CONTINUOUS-CASTING NOZZLE

Abstract

 The present invention is intended to, in an outside insertion-type continuous-casting nozzle used under the condition that it undergoes fitting engagement with a stopper, suppress a situation where an ejection amount of gas ejected from a through-hole decreases. A continuous-casting nozzle according to the present invention is an outside insertion-type continuous-casting nozzle A which is positioned below a stopper B for controlling the flow rate of molten steel in continuous casting of molten steel, and configured to be fittingly engageable with the stopper B and to be attached and detached from the outside of a molten steel vessel, wherein the outside insertion-type continuous-casting nozzle A comprises a nozzle body 1 made of a refractory material and formed to have an inner bore 11 in an up-down direction to allow molten steel to pass therethrough. The nozzle body 1 integrally has: an enlarged bore portion 12 which includes a fitting engagement area 121 configured to be fittingly engageable with the stopper B and in which the diameter of the inner bore 11 increases toward the upper end of the nozzle body 1; and a straight portion 13 which is continuous downwardly from the lower end of the enlarged bore portion 12 and in which the inner bore 11 has a straight shape. A gas pool 14 is provided only in the straight portion 13, and a through-hole 15 which is communicated with the gas pool 14 and through which gas is ejected from the enlarged bore portion 12 is provided in the nozzle body 1.

Description

TECHNICAL FIELD

[0001] The present invention relates to a continuous-casting nozzle configured to be fittingly engageable with a stopper for performing flow rate control when discharging molten steel from a molten steel vessel such as a tundish, in continuous casting of molten steel.

BACKGROUND ART

[0002] In continuous casting of molten steel, inclusions such as alumina are likely to adhere to a fitting engagement region including a fitting engagement interface between a stopper and a nozzle body of a continuous-casting nozzle, causing difficulty in flow rate control.

[0003] As a measure to prevent inclusions from adhering to the fitting engagement region, for example, Patent Document 1 discloses a through-hole type continuous-casting nozzle configured to eject gas from a through-hole communicated with a gas pool provided in a nozzle body.

[0004] Meanwhile, in terms of a method of attaching and detaching a continuous-casting nozzle with respect to a molten steel vessel such as a tundish, the continuous-casting nozzle is classified roughly into an "outside insertion type" in which it is attached and detached from the outside of the molten steel vessel, and an "inside insertion type" in which it is attached and detached from the inside of the molten steel vessel, as shown in, e.g., paragraph [0003] of Patent Document 2. In the case of the "outside insertion type", the nozzle body has a shape in which the outer diameter thereof gradually decreases in an up direction, so as to enable the attaching and detaching from the outside of the molten steel vessel, and in the case of the "inside insertion type", the nozzle body has a shape in which the outer diameter thereof gradually decreases in a down direction, so as to enable the attaching and detaching from the inside of the molten steel vessel. That is, the continuous-casting nozzle disclosed in the Patent Document 1 is an "inside insertion type".

PRIOR ART DOCUMENTS

[Patent Document]

[0005] 

Parent Document 1: JP 2020-146702 A

Patent Document 2: JP H10-305357 A

SUMMARY OF INVENTION

[Technical Problem]

[0006] The present inventors repeatedly conducted testing using an outside insertion-type continuous-casting nozzle, under the condition that a nozzle body thereof provided with a gas pool and a through-hole undergoes fitting engagement with a stopper. As a result, a phenomenon that an ejection amount of gas ejected from the through-hole decreases was observed occasionally.

[0007] The technical problem to be solved by the present invention is to, in an outside insertion-type continuous-casting nozzle used under the condition that it undergoes fitting engagement with a stopper, suppress a situation where an ejection amount of gas ejected from a through hole decreases.

[Solution to Technical Problem]

[0008] As a result of recoverin continuous-casting nozzles in which the phenomenon that an ejection amount of gas ejected from the through-hole decreases was observed, and checking each cross-section thereof and others, the occurrence of cracks was observed in an upper portion of the nozzle body including a fitting engagement area with the stopper. Further, the present inventors have found that these cracks connect to the through-hole or the gas pool to thereby cause gas leakage, resulting in occurrence of a phenomenon that a back pressure of the gas decreases and thus the ejection amount of the gas decreases. It has also been found that such a phenomenon is particularly likely to occur in the case of the "outside insertion type". That is, since in the "outside insertion type", the nozzle body has a shape in which the outer diameter thereof gradually decreases in an up direction, the thickness of a refractory wall becomes particularly thinned in the upper portion of the nozzle body including the fitting engagement area with the stopper, and thus cracks become more likely to occur.

[0009] In order to solve the above technical problem, based on the above analysis of the current situation, the present inventors have found that it is effective to avoid providing the gas pool in the upper portion (after-mentioned "enlarged bore portion") of the nozzle body including the fitting engagement area with the stopper, and provide the gas pool only in a portion (after-mentioned "straight portion") of the nozzle body below the upper portion, and have come to complete the present invention.

[0010] Specifically, according to one aspect of the present invention, the following continuous-casting nozzle is provided.

