharge flows from the outer discharge holes 33aa and 33ba.

It is needless to say that an excessive collision flow velocity is risky and is not desirable from the viewpoint of preventing the solidified shell from being redissolved. However, it is desirable to form a clear pattern toward the short-side solidified shell as a flowing movement pattern, from the viewpoint of generating more stable flowing movements.

From the viewpoint of generating more stable flowing movements, the upper limit of Q_IN/Qom is preferably equal to or smaller than 0.8, and is more preferably equal to or smaller than 0.6.

In the equation (2), the lower limit of Q_IN/Q_out is defined as 0.1.

That is, the discharge flow rate Q_IN from the inner discharge holes 33ab and 33bb is ensured to be equal to or more than 0.1 times the discharge flow rate Q_out from the outer discharge holes 33aa and 33ba.

This achieves the original object of the present disclosure of distributing the discharge flow to the inner discharge holes 33ab and 33bb to stabilize the flowing movements in the mold.

The lower limit of Q_IN/Qom may be equal to or more than 0.2.

It is possible to calculate the discharge flow rates Q_out and Q_IN, by performing a water model experiment having an actual size and measuring the amount of water to be discharged from each discharge hole.

As described above, this is because the dynamic viscosities of the molten steel and water are substantially equal to each other, and the flow of the molten steel and the flow of water in the immersion nozzle can be regarded as being similar to each other.

With regard to the experimental conditions, the flow velocity/flow rate conditions same with the actual operating conditions are adopted.

For example, the flow velocity of the downward flow that passes through the straight body portion 10 is set to the same condition.

In addition, the time while water is caused to flow through the immersion nozzle 100 is set to at least one minute.

Accordingly, it becomes possible to accurately confirm whether the characteristic 2 is achieved.

In the immersion nozzle 100, in a case where not only the above characteristics 1 and 2 but also the following characteristic 3 are provided, this is desirable because the immersion nozzle 100 is capable of fulfilling the flow rate distribution function in a more sufficient manner.

Characteristic 3

In each of the region R1 and the region R2, an outer discharge angle α1, which is defined by the angle of the wall surface that forms the outer discharge holes 33aa and 33ba, is equal to or larger than downward 40 degrees and equal to or smaller than downward 75 degrees, and in addition, a relationship between the outer discharge angle α1 and an inner discharge angle α2, which is defined by the angle of the wall surface that forms the inner discharge holes 33ab and 33bb, satisfies an equation (3).

The downward angle is an angle with respect to the width direction.

−5 degrees≤|α2|−|α1|≤15 degrees  (3)

The outer discharge angle α1 and the inner discharge angle α2 are determined from the cross-sectional shape of the immersion nozzle 100, which is divided by a plane in the width direction that passes through the axial center C.

As the outer discharge angle α1, in a case where the angles of opposite wall surfaces of the outer discharge hole are the same with each other, the angle of the wall surface is adopted, and in a case where the angles of the opposite wall surfaces of the outer discharge hole are different from each other, the average value of these angles is adopted.

Similarly, as the inner discharge angle α2, in a case where the angles of the opposite wall surfaces of the inner discharge hole are the same with each other, the angle of the wall surface is adopted, and in a case where the angles of the opposite wall surfaces of the inner discharge hole are different from each other, the average value of these angles is adopted.

Note that in order to facilitate entering and exiting of the molten steel, the outer discharge holes 33aa and 33ba and the inner discharge holes 33ab and 33bb each have a tapered or curved surface in an inlet or an outlet of a hole, in some cases.

In such cases, the discharge angle is calculated by excluding the tapered or the curved surface.

The outer discharge angle α1 and the inner discharge angle α2 are calculated for each of the region R1 and the region R2, and it is sufficient to satisfy the equation (3) in both regions.

In a case where the high-speed casting at a casting speed equal to or higher than 3 m/min is assumed, the outer discharge angle α1 is desirably equal to or larger than downward 40 degrees, and is more desirably equal to or larger than downward 45 degrees, from the viewpoint of suppressing waves on the molten steel surface in the mold.

On the other hand, an excessive discharge angle leads to instability of the flowing movements in the mold. Therefore, it is desirable to limit the outer discharge angle α1 to downward 75 degrees, and a more desirable upper limit value is downward 65 degrees.

In addition, the relationship between the outer discharge angle α1 and the inner discharge angle α2 satisfies the equation (3).

The meaning of the equation (3) is as follows.

The inner discharge angle α2 is usually set to be larger than the outer discharge angle α1, from the viewpoint of distributing the discharge flow and dispersing the kinetic energy.

As a result of studies through experimental and numerical analyses, the present inventors have found out that the discharge flows tend to attract each other and join together, in a case where the values of both discharge angles are closer to each other. In addition, the present inventors have found out that the tendency of the outer discharge flow and the inner discharge flow to join together operates advantageously for the self-stabilizing function of the distribution block 36.

On the basis of such findings, the present inventors have found out that the difference between the inner discharge angle α2 and the outer discharge angle α1 is preferably equal to or smaller than 15 degrees.

Such a difference between these angles is more preferably equal to or smaller than 10 degrees.

On the other hand, in a case where the difference between two angles is negative, that is, the inner discharge angle α2 is set to be smaller than the outer discharge angle α1, such a setting is disadvantageous for dispersing the kinetic energy due to the discharge flow distribution. Therefore, the minimum value of the difference between two angles is set to −5 degrees.

The minimum value is 0, that is, it is more preferable that the inner discharge angle α2 and the outer discharge angle α1 are set to the same values.

