CONTINUOUS CASTING NOZZLE

Description

TECHNICAL FIELD

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

BACKGROUND ART

A continuous casting nozzle involves a need for replacement for the reason of durability limit, cracking, breakage, or the like due to wear damage caused by molten steel, or inner bore clogging caused by adhesion and buildup of inclusions, such as alumina particles which are non-metal, in molten steel and for such replacement, it has been necessary to interrupt or terminate an operation of continuous casting of steel.

However, from the need for improvement in operational efficiency, an apparatus for replacing a continuous casting nozzle with a new continuous casting nozzle without interrupting the operation of continuous casting of the steel is being introduced (e.g. Patent Documents 1 and 2), as a means to realize prolonged pouring.

A basic structure of a continuous casting nozzle to be applied to such a continuous casting nozzle replacement apparatus can be roughly divided into two: a tube-shaped nozzle body portion having an inner bore, which is a molten steel-passing path, in a vertical direction, and a flange portion which is supported from therebelow by a support of the continuous casting nozzle replacement apparatus so as to cause the nozzle body portion to be pushed upwardly while being supported against gravity, and brought into contact with a member thereabove (upper nozzle member), wherein a boundary portion therebetween in which a cross-sectional area of the continuous casting nozzle increases will be referred to as a neck portion.

It is known that the neck portion is a stress concentration portion in structure, and a crack can be created when thermal stress and mechanical stress are applied thereto. Such a crack of the neck portion is problematic in terms of durable life of the immersion nozzle, and the quality of steel. When molten steel flows through the inner bore of the continuous casting nozzle, the pressure level of a space of the inner bore tends to negative pressure, so that air is sucked from the crack of the neck portion, and carbon components constituting a refractory material are oxidized, possibly causing leakage of steel, and contamination of steel by oxygen.

Therefore, from a viewpoint of mitigating the stress concentration on the neck portion as mentioned above, there has been taken a measure in which a lower surface (bearing surface) of a flange portion supported from therebelow by a support of a continuous casting nozzle replacement apparatus is formed as a tapered surface inclined downwardly, as disclosed in, e.g., Patent Document 3.

However, in the configuration in which the bearing surface is formed as a tapered surface, there has been a problem that the continuous casting nozzle is displaced downwardly along the tapered surface, as pointed out in, e.g., Patent Document 4. In view of this, Patent Document 4 proposes that a horizontal planar hanging portion is formed in a metal case fittingly attached to the outer periphery of the nozzle body through a bonding material such as mortar, and a metal ring is interposed in a cross-sectionally triangular-shaped gap between the tapered surface of the nozzle body and the hanging portion of the metal case.

However, according to experimental tests of the present inventors, it was found that downward displacement of the continuous casting nozzle still occurred even in the configuration of Patent Document 4.

It should be noted that the problem of stress concentration on the neck portion and the problem of downward displacement of the continuous casting nozzle arise not only in a continuous casting nozzle applied to a continuous casting nozzle replacement apparatus, particularly in an immersion nozzle, but also in a continuous casting nozzle which is not applied to a continuous casting nozzle replacement apparatus, for example in a long nozzle, as pointed out in Patent Document 5.

Prior Art Documents

Patent Document

• • Patent Document 1: JP 2793039 B2
  • Patent Document 2: JP H04-050100 B2
  • Patent Document 3: JP 5926230 B2
  • Patent Document 4: JP 4097795 B2
  • Patent Document 5: JP 2587873 B2

SUMMARY OF INVENTION

Technical Problem

The technical problem to be solved by the present invention is to provide a continuous casting nozzle capable of mitigating stress concentration on a neck portion thereof and suppressing downward displacement thereof.

Solution to Technical Problem

In solving the above technical problem, the present inventors first considered causal factors of the downward displacement of the continuous casting nozzle in detail. In this respect, the above-mentioned Patent Documents 4 and 5 describe that thermal expansion of the metal case (nozzle case) and the support (holder) is regarded primarily as a causal factor of the downward displacement. However, according to experimental tests and studies of the present inventors, it has been found that buckling of the mortar interposed between the nozzle body and the metal case is a key causal factor of the downward displacement, although the details thereof will be described later. Then, based on this causal factor analysis, the present inventors further conducted experimental tests and studies for realizing a continuous casting nozzle capable of achieving both suppression of the downward displacement and mitigation of the stress concentration on the neck portion. As a result, the present inventors have arrived at the present invention.

Specifically, according to one aspect of the present invention, the following continuous casting nozzle is provided.

