Nozzle system

Abstract

To provide a system, when molten metal is fed downward from a ladle to a tundish via a long nozzle, which can pour the molten metal into a secondary meniscus in the nozzle to generate many bubbles and suitably recover the bubbles into the nozzle.SOLUTION: Provided is a nozzle system which satisfies conditions (1) of TP<5 ton / min, θ>15°, H≥600 mm, 250 mm≤LD450 mm and 150 mm≤D2≤350 mm or satisfies conditions (2) of TP≥5 ton / min, 0°<θ≤15°, 400 mm≤LD≤600 mm and 150 mm≤D2≤350 mm or satisfies conditions (3) of TP≥5 ton / min, θ>15°, H<600 mm, 400 mm≤LD≤600 mm and 150 mm≤D2≤350 mm.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present application discloses a nozzle system for supplying molten metal from a ladle to a tundish via a long nozzle.

Background Art

[0002] In the 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 multiple functions such as (1) a function of stabilizing the supply amount of molten steel to the mold, (2) a function of distributing molten steel to multiple molds, (3) a buffer function for continuously performing continuous casting using multiple molten steel ladles, and (4) a function of removing non-metallic inclusions. In particular, when efficiently producing high-grade steel materials with high cleanliness, the (4) function of removing non-metallic inclusions becomes extremely important.

[0003] Non-metallic inclusions in molten steel mainly originate from oxides, nitrides, sulfides, etc. generated during the steelmaking process. When such non-metallic inclusions remain in the final product, it is known that they can, for example, become the starting point of fracture due to stress concentration and deteriorate the quality of the final product. Also, in the steelmaking process itself, non-metallic inclusions adhere and accumulate on the inner wall of the refractory material flow path, causing narrowing and blockage of the flow path, which not only hinders smooth production but can also generate defects in both the surface and interior of the base material during processing such as casting, thus becoming a factor that presses the manufacturing cost, such as reducing the product yield. Therefore, in many cases, it is necessary to remove non-metallic inclusions from the molten steel in the limited processes from secondary refining where the final adjustment of the molten steel composition is performed to the mold.

[0004] In order to remove non-metallic inclusions from molten steel, generally, a method is adopted in which the non-metallic inclusions are floated in the molten steel by utilizing the specific gravity difference between the molten steel and the non-metallic inclusions, and then recovered in a floating layer of oxides called flux. However, it is known that the floating speed at this time decreases as the size of the non-metallic inclusions becomes smaller, and the time required to recover them in the flux layer becomes longer. Therefore, in order to reduce the non-metallic inclusions in the molten steel, it is considered effective to increase the residence time of the non-metallic inclusions in the tundish in order to ensure the time required for the non-metallic inclusions to float.

[0005] Generally, the supply of molten steel from the ladle to the tundish is carried out by flowing it down by utilizing the potential energy through a sliding nozzle having a flow rate adjustment function and a long nozzle which is a cylindrical refractory used by immersing the lower end in the molten steel in the tundish. However, since the high-speed discharge flow from the long nozzle may collide with the bottom of the tundish to form a short-circuit flow called a short path toward the mold (see Fig. 5), it is not always easy to ensure the residence time of the molten steel in the tundish. A general countermeasure against this problem is a method of diverting the molten steel flow by providing a weir inside the tundish. However, constructing a refractory inside the tundish causes an increase in material costs, construction time, and work load. In addition, a space where there is almost no flow near the weir and which does not contribute to floating and removing is generated, and a new flow that goes toward the mold at high speed while diverting can be induced, so it does not necessarily assist the floating of the inclusions. In particular, small inclusions have a small buoyancy and are easily followed by the flow of molten steel, so the effect of diversion is likely to be limited to the removal of large 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 5). 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 molten steel flow near the long nozzle can cause re-oxidation of the molten steel by the lower oxides in the slag.

[0007] According to the inventor's new findings, in order to suppress the short pass described above and to suppress the bare molten metal caused by the reverse upward flow, it is effective to supply molten steel from the ladle to the tundish via a long nozzle, causing the falling flow of molten steel to collide with the surface of the molten metal (secondary meniscus) inside the long nozzle, thereby injecting the surrounding atmosphere and generating a cluster of bubbles (plume), and reducing the injection flow velocity of the molten steel with the large buoyancy of the bubbles. However, if the generated plume is not retained and collected inside the long nozzle and flows out from the outlet of the long nozzle, boiling (a phenomenon in which bubbles rise to the surface of the tundish molten metal, pushing aside the flux and exposing the bare molten metal to the atmosphere) may occur in the molten steel inside the tundish, and there is a risk that the molten steel will be re-oxidized.

[0008] To suppress re-oxidation due to boiling, it is necessary to reduce the amount of plume that flows out of the long nozzle outlet. The inventors considered that by expanding the lower part of the long nozzle, as disclosed in Patent Documents 1 and 2, the plume would be more easily retained within the long nozzle and more easily recovered within the long nozzle. However, according to the inventors' new findings, the amount of plume generated within the long nozzle varies greatly depending on the shape of the long nozzle, the throughput of the molten steel, and the position of the long nozzle. Under certain conditions, a sufficient amount of plume is generated, which reduces the injection rate of molten steel and suppresses short passes, but this can lead to the problem of re-oxidation due to boiling. Under other conditions, the amount of plume generated is small, and although the problem of re-oxidation due to boiling does not occur, the injection rate of molten steel cannot be reduced, resulting in problems of short passes and bare molten metal due to reverse upward flow. In other words, simply improving the shape of the long nozzle is not enough to solve the problems of short passes in the tundish, reverse upward flow, and re-oxidation of molten metal due to boiling. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2002-001496 [Patent Document 2] Japanese Patent Application Publication No. 11-010292 [Overview of the project] [Problems that the invention aims to solve]

[0010] This invention discloses a novel technology that suppresses re-oxidation of the molten metal due to boiling by efficiently retaining and recovering the generated plume within the long nozzle while suppressing the flow of molten metal from the ladle to the tundish via a long nozzle. This is achieved by causing the falling flow of molten metal to collide with the secondary meniscus within the long nozzle, thereby generating a sufficient amount of plume. [Means for solving the problem]