The mode of each member in the immersion nozzle 100 is appropriately set to have the above-described flow rate distribution characteristics.

The mode of the immersion nozzle having the flow rate distribution characteristics is achieved by strictly adjusting the mode (shape, size, arrangement, and the like) of each member. However, the mode varies largely, and it is difficult to describe all modes.

Hereinafter, each member of the immersion nozzle 100 will be described, but they are examples.

The mode of the immersion nozzle in the present disclosure is not limited, as long as it has the flow rate distribution characteristics.

The discharge portion 30 has a substantially fan shape, and four discharge holes 33 are disposed on the bottom portion 31, which constitutes an arc of its shape.

The disposed positions, sizes, angles, and the like of these discharge holes 33 are appropriately set to achieve the flow rate distribution characteristics.

The angles of the inner discharge holes 33ab and 33bb are usually set to be larger than the angles of the outer discharge holes 33aa and 33ba.

The angle of the discharge hole denotes an angle formed by a straight line that divides the width (for example, the width of the outer opening) of the discharge hole into two equal parts and a straight line that extends in the width direction, on a cross-section in the width direction that passes through the axial center C.

For example, the angles of the inner discharge holes 33ab and 33bb may be equal to or larger than 60 degrees, may be equal to or larger than 70 degrees, may be equal to or larger than 75 degrees, or may be equal to or smaller than 90 degrees.

The angles of the outer discharge holes 33aa and 33ba may be equal to or larger than 40 degrees, may be equal to or larger than 50 degrees, may be equal to or larger than 60 degrees, may be equal to or smaller than 90 degrees, and may be equal to or smaller than 75 degrees.

The internal barrier 34 has a role of distributing the downward flow (the molten steel) supplied from the straight body portion 10 to the region R1 and the region R2 (one side and the other side in the width direction).

In addition, the internal barrier 34 is disposed on the straight body portion 10 side relative to the distribution blocks 36, and in addition, is disposed to be lower than the lower end of the straight body portion 10.

In the internal barrier 34, the space between the internal barrier 34 and the side wall 32 in the thickness direction may be completely closed, from the viewpoint of appropriately distributing the downward flow to the region R1 and the region R2 (one side and the other side in the width direction).

In other words, the internal barrier 34 may be formed over the thickness direction of the discharge portion 30.

FIG. 6 is a projection view of the immersion nozzle 100, which is projected on a horizontal plane (a plane formed with the width direction and the thickness direction), and is a view when attention is focused on the flow passage 11 and the internal barrier 34.

A projection area S34, in a case where the internal barrier 34 is projected on a horizontal plane, is preferably equal to or larger than the flow passage area S11 of the straight body portion 10.

Accordingly, unevenness in distributing the downward flow to the region R1 and the region R2 can be effectively suppressed.

From the viewpoint of suppressing the unevenness more effectively, the projection area S34 of the internal barrier 34 is more preferably equal to or more than 1.2 times the flow passage area S11 of the straight body portion 10, and is more preferably equal to or more than 1.5 times.

On the other hand, in a case where the projection area S34 of the internal barrier 34 is excessively large, the flow rate decreases. Therefore, the projection area S34 of the internal barrier 34 is preferably equal to or less than 3 times the flow passage area S11 of the straight body portion 10, and is more preferably equal to or less than 2 times.

FIG. 7 illustrates an enlarged view of the internal barrier 34.

The internal barrier 34 includes an upper surface 34a on the straight body portion 10 side, a lower surface 34b on the bottom portion 31 side, and side surfaces 34c, each of which is connected with the upper surface 34a and the lower surface 34b.

The upper surface 34a is a surface of the internal barrier 34 on a side that receives the molten steel (the downward flow) that has been supplied from the tundish (the straight body portion 10).

The downward flow can be distributed to the region R1 and the region R2 by the upper surface 34a.

As illustrated in FIGS. 3 and 7, the upper surface 34a preferably includes a recessed portion 34aa.

The recessed portion 34aa includes a bottom surface portion 34aa1 and side surface portions 34aa2, which respectively extend from both end portions of the bottom surface portion 34aa1, and is open on the straight body portion 10 side.

The immersion nozzle 100 includes the recessed portion 34aa, so that the unevenness in the flow rates of the branch flows can be suppressed.

That is, the self-stabilizing function can be further enhanced.

However, the upper surface of the internal barrier in the present disclosure may not necessarily include the recessed portion.

For example, the upper surface of the internal barrier may be flat.

The present inventors estimate the following mechanism regarding the effect of the recessed portion 34aa.

That is, when the downward flow collides with the internal barrier 34 and the downward flow is distributed as branch flows to the region R1 and the region R2, and if unevenness occurs in the flow rates of the branch flows, it is estimated that the branch flow having a larger flow rate will be partially bounced back along the surface extending from the side surface portion 34aa2 to the bottom surface portion 34aa1 of the recessed portion 34aa, and the bounced molten steel will be added to the branch flow having a smaller flow rate, so that the unevenness in the flow rates of the branch flows can be suppressed.

The recessed portion 34aa may be disposed on the entire upper surface 34a, or may be disposed on a part of the upper surface 34a.

In a case where the recessed portion 34aa is disposed in a part of the upper surface 34a, the recessed portion 34aa is disposed at the center in the width direction, as illustrated in FIG. 7.

A projection area S34aa (a projection area of an opening portion) of the recessed portion 34aa, which is projected on a horizontal plane, is not particularly limited, but may be approximately the same as the flow passage area S11 of the straight body portion 10.