A continuous casting nozzle, comprising a nozzle body made of a refractory material and having, in a vertical direction, an inner bore through which molten steel passes, wherein the nozzle body includes a flange portion at an upper end thereof, the flange portion having: an outer surface including a tapered part inclining downwardly towards the inner bore; and a lower surface including a horizontal part extending horizontally from a lower edge of the tapered part towards the inner bore, wherein the continuous casting nozzle further comprises a metal case covering an outer periphery of the flange portion, the metal case including a horizontal plate portion which faces the horizontal part of the flange portion through mortar having a constant thickness, wherein the continuous casting nozzle is configured to receive a pressing force from thereoutside and therebelow by the horizontal plate portion of the metal case.

Advantageous Effects of Invention

The continuous casting nozzle according to the present invention is capable of mitigating stress concentration on the neck portion thereof and suppressing downward displacement thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a continuous casting nozzle according to one embodiment of the present invention, wherein FIG. 1A is a top plan view, and FIG. 1B is a sectional view taken in the A-A direction of FIG. 1A.

FIG. 2 is a fragmentary perspective view of an upper portion of a nozzle body of the continuous casting nozzle of FIGS. 1A and 1B as viewed from therebelow.

FIG. 3 is a fragmentary sectional view of an upper portion of the nozzle body of the continuous casting nozzle of FIGS. 1A and 1B.

FIG. 4 is a fragmentary sectional view of an upper portion of a nozzle body of a conventional continuous casting nozzle.

FIG. 5 is a top plan view of a continuous casting nozzle according to another embodiment of the present invention.

FIGS. 6A and 6B are model diagrams for explaining downward displacement of a nozzle body due to buckling of mortar, wherein FIG. 6A illustrates an inventive example, and FIG. 6B illustrates a comparative example.

FIG. 7 is a graph showing a calculation example of stress to be generated in a neck portion of a nozzle body.

DESCRIPTION OF EMBODIMENTS

FIGS. 1A and 1B illustrate a continuous casting nozzle according to one embodiment of the present invention, wherein FIG. 1A is a top plan view, and FIG. 1B is a sectional view taken in the A-A direction of FIG. 1A. It should be noted that FIG. 1B shows only an upper portion of the continuous casting nozzle while omitting a lower portion thereof. FIG. 2 is a fragmentary perspective view of an upper portion of the continuous casting nozzle of FIGS. 1A and 1B as viewed from therebelow, and FIG. 3 is a fragmentary sectional view of an upper portion of the nozzle body of the continuous casting nozzle of FIGS. 1A and 1B.

The continuous casting nozzle 1 illustrated in FIGS. 1A and 1B is an immersion nozzle used when molten steel is poured into a mold from a tundish facility during continuous casting of steel, and is applied to the aforementioned continuous casting nozzle replacement apparatus.

This immersion nozzle 1 comprises a nozzle body 2 made of a refractory material. The nozzle body 2 has, in a vertical direction, an inner bore 21 which is a molten steel-passing path, and includes a flange portion 22 at an upper end thereof. In this embodiment, the flange portion 22 is composed of a lower flange portion 22a formed integrally with the nozzle body 2 using the same refractory material as the nozzle body 2, and an upper flange portion 22b formed separately from the nozzle body 2 using a refractory material different from that of the nozzle body 2. However, the entirety of the flange portion 22 may be formed integrally with the nozzle body 2 using the same refractory material as that of the nozzle body 2, or, conversely, may be formed separately from the nozzle body 2 using a refractory material different from that of the nozzle body 2, and then joined to the nozzle body 2 directly or through an adhesive.

In any case, the flange portion 22 has an outer surface including a tapered part 221 inclining downwardly toward the inner bore 21, and a lower surface including a horizontal part 222 extending horizontally from a lower edge of the tapered part 221 toward the inner bore 21.

The immersion nozzle 1 comprises a metal case 3 covering an outer periphery of the flange portion 22. Here, the outer periphery of the flange portion 22 is a concept which collectively refers to the above-mentioned outer and lower surfaces. In this embodiment, the metal case 3 is disposed to cover the outer periphery of the flange portion 22 and an outer periphery of a portion of the nozzle body 2 located below the flange portion 22. In this embodiment, an upper end of the outer surface in the outer periphery of the flange portion 22 is exposed without being covered with the metal case 3. However, the entirety of the outer periphery of the flange portion 22 may be covered with the metal case 3.

As shown in FIG. 1B, the metal case 3 includes a horizontal plate portion 31 which faces the horizontal part 222 of the flange portion 22 through mortar 4 having a constant thickness. The immersion nozzle 1 is configured to receive a pressing force from thereoutside and therebelow by the horizontal plate portion 31. The pressing force received from outside and below the immersion nozzle 1 by the horizontal plate portion 31 is transmitted to the horizontal part 222 of the flange portion 22 through the mortar 4. Thus, the immersion nozzle 1 is pushed upwardly and brought into contact with a member therebelow (upper nozzle member).

