JP2023143363A - Long nozzle and nozzle system - Google Patents

Abstract

To provide a long nozzle for feeding a molten metal downwards from a ladle to a tundish, and when a molten metal is hammered into a secondary meniscus within the nozzle to generate many bubbles, capable of efficiently recovering the bubbles into the nozzle.SOLUTION: A cylindrical single hole long nozzle is used for feeding a molten metal downwards from a ladle to a tundish, and comprises: an inflow port; an outflow port; a smallest diameter part; and a diameter expansion part. The smallest diameter part is present on the side of the inflow port with respect to the outflow port, the diameter expansion part is present from the smallest diameter part to the outflow port, the inside diameter of the nozzle is expanded from the smallest diameter part to the outflow port, and in the longitudinal cross-sectional shape, an angle θ between a nozzle inner wall and a nozzle axis in the diameter expansion part is 5 or more to 10° or less.SELECTED DRAWING: Figure 1

Description

The present application discloses a long nozzle for supplying molten metal from a ladle to a tundish, and a nozzle system using the same.

In a continuous casting process of molten metal, a tundish is used as an intermediate container for supplying molten metal from a ladle to a mold. For example, assuming continuous casting of steel, the tundish has the following functions: (1) stabilizing the amount of molten steel supplied to the mold, (2) distributing the molten steel to multiple molds, and (3) distributing the molten steel to multiple molds. It has multiple functions such as a buffer function for continuous operation using a pot, and (4) a function to remove non-metallic inclusions. In particular, (4) the ability to remove nonmetallic inclusions is extremely important when efficiently producing high-grade steel materials with high cleanliness.

Nonmetallic inclusions in molten steel are mainly derived from impurities in steel such as oxides, nitrides, sulfides, and bubbles generated during the steelmaking process. It is known that when such nonmetallic inclusions remain in a final product, they become a starting point for fracture due to stress concentration, for example, and deteriorate the material quality of the final product. In addition, during the steelmaking process itself, non-metallic inclusions adhere and accumulate on the inner walls of refractory flow channels, causing narrowing and blockage of the flow channels, which not only impede smooth manufacturing, but also hinder processing such as casting. Since defects can sometimes occur on both the surface and inside of the base material, this is a factor that reduces product yield and puts pressure on manufacturing costs. Therefore, in many cases, it is necessary to remove nonmetallic inclusions from molten steel in a limited number of steps from secondary refining, where the final adjustment of molten steel components is made, to molding.

In order to remove nonmetallic inclusions from molten steel, the nonmetallic inclusions are generally floated in the molten steel using the difference in specific gravity between the molten steel and the nonmetallic inclusions, and then an oxide called flux is removed. However, it is known that the smaller the nonmetallic inclusions are, the lower the floating speed is, and the longer it takes to collect them in the flux layer. Therefore, when reducing non-metallic inclusions in molten steel, it is effective to lengthen the residence time of non-metallic inclusions in the tundish in order to secure the time necessary for the non-metallic inclusions to float. Conceivable.

Generally, molten steel is supplied from the molten steel ladle to the tundish through a sliding nozzle with a flow rate adjustment function and a long nozzle, which is a cylindrical refractory whose lower end is immersed in the molten steel in the tundish. This is done by using energy to flow down. However, when the high-speed discharge flow from the long nozzle collides with the bottom of the tundish, it can form a short-circuit flow toward the mold called a short path (see Figure 6). Securing it is not always easy. A common countermeasure to this problem is to bypass the flow of molten steel by installing a weir inside the tundish. In addition, a space is created near the weir where there is almost no flow and does not contribute to flotation removal, and a new flow that detours toward the mold at high speed may be induced, so it is not always possible to prevent inclusions from flotation. I can't help. In particular, small inclusions have low buoyancy and tend to follow the flow of molten steel, so the effect of detouring is likely to be limited to the removal of large inclusions.

Furthermore, in the steelmaking process, attention must be paid to the unintentional increase in nonmetallic inclusions due to reoxidation of molten steel. In general, molten steel used for continuous casting is subjected to deoxidation treatment during the refining process to prevent stable casting from becoming difficult due to gas generation as the temperature of molten steel decreases, and the concentration of soluble oxygen is reduced. The oxygen concentration is much lower than the average temperature, making it extremely easy to absorb oxygen. When air or lower oxides come into contact with molten steel, the molten steel absorbs oxygen and combines with elements that have a higher affinity for oxygen than the molten steel (such as Al and Si dissolved in the molten steel), resulting in nonmetallic formation. A reoxidation phenomenon that generates inclusions occurs. Therefore, in molten steel pots and tundishes, it is necessary to reduce the oxygen concentration inside the tundish by replacing the atmosphere with an inert gas, or to use a low-reactivity flux with a low content of lower oxides. It is necessary to shield the molten steel from the outside air by coating the surface. However, when molten steel is supplied to a tundish by a long nozzle, as the molten steel flow discharged from the nozzle is very high speed as described above, the reverse upward flow generated by colliding with the bottom of the tundish causes the molten steel to flow near the long nozzle. The flux covering the surface of the molten steel is pushed away, the surface of the molten steel is directly exposed to the outside air as bare hot water, and a reoxidation phenomenon can occur in which the molten steel absorbs oxygen in the atmosphere (see FIG. 6). Alternatively, since there is slag with a high concentration of lower oxides such as FeO that has flowed out from the ladle near the long nozzle, the intense flow of molten steel near the long nozzle may cause reoxidation of the molten steel by the lower oxides in the slag. .

Conventionally, various means for solving the above problems have been proposed. For example, Patent Document 1 discloses a continuous casting method using an injection pipe that blocks the injection flow from the outside air with a refractory cylindrical body having an inner diameter of 300 mm or more. According to the technology disclosed in Patent Document 1, the injection flow falling from the nozzle hits the gas in the pipe at the liquid level in the pipe, thereby introducing a large number of bubbles into the molten steel, and the large buoyancy of the bubbles increases the injection flow rate. It is believed that it is possible to reduce the flow rate to create a gentle upward flow within the tundish. In addition, since solid inclusions have poor wettability with molten steel and easily adhere to bubbles, they are expected to float away at high speed due to the large buoyancy of the bubbles. On the other hand, with the above-mentioned injection pipe, if the molten steel splashed from the ladle nozzle or the molten steel scattered on the bath surface adheres to the inner wall of the pipe, the heat dissipated from the deposits is significant due to the large diameter of the pipe, and the deposits are damaged. They tend to coagulate and stack up, leading to blockage. This is a major problem that makes it difficult to continue continuous casting operations. In addition, in order to prevent the molten steel from absorbing oxygen and nitrogen from the gas phase, injection pipes must be filled with a large amount of inert gas, compared to when a long nozzle is immersed in the molten steel. There is a problem of high operating costs.

Patent Document 2 discloses a nozzle in which a flow control section is provided in the body in order to prevent bare hot water from being exposed due to an upward flow reversed at the bottom of the tundish. However, in the technique disclosed in Patent Document 2, it is necessary to take additional measures against the occurrence of short paths, which increases manufacturing costs. In addition, the weight of the nozzle increases, which places a large load on the device that grips the nozzle, which may not be able to fully support the nozzle during casting, and there is a risk that molten steel may spout from the joint of the long nozzle.