Accordingly, it becomes possible to further improve the effect of suppressing the unevenness in the flow rates of the branch flows.

In a case where the projection area S34aa of the recessed portion 34aa is too small, the effect of forming the recessed portion 34aa cannot be sufficiently obtained. Therefore, the projection area S34aa of the recessed portion 34aa is preferably equal to or more than 0.8 times the flow passage area S11 of the straight body portion 10, and is more preferably equal to or more than 0.9 times.

On the other hand, in a case where the projection area S34aa of the recessed portion 34aa is too large, the internal barrier 34 itself also increases in size. Therefore, the projection area S34aa of the recessed portion 34aa is preferably equal to or less than 1.5 times the flow passage area S11 of the straight body portion 10, and is more preferably equal to or less than 1.2 times.

A depth H34aa of the recessed portion 34aa (a length in the height direction from bottom surface portion 34aa1 to an end surface 34ae) is not particularly limited, but is preferably set as follows.

The depth H34aa of the recessed portion 34aa is preferably equal to or larger than 10 mm.

Such a setting enables the effect of suppressing the unevenness in the flow rates of the branch flows in a more reliably manner.

The depth H34aa of the recessed portion 34aa is preferably equal to or smaller than 30 mm, and is more preferably equal to or smaller than 20 mm.

Such a setting enables avoidance of an unnecessary increase in the nozzle outer dimension.

A projection area S34aa1 of the bottom surface portion 34aa1 is not particularly limited, but is preferably equal to or less than 1.0 times the projection area S34aa (the projection area of the opening portion) of the recessed portion 34aa, is more preferably equal to or less than 0.9 times, and is still more preferably equal to or less than 0.8 times in order to avoid an unnecessary increase in the nozzle outer dimension.

The projection area S34aa1 of the bottom surface portion 34aa1 may be equal to or more than 0.5 times the projection area S34aa of the recessed portion 34aa, or may be equal to or more than 0.6 times.

The side surface portion 34aa2 may be formed to be perpendicular to a bottom surface 34ab, or may have an inclination.

In a case where the side surface portion 34aa2 has an inclination, the inclination may be linear or curved.

In a case where the recessed portion 34aa is disposed in a part of the upper surface 34a, the end surface 34ae is disposed between an end portion of the upper surface 34a and the recessed portion 34aa.

The end surface 34ae may be horizontal, or may have an inclination.

The inclination of the end surface 34ae may decrease or increase in height toward an inner side. Alternatively, the end surface 34ae may be a curved surface.

The lower surface 34b may include an inclined portion 34ba, the height of which decreases toward the inner side.

In order to form a distribution flow passage 36b to be described later, at least the inclined portion 34ba may be disposed at a position that faces an upper surface 36a of the distribution block 36.

In FIGS. 3 and 7, the inclined portions 34ba are respectively disposed in both end portions in the width direction of the lower surface 34b.

The lower surface 34b may include a horizontal surface 34bb, which defines a lower end height of the inclined portion 34ba.

Alternatively, the entirety of the lower surface 34b may be the horizontal surface 34bb.

For example, in a case where the distance from the upper surface 36a of the distribution block 36 to the lower surface 34b is large, the entirety of the lower surface may be the horizontal surface 34bb without the inclined portion 34ba.

In a case where the entirety of the lower surface 34b is the horizontal surface 34bb, the distribution flow passage 36b is formed by the horizontal surface 34bb and the upper surface 36a of the distribution block 36.

The side surface 34c has a role of forming the branch flow passage 35 together with the side wall 32.

The shape of the side surface 34c is not particularly limited, may be a flat surface, may be a perpendicular surface, may be an inclined surface, or may be a curved surface, or may have any shape in combination of them.

In addition, the side surface 34c may be inclined such that the height decreases toward the outer side in the width direction.

Accordingly, the branch flow can be caused to flow smoothly.

Next, the branch flow passage 35 will be described.

As described above, the branch flow passage 35 is formed between the side surface 34c of the internal barrier 34 and the side wall 32.

The flow passage area S35 of the branch flow passage 35 is not particularly limited, but if it is too small, it will hinder the high-speed casting, in some cases. Therefore, the flow passage area S35 is preferably equal to or more than 0.4 times the flow passage area S11 of the straight body portion 10, and is more preferably equal to or more than 0.5 times.

On the other hand, if the flow passage area S35 of the branch flow passage 35 is too large, the self-stabilizing function will not be sufficiently achievable, in some cases. Therefore, the flow passage area S35 of the branch flow passage 35 is preferably equal to or less than 1.5 times the flow passage area S11 of the straight body portion 10, and is more preferably equal to or less than 1 time.

The flow passage area S35 of the branch flow passage 35 denotes the minimum flow passage area of either one of the branch flow passages 35.

For example, in a case where the flow passage area of the branch flow passage 35 has a mode of gradually decreasing downward as will be described later, the flow passage area of the branch flow passage 35 in a position where the flow passage area is the smallest is regarded as the minimum flow passage area.

In a case where the flow passage areas S35 of the branch flow passages 35 are different between the left and the right, the minimum flow passage area of the branch flow passage 35 having a smaller flow passage area S35 is regarded as the flow passage area S35 of the branch flow passage 35.

The flow passage area S35 of the branch flow passage 35 may have a mode of not being constant.

For example, the flow passage area S35 of the branch flow passage 35 may have a mode of gradually decreasing.