FIG. 3 conceptually shows an upward pressing force F (hereinafter referred to simply as “force F”) acting from outside and below the immersion nozzle 1 on the horizontal part 222 of the flange portion 22 of the nozzle body 2. As mentioned above, since the horizontal part 222 is present such that it extends horizontally from the lower edge of the tapered part 221 toward the inner bore 21, a horizontal length L1 of the horizontal part 222 on which the force F acts is shortened by a horizontal length L2 of the tapered part 221, as compared with a nozzle body 2 of a conventional immersion nozzle having no tapered part, illustrated in FIG. 4. Therefore, stress (moment force) due to the force F, acting on a neck portion 23 of the nozzle body 2 is also reduced accordingly, and stress concentration to the neck portion 23 is mitigated.

Here, the horizontal length L1 of the horizontal part 222 preferably falls within the range of 20% to 80%, with respect to the summed length L of this L1 and the horizontal length L2 of the tapered part 221. If L1 exceeds 80% of L, the above-mentioned effect of mitigating stress concentration on the neck portion 23 is less likely to be significantly exerted. On the other hand, if L1 is less than 20% of L, the below-mentioned effect of suppressing downward displacement of the nozzle body 2 is less likely to be significantly exerted.

Next, a definition (determination method) of L including L1 and L2 will be described with reference, particularly, to FIGS. 1A and 5. In the present invention, the summed length L of the horizontal length L1 of the horizontal part 222 and the horizontal length L2 of the tapered part 221 is defined as a length on a straight line where a length corresponding to L in a horizontal straight line passing through the center 211 of the inner bore 21 is the shortest, in a region where there is a point-of-effort part P on which the force F acts.

For example, since the immersion nozzle 1 according to this embodiment is applied to the continuous casting nozzle replacement apparatus as mentioned above, the point-of-effort part P on which the force F acts is present in a number of two, wherein the two point-of-effort parts P are located symmetrically across the inner bore 21 on the lower surface of the flange portion 22 having an approximately quadrangular shape in top plan view as conceptually shown in FIG. 1A. In this case, a straight line X1 illustrated in FIG. 1A is the above-mentioned straight line on which the length L is the shortest, i.e., the summed length of the horizontal length L1 of the horizontal part 222 and the horizontal length L2 of the tapered part 221 on this straight line X1 is L.

On the other hand, in the case of a continuous casting nozzle which is not applied to the continuous casting nozzle replacement apparatus, for example, in case of a long nozzle, the point-of-effort part P on which the force F acts is present in a ring shape to surround the inner bore 21 as conceptually shown in FIG. 5, in some cases. In such cases, a straight line X2 illustrated in FIG. 5 is the above-mentioned straight line on which the length L is the shortest, i.e., the summed length of the horizontal length L1 of the horizontal part 222 and the horizontal length L2 of the tapered part 221 on this straight line X2 is L.

As above, L including L1 and L2 in the present invention is determined in the region where there is the point-of-effort part P on which the force Facts. This is because a region where the length L including L1 and L2 becomes a problem from a viewpoint of stress concentration or the like is the region where there is the point-of-effort part P on which the force Facts. Further, from the same viewpoint, the tapered part 221 may be formed in a region corresponding to the region where there is the point-of-effort part P. For example, in the immersion nozzle 1 of this embodiment, the tapered part 221 is formed only in one pair of regions of the outer surface corresponding to the regions where there are the two point-of-effort parts P, as appearing in FIG. 1A, etc., and no tapered part is formed in the other pair of regions of the outer surface. It should be understood that a tapered part may also be formed in the other pair of regions of the outer surface.

As appearing in FIG. 1B, mortar 4 is filled between the metal case 3 and the tapered part 221 in the immersion nozzle 1 according to this embodiment. This mortar 4 is made of the same material as that of mortar 4 interposed between the horizontal plate portion 31 of the metal case 3 and the horizontal part 222, and integrated with the interposed mortar 4. By filling the mortar 4 between the metal case 3 and the tapered part 221 in this manner, it becomes possible to stably cover the outer periphery of the flange portion 22 by the metal case 3 without any gap. It should be noted that a ring-shaped metal member or a ceramic member may be separately disposed between the metal case 3 and the tapered part 221, in place of the mortar 4. However, from a viewpoint of workability when covering the outer periphery of the flange portion 22 by the metal case 3, and stability, it is preferable that the mortar 4 is fille entirely between the metal case 3 and the outer periphery of the flange portion 22 as in this embodiment. Specifically, by applying the mortar 4 to the outer periphery of the flange portion 22 and then attaching the metal case 3, it is possible to fill the mortar 4 entirely between the metal case 3 and the outer periphery of the flange portion 22.

