Long nozzle and nozzle system, and continuous casting method for molten metal.

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

[Technical Field]

[0001] This invention discloses a long nozzle for supplying molten metal from a ladle to a tundish, and a nozzle system using the same. [Background technology]

[0002] In the continuous casting process of molten metal, a tundish is used as an intermediate container to supply molten metal from the ladle to the mold. For example, in the case of continuous casting of steel, the tundish has several functions, including (1) stabilizing the amount of molten steel supplied to the mold, (2) distributing molten steel to multiple molds, (3) acting as a buffer to continuously carry out continuous casting using multiple molten steel volcanoes, and (4) removing non-metallic inclusions. In particular, when efficiently producing high-grade steel with a high degree of cleanliness, the function of removing non-metallic inclusions (4) is extremely important.

[0003] Nonmetallic inclusions in molten steel primarily originate from impurities in the steel, such as oxides, nitrides, sulfides, and bubbles, which are generated during the steelmaking process. If such nonmetallic inclusions remain in the final product, they are known to degrade the material quality of the final product, for example, by becoming the starting point for fracture due to stress concentration. Furthermore, in the steelmaking process itself, nonmetallic inclusions can adhere to and accumulate on the inner walls of refractory channels, causing narrowing and blockage of the channels. This not only hinders smooth production but can also cause defects in both the surface and interior of the base material during processing such as casting, reducing product yield and thus increasing manufacturing costs. Therefore, in most cases, nonmetallic inclusions need to be removed from the molten steel during the limited processes from secondary refining, where the final adjustment of the molten steel composition takes place, to the molding stage.

[0004] To remove nonmetallic inclusions from molten steel, a common method involves using the difference in specific gravity between the molten steel and the nonmetallic inclusions to cause them to float to the surface, and then recovering them in a suspended oxide layer called flux. However, it is known that the floating rate decreases as the size of the nonmetallic inclusions decreases, and the time required to recover them in the flux layer becomes longer. Therefore, to reduce nonmetallic inclusions in molten steel, it is considered effective to increase the residence time of nonmetallic inclusions in the tundish in order to ensure the necessary time for the nonmetallic inclusions to float to the surface.

[0005] Generally, molten steel is supplied from the ladle to the tundish by utilizing potential energy through a sliding nozzle with a flow rate adjustment function and a long nozzle, which is a cylindrical refractory material whose lower end is immersed in the molten steel in the tundish. However, because the high-speed discharge flow from the long nozzle can collide with the bottom of the tundish, forming a short-circuit flow towards the mold called a short path (see Figure 6), ensuring sufficient residence time for the molten steel in the tundish is not always easy. A common solution to this problem is to create a weir inside the tundish to divert the molten steel flow. However, constructing a refractory material inside the tundish increases material costs, construction time, and workload. Furthermore, it creates a space near the weir where there is little flow and does not contribute to the removal of inclusions by flotation. In addition, a new high-speed flow towards the mold may be induced even while diverting, so it does not necessarily help the inclusions to float to the surface. In particular, small inclusions have low buoyancy and tend to follow the flow of molten steel, so the effect of bypassing them tends to be limited to the removal of larger inclusions.

[0006] Furthermore, in the steelmaking process, attention must be paid to the unintentional increase in nonmetallic inclusions due to the reoxidation of molten steel. Generally, to avoid difficulties in stable casting due to gas generation as the temperature of the molten steel decreases, molten steel used in continuous casting undergoes deoxidation treatment in the refining process, resulting in an oxygen concentration significantly below the soluble oxygen concentration, making it highly susceptible to oxygen absorption. When molten steel comes into contact with air or lower oxides, the molten steel absorbs oxygen, and a reoxidation phenomenon occurs in which nonmetallic inclusions are generated when the molten steel combines with elements that have a higher affinity for oxygen than the molten steel (such as Al and Si dissolved in the molten steel). Therefore, in molten steel pits and tundishes, it is necessary to either create a low oxygen concentration inside the tundish by replacing the atmosphere with an inert gas, or to isolate the molten steel from the outside air by coating the surface of the molten steel with a low-reactivity flux containing a small amount of lower oxides. However, when molten steel is supplied to the tundish using a long nozzle, as described above, the molten steel flow discharged from the nozzle is at a very high speed. As a result, the flux covering the molten steel surface near the long nozzle is pushed aside by the reverse upward flow generated when it collides with the bottom of the tundish, and the molten steel surface is directly exposed to the outside air as bare molten steel, which can cause a re-oxidation phenomenon in which the molten steel absorbs oxygen from the atmosphere (see Figure 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 re-oxidation of the molten steel by the lower oxides in the slag can occur due to the intense molten steel flow near the long nozzle.

[0007] Conventionally, various means have been proposed to solve the above problems. For example, Patent Document 1 discloses a continuous casting method using an injection pipe that isolates the injection flow from the outside air with a refractory cylindrical body with an inner diameter of 300 mm or more. According to the technology disclosed in Patent Document 1, it is thought that the injection flow falling from the nozzle can introduce a large number of bubbles into the molten steel by striking the gas inside the pipe at the liquid surface inside the pipe, and the large buoyancy of the bubbles reduces the injection flow velocity, thereby creating a gentle upward flow in the tundish. In addition, solid inclusions have poor wettability with the molten steel and easily adhere to the bubbles, so it is expected that they will float up and be removed at high speed by the large buoyancy of the bubbles. On the other hand, in an injection pipe like the one described above, if molten steel splashes released from the ladle nozzle or molten steel scattered on the surface of the bath adhere to the inner wall of the pipe, the heat dissipation of the adhering material is significant due to the large pipe diameter, and the adhering material tends to solidify and accumulate, leading to blockage. This is a major problem that makes it difficult to continue continuous casting operations. In addition, with injection pipes, it is necessary to fill the inside of the pipe with a large amount of inert gas to prevent the molten steel from absorbing oxygen and nitrogen from the gas phase, which results in significantly higher operating costs compared to immersing a long nozzle in the molten steel.

[0008] Patent Document 2 discloses a nozzle equipped with a flow control unit on its body to prevent exposure of bare molten metal due to the upward flow reversed at the bottom of the tundish. However, the technology disclosed in Patent Document 2 requires separate measures to prevent short passes, which increases manufacturing costs. In addition, the increased weight of the nozzle places a heavy load on the device that grips the nozzle, potentially causing it to become unable to support the nozzle during casting, and potentially leading to molten steel gushing out from the joint of the long nozzle.