Patent Document 3 discloses that an inert gas gas space is formed inside the injection nozzle, the inert gas is involved in the injection flow at the steel bath surface in the nozzle, and the inert gas is stirred in the stirring box installed on the bottom of the tundish. A continuous casting method and a continuous casting apparatus are disclosed that promote aggregation of inclusions and bubbles in molten steel by stirring the injection stream. In the technique disclosed in Patent Document 3, since the injection nozzle of the continuous casting apparatus has a sufficiently large inner diameter of the discharge hole, a gas space is stably formed. On the other hand, in the technology disclosed in Patent Document 3, in order to avoid that all the bubbles involved in the injection flow resurface into the injection nozzle and the stirring action in the stirring box is not sufficiently exerted, Although the inner diameter of the nozzle is set to a predetermined value or less, air bubbles that leave the injection nozzle and float to the surface of the molten steel in the tundish may cause reoxidation as described above. There is also the problem that the stirring box is costly and requires time and effort to construct.

As a long nozzle for feeding molten steel from a ladle to a tundish, for example, a straight nozzle without an enlarged diameter part as disclosed in Patent Document 3, or a straight nozzle as disclosed in Patent Documents 2 and 4. Those having an enlarged diameter portion (conical portion) are known. However, conventional long nozzles may not be able to sufficiently suppress the occurrence of bare hot water or short paths in the tundish.

Patent No. 6575355 Special Publication No. 2020-530813 Japanese Patent Application Publication No. 2011-235339 Japanese Patent Application Publication No. 11-010292

When supplying molten metal from a ladle to a tundish through a long nozzle, a gas phase region is formed in the long nozzle, and a liquid surface (secondary meniscus) of the molten metal is formed, and the molten metal is supplied to the tundish. It is thought that by pounding and generating a large number of bubbles, the flow velocity of the molten metal can be reduced, and the generation of the above-mentioned short paths and bare hot water can be suppressed. In this case, in order to maintain a large number of bubbles within the long nozzle, it is necessary to prevent the generated bubbles from leaving the long nozzle as much as possible, and to efficiently collect the generated bubbles into the gas phase region. The present application is a long nozzle for supplying molten metal downward from a ladle to a tundish, and when the molten metal is struck into the secondary meniscus in the nozzle to generate a large number of bubbles, the bubbles are Discloses something that can be efficiently collected into a nozzle.

This application, as one of the means to solve the above problems,
A cylindrical single-hole long nozzle for supplying molten metal downward from a ladle to a tundish,
It has an inlet, a minimum diameter part, an enlarged diameter part, and an outlet,
the minimum diameter portion is located closer to the inlet than the outlet;
The expanded diameter portion is present from the minimum diameter portion to the outlet, and the inner diameter of the nozzle increases from the minimum diameter portion toward the outlet,
In the longitudinal cross-sectional shape of the nozzle, the angle θ between the inner wall surface of the nozzle at the enlarged diameter portion and the axis X of the nozzle is 5° or more and 10° or less;
Disclose.

In the long nozzle of the present disclosure, a ratio L ₁ /D ₂ of a length L ₁ from the minimum diameter portion to the outlet and an inner diameter D ₂ of the nozzle at the outlet is 2.0 or more. Good too.

In the long nozzle of the present disclosure, a ratio D ₁ /D ₂ of an inner diameter D ₁ of the nozzle at the minimum diameter portion to an inner diameter D ₂ of the nozzle at the outlet is 0.3 or more and 0.6 or less. Good too.

In the long nozzle of the present disclosure, in the longitudinal cross-sectional shape of the nozzle, the shape of the inner wall surface of the nozzle at the enlarged diameter portion may be at least one of a linear shape, a broken line shape, and a curved shape.

The long nozzle of the present disclosure may have a straight body portion between the inlet and the minimum diameter portion.

This application, as one of the means to solve the above problems,
A nozzle system for supplying molten metal downward from a ladle through a long nozzle to a tundish, the system comprising:
The long nozzle is the long nozzle of the present disclosure,
The outlet of the long nozzle is located below the liquid level of the molten metal in the tundish and above the bottom surface of the tundish,
A gas phase region containing an inert gas and a secondary meniscus of the molten metal are present inside the long nozzle,
The secondary meniscus is located closer to the outlet than the minimum diameter part,
Disclose.

In the nozzle system of the present disclosure, even if the ratio L _D /D ₂ between the immersion depth L _D of the long nozzle and the inner diameter D ₂ of the nozzle at the outlet is 1.6 or more and 2.2 or less. good.

In the nozzle system of the present disclosure, the height ΔH of the secondary meniscus defined by the following formula (1) may be greater than or equal to −10 cm and less than or equal to 20 cm.

ΔH=(P _T - P _L )/(ρ・g)...(1)
here,
P _T is the atmospheric pressure in the tundish,
P _L is the pressure of the gas phase region in the long nozzle,
ρ is the density of the molten metal,
g is the gravitational acceleration.

In the nozzle system of the present disclosure, the tundish may not have a weir inside.

According to the long nozzle of the present disclosure, when supplying molten metal downward from the ladle to the tundish, when the molten metal is struck into the secondary meniscus in the nozzle to generate a large number of bubbles, the bubbles are It is possible to efficiently collect it into the nozzle. This makes it easier to maintain a large number of bubbles in the nozzle, making it easier to reduce the flow rate of molten metal, and making it easier to prevent short passes and bare hot water from occurring in the tundish. As a result, the cleanliness of the molten metal tends to increase.

An example of a longitudinal cross-sectional shape of a long nozzle is schematically shown. FIG. 2 is a schematic diagram for explaining that air bubble collection efficiency is improved by forming a gas film on the enlarged diameter portion of the long nozzle. Another example of the longitudinal cross-sectional shape of the long nozzle is schematically shown. An example of the positional relationship of a ladle, a long nozzle, and a tundish is schematically shown. An example of a state in which molten metal is supplied from a ladle to a tundish via a long nozzle is schematically shown. 1 schematically illustrates problems in the prior art. The shape of the long nozzle used in Examples and Comparative Examples is schematically shown. In addition, in A, for the sake of clarity, the molten steel injection flow above the secondary meniscus is omitted, and the secondary meniscus position and the molten steel surface position in the tundish are shown.

1. Long Nozzle The long nozzle of the present disclosure is a cylindrical single-hole long nozzle for supplying molten metal downward from a ladle to a tundish. The long nozzle of the present disclosure has an inlet, a minimum diameter section, an expanded diameter section, and an outlet. Here, the minimum diameter portion exists closer to the inflow port than the outflow port, and the enlarged diameter portion exists from the minimum diameter portion to the outflow port, and the enlarged diameter portion exists from the minimum diameter portion to the outflow port. The inner diameter of the nozzle increases toward the exit. In the long nozzle of the present disclosure, in the longitudinal cross-sectional shape of the nozzle, the angle θ between the inner wall surface of the nozzle at the expanded diameter portion and the axis X of the nozzle is 5° or more and 10° or less.