Also in this case, the flow passage area S35 (the minimum flow passage area) of the branch flow passage 35 may satisfy the above range.

It is possible to form such a branch flow passage 35 by adjusting the inclination angle of the side surface 34c and/or the side wall 32.

In a case where the flow passage area S35 of the branch flow passage 35 has a mode of gradually decreasing, the branch flow is appropriately guided to the distribution block 36, as compared with the case where the flow passage area S35 has a mode of gradually increasing, so that the self-stabilizing function can be further enhanced.

Subsequently, the distribution block 36 will be described.

As described above, the distribution block 36 is a member that further distributes the branch flow that has passed through the branch flow passage 35 and that supplies the branch flow to each of the discharge holes 33, and is a member that distributes the downward flow in the second stage.

Here, the distribution ratio of the branch flow can be controlled by the shape of the distribution block 36.

By controlling the distribution ratio, it becomes possible to suppress the unevenness in the flow rate distribution.

Hereinafter, the shape of the distribution block 36 will be described.

FIG. 8 is an enlarged view of the bottom portion 31 side of the discharge portion 30.

As illustrated in FIG. 8, the distribution block 36 is disposed in each of the regions R1 and R2, serves as a partition wall that separates the outer discharge hole and the inner discharge hole, and is a part of the bottom portion 31.

The bottom portion 31 includes a central block 37, which separates the two inner discharge holes 33ab and 33bb from each other.

The distribution block 36 has a role of distributing the branch flow, and has a characteristic on the upper surface 36a, with which the branch flow collides.

Side surfaces and a lower surface of the distribution block 36 may be appropriately set in accordance with the shape of the discharge hole 33.

In the example illustrated in FIG. 8, the distribution block 36 has a shape similar to a trapezoid.

The upper surface 36a of the distribution block 36 includes a first part 36aa, which faces the internal barrier 34, and a second part 36ab, which is a remaining part.

However, the shape of the distribution block 36 is not limited to this, may be a shape having only the second part 36ab, may be constituted of a combination of several flat surfaces having different angles, or may be formed of a complicated curved surface.

Assuming that an intersection point C is defined as a point at which a line segment A-B connecting an outer end portion A and an inner end portion B of the upper surface 36a of the distribution block 36 intersects an extension line L of the side surface 34c of the internal barrier 34, the first part 36aa and the second part 36ab can be defined as follows.

The first part 36aa=a range between the inner end portion B and the intersection point C

The second part 36ab=a range between the outer end portion A and the intersection point C

The first part 36aa mainly contributes to the formation of a flow passage of a branch flow (a distribution flow passage 36b) to be distributed to the inner discharge hole side.

The distribution flow passage 36b is formed between the lower surface 34b (the inclined portion 34ba) of the internal barrier 34 and the upper surface 36a of the distribution block 36, and supplies the branch flow to the two inner discharge holes 33ab and 33bb.

In this situation, for example, when attention is focused on the distribution flow passage 36b and the upper surface shape of the central block 37 in the region R1, the distribution flow passage 36b and the upper surface shape of the central block 37 are set such that the branch flow to be distributed to the inner discharge hole 33bb is larger in ratio than the inner discharge hole 33ab.

Accordingly, the unevenness in the flow rate distribution can be corrected.

The distribution flow passage 36b having such an effect is achievable by setting, for example, the shapes of the internal barrier 34, the distribution block 36, and the central block 37 so that the flow (a streamline F) of the molten steel that passes through the distribution flow passage 36b passes over the inner discharge hole 33ab in the same region and flows toward the inner discharge hole 33bb in the other region.

It is possible to confirm the streamline F as the direction of the main flow, by causing a tracer (for example, fine bubbles or India ink) to flow for visualizing the flow in the water model experiment.

In FIG. 8, the streamline close to a middle line between the inclined portion 34ba of the internal barrier and the upper surface 36a of the distribution block is drawn for the sake of convenience.

The streamline here is not a geometrically obtained one, but is an experimentally obtained one.

The flow passage area S36b of the distribution flow passage 36b is not particularly limited, but is preferably equal to or more than 0.3 times the flow passage area S11 of the straight body portion 10, and is more preferably equal to or more than 0.4 times.

The flow passage area S36b of the distribution flow passage 36b is preferably equal to or less than 1.5 times the flow passage area S11 of the straight body portion 10, and is more preferably equal to or less than 1 time.

The flow passage area S36b of the distribution flow passage 36b denotes a minimum flow passage area of the distribution flow passage 36b.

For example, in a case where the flow passage area S36b of the distribution flow passage 36b has a mode of gradually decreasing downward (downstream), the flow passage area of the distribution flow passage 36b in the position where the flow passage area is the smallest is regarded as the minimum flow passage area.

In a case where the flow passage areas S36b of the distribution flow passage 36b are different between the left and the right, the minimum flow passage area of the distribution flow passage 36b having a smaller flow passage area S36b is regarded as the flow passage area S36b of the distribution flow passage 36b.

The second part 36ab contributes to the distribution ratio when the branch flow that has been distributed by the internal barrier 34 is further distributed to the outer discharge hole side and the inner discharge hole side.

A length L36a (between points A and B) of the upper surface 36a is not particularly limited, but is preferably equal to or more than 0.3 times the length W11 of the flow passage 11 in the width direction, and is more preferably equal to or more than 0.8 times.

The length L36a of the upper surface 36a is preferably equal to or less than 1.5 times the length W11 of the flow passage 11 in the width direction, and is more preferably equal to or less than 1.0 times.