In this embodiment, the portion of the metal case 3 facing the tapered part 221 of the flange portion 22 is formed in a horizontal plate shape by extending the horizontal plate portion 31 which faces the horizontal part 222 of the flange portion 22 through the mortar 4 having a constant thickness. Alternatively, it may be formed in a tapered shape by following the tapered part 221 of the flange portion 22 as shown in the below-mentioned FIG. 6A.

In this embodiment, the tapered part 221 is formed by a “planar surface”, but the present invention is not limited thereto. For example, it may be formed by a “curved surface”, or may be formed by a “stair-like stepped surface”. In any case, in the present invention, the “tapered part” may be a part “inclined downwardly toward the inner bore”. Further, the “tapered part inclined downwardly toward the inner bore” may be a part inclined downwardly toward the inner bore in its entirety. However, in view of ease of forming the tapered part, etc., the tapered part is preferably formed by a “planar surface” as in this embodiment.

In this embodiment, the shape of the flange portion 22 in top plan view is an approximately quadrangular shape. Alternatively, it may be a polygonal shape, an elliptical shape, or a circular shape. Further, the shape of the nozzle body 2 except for the flange portion 22, in top plan view, is not limited to a circular shape, but may be, e.g., a rectangular or elliptical shape.

EXAMPLES

First, the downward displacement of the nozzle body due to buckling of mortar will be described. FIGS. 6A and 6B are model diagrams for that, wherein FIG. 6A is an inventive example, and FIG. 6B is a comparative example. In the inventive example illustrated in FIG. 6A, the horizontal length L1 of the horizontal part 222, the horizontal length L2 of the tapered part 221, the summed length L of L1 and L2, the height H of the tapered part 221, and the thickness T of the mortar 4 interposed between the horizontal part 222 and the horizontal plate portion 31 are set, respectively, to 10 mm, 20 mm, 30 mm, 75 mm, and 2 mm. In such a configuration, when a vertically downward force acts on the nozzle body 2 as a reaction force due to contact with a not-shown member below the nozzle body 2 (upper nozzle member), the mortar 4 is buckled, and the nozzle body 2 is displaced downwardly. However, in this inventive example, the presence of the horizontal part 222 enables the downward displacement of the nozzle body 2 to be quit for the thickness T of the mortar 4, i.e., 2 mm. On the other hand, in the comparative example illustrated in FIG. 6B, there is only the tapered part 221 without the horizontal part 222. In this case, since the thickness of the mortar 4 in the vertical direction is large in the tapered part 221, the downward displacement of the nozzle body 2 due to the buckling of the mortar 4 increases. In this comparative example, it becomes 5.4 mm in calculation, which is twice or more of that in the inventive example.

Such a problem of buckling of mortar has not been heretofore recognized. However, according to experimental tests and studies of the present inventors, it has been found that such buckling of mortar is a key causal factor of the downward displacement of the nozzle body. Therefore, in the present invention, by providing the horizontal part 222 together with the tapered part 221, it becomes possible to obtain the effect of suppressing the downward displacement of the nozzle body 2.

Next, the effect of suppressing stress concentration on the neck portion will be described. FIG. 7 shows a result obtained by calculating stress to be generated in the neck portion, while changing the rate of the length LI of the horizontal part 222 with respect to the summed length L of the horizontal lengths of the tapered part 221 and the horizontal part 222, in FIG. 3. Here, when the rate of the length L1 of the horizontal part 222 is 100%, it is equivalent to the nozzle body 2 of the conventional immersion nozzle illustrated in FIG. 4, and the vertical axis “neck portion stress index” of FIG. 7 is an index based on 100 which is stress generated in the neck portion 23 when the rate of L1 is 100%. As is clear from FIG. 7, it has been confirmed that as the rate of the length L1 of the horizontal part 222 becomes smaller, i.e., as the rate of the length L2 of the tapered part 221 becomes larger, the stress generated in the neck portion 23 becomes lower. That is, it has been confirmed that the effect of suppressing stress concentration on the neck portion can be obtained by providing the tapered part 221.

List of Reference Signs

• • 1: immersion nozzle (continuous casting nozzle)
  • 2: nozzle body
  • 21: inner bore
  • 211: center of inner body
  • 22: flange portion
  • 22a: lower flange portion
  • 22b: upper flange portion
  • 221: tapered part
  • 222: horizontal part
  • 23: neck portion
  • 3: metal case
  • 31: horizontal plate portion
  • 4: mortar
  • P: point-of-effort part