JP2018058097A - Immersion nozzle, continuous casting machine, and continuous casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the quality of a cast piece by accelerating floating of bubbles in a cast during continuous casting.SOLUTION: A cylindrical immersion nozzle roughly uniform in inner diameter is installed so as to extend roughly in a vertical direction above a cast in a continuous casting machine, and supplies moten metal stored in a tundish into the cast. A pair of discharge holes are oppositely formed in a side wall near the bottom end of the immersion nozzle so as to discharge the molten metal into the cast. A gas blowing-in mechanism for blowing an inactive gas into the immersion nozzle is provided. In a cylinder that extends roughly in the vertical direction of the immersion nozzle, a projecting part is provided to one of wall surfaces vertical to the opening direction of the pair of discharge holes within a horizontal plane and above the discharge holes.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an immersion nozzle for supplying molten metal to a mold in continuous casting, a continuous casting machine provided with the immersion nozzle, and a continuous casting method performed using the continuous casting machine.

  In continuous casting, molten metal (for example, molten steel) once stored in the tundish is supplied from above into the mold through an immersion nozzle, and the outer peripheral surface is cooled and solidified slab is pulled out from the lower end of the mold. Thus, continuous casting is performed. The solidified portion of the outer peripheral surface of the slab is called a solidified shell.

  In continuous casting, it is known that the flow of molten metal in the mold during continuous casting greatly affects the quality of the slab. For example, if the momentum of the downward flow in the molten metal is strong, inclusions and the like are easily taken into the slab, and defects caused by the inclusions and the like can increase. In addition, for example, if the momentum of the upward flow in the molten metal is strong, the molten metal surface fluctuation increases, and the possibility that the mold powder is caught increases, so that the quality of the slab can be deteriorated.

  Here, in general, the immersion nozzle may be provided with a pair of discharge holes so as to face the short side surfaces on both sides of the mold. The jet of molten metal (that is, the discharge flow) from the discharge hole collides with the opposing mold short side surface, whereby the above-described downward flow and upward flow can be formed. Thus, the discharge flow from the immersion nozzle greatly affects the flow of the molten steel in the mold. Therefore, in order to control the flow of molten metal in the mold, a technique for devising the structure of the immersion nozzle and controlling the discharge flow from the immersion nozzle has been developed.

  For example, Patent Document 1 discloses an immersion nozzle in which an inner diameter is changed stepwise by providing a step structure on an inner wall. According to Patent Document 1, such a configuration provides an effect of suppressing the drift of the molten metal in the immersion nozzle, so that the flow of the molten metal in the mold can be stabilized, and the quality of the slab can be improved. It can be planned. Further, according to Patent Document 1, by providing the step structure described above, a phenomenon (nozzle clogging) that causes the clogging of the immersion nozzle due to inclusions (such as alumina) in the molten metal adhering to and depositing on the inner wall. You can prevent it.

  Moreover, for example, Patent Document 2 discloses a structure in which swirl vanes are provided in an immersion nozzle for a one-hole immersion nozzle having an opening on the bottom instead of a two-hole immersion nozzle. According to Patent Document 2, with this configuration, a swirl flow is formed in the immersion nozzle, and the molten metal is discharged from the entire discharge hole at a substantially uniform flow rate. Therefore, the flow rate of the discharge flow can be reduced. I can do it. Thereby, while the molten metal surface fluctuation | variation in a casting_mold | template is suppressed, since the penetration | invasion of an inclusion can be made shallow, it is supposed that the quality of slab can be improved.

  Further, for example, Patent Document 3 discloses a structure in which a rectifying protrusion is provided at a position corresponding to the curved outer side of the inner wall of the immersion nozzle for the purpose of improving the quality of a slab in continuous casting using a curved continuous casting machine. Yes. In Patent Document 3, such a configuration can form a flow pattern of a discharge flow that is a downward flow on the inside of the curve and an upflow on the outside of the curve, so that inclusions are trapped and accumulated in the solidified shell on the inside of the curve. The quality of the slab can be improved.

Japanese Patent Laid-Open No. 11-123509 JP 2000-237852 A JP 2010-188402 A

  Here, as described above, according to the technique described in Patent Document 1, it is possible to suppress the occurrence of nozzle clogging by providing a step structure on the inner wall of the immersion nozzle. However, the general immersion nozzle has a cylindrical shape with a substantially uniform inner diameter and a relatively simple structure, whereas the immersion nozzle described in Patent Document 1 has a step structure on the inner wall. Since it has a complicated structure, it is not practical from the viewpoint of cost to actually employ the immersion nozzle described in Patent Document 1.

  Therefore, in general, in order to prevent nozzle clogging, an inert gas such as argon gas or nitrogen is blown together with molten metal to suppress the attachment of inclusions to the inner wall of the nozzle. Although this blown inert gas adsorbs inclusions such as alumina and is discharged into the mold from the discharge hole of the immersion nozzle, it is expected to float inside the mold and desorb from the molten metal surface, It is known that some are trapped by the solidified shell and become defective in the slab. Therefore, in order to improve the quality of the slab, it is important to improve the floatability of the inert gas bubbles in the mold in order to reduce defects caused by the inert gas bubbles.

  With regard to this point, the technique described in Patent Document 3 is intended for a curved continuous casting machine, and is intended to intentionally form an asymmetric flow according to the bending direction. There is no consideration for increasing the flying height.

  On the other hand, in the technique described in Patent Document 2, there is a possibility that the rising of the bubbles may be promoted by reducing the flow velocity of the discharge flow. However, as described above, the technique described in Patent Document 2 is intended for a one-hole immersion nozzle, and when this technique is applied to a general two-hole immersion nozzle, the same effect is obtained. Whether it is obtained is unknown. Moreover, when the structure which provides a turning blade | wing in an immersion nozzle is employ | adopted, the structure of an immersion nozzle will become complicated and it will lead to an increase in cost. In addition, since there is a concern that the operation of the swirl blade may not be performed normally due to the adhesion and accumulation of inclusions, the immersion nozzle described in Patent Document 3 cannot withstand long-term use and has a sustained effect. There may be challenges.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to further improve the quality of a slab by further promoting the floating of bubbles in a mold in continuous casting. It is an object of the present invention to provide a new and improved immersion nozzle, a continuous casting machine in which the immersion nozzle is installed, and a continuous casting method performed using the continuous casting machine.

  In order to solve the above problems, according to one aspect of the present invention, a continuous casting machine is installed so as to extend in a substantially vertical direction above a mold, and molten metal stored in a tundish is placed in the mold. A cylindrical immersion nozzle having a substantially uniform inner diameter is formed, and a pair of discharge holes for discharging molten metal into the mold are formed on the side wall near the lower end so as to face each other. A gas blowing mechanism for blowing an inert gas is provided in the cylinder extending in the substantially vertical direction of the immersion nozzle, and is a wall surface above the discharge hole, and the opening direction of the pair of discharge holes in a horizontal plane An immersion nozzle is provided in which a protrusion is provided on one wall surface in a direction perpendicular to the vertical direction.