[0011] This application discloses several embodiments as means for solving the above-mentioned problems. (Aspect 1) A nozzle system that supplies molten metal from a ladle to a tundish via a long nozzle, The long nozzle is a cylindrical single-hole nozzle having an inlet, a minimum diameter section, an enlarged diameter section, a straight cylindrical section, and an outlet. The minimum diameter portion is located on the inlet side of the outlet side, The enlarged diameter portion exists from the minimum diameter portion to the straight cylindrical portion, and the inner diameter of the nozzle expands from the minimum diameter portion towards the straight cylindrical portion. The straight cylindrical portion extends from the lower end of the enlarged diameter portion to the outlet, The outlet 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, Either conditions 1-1 to 1-5 below are met, or conditions 2-1 to 2-4 below are met, or conditions 3-1 to 3-5 below are met. Nozzle system. Condition 1-1: TP<5ton / min Condition 1-2: θ > 15° Condition 1-3: H≧600mm Condition 1-4: 250mm≦L D ≤450mm Condition 1-5: 150mm≦D2≦350mm Condition 2-1: TP≧5ton / min Condition 2-2: 0°<θ≦15° Condition 2-3: 400mm≦L D ≤600mm Condition 2-4: 150mm≦D2≦350mm Condition 3-1: TP≧5ton / min Condition 3-2: θ > 15° Condition 3-3:H<600mm Condition 3-4: 400mm≦L D ≤600mm Condition 3-5: 150mm≦D2≦350mm Here, TP is the throughput of molten metal. θ is the angle between the inner wall surface of the nozzle and the nozzle axis in the enlarged diameter portion of the longitudinal cross-sectional shape of the nozzle. H is the distance from the minimum diameter portion to the liquid surface of the molten metal in the tundish, L D This is the immersion depth of the long nozzle, D2 is the inner diameter of the nozzle at the outlet. (Aspect 2) The nozzle system of Embodiment 1, wherein condition 3-3 is the condition H ≤ 400 mm. (Aspect 3) A nozzle system according to embodiment 1 or 2, wherein the following condition 4-1 is satisfied. Condition 4-1: 50mm≦D1≦200mm Here, D1 is the inner diameter of the nozzle at the minimum diameter portion. (Aspect 4) A nozzle system according to any of embodiments 1 to 3, wherein the following condition 4-2 is met. Condition 4-2: 0.2≦D1 / D2≦1.0 (Aspect 5) The nozzle system according to any of embodiments 1 to 4, wherein the tundish does not have a weir. [Effects of the Invention]

[0012] According to the nozzle system of this disclosure, when supplying molten metal from a ladle to a tundish via a long nozzle, the falling flow of molten metal inside the long nozzle is made to collide with a secondary meniscus to generate a sufficient amount of plume. This suppresses the production of bare molten metal due to short passes and reversed upward flows, while efficiently recovering the generated plume inside the long nozzle, thereby suppressing the re-oxidation of the molten metal due to boiling. [Brief explanation of the drawing]

[0013] [Figure 1] This diagram schematically shows an example of the positional relationship between the ladle, long nozzle, and tundish in a nozzle system. [Figure 2] This diagram schematically shows an example of the configuration around a long nozzle in a nozzle system. [Figure 3] A schematic example of the cross-sectional shape of a long nozzle is shown. [Figure 4A] This diagram schematically illustrates an example of the flow conditions inside a long nozzle. It shows the case where the diameter expansion ratio in the expanded section is small (angle θ is small). [Figure 4B] This diagram schematically illustrates an example of the flow conditions inside a long nozzle. It shows the case where the diameter expansion ratio in the expanded section is large (angle θ is large). [Figure 5] This outlines the challenges of conventional technologies. [Modes for carrying out the invention]

[0014] 1. Nozzle System A nozzle system according to an embodiment will be described with reference to the drawings. As shown in Figure 1, a nozzle system 100 according to one embodiment supplies molten metal 105 from a ladle 101 to a tundish 102 via a long nozzle 10. As shown in Figures 2 and 3, the long nozzle 10 is a cylindrical single-hole nozzle having an inlet 11, a minimum diameter section 12, an enlarged diameter section 13, a straight section 14, and an outlet 15. The minimum diameter section 12 is located on the inlet 11 side of the outlet 15. The enlarged diameter section 13 extends from the minimum diameter section 12 to the straight section 14, and the inner diameter of the nozzle expands from the minimum diameter section 12 to the straight section 14. The straight section 14 extends from the lower end of the enlarged diameter section 13 to the outlet 15. The outlet 15 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. As shown in Figures 2, 4A, and 4B, the inside of the long nozzle 10 contains a gas phase region 10a containing an inert gas and a secondary meniscus 10b of the molten metal 105. The secondary meniscus 10b is located on the outlet 15 side of the minimum diameter portion 12. In the nozzle system 100 according to one embodiment, either the following conditions 1-1 to 1-5 are met, or the following conditions 2-1 to 2-4 are met, or the following conditions 3-1 to 3-5 are met.

[0015] Condition 1-1: TP<5ton / min Condition 1-2: θ > 15° Condition 1-3: H≧600mm Condition 1-4: 250mm≦L D ≤450mm Condition 1-5: 150mm≦D2≦350mm

[0016] Condition 2-1: TP≧5ton / min Condition 2-2: 0°<θ≦15° Condition 2-3: 400mm≦L D ≤600mm Condition 2-4: 150mm≦D2≦350mm

[0017] Condition 3-1: TP≧5ton / min Condition 3-2: θ > 15° Condition 3-3:H<600mm Condition 3-4: 400mm≦L D ≤600mm Condition 3-5: 150mm≦D2≦350mm

[0018] Here, TP is the throughput of the molten metal 105, θ is the angle between the inner wall surface of the nozzle in the enlarged diameter portion 13 and the axis of the nozzle in the longitudinal cross-sectional shape of the nozzle, H is the distance from the minimum diameter portion 12 to the liquid surface 105a of the molten metal 105 in the tundish 102, and L D D is the immersion depth of the long nozzle 10, and D2 is the inner diameter of the nozzle at the outlet 15.

[0019] 1.1 Ladle The ladle 101 is a container that supplies molten metal 105 to the tundish 102. As shown in Figures 1 and 2, 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 only needs to be made 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 2, 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.

[0020] 1.2 Tan Dish The tundish 102 is a container that receives molten metal 105 from the ladle 101. As shown in Figures 1 and 2, 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 1, 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 20 may be directly or indirectly connected to the outlet 102ax of the tundish 102. The connection method between the tundish 102 and the nozzle 20 is not particularly limited; for example, they can be connected by fitting. The tundish 102 and the nozzle 20 may also be connected via some kind of intermediate member.

[0021] As shown in Figure 2, 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 of this disclosure can reduce the reverse upward flow (see Figure 5) 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, and can also suppress boiling, making 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 to occur, thus making it less likely for the problem of re-oxidation by bare molten metal to occur.

[0022] As shown in Figure 1, 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 the phenomenon of entraining the gas phase (formation of a bubble plume) when the falling flow of molten metal 105 collides with the secondary meniscus 10b makes it easier to reduce the downward flow velocity of the molten metal 105, and also makes it easier to suppress short passes of the molten metal 105 in the tundish 102 (see Figure 5). 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.

