Nozzle system

Abstract

To disclose a technique which suppresses occurrences of reoxidation of molten metal, and bare melts and short paths in a tundish when molten metal is supplied from a ladle to a tundish via a nozzle, in order to enhance the cleanliness of molten metal.SOLUTION: In a nozzle system for supplying molten metal from a ladle to a tundish via a long nozzle, inert gas is supplied from the outside of the long nozzle to the inside, and a gas phase region containing the inert gas inside the long nozzle, and a secondary meniscus of the molten metal exist, and a height ΔH of the secondary meniscus is 0 cm to 20 cm according to control of pressure in the gas phase region.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] In the continuous casting process of molten metal, a tundish is used as an intermediate vessel 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, and impurities in steel such as bubbles generated during the steelmaking process. When such non-metallic inclusions remain in the final product, it is known to deteriorate the material properties of the final product, for example, as a starting point for fracture due to stress concentration. 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 also can 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 components 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 ensure the time required for the floating of non-metallic inclusions when reducing non-metallic inclusions in molten steel, it is considered effective to increase the residence time of non-metallic inclusions in the tundish.

[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 leading to the mold (see Fig. 3), it is not always easy to ensure the residence time of 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 removal is generated, and a new flow that travels at high speed toward the mold while detouring can be induced, so it does not necessarily assist the floating of inclusions. In particular, small inclusions have a small buoyancy and are easily followed by the flow of molten steel, so the effect of detouring is likely to be limited to the removal of large inclusions.

[0006] In the steelmaking process, attention must also be paid to the unintentional increase in non-metallic inclusions due to the reoxidation of molten steel. Generally, from the perspective of avoiding difficulties in stable casting caused by gas generation accompanying the temperature drop of molten steel, etc., the molten steel used for continuous casting is subjected to deoxidation treatment in the refining process and has an oxygen concentration far lower than the soluble oxygen concentration, being in a state where it is very easy to absorb oxygen. When air or lower oxides come into contact with the molten steel, the molten steel absorbs oxygen, and a reoxidation phenomenon occurs in which non-metallic inclusions are formed by combining with elements having a higher affinity for oxygen than the molten steel (such as Al and Si dissolved in the molten steel). Therefore, in the ladle and tundish, it is necessary to make the inside of the tundish have a low oxygen concentration by replacing the atmosphere with an inert gas, or to shield the molten steel from the outside air by coating the surface of the molten steel with a low-reactivity flux having a low content of lower oxides. However, when supplying molten steel to the tundish through a long nozzle, since the molten steel flow discharged from the nozzle is very fast as described above, the flux covering the surface of the molten steel near the long nozzle is pushed back by the reverse upward flow generated by the collision at the bottom of the tundish, and the surface of the molten steel is directly exposed to the outside air as bare molten steel, and a reoxidation phenomenon in which the molten steel absorbs oxygen in the atmosphere may occur (see Figure 3). Alternatively, since there is slag with a high concentration of lower oxides such as FeO flowing out from the ladle near the long nozzle, reoxidation of the molten steel by the lower oxides in the slag may occur due to the intense molten steel flow near the long nozzle.

[0007] Conventionally, various means for solving the above problems have been proposed. For example, Patent Document 1 discloses a continuous casting method using an injection tube that blocks the injection flow from the outside air with a cylindrical body having a refractory property with an inner diameter of 300 mm or more. According to the technique disclosed in Patent Document 1, the injection flow that has fallen from the nozzle strikes the gas inside the tube at the liquid level inside the tube, introducing a large number of bubbles into the molten steel. It is considered possible to reduce the injection flow rate by the large buoyancy of the bubbles, generating a gentle upward flow in the tundish. In addition, since the solid inclusions have poor wettability with the molten steel and easily adhere to the bubbles, it is also expected that they will float and be removed at high speed by the large buoyancy of the bubbles. On the other hand, in the injection tube as described above, when the droplets of molten steel discharged from the ladle nozzle or the molten steel scattered on the bath surface adhere to the inner wall of the tube, since the tube diameter is large, the heat extraction of the adherent is remarkable, and the adherent is likely to solidify and accumulate, leading to blockage. This is a major problem that makes it difficult to continue the operation of continuous casting. In addition, in the injection tube, in order to prevent the molten steel from absorbing oxygen or nitrogen from the gas phase, it is necessary to fill the inside of the tube with a large amount of inert gas, which results in a problem of high operating costs compared to the case where the long nozzle is immersed in the molten steel.