  In the immersion nozzle, the continuous casting machine may be a vertical bending type continuous casting machine.

  Moreover, in the said immersion nozzle, 0.15 times or more and less than 0.5 times the internal diameter of the said immersion nozzle may be sufficient as the height of the said projection part in the horizontal surface direction.

  In the immersion nozzle, the height from the center position in the height direction of the discharge hole to the lower end of the protrusion is 0.5 times or more and less than 0.75 times the inner diameter of the immersion nozzle. Also good.

  Moreover, in order to solve the said subject, according to another viewpoint of this invention, the said immersion nozzle is installed so that a pair of said discharge hole may each oppose the short side surface of the both sides of the said mold | type, respectively. A casting machine is provided.

  Moreover, in order to solve the said subject, according to another viewpoint of this invention, the continuous casting method which performs continuous casting using the said continuous casting machine is provided.

  As described above, according to the present invention, in continuous casting, it is possible to further improve the quality of a slab by further promoting the floating of bubbles in a mold.

It is sectional drawing in the cross section parallel to the mold width direction of the common existing immersion nozzle in which the sliding nozzle was installed in the inlet_port | entrance. It is sectional drawing in a cross section parallel to the mold thickness direction of the immersion nozzle shown in FIG. It is sectional drawing in the cross section parallel to the mold width direction of the general existing immersion nozzle in which the stopper was installed in the inlet_port | entrance. It is sectional drawing in a cross section parallel to the casting_mold | template thickness direction of the immersion nozzle shown in FIG. It is sectional drawing in the cross section parallel to the mold width direction of the immersion nozzle which concerns on this embodiment. It is sectional drawing in a cross section parallel to the mold thickness direction of the immersion nozzle shown in FIG. It is a figure which expands and shows the projection part vicinity of the immersion nozzle shown in FIG. It is sectional drawing in the horizontal cross section which passes along the projection part of the immersion nozzle shown in FIG. It is a figure for demonstrating the structure of the gas blowing mechanism provided with respect to the immersion nozzle which concerns on this embodiment. It is sectional drawing in a mold width direction which shows a mode that the immersion nozzle which concerns on this embodiment was installed with respect to the mold. It is a figure which shows a mode that the vicinity of the discharge hole of the immersion nozzle shown in FIG. 10 was seen from the mold width direction, and the state of the bubble rising in the mold when the immersion nozzle according to this embodiment is used is schematically shown. FIG. It is a figure for a comparison, and is a figure which shows roughly a mode that a bubble floats in a casting mold seen from a direction corresponding to Drawing 11 at the time of using a conventional existing immersion nozzle. It is sectional drawing in a cross section parallel to the mold width direction of the structure by which the stopper was provided with respect to the immersion nozzle which concerns on this embodiment. It is sectional drawing in the cross section parallel to the casting_mold | template thickness direction of the immersion nozzle and stopper shown in FIG. It is side sectional drawing which shows roughly the example of 1 structure of the continuous casting machine with which the immersion nozzle which concerns on this embodiment can be applied.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  In each drawing shown in this specification, the size of some constituent members may be exaggerated for explanation. The relative sizes of the members illustrated in the drawings do not necessarily accurately represent the magnitude relationship between actual members.

  In the following, an embodiment in which the object of continuous casting is steel and the molten metal is molten steel will be described as an example. However, the present invention is not limited to such an example, and the present invention may be applied to continuous casting for other metals.

(1. Background to the examination of the prior art and the idea of the present invention)
Prior to the description of preferred embodiments of the present invention, in order to make the present invention clearer, the background that the inventors have conceived of the present invention will be described.

(1-1. Examination of conventional immersion nozzle)
As described above, in continuous casting, in order to control the flow of molten steel in a mold, a technique for devising the structure of the immersion nozzle and controlling the discharge flow from the immersion nozzle has been developed.

  For example, in the submerged nozzle, not a stable flow along the flow path, but a biased flow (diffusion) deviating from the flow path may occur. When such uneven flow occurs, the discharge flow becomes unstable, which may adversely affect the flow of molten steel in the mold.

  For example, the drift of molten steel in the immersion nozzle may occur due to the flow control of the molten steel. Specifically, in continuous casting of steel, a device called a sliding nozzle (also called a sliding gate) is installed at the inlet (upper end) of the immersion nozzle in order to control the flow rate of molten steel supplied from the tundish into the mold. Two types of flow rate control methods are generally used: a method or a method of installing a device called a stopper.

  1 to 4 are diagrams schematically illustrating a configuration of a general existing immersion nozzle provided with a sliding nozzle or a stopper. FIG. 1 is a cross-sectional view in a cross section parallel to the mold width direction of a general existing immersion nozzle in which a sliding nozzle is installed at an inlet. FIG. 2 is a cross-sectional view of the immersion nozzle shown in FIG. 1 in a cross section parallel to the mold thickness direction. FIG. 3 is a cross-sectional view in a cross section parallel to the mold width direction of a general existing immersion nozzle in which a stopper is installed at the inlet. FIG. 4 is a cross-sectional view of the immersion nozzle shown in FIG. 3 in a cross section parallel to the mold thickness direction. In FIGS. 1 to 4, the flow of molten steel in the immersion nozzle is schematically shown by arrows in each of FIGS.

  In the following description, the vertical direction is also referred to as the z-axis direction. The vertical direction is also called the vertical direction or the height direction. Two directions orthogonal to each other in a plane (horizontal plane) perpendicular to the z-axis direction are also referred to as an x-axis direction and a y-axis direction, respectively. Further, the x-axis direction is defined as a direction parallel to the mold width direction in the horizontal plane, and the y-axis direction is defined as a direction parallel to the mold thickness direction in the horizontal plane.

  1 and 2, a typical existing immersion nozzle 50 has a cylindrical shape with a substantially uniform inner diameter. A pair of discharge holes 501 are provided on the side wall near the lower end of the immersion nozzle 50 so as to face each other. When the immersion nozzle 50 is installed in a continuous casting machine, the opening direction of the pair of discharge holes 501 is oriented in the mold width direction (x-axis direction) (that is, the pair of discharge holes 501 is the mold short side surface). And the immersion nozzle 50 is installed on the mold.

  The sliding nozzle 301 is configured by superimposing three refractory plates 303 provided with openings. Molten steel is injected into the immersion nozzle through the openings of these three plates 303. Among these three plates 303, the intermediate plate 303 is configured to be movable relative to the other two plates 303 in the horizontal plane direction. The effective area of the part 305 can be changed and the flow rate of molten steel can be adjusted.

  On the other hand, referring to FIG. 3 and FIG. 4, the stopper 310 is composed of a refractory rod. By changing the distance between the lower end of the rod and the opening at the upper end of the immersion nozzle 50, the opening area of the upper end of the immersion nozzle 50 can be changed to adjust the flow rate of the molten steel.

  In general, the sliding nozzle 301 has higher controllability than the stopper 310, so that it is often used when the throughput is relatively large, and the stopper 310 is often used when the throughput is relatively small.