FIGS. 1A and 1B schematically show an example of a longitudinal cross-sectional shape of a long nozzle. As shown in FIGS. 1(A) and 1(B), the long nozzle 10 according to one embodiment has an inlet 11, a minimum diameter portion 12, an enlarged diameter portion 13, and an outlet 14. The long nozzle 10 is a cylindrical single-hole nozzle having only one outlet 14. Although not shown, the opening shape of the long nozzle 10 (the cross-sectional shape perpendicular to the axis X of the nozzle) is basically circular. However, it does not have to be a perfect circle, and may be partially deformed as long as the desired effect can be obtained. In the long nozzle 10, the enlarged diameter portion 13 exists from the minimum diameter portion 12 to the outlet 14, in other words, the diameter increases from the minimum diameter portion 12 to the outlet 14. As shown in FIG. 1(A), in the long nozzle 10, an angle θ is provided between the nozzle inner wall surface in the enlarged diameter portion 13 and the nozzle axis X, and the angle θ is 5° or more and 10 It is considered to be within the range of ° or less. Note that when the long nozzle 10 is used, the axis X of the nozzle substantially coincides with the up-down direction (vertical direction). The long nozzle 10 may be made of a known refractory material.

1.1 Inflow Port The inflow port 11 is located at the upstream end of the long nozzle 10. The inlet 11 may be connected to another member (for example, the lower end of another nozzle, such as a collector nozzle, or the outlet of a ladle, etc.). The inner diameter of the nozzle at the inlet 11 may be substantially the same as the inner diameter of the nozzle at the minimum diameter portion 12, which will be described later, or may be different. The inner diameter D ₀ of the nozzle at the inlet 11 may be, for example, 50 mm or more, 70 mm or more, or 100 mm or more, or 200 mm or less, 170 mm or less, or 150 mm or less.

1.2 Minimum Diameter Portion The minimum diameter portion 12 is located closer to the inlet 11 than the outlet 14 . The position of the minimum diameter portion 12 may coincide with the position of the inlet 11, or may be located closer to the outlet 14 than the inlet 11. The inner diameter D ₁ of the nozzle at the minimum diameter portion 12 may be, for example, 50 mm or more, 70 mm or more, or 100 mm or more, or 200 mm or less, 170 mm or less, or 150 mm or less.

1.3 Expanded Diameter Portion The expanded diameter portion 13 exists from the minimum diameter portion 12 to the outlet 14 . That is, the long nozzle 10 is tapered from the minimum diameter portion 12 to the lower end of the nozzle. In this way, when the enlarged diameter part 13 exists from the minimum diameter part 12 to the outlet 14, the lower end of the long nozzle 10 is immersed in the molten metal in the tundish while Flowing molten metal into the nozzle at enlarged diameter section 13 may form a gas phase region and a secondary meniscus. When molten metal is supplied from the smallest diameter portion 12 to the secondary meniscus, the molten metal is driven into the secondary meniscus, and a large number of bubbles (bubble plume) can be generated. The generation of the bubble plume has various effects such as slowing down the flow rate of molten metal and raising non-metallic inclusions, so it is easy to suppress the occurrence of bare hot water and short paths in the tundish. Therefore, the cleanliness of the molten metal can be easily improved.

Here, when the angle θ at the enlarged diameter portion 13 is 5° or more and 10° or less, the following effects can be expected. That is, as shown in FIG. 2, when the molten metal is hammered into the secondary meniscus and a large number of bubbles are generated, when the bubbles in the molten metal rise, the bubbles are formed on the inner wall surface of the nozzle in the enlarged diameter section 13. A film is formed, and the film can be levitated at high speed. As a result, the bubbles generated in the molten metal can be quickly collected into the gas phase region within the nozzle, and the bubbles are less likely to flow out of the nozzle from the outlet 14 of the nozzle. As a result, the gas phase region, secondary meniscus, and bubble plume are more likely to be maintained within the nozzle, and the aforementioned effects of slowing down the flow rate of molten metal, raising nonmetallic inclusions, etc. are more likely to be exhibited. As a result, the occurrence of bare hot water and short passes in the tundish can be easily suppressed, and the cleanliness of the molten metal can be easily improved. Since the enlarged diameter portion 13 exists up to the outlet 14 of the nozzle, a gas film can be formed from the lower end of the nozzle, so that the efficiency of recovering air bubbles due to the formation of the gas film is further increased. When the angle θ is less than 5° or is negative (when the diameter is reduced), almost no gas film is formed, making it difficult to efficiently collect air bubbles. From the viewpoint of forming a gas film more easily, the angle θ may be 6° or more or 7° or more. On the other hand, if the angle θ is too large, although a gas film is formed, the floating speed of the gas film decreases and becomes slower than the floating speed of bubbles. According to the findings of the present inventors, when the angle θ is 10° or less, the floating speed of the film becomes faster than the floating speed of the bubbles, and the above-mentioned advantageous effects are more likely to be exhibited. Note that the reason why the floating speed of the gas film is faster than that of the bubbles is considered to be because the resistance during levitation is reduced due to the flat shape of the gas film.

In the longitudinal cross-sectional shape of the nozzle, the shape of the nozzle inner wall surface in the enlarged diameter portion 13 may be at least one of a linear shape, a broken line shape, and a curved shape. In other words, in the enlarged diameter portion 13, the nozzle inner diameter may be increased linearly (expanded monotonically) from the upstream side to the downstream side, or may be expanded in a curved manner. Further, in the enlarged diameter portion 13, the nozzle inner diameter may be continuously enlarged from the upstream side to the downstream side, or may be enlarged intermittently. FIG. 1 illustrates an example in which the angle θ at the enlarged diameter portion 13 is constant from upstream to downstream of the nozzle (in the longitudinal cross-sectional shape of the nozzle, the shape of the inner wall surface of the nozzle in the enlarged diameter portion 13 is linear). However, the angle θ at the enlarged diameter portion 13 may change from upstream to downstream of the nozzle. For example, in the enlarged diameter portion 13, the angle θ may increase continuously or intermittently from upstream to downstream of the nozzle. That is, as shown in FIG. 3, the enlarged diameter portion 13 has an angle θ ₁ on the upstream side and an angle θ ₂ on the downstream side, and the angle θ ₂ may be larger than the angle θ ₁ . . Alternatively, the angle θ may decrease continuously or intermittently from upstream to downstream of the nozzle (that is, θ ₁ >θ ₂ ). In any case, in the long nozzle of the present disclosure, the angle θ at the enlarged diameter portion is within a range of 5° or more and 10° or less. In other words, the long nozzle of the present disclosure does not have any portion where the angle θ is less than 5° or any portion where the angle θ is more than 10° from the minimum diameter portion 12 to the outlet 14.

The length _L1 from the minimum diameter portion 12 to the outlet 14 (total length of the enlarged diameter portion 13) may be, for example, 300 mm or more or 500 mm or more, or 1000 mm or less or 800 mm or less. The larger the total length _L1 of the enlarged diameter portion 13, the larger the volume from the secondary meniscus in the nozzle to the lower end of the nozzle, and the larger the bubble plume retention volume. Therefore, various effects such as the effect of reducing the flow rate of molten metal and the effect of elevating non-metallic inclusions become more easily obtained. On the other hand, if the total length _L1 of the enlarged diameter portion 13 is too large, these effects will be saturated and the nozzle weight will likely become excessively heavy.