[0008] Patent Document 2 discloses a nozzle provided with a flow control part in the body part in order to prevent the exposure of the bare bath due to the upward flow reversed at the bottom of the tundish. However, in the technique disclosed in Patent Document 2, it is necessary to take separate measures against the occurrence of short circuits, increasing the manufacturing cost. In addition, since the weight of the nozzle increases, the load on the device that grips the nozzle is large, and it may become impossible to support the nozzle during casting, and there is a risk that the molten steel will spout from the joint part of the long nozzle.

[0009] Patent Document 3 discloses a continuous casting method and a continuous casting apparatus that form a gas space for an inert gas inside an injection nozzle, entrain the inert gas into the injection flow at the molten steel surface in the nozzle, and stir the injection flow in a stirring box installed at the bottom of the tundish to promote the aggregation of inclusions and bubbles in the molten steel. 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 situation where all the bubbles entrained by the injection flow re-ascend into the injection nozzle and the stirring action in the stirring box is not fully exerted, the inner diameter of the injection nozzle is set to be equal to or less than a predetermined value. However, the bubbles that rise to the molten steel surface of the tundish after leaving the injection nozzle 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.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0011] This application discloses a technique capable of suppressing re-oxidation of molten metal, generation of bare molten metal and short circuit in the tundish, etc., and enhancing the cleanliness of molten metal when supplying molten metal from a ladle to a tundish through a long nozzle.

Means for Solving the Problems

[0012] As one of the means for solving the above problems, this application A nozzle system for supplying molten metal from a ladle to a tundish through a long nozzle, wherein the long nozzle has an inlet on the ladle side which is the upstream side, an outlet on the tundish side which is the downstream side, and is a cylindrical single-hole nozzle extending downward from the upstream side to the downstream side, wherein 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, wherein an inert gas is supplied from the outside to the inside of the long nozzle, and a gas phase region containing the inert gas and a secondary meniscus of the molten metal exist inside the long nozzle, wherein by controlling the pressure of the gas phase region, the secondary meniscus height ΔH defined by the following formula (1) is configured to be 0 cm or more and 20 cm or less, Nozzle system is disclosed.

[0013] ΔH=(P T -P L ) / (ρ·g) …(1) Here, P T is the atmospheric pressure in the tundish, P L is the pressure of the gas phase region in the long nozzle, ρ is the density of the molten metal, g is the acceleration due to gravity.

[0014] The nozzle system of the present disclosure may be configured such that when the pressure of the gas phase region is higher than a first threshold value, the amount of the inert gas supplied to the gas phase region decreases and the pressure of the gas phase region decreases.

[0015] The nozzle system of the present disclosure may be configured such that when the pressure of the gas phase region is lower than a second threshold value, the amount of the inert gas supplied to the gas phase region increases and the pressure of the gas phase region increases.

[0016] In the nozzle system of the present disclosure, the long nozzle may have at least one communication hole, and the gas phase region in the long nozzle and the atmosphere in the tundish may be configured to communicate with each other through the communication hole.

[0017] In the nozzle system of the present disclosure, the tundish may not have a weir inside.