L36aa:L36ab, which is the ratio of a length L36aa of the first part 36aa (between the point C and the point B) to a length L36ab of the second part 36ab (between the point A and the point C), is not particularly limited, but is, for example, from 1:4 to 3:2.

An angle β (an angle formed by a straight line that passes through the points A and B and a straight line along the width direction) of the upper surface 36a is not particularly limited, but may be appropriately set in accordance with the streamline F.

For example, in usual design, it falls within a range of downward 20 degrees to downward 60 degrees.

Note that FIG. 8 illustrates a mode in which the upper surface 36a of the distribution block 36 is flat. However, the upper surface 36a of the distribution block may be a combination of a plurality of flat surfaces respectively having different angles, or may be a curved surface.

Alternatively, the upper surface 36a of the distribution block 36 may include a recessed portion or a protrusion.

Second Embodiment

A second embodiment relates to an immersion nozzle 200, in which the distribution block 36 in the first embodiment is independent of the bottom portion 31 of the discharge portion 30.

Hereinafter, the immersion nozzle 200 will be described. However, the descriptions of the constitutions common to those in the immersion nozzle 100 will be omitted.

The immersion nozzle 200 includes a discharge portion 130, in which a distribution block 136 is independent of a bottom portion 131.

FIG. 9 is a cross-sectional view, in the width direction, that passes through the axial center C of the discharge portion 130 of the immersion nozzle 200.

In addition, FIG. 10 is an enlarged view of the bottom portion 131 side of the discharge portion 130.

As illustrated in FIGS. 9 and 10, the immersion nozzle 200 includes the distribution block 136, which is independent of the bottom portion 131 in each of the regions R1 and R2.

Accordingly, partition walls 131a, each of which partitions the outer discharge hole and the inner discharge hole, are disposed on the bottom portion 131.

In addition, the distribution block 136 is constituted to be independent, and the shape of an internal barrier 134 is also changed.

The distribution block 136 includes an upper surface 136a, which is similar to that of the distribution block 36.

For example, a distribution flow passage 136b is so formed that the streamline F of the distribution flow passage 136b is included in the upper surface of the bottom portion 131 in the other region.

Accordingly, the unevenness in the flow rate distribution can be corrected.

Other constitutions of the distribution block 136 are not particularly limited.

For example, the distance between the distribution block 136 and the bottom portion 131 is not particularly limited, and it is sufficient to appropriately set so that the immersion nozzle 200 has the flow rate distribution characteristics.

Heretofore, the immersion nozzles in the present disclosure have been described, based on the first embodiment and the second embodiment.

In the immersion nozzles in the present disclosure, even when the unevenness in the flow rate distribution occurs due to the flow rate distribution in the first stage with use of the internal barrier, such unevenness in the flow rate distribution is corrected by the flow rate distribution in the second stage with use of the distribution block.

Therefore, with the immersion nozzles in the present disclosure, the unevenness in the flowing movement in the mold can be suppressed.

EXAMPLES

Hereinafter, the immersion nozzles in the present disclosure will be further described by experimental examples.

FIGS. 11A to 11M illustrate modes of discharge portions 30A to 30M of the immersion nozzles used in Experimental Examples A to M.

FIGS. 11A to 11M each illustrate a cross-sectional view, in the width direction, of the immersion nozzle.

The structures and conditions of the discharge portions 30A to 30M of the immersion nozzles used in Experimental Examples A to M are indicated in Table 1.

TABLE 1
Experimental Example	A	B	C	D	E	F	G	H
Straight body portion flow	56	56	56	56	56	56	56	56
passage width (mm)
Straight body portion flow	31	31	31	31	31	31	31	31
passage thickness (mm)
Internal barrier	Presence	Presence	Presence	Presence	Presence	Presence	Presence	Presence
Internal barrier maximum width	79	79	79	50	50	112	79	79
(mm)
Internal barrier recessed portion	Presence	Presence	Absence	Absence	Presence	Presence	Presence	Presence
Internal barrier recessed portion	52	52	—	—	30	90	52	52
width (mm)
Internal barrier recessed portion	10	10	—	—	10	10	10	10
depth (mm)
Distribution block mode	Integrated	Integrated	Integrated	Separated	Integrated	Integrated	Integrated	Integrated
The number of discharge holes	4	4	4	4	4	4	4	4
Outer discharge hole	50	50	50	50	50	50	50	50
Discharge angle α1(°)
Inner discharge hole	55	75	75	75	55	55	55	55
Discharge angle α2(°)
Angle difference (°)	5	25	25	25	5	5	5	5
Projection area of internal	1.41	1.41	1.41	0.89	0.89	2.0	1.41	1.41
barrier/Flow passage area of
straight body portion
Flow passage area of branch	0.79	0.79	0.79	0.77	1.1	0.45	0.79	0.79
flow/Flow passage area of
straight body portion
Flow passage area of	0.45	0.45	0.45	0.45	0.45	0.35	0.25	1.7
distribution flow/
Flow passage area of straight
body portion
Downward flow velocity (m/s)	2	2	3	2.5	2.	2	2	2
Qa/Qb	1.2	1.2	1.3	1.9	1.5	1.2	1.4	1.1
QIN/Qout	0.5	0.5	0.5	0.7	0.9	0.1	0.2	0.6
Classification	Invention	Invention	Invention	Invention	Invention	Invention	Invention	Invention
	example	example	example	example	example	example	example	example
	Experimental Example	I	J	K	L	M
	Straight body portion flow	56	56	56	56	56
	passage width (mm)
	Straight body portion flow	31	31	31	31	31
	passage thickness (mm)
	Internal barrier	Presence	Presence	Presence	Absence	Presence
	Internal barrier maximum width	50	79	79	—	79
	(mm)
	Internal barrier recessed portion	Absence	Presence	Presence	—	Presence
	Internal barrier recessed portion	—	52	52	—	52
	width (mm)
	Internal barrier recessed portion	—	10	10	—	10
	depth (mm)
	Distribution block mode	—	Integrated	Integrated	—	—
	The number of discharge holes	4	3	5	4	4
	Outer discharge hole	50	—	—	50	50
	Discharge angle α1(°)
	Inner discharge hole	75	—	—	75	75
	Discharge angle α2(°)
	Angle difference (°)	25	—	—	25	25
	Projection area of internal	0.89	1.41	1.41	—	1.41
	barrier/Flow passage area of
	straight body portion
	Flow passage area of branch	0.77	0.79	0.79	—	0.79
	flow/Flow passage area of
	straight body portion
	Flow passage area of	1.00	0.45	0.45	0.45	0.70
	distribution flow/
	Flow passage area of straight
	body portion
	Downward flow velocity (m/s)	2.5	2.	2	2	2
	Qa/Qb	0.6	—	—	—	0.5
	QIN/Qout	0.6	—	—	1.4	0.6
	Classification	Comparative	Comparative	Comparative	Comparative	Comparative
		example	example	example	example	example