[0009] In Patent Document 3, a gas space of an inert gas is formed inside an injection nozzle, an inert gas is entrained in an injection flow at the molten steel surface in the nozzle, and the injection flow is stirred in a stirring box installed at the bottom of the tundish, thereby promoting the aggregation of inclusions and bubbles in the molten steel. A continuous casting method and a continuous casting apparatus are disclosed. In the technique disclosed in Patent Document 3, since the inner diameter of the discharge hole of the injection nozzle of the continuous casting apparatus is sufficiently large, a gas space is stably formed. On the other hand, in the technique disclosed in Patent Document 3, in order to avoid the problem that all the bubbles entrained in the injection flow re-float into the injection nozzle and the stirring action in the stirring box is not sufficiently exerted, the inner diameter of the injection nozzle is set to be less than or equal to a predetermined value. However, the bubbles that have left the injection nozzle and floated on the molten steel surface of the tundish can cause re-oxidation as described above. There is also a problem that the cost of the stirring box and the construction labor are high.

[0010] As a long nozzle for supplying molten steel from a ladle to a tundish, for example, a straight nozzle having no enlarged diameter portion as disclosed in Patent Document 3, or a nozzle having an enlarged diameter portion (conical portion) as disclosed in Patent Documents 2 and 4 is known. However, in a conventional long nozzle, the occurrence of bare molten steel and short paths in the tundish may not be sufficiently suppressed.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0012] When supplying molten metal from a ladle to a tundish via a long nozzle, it is believed that the flow velocity of the molten metal can be reduced by forming a gas phase region and a liquid surface (secondary meniscus) of molten metal within the long nozzle, and by striking the molten metal into this surface to generate numerous bubbles, thereby suppressing the occurrence of the aforementioned short passes and bare molten metal. 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 detaching from the long nozzle as much as possible, and to efficiently recover the generated bubbles into the gas phase region. This invention discloses a long nozzle for supplying molten metal downward from a ladle to a tundish, which is capable of efficiently recovering bubbles within the nozzle when molten metal is struck into the secondary meniscus within the nozzle to generate numerous bubbles. [Means for solving the problem]

[0013] This application is one means of solving the above problem, A cylindrical, single-hole long nozzle for supplying molten metal downwards from a ladle to a tundish, It has an inlet, a minimum diameter section, a widened diameter section, and an outlet, The minimum diameter portion is located on the inlet side of the outlet side, The enlarged diameter portion extends from the minimum diameter portion to the outlet, and the inner diameter of the nozzle expands from the minimum diameter portion towards the outlet. In the longitudinal cross-sectional shape of the nozzle, the angle θ between the inner wall surface of the nozzle and the nozzle axis X in the enlarged diameter portion is 5° or more and 10° or less. Disclose the following.

[0014] In the long nozzle of this disclosure, the ratio L1 / D2 of the length L1 from the minimum diameter portion to the outlet to the inner diameter D2 of the nozzle at the outlet may be 2.0 or greater.

[0015] In the long nozzle of this disclosure, the ratio D1 / D2 of the inner diameter D1 of the nozzle at the minimum diameter portion to the inner diameter D2 of the nozzle at the outlet portion may be 0.3 or more and 0.6 or less.

[0016] In the long nozzle of this disclosure, the shape of the inner wall surface of the nozzle in the enlarged diameter portion may be at least one of the following shapes: straight, folded, and curved.

[0017] The long nozzle of this disclosure may have a straight body portion between the inlet and the minimum diameter portion.

[0018] This application is one means of solving the above problem, A nozzle system for supplying molten metal downwards from a ladle to a tundish via a long nozzle, The long nozzle is the long nozzle of the present disclosure 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. Inside the long nozzle, there is a gaseous region containing an inert gas and a secondary meniscus of the molten metal. The secondary meniscus is located on the outlet side of the minimum diameter portion. Disclose the following.

[0019] In the nozzle system disclosed herein, the immersion depth L of the long nozzle D The ratio L of the inner diameter D2 of the nozzle at the outlet. D / D2 may be between 1.6 and 2.2.

[0020] In the nozzle system of this disclosure, the height ΔH of the secondary meniscus, as defined by the following formula (1), may be -10 cm or more and 20 cm or less.

[0021] ΔH=(P T -P L ) / (ρ·g) …(1) Here, P T This is the atmospheric pressure inside the tundish, P L This is the pressure in the gas phase region within the long nozzle, ρ is the density of the molten metal, g is the acceleration due to gravity.

[0022] In the nozzle system of this disclosure, the tundish may not have a weir inside. [Effects of the Invention]

[0023] According to the long nozzle of this disclosure, when molten metal is supplied downward from the ladle to the tundish, if the molten metal is struck into the secondary meniscus within the nozzle to generate numerous bubbles, these bubbles can be efficiently collected within the nozzle. This makes it easier to maintain a large number of bubbles within the nozzle, reduces the flow rate of the molten metal, and suppresses the occurrence of short passes and bare molten metal in the tundish. As a result, the cleanliness of the molten metal is more easily improved. [Brief explanation of the drawing]

[0024] [Figure 1] A schematic example of the longitudinal cross-sectional shape of a long nozzle is shown. [Figure 2] This is a schematic diagram illustrating how the formation of a gas film in the enlarged diameter portion of the long nozzle improves bubble recovery efficiency. [Figure 3] Another example of the longitudinal cross-sectional shape of a long nozzle is schematically shown. [Figure 4] This diagram schematically shows an example of the relative positions of the ladle, long nozzle, and tundish. [Figure 5] This diagram schematically illustrates an example of supplying molten metal from a ladle to a tundish via a long nozzle. [Figure 6] This outlines the challenges of conventional technologies. [Figure 7]The shapes of the long nozzles used in the examples and comparative examples are schematically shown. In A, for clarity, the molten steel injection flow above the secondary meniscus is omitted, while the position of the secondary meniscus and the molten steel surface position in the tundish are shown. [Modes for carrying out the invention]

[0025] 1. Long nozzle The long nozzle of this disclosure is a cylindrical, single-hole long nozzle for supplying molten metal downward from a ladle to a tundish. The long nozzle of this disclosure has an inlet, a minimum diameter section, an enlarged diameter section, and an outlet. Here, the minimum diameter section is located closer to the inlet than the outlet, and the enlarged diameter section extends from the minimum diameter section to the outlet, with the inner diameter of the nozzle increasing from the minimum diameter section toward the outlet. In the long nozzle of this disclosure, in the longitudinal cross-sectional shape of the nozzle, the angle θ between the inner wall surface of the nozzle in the enlarged diameter section and the axis X of the nozzle is 5° or more and 10° or less.