Advantages of the Invention

[0018] According to the technology of the present disclosure, when supplying molten metal from the ladle to the tundish through the long nozzle, reoxidation of the molten metal, generation of bare molten metal or short circuit in the tundish, etc. can be suppressed, and the cleanliness of the molten metal can be improved.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0020] 1. Nozzle System Figs. 1 and 2 schematically show the configuration of a nozzle system 100 according to an embodiment. As shown in Fig. 1, the nozzle system 100 is a system that supplies molten metal 105 from a ladle 101 to a tundish 102 via a long nozzle 110. As shown in Fig. 2, the long nozzle 110 has an inlet 110x on the ladle 101 side, which is the upstream side, and an outlet 110y on the tundish 102 side, which is the downstream side, and is a cylindrical single-hole nozzle that extends downward from the upstream side to the downstream side. Further, the outlet 110y of the long nozzle 110 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, an inert gas is supplied from the outside to the inside of the long nozzle 110, and a gas phase region 110a containing the inert gas and a secondary meniscus 110b of the molten metal 105 exist inside the long nozzle 110. On the premise that the nozzle system 100 has the above-described configuration, further, by controlling the pressure of the gas phase region 110a, the secondary meniscus height ΔH defined by the following formula (1) is configured to be 0 cm or more and 20 cm or less.

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

[0022] 1.1 Ladle The ladle 101 is a container that serves as a source for supplying molten metal 105 to the tundish 102. As shown in FIGS. 1 and 2, in the nozzle system 100, the ladle 101 has a bottom surface 101a and side walls 101b and holds the molten metal 105. The ladle 101 may further have a lid (not shown). The ladle 101 may be made of any shape and material capable of holding the molten metal 105. Also, an outlet 101ax may be provided in a part of the bottom surface 101a of the ladle 101 so that the molten metal 105 can flow out therefrom. An opening / closing mechanism for controlling the outflow amount of the molten metal 105 may be provided at the outlet 101ax. The long nozzle 110 can be directly or indirectly connected to the outlet 101ax of the ladle 101. For example, as shown in FIG. 2, the long nozzle 110 may be connected to the outlet 101ax of the ladle 101 via a collector nozzle 111 or a sliding nozzle 112. The connection form between the ladle 101 and the nozzle is not particularly limited, and for example, they can be connected by fitting. The ladle 101 and the nozzle may be connected via some intermediate member.

[0023] 1.2 Tundish The tundish 102 is a container that serves as a supply destination for the molten metal 105 from the ladle 101. As shown in FIGS. 1 and 2, the tundish 102 has a bottom surface 102a and side walls 102b, and holds 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 any shape and material that can hold the molten metal 105. As shown in FIG. 1, an outlet 102ax may be provided in a part of the bottom surface 102a of the tundish 102, and may be configured such that the molten metal 105 can flow out therefrom to another container (for example, a mold). An opening / closing mechanism for controlling the outflow amount of the molten metal 105 may be provided at the outlet 102ax. A nozzle 120 may be directly or indirectly connected to the outlet 102ax of the tundish 102. The connection form between the tundish 102 and the nozzle 120 is not particularly limited, and for example, they can be connected by fitting. The tundish 102 and the nozzle 120 may be connected via some intermediate member.

[0024] As shown in FIG. 2, a floating layer 106 containing a flux may exist on the liquid surface 105a of the molten metal 105 supplied to the tundish 102. A known flux may be adopted as the flux. By covering the liquid surface 105a of the molten metal 105 with the flux in this way, the molten metal 105 can be shielded from the outside air. Further, non-metallic inclusions in the molten metal 105 can be recovered by the flux. Furthermore, an inert gas may be supplied into the tundish 102 so that outside air hardly enters the tundish 102. Thereby, reoxidation of the molten metal 105 can be further suppressed. Incidentally, as will be described later, according to the nozzle system 100, due to the deceleration effect of the molten metal 105 by the bubble plume and the like, the reverse upward flow (see FIG. 3) caused by the molten metal 105 flowing out from the long nozzle 110 colliding with the bottom surface 102a of the tundish 102 can be greatly suppressed, the liquid surface 105a of the tundish 102 is hardly disturbed, and the flux is hardly pushed back or interrupted due to the disturbance of the liquid surface 105a, so that the problem of reoxidation due to the bare bath hardly occurs.