1.4 Outlet The outlet 14 is located at the downstream end of the long nozzle 10. The outlet 14 is open to the molten metal in the tundish. The inner diameter _D2 of the nozzle at the outlet 14 may be any size as long as the above-mentioned angle θ is achieved. For example, it may be 100 mm or more, 130 mm or more, or 150 mm or more, and may be 350 mm or less, 330 mm or less, or 300 mm or less.

1.5 Straight body part As shown in FIGS. 1A and 1B, the long nozzle 10 may have a straight body part 15 between the inlet 11 and the minimum diameter part 12. The straight body portion refers to a portion where the inner diameter of the nozzle does not substantially change from upstream to downstream. In this case, the inner diameter of the nozzle may be substantially the same from the inlet 11 to the lower end of the straight body portion 15. The minimum diameter portion 12 may exist from the inlet 11 to the lower end of the straight body portion 15. By providing such a straight body part 15, the flow velocity and flow direction of the molten metal in the nozzle are stabilized, the gas phase region and the secondary meniscus in the nozzle are stabilized, and the downstream side of the straight body part 15 is stabilized. This makes it easier to generate bubble plumes. The length L ₀ of the straight body portion 15 may be, for example, 300 mm or more or 500 mm or more, or 1000 mm or less or 800 mm or less.

1.6 Full length of enlarged diameter part/outlet diameter In the long nozzle 10, the length from the minimum diameter part 12 to the outlet 14 (total length of the enlarged diameter part 13) _L1 , the inner diameter of the nozzle at the outlet 14 D2 _, and The ratio L ₁ /D ₂ is not particularly limited. From the viewpoint of more easily ensuring the above-mentioned effects of the enlarged diameter portion 13, the ratio L ₁ /D ₂ is 1.0 or more, 1.2 or more, 1.4 or more, 1.6 or more, 1.8 or more, or 2. It may be 0 or more.

1.7 Minimum Diameter/Outlet Aperture In the long nozzle 10, the ratio D ₁ /D ₂ of the inner diameter D ₁ of the nozzle at the minimum diameter portion 12 to the inner diameter D ₂ of the nozzle at the outlet 14 should be less than 1.0. Bye. However, if the ratio D ₁ /D ₂ is too small, it will be necessary to increase the total length L ₁ of the enlarged diameter portion 13 in order to satisfy the above angle θ. Moreover, if the ratio D ₁ /D ₂ is too large, it will be necessary to shorten the total length L ₁ of the enlarged diameter portion 13 in order to satisfy the above angle θ. From the viewpoint of more easily ensuring the above effect of the enlarged diameter portion 13, the ratio D ₁ /D ₂ may be 0.1 or more, 0.2 or more, or 0.3 or more, and 0.8 or less, 0.7. It may be less than or equal to 0.6.

1.8 Total Nozzle Length The total length L of the long nozzle 10 (the length from the inlet 11 to the outlet 14) may be, for example, 1000 mm or more or 1200 mm or more, or 1800 mm or less or 1600 mm or less.

2. Nozzle System The nozzle system of the present disclosure feeds molten metal downward from a ladle through a long nozzle and into a tundish. The long nozzle is the long nozzle of the present disclosure described above. In the nozzle system of the present disclosure, the outlet of the long nozzle is located below the liquid level of the molten metal in the tundish and above the bottom surface of the tundish, and is located inside the long nozzle. A gas phase region containing an inert gas and a secondary meniscus of the molten metal are present in the molten metal, and the secondary meniscus is located closer to the outlet (i.e., the enlarged diameter portion) than the minimum diameter portion.

4 and 5 schematically show the configuration of a nozzle system 100 according to one embodiment. As shown in FIGS. 4 and 5, nozzle system 100 supplies molten metal 105 downwardly from ladle 101 through long nozzle 10 to tundish 102. As shown in FIGS. As shown in FIGS. 4 and 5, the long nozzle 10 has an inlet 11 on the ladle 101 side that is the upstream side, and an outlet 14 on the tundish 102 side that is the downstream side. It is a cylindrical single-hole nozzle that extends downward toward the downstream side. Further, the outlet 14 of the long nozzle 10 is located below the liquid level 105a of the molten metal 105 in the tundish 102 and above the bottom surface 102a of the tundish 102. Further, in the nozzle system 100, a gas phase region 10a containing an inert gas and a secondary meniscus 10b of the molten metal 105 are present in the enlarged diameter portion 13 inside the long nozzle 10.

2.1 Ladle The ladle 101 is a container from which molten metal 105 is supplied to the tundish 102. As shown in FIGS. 4 and 5, in nozzle system 100, ladle 101 has a bottom surface 101a and side walls 101b, and holds molten metal 105. As shown in FIGS. Ladle 101 may further include a lid (not shown). The ladle 101 may be of any shape and material that can hold the molten metal 105. Further, the ladle 101 may be configured such that an outlet 101ax is provided in a part of the bottom surface 101a, and the molten metal 105 can flow out from the outlet 101ax. The outflow port 101ax may be provided with an opening/closing mechanism for controlling the outflow amount of the molten metal 105. The long nozzle 10 may be connected directly or indirectly to the outlet 101ax of the ladle 101. For example, as shown in FIG. 5, the long nozzle 10 may be connected to the outlet 101ax of the ladle 101 via a collector nozzle 111 or a sliding nozzle 112. The connection form between the ladle 101 and the nozzle is not particularly limited, and the connection can be made by fitting, for example. The ladle 101 and the nozzle may be connected via some intermediate member.

2.2 Tundish Tundish 102 is a container to which molten metal 105 from ladle 101 is supplied. As shown in FIGS. 4 and 5, the tundish 102 has a bottom surface 102a and a side wall 102b, and holds molten metal 105 supplied from the ladle 101. The tundish 102 may further include a lid 102c. The tundish 102 may be of any shape and material that can hold the molten metal 105. As shown in FIG. 4, a part of the bottom surface 102a of the tundish 102 may be provided with an outlet 102ax from which the molten metal 105 can flow out into another container (for example, a mold). may be configured. The outflow port 102ax may be provided with an opening/closing mechanism for controlling the outflow amount of the molten metal 105. A nozzle 120 (immersion nozzle) may be directly or indirectly connected to the outlet 102ax of the tundish 102. The connection form between the tundish 102 and the nozzle 120 is not particularly limited, and the connection can be made by fitting, for example. The tundish 102 and the nozzle 120 may be connected via some intermediate member.

As shown in FIG. 5, a floating layer 106 containing flux may be present on the liquid surface 105a of the molten metal 105 supplied to the tundish 102. Any known flux may be used as the flux. By covering the liquid surface 105a of the molten metal 105 with flux in this manner, the molten metal 105 can be shielded from the outside air. Furthermore, non-metallic inclusions in the molten metal 105 can be recovered by the flux. Furthermore, an inert gas may be supplied into the tundish 102 to prevent outside air from entering the tundish 102 as much as possible. Thereby, reoxidation of the molten metal 105 can be further suppressed. As will be described later, according to the nozzle system 100, the molten metal 105 flowing out from the long nozzle 10 collides with the bottom surface 102a of the tundish 102 due to the deceleration effect of the molten metal 105 due to the bubble plume, resulting in a reverse upward flow. (See Figure 6) can be kept small, the liquid level 105a of the tundish 102 is not easily disturbed, and the flux is not easily displaced or interrupted due to disturbances in the liquid level 105a, so the problem of reoxidation due to bare hot water is unlikely to occur. .