[0026] Figures 1(A) and (B) schematically show an example of the longitudinal cross-sectional shape of a long nozzle. As shown in Figures 1(A) and (B), a long nozzle 10 according to one embodiment has an inlet 11, a minimum diameter section 12, an enlarged diameter section 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 nozzle axis X) is basically circular. However, it does not need to be a perfect circle, and some deformation may be applied as long as the desired effect is obtained. In the long nozzle 10, the enlarged diameter section 13 exists from the minimum diameter section 12 to the outlet 14, in other words, it is tapered from the minimum diameter section 12 to the outlet 14. As shown in Figure 1(A), in the long nozzle 10, an angle θ is provided between the inner wall surface of the nozzle in the enlarged diameter section 13 and the nozzle axis X, and this angle θ is within the range of 5° to 10°. Furthermore, when using the long nozzle 10, the nozzle axis X substantially coincides with the vertical direction. The long nozzle 10 may be made of known refractory materials or the like.

[0027] 1.1 Inlet The inlet 11 is located at the upstream end of the long nozzle 10. The inlet 11 may be connected to other components (for example, the lower end of other nozzles 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 or different from the inner diameter of the nozzle at the minimum diameter section 12, which will be described later. The inner diameter D0 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.

[0028] 1.2 Minimum diameter The minimum diameter portion 12 is located on the inlet side 11 rather than the outlet 14. The position of the minimum diameter portion 12 may coincide with the position of the inlet 11, or it may be located on the outlet side 14 rather than the inlet 11. The inner diameter D1 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.

[0029] 1.3 Expanded diameter section The enlarged diameter section 13 extends from the minimum diameter section 12 to the outlet 14. In other words, the long nozzle 10 is tapered from the minimum diameter section 12 to the lower end of the nozzle. When the enlarged diameter section 13 extends from the minimum diameter section 12 to the outlet 14, and the lower end of the long nozzle 10 is immersed in the molten metal in the tundish while the molten metal is flowed from the minimum diameter section 12 to the outlet 14, a gas phase region and a secondary meniscus can be formed within the nozzle in the enlarged diameter section 13. When molten metal is supplied from the minimum diameter section 12 to the secondary meniscus, the molten metal is hammered into the secondary meniscus, and a large number of bubbles (bubble plumes) can be generated. The generation of these bubble plumes has various effects, such as slowing down the flow velocity of the molten metal and increasing the amount of non-metallic inclusions. As a result, the occurrence of bare molten metal and short paths in the tundish is easily suppressed, and the cleanliness of the molten metal is easily improved.

[0030] Here, if the angle θ in the enlarged diameter section 13 is between 5° and 10°, the following effects can be expected. That is, as shown in Figure 2, when molten metal is hammered into the secondary meniscus and a large number of bubbles are generated, as these bubbles rise in the molten metal, a gas film is formed on the inner wall surface of the nozzle in the enlarged diameter section 13, and this gas film can be made to float up at high speed. As a result, the bubbles generated in the molten metal can be quickly recovered into the gas phase region inside the nozzle, and the bubbles are less likely to flow out of the nozzle from the nozzle outlet 14. As a result, the gas phase region, secondary meniscus, and bubble plume are more easily maintained inside the nozzle, and the effects of slowing down the flow velocity of the molten metal and raising non-metallic inclusions are more easily exerted. As a result, the occurrence of bare molten metal and short passes in the tundish is more easily suppressed, and the cleanliness of the molten metal is more easily improved. Because the enlarged diameter section 13 extends to the nozzle outlet 14, a gas film can be formed from the lower end of the nozzle, further increasing the efficiency of bubble recovery through gas film formation. When the angle θ is less than 5° or negative (when the diameter is reduced), almost no gas film is formed, making it difficult to efficiently recover bubbles. From the viewpoint of making it easier to form a gas film, the angle θ may be 6° or more, or 7° or more. On the other hand, if the angle θ is too large, a gas film is formed, but the floating velocity of the gas film decreases, and becomes slower than the floating velocity of the bubbles. According to the inventor's findings, when the angle θ is 10° or less, the floating velocity of the gas film becomes faster than the floating velocity of the bubbles, and the above-mentioned advantageous effects are more easily achieved. It is thought that the reason why the floating velocity of the gas film becomes faster than the floating velocity of the bubbles is due to the fact that the gas film is flattened, which reduces the resistance during floating.

[0031] In the longitudinal cross-sectional shape of the nozzle, the shape of the inner wall surface of the nozzle in the enlarged diameter section 13 may be at least one of the following shapes: linear, polylinear, and curved. In other words, in the enlarged diameter section 13, the inner diameter of the nozzle may expand linearly (monotonically) from the upstream side to the downstream side, or it may expand curved. Furthermore, in the enlarged diameter section 13, the inner diameter of the nozzle may expand continuously from the upstream side to the downstream side, or it may expand intermittently. Figure 1 illustrates a configuration in which the angle θ in the enlarged diameter section 13 is constant from the upstream to the downstream side of the nozzle (a configuration in which the shape of the inner wall surface of the nozzle in the enlarged diameter section 13 is linear in the longitudinal cross-sectional shape of the nozzle), but the angle θ in the enlarged diameter section 13 may change from the upstream to the downstream side of the nozzle. For example, in the enlarged diameter section 13, the angle θ may increase continuously or intermittently as you move from the upstream to the downstream side of the nozzle. That is, as shown in Figure 3, the enlarged diameter section 13 has an angle θ1 on the upstream side and an angle θ2 on the downstream side, and angle θ2 may be greater than angle θ1. Alternatively, the angle θ may decrease continuously or intermittently as you move from the upstream to the downstream side of the nozzle (i.e., θ1 > θ2). In any case, in the long nozzle of this disclosure, the angle θ in the enlarged diameter section is within the range of 5° to 10°. In other words, the long nozzle of this disclosure does not have any sections between the minimum diameter section 12 and the outlet 14 where the angle θ is less than 5° or where the angle θ is greater than 10°.

[0032] The length L1 from the minimum diameter section 12 to the outlet 14 (total length of the enlarged diameter section 13) may be, for example, 300 mm or more, 500 mm or more, or 1000 mm or less, or 800 mm or less. The larger the total length L1 of the enlarged diameter section 13, the larger the volume from the secondary meniscus in the nozzle to the lower end of the nozzle tends to be, and the larger the volume of the bubble plume that can be held. As a result, various effects such as the effect of slowing down the flow velocity of the molten metal and the effect of raising non-metallic inclusions become more pronounced. On the other hand, if the total length L1 of the enlarged diameter section 13 is too large, these effects will saturate, and the nozzle weight tends to become excessively heavy.

[0033] 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 can be any size that achieves the angle θ described above. For example, it may be 100 mm or more, 130 mm or more, or 150 mm or more, and it may be 350 mm or less, 330 mm or less, or 300 mm or less.