[0025] As shown in FIG. 1, the tundish 102 may not have a weir inside. In the nozzle system 100 of the present disclosure, a secondary meniscus 110b is formed inside the long nozzle 110, and when the falling flow of the molten metal 105 collides with the secondary meniscus 110b, the downward flow velocity of the molten metal 105 is likely to be reduced due to the phenomenon of entraining the gas phase (formation of a bubble plume), and the short path of the molten metal 105 in the tundish 102 (see FIG. 3) is also likely to be suppressed. Therefore, it is easy to remove non-metallic inclusions and the like contained in the molten metal 105 without providing a weir inside the tundish 102.

[0026] 1.3 Nozzle 1.3.1 Long Nozzle As shown in FIGS. 1 and 2, the molten metal 105 is supplied from the ladle 101 to the tundish 102 through the long nozzle 110. The long nozzle 110 has an inlet 110x on the ladle 101 side which is the upstream side, and an outlet 110y on the tundish 102 side which is the downstream side. The long nozzle 110 is a nozzle with a single cylindrical hole extending downward from the upstream side to the downstream side. Specifically, the long nozzle 110 may be a cylindrical body having a central axis in the vertical direction. Note that the long nozzle 110 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 to the lid of the tundish is different from that of the long nozzle referred to in the present application.

[0027] As shown in FIGS. 1 and 2, the outlet 110y of the long nozzle 110 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 110 on the downstream side is immersed in the molten metal 105 inside the tundish 102. As shown in FIG. 2, in the nozzle system 100, there may be a distance h1 between the liquid level 105a of the molten metal 105 in the tundish 102 and the outlet 110y of the long nozzle 110, and there may be a distance h2 between the outlet 110y of the long nozzle 110 and the bottom surface 102a of the tundish 102. The specific values of h1 and h2 and the relationship between h1 and h2 are not particularly limited. For example, h1 may be 100 mm or more and 600 mm or less, h2 may be 200 mm or more and 900 mm or less, the ratio h1 / h2 of h1 and h2 may be 0.2 or more and 1.0 or less, and the ratio D3 / h2 of the nozzle inner diameter D3 at the outlet 110y and h2 may be 0.2 or more and 3.0 or less. By adjusting h1 and h2, it becomes easier to further suppress the detachment of the bubbles generated by the mechanism described later from the long nozzle 110.

[0028] As shown in FIG. 2, the long nozzle 110 may have a minimum inner diameter D1 upstream of the secondary meniscus 110b, an inner diameter D2 at the secondary meniscus 110b, and an inner diameter D3 at the outlet 110y downstream of the secondary meniscus 110b. Note that D2 may vary between D1 and D3. The specific values of the inner diameters D1 to D3 are not particularly limited. For example, D1 may be 100 mm or more and 150 mm or less, D2 may be 100 mm or more and 300 mm or less, and D3 may be 150 mm or more and 300 mm or less.

[0029] Also, the long nozzle 110 may have a length L1 between the inlet 110x and the position of the secondary meniscus 110b, and may have a length L2 between the position of the secondary meniscus 110b and the outlet 110y. The overall length L of the long nozzle 110 may be L1 + L2. The specific values of L, L1, and L2 are not particularly limited. For example, L may be 1000 mm or more and 1700 mm or less, L1 may be 750 mm or more and 1000 mm or less, and L2 may be 250 mm or more and 700 mm or less.

[0030] As shown in FIG. 2, between the portion having the minimum inner diameter D1 and the outlet 110y of the long nozzle 110, it is better not to have a diameter-reducing portion where the inner diameter decreases from the upstream side to the downstream side. In particular, between the portion where the secondary meniscus 110b is located and the outlet 110y, it is better not to have a diameter-reducing portion where the inner diameter decreases from the upstream side to the downstream side. This is because if there is a diameter-reducing portion downstream of the secondary meniscus 110b, the downward flow velocity of the molten metal 105 increases in that portion, and there is a risk that the effect of the nozzle system 100 will be slightly reduced.