In all Experimental Examples A to M, straight body portions each having cross-sectional dimensions of the flow passage that are 56 mm in width and 31 mm in thickness were adopted.

In Experimental Examples A to C, G, H, J, K, and M, an internal barrier having a maximum width of 79 mm was adopted.

In Experimental Examples D, E, and I, an internal barrier having a maximum width of 50 mm was adopted.

In Experimental Example F, an internal barrier having a maximum width of 112 mm was adopted.

In Experimental Example L, an internal barrier was not adopted.

Among Experimental Examples A to K and M in which the internal barrier was adopted, a recessed portion was provided on the internal barrier in Experimental Examples A, B, E to H, J, K and M.

Among Experimental Examples A to K and M in which the internal barrier was adopted, a recessed portion was not provided on the internal barrier in Experimental Examples C, D, and I.

In Experimental Examples A to C, E to H, J, and K, a mode of “integrated” in which the distribution block also serves as the bottom portion outer wall was adopted.

In Experimental Example D, a mode of “separated” in which the distribution block is independent of the bottom surface was adopted.

In Experimental Examples I and M, which are Comparative Examples, neither the internal barrier nor the distribution block is provided in such a mode of satisfying the following equations.

$\begin{array}{cc}\mathrm{Qa}/\mathrm{Qb}>1.& \left(1\right)\end{array}$ $\begin{array}{cc}0.1\le Q_{\mathrm{IN}}/Q_{\mathrm{out}}\le 1.& \left(2\right)\end{array}$

Specifically, in Experimental Example I, the internal barrier was disposed on an upper side than those in the other Experimental Examples, and in Experimental Example M, the shape of the partition wall that separates between the outer discharge hole and the inner discharge hole was adjusted to be thin, so that the flow rate distribution in the second stage was not achievable.

The internal barrier is not provided in Experimental Example L, which is a Comparative Example. Therefore, the branch flow is not present, and the distribution flow is not present, accordingly.

Experimental Examples A to I, L, and M each were constituted to include four discharge holes.

Experimental Example J was constituted to include three discharge holes.

Experimental Example K was constituted to include five discharge holes.

In Experimental Examples A and E to H, an outer discharge hole discharge angle α1 is set to 50 degrees, and an inner discharge hole discharge angle α2 is set to 55 degrees, so an angle difference was set to 5 degrees.

In Experimental Examples B to E, I, L, and M, the outer discharge hole discharge angle α1 is set to 50 degrees, and the inner discharge hole discharge angle α2 is set to 75 degrees, so an angle difference was set to 25 degrees.

For each of Experimental Examples A to M, following values are indicated in Table 1.

• • The projection area of the internal barrier/the flow passage area of the straight body portion
  • The flow passage area of the branch flow passage/the flow passage area of the straight body portion
  • The flow passage area of the distribution flow passage/the flow passage area of the straight body portion.

In Experimental Examples A to I and M, the value of Qa/Qb was obtained by performing a water model experiment in a state in which the region on the left side of the internal barrier in the immersion nozzle was completely closed.

Specifically, water was supplied to the immersion nozzle at a predetermined downward flow velocity in the cross-sectional region of the straight body portion, and the flow rates of water discharged from the left and right inner discharge holes were measured.

The “downward flow velocity” in each Experimental Example is as indicated in Table 1.

Then, Qa denotes the flow rate of water that has been discharged from the left inner discharge hole, and Qb denotes the flow rate of water that has been discharged from the right inner discharge hole, and value of Qa/Qb was obtained.

In Experimental Examples J and K in which there are an odd number of discharge holes and Experimental Example L in which the internal barrier is not present, it is impossible to measure the value of Qa and Qb defined in the present application, and thus a hyphen (-) is indicated in Table 1.

In Experimental Examples A to I, L, and M, the water model experiments were conducted to determine the value of Q_IN/Q_OUT.

Specifically, water was supplied to the immersion nozzle at a predetermined downward flow velocity in the cross-sectional region of the straight body portion, and the flow rates of water discharged from the left and right inner discharge holes and the left and right outer discharge holes were measured.