[0034] 1.5 Straight body part As shown in Figures 1(A) and (B), the long nozzle 10 may have a straight section 15 between the inlet 11 and the minimum diameter section 12. The straight section refers to the part of the nozzle where there is no substantial change in the inner diameter 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 section 15. The minimum diameter section 12 may exist from the inlet 11 to the lower end of the straight section 15. By providing such a straight section 15, the flow velocity and flow direction of the molten metal in the nozzle are stabilized, the gas phase region and secondary meniscus in the nozzle are stabilized, and it becomes easier to stably generate a bubble plume downstream of the straight section 15. The length L0 of the straight section 15 may be, for example, 300 mm or more or 500 mm or more, or 1000 mm or less or 800 mm or less.

[0035] 1.6 Enlarged diameter section total length / outlet diameter In the long nozzle 10, the ratio L1 / D2 between the length L1 from the minimum diameter portion 12 to the outlet 14 (total length of the enlarged diameter portion 13) and the inner diameter D2 of the nozzle at the outlet 14 is not particularly limited. From the viewpoint of making it easier to ensure the above effect by the enlarged diameter portion 13, the ratio L1 / D2 may be 1.0 or more, 1.2 or more, 1.4 or more, 1.6 or more, 1.8 or more, or 2.0 or more.

[0036] 1.7 Minimum diameter / outlet diameter In the long nozzle 10, the ratio D1 / D2 between the inner diameter D1 of the nozzle at the minimum diameter section 12 and the inner diameter D2 of the nozzle at the outlet 14 should be less than 1.0. However, if the ratio D1 / D2 is too small, it becomes necessary to lengthen the total length L1 of the enlarged diameter section 13 in order to satisfy the angle θ. Conversely, if the ratio D1 / D2 is too large, it becomes necessary to shorten the total length L1 of the enlarged diameter section 13 in order to satisfy the angle θ. From the viewpoint of making it easier to secure the above effect by the enlarged diameter section 13, the ratio D1 / D2 may be 0.1 or more, 0.2 or more, or 0.3 or more, and may be 0.8 or less, 0.7 or less, or 0.6 or less.

[0037] 1.8 Nozzle total length The total length L of the long nozzle 10 (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.

[0038] 2. Nozzle System The nozzle system of the present disclosure supplies molten metal downward from a ladle to a tundish via a long nozzle. 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 a gas phase region containing an inert gas and a secondary meniscus of the molten metal exist inside the long nozzle, and the secondary meniscus is located on the outlet side (i.e., the widened diameter portion) of the minimum diameter portion.

[0039] Figures 4 and 5 schematically show the configuration of a nozzle system 100 according to one embodiment. As shown in Figures 4 and 5, the nozzle system 100 supplies molten metal 105 downward from the ladle 101 to the tundish 102 via the long nozzle 10. As shown in Figures 4 and 5, the long nozzle 10 is a cylindrical single-hole nozzle that has an inlet 11 on the upstream side, the ladle 101 side, and an outlet 14 on the downstream side, the tundish 102 side, and extends downward from the upstream side to the downstream side. 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. In the nozzle system 100, a gas phase region 10a containing an inert gas and a secondary meniscus 10b of the molten metal 105 exist in the enlarged diameter portion 13 inside the long nozzle 10.

[0040] 2.1 Ladle The ladle 101 is a container that supplies molten metal 105 to the tundish 102. As shown in Figures 4 and 5, in the nozzle system 100, the ladle 101 has a bottom surface 101a and side walls 101b to hold the molten metal 105. The ladle 101 may further have a lid (not shown). The ladle 101 is only required to be of a shape and material capable of holding the molten metal 105. The ladle 101 may also be configured to have an outlet 101ax provided in a part of the bottom surface 101a, from which the molten metal 105 can be discharged. The outlet 101ax may be provided with an opening and closing mechanism for controlling the amount of molten metal 105 discharged. A long nozzle 10 can be directly or indirectly connected to the outlet 101ax of the ladle 101. For example, as shown in Figure 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 method between the ladle 101 and the nozzle is not particularly limited, and they can be connected, for example, by fitting. The ladle 101 and the nozzle may also be connected via some kind of intermediate member.

[0041] 2.2 Tan Dish The tundish 102 is a container that receives the molten metal 105 from the ladle 101. As shown in Figures 4 and 5, the tundish 102 has a bottom surface 102a and side walls 102b to hold the molten metal 105 supplied from the ladle 101. The tundish 102 may further have a lid 102c. The tundish 102 may be made of a shape and material capable of holding the molten metal 105. As shown in Figure 4, a part of the bottom surface 102a of the tundish 102 may be provided with an outlet 102ax, which may be configured to allow the molten metal 105 to flow out to another container (e.g., a mold). The outlet 102ax may be provided with an opening and closing mechanism for controlling the amount of molten metal 105 that flows out. A nozzle 120 (immersion nozzle) may be directly or indirectly connected to the outlet 102ax of the tundish 102. The connection method between the tundish 102 and the nozzle 120 is not particularly limited; for example, they can be connected by fitting. The tundish 102 and the nozzle 120 may also be connected via some kind of intermediate member.

[0042] As shown in Figure 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. By covering the liquid surface 105a of the molten metal 105 with flux in this way, the molten metal 105 can be isolated from the outside air. In addition, nonmetallic 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. This can further suppress the re-oxidation of the molten metal 105. Furthermore, as will be described later, the nozzle system 100 allows for a reduction in the upward reversal flow (see Figure 6) caused by the molten metal 105 flowing out of the long nozzle 10 colliding with the bottom surface 102a of the tundish 102, due to the deceleration effect of the bubble plume on the molten metal 105. This makes it less likely for the liquid surface 105a of the tundish 102 to be disturbed, and less likely for the flux to be pushed aside or interrupted due to disturbance of the liquid surface 105a, thus reducing the problem of re-oxidation by the bare molten metal.

[0043] As shown in Figure 4, the tundish 102 may not have a weir inside. In the nozzle system 100 of this 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, the phenomenon of entrainment of the gas phase (formation of a bubble plume) easily reduces the downward flow velocity of the molten metal 105, and short passes of the molten metal 105 in the tundish 102 (see Figure 6) are also easily suppressed. As a result, nonmetallic inclusions and the like contained in the molten metal 105 can be easily removed without providing a weir inside the tundish 102.

[0044] 2.3 Nozzle 2.3.1 Long Nozzle As shown in FIGS. 4 and 5, the molten metal 105 is supplied from the ladle 101 to the tundish 102 through the long nozzle 10. The details of the long nozzle 10 are as described above. Incidentally, the long nozzle 10 is installed independently of the tundish 102 and does not need to be fixed to the tundish 102. In this regard, it can be said that the configuration of the injection pipe installed and fixed on the lid of the tundish is different from that of the long nozzle referred to in the present application.