[0031] On the other hand, as shown in FIG. 2, the long nozzle 110 may have a diameter-expanding portion 110c whose inner diameter increases from the upstream side to the downstream side. The diameter expansion rate in the diameter-expanding portion 110c is not particularly limited. In the diameter-expanding portion 110c, the nozzle inner diameter may linearly expand (expand with a monotonic increase) from the upstream side to the downstream side, or may expand curvilinearly. Further, in the diameter-expanding portion 110c, the nozzle inner diameter may continuously expand or may expand intermittently from the upstream side to the downstream side. Also, the ratio of the length of the diameter-expanding portion 110c to the overall length of the long nozzle 110 is not particularly limited. In the long nozzle 110, the nozzle inner diameter at the lower end of the diameter-expanding portion 110c (the portion where the diameter expansion ends) and the nozzle inner diameter D3 at the outlet 110y may be substantially the same or may be different from each other. Further, the long nozzle 110 may have a plurality of diameter-expanding portions.

[0032] 1.3.2 Collector Nozzle As shown in FIG. 2, in the nozzle system 100, a collector nozzle 111 may be provided upstream of the long nozzle 110. The upstream end of the collector nozzle 111 can be directly or indirectly connected to the ladle 101. Also, the downstream end of the collector nozzle 111 can be connected to the upstream end of the long nozzle 110. As shown in FIG. 2, the collector nozzle 111 may have an inner diameter D0 at the connection portion with the long nozzle 110. The specific value of D0 is not particularly limited. For example, the relationship 1.0 ≦ D1 / D0 ≦ 1.4 may be satisfied between D0 and the above-described D1. That is, at the connection portion between the long nozzle 110 and the collector nozzle 111, the ratio D1 / D0 of the minimum inner diameter D1 (cm) of the long nozzle 110 to the inner diameter D0 (cm) of the collector nozzle 111 may be 1.0 or more and 1.4 or less. If this ratio is too small, a step may occur due to a reduction in diameter from the upstream side to the downstream side at or near the connection portion between the long nozzle 110 and the collector nozzle 111, which may cause leakage of the molten metal 105 or abnormal wear of the refractory. On the other hand, if this ratio is too large, the molten metal 105 is likely to adhere to the inner wall of the long nozzle 110 due to the influence of heat radiation from the side surface of the long nozzle 110. There is also a risk that the weight of the long nozzle 110 will increase unnecessarily. The collector nozzle 111 may be appropriately selected and configured from conventionally known collector nozzles. The structure at the connection portion between the long nozzle 110 and the collector nozzle 111 may be the same as conventional ones. For example, the connection portion may be configured by fitting the upper end of the long nozzle 110 and the lower end of the collector nozzle 111 together.

[0033] 1.3.3 Sliding Nozzle As shown in FIG. 2, in the nozzle system 100, a flow rate adjustment mechanism 112 may be provided upstream of the collector nozzle 111. Specific examples of the flow rate adjustment mechanism 112 include, for example, a sliding nozzle as shown in FIG. 2. In the sliding nozzle, at least one slide plate 112a having a flow passage opening is slid in a direction intersecting the flow direction of the molten metal 105, so that the flow path can change. Alternatively, the flow rate adjustment mechanism 112 may be an opening / closing mechanism other than the sliding nozzle. Since the form of the flow rate adjustment mechanism 112 is well known, further explanation is omitted here.

[0034] 1.4 Inert gas supply mechanism As shown in FIG. 2, in the nozzle system 100, an inert gas is supplied from the outside to the inside of the long nozzle 110, and a gas phase region 110a containing the inert gas and a secondary meniscus 110b of the molten metal 105 are formed inside the long nozzle 110. The method and means for supplying the inert gas from the outside to the inside of the long nozzle 110 are not particularly limited. For example, as shown in FIG. 2, the nozzle system 100 may have an inert gas supply mechanism 113 for supplying the inert gas from the outside to the inside of the long nozzle 110. In addition, when the molten metal 105 is supplied from the ladle 101 to the tundish 102 through the nozzle, outside air may be taken into the inside of the long nozzle 110 by an ejector from the connection part between the ladle 101 and the nozzle or the connection part between the nozzles. However, in the nozzle system 100, separately from this, a mechanism 113 for intentionally supplying the inert gas to the inside of the long nozzle 110 can be adopted.