As shown in FIG. 4, the tundish 102 may not have a weir inside it. In the nozzle system 100 of the present disclosure, a secondary meniscus 10b is formed inside the long nozzle 10, and when the falling flow of molten metal 105 collides with the secondary meniscus 10b, a phenomenon in which a gas phase is involved (formation of a bubble plume) ), the downward flow velocity of the molten metal 105 is easily reduced, and the short path of the molten metal 105 in the tundish 102 (see FIG. 6) is also easily suppressed. It is easy to remove non-metallic inclusions, etc. contained in

2.3 Nozzle 2.3.1 Long Nozzle As shown in FIGS. 4 and 5, molten metal 105 is supplied from ladle 101 to tundish 102 via long nozzle 10. The details of the long nozzle 10 are as described above. Note that the long nozzle 10 is installed independently of the tundish 102 and does not need to be fixed to the tundish 102. In this respect, it can be said that the configurations of the injection pipe installed and fixed on the lid of the tundish and the long nozzle referred to in the present application are different.

As shown in FIGS. 4 and 5, the outlet 14 of the long nozzle 10 is located below the liquid level 105a of the molten metal 105 in the tundish 102 and above the bottom surface 102a of the tundish 102. . That is, the downstream end of the long nozzle 10 is immersed in the molten metal 105 inside the tundish 102 . As shown in FIG. 5, the nozzle system 100 may have an immersion depth L _D between the liquid level 105a of the molten metal 105 in the tundish 102 and the outlet 14 of the long nozzle 10. There may be a distance _LS between the outlet 14 of the long nozzle 10 and the bottom surface 102a of the tundish 102. The specific values of _LD and _LS and the relationship between _LD and _LS are not particularly limited. For example, _LD may be 100 mm or more, 150 mm or more, 200 mm or more, 250 mm or more, 300 mm or more, 350 mm or more, 400 mm or more, or 450 mm or more, and may be 750 mm or less, 700 mm or less, or 650 mm or less. Moreover, L _S may be 200 mm or more and 900 mm or less. Moreover, the ratio L _D /L _S of L _D and L _S may be 0.2 or more and 1.0 or less. Further, the ratio D ₂ /L _S between the nozzle inner diameter D ₂ and L _S at the outlet 14 may be 0.2 or more and 3.0 or less. Furthermore, the ratio L _D /D ₂ between the immersion depth L _D of the long nozzle and the inner diameter D ₂ of the nozzle at the outlet may be 1.6 or more and 2.2 or less. By adjusting L _D and L _S , it becomes easier to suppress bubbles from leaving the long nozzle 10 .

As shown in FIG. 4, the long nozzle 10 has a minimum inner diameter _D1 upstream of the secondary meniscus 10b, an inner diameter D _M at the secondary meniscus 10b, and a minimum inner diameter D1 downstream of the secondary meniscus 10b. The outlet 14 may have an inner diameter _D2 . Note that _DM may remain greater than _D1 and less than _D2 .

2.3.2 Collector Nozzle As shown in FIG. 5, in the nozzle system 100, a collector nozzle 111 may be provided upstream of the long nozzle 10. Collector nozzle 111 may be connected at its upstream end to ladle 101 directly or indirectly. Further, the downstream end of the collector nozzle 111 may be connected to the upstream end of the long nozzle 10. As shown in FIG. 5, the inner diameter of the lower end of the collector nozzle 111 may be smaller than the inner diameter _D0 of the inlet port 11 of the long nozzle 10. The specific value of the inner diameter _DC of the collector nozzle 111 is not particularly limited. For example, D _C and the above-mentioned D ₀ may satisfy the relationship 1.0≦D ₀ /D _C ≦1.4. That is, at the connection portion between the long nozzle 10 and the collector nozzle 111, the ratio D _{0 /} D _C of the inner diameter D ₀ (cm) of the long nozzle 10 to the inner diameter D C (cm) of the collector nozzle 111 is 1.0 or more. It may be 4 or less. If this ratio is too small, a step may occur at or near the connection between the long nozzle 10 and the collector nozzle 111 due to the diameter decreasing from the upstream side to the downstream side, resulting in leakage of the molten metal 105 and fireproofing. There is a risk of abnormal wear and tear on items. On the other hand, if this ratio is too large, the molten metal 105 tends to stick to the inner wall of the long nozzle 10 due to the influence of heat radiation from the side surface of the long nozzle 10. Moreover, there is also a possibility that the weight of the long nozzle 10 will increase unnecessarily. The collector nozzle 111 may be appropriately selected from conventionally known collector nozzles. The structure at the connection part between the long nozzle 10 and the collector nozzle 111 may be the same as the conventional one. For example, the connection portion may be formed by fitting the upper end of the long nozzle 10 and the lower end of the collector nozzle 111 into each other.

2.3.3 Sliding Nozzle As shown in FIG. 5, in the nozzle system 100, a flow rate adjustment mechanism 112 may be provided upstream of the collector nozzle 111. A specific example of the flow rate adjustment mechanism 112 is a sliding nozzle as shown in FIG. 5, for example. In the sliding nozzle, the flow path diameter can be changed by sliding at least one slide plate 112a having a flow port in a direction crossing the flow direction of the molten metal 105. Alternatively, the flow rate adjustment mechanism 112 may be an opening/closing mechanism other than a sliding nozzle. Since the form of the flow rate adjustment mechanism 112 is well known, further explanation will be omitted here.

2.4 Inert gas supply mechanism As shown in FIG. 5, in the nozzle system 100, inert gas is supplied from the outside to the inside of the long nozzle 10, and the inside of the long nozzle 10 contains the inert gas. A gas phase region 10a and a secondary meniscus 10b of molten metal 105 are formed. The method or means for supplying inert gas from the outside to the inside of the long nozzle 10 is not particularly limited. For example, as shown in FIG. 5, the nozzle system 100 may include an inert gas supply mechanism 113 that supplies inert gas from the outside to the inside of the long nozzle 10. Note that when the molten metal 105 is supplied from the ladle 101 to the tundish 102 via the nozzle, outside air is pumped into the long nozzle 10 by an ejector from the connection between the ladle 101 and the nozzle, the connection between the nozzles, etc. However, in the nozzle system 100, a mechanism 113 for intentionally supplying inert gas into the inside of the long nozzle 10 may be adopted. Alternatively, the gas phase region 10a and the secondary meniscus 10b may be formed only by the ejector described above without using the mechanism 113.