[0023] 1.3 Long nozzle As shown in Figures 1 and 2, molten metal 105 is supplied from the ladle 101 to the tundish 102 via the long nozzle 10. The long nozzle 10 has an inlet 11 on the upstream side, the ladle 101 side, and an outlet 15 on the downstream side, the tundish 102 side. The long nozzle 10 is a cylindrical, single-hole nozzle that extends downward from the upstream side to the downstream side. Specifically, the long nozzle 10 may be a cylindrical body having a central axis in the vertical direction. 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, the configuration of the so-called "injection pipe" installed and fixed to the lid of the tundish is different from that of the long nozzle referred to in this application.

[0024] 1.3.1 Basic configuration As shown in Figure 3, the long nozzle 10 is a cylindrical single-hole nozzle having an inlet 11, a minimum diameter section 12, an enlarged diameter section 13, a straight section 14, and an outlet 15. The inlet 11 may be connected to another component (for example, the lower end of another nozzle such as a collector nozzle, or the outlet of a ladle). The minimum diameter section 12 is located on the inlet 11 side of the outlet 15. The position of the minimum diameter section 12 may coincide with the position of the inlet 11, or it may be located on the outlet 15 side of the inlet 11. The enlarged diameter section 13 extends from the minimum diameter section 12 to the straight section 14, and the inner diameter of the nozzle expands from the minimum diameter section 12 to the straight section 14. The straight section 14 extends from the lower end of the enlarged diameter section 13 to the outlet 15. As shown in Figure 2, the outlet 15 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. The nozzle shape from the inlet 11 to the minimum diameter section 12 only needs to have a diameter greater than or equal to the diameter of the minimum diameter section 12. For example, as shown in Figure 3, the long nozzle 10 may have a second straight cylindrical section 16 from the inlet 11 to the minimum diameter section 12. In the enlarged diameter section 13, the nozzle inner diameter may expand linearly (monotonically) from the upstream side to the downstream side, or it may expand curvilinearly. In the enlarged diameter section 13, the nozzle inner diameter may expand continuously from the upstream side to the downstream side, or it may expand intermittently. Furthermore, as shown in Figure 3, it is preferable that the long nozzle 10 does not have a diameter-reducing section from the minimum diameter section 12 to the outlet 15, where the inner diameter decreases from the upstream side to the downstream side. In particular, it is preferable that there is no diameter-reducing section between the portion where the secondary meniscus 10b is located and the outlet 15, where the inner diameter decreases from the upstream side to the downstream side. This is because if a diameter-reducing section exists downstream of the secondary meniscus 10b, the downward flow velocity of the molten metal 105 will increase in that portion, which may reduce the effectiveness of the nozzle system 100.

[0025] 1.3.2 Inner diameter As shown in FIG. 3, the long nozzle 10 may have an inner diameter D0 at the inlet 11, a minimum inner diameter D1 at the minimum diameter portion 12 upstream of the secondary meniscus 10b, and an inner diameter D2 at the outlet 15 downstream of the secondary meniscus 10b. The inner diameter of the nozzle at the secondary meniscus 10b may vary between D1 and D2. Further, as shown in FIGS. 2 and 3, the inner diameter of the nozzle at the diameter-expanded portion 13 increases from the minimum diameter portion 12 side toward the straight cylinder portion 14 side. Specific values and relationships of D0, D1, and D2 will be described later. Note that the "inner diameter" is the equivalent diameter of the area circle for the opening shape of the nozzle.

[0026] 1.3.3 Length As shown in FIG. 3, the long nozzle 10 has a length L from the inlet 11 to the outlet 15, a length L0 from the inlet 11 to the downstream end of the minimum diameter portion 12 (the upstream end of the diameter-expanded portion 13), a length L1 from the downstream end of the minimum diameter portion 12 (the upstream end of the diameter-expanded portion 13) to the outlet 15, and a length L2 from the upstream end of the straight cylinder portion 14 to the outlet 15. Specific values and relationships of L, L0, L1, and L2 will be described later.

[0027] 1.3.4 Immersion Depth and Distance between Nozzle Lower End and Tundish Bottom As shown in FIG. 2, the outlet 15 of the long nozzle 10 is located below the liquid surface 105a of the molten metal 105 in the tundish 102 and above the bottom surface 102a of the tundish 102. That is, the downstream tip of the long nozzle 10 is immersed in the molten metal 105 inside the tundish 102. As shown in FIG. 2, in the nozzle system 100, there is a distance L D (immersion depth L D ) between the liquid surface 105a of the molten metal 105 in the tundish 102 and the outlet 15 of the long nozzle 10, and there may be a distance L S between the outlet 15 of the long nozzle 10 and the bottom surface 102a of the tundish 102. L D and L SThe specific values ​​and relationships will be discussed later.

[0028] 1.3.5 Molten metal flow in the nozzle The molten metal 105 flows into the long nozzle 10 through the inlet 11 at a predetermined throughput TP and flows out to the outside of the long nozzle 10 through the outlet 15. According to the inventor's new findings, the flow of molten metal inside the nozzle can change depending on the magnitude of the angle θ in the enlarged diameter section 13. When the angle θ is small (for example, 15° or less), as shown in Figure 4A, the molten metal 105 inside the long nozzle 10 may flow down the inner wall of the nozzle from the vicinity of the minimum diameter section 12 and collide with the secondary meniscus 10b. On the other hand, when the angle θ is large (for example, greater than 15°), as shown in Figure 4B, the molten metal 105 inside the long nozzle 10 may collide with the secondary meniscus 10b by free fall from the vicinity of the minimum diameter section 12. Also, as shown in Figure 2, the long nozzle 10 may have a height H between the minimum diameter section 12 and the liquid surface 105a of the tundish 102. The larger the height H, the more likely it is that bubbles will be generated when the falling flow of molten metal collides with the secondary meniscus 10b. Also, as shown in Figure 2, in the nozzle system 100, a height ΔH may exist between the liquid surface of the molten metal 105 in the tundish 102 and the secondary meniscus 10b. The specific values ​​of TP, θ, H, and ΔH will be described later.

[0029] 1.4 Conditions 1-1~1-5 In its first embodiment, the nozzle system 100 of this disclosure satisfies the above conditions 1-1 to 1-5: TP < 5 ton / min, θ > 15°, H ≥ 600 mm, and L ≤ 250 mm. D The conditions ≤450mm and ≤150mm ≤ D2 ≤ 350mm are met.

[0030] 1.4.1 Condition 1-1 According to the inventor's new findings, when the throughput TP of the molten metal 105 is less than 5 ton / min, the energy of the molten metal 105 when it collides with the secondary meniscus 10b is small, making it difficult to generate a sufficient amount of plume. As a result, the falling flow of the molten metal 105 cannot be sufficiently slowed down by the plume, and short paths and reversed upward flows are likely to occur. Therefore, it is necessary to increase the amount of plume generated by modifying conditions other than throughput TP. Regarding condition 1-1, the throughput TP may be 4 ton / min or less, 3 ton / min or less, or 2 ton / min or less.