[0045] 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 tip of the long nozzle 10 on the downstream side is immersed in the molten metal 105 inside the tundish 102. As shown in FIG. 5, in the nozzle system 100, there may be an immersion depth L between the liquid level 105a of the molten metal 105 in the tundish 102 and the outlet 14 of the long nozzle 10. D There may also be a distance L between the outlet 14 of the long nozzle 10 and the bottom surface 102a of the tundish 102. S There may be. L D or L S The specific values of and L D and L S The relationship between and is not particularly limited. For example, L D 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. Also, L S may be 200 mm or more and 900 mm or less. Also, L D and L S The ratio L D / L S may be 0.2 or more and 1.0 or less. Also, the ratio D2 / L S between the nozzle inner diameter D2 at the outlet 14 and L S may be 0.2 or more and 3.0 or less. Furthermore, the immersion depth L of the long nozzle DThe ratio L of the inner diameter D2 of the nozzle at the outlet. D / D2 may be between 1.6 and 2.2. D Ya L S By adjusting this setting, the detachment of air bubbles from the long nozzle 10 becomes even easier to suppress.

[0046] As shown in Figure 4, the long nozzle 10 has the smallest inner diameter D1 upstream of the secondary meniscus 10b, and the inner diameter D M It may have an inner diameter D2 at the outlet 14 downstream of the secondary meniscus 10b. M It can remain between D1 and D2.

[0047] 2.3.2 Collector Nozzle As shown in Figure 5, in the nozzle system 100, a collector nozzle 111 may be provided upstream of the long nozzle 10. The upstream end of the collector nozzle 111 may be directly or indirectly connected to the ladle 101. The downstream end of the collector nozzle 111 may be connected to the upstream end of the long nozzle 10. As shown in Figure 5, the inner diameter of the lower end of the collector nozzle 111 may be smaller than the inner diameter D0 of the inlet 11 of the long nozzle 10. Inner diameter D of the collector nozzle 111 C The specific value of D is not particularly limited. For example, D C And the above-mentioned D0 is 1.0 ≤ D0 / D C The relationship ≤ 1.4 may also be satisfied. That is, at the connection between the long nozzle 10 and the collector nozzle 111, the inner diameter D of the collector nozzle 111 C The ratio of the inner diameter D0 (cm) of the long nozzle 10 to (cm) is D0 / D CThe ratio may be between 1.0 and 1.4. 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 a decrease in diameter from the upstream side to the downstream side, which may cause leakage of molten metal 105 or abnormal wear of the refractory material. On the other hand, if this ratio is too large, the molten metal 105 is more likely to adhere to the inner wall of the long nozzle 10 due to heat dissipation from the side of the long nozzle 10. There is also a risk 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 of the connection between the long nozzle 10 and the collector nozzle 111 may be the same as in the conventional design. For example, the connection may be formed by fitting the upper end of the long nozzle 10 and the lower end of the collector nozzle 111 together.

[0048] 2.3.3 Sliding Nozzle As shown in Figure 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 Figure 5. In a sliding nozzle, the flow path diameter can be changed by sliding at least one slide plate 112a having a flow port in a direction intersecting 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. As the form of the flow rate adjustment mechanism 112 is well known, further explanation is omitted here.

[0049] 2.4 Inert Gas Supply Mechanism As shown in Figure 5, in the nozzle system 100, an inert gas is supplied from the outside to the inside of the long nozzle 10, forming a gas phase region 10a containing the inert gas and a secondary meniscus 10b of molten metal 105 inside the long nozzle 10. The method and means of supplying the inert gas from the outside to the inside of the long nozzle 10 are not particularly limited. For example, as shown in Figure 5, the nozzle system 100 may have an inert gas supply mechanism 113 that supplies the inert gas from the outside to the inside of the long nozzle 10. When supplying molten metal 105 from the ladle 101 to the tundish 102 via the nozzle, outside air may be drawn into the long nozzle 10 by an ejector from the connection between the ladle 101 and the nozzle or the connection between the nozzles themselves. However, in the nozzle system 100, a mechanism 113 may be employed to intentionally supply an inert gas into the long nozzle 10 separately from this. Alternatively, the gas phase region 10a and the secondary meniscus 10b may be formed solely by the ejector without using the mechanism 113.

[0050] In the nozzle system 100, a gas phase region 10a and a secondary meniscus 10b may be formed inside the long nozzle 10 during the supply of molten metal 105, and the secondary meniscus height ΔH may be maintained within a predetermined range. When the downward flow of molten metal 105 collides with the secondary meniscus 10b, gas is drawn into the molten metal 105 from the gas phase region 10a, and various sizes of bubbles may be generated in the molten metal 105. By having a mechanism 113 that supplies inert gas to the inside of the long nozzle 100, it becomes easier to maintain the gas phase region 10a inside the long nozzle 10, and the control of the secondary meniscus height ΔH also becomes easier. Examples of inert gas include Ar. The amount of inert gas supplied to the long nozzle 10 is not particularly limited, nor is the pressure in the gas phase region 10a. The inert gas supply mechanism 113 may include a control unit that controls the amount and pressure of the inert gas supply. For example, based on signals from the control unit, the opening and closing of the inert gas supply valve can be controlled, and the amount and pressure of the inert gas supplied can be controlled to target values.

[0051] The specific form of the mechanism 113 for supplying inert gas into the long nozzle 10 is not limited. For example, the mechanism 113 can be configured by directly or indirectly connecting an inert gas supply source (such as a container filled with high-pressure inert gas) to the long nozzle 10 via piping, valves, etc. Alternatively, the inert gas supply source may be connected to a location upstream of the long nozzle 10 (for example, a collector nozzle 111, a sliding nozzle 112, or a ladle 101) so that the molten metal 105 supplied with inert gas flows into the long nozzle 10. However, if the inert gas supply mechanism 113 is directly connected to the long nozzle 10 or connected near the long nozzle 10, it becomes easier to control the amount of inert gas blown into the long nozzle 10. For example, the location where the inert gas is supplied by the mechanism 113 may be at or near the connection point between the long nozzle 10 and the collector nozzle 111, and specifically, it may be within a range of 100 mm from the connection point. Within this range, the mechanism 113 is easy to install. Furthermore, supplying an inert gas within this range makes it easier to form a gas phase region 10a inside the long nozzle 10. Alternatively, the inert gas supply mechanism 113 may be provided upstream of or within the enlarged diameter portion 13 of the long nozzle 10.

[0052] In the nozzle system 100, for example, the pressure in the gas phase region 10a may be controlled so that the secondary meniscus height ΔH, defined by the following formula (1), is between -10 cm and 20 cm. ΔH may be between -5 cm and 0 cm, or between 15 cm and 15 cm.