[0011] An outside insertion-type continuous-casting nozzle which is positioned below a stopper for controlling a flow rate of molten steel in continuous casting of molten steel, and configured to be fittingly engageable with the stopper and to be attached and detached from an outside of a molten steel vessel, the continuous-casting nozzle comprising a nozzle body made of a refractory material and formed to have an inner bore in an up-down direction to allow molten steel to pass therethrough, wherein the nozzle body integrally has: an enlarged bore portion which includes a fitting engagement area configured to be fittingly engageable with the stopper and in which a diameter of the inner bore increases toward an upper end of the nozzle body; and a straight portion which is continuous downwardly from a lower end of the enlarged bore portion and in which the inner bore has a straight shape, and wherein: a gas pool is provided only in the straight portion; and a through-hole which is communicated with the gas pool and through which gas is ejected from the enlarged bore portion is provided in the nozzle body.

[Advantageous Effects of Invention]

[0012] The present invention makes it possible to, in the outside insertion-type continuous-casting nozzle used under the condition that it undergoes fitting engagement with the stopper, suppress a situation where the ejection amount of gas ejected from the through-hole decreases.

BRIEF DESCRIPTION OF DRAWINGS

[0013] 

FIG. 1 is an up-down directional cross-sectional view of a continuous-casting nozzle according to one embodiment of the present invention.

FIG. 2 is an up-down directional cross-sectional view of a conventional continuous-casting nozzle.

DESCRIPTION OF EMBODIMENTS

[0014] FIG. 1 shows a continuous-casting nozzle according to one embodiment of the present invention, in the form of up-down directional cross-section. The continuous-casting nozzle A illustrated in FIG. 1 is an outside insertion-type upper nozzle configured to be attached and detached from the outside (underside) of a tundish which is a molten steel vessel and to be fittingly engageable with a stopper B for performing flow rate control when discharging molten steel from the tundish to a mold in continuous casting of molten steel.

[0015] This upper nozzle A comprises a nozzle body 1 which is made of a refractory material and formed to have an inner bore 11 in an up-down direction to serve as a molten steel passing pathway. Here, the up-down direction means a direction along a central axis 111 of the inner bore 11, and the up-down directional cross-section means a cross-section taken along the central axis 111 of the inner bore 11.

[0016] In the upper nozzle A, the nozzle body 1 integrally has an enlarged bore portion 12 and a straight portion 13. More specifically, the enlarged bore portion 12 and the straight portion 13 are integrally formed by integral molding of a refractory material. The enlarged bore portion 12 includes a fitting engagement area 121 configured to be fittingly engageable with the stopper B, wherein the inner bore 11 has a shape in which the diameter thereof increases toward an upper end of the nozzle body 1. The straight portion 13 is continuous downwardly from a lower end 122 of the enlarged bore portion 12, wherein the inner bore 11 has a straight shape. Here, the expression that the inner bore 11 has a straight shape means that the inner bore 11 has a shape defined by a straight line in the up-down directional cross-section, i.e., it is not necessarily required that the diameter of the inner bore 11 is constant. For example, when forming the inner bore 11, generally, molding is performed using a core rod, and after the molding, the core rod is pulled out. In this process, in order to facilitate the pulling-out of the core rod, the core rod can be formed in a taper shape in which the diameter thereof increases in a down direction, and in this case, the diameter of the inner bore 11 also increases downwardly in a (linear) taper shape. Such a shape will also be referred to as a straight shape. On the other hand, in the enlarged bore portion 12, the inner bore 11 is defined by a curve (curvilinearly) in the up-down directional cross-section. Therefore, the enlarged bore portion 12 and the straight portion 13 can be clearly distinguished from each other in the nozzle body 1.

[0017] Here, since the upper nozzle A is an "outside insertion type", the nozzle body 1 has a so-called taper shape in which the outer diameter thereof gradually decreases in the up direction. Therefore, in the enlarged bore portion 12 which is the upper portion of the nozzle body 1, the thickness of a refractory wall is gradually particularly thinned in the up direction.

[0018] Further, a gas pool 14 is provided in the straight portion 13. More accurately, the gas pool 14 is provided only in the straight portion 13 and is not provided in the enlarged bore portion 12. This is because in the enlarged bore portion 12, the thickness of the refractory wall is gradually particularly thinned in the up direction, as mentioned above. That is, in the upper nozzle A, the gas pool 14 which is a void space and can become a starting point for crack initiation is provided only in the straight portion 13, and is not provided in the enlarged bore portion 12 in which the thickness of the refractory wall is small, so that it becomes possible to suppress occurrence of cracks in the enlarged bore portion 12. From another point of view, in the upper nozzle A, since the gas pool 14 is not present in the enlarged bore portion 13, structural strength of the enlarged bore portion 13 becomes high, and thus the occurrence of cracks in the enlarged bore portion 13 can be suppressed.

[0019] In the upper nozzle A, the gas pool 14 is provided over the entire periphery in a circumferential direction of the nozzle body 1 so as to surround the inner bore 11. However, it should be noted that the gas pool 14 does not necessarily need to be provided over the entire periphery, but may be provided in a part of the periphery in the circumferential direction.