[0031] 1.4.2 Condition 1-2 To generate a sufficient amount of plume when the throughput TP is less than 5 tons / min, as shown in Figure 4B, the angle θ in the enlarged diameter section 13 should be increased to more than 15°, allowing the molten metal 105 to free-fall inside the long nozzle 10, thereby increasing the energy of the falling flow of molten metal 105 when it collides with the secondary meniscus 10b. Regarding conditions 1-2, the angle θ may be 16° or more, 17° or more, 18° or more, 19° or more, or 20° or more, and may be 60° or less, 50° or less, 40° or less, or 30° or less.

[0032] 1.4.3 Condition 1-3 To generate a sufficient amount of plume when the throughput TP is less than 5 tons / min, it is advisable to increase the height H from the minimum diameter section 12 to the liquid surface 105a of the molten metal 105 to 600 mm or more, thereby increasing the free fall distance of the molten metal 105 inside the long nozzle 10, and increasing the energy when the falling flow of the molten metal 105 collides with the secondary meniscus 10b.

[0033] 1.4.4 Conditions 1-4 In the nozzle system 100, when conditions 1-1 to 1-3 are met, an appropriate amount of plume can be generated inside the long nozzle 10. When an appropriate amount of plume is generated in this way, the immersion depth L of the long nozzle 10 DIf the immersion depth L is too shallow, the volume for holding and collecting the plume inside the long nozzle 10 becomes small, causing bubbles to flow out from the outlet 15 of the long nozzle 10 and resulting in boiling. D If the depth is 250mm or more, this problem is less likely to occur. On the other hand, from the standpoint of suppressing boiling, the immersion depth L D There's no problem if it's too deep. However, the immersion depth L D If the immersion depth L is too deep, the distance between the outlet 15 of the long nozzle 10 and the bottom surface 102a of the tundish 102 becomes too short, which may increase the likelihood of reverse upward flow and short paths. D If the immersion depth is 450 mm or less, this problem is less likely to occur. Regarding conditions 1-4, immersion depth L D It may be 300 mm or more or 350 mm or more, and may be 425 mm or less or 400 mm or less.

[0034] 1.4.5 Conditions 1-5 In the nozzle system 100, when conditions 1-1 to 1-3 are met, an appropriate amount of plume can be generated inside the long nozzle 10. When an appropriate amount of plume is generated in this way, if the inner diameter D2 of the outlet 15 of the long nozzle 10 is too small, bubbles will flow out of the outlet 15 of the long nozzle 10, causing boiling. In this respect, if the inner diameter D2 is 150 mm or more, this problem is less likely to occur. On the other hand, from the standpoint of suppressing boiling, a larger inner diameter D2 is not a problem. However, if the inner diameter D2 is too large, there is a risk that the weight of the long nozzle 10 will increase excessively. In this respect, if the inner diameter D2 is 350 mm or less, this problem is less likely to occur. Regarding condition 1-5, the inner diameter D2 may be 200 mm or more or 250 mm or more, or 325 mm or less or 300 mm or less.

[0035] 1.5 Conditions 2-1~2-4 In its second embodiment, the nozzle system 100 of this disclosure satisfies the above conditions 2-1 to 2-4: TP ≥ 5 ton / min, 0° < θ ≤ 15°, and 400 mm ≤ L. DThe conditions ≤600mm and ≤150mm ≤ D2 ≤ 350mm are met.

[0036] 1.5.1 Condition 2-1 According to the inventor's new findings, when the throughput TP of the molten metal 105 is 5 ton / min or more, the energy of the molten metal 105 when it collides with the secondary meniscus 10b is large, generating an excessive amount of plume and making boiling likely. Therefore, it is necessary to suppress the amount of plume generated and / or prevent the generated plume from flowing out of the outlet 15 of the long nozzle 10 by adjusting conditions other than throughput TP. Regarding condition 2-1, the throughput TP may be 6 ton / min or more, 7 ton / min or more, 8 ton / min or more, or 9 ton / min or more. The upper limit of TP is not particularly limited, and an appropriate TP should be determined by the operating conditions of the nozzle system 100. TP may be 15 ton / min or less, 13 ton / min or less, or 10 ton / min or less.

[0037] 1.5.2 Condition 2-2 To suppress plume generation when the throughput TP is 5 tons / min or more, as shown in Figure 4A, the angle θ in the enlarged diameter section 13 should be reduced to 15° or less, so that the molten metal 105 flows down the inner wall of the long nozzle 10, thereby reducing the energy when the molten metal 105 collides with the secondary meniscus 10b. Regarding condition 2-2, the angle θ may be 14° or less, 13° or less, 12° or less, 11° or less, or 10° or less, and may be greater than 0°, and 2° or more, 4° or more, 6° or more, or 8° or more.

[0038] 1.5.3 Condition 2-3 According to the inventor's new findings, in the nozzle system 100, when conditions 2-1 and 2-2 are met, the amount of plume generated inside the long nozzle 10 can be suppressed to some extent, but the amount of plume generated still tends to be high. When the amount of plume generated is high in this way, the immersion depth L of the long nozzle 10 DIf the immersion depth L is too shallow, the volume for holding and collecting the plume inside the long nozzle 10 becomes small, causing bubbles to flow out from the outlet 15 of the long nozzle 10 and resulting in boiling. D If the depth is 400mm or more, this problem is less likely to occur. On the other hand, from the standpoint of suppressing boiling, the immersion depth L D There's no problem if it's too deep. However, the immersion depth L D If the immersion depth L is too deep, the distance between the outlet 15 of the long nozzle 10 and the bottom surface 102a of the tundish 102 becomes too short, which may increase the likelihood of reverse upward flow and short paths. D If the depth is 600 mm or less, this problem is less likely to occur. Regarding conditions 2-3, immersion depth L D It may be 425 mm or more or 450 mm or more, and it may be 550 mm or less or 500 mm or less.

[0039] 1.5.4 Condition 2-4 As described above, in the nozzle system 100, when conditions 2-1 to 2-3 are met, there is a tendency for a large amount of plume to be generated, but the immersion depth L D By adjusting this, the occurrence of boiling can be suppressed. However, the immersion depth L D Even if the adjustments are made, if the inner diameter D2 of the outlet 15 of the long nozzle 10 is too small, bubbles will flow out of the outlet 15 of the long nozzle 10, causing boiling. In this respect, if the inner diameter D2 is 150 mm or more, this problem is less likely to occur. On the other hand, from the standpoint of suppressing boiling, there is no problem if the inner diameter D2 is large. However, if the inner diameter D2 is too large, there is a risk that the weight of the long nozzle 10 will increase excessively. In this respect, if the inner diameter D2 is 350 mm or less, this problem is less likely to occur. Regarding condition 2-4, the inner diameter D2 may be 200 mm or more or 250 mm or more, or 325 mm or less or 300 mm or less.