[0053] ΔH=(P T -P L ) / (ρ·g) …(1) Here, P T This is the atmospheric pressure inside the tundish, P L This is the pressure in the gas phase region within the long nozzle, ρ is the density of the molten metal, g is the acceleration due to gravity.

[0054] As shown in Figure 5, ΔH corresponds to the difference between the height of the secondary meniscus 10b inside the long nozzle 10 and the height of the liquid surface 105a of the molten metal 105 in the tundish 102. As shown in equation (1) above, in the nozzle system 100, the higher the pressure in the gas phase region 10a inside the long nozzle 10, the smaller ΔH becomes. When ΔH is 0 cm, it corresponds to the case where the pressure in the gas phase region 10a matches the atmospheric pressure inside the tundish 102. In the nozzle system 100, if ΔH becomes excessively negative (when the pressure in the gas phase region 10a inside the long nozzle 10 is excessively positive relative to the atmospheric pressure inside the tundish 102), the volume of the long nozzle 10 from the secondary meniscus 10b to the outlet 14 decreases, making it difficult for the effect of the bubble plume to be exerted, and may also have an unfavorable effect on retaining bubbles inside the long nozzle 10. 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, making it easier for outside air to be drawn in. Also, if ΔH becomes excessively large, the free fall distance of the molten metal 105 is shortened, the impact force when the downward flow of molten metal 105 collides with the secondary meniscus 10b decreases, the entrainment of gas from the gas phase region 10a into the molten metal 105 decreases, and there is a risk that the amount of bubble plume generated will decrease. 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 even more preferably 0 cm or more, the volume of the long nozzle 10 can be sufficiently secured between the secondary meniscus 10b and the outlet 14, the effect of the bubble plume is exerted, and it becomes easier to retain bubbles within the long nozzle 10. As a result, the occurrence of bare molten metal and short paths 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 become excessively negative, the intake of outside air is suppressed, and as a result the re-oxidation of the molten metal is further suppressed, and the cleanliness of the molten metal 105 can be further improved.

[0055] The atmospheric pressure P inside the tundish 102 is required for the calculation of equation (1). T This can be measured by a pressure gauge installed in piping leading to the inside of the tundish 102. Furthermore, the pressure P in the gas phase region 10a inside the long nozzle 10 can also be measured. L Similarly, it is possible to measure the flow rate of the inert gas supplied to the inside of the long nozzle 10 and the pressure P of the gas phase region 10a inside the long nozzle 10 by drilling a passage in the refractory material and installing a pressure gauge on a pipe connected to that passage. Alternatively, preliminary experiments can determine the flow rate of the inert gas supplied to the inside of the long nozzle 10 and the pressure P of the gas phase region 10a inside the long nozzle 10. L Determine the relationship between and and and P from the supply flow rate of the inert gas L It is acceptable to leave it in a state where it can be estimated. When calculating ΔH using equation (1), make sure all units are in SI units. The unit of the obtained ΔH will be m, but this can be converted to cm.

[0056] The pressure in the gas phase region 10a can be measured continuously or intermittently using the pressure gauge described above, and the secondary meniscus height ΔH can be controlled by increasing or decreasing the amount of inert gas supplied to the gas phase region 10a according to the measured pressure. Specifically, the nozzle system 100 may be configured such that when the pressure in the gas phase region 10a is higher than a first threshold, the amount of inert gas supplied to the gas phase region 10a decreases, thereby lowering the pressure in the gas phase region. Alternatively, the nozzle system 100 may be configured such that when the pressure in the gas phase region 10a is lower than a second threshold, the amount of inert gas supplied to the gas phase region 10a increases, thereby raising the pressure in the gas phase region. The amount of inert gas supplied can be controlled, for example, by controlling an on / off valve by the control unit as described above. The "first threshold" is not particularly limited; for example, an appropriate threshold can be set based on the pressure at which the above-mentioned ΔH exceeds a predetermined level. Furthermore, the "second threshold" is not particularly limited; for example, any appropriate threshold can be set based on the pressure at which the above-mentioned ΔH falls below a predetermined level. The first threshold and the second threshold may be different from each other, or they may be the same.

[0057] Alternatively, by connecting the gas phase region 10a and the atmosphere inside the tundish 102, the pressure in the gas phase region 10a can be matched with the atmosphere inside the tundish 102, resulting in ΔH being 0 cm. In this regard, the nozzle system 100 may have at least one communication hole (not shown), and the gas phase region 10a inside the long nozzle 10 and the atmosphere inside the tundish 102 may be configured to communicate with each other through this communication hole. As described above, the tundish 102 may be configured such that an inert gas is supplied inside it to prevent outside air from entering the tundish 102 as much as possible. In this case, (1) the gas phase region 10a may be kept open to the tundish 102 at all times through the communication holes, thereby maintaining the secondary meniscus height ΔH at all times at 0 cm; (2) when the pressure in the gas phase region 10a is higher than a first threshold, inert gas may be discharged from the gas phase region 10a to the tundish 102 through the communication holes; or (3) when the pressure in the gas phase region 10a is lower than a second threshold, inert gas may be supplied from the tundish 102 to the gas phase region 10a through the communication holes. That is, the communication holes may be kept open at all times between the gas phase region 10a and the atmosphere inside the tundish 102, or they may be controlled to open and close by valves or the like. The size and number of communication holes are not particularly limited. Furthermore, in the nozzle system 100, for example, if the pressure in the gas phase region 10a inside the long nozzle 10 becomes excessively high, the gas phase region 10a may be opened to the outside air. However, in this case, some measures (for example, providing a check valve) will be necessary to prevent outside air from being taken into the long nozzle 10 and to prevent the re-oxidation of the molten metal 105.

[0058] 2.5 Other Configurations and Conditions In the nozzle system 100, the configuration and conditions other than those described above are not particularly limited. Examples of other conditions and configurations are shown below.

[0059] 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 is, for example, 8000 cm³. 3 The average residence time τ of the molten metal 105 in the tundish 102 may be 240 seconds or more, and the average residence time τ of the molten metal 105 in the tundish 102 may be 240 seconds or more. The effect of reducing the flow velocity of the molten metal 105 in the nozzle system 100 is particularly useful in high-productivity continuous casting where a large flow rate of molten metal 105 passes through the tundish. Specifically, when the flow rate Q of the molten metal 105 is 8000 cm³ 3 This is the case when the flow rate is 18,000 cm³ or more. 3 It is even more useful if the flow rate is 40,000 cm³ or higher. While there is no particular upper limit to the flow rate, it is generally 40,000 cm³. 3 Continuous casting exceeding / s is not practical because other processes cannot keep up with such a high production speed. 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 on the molten metal 105. It is thought that if the residence time is 240 seconds or more, even inclusions of about 50 to 100 microns can be easily removed by flotation. There is no particular upper limit to the residence time, but it is not practical for the residence time to exceed 1500 seconds during steady operation of continuous casting. This is because if the average residence time is too long, the temperature drop of the molten metal 105 in the tundish 102 will be too large. The average residence time τ is calculated based on the capacity V of the tundish 102. τ (cm 3 ) and the flow rate Q (cm) of molten metal from the nozzle 3 V (ratio of / s) τ It can be calculated as / Q.