[0035] In the nozzle system 100, during the supply of the molten metal 105, a gas phase region 110a and a secondary meniscus 110b are formed inside the long nozzle 110, and the height ΔH of the secondary meniscus is maintained within a predetermined range. When the downward flow of the molten metal 105 collides with the secondary meniscus 110b, gas is entrained from the gas phase region 110a into the molten metal 105, and various bubble groups of different sizes can be generated in the molten metal 105. Since the nozzle system 100 has a mechanism 113 for supplying an inert gas into the long nozzle 110, it becomes easier to maintain the gas phase region 110a inside the long nozzle 110, and the control of the height ΔH of the secondary meniscus also becomes easier. Examples of the inert gas include Ar. The supply amount of the inert gas to the long nozzle 110 is not particularly limited, and the pressure in the gas phase region 110a is not particularly limited either, as long as the height ΔH of the secondary meniscus is within a predetermined range for both. The inert gas supply mechanism 113 may include a control unit for controlling the supply amount and pressure of the inert gas. For example, based on a signal from the control unit or the like, opening and closing control of the inert gas supply valve or the like is performed, and the supply amount and pressure of the inert gas can be controlled to a target value.

[0036] The specific form of the mechanism 113 for supplying the inert gas into the long nozzle 110 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) and the long nozzle 110 via piping, valves, etc. Alternatively, the inert gas supply source can be connected to a position upstream of the long nozzle 110 (such as the collector nozzle 111, the sliding nozzle 112, or the ladle 101) so that the molten metal 105 supplied with the inert gas flows into the long nozzle 110. However, when the inert gas supply mechanism 113 is directly connected to the long nozzle 110 or connected in the vicinity of the long nozzle 110, it becomes easier to control the amount of the inert gas blown into the long nozzle 110. For example, the position where the inert gas is supplied by the above mechanism 113 may be at or near the connection portion between the long nozzle 110 and the collector nozzle 111, specifically, it may be within a range of 100 mm from the connection portion. Within this range, it is easy to install the above mechanism 113. Also, by supplying the inert gas within this range, it becomes easier to further form the gas phase region 110a inside the long nozzle 110. Alternatively, when the long nozzle 110 includes the above-described enlarged diameter portion 110c, the inert gas supply mechanism 113 may be provided in the enlarged diameter portion 110c.

[0037] 1.5 Equation (1) In the nozzle system 100, it is important that the pressure of the gas phase region 110a in the long nozzle 110 is controlled so that the secondary meniscus height ΔH defined by the above equation (1) is 0 cm or more and 20 cm or less. ΔH may be 15 cm or less.

[0038] As shown in FIG. 2, ΔH corresponds to the difference between the height position of the secondary meniscus 110b inside the long nozzle 110 and the height position of the liquid surface 105a of the molten metal 105 in the tundish 102. As shown in the above formula (1), in the nozzle system 100, the higher the pressure in the gas phase region 110a inside the long nozzle 110, the smaller ΔH becomes. The case where ΔH is 0 cm corresponds to the case where the pressure in the gas phase region 110a is equal to the atmospheric pressure inside the tundish 102. That is, in the nozzle system 100, the pressure in the gas phase region 110a inside the long nozzle 110 is the same as or lower than the atmospheric pressure inside the tundish 102.

[0039] In the nozzle system 100, when ΔH becomes negative (when the pressure in the gas phase region 110a inside the long nozzle 110 is positive with respect to the atmospheric pressure inside the tundish 102), the volume of the long nozzle 110 from the secondary meniscus 110b to the outlet 110y decreases, and it becomes difficult to exert the action effect by the bubble plume. Also, it may become difficult to retain the bubbles inside the long nozzle 110. On the other hand, when the pressure in the gas phase region 110a of the long nozzle 110 is excessively decreased, it becomes difficult to maintain airtightness, and it is likely to cause suction of outside air. Further, when ΔH becomes excessively large, the free fall distance of the molten metal 105 becomes short, the impact force when the downward flow of the molten metal 105 collides with the secondary meniscus 110b decreases, the entrainment of gas from the gas phase region 110a into the molten metal 105 decreases, and there is a possibility that a sufficient bubble plume is not generated.