[0040] As mentioned above, when condition 2-2 is met in the nozzle system 100, the molten metal 105 flows down the inner wall of the long nozzle 10. Therefore, even if the height H from the minimum diameter portion 12 to the liquid surface 105a of the molten metal 105 changes, the amount of plume generated does not change substantially. In other words, when conditions 2-1 to 2-4 are met, there is no particular restriction on the height H. In this case, the height H may be, for example, 100 mm or more and 1000 mm or less.

[0041] 1.6 Conditions 3-1~3-5 In its third embodiment, the nozzle system 100 of this disclosure satisfies the above conditions 3-1 to 3-5: TP ≥ 5 ton / min, θ > 15°, H < 600 mm, and L ≤ 400 mm. D The conditions ≤600mm and ≤150mm ≤ D2 ≤ 350mm are met.

[0042] 1.6.1 Condition 3-1 As described above, when the throughput TP of the molten metal 105 is 5 ton / min or more, the energy of the molten metal 105 when it collides with the secondary meniscus 10b is large, and an excessive amount of plume is generated, making boiling likely. Therefore, it is necessary to reduce the amount of plume generated and / or prevent the generated plume from flowing out of the outlet 15 of the long nozzle 10 by adjusting conditions other than throughput TP. Regarding condition 3-1, the throughput TP may be 6 ton / min or more, 7 ton / min or more, 8 ton / min or more, or 9 ton / min or more. There is no particular upper limit to the throughput TP, and an appropriate TP should be determined by the operating conditions of the nozzle system 100. TP may be 15 ton / min or less, 13 ton / min or less, or 10 ton / min or less.

[0043] 1.6.2 Condition 3-2 When the throughput TP is 5 tons / min or more, as shown in Figure 4B, if the angle θ in the enlarged diameter section 13 is increased to more than 15°, allowing the molten metal 105 to free-fall inside the long nozzle 10 and increasing the energy upon impact with the secondary meniscus 10b, the amount of plume generated inside the long nozzle 10 will further increase. Therefore, it is necessary to suppress the amount of plume generated and / or prevent the generated plume from flowing out of the outlet 15 of the long nozzle 10 by adjusting conditions other than TP and θ. Regarding condition 3-2, the angle θ may be 16° or more, 17° or more, 18° or more, 19° or more, or 20° or more, and may also be 60° or less, 50° or less, 40° or less, or 30° or less.

[0044] 1.6.3 Condition 3-3 When the throughput TP is 5 tons / min or more and the angle θ is greater than 15°, in order to suppress the amount of plume generated inside the long nozzle 10, it is preferable to lower the height H from the minimum diameter section 12 to the liquid surface 105a of the molten metal 105 to less than 600 mm, thereby shortening the free fall distance of the molten metal 105 inside the long nozzle 10 and reducing the energy when the falling flow of the molten metal 105 collides with the secondary meniscus 10b. Regarding condition 3-3, the height H may be 550 mm or less, 500 mm or less, 450 mm or less, or 400 mm or less. The lower limit of the height H is not particularly limited, and an appropriate height H should be determined by the operating conditions of the nozzle system 100. The height H may be 200 mm or more, 250 mm or more, 300 mm or more, or 350 mm or more.

[0045] 1.6.4 Condition 3-4 According to the inventor's new findings, in the nozzle system 100, when conditions 3-1 to 3-3 are met, the amount of plume generated inside the long nozzle 10 can be suppressed to some extent, but the amount of plume generated still tends to be high. When the amount of plume generated is high in this way, the immersion depth L of the long nozzle 10 DIf the immersion depth L is too shallow, the volume for holding and collecting the plume inside the long nozzle 10 becomes small, causing bubbles to flow out from the outlet 15 of the long nozzle 10 and resulting in boiling. D If the depth is 400mm or more, this problem is less likely to occur. On the other hand, from the standpoint of suppressing boiling, the immersion depth L D There's no problem if it's too deep. However, the immersion depth L D If the immersion depth L is too deep, the distance between the outlet 15 of the long nozzle 10 and the bottom surface 102a of the tundish 102 becomes too short, which may increase the likelihood of reverse upward flow and short paths. D If the depth is 600 mm or less, this problem is less likely to occur. Regarding conditions 3-4, immersion depth L D It may be 425 mm or more or 450 mm or more, and it may be 550 mm or less or 500 mm or less.

[0046] 1.6.5 Condition 3-5 As described above, in the nozzle system 100, when conditions 3-1 to 3-4 are met, there is a tendency for a large amount of plume to be generated, but the immersion depth L D By adjusting this, the occurrence of boiling can be suppressed. However, the immersion depth L D Even if the adjustments are made, if the inner diameter D2 of the outlet 15 of the long nozzle 10 is too small, bubbles will flow out of the outlet 15 of the long nozzle 10, causing boiling. In this respect, if the inner diameter D2 is 150 mm or more, this problem is less likely to occur. On the other hand, from the standpoint of suppressing boiling, there is no problem if the inner diameter D2 is large. However, if the inner diameter D2 is too large, there is a risk that the weight of the long nozzle 10 will increase excessively. In this respect, if the inner diameter D2 is 350 mm or less, this problem is less likely to occur. Regarding condition 3-5, the inner diameter D2 may be 200 mm or more or 250 mm or more, or 325 mm or less or 300 mm or less.

[0047] 1.7 Other conditions The following describes the conditions common to each of the first, second, and third forms.

[0048] 1.7.1 Inlet diameter D0 The inner diameter D0 of the nozzle at the inlet 11 may be substantially the same as, or different from, the inner diameter D1 of the nozzle at the minimum diameter section 12 described later. The inner diameter D0 of the nozzle at the inlet 11 may be, for example, 70 mm or more, 100 mm or more, 200 mm or less, 170 mm or less, or 150 mm or less.

[0049] 1.7.2 Inner diameter D1 at the minimum diameter section The inner diameter D1 of the nozzle at the minimum diameter section 12 may, for example, satisfy the following condition 4-1. The inner diameter D1 may be 70 mm or more, 90 mm or more, 190 mm or less, 180 mm or less, or 150 mm or less. Furthermore, the ratio D1 / D2 of the inner diameter D1 of the nozzle at the minimum diameter section 12 and the inner diameter D2 of the nozzle at the outlet 15 may satisfy the following condition 4-2. The ratio D1 / D2 may be 0.3 or more, 0.4 or more, 0.9 or less, or 0.8 or less.