In the nozzle system 100, the gas phase region 10a and the secondary meniscus 10b are formed inside the long nozzle 10 while the molten metal 105 is being supplied, and the secondary meniscus height ΔH is maintained within a predetermined range. good. When the downward flow of the molten metal 105 collides with the secondary meniscus 10b, gas is drawn into the molten metal 105 from the gas phase region 10a, and bubble groups of various sizes can be generated in the molten metal 105. Since the nozzle system 100 has the mechanism 113 for supplying inert gas into the inside of the long nozzle 10, it becomes easier to maintain the gas phase region 10a inside the long nozzle 10, and the secondary meniscus height ΔH can also be controlled. It becomes easier. Examples of the inert gas include Ar. The amount of inert gas supplied to the long nozzle 10 is not particularly limited, and the pressure in the gas phase region 10a is also not particularly limited. The inert gas supply mechanism 113 may include a control section that controls the supply amount and pressure of the inert gas. For example, the inert gas supply valve may be controlled to open or close based on a signal or the like from the control unit, and the supply amount and pressure of the inert gas may be controlled to a target value.

The specific form of the mechanism 113 that supplies inert gas into the long nozzle 10 is not limited. For example, the mechanism 113 may be configured by directly or indirectly connecting an inert gas supply source (a container filled with high-pressure inert gas, etc.) and the long nozzle 10 via piping, valves, etc. obtain. Alternatively, the molten metal 105 to which the inert gas has been supplied can be It may also be configured to flow into the nozzle 10. However, when the inert gas supply mechanism 113 is connected directly to the long nozzle 10 or when it is connected near the long nozzle 10, the amount of inert gas blown into the long nozzle 10 can be reduced. Easier to control. For example, the position where the inert gas is supplied by the mechanism 113 described above may be at or near the connection between the long nozzle 10 and the collector nozzle 111, and specifically, within a range of 100 mm from the connection. It's okay. Within this range, it is easy to install the mechanism 113 described above. Further, by supplying the inert gas within this range, it becomes easier to form the gas phase region 10a inside the long nozzle 10. Alternatively, the inert gas supply mechanism 113 may be provided upstream of the enlarged diameter portion 13 of the long nozzle 10 or in the enlarged diameter portion 13 .

The nozzle system 100 is configured such that the secondary meniscus height ΔH defined by the following formula (1) is -10 cm or more and 20 cm or less, for example, by controlling the pressure in the gas phase region 10a. It's okay. ΔH may be -5 cm or more, 0 cm or more, or 15 cm or less.

ΔH=(P _T - P _L )/(ρ・g)...(1)
here,
P _T is the atmospheric pressure in the tundish,
P _L is the pressure of the gas phase region in the long nozzle,
ρ is the density of the molten metal,
g is the gravitational acceleration.

As shown in FIG. 5, ΔH corresponds to the difference between the height position of the secondary meniscus 10b inside the long nozzle 10 and the height position of the liquid level 105a of the molten metal 105 in the tundish 102. As shown in the above equation (1), in the nozzle system 100, the higher the pressure in the gas phase region 10a inside the long nozzle 10, the smaller ΔH becomes. The case where ΔH is 0 cm corresponds to the case where the pressure in the gas phase region 10a matches the atmospheric pressure in the tundish 102. In the nozzle system 100, if ΔH becomes excessively negative (if the pressure in the gas phase region 10a inside the long nozzle 10 is excessively positive with respect to the atmospheric pressure in the tundish 102), the secondary The volume of the long nozzle 10 from the meniscus 10b to the outlet 14 decreases, making it difficult for the bubble plume to exert its effects, and also working against the retention of bubbles within the long nozzle 10 in some cases. On the other hand, if the pressure in the gas phase region 10a of the long nozzle 10 is excessively reduced, it becomes difficult to maintain airtightness, and outside air is likely to be sucked in. In addition, when ΔH becomes excessively large, the free fall distance of the molten metal 105 becomes short, and the collision force when the downward flow of the molten metal 105 collides with the secondary meniscus 10b decreases, causing the molten metal to fall from the gas phase region 10a. There is a possibility that gas entrainment into 105 will be reduced and the amount of bubble plume generated will be reduced. By controlling the pressure in the gas phase region 10a so that ΔH is preferably -10 cm or more, more preferably -5 cm or more, and still more preferably 0 cm or more, the distance between the secondary meniscus 10b and the outlet 14 is long. A sufficient volume of the nozzle 10 can be secured, the effects of the bubble plume can be exerted, and the bubbles can be more easily held in the long nozzle 10. As a result, the occurrence of bare hot water and short passes in the tundish 102 is further suppressed, and the cleanliness of the molten metal 105 can be further improved. On the other hand, by controlling the pressure in the gas phase region 10a so that the secondary meniscus height ΔH is preferably 20 cm or less, the gas phase region 10a does not have an excessively negative pressure, and the intake of outside air is suppressed. As a result, reoxidation of the molten metal is further suppressed, and the cleanliness of the molten metal 105 can be further improved.

The atmospheric pressure P _T inside the tundish 102 necessary for calculating equation (1) can be measured with a pressure gauge installed in a pipe leading to the inside of the tundish 102 . Similarly, the pressure P _L in the gas phase region 10a inside the long nozzle 10 is determined by boring a flow path in the refractory material and connecting it to the flow path. It can be measured with a pressure gauge. Alternatively, the relationship between the flow rate of the inert gas supplied to the inside of the long nozzle 10 and the pressure P _L of the gas phase region 10a inside the long nozzle 10 is determined by a preliminary experiment, and P L is determined from the flow rate of the inert gas supplied. It is also possible to make it possible to estimate _L. Note that when calculating ΔH using equation (1), the units are all set to SI units. The unit of the obtained ΔH is m, which may be converted to cm.

The pressure in the gas phase region 10a may be measured continuously or intermittently using the above-mentioned pressure gauge, etc., and the amount of inert gas supplied to the gas phase region 10a may be increased or decreased according to the measured pressure. Thus, the secondary meniscus height ΔH can be controlled. Specifically, in the nozzle system 100, when the pressure in the gas phase region 10a is higher than the first threshold, the amount of inert gas supplied to the gas phase region 10a decreases, and the pressure in the gas phase region 10a decreases. It may be configured such that the pressure decreases. Further, in the nozzle system 100, when the pressure in the gas phase region 10a is lower than the second threshold, the amount of inert gas supplied to the gas phase region 10a increases, and the pressure in the gas phase region increases. It may be configured to do so. The supply amount of the inert gas can be controlled, for example, by controlling the on-off valve by the control unit as described above. Note that the "first threshold value" is not particularly limited, and an appropriate threshold value may be set, for example, based on the pressure at which the above-mentioned ΔH is equal to or greater than a predetermined value. Further, the "second threshold value" is not particularly limited either, and may be set as an appropriate threshold value, for example, based on the pressure at which the above-mentioned ΔH is equal to or less than a predetermined value. The first threshold value and the second threshold value may be different threshold values from each other, or may be the same threshold value.