[0060] 2.5.2 Weir in the tundish As described above, in the nozzle system 100, there is no need to install a weir inside the tundish 102 that has a flow control function for the molten metal 105. With 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, installing a weir in the tundish 102 creates a stagnant area called a dead zone, which reduces the effective tundish capacity, and also increases costs.

[0061] 2.5.3 Height Dimensions The height dimension of the nozzle system 100 is not particularly limited. This dimension is determined by the distance between the collector nozzle 111 on the ladle side 101 and the liquid surface 105a of the tundish 102, and the immersion depth of the long nozzle 10, and is generally between 1m and 2.5m.

[0062] 2.5.4 Types of molten metals There are no particular restrictions on the type of molten metal 105 supplied from the ladle 101 to the tundish 102 via the long nozzle 10. In particular, the technology of this disclosure can be expected to be highly effective when the molten metal 105 is molten steel. The type of steel used for the molten steel is not particularly limited.

[0063] 3. Action and Effects As described above, with the long nozzle 10 and nozzle system 100 using the same, when molten metal 105 is hammered into the secondary meniscus 10b and a large number of bubbles are generated, a gas film is formed on the inner wall of the enlarged diameter portion 13 as the bubbles in the molten metal 105 rise, and the gas film can be made to float up at high speed. As a result, the bubbles generated in the molten metal 105 can be quickly collected into the gas phase region 10a inside the nozzle, and the bubbles are less likely to flow out of the nozzle from the nozzle outlet 14. As a result, it becomes easier to properly maintain the gas phase region 10a, the secondary meniscus 10b, and the bubble plume inside the nozzle, and effects such as slowing down the flow velocity of the molten metal 105 and raising non-metallic inclusions are exhibited, making it easier to suppress the occurrence of bare molten metal and short paths in the tundish 102, and making it easier to improve the cleanliness of the molten metal 105.

[0064] 4. Continuous casting method of molten metal The technology of this disclosure also has aspects as a continuous casting method for molten metal. The continuous casting method for molten metal of this disclosure is characterized by the use of the nozzle system 100 of this disclosure. The continuous casting method of this disclosure may include, for example, supplying molten metal 105 from a ladle 101 to a tundish 102 via a long nozzle 10 using the nozzle system 100, supplying molten metal 105 from the tundish 102 to a mold (not shown) via a nozzle 120, and continuously drawing cast slabs from the mold. In the continuous casting method for molten metal of this disclosure, general continuous casting conditions may be employed, except for the use of the nozzle system 100 described above. Alternatively, as described above, the flow rate Q and the average residence time τ may be adjusted to be above a predetermined level.

[0065] 5. Supplement Furthermore, the experimental apparatus described in Patent No. 6750533 by the present applicant can be used to explore the various indicators mentioned above and their appropriate ranges. This experimental apparatus faithfully reproduces the effects of gravity, inertial force, viscous force, and surface tension acting on molten metal flow, and can accurately reproduce gas-liquid two-phase flow phenomena, including the buoyancy and rising velocity of bubbles. [Examples]

[0066] 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 for the adoption of various conditions without departing from its essence and insofar as it achieves its objective.

[0067] 1.Conditions Continuous casting of steel was performed using the system shown in Figures 4 and 5. For the long nozzle, one of the shapes A to C shown in Figure 7 was used. Furthermore, the molten steel throughput Q during continuous casting was set to 5 ton / min or 10 ton / min (12,000 cm³). 3 / s or 23800cm 3 The setting was adjusted to be / s). In addition, the lower end of the long nozzle was immersed in the molten steel in the tundish to a depth L. DThe slabs were immersed in [a specific solution]. Furthermore, during continuous casting, the secondary meniscus height ΔH inside the long nozzle was controlled by supplying an inert gas to the inside of the long nozzle as needed. Table 1 below shows the continuous casting conditions for each of the examples and comparative examples. Table 2 below shows the composition of the cast slabs used in the examples and comparative examples.

[0068] In Table 1, the "Steel Cleanliness Index" refers to the total amount of oxides in 5mm x 50mm samples taken from six locations: 1 / 4 thickness in the center of the width, 1 / 4 thickness in the 1 / 4 width, 1 / 4 thickness in the 3 / 4 width, 3 / 4 thickness in the center of the width, 3 / 4 thickness in the 1 / 4 width, and 3 / 4 thickness in the 3 / 4 width. This value is then indexed with the value of Comparative Example 4, shown later, set to 10. A smaller index indicates higher molten steel cleanliness.

[0069] When bubbles inside the nozzle escape, they float to the surface of the tundish water, causing the water to boil (sudden boiling). The "bubble recovery rate" in Table 1 is evaluated based on the degree of boiling, which was captured by a camera, according to the following criteria. ○: No water boiling occurs at all. △: The water boils occasionally. ×: Hot water is constantly being generated.

[0070] [Table 1]

[0071] [Table 2]

[0072] 2.Results In Examples 1-4, the angle θ(θ1, θ2) at the enlarged diameter section of the long nozzle was between 5° and 10°. When molten metal was hammered into the secondary meniscus and numerous bubbles were generated, a gas film was formed on the inner wall of the enlarged diameter section as the bubbles rose in the molten metal, and this gas film could be rapidly lifted. As a result, the bubbles generated in the molten metal could be quickly recovered into the gas phase region within the nozzle, and the outflow of bubbles from the nozzle outlet was suppressed. Consequently, the gas phase region, secondary meniscus, and bubble plume were maintained within the nozzle, resulting in effects such as slowing the flow rate of molten steel and raising non-metallic inclusions. This suppressed the occurrence of bare molten metal (boiling) and short passes in the tundish, and improved the cleanliness of the steel. Furthermore, because the enlarged diameter section extended to the nozzle outlet, a gas film was formed from the lower end of the nozzle, further increasing the efficiency of bubble recovery through gas film formation. In contrast, in Comparative Examples 1-4, the angle θ(θ1, θ2) at the enlarged diameter section of the long nozzle was less than 5° or greater than 10°. As a result, boiling occurred and the cleanliness of the steel deteriorated in both cases, regardless of whether the molten steel throughput was low or high. Specifically, in Comparative Examples 1 and 2, the lower end of the nozzle was a straight section (θ2=0°), making it impossible to form a gas film at the lower end of the nozzle, and thus air bubbles could not be efficiently collected. In Comparative Examples 3 and 4, the angle of the enlarged diameter section was too large at 20°, so although a gas film was formed, the buoyancy rate of the gas film was actually lower than that of the air bubbles.