  Here, in the sliding nozzle 301, as shown in FIG. 2, the intermediate plate 303 is usually slid in the mold thickness direction to adjust the flow rate of the molten steel. Therefore, the opening 305 of each plate 303 is eccentric in the mold thickness direction at the entrance of the immersion nozzle 50, so that drift can occur in the immersion nozzle 50. Further, when the stopper 310 is used, the molten steel is injected into the immersion nozzle 50 through a space between the lower end of the stopper 310 and the opening at the upper end of the immersion nozzle 50. Since the central axis of the nozzle and the central axis of the immersion nozzle 50 do not exactly coincide with each other, the space cannot necessarily be formed symmetrically with respect to the central axis of the immersion nozzle 50. Therefore, a drift can also occur in the immersion nozzle 50.

  As a result of the inventors analyzing the behavior of the molten steel drift in the general existing immersion nozzle 50 by a water model experiment or numerical analysis simulation, the flow of the molten steel in the discharge hole 501 is in the x-axis direction. It has been found that a vortex is formed with a substantially parallel direction as a rotation axis (more strictly, a direction substantially parallel to the extending direction of the discharge hole 501 as a rotation axis). That is, it was found that the discharge flow is formed as a swirl flow.

  Here, generally, at the time of continuous casting, the upper end of the discharge hole 501 of the immersion nozzle 50 is located 100 mm to 400 mm below the molten steel surface in the mold. And since the space of a predetermined | prescribed area is needed above a hot_water | molten_metal surface from a viewpoint of weakening the radiant heat from a hot_water | molten_metal surface and ensuring work space, the length of the immersion nozzle 50 is about 1 m, for example. Moreover, the internal diameter of the immersion nozzle 50 is about 100 mm, for example. Thus, in the immersion nozzle 50, since the ratio of the length to the inner diameter is large, the flow of molten steel in the immersion nozzle 50 becomes complicated. Specifically, as a result of analysis, it was found that the drift in the immersion nozzle 50 stagnates or the direction of rotation changes periodically.

  Due to the complicated behavior of the drift in the immersion nozzle 50, the position of the rotating shaft of the swirling flow in the discharge flow, the size of the swirling flow, the flow velocity of the molten steel in the swirling flow, etc. It turns out that it fluctuates. Moreover, when the slab obtained by actually performing continuous casting using the submerged nozzle 50 was investigated, the slab quality time variation considered to be caused by the temporal variation of the swirl flow characteristics in such a discharge flow Was confirmed.

  From the above results, in order to improve the quality of the slab, it is considered effective to suppress the time fluctuation of the swirling flow characteristics caused by the molten steel drift in the immersion nozzle 50. .

  On the other hand, in the immersion nozzle, it is known that alumina generated by oxidation of aluminum used for refining deoxidation adheres to and accumulates on the inner wall of the immersion nozzle and causes nozzle clogging. Therefore, in continuous casting using a general immersion nozzle 50 as shown in FIGS. 1 to 4, an inert gas such as argon gas or nitrogen is introduced into the immersion nozzle 50 together with molten steel in order to prevent nozzle clogging. Blowing into is widely done.

  Here, it is expected that the blown inert gas adsorbs inclusions such as alumina and is discharged from the discharge hole 501 into the mold, and then floats inside the mold and desorbs from the molten metal surface. However, it is known that a part is captured by the solidified shell and becomes a defect in the slab. Therefore, in order to improve the quality of the slab, it is important to improve the floatability of bubbles in the molten steel. More specifically, the rising behavior of the bubbles so that the bubbles ejected from the discharge holes together with the discharge flow reaches the molten steel surface without colliding with the solidified shell is required.

  As described above, in order to improve the quality of the slab in continuous casting, it is possible to suppress temporal fluctuations in the characteristics of the swirling flow in the discharge flow caused by molten steel drift in the immersion nozzle 50, and in the molten steel. It is thought that it is important to improve both the floatability of the inert gas bubbles.

  Examining the prior art that can achieve both of these two purposes, for example, Patent Document 1 discloses an immersion nozzle having a step structure on the inner wall. According to Patent Document 1, such a configuration provides an effect of suppressing the drift of molten steel in the immersion nozzle and an effect of suppressing nozzle blockage. Therefore, by using the immersion nozzle described in Patent Document 1, it is possible to prevent the discharge flow from being formed as a swirl flow in the first place, and it is not necessary to blow in an inert gas to prevent nozzle clogging. Therefore, there is a possibility that both of the above two purposes can be achieved. However, as described above, since the structure of the immersion nozzle described in Patent Document 1 is complicated, it is not practical from the viewpoint of cost and the like to employ such a structure.

  On the other hand, for example, Patent Document 2 discloses a structure in which swirl vanes are provided in a vertical portion in an immersion nozzle (that is, a cylindrical channel extending to a discharge hole). According to Patent Document 2, with this configuration, a swirl flow is formed in the immersion nozzle, and the molten metal is discharged from the entire discharge hole at a substantially uniform flow rate. Therefore, the flow rate of the discharge flow can be reduced. It is said that it can improve the floating property of bubbles. Further, according to the immersion nozzle described in Patent Document 2, the swirl flow can be stably formed by the swirl blades, and the internal pressure is increased, so that the left-right uneven flow of the discharge flow is suppressed (that is, the left-right discharge flow) It is considered that an effect that a substantially uniform flow can be formed is obtained.

  However, the technique described in Patent Document 2 is intended for a one-hole immersion nozzle, and when this technique is applied to a two-hole immersion nozzle, a stable swirling flow is formed in the vertical portion. Although it can be considered, the swirlability of the discharge flow is not always stable. That is, in the technique described in Patent Document 2, it is unclear whether temporal fluctuations in the characteristics of the swirling flow in the discharge flow of the two-hole immersion nozzle can be effectively suppressed. Moreover, if the swirl vane is provided in the middle of the flow path, there is a concern that inclusions adhere to and accumulate on the swirl vane and the swirl vane does not operate normally. That is, the immersion nozzle described in Patent Document 2 cannot withstand long-term use and may have a problem in sustainability.

(1-2. Background to the present invention and the basic principle of the present invention)
The present inventors have described the results of studies on conventional immersion nozzles. As described above, in order to improve the quality of the slab, in order to improve the quality of the slab, the fluctuation of the swirl flow characteristics in the discharge flow caused by the drift of the molten steel in the immersion nozzle is suppressed, and the inert gas in the molten steel It is thought that it is important to improve both the air bubble floatability. However, with conventional immersion nozzles, it has been difficult to suitably achieve these two objectives.

  In view of the above circumstances, the present inventors have come up with the present invention as a result of intensive studies on techniques that can suitably achieve these two objects. Specifically, as a result of intensive studies, the present inventors have arrived at the following idea.