Alternatively, by making the gas phase region 10a and the atmosphere in the tundish 102 communicate with each other, the pressure in the gas phase region 10a can be made to match the atmosphere in the tundish 102, and as a result, ΔH becomes 0 cm. In this regard, in the nozzle system 100, the long nozzle 10 may have at least one communication hole (not shown), so that the gas phase region 10a in the long nozzle 10 and the atmosphere in the tundish 102, They may be configured to be able to communicate with each other via the communication hole. As mentioned above, the tundish 102 may be configured to have an inert gas supplied therein to prevent outside air from entering the tundish 102 as much as possible. In this case, (1) the gas phase region 10a may be always open in the tundish 102 through the communication hole to maintain the secondary meniscus height ΔH at 0 cm, or (2) the gas phase region When the pressure in the gas phase region 10a is higher than the first threshold, the inert gas may be discharged from the gas phase region 10a into the tundish 102 through the communication hole; Inert gas may be supplied from inside the tundish 102 to the gas phase region 10a via the communication hole when the pressure in the region 10a is lower than the second threshold. That is, the communication hole may be open at all times between the gas phase region 10a and the atmosphere in the tundish 102, or may be opened and closed by a valve or the like. The size and number of communicating holes are not particularly limited. In the nozzle system 100, for example, when the pressure in the gas phase region 10a in the long nozzle 10 becomes excessively high, the gas phase region 10a may be opened to the outside air, but in this case, In order to prevent the intake of outside air into the long nozzle 10 and the reoxidation of the molten metal 105, some kind of device (for example, providing a check valve) is required.

2.5 Other configurations and conditions In the nozzle system 100, configurations and conditions other than those described above are not particularly limited. Examples of other conditions and configurations are shown below.

2.5.1 Flow rate of molten metal and average residence time in the tundish The flow rate Q of the molten metal 105 supplied to the long nozzle 10 may be, for example, 8000 cm ³ /s or more, and the molten metal in the tundish 102 The average residence time τ of 105 may be, for example, 240 seconds or more. The effect of reducing the flow rate of molten metal 105 in nozzle system 100 is particularly useful in high productivity continuous casting where large flows of molten metal 105 pass through the tundish. Specifically, this is a case where the flow rate Q of the molten metal 105 is 8000 cm ³ /s or more. Furthermore, it is still useful if the flow rate is 18000 cm ³ /s or more. Although the upper limit of the flow rate is not particularly limited, continuous casting exceeding 40,000 cm ³ /s is not realistic. This is because other processes cannot follow such a high production rate. On the other hand, if the average residence time τ in the tundish 102 is too short, it may be difficult to obtain a sufficient cleaning effect for the molten metal 105. It is considered that by setting the same time to 240 seconds or more, inclusions of, for example, about 50 to 100 microns can be easily removed by flotation. Although the upper limit of the same time is not particularly limited, it is not realistic for the same time to exceed 1500 seconds during steady operation of continuous casting. This is because if the average residence time is too long, the temperature of the molten metal 105 in the tundish 102 will decrease too much. Note that the average residence time τ can be calculated as the ratio V _τ /Q of the volume V _τ (cm ³ ) of the tundish 102 and the flow rate Q (cm ³ /s) of molten metal from the nozzle.

2.5.2 Weir in the Tundish As described above, in the nozzle system 100, there is no need to provide a weir having a function of controlling the flow of the molten metal 105 inside the tundish 102. According to the nozzle system 100, it is possible to ensure the residence time of the molten metal 105 inside the tundish 102 without using a weir. Rather, if a weir is installed in the tundish 102, there is a problem that a stagnation area called a dead zone is formed, which reduces the actual tundish capacity, and that the cost increases.

2.5.3 Height Dimension The height dimension of the nozzle system 100 is not particularly limited. The same dimension is determined from the distance between the collector nozzle 111 on the ladle 101 side and the liquid level 105a of the tundish 102, and the immersion depth of the long nozzle 10, and is often approximately 1 m to 2.5 m.

2.5.4 Type of Molten Metal There is no particular restriction on the type of molten metal 105 supplied from the ladle 101 to the tundish 102 via the long nozzle 10. In particular, when the molten metal 105 is molten steel, high effects can be expected from the technology of the present disclosure. The steel type of the molten steel is not particularly limited.

3. Functions and Effects As described above, according to the long nozzle 10 of the present disclosure and the nozzle system 100 using the same, when the molten metal 105 is struck into the secondary meniscus 10b and a large number of bubbles are generated, the When the bubble rises, a gas film is formed on the inner wall of the enlarged diameter portion 13, and the gas film can be floated at high speed. Thereby, the bubbles generated in the molten metal 105 can be quickly collected into the gas phase region 10a inside the nozzle, making it difficult for the bubbles to flow out of the nozzle from the outlet 14 of the nozzle. As a result, it becomes easier to maintain the gas phase region 10a, secondary meniscus 10b, and bubble plume appropriately within the nozzle, and the effect of slowing down the flow velocity of the molten metal 105 and raising nonmetallic inclusions is exhibited, and the tank The occurrence of bare hot water and short passes in the dish 102 can be more easily suppressed, and the cleanliness of the molten metal 105 can be more easily improved.

4. Method for Continuous Casting of Molten Metal The technology of the present disclosure also has an aspect as a method for continuous casting of molten metal. The continuous casting method of molten metal of the present disclosure is characterized by using the nozzle system 100 of the present disclosure. The continuous casting method of the present disclosure includes, for example, supplying molten metal 105 from a ladle 101 to a tundish 102 via a long nozzle 10 using a nozzle system 100, and supplying molten metal 105 from a tundish 102 via a nozzle 120 to a mold. (not shown) and continuously withdrawing the slab from the mold. In the method for continuous casting of molten metal of the present disclosure, general continuous casting conditions may be employed, except that the nozzle system 100 described above is employed. Alternatively, as described above, the flow rate Q and the average residence time τ may be adjusted to be equal to or greater than a predetermined value.

5. Supplementary note: In order to search for the above-mentioned various indicators and their appropriate ranges, it is possible to utilize the experimental device disclosed in Patent No. 6750533 by the present applicant. The experimental device is a device that can faithfully reproduce the effects of gravity, inertia force, viscous force, and surface tension that act on molten metal flow, and can accurately reproduce gas-liquid two-phase flow phenomena, including bubble buoyancy and floating speed. It is.

The present invention will be further described below with reference to Examples, but the present invention is not limited to the following Examples. The present invention allows various conditions to be adopted as long as the purpose is achieved without departing from the gist thereof.

1. Conditions Continuous casting of steel was performed using a system as shown in Figures 4 and 5. As the long nozzle, one having one of the shapes A to C shown in FIG. 7 was adopted. Further, the throughput Q of molten steel during continuous casting was set to 5 ton/min or 10 ton/min (12000 cm ³ /s or 23800 cm ³ /s). Further, the lower end of the long nozzle was immersed in the molten steel in the tundish to an immersion depth _LD . Furthermore, during continuous casting, the secondary meniscus height ΔH inside the long nozzle was controlled by supplying inert gas into the inside of the long nozzle as needed. Table 1 below shows the continuous casting conditions for each of the examples and comparative examples. Further, Table 2 below shows the composition of the slabs employed in the Examples and Comparative Examples.

In addition, the "steel cleanliness index" in Table 1 refers to the inclusion concentration in a slab solidified to a thickness of 250 mm and a width of 1800 mm. Total amount of oxides in 5 mm square x 50 mm long samples collected from 6 locations: 1/4 thickness, 3/4 thickness at center width, 1/4 width at 3/4 thickness, 3/4 width at 3/4 thickness. The values analyzed as follows are indexed with the value of Comparative Example 4 shown later set as 10. The smaller the index, the higher the cleanliness of the molten steel.