[0050] Condition 4-1: 50mm≦D1≦200mm Condition 4-2: 0.2≦D1 / D2≦1.0

[0051] 1.7.3 Length of the long nozzle L The long nozzle 10 may have a length (total length) L from the inlet 11 to the outlet 15. The length L is equal to the sum of the lengths L0 and L1 described below.

[0052] 1.7.4 Length L0 from the inlet to the downstream end of the smallest diameter section The long nozzle 10 may have a length L0 from the inlet 11 to the downstream end of the minimum diameter section 12 (the upstream end of the enlarged diameter section 13). Also, as described above, the long nozzle 10 may have a second straight cylindrical section 16 from the inlet 11 to the minimum diameter section 12. By providing such a straight cylindrical section 16, the flow velocity and flow direction of the molten metal 105 in the nozzle are stabilized, the gas phase region 10a and the secondary meniscus 10b in the nozzle are stabilized, and it becomes easier to generate a stable plume downstream of the straight cylindrical section 16. In this case, the length L0 may be the same as the length of the second straight cylindrical section 16. The length L0 may be, for example, 250 mm or more or 500 mm or more, or 1000 mm or less or 800 mm or less.

[0053] 1.7.5 Length L1 from the downstream end of the smallest diameter section to the outlet The length L1 from the downstream end of the minimum diameter section 12 (the upstream end of the enlarged diameter section 13) to the outlet 15 may be, for example, 300 mm or more, 400 mm or more, or 500 mm or more, or it may be 1200 mm or less, 1000 mm or less, or 800 mm or less. Also, the ratio L0 / L1 of length L0 to length L1 may be, for example, 0.3 or more, 0.4 or more, or 0.5 or more, or it may be 2.0 or less, 1.8 or less, or 1.6 or less. The longer the length L1, the larger the volume from the secondary meniscus 10b inside the nozzle to the lower end of the nozzle tends to be, and the larger the plume retention volume tends to be. As a result, various effects such as the effect of slowing down the flow velocity of molten metal and the effect of increasing non-metallic inclusions tend to be obtained more significantly. On the other hand, if the length L1 is too long, these effects will saturate, and the nozzle weight tends to become excessively heavy. Furthermore, if the length L1 is too long or too short, the height H and immersion depth L mentioned above will also be affected. D There is a risk that the conditions related to this may not be met.

[0054] 1.7.6 Length L2 from the upstream end of the straight pipe to the outlet The length L2 from the upstream end of the straight cylinder section 14 to the outlet 15 may be, for example, 300 mm or more, 350 mm or more, or 400 mm or more, or 1000 mm or less, 900 mm or less, or 800 mm or less. Also, the ratio L1 / L2 of length L1 to length L2 may be, for example, 0.3 or more, 0.4 or more, or 0.5 or more, or 2.0 or less, 1.8 or less, or 1.6 or less. The longer the length L2, the larger the volume for holding and recovering the plume inside the long nozzle 10 tends to be, and the immersion depth L D It is easy to enlarge.

[0055] 1.7.7 Distance L from the outlet to the bottom of the tundish S The distance L from the outlet 15 of the long nozzle 10 to the bottom surface 102a of the tundish 102. S For example, it may be between 200 mm and 900 mm. Also, the immersion depth L D distance L S Ratio L D / L S For example, it may be between 0.2 and 2.0. Also, the inner diameter D2 of the nozzle at the outlet 15 and the distance L S The ratio D2 / L S For example, it may be between 0.2 and 2.0.

[0056] 1.7.8 Secondary Meniscus Height ΔH As described above, a gas phase region 10a and a secondary meniscus 10b are formed inside the long nozzle 10. Here, the height ΔH of the secondary meniscus 10b may change slightly depending on the pressure in the gas phase region 10a. The secondary meniscus height ΔH can be defined by the following equation (1). In the nozzle system, the height ΔH of the secondary meniscus may be between -10 cm and 20 cm. ΔH may be between -7 cm and -5 cm and -3 cm and -1 cm and -1 cm or -10 cm or less, 7 cm or less, 5 cm or less, 3 cm or less and -1 cm or -1 cm or -1 cm or -1 cm or -10 cm or less and -7 cm or less and -5 cm or less and -3 cm or -1

[0057] ΔH=(P T -P L ) / (ρ·g) …(1) Here, P T This is the atmospheric pressure inside the tundish 102. P L This is the pressure in the gas phase region 10a within the long nozzle 10. ρ is the density of molten metal 10⁵, g is the acceleration due to gravity.

[0058] 1.7.9 Average residence time τ in a tundish The average residence time τ of the molten metal 105 in the tundish 102 may be, for example, 240 seconds or more. 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 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 time, but it is not practical for the time to exceed 1500 seconds during steady operation of continuous casting. This is because if the average residence time τ 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 volume 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.

[0059] 1.8 Other Configurations 1.8.1 Collector Nozzle As shown in Figure 2, in the nozzle system, 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. At the connection point with the long nozzle 10, the collector nozzle 111 has an inner diameter D C It may have D C The specific value of D is not particularly limited. For example, D C And the above-mentioned D1 is 1.0 ≤ D1 / DC 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 minimum inner diameter D1 (cm) of the long nozzle 10 to (cm) is D1 / D C The 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.

[0060] 1.8.2 Sliding Nozzle As shown in Figure 2, in the nozzle system, 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 2. 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.

[0061] 1.8.3 Inert Gas Supply Mechanism As shown in Figure 2, in the nozzle system, an inert gas may be supplied from the outside to the inside of the long nozzle 10 so that a gas phase region 10a containing the inert gas and a secondary meniscus 10b are formed 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 2, the nozzle system 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 the ejector effect from the connection between the ladle 101 and the nozzle or the connections between the nozzles. However, in the nozzle system, a mechanism 113 may be employed to intentionally supply an inert gas into the long nozzle 10 separately from this.

[0062] As shown in Figure 2, 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. 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 a signal from the control unit, the opening and closing of the inert gas supply valve may be controlled, and the amount and pressure of the inert gas supply can be controlled to target values.

[0063] 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 in the enlarged diameter portion 13 of the long nozzle 10.

[0064] 1.8.4 Weir in the tundish As described above, in the nozzle system of this disclosure, there is no need to install a weir inside the tundish 102 that has a flow control function for the molten metal 105. According to the nozzle system 100 of this disclosure, it is possible to prevent short passes 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.

[0065] 1.8.5 Height Dimensions The height dimension of the nozzle system 100 in this disclosure is not particularly limited. This dimension is 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 L of the long nozzle 10. DThe length is determined based on various factors, and is generally between 1m and 2.5m.

[0066] 1.8.6 Types of molten metals In the nozzle system 100 of this disclosure, 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 nozzle system of this disclosure can be expected to be highly effective when the molten metal 105 is molten steel. The type of steel of the molten steel is not particularly limited.