  Bubbles flowing out from the discharge hole of the immersion nozzle try to float on the molten steel surface in the mold while diffusing (that is, spreading in the horizontal plane). Therefore, although it depends on casting conditions (immersion depth of immersion nozzle, flow rate for supplying molten steel, etc.), suitable conditions for causing bubbles to rise to the molten metal surface without colliding with the solidified shell are as follows. It is considered that the starting point of the bubble outflow is concentrated at the approximate center of the discharge hole. By causing the bubbles to flow intensively from the approximate center of the discharge hole instead of flowing out from the entire discharge hole, the degree of bubble diffusion in the molten steel can be further reduced, and the bubble collides with the solidified shell. This is because it is considered that the possibility of being reduced can be reduced. In addition, by concentrating the bubbles at the approximate center of the discharge hole, it can be expected that the bubbles are accumulated and combined. As the bubbles accumulate and coalesce and the volume increases, the ascent rate increases accordingly, so that the extent of bubbles in the molten steel during levitation can be further reduced, and the bubbles can collide with the solidified shell. It is thought that the property can be further reduced.

  In order to realize this, the present inventors have come up with the idea of using the discharge flow vortex generated due to the molten steel drift in the immersion nozzle described above. Specifically, if the discharge flow vortex can be stably formed, that is, if the discharge flow can be a stable swirl flow, bubbles having a specific gravity smaller than that of the molten steel due to the centrifugal force of the swirl flow. Can be collected in the vicinity of the rotational axis of the swirling flow. That is, it is possible to concentrate the bubbles at the approximate center of the discharge hole. Specifically, a swirling flow having a rotation axis that is substantially parallel to the extending direction of the discharge hole (that is, substantially parallel to the x-axis direction (the mold width direction)) is provided inside the immersion nozzle and provided with the discharge hole. It is desirable to form stably in the site | part (namely, lower part of immersion nozzle) to be formed. Thereby, a discharge flow can be made into a stable swirl flow. In addition, if such a swirl flow can be stably formed in the immersion nozzle, it is difficult for the molten steel to stay in the immersion nozzle, so that the effect of suppressing nozzle blockage can also be obtained.

  The present inventors can stabilize the swirling flow by providing a protrusion on the inner wall of the vertical part of the submerged nozzle, which is one of the inner walls in the y-axis direction (mold thickness direction) above the discharge hole. Has been found to be formed. According to such a configuration, the molten steel flowing through the vertical portion in the immersion nozzle collides with the projection, and thus has a rotation axis substantially parallel to the x-axis direction in the space below the projection. A unidirectional swirling flow can be forcibly generated. As a result, it is possible to stably generate a swirling flow having a rotation axis substantially parallel to the extending direction of the discharge hole in the lower part of the immersion nozzle.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention conceived by the present inventors will be described in detail with reference to the drawings.

(2. Structure of immersion nozzle)
With reference to FIGS. 5-9, the structure of the immersion nozzle which concerns on one Embodiment of this invention is demonstrated. FIG. 5 is a cross-sectional view in a cross section parallel to the mold width direction of the immersion nozzle according to the present embodiment. FIG. 6 is a cross-sectional view of the immersion nozzle shown in FIG. 5 in a cross section parallel to the mold thickness direction. FIG. 7 is an enlarged view showing the vicinity of a protrusion described later of the immersion nozzle shown in FIG. FIG. 8 is a cross-sectional view of the immersion nozzle shown in FIG. 5 in a horizontal cross section passing through a protrusion described later. FIG. 9 is a diagram for explaining a configuration of a gas blowing mechanism provided for the immersion nozzle according to the present embodiment. In FIGS. 5, 6 and 9, the flow of molten steel in the immersion nozzle is schematically shown by arrows.

  5 and 6, the immersion nozzle 10 according to the present embodiment has a cylindrical shape with a substantially uniform inner diameter. Further, a pair of discharge holes 101 are provided on the side wall near the lower end of the immersion nozzle 10 so as to face each other. When the immersion nozzle 10 is installed in a continuous casting machine, the opening direction of the pair of discharge holes 101 is oriented in the mold width direction (x-axis direction) (that is, the pair of discharge holes 101 is the mold short side surface). And the immersion nozzle 10 is installed with respect to the mold. At the time of continuous casting, the immersion nozzle 10 is installed so that a region at a predetermined distance from the lower end is immersed in the molten steel in the mold. And molten steel is inject | poured in the immersion nozzle 10 from an upper end, and is supplied in a casting_mold | template from the discharge hole 101 of a lower end.

  In the illustrated configuration example, the pair of discharge holes 101 opens obliquely downward. In general, many so-called two-hole immersion nozzles have such discharge holes that open obliquely downward. However, this embodiment is not limited to this example. In the present embodiment, the immersion nozzle 10 may be a two-hole immersion nozzle having a pair of discharge holes 101 provided to face each other. For example, the pair of discharge holes 101 opens in a substantially horizontal plane direction. It may be.

  5 and 6 illustrate a configuration in which the sliding nozzle 301 is provided with respect to the immersion nozzle 10 as an example. In the immersion nozzle 10, the effective area of the opening 305 is changed by adjusting the middle plate 303 of the three plates 303 constituting the sliding nozzle 301 in the mold thickness direction, thereby adjusting the flow rate of the molten steel. can do.

  Moreover, in this embodiment, the immersion nozzle 10 presupposes that an inert gas is blown in and used with molten steel, in order to prevent nozzle obstruction | occlusion. Accordingly, although not shown in FIGS. 5 and 6, in practice, the immersion nozzle 10 has a gas blowing mechanism 201 for blowing an inert gas into the immersion nozzle 10 as shown in FIG. 9. Provided.

  Referring to FIG. 9, the gas blowing mechanism 201 covers the boundary between the gas space 203 provided by hollowing out the inner wall of the immersion nozzle 10 in the circumferential direction, and the space between the gas space 203 and the space inside the immersion nozzle 10. , A porous sleeve 205 fitted to the inner wall of the immersion nozzle 10 and a pipe 207 for supplying an inert gas to the gas space 203 from the outside. The porous sleeve 205 is a cylindrical member formed of a refractory, and a large number of holes for allowing an inert gas to pass therethrough are formed on the wall surface. The inert gas supplied from the outside by the pipe 207 is stored in the gas space 203 and is blown into the immersion nozzle 10 through the hole formed in the porous sleeve 205.

  Note that the configuration of the illustrated gas blowing mechanism 201 is merely an example, and in this embodiment, other types of gas blowing mechanisms may be used for blowing inert gas. As the gas blowing mechanism 201, various known ones can be applied.

  As shown in FIG. 5 to FIG. 8, the immersion nozzle 10 is a partial region of the inner wall of the vertical portion and is a partial region on one side in the y-axis direction above the discharge hole 101 (that is, in a horizontal plane). The protrusion 103 is provided in a partial region on one side in a direction perpendicular to the opening direction of the pair of discharge holes 101 in FIG. By providing the protrusion 103, the molten steel flowing through the vertical portion in the immersion nozzle 10 collides with the protrusion 103, and in the space below the protrusion 103, that is, in the lower part of the immersion nozzle 10. Thus, it is possible to stably generate a swirling flow having a rotation axis substantially parallel to the extending direction of the discharge hole 101. Therefore, the discharge flow can be a stable swirl flow. Further, since it is difficult for stagnation of molten steel in the immersion nozzle 10, it is possible to suppress nozzle blockage.