When the air bubbles in the nozzle flow out of the nozzle, the air bubbles rise to the surface of the tundish and cause naked water (boiling water). The "bubble recovery rate" in Table 1 is obtained by photographing the occurrence of hot water with a camera and evaluating the extent of the occurrence using the following criteria.
〇: Hot water does not occur at all △: Hot water sometimes occurs ×: Hot water always occurs

2. Results For Examples 1 to 4, the angle θ (θ1, θ2) at the expanded diameter part of the long nozzle was 5° or more and 10° or less, and when the molten metal was struck into the secondary meniscus and a large number of bubbles were generated. In addition, when the bubbles in the molten metal rose, a gas film was formed on the inner wall of the enlarged diameter portion, and the gas film was able to float at high speed. As a result, the bubbles generated in the molten metal could be quickly collected into the gas phase region within the nozzle, and the bubbles could be prevented from flowing out of the nozzle from the outlet of the nozzle. As a result, a gas phase region, a secondary meniscus, and a bubble plume are maintained within the nozzle, which has the effect of slowing down the flow rate of molten steel and lifting nonmetallic inclusions. This suppresses the occurrence of short passes and improves the cleanliness of the steel. In addition, since the enlarged diameter portion existed up to the outlet of the nozzle, a gas film was formed from the lower end of the nozzle, and the efficiency of collecting air bubbles due to the formation of the gas film was further increased. On the other hand, for Comparative Examples 1 to 4, the angle θ (θ1, θ2) at the enlarged diameter part of the long nozzle was less than 5° or more than 10°, so the molten steel throughput was small and large. In both cases, hot water occurred and the cleanliness of the steel deteriorated. Specifically, in Comparative Examples 1 and 2, since the lower end of the nozzle is a straight body part (θ2 = 0°), it is not possible to generate a gas film at the lower end of the nozzle, and the air bubbles cannot be efficiently generated. could not be recovered. In Comparative Examples 3 and 4, the angle of the enlarged diameter portion was too large, 20°, so although a gas film was formed, the floating speed of the gas film was lower than that of the bubbles.

Furthermore, when using a long nozzle that does not have an expanded diameter section (for example, a straight nozzle), it is not possible to stably maintain the gas phase region and the secondary meniscus within the long nozzle, resulting in the formation of air bubbles due to the pounding of molten steel. was difficult. In order to stably maintain the gas phase region and the secondary meniscus within the long nozzle, it is preferable that the long nozzle has an enlarged diameter section downstream of the minimum diameter section.

From the above results, according to the following long nozzle (1) and nozzle system (2), when molten metal is supplied downward from the ladle to the tundish, the molten metal is struck into the secondary meniscus in the long nozzle. When a large number of bubbles are generated, it is possible to efficiently collect the bubbles into the gas phase region within the nozzle. This makes it easier to maintain the gas phase region, secondary meniscus, and bubble plume within the nozzle, making it easier to reduce the flow rate of molten metal, and making it easier to suppress short passes and bare hot water in the tundish. As a result, the cleanliness of the molten metal tends to increase.

(1) A long cylindrical single-hole nozzle for supplying molten metal downward from a ladle to a tundish,
It has an inlet, a minimum diameter part, an enlarged diameter part, and an outlet,
the minimum diameter portion is located closer to the inlet than the outlet;
The expanded diameter portion is present from the minimum diameter portion to the outlet, and the inner diameter of the nozzle increases from the minimum diameter portion toward the outlet,
In the longitudinal cross-sectional shape of the nozzle, the angle θ between the inner wall surface of the nozzle at the enlarged diameter portion and the axis X of the nozzle is 5° or more and 10° or less.
(2) A nozzle system for supplying molten metal downward from a ladle to a tundish via a long nozzle,
The long nozzle is as described above,
The outlet of the long nozzle is located below the liquid level of the molten metal in the tundish and above the bottom surface of the tundish,
A gas phase region containing an inert gas and a secondary meniscus of the molten metal are present inside the long nozzle,
The secondary meniscus is located closer to the outlet than the minimum diameter portion.

10 Long nozzle 11 Inflow port 12 Minimum diameter portion 13 Expanded diameter portion 14 Outlet port 15 Straight body portion 100 Nozzle system 101 Ladle 101a Bottom surface 101b Side wall 102 Tundish 102a Bottom surface 102b Side wall 102c Lid 105 Molten metal 111 Collector nozzle 11 2 Flow rate adjustment mechanism (Sliding nozzle)
112a Slide plate 113 Inert gas supply mechanism 120 Nozzle

Claims (9)

A cylindrical single-hole long nozzle for supplying molten metal downward from a ladle to a tundish,
It has an inlet, a minimum diameter part, an enlarged diameter part, and an outlet,
the minimum diameter portion is located closer to the inlet than the outlet;
The expanded diameter portion is present from the minimum diameter portion to the outlet, and the inner diameter of the nozzle increases from the minimum diameter portion toward the outlet,
In the longitudinal cross-sectional shape of the nozzle, an angle θ between the inner wall surface of the nozzle at the enlarged diameter portion and the axis X of the nozzle is 5° or more and 10° or less;
long nozzle. The ratio L ₁ /D ₂ of the length L ₁ from the minimum diameter portion to the outlet and the inner diameter D ₂ of the nozzle at the outlet is 2.0 or more;
The long nozzle according to claim 1. The ratio D ₁ /D ₂ of the inner diameter D ₁ of the nozzle at the minimum diameter portion and the inner diameter D ₂ of the nozzle at the outlet is 0.3 or more and 0.6 or less.
The long nozzle according to claim 1 or 2. In the longitudinal cross-sectional shape of the nozzle, the shape of the inner wall surface of the nozzle at the enlarged diameter portion is at least one of a linear shape, a broken line shape, and a curved shape.
The long nozzle according to any one of claims 1 to 3. having a straight body portion between the inflow port and the minimum diameter portion;
The long nozzle according to any one of claims 1 to 4. A nozzle system for supplying molten metal downward from a ladle through a long nozzle to a tundish, the system comprising:
The long nozzle is the long nozzle according to any one of claims 1 to 5,
The outlet of the long nozzle is located below the liquid level of the molten metal in the tundish and above the bottom surface of the tundish,
A gas phase region containing an inert gas and a secondary meniscus of the molten metal are present inside the long nozzle,
the secondary meniscus is present closer to the outlet than the minimum diameter portion;
nozzle system. The ratio L _D /D ₂ of the immersion depth L _D of the long nozzle to the inner diameter D ₂ of the nozzle at the outlet is 1.6 or more and 2.2 or less;
A nozzle system according to claim 6. The height ΔH of the secondary meniscus defined by the following formula (1) is -10 cm or more and 20 cm or less,
A nozzle system according to claim 6 or 7.
ΔH=(P _T - P _L )/(ρ・g)...(1)
here,
P _T is the atmospheric pressure in the tundish,
P _L is the pressure of the gas phase region in the long nozzle,
ρ is the density of the molten metal,
g is the gravitational acceleration. The tundish does not have a weir inside;
Nozzle system according to any one of claims 6 to 8.

Images