[0073] Furthermore, when a long nozzle without an enlarged diameter section (for example, a straight nozzle) is used, it is not possible to stably maintain a gas phase region and a secondary meniscus within the long nozzle, making it difficult to generate bubbles by hammering in molten steel. In order to stably maintain a gas phase region and a secondary meniscus within the long nozzle, it is preferable for the long nozzle to have an enlarged diameter section downstream of the minimum diameter section.

[0074] Based on the above results, it can be said that with the following long nozzle (1) and nozzle system (2), when molten metal is supplied downward from the ladle to the tundish, if the molten metal is struck into the secondary meniscus within the long nozzle to generate numerous bubbles, these bubbles can be efficiently collected 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 velocity of the molten metal and suppress the occurrence of short passes and bare molten metal in the tundish. As a result, the cleanliness of the molten metal tends to increase.

[0075] (1) A cylindrical, single-hole long nozzle for supplying molten metal downward from a ladle to a tundish, It has an inlet, a minimum diameter section, a widened diameter section, and an outlet, The minimum diameter portion is located on the inlet side of the outlet side, The enlarged diameter portion extends from the minimum diameter portion to the outlet, and the inner diameter of the nozzle expands from the minimum diameter portion towards the outlet. In the longitudinal cross-sectional shape of the nozzle, the angle θ between the inner wall surface of the nozzle and the nozzle axis X in the enlarged diameter portion 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. Inside the long nozzle, there is a gaseous region containing an inert gas and a secondary meniscus of the molten metal. The secondary meniscus is located on the outlet side of the minimum diameter portion. [Explanation of Symbols]

[0076] 10 Long Nozzles 11 Inlet 12 Minimum diameter part 13 Expanded diameter part 14 Outlet 15 Straight body part 100 Nozzle System 101 Ladle 101a Bottom 101b side wall 102 Tan Dish 102a Bottom 102b side wall 102c lid 105 Molten metal 111 Collector nozzle 112 Flow rate adjustment mechanism (sliding nozzle) 112a Slide plate 113 Inert gas supply mechanism 120 nozzles

Claims

1. A cylindrical, single-hole long nozzle for supplying molten metal downwards from a ladle to a tundish, It has an inlet, a minimum diameter section, a widened diameter section, and an outlet, The minimum diameter portion is located on the inlet side of the outlet side, The enlarged diameter portion extends from the minimum diameter portion to the outlet, and the inner diameter of the nozzle expands from the minimum diameter portion towards the outlet. In the longitudinal cross-sectional shape of the nozzle, the angle θ between the inner wall surface of the nozzle and the nozzle axis X in the enlarged diameter portion is 5° or more and 10° or less. The long nozzle has an inert gas supply mechanism that supplies inert gas from the outside to the inside of the long nozzle, either upstream of the enlarged diameter portion or to the enlarged diameter portion. Long nozzle.

2. The length L from the minimum diameter portion to the outlet １ And the inner diameter D of the nozzle at the outlet. ２ The ratio L １ / D ２ However, it is 2.0 or higher. The long nozzle according to claim 1.

3. The inner diameter D of the nozzle at the minimum diameter portion １ And the inner diameter D of the nozzle at the outlet. ２ Ratio D １ / D ２ However, it is between 0.3 and 0.

6. The long nozzle according to claim 1 or 2.

4. In the longitudinal cross-sectional shape of the nozzle, the shape of the inner wall surface of the nozzle in the enlarged diameter portion is at least one of the following shapes: straight, folded, and curved. A long nozzle according to any one of claims 1 to 3.

5. A straight body section is located between the inlet and the minimum diameter section. A long nozzle according to any one of claims 1 to 4.

6. A nozzle system for supplying molten metal downwards from a ladle to a tundish via a long nozzle, The nozzle system includes the ladle, the long nozzle, the tundish, and an inert gas supply mechanism. The long nozzle has an inlet, a minimum diameter section, an enlarged diameter section, and an outlet. The minimum diameter portion is located on the inlet side of the outlet side, The enlarged diameter portion extends from the minimum diameter portion to the outlet, and the inner diameter of the nozzle expands from the minimum diameter portion towards the outlet. In the longitudinal cross-sectional shape of the nozzle, the angle θ between the inner wall surface of the nozzle and the nozzle axis X in the enlarged diameter portion is 5° or more and 10° or less. 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. The inert gas supply mechanism includes a control unit that controls the amount and pressure of the inert gas supplied. The inert gas supply mechanism supplies the inert gas from the outside to the inside of the long nozzle such that a gas phase region containing an inert gas and a secondary meniscus of the molten metal exist inside the long nozzle, and the secondary meniscus is located on the outlet side of the minimum diameter portion. Nozzle system.

7. The ratio L1 / D2 of the length L1 from the minimum diameter portion to the outlet to the inner diameter D2 of the nozzle at the outlet is 2.0 or more. The nozzle system according to claim 6.

8. The ratio D1 / D2 of the inner diameter D1 of the nozzle at the minimum diameter portion to the inner diameter D2 of the nozzle at the outlet portion is 0.3 or more and 0.6 or less. The nozzle system according to claim 6 or 7.

9. In the longitudinal cross-sectional shape of the long nozzle, the shape of the inner wall surface of the nozzle in the enlarged diameter portion is at least one of a straight line, a folded line, and a curved shape. The nozzle system according to any one of claims 6 to 8.

10. The long nozzle has a straight body portion between the inlet and the minimum diameter portion, The nozzle system according to any one of claims 6 to 9.

11. The immersion depth L of the long nozzle Ｄ and the inner diameter D of the nozzle at the outlet ２ the ratio L Ｄ / D ２ is 1.6 or more and 2.2 or less The nozzle system according to any one of claims 6 to 10.

12. The height ΔH of the secondary meniscus, as defined by the following formula (1), is set to be between -10 cm and 20 cm. The nozzle system according to any one of claims 6 to 11. ΔH=(P Ｔ -P Ｌ ) / (ρ・g) …(1) Here, P Ｔ This is the atmospheric pressure inside the tundish, P Ｌ This is the pressure in the gas phase region within the long nozzle, ρ is the density of the molten metal, g is the acceleration due to gravity.

13. The aforementioned tundish does not have a weir inside. The nozzle system according to any one of claims 6 to 12.

14. Using the nozzle system described in any one of claims 6 to 13, A method for continuous casting of molten metal.

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