  The structure of the immersion nozzle 10 may be the same as the structure of a general immersion nozzle except that the protrusion 103 is provided. For example, the length of the immersion nozzle 10 is about 1 m, and the upper end of the discharge hole 101 is located 100 mm to 400 mm below the molten steel surface in the mold during continuous casting. Moreover, the internal diameter of the immersion nozzle 10 is about 100 mm, for example.

  For example, the immersion nozzle 10 may be manufactured by attaching the protrusion 103 to a general existing immersion nozzle. Thereby, the manufacturing cost can be reduced. The method for attaching the protrusion 103 to the inner wall of the immersion nozzle 10 is not particularly limited, and any method such as pinning may be used.

  In the example illustrated, the protrusion 103 has a substantially rectangular shape in both the cross section in the xz plane and the cross section in the yz plane, and a part of the circular opening of the immersion nozzle 10 in the xy plane. It has an arcuate shape that fills the surface. However, this embodiment is not limited to this example. The protrusion 103 only needs to be able to form a stable swirling flow, and its installation position, shape, and / or number may be arbitrary. However, the protrusion 103 needs to be provided only on one side in the y-axis direction on the inner wall of the immersion nozzle 10. The specific installation position, shape, and / or number of the protrusions 103 may be appropriately set according to the shape and casting conditions of the immersion nozzle 10 by performing, for example, a water model experiment or numerical analysis simulation.

  As a result of studies by the present inventors, in the immersion nozzle 10 having the same configuration as that of a general immersion nozzle except that the protrusion 103 as described above is provided, when general casting conditions are assumed, In order to form a stable swirling flow, the height T0 from the center position in the height direction of the discharge hole 101 to the lower end of the protrusion 103 is 0.5 times or more the inner diameter φ of the immersion nozzle 10, and 0. It turned out that it is preferable that it is less than about 75 times (refer also the Example mentioned later). By setting the height T0 in such a range, a sufficiently large space can be secured below the protrusion 103, so that a substantially circular stable swirl flow can be formed in the space. It becomes. In addition, with this configuration, a sufficient flow velocity is created in the space below the protrusion 103 where inclusions are likely to deposit, and it is difficult for the molten steel flow to stay in the space. Occlusion can also be suppressed.

  Here, in the present specification, the center position in the height direction of the discharge hole 101 is the horizontal plane passing through the highest point among the openings of the discharge holes 101 and the most of the openings of the discharge holes 101. This means the center position in the height direction between the horizontal plane passing through a point having a low position. As shown in FIG. 7, when the discharge hole 101 is opened obliquely downward, the highest position among the openings of the discharge hole 101 is the opening of the discharge hole 101 on the inner wall of the immersion nozzle 10. It becomes a point (point X shown in FIG. 7) that hits the upper end of the part. And the point where the position is the lowest among the openings of the discharge hole 101 is a point (point Y shown in FIG. 7) that hits the lower end of the opening of the discharge hole 101 on the outer wall of the immersion nozzle 10. The center position in the height direction between the horizontal plane passing through the point X and the horizontal plane passing through the point Y is the center position in the height direction of the discharge hole 101 and corresponds to the lower end of the height T0 shown in FIG. It becomes the position to do.

  On the other hand, the height D in the horizontal plane direction of the protrusion 103 (the thickness of the protrusion 103 in the y-axis direction) is a horizontal cross section at the portion where the protrusion 103 of the immersion nozzle 10 is provided so as not to hinder the flow control of the molten steel. It is necessary to make the opening area at this point larger than the opening area of the sliding nozzle 301. For example, assuming general casting conditions, the upper limit of the height D may be about 0.5 times the inner diameter φ of the immersion nozzle 10. On the other hand, if the height D of the protrusion 103 is too small, rectification occurs due to the buoyancy of the inert gas blown into the molten steel, and the swirlability of the molten steel flow is weakened. As a result of the study by the present inventors, in order to obtain a stable swirling flow, the lower limit of the height D is about 0.15 times the inner diameter φ of the immersion nozzle 10 (if the inner diameter φ = 100 mm). It was found that the height D is preferably about 15 mm. From the above examination, it is preferable that the height D of the protrusion 103 in the horizontal plane direction is 0.15 times or more and less than 0.5 times the inner diameter φ of the immersion nozzle 10 (see also examples described later). . Note that, as described above, in the illustrated example, the protrusion 103 has a substantially rectangular shape in a cross section on the yz plane, and thus the height D is substantially uniform in the z-axis direction. The shape is not limited to such an example. The height D may have a distribution in the z-axis direction.

  In addition, from the viewpoint of forming a stable swirling flow, the height T in the z-axis direction of the protrusion 103 may be arbitrary. Further, since the inner diameter φ of the immersion nozzle 10 is substantially uniform, if the height D of the protrusion 103 in the horizontal plane is determined, the width W of the protrusion 103 in the x-axis direction is also determined. In other words, when setting the installation position and shape of the protrusion 103, the height T0 from the center position in the height direction of the discharge hole 101 to the lower end of the protrusion 103 and the height D in the horizontal plane are defined. It ’s enough. Therefore, these parameters T0 and D may be set by a water model experiment or the like. In addition, the protrusion part 103 should just be provided in any one of a y-axis direction in the inner wall of the immersion nozzle 10, and the installation position may be any of a y-axis direction.

  Here, with reference to FIGS. 10-12, the effect which improves the floating property of the bubble by the immersion nozzle 10 which concerns on this embodiment is demonstrated. FIG. 10 is a cross-sectional view in the mold width direction showing a state in which the immersion nozzle 10 according to the present embodiment is installed on the mold. FIG. 11 is a diagram showing a state in which the vicinity of the discharge hole 101 of the immersion nozzle 10 shown in FIG. 10 is viewed from the mold width direction, and bubbles in the mold when the immersion nozzle 10 according to the present embodiment is used. It is a figure which shows the mode of levitation roughly. FIG. 12 is a diagram for comparison, and is a diagram schematically showing the state of air bubbles rising in the mold as seen from the direction corresponding to FIG. 11 when a conventional existing immersion nozzle is used. is there.

  As shown in FIG. 10, the immersion nozzle 10 can be installed at the approximate center in the width direction of the mold 6 so that the pair of discharge holes 101 face the short side surfaces on both sides of the mold 6. Molten steel 2 is supplied into the mold 6 from the discharge hole 101 of the immersion nozzle 10. The mold 6 is made of, for example, a water-cooled copper plate, and the molten steel 2 that comes into contact with the mold 6 is cooled to manufacture the slab 3. As the slab 3 moves toward the lower side of the mold 6, solidification of the inner unsolidified portion 3b proceeds, and the thickness of the solidified shell 3a of the outer shell gradually increases. The slab 3 including the solidified shell 3a and the unsolidified portion 3b is pulled out from the lower end of the mold 6 so that casting is continuously performed.