The “downward flow velocity” in each Experimental Example is as indicated in Table 1.

Then, Q_out denotes a discharge flow rate of water discharged from the outer discharge holes (total of the left and right ones), Q_IN denotes a discharge flow rate of water discharged from the inner discharge holes (total of the left and right ones), and value of Q_IN/Q_OUT was obtained.

In Experimental Examples J and K in which there are an odd number of discharge holes, it is impossible to measure the values of Q_IN and Q_OUT defined in the present application, and thus a hyphen (-) is indicated in Table 1.

A flowing movement stability index and a drift flow index were evaluated for Experimental Examples A to M in order to confirm effects of the present application.

Full-scale water model experiments were conducted with use of the immersion nozzles in Experimental Examples A to M, and the stable situation of the flowing movement in the mold was evaluated.

FIG. 12 illustrates a schematic diagram of a full-scale water model experiment.

In addition, Table 2 indicates experimental conditions.

TABLE 2
Mold cross-     90 × 1000
sectional
size
(mm × mm)
Casting speed   6
(m/min)
Water injection (1) Absence of area-reduction mechanism
condition       (2) Presence of area-reduction mechanism:
(Presence or    Only right half of nozzle upper end portion
absence of      is opened
area-reduction
mechanism)
Flow velocity   Measurement position: ¼ width in mold
measurement     (left-right direction) - ½ thickness (depth
                direction) - 30 mm below water surface
                (height direction)
                (Two points indicated by • in FIG. 12)
                Measurement flow velocity direction:
                Horizontal flow velocity

First, a full-scale water model experiment for injecting water without area-reduction mechanism was conducted.

In a case where the water injection condition is absence of area-reduction mechanism, the left-right symmetrical downward flow enters the nozzle, and the drift flows to the left and the right hardly occurs on a time average.

On the other hand, even in the case of the absence of area-reduction mechanism, a fluctuation phenomenon like self-excited vibration of the drift flows to the left and the right occurs in a cycle of several tens of seconds to several minutes.

Therefore, for the degree of such a fluctuation, a value obtained by dividing the standard deviation in change of a horizontal flow velocity at the flow velocity measurement point by the average flow velocity was used as a parameter for evaluation.

Such a parameter was defined as a flowing movement stability index, and the evaluation was conducted with use of an average value of the values that have been calculated in each of the left and right flow velocity measurement points.

The flow velocity measurement time was set to 15 minutes per condition.

Next, a full-scale water model experiment was conducted under the condition that the water injection condition was left-right asymmetric, the left side ½ was closed at the inlet of the nozzle, and the water flowed into the nozzle through only the right side ½.

The left-right asymmetric downward flow causes drift flow to the left and the right, and a value obtained by dividing the absolute value of a difference between the left and the right in the horizontal flow velocity at the flow velocity measurement point of the drift flow by an average value between the left and the right in the horizontal flow velocity was used as a parameter for evaluation.

Such a parameter was defined as an drift flow index.

The flow velocity measurement time was set to 15 minutes per condition.

Table 3 indicates results.

TABLE 3
Experimental Example	A	B	C	D	E	F	G
Flowing	0.33	0.38	0.41	0.48	0.54	0.35	0.40
movement
stability index (−)
Drift flow index	0.15	0.18	0.25	0.30	0.35	0.18	0.27
(−)
Classification	Invention	Invention	Invention	Invention	Invention	Invention	Invention
	example	example	example	example	example	example	example
Experimental Example	H	I	J	K	L	M
Flowing	0.42	0.59	0.55	0.61	0.71	0.56
movement
stability index (−)
Drift flow index	0.29	0.50	0.67	0.63	0.78	0.46
(−)
Classification	Invention	Comparative	Comparative	Comparative	Comparative	Comparative
	example	example	example	example	example	example

It was found out that in Experimental Examples A to H that satisfy suitable conditions, the flowing movement stability indexes were smaller than those in Experimental Examples I to M, and the flowing movement in the mold was stable.

This is because the immersion nozzle includes the internal barrier and the distribution block disposed in a mode of satisfying the following equations,

$\begin{array}{cc}\mathrm{Qa}/\mathrm{Qb}>1.\mathrm{and}& \left(1\right)\end{array}$ $\begin{array}{cc}0.1\le Q_{\mathrm{IN}}/Q_{\mathrm{out}}\le 1.,& \left(2\right)\end{array}$

• • and the effect of suppressing the temporary drift flow caused by the fluctuation of the flowing movement in the immersion nozzle is achieved. As a result, it is shown that the fluctuation of the flowing movement in the mold can also be suppressed.

That is, it is understood that the immersion nozzle includes the internal barrier and the distribution block, and thus the self-stabilizing function for the discharge flow distribution is fulfilled, and effects are achieved for a temporary drift flow phenomenon caused by the fluctuation.

In addition, it is understood that Experimental Examples A to H that satisfy suitable conditions each have a smaller drift flow index than those of Experimental Examples I to M, and the flowing movement in the mold is stable.

This is because the immersion nozzle includes the internal barrier and the distribution block, and it is shown that the effect of suppressing the drift flow on a time average caused by the unevenness in the downward flow in an upper part of the immersion nozzle is achieved, and as a result, the unevenness in the flowing movement in the mold can also be suppressed.