[0067] 1.9 Action and Effects As described above, in the nozzle system 100 of this disclosure, when conditions 1-1 to 1-5, conditions 2-1 to 2-4, or conditions 3-1 to 3-5 are met, when molten metal 105 is supplied from the ladle 101 to the tundish 102 via the long nozzle 10, the falling flow of molten metal 105 inside the long nozzle 10 is made to collide with the secondary meniscus 10b, generating a sufficient amount of plume. This suppresses the production of bare molten metal due to short passes and reversed upward flow, while efficiently recovering the generated plume inside the long nozzle 10, thereby suppressing the re-oxidation of molten metal 105 due to boiling.

[0068] 2. Continuous casting method of molten metal The technology of this disclosure also has aspects as a method for continuous casting of 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 of this disclosure, supplying molten metal 105 from the tundish 102 to a mold (not shown) via a nozzle 20, and continuously drawing 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 average residence time τ may be adjusted to be above a predetermined level.

[0069] 3. 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]

[0070] 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.

[0071] 1. Preliminary experiment A model experiment was conducted using water as the working fluid. The working fluid, water (hereinafter simply referred to as water), flowed along the inner wall until the start of the enlarged diameter section of the long nozzle. When the angle θ of the enlarged diameter section was less than 15°, it was confirmed that the water continued along the inner wall and collided with the secondary meniscus inside the long nozzle (Figure 4A). On the other hand, when the angle θ of the enlarged diameter section was 15° or more, the water flow separated from the inner wall surface and collided with the secondary meniscus as a completely free-falling flow (Figure 4B). It was found that, when the water throughput was the same, the latter case resulted in a greater amount of bubble (plume) generation.

[0072] Furthermore, water model experiments confirmed that if the amount of bubble generation is excessively low, the effect of reducing the flow velocity of the downflow water becomes small, making it easier for short paths to occur. On the other hand, if the amount of bubble generation is excessively high, even if the lower part of the long nozzle is expanded, it becomes difficult to collect the plume inside the long nozzle, and boiling occurs. It was also confirmed that the amount of plume generation changes depending on the water flow rate (throughput), free fall distance, and surface turbulence of the falling flow. For example, it was confirmed that the amount of bubble generation increases as the water throughput TP is large, the free fall distance H is long, and the surface turbulence of the falling flow is large. For example, when the throughput is small, equivalent to less than 5 tons / min of molten metal, and the angle θ of the expanded section is small, less than 15°, the amount of plume generation is small (Figure 4A), and short paths are easily formed. On the other hand, if the throughput is high, equivalent to 5 tons / min or more of molten metal, the angle θ of the expanded section is 15° or more, and the starting position of the expanded section is far from the tundish surface, the amount of plume generated increases (Figure 4B), making it difficult to recover the plume even if the lower part of the long nozzle is expanded.

[0073] Preliminary experiments conducted under various conditions confirmed that when the water throughput TP is small (less than 5 tons / min in terms of molten metal), setting the angle θ of the expanding section to 15° or more, and positioning the starting point of the expanding section at a distance from the tundish molten metal surface (600 mm ≤ H), thereby increasing the free fall distance, can result in an appropriate amount of plume generation (First Form). Furthermore, when the throughput TP is large (more than 5 tons / min in terms of molten metal), setting the angle θ of the expanding section to 15° or less, and allowing the molten metal to flow down the inner wall of the nozzle and collide with the secondary meniscus, can result in an appropriate amount of plume generation (Second Form). Alternatively, when the throughput TP is large, equivalent to 5 tons / min or more in terms of molten metal, and the angle θ of the enlarged diameter section is large, equivalent to 15° or more, it has been confirmed that the amount of plume generated can be suppressed to an appropriate level by setting the starting position of the enlarged diameter section near the tundish surface (H < 600 mm, preferably H ≤ 400 mm) and shortening the free fall distance (third form).

[0074] 2. Continuous casting test Continuous casting tests were conducted to confirm the relationship between molten metal flow rate (throughput), free fall distance, and surface turbulence of the falling flow, and to confirm that the effects of the first to third forms described above were valid. Specifically, continuous casting of steel was performed using the system shown in Figures 1 to 3. Table 1 below shows the continuous casting conditions for each of the examples and comparative examples. TP, D0, D1, D2, θ, L, L0, L1, L2, L in Table 1 D The details of H are as shown in Figures 2 and 3. Furthermore, Table 2 below shows the composition of the cast slabs used in the examples and comparative examples.

[0075] In Table 1, the "Steel Cleanliness Index" refers to the total oxide content (TO) of 5mm square x 50mm long (casting direction length) 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.

[0076] When bubbles in the long nozzle escape to the outside of the nozzle, these bubbles float to the surface of the tundish water, causing the water to boil. The "bubble recovery rate" in Table 1 is evaluated based on the degree of boiling observed by a camera, according to the following criteria. ○: No water boiling occurs at all. △: The water boils occasionally. ×: Hot water is constantly being generated.

[0077] [Table 1]

[0078] [Table 2]

[0079] Examples 1-4 have TP < 5 ton / min, θ > 15°, H ≥ 600 mm, and L ≤ 250 mm. D This is an example that satisfies the conditions ≤450mm and 150mm ≤ D2 ≤ 350mm, and corresponds to the first form described above. In Examples 1 to 4, although the throughput TP was small, by increasing the angle θ of the enlarged diameter section and increasing the height H, the molten steel inside the long nozzle separated from the nozzle wall and was driven into the secondary meniscus as a free-fall flow, generating many bubbles (plumes). In Examples 1 to 4, a sufficient amount of plume was generated and was able to be recovered inside the long nozzle, so it is thought that boiling and short passes in the tundish were suppressed, and the cleanliness of the steel was improved. In contrast, in Comparative Example 1, TP < 5 ton / min, 250 mm ≤ L D Although the conditions of ≤450mm and 150mm ≤ D2 ≤ 350mm were met, the conditions of θ > 15° and H ≥ 600mm were not met. As a result, it is thought that the amount of plume generated inside the long nozzle was insufficient, short passes occurred, and the cleanliness index of the steel deteriorated.

[0080] Examples 5-8 have the following conditions: TP ≥ 5 ton / min, 0° < θ ≤ 15°, 400 mm ≤ L D This is an example that satisfies the conditions ≤600mm and 150mm ≤ D2 ≤ 350mm, and corresponds to the second form described above. In Examples 5 to 8, although the throughput TP is large, the angle θ of the enlarged diameter section is made small, and the immersion depth L D By increasing the depth, an appropriate amount of plume was generated inside the long nozzle and could be collected within the long nozzle, which suppressed boiling and short-path occurrence in the tundish and improved the cleanliness of the steel. In contrast, in Comparative Example 2, although the conditions TP≧5ton / min, 0°<θ≦15°, and 150mm≦D2≦350mm were met, 400mm≦L D It is believed that the condition of ≤600mm was not met, which prevented the generated plume from being retained and collected within the long nozzle, resulting in boiling and a deterioration of the steel's cleanliness index.