  FIG. 11 schematically illustrates the behavior of bubbles ejected from the discharge hole 101 of the immersion nozzle 10. As schematically shown in FIG. 11, by using the immersion nozzle 10 according to the present embodiment, the bubbles are concentrated at the approximate center of the discharge hole 101, so that the coalescence of the bubbles is promoted and relatively large bubbles are formed. obtain. Therefore, the spread when the bubbles rise is suppressed, and the possibility that the bubbles collide with the solidified shell 3a can be reduced. That is, the occurrence of bubble defects can be suppressed.

  On the other hand, as shown schematically in FIG. 12, when the conventional existing immersion nozzle 50 is used, the bubbles can be ejected substantially uniformly from the entire discharge hole 501. Small bubbles will rise. Accordingly, the bubbles are more easily diffused when they rise, and the possibility that the bubbles collide with the solidified shell 3a is increased. That is, defects due to bubbles are likely to occur.

  The configuration of the immersion nozzle 10 according to the present embodiment has been described above with reference to FIGS. Moreover, with reference to FIGS. 10-12, the effect which improves the floating property of the bubble by the immersion nozzle 10 which concerns on this embodiment was demonstrated.

  5 to 9, as an example, a configuration in which the sliding nozzle 301 is provided with respect to the immersion nozzle 10 is illustrated, but the present embodiment is not limited to such an example. The flow rate control in the immersion nozzle 10 may be performed by the stopper 310.

  13 and 14 schematically show a configuration in which a stopper 310 is provided for the immersion nozzle 10 according to the present embodiment. FIG. 13 is a cross-sectional view in a cross section parallel to the mold width direction of the configuration in which the stopper 310 is provided for the immersion nozzle 10 according to the present embodiment. FIG. 14 is a cross-sectional view of the immersion nozzle 10 and the stopper 310 shown in FIG. 13 in a cross section parallel to the mold thickness direction. Even when the flow rate is controlled by the stopper 310 as in the configuration examples shown in FIGS. 13 and 14, the effect of forming a stable swirl flow is the same as the configuration in which the sliding nozzle 301 is provided. It is possible to obtain

  As described above, according to the present embodiment, by providing the protrusion 103, a swirling flow having a rotation axis substantially parallel to the extending direction of the discharge hole 101 is stably generated in the lower part of the immersion nozzle 10. Therefore, the discharge flow can be a stable swirl flow. Thereby, the floating property of a bubble can be improved. Moreover, since a stable swirl flow is formed in the immersion nozzle 10, it is difficult for the molten steel to stay in the immersion nozzle 10, so that the nozzle blockage can be suppressed. As described above, according to the present embodiment, it is possible to suppress time fluctuations in the characteristics of the swirl flow in the discharge flow caused by the molten steel drift in the immersion nozzle 10 and to float the bubbles of the inert gas in the molten steel. It is possible to improve both of the properties. Therefore, the quality improvement of a slab is implement | achieved.

  Here, Patent Document 2 discloses a configuration in which swirl vanes are provided in the vertical portion of the immersion nozzle. Even with such a configuration, a stable swirl flow can be generated at least in the vertical portion. However, as described above, when the technique described in Patent Document 2 is applied to a two-hole immersion nozzle, the swirlability of the discharge flow is not always stable. Even if the discharge flow is stably formed, the swirl force is considered to be weakened when the swirl flow branches from the vertical portion to the two discharge holes, so that bubbles are accumulated near the rotation axis. The effect can be reduced. Therefore, with the technique described in Patent Document 2, it is difficult to suitably obtain the effect of improving the bubble floating property.

  Moreover, the said patent document 3 is disclosing the immersion nozzle by which the projection part was provided in the inner wall of the vertical part similarly to the immersion nozzle 10 which concerns on this embodiment. However, the purpose is different between the immersion nozzle 10 according to the present embodiment and the immersion nozzle described in Patent Document 3.

  Specifically, the immersion nozzle described in Patent Document 3 is intended to prevent the trapping and accumulation of inclusions in the solidified shell inside the curved shape in the curved type continuous casting machine. By providing the flow pattern, it is possible to form a flow pattern of the discharge flow that is a downward flow inside the curve and an upward flow outside the curve. That is, the immersion nozzle described in Patent Document 3 is specialized for use in a curved continuous casting machine. For example, the immersion nozzle is applied to a continuous casting machine having another structure such as a vertical mold or a vertical bending mold. Even if is applied, it is considered that the effect of improving the quality of the slab cannot be suitably obtained. Further, in Patent Document 3, in order to form the flow pattern of the discharge flow as described above, the protrusions must be provided at portions corresponding to the curved outer side of the inner wall of the submerged nozzle, It is described that the height in the direction (corresponding to the height D in the horizontal plane direction in the present embodiment described above) is 0.05 to 0.15 times the inner diameter of the immersion nozzle. Furthermore, in Patent Document 3, there is no mention of defects caused by bubbles due to the blowing of an inert gas, so it is unclear whether or not the immersion nozzle contributes to the reduction of defects caused by the bubbles.

  On the other hand, in this embodiment, the temporal fluctuation of the swirl flow characteristics in the discharge flow caused by the molten steel drift in the immersion nozzle 10 is suppressed, and the floatability of the inert gas bubbles in the molten steel is enhanced. By providing the protrusion 103, a stable swirling flow is formed inside the immersion nozzle 10, thereby realizing a stable swirling flow. is there. Since the effect is achieved regardless of the structure of the continuous casting machine, the immersion nozzle 10 according to the present embodiment can be applied to a continuous casting machine other than the curved type, even if it is a cast piece. The effect of quality improvement can be suitably obtained. Further, as described above, in the present embodiment, for the purpose of obtaining a stable swirling flow, the protrusion 103 may be provided in any of the mold thickness directions, and the height D in the horizontal plane direction thereof. Is preferably at least about 0.15 times the inner diameter φ of the immersion nozzle.

  As described above, since the purpose is different between the immersion nozzle 10 according to the present embodiment and the immersion nozzle described in Patent Document 3, the installation position and shape of the protrusion 103 are also greatly different. And the effect acquired by the projection part 103 also differs greatly. Thus, it should be noted that the immersion nozzle 10 according to the present embodiment is completely different from the immersion nozzle described in Patent Document 3.

(3. Application example)
As an application example of the immersion nozzle 10 according to the present embodiment described above, the configuration of a continuous casting machine to which the immersion nozzle 10 is applied and a continuous casting method using the continuous casting machine will be described with reference to FIG. To do. FIG. 15 is a side sectional view schematically showing a configuration example of a continuous casting machine to which the immersion nozzle 10 according to the present embodiment can be applied.

  As shown in FIG. 15, the continuous casting machine 1 according to this embodiment is an apparatus for continuously casting a molten steel 2 using a continuous casting mold 6 to manufacture a slab 3 such as a slab. The continuous casting machine 1 includes a mold 6, a ladle 4, a tundish 5, an immersion nozzle 10, a secondary cooling device 7, and a slab cutting machine 8.