That is, the immersion nozzle includes the internal barrier and the distribution block disposed in a mode of satisfying the following equations

$\begin{array}{cc}\mathrm{Qa}/\mathrm{Qb}>1.& \left(1\right)\end{array}$ $\begin{array}{cc}0.1\le Q_{\mathrm{IN}}/Q_{\mathrm{out}}\le 1.,& \left(2\right)\end{array}$

• • and it is understood that the self-stabilizing function for the discharge flow distribution is fulfilled, and the effect is achieved for the drift flow phenomenon on a time average caused by disturbance.

As shown in Experimental Examples heretofore, the immersion nozzle in the present disclosure fulfills a self-stabilizing function for both a drift flow phenomenon on a time average caused by disturbance and a drift flow phenomenon like self-excited vibration caused by fluctuation, and is capable of maintaining stable flowing movement in the mold.

FIELD OF INDUSTRIAL APPLICATION

According to the immersion nozzle in the present disclosure, unevenness in the flowing movement of the molten steel in the mold can be suppressed.

BRIEF DESCRIPTION OF THE REFERENCE SYMBOLS

• • 10 Straight body portion
  • 11 Flow passage
  • 20 Connection portion
  • 30 Discharge portion
  • 31, 131 Bottom portion
  • 131 a Partition wall
  • 32 Side wall
  • 33 Discharge hole
  • 33 aa, 33ba Outer discharge hole
  • 33 ab, 22bb Inner discharge hole
  • 34 Internal barrier
  • 34 a Upper surface
  • 34 aa Recessed portion
  • 34 aa 1 Bottom surface portion
  • 34 aa 2 Side surface portion
  • 34 ae End surface
  • 34 b Lower surface
  • 34 ba Inclined portion
  • 34 bb Horizontal surface
  • 34 c Side surface
  • 35 Branch flow passage
  • 36 Distribution block
  • 36 a Upper surface
  • 36 b Distribution flow passage
  • 37 Center block
  • 100, 200 Immersion nozzle

Claims

1. An immersion nozzle for discharging molten steel supplied from a tundish into a mold for continuous casting of a slab, the immersion nozzle comprising a discharge portion that supplies the molten steel to the mold, whereinthe immersion nozzle includes two regions divided by a plane in a thickness direction, the plane passing through an axial center,the discharge portion includes:a bottom portion; anda side wall that extends in a height direction from an outer edge of the bottom portion,four discharge holes are formed in the discharge portion,two discharge holes are arranged side by side in a width direction in each of the regions in the bottom portion of the discharge portion,the discharge portion includes:an internal barrier that is disposed at the center in the width direction and that distributes the molten steel supplied from the tundish to each of the regions;a branch flow passage through which a branch flow, which is the molten steel that has been distributed by the internal barrier, flows between the side wall of each of the regions and the internal barrier; anda distribution block, on a bottom portion side relative to the internal barrier, that further distributes the branch flow that has passed through the branch flow passage to a distribution flow passage in each of the regions to supply the branch flow to each of the discharge holes,in a case where out of the two discharge holes disposed in each of the regions, the discharge hole disposed on an outer side in the width direction is defined as an outer discharge hole, the discharge hole disposed on an inner side in the width direction is defined as an inner discharge hole, and when either one of the branch flow passages is closed, a relationship between a flow rate Qa of the molten steel to be discharged from the inner discharge hole disposed in a region where the branch flow passage is closed and a flow rate Qb of the molten steel to be discharged from the inner discharge hole disposed in a region in which the branch flow passage is not closed satisfies an equation (1), anda relationship between a discharge flow rate Qout of the molten steel to be discharged from the outer discharge hole and a discharge flow rate QIN of the molten steel to be discharged from the inner discharge hole satisfies an equation (2).

2. The immersion nozzle according to claim 1, wherein the immersion nozzle includes a straight body portion that receives the molten steel supplied from the tundish, the discharge portion, and a connection portion that connects the straight body portion with the discharge portion, anda projection area of the internal barrier, when the immersion nozzle is projected on a horizontal plane, is equal to or larger than a flow passage area of the straight body portion.

3. The immersion nozzle according to claim 1, wherein a surface of the internal barrier on a side that receives the molten steel supplied from the tundish includes a recessed portion.

4. The immersion nozzle according to claim 1, wherein in each of the regions, an outer discharge angle α1, which is defined by an angle of a wall surface that forms the outer discharge hole, is between equal to or larger than downward 40 degrees and equal to or smaller than downward 75 degrees, and a relationship between α1 and an inner discharge angle α2, which is defined by an angle of a wall surface that forms the inner discharge hole, satisfies an equation (3). −5 degrees≤|α2|−|α1|≤15 degrees  (3)

5. The immersion nozzle according to claim 2, wherein a value obtained by dividing a flow passage area of the branch flow passage by a flow passage area of the straight body portion is equal to or larger than 0.4 and equal to or smaller than 1.5.

6. The immersion nozzle according to claim 2, wherein a value obtained by dividing a flow passage area of the distribution flow passage by a flow passage area of the straight body portion is equal to or larger than 0.3 and equal to or smaller than 1.5.

7. The immersion nozzle according to claim 2, wherein a surface of the internal barrier on a side that receives the molten steel supplied from the tundish includes a recessed portion.

8. The immersion nozzle according to claim 2, wherein in each of the regions, an outer discharge angle α1, which is defined by an angle of a wall surface that forms the outer discharge hole, is between equal to or larger than downward 40 degrees and equal to or smaller than downward 75 degrees, and a relationship between α1 and an inner discharge angle α2, which is defined by an angle of a wall surface that forms the inner discharge hole, satisfies an equation (3).