[0081] Examples 9-12 have the following conditions: TP ≥ 5 ton / min, θ > 15°, H < 600 mm, L ≤ 400 mm. D This is an example that satisfies the conditions ≤600mm and 150mm ≤ D2 ≤ 350mm, and corresponds to the third form described above. In Examples 9 to 12, the throughput TP is large and the angle θ of the enlarged diameter section is large, but the height H is low and the immersion depth L D By increasing the depth, an appropriate amount of plume was generated inside the long nozzle and could be collected within the long nozzle, which suppressed boiling and short-path generation in the tundish and improved the cleanliness of the steel. In contrast, in Comparative Example 3, TP ≥ 5 ton / min, θ > 15°, 400 mm ≤ L D Although the conditions of ≤600mm and 150mm ≤ D2 ≤ 350mm were met, the condition H < 600mm was not met. As a result, excessive plume was generated, and the generated plume could not be retained and collected within the long nozzle, causing boiling and a deterioration in the cleanliness index of the steel.

[0082] Furthermore, in Comparative Example 4, the inner diameter D2 of the outlet of the long nozzle was too small, causing the plume generated inside the long nozzle to flow out from the outlet. Moreover, the generated plume could not be retained or recovered within the long nozzle, resulting in boiling and a deterioration of the steel's cleanliness index.

[0083] In the above examples, we have illustrated the case where molten steel having a predetermined composition is used as the molten metal, but the effects of the above examples can be similarly expected when molten metals other than molten steel are used.

[0084] 3. Summary Based on the above results, it can be said that with the following nozzle system, when supplying molten metal from the ladle to the tundish via the long nozzle, the falling flow of molten metal inside the long nozzle collides with the secondary meniscus to generate a sufficient amount of plume. This suppresses the production of bare molten metal due to short passes and reversed upward flows, while efficiently recovering the generated plume inside the long nozzle, thereby suppressing the re-oxidation of the molten metal due to boiling.

[0085] A nozzle system that supplies molten metal from a ladle to a tundish via a long nozzle, The long nozzle is a cylindrical single-hole nozzle having an inlet, a minimum diameter section, an enlarged diameter section, a straight cylindrical section, and an outlet. The minimum diameter portion is located on the inlet side of the outlet side, The enlarged diameter portion exists from the minimum diameter portion to the straight cylindrical portion, and the inner diameter of the nozzle expands from the minimum diameter portion towards the straight cylindrical portion. The straight cylindrical portion extends from the lower end of the enlarged diameter portion to the outlet, The outlet 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, Either conditions 1-1 to 1-5 below are met, or conditions 2-1 to 2-4 below are met, or conditions 3-1 to 3-5 below are met. Nozzle system. Condition 1-1: TP<5ton / min Condition 1-2: θ > 15° Condition 1-3: H≧600mm Condition 1-4: 250mm≦L D ≤450mm Condition 1-5: 150mm≦D2≦350mm Condition 2-1: TP≧5ton / min Condition 2-2: 0°<θ≦15° Condition 2-3: 400mm≦L D ≤600mm Condition 2-4: 150mm≦D2≦350mm Condition 3-1: TP≧5ton / min Condition 3-2: θ > 15° Condition 3-3:H<600mm Condition 3-4: 400mm≦L D ≤600mm Condition 3-5: 150mm≦D2≦350mm Here, TP is the throughput of molten metal. θ is the angle between the inner wall surface of the nozzle and the nozzle axis in the enlarged diameter portion of the longitudinal cross-sectional shape of the nozzle. H is the distance from the minimum diameter portion to the liquid surface of the molten metal in the tundish, L D This is the immersion depth of the long nozzle, D2 is the inner diameter of the nozzle at the outlet. [Explanation of Symbols]

[0086] 100 Nozzle System 101 Ladle 101a Bottom 101b side wall 102 Tan Dish 102a Bottom 102b side wall 102c lid 105 Molten metal 10 Long Nozzles 11 Inlet 12 Minimum diameter part 13 Expanded diameter part 14 Straight cylinder part 15 Outlet 16 Second straight section 10a Gas phase region 10b Secondary Meniscus 111 Collector nozzle 112 Flow rate adjustment mechanism (sliding nozzle) 112a Slide plate 113 Inert gas supply mechanism 20 nozzles

Claims

1. A nozzle system that supplies molten metal from a ladle to a tundish via a long nozzle, The long nozzle is a cylindrical single-hole nozzle having an inlet, a minimum diameter section, an enlarged diameter section, a straight cylindrical 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 straight cylindrical portion, and the inner diameter of the nozzle expands from the minimum diameter portion towards the straight cylindrical portion. The straight cylindrical portion extends from the lower end of the enlarged diameter portion to the outlet, The outlet 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, Either conditions 1-1 to 1-5 below are met, or conditions 2-1 to 2-4 below are met, or conditions 3-1 to 3-5 below are met. Nozzle system. Condition 1-1: TP<5ton / min Condition 1-2: θ > 15° Condition 1-3: H≧600mm Conditions 1-4: 250mm ≤ L Ｄ ≤450mm Conditions 1-5: 150mm ≤ D ２ ≤350mm Condition 2-1: TP≧5ton / min Condition 2-2: 0°<θ≦15° Conditions 2-3: 400mm ≤ L Ｄ ≤600mm Conditions 2-4: 150mm ≤ D ２ ≤350mm Condition 3-1: TP≧5ton / min Condition 3-2: θ > 15° Condition 3-3: H<600mm Conditions 3-4: 400mm ≤ L Ｄ ≤600mm Conditions 3-5: 150mm ≤ D ２ ≤350mm Here, TP is the throughput of molten metal. θ is the angle between the inner wall surface of the nozzle and the nozzle axis in the enlarged diameter portion of the longitudinal cross-sectional shape of the nozzle. H is the distance from the minimum diameter portion to the liquid surface of the molten metal in the tundish, L Ｄ This is the immersion depth of the long nozzle, D ２ This is the inner diameter of the nozzle at the outlet.

2. The above condition 3-3 is the condition H ≤ 400 mm. The nozzle system according to claim 1.

3. The following condition 4-1 is met: The nozzle system according to claim 1. Condition 4-1: 50mm ≤ D １ ≤200mm Here, D １ This is the inner diameter of the nozzle at the minimum diameter portion.

4. The following condition 4-2 is met: The nozzle system according to claim 3. Condition 4-2: 0.2≦D １ / D ２ ≤ 1.0

5. The aforementioned tundish does not have a weir. The nozzle system according to any one of claims 1 to 4.

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