[0020] The nozzle body 1 is provided with a through-hole 15 which is communicated with the gas pool 14 and through which gas is ejected from the enlarged bore portion 12. In the present embodiment, the through-hole 15 is provided plurally, wherein the plurality of through-holes 15 are arranged at even intervals along the circumferential direction of the nozzle body 1. Further, the nozzle body 1 is provided with a gas introduction hole 16 which is communicated with the gas pool 14 and through which gas is introduced into the gas pool 14.

[0021] In the upper nozzle A having the above configuration, gas is introduced into the gas pool 14 from the gas introduction hole 16, and is ejected into molten steel from the enlarged bore portion 12 via the through-hole 15. In this process, since in the upper nozzle A, the gas pool 14 which is a void space and can become a starting point for crack initiation is provided only in the straight portion 13, and is not provided in the enlarged bore portion 12 in which the thickness of the refractory wall is small, so that it becomes possible to suppress occurrence of cracks in the enlarged bore portion 12, as described above. This makes it possible to suppress a situation where a back pressure of the gas decreases and thus the ejection amount of the gas from the through-hole 15 decreases.

[0022] Here, it is preferable that an upper end 141 of the gas pool 14 is located downwardly at a distance within a range of 10 mm to 100 mm on the basis of an upper end 131 of the straight portion 13. When the upper end 141 of the gas pool 14 is located downwardly at a distance of 10 mm or more on the basis of the upper end 131 of the straight portion 13, the influence of the gas pool 14 which is a void space and can become a starting point for crack initiation, on the enlarged bore portion 12, is mitigated, so that it is possible to further suppress occurrence of cracks in the enlarged bore portion 12. Further, when the upper end 141 of the gas pool 14 is located downwardly at a distance of 100 mm or less on the basis of the upper end 131 of the straight portion 13, the length of the through-hole 15 can be shortened, so that it is possible to facilitate the formation of the through-hole 15 and mitigate a pressure loss in the through-hole 15.

[0023] The upper end 131 of the straight portion 13 is also the lower end 122 of the enlarged bore portion 12, i.e., the boundary between the enlarged bore portion 12 and the straight portion 13.

EXAMPLES

[0024] As an inventive example, the upper nozzle A illustrated in FIG. 1 was subjected to actual operation (continuous casting of molten steel). As a comparative example, an upper nozzle A' illustrated in FIG. 2 was also subjected to the actual operation. The upper nozzle A' of the comparative example was obtained by modifying the upper nozzle A of the inventive example such that the upper end 141 of the gas pool 14 is expended to the enlarged bore portion 12, and the configuration thereof other than the above was the same as the upper nozzle A of the inventive example. In the upper nozzle A of the inventive example, the gas pool 14 was provided such that the upper end 141 thereof is located downwardly at a distance of 35 mm from the upper end 131 of the straight portion 13.

[0025] During the actual operation, the back pressure and the ejection amount of the gas were monitored in each of the upper nozzle A of the inventive example and the upper nozzle A' of the comparative example. As a result, no decreases in the back pressure and the ejection amount were observed in the upper nozzle A of the inventive example. On the other hand, decreases in the back pressure and the ejection amount were observed in the upper nozzle A' of the comparative example. Further, after the completion of the actual operation, each of the upper nozzles A, A" was recovered, and subjected to cross-section observation. As a result, no occurrence of cracks was observed in the upper nozzle A of the inventive example. On the other hand, as is conceptually shown in FIG. 2, a crack C crossing over the gas pool 14 was observed in the upper nozzle A' of the comparative example. The occurrence of such a crack would cause decreases in the back pressure and the ejection amount.

LIST of REFERENCE CODES

[0026] 

A, A': upper nozzle (outside insertion-type upper nozzle for continuous casting)

B: stopper

C: crack

1: nozzle body

11: inner bore

111: central axis of inner bore

12: enlarged bore portion

121: fitting engagement area with stopper

122: lower end of enlarged bore portion

13: straight portion

131: upper end of straight portion

14: gas pool

141: upper end of gas pool

15: through-hole

16: gas introduction hole

Claims

1. An outside insertion-type continuous-casting nozzle which is positioned below a stopper for controlling a flow rate of molten steel in continuous casting of molten steel, and configured to be fittingly engageable with the stopper and to be attached and detached from an outside of a molten steel vessel, the continuous-casting nozzle comprising a nozzle body made of a refractory material and formed to have an inner bore in an up-down direction to allow molten steel to pass therethrough,

wherein the nozzle body integrally has: an enlarged bore portion which includes a fitting engagement area configured to be fittingly engageable with the stopper and in which a diameter of the inner bore increases toward an upper end of the nozzle body; and a straight portion which is continuous downwardly from a lower end of the enlarged bore portion and in which the inner bore has a straight shape,

and wherein: a gas pool is provided only in the straight portion; and a through-hole which is communicated with the gas pool and through which gas is ejected from the enlarged bore portion is provided in the nozzle body.

2. The continuous-casting nozzle as claimed in claim 1, wherein an upper end of the gas pool is located downwardly at a distance within a range of 10 mm to 100 mm on the basis of an upper end of the straight portion.

Drawing