  The ladle 4 is a movable container for conveying the molten steel 2 from the outside to the tundish 5. The ladle 4 is disposed above the tundish 5, and the molten steel 2 in the ladle 4 is supplied to the tundish 5. The tundish 5 is disposed above the mold 6, stores the molten steel 2, and removes inclusions in the molten steel 2. The immersion nozzle 10 extends substantially vertically downward from the lower end of the tundish 5 toward the mold 6, and the tip thereof is immersed in the molten steel 2 in the mold 6. The immersion nozzle 10 continuously supplies the molten steel 2 from which inclusions have been removed by the tundish 5 into the mold 6.

  Although detailed illustration is omitted in order to avoid complication of the drawing, as described above, the immersion nozzle 10 is formed with a pair of discharge holes 101 so as to face both short sides of the mold 6, respectively. Has been. Further, a projection 103 is provided on the inner wall. With this protrusion 103, a stable swirl flow can be formed as a discharge flow in the immersion nozzle 10.

  The mold 6 has a rectangular tube shape corresponding to the width and thickness of the slab 3 and is assembled, for example, such that a pair of long side mold plates sandwich a pair of short side mold plates from both sides. The long side mold plate and the short side mold plate (hereinafter may be collectively referred to as a mold plate) are, for example, water-cooled copper plates provided with water channels through which cooling water flows. The mold 6 cools the molten steel 2 that comes into contact with the mold plate to produce the slab 3. As the slab 3 moves toward the lower side of the mold 6, solidification of the inner unsolidified portion 3b proceeds, and the thickness of the outer solidified shell 3a gradually increases. The slab 3 including the solidified shell 3 a and the unsolidified portion 3 b is pulled out from the lower end of the mold 6.

  The secondary cooling device 7 is provided in the secondary cooling zone 9 below the mold 6, and cools the slab 3 drawn out from the lower end of the mold 6 while supporting and transporting it. The secondary cooling device 7 includes a plurality of pairs of support rolls (for example, a support roll 11, a pinch roll 12 and a segment roll 13) disposed on both sides in the thickness direction of the slab 3, and cooling water for the slab 3. A plurality of spray nozzles (not shown).

  The support rolls provided in the secondary cooling device 7 are arranged in pairs on both sides in the thickness direction of the slab 3 and function as a support and transport means for transporting the slab 3 while supporting it. By supporting the slab 3 from both sides in the thickness direction with the support roll, breakout and bulging of the slab 3 during solidification in the secondary cooling zone 9 can be prevented.

  The support roll 11, the pinch roll 12, and the segment roll 13, which are support rolls, form a transport path (pass line) for the cast piece 3 in the secondary cooling zone 9. As shown in the figure, this pass line is vertical immediately below the mold 6, then curved in a curved line, and finally becomes horizontal. In the secondary cooling zone 9, a portion where the pass line is vertical is called a vertical portion 9A, a curved portion is called a curved portion 9B, and a horizontal portion is called a horizontal portion 9C. The continuous casting machine 1 having such a pass line is referred to as a vertical bending type continuous casting machine 1.

  The support roll 11 is a non-driven roll provided in the vertical portion 9 </ b> A immediately below the mold 6, and supports the slab 3 immediately after being pulled out of the mold 6. The slab 3 immediately after being drawn out from the mold 6 is in a state where the solidified shell 3a is thin, and therefore it is necessary to support it at a relatively short interval (roll pitch) in order to prevent breakout and bulging. Therefore, as the support roll 11, it is desirable to use a roll with a small diameter that can shorten the roll pitch. In the example shown in FIG. 1, three pairs of support rolls 11 made of small-diameter rolls are provided at a relatively narrow roll pitch on both sides of the slab 3 in the vertical portion 9A.

  The pinch roll 12 is a drive roll that is rotated by drive means such as a motor, and has a function of pulling the cast piece 3 out of the mold 6. The pinch rolls 12 are respectively arranged at appropriate positions in the vertical portion 9A, the curved portion 9B, and the horizontal portion 9C. The slab 3 is pulled out of the mold 6 by the force transmitted from the pinch roll 12 and is conveyed along the pass line. In addition, arrangement | positioning of the pinch roll 12 is not limited to the example to show in figure, The arrangement position may be set arbitrarily.

  The segment roll 13 (also referred to as a guide roll) is a non-driving roll provided in the curved portion 9B and the horizontal portion 9C, and supports and guides the slab 3 along the pass line. The segment roll 13 depends on the position on the pass line, and on either the F surface (Fixed surface, lower left surface in FIG. 15) or L surface (Loose surface, upper right surface in FIG. 15) of the slab 3 Depending on whether they are provided, they may be arranged with different roll diameters and roll pitches.

  The slab cutting machine 8 is disposed at the end of the horizontal portion 9C of the pass line, and cuts the slab 3 conveyed along the pass line to a predetermined length. The cut thick plate-shaped slab 14 is transported to the next process equipment by the table roll 15.

  The configuration of the continuous casting machine to which the immersion nozzle 10 according to the present embodiment is applied and the continuous casting method using the continuous casting machine have been described above with reference to FIG. In addition, the continuous casting machine to which the immersion nozzle 10 which concerns on this embodiment can be applied is not limited to what was illustrated, The thing of all structures may be used as a continuous casting machine. For example, the immersion nozzle 10 according to the present embodiment can be applied not only to the vertical bending type continuous casting machine 1 as illustrated, but also to various other continuous casting machines such as a curved type or a vertical type.

  An example in which an immersion nozzle having the same configuration as the immersion nozzle 10 according to the present embodiment described with reference to FIGS. 5 to 9 is applied to a continuous casting machine that is actually used in an operation in a steel plant will be described. To do.

  The conditions for continuous casting are as follows. That is, as the continuous casting machine, a vertical bending type continuous casting machine having a bending radius of 7.5 m and a vertical portion length of 2.5 m was used. The mold has a width of 1200 mm, a height of 900 mm, and a thickness of 250 mm. The immersion nozzle was installed so that its discharge hole was located 300 mm in the depth direction from the meniscus at the center in the mold width direction. The outer diameter of the immersion nozzle is 150 mm, and the inner diameter φ is 90 mm. The diameter of the discharge hole is 60 mm, and the discharge angle θ is 30 degrees downward. The steel type is an ultra-low-carbon aluminum killed steel for automobiles, and the casting speed was 1.5 m / min. At the entrance of the immersion nozzle, a sliding nozzle composed of three plates having an opening with a diameter of 60 mm was provided, and the flow rate of the molten steel was adjusted by the sliding nozzle. In addition, argon gas was blown into the immersion nozzle through the porous sleeve at a rate of 6 NL / min by a gas blowing mechanism installed above the immersion nozzle.

  In order to confirm the effect of the present invention, an immersion nozzle having a protrusion on the inner wall and an immersion nozzle having no protrusion on the inner wall as in this embodiment were prepared. Furthermore, as for the immersion nozzle provided with the protrusion, eight types of immersion nozzles having different installation positions and shapes of the protrusions were prepared. Specifically, the vertical height T of the protrusion is fixed at 30 mm, and the height D in the horizontal plane direction is 5 mm (= 0.056 φ (mm)), 9 mm (= 0.10 φ (mm)), While changing in 6 levels of 15mm (= 0.17φ (mm)), 30mm (= 0.33φ (mm)), 40mm (= 0.44φ (mm)), 45mm (= 0.50φ (mm)) The height T0 from the center position in the height direction of the discharge hole to the lower end of the protrusion is 45 mm (= 0.50 φ (mm)), 67.5 mm (= 0.75 φ (mm)), 90 mm (= 1. It was changed at three levels of 0φ (mm).

  About these nine types of immersion nozzles, continuous casting was performed under the above conditions, and the number of defects caused by bubbles in the cast slab was counted to evaluate the quality of the slab. Specifically, the number of defects caused by air bubbles having a diameter of 0.5 mm or more was counted by observing and counting at a pitch of 1 mm up to a depth of 5 mm on the surface layer of the cast slab. The number of defects due to the bubbles in the case of using was evaluated as a relative index with 1. Moreover, about each immersion nozzle, the presence or absence of nozzle obstruction | occlusion after performing a continuous casting machine for the predetermined time was confirmed visually.

  The results are shown in Table 1 below. In addition, in Table 1 below, regarding the nozzle clogging, “◯” is indicated when almost no occurrence is confirmed, “△” is indicated when occurrence is somewhat, and large-scale occurrence is confirmed. Items are indicated by “x”.

  From Table 1, comparing the result in Condition 1 using an immersion nozzle without a protrusion and the results in Conditions 2 to 9 using an immersion nozzle with a protrusion, the installation by providing the protrusion It turns out that the effect which reduces the defect resulting from a bubble is acquired irrespective of a position and a shape.

  Further, from the results in Condition 2 to Condition 7, when the height D of the protrusion in the horizontal plane direction is about 0.10 times or less the inner diameter φ of the immersion nozzle (that is, Conditions 2 and 3), Although the number of defects due to bubbles can be reduced as compared with the case where no protrusion is provided, the index representing the number of defects exceeds 0.5, and the reduction rate is not so large. On the other hand, when the height D is about 0.15 times or more of the inner diameter φ of the immersion nozzle (that is, conditions 4 to 7), defects caused by bubbles are smaller than when no protrusion is provided. It can be seen that the number can be reduced to less than half considered to be a sufficient quality improvement level.

  Further, from the results in conditions 5, 8, and 9, the height T0 from the center position in the height direction of the discharge hole to the lower end of the protrusion is about 0.75 times the inner diameter φ of the immersion nozzle (ie, In condition 8), it can be seen that the number of defects caused by bubbles can be reduced to half or less, which is considered to be a sufficient quality improvement level, as compared with the case where no protrusion is provided. It can also be seen that the number of defects caused by bubbles can be further reduced by reducing the height T0 to about 0.50 times the inner diameter φ of the immersion nozzle (ie, condition 5). On the other hand, when the height T0 is increased to about 1.0 times the inner diameter φ of the immersion nozzle (that is, the condition 9), the index representing the number of defects caused by bubbles exceeds 0.5, It turns out that the decreasing rate of the number of the said defects will fall.

  From the above results, in order to suitably obtain the effect of reducing defects caused by air bubbles in the immersion nozzle according to the present embodiment, the height D in the horizontal plane direction of the protrusion is at least 0. The height T0 from the center position in the height direction of the discharge hole to the lower end of the protrusion is at least about 0.50 times and not more than about 0.75 times the inner diameter φ of the immersion nozzle. Is considered effective.

  On the other hand, paying attention to the occurrence of nozzle clogging, when the height D of the protrusion in the horizontal plane is increased to about 0.50 times the inner diameter φ of the immersion nozzle from the result in Condition 7, some nozzle clogging occurs. It can be seen that has occurred. Further, from the result in Condition 8, when the height T0 from the center position in the height direction of the discharge hole to the lower end of the protrusion is increased to about 0.75 times the inner diameter φ of the submerged nozzle, some nozzles are similarly used. It can be seen that an occlusion has occurred. It is considered that the cause of such nozzle clogging is that, under these conditions, a sufficiently stable swirl flow is not formed in the immersion nozzle, and the flow of molten steel is retained.

  From the above results, in order to form a stable swirling flow in the immersion nozzle according to the present embodiment and to suitably suppress nozzle blockage, the height D in the horizontal plane direction of the protrusion is at least the inner diameter φ of the immersion nozzle. It is effective that the height T0 from the center position in the height direction of the discharge hole to the lower end of the protrusion is at least smaller than about 0.75 times the inner diameter φ of the immersion nozzle. It is thought that.

  In summary, from the results of this example, at least in the above-described casting conditions corresponding to this example, defects caused by bubbles are suitably reduced and nozzle blockage is suitably suppressed by the immersion nozzle according to this embodiment. In order to achieve this, the height D of the projection in the horizontal plane is set to be about 0.15 times or more and less than about 0.50 times the inner diameter φ of the immersion nozzle, and the height of the projection from the center position in the height direction of the discharge hole. It is considered effective to set the height T0 to the lower end to about 0.50 times or more and less than about 0.75 times the inner diameter φ of the immersion nozzle.

(4. Supplement)
The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Continuous casting machine 2 Molten steel 3 Cast slab 3a Solidified shell 3b Unsolidified part 4 Ladle 5 Tundish 6 Mold 10, 50 Immersion nozzle 101, 501 Discharge hole 103 Protrusion part 201 Gas blowing mechanism 203 Gas space 205 Porous sleeve 207 Pipe 301 Sliding nozzle 303 Plate 305 Opening 310 Stopper

Claims (6)

A cylindrical casting nozzle having a substantially uniform inner diameter, which is installed so as to extend in a substantially vertical direction above a mold in a continuous casting machine, and supplies molten metal stored in a tundish into the mold.
A pair of discharge holes for discharging molten metal into the mold is formed on the side wall near the lower end so as to face each other,
A gas blowing mechanism for blowing an inert gas into the immersion nozzle is provided,
In the cylinder extending in the substantially vertical direction of the immersion nozzle, a protrusion is formed on a wall surface above the discharge hole and in a wall surface in a direction perpendicular to the opening direction of the pair of discharge holes in the horizontal plane. Part is provided,
Immersion nozzle. The continuous casting machine is a vertical bending type continuous casting machine,
The immersion nozzle according to claim 1. The height in the horizontal plane direction of the protrusion is 0.15 times or more and less than 0.5 times the inner diameter of the immersion nozzle.
The immersion nozzle according to claim 1 or 2. The height from the center position in the height direction of the discharge hole to the lower end of the protrusion is 0.5 times or more and less than 0.75 times the inner diameter of the immersion nozzle.
The immersion nozzle according to any one of claims 1 to 3. The immersion nozzle according to any one of claims 1 to 4, wherein the pair of discharge holes are installed so as to face the short side surfaces on both sides of the mold, respectively.
Continuous casting machine. Continuous casting is performed using the continuous casting machine according to claim 5.
Continuous casting method.

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