[0040] On the other hand, in the nozzle system 100, by controlling the pressure in the gas phase region 110a so that the height ΔH of the secondary meniscus is 0 cm or more, a sufficient volume of the long nozzle 110 can be ensured between the secondary meniscus 110b and the outlet 110y. The action effect of the bubble plume is exerted, and bubbles are easily retained in the long nozzle 110. As a result, the occurrence of bare molten metal and short paths in the tundish 102 is suppressed, and the cleanliness of the molten metal 105 can be improved. On the other hand, by controlling the pressure in the gas phase region 110a so that the height ΔH of the secondary meniscus is 20 cm or less, the gas phase region 110a does not become excessively negative in pressure, the intake of outside air is suppressed, and as a result, the reoxidation of the molten metal is suppressed, and the cleanliness of the molten metal 105 can be improved.

[0041] The atmospheric pressure P inside the tundish 102 required for the calculation of Equation (1) T can be measured by a pressure gauge installed in a pipe or the like that communicates with the inside of the tundish 102. Also, the pressure P in the gas phase region 110a inside the long nozzle 110 L can similarly be measured by a pressure gauge installed in a pipe or the like that penetrates a refractory to form a flow path communicating with the gas phase region 110a inside the long nozzle 110 and is connected to that flow path. Alternatively, the relationship between the flow rate of the inert gas supplied into the long nozzle 110 and the pressure P in the gas phase region 110a inside the long nozzle 110 L is obtained through preliminary experiments, and P L may be estimated from the supply flow rate of the inert gas. When calculating ΔH using Equation (1), all units should be unified into SI units for calculation. The unit of the obtained ΔH is m, which may be converted to cm.

[0042] The pressure in the gas phase region 110a may be measured continuously or intermittently with the above-described pressure gauge or the like, and the height of the secondary meniscus ΔH can be maintained between 0 cm and 20 cm by increasing or decreasing the amount of the inert gas supplied to the gas phase region 110a according to the measured pressure. Specifically, the nozzle system 100 may be configured such that when the pressure in the gas phase region 110a is higher than the first threshold value, the amount of the inert gas supplied to the gas phase region 110a decreases, and the pressure in the gas phase region decreases. Further, the nozzle system 100 may be configured such that when the pressure in the gas phase region 110a is lower than the second threshold value, the amount of the inert gas supplied to the gas phase region 110a increases, and the pressure in the gas phase region increases. The control of the supply amount of the inert gas can be performed, for example, by controlling an on-off valve by a control unit as described above. Note that the "first threshold value" is not particularly limited, and for example, an appropriate threshold value may be set based on the pressure at which the above-described ΔH becomes 0 cm. Also, the "second threshold value" is not particularly limited, and for example, an appropriate threshold value may be set based on the pressure at which the above-described ΔH becomes 20 cm. The first threshold value and the second threshold value may be different from each other or the same threshold value.

[0043] Alternatively, by communicating the gas phase region 110a with the atmosphere inside the tundish 102, the pressure in the gas phase region 110a can be made to coincide with the atmosphere inside the tundish 102, and as a result, ΔH becomes 0 cm. In this regard, in the nozzle system 100, the long nozzle 110 may have at least one communication hole (not shown), and the gas phase region 110a inside the long nozzle 110 and the atmosphere inside the tundish 102 may be configured to be communicable with each other via the communication hole. As described above, the tundish 102 may be configured such that an inert gas is supplied therein so that outside air hardly enters the tundish 102. In this case, (1) the gas phase region 110a may be constantly opened into the tundish 102 via the communication hole to always maintain the secondary meniscus height ΔH at 0 cm, or (2) when the pressure in the gas phase region 110a is higher than the first threshold value, the inert gas may be discharged from the gas phase region 110a into the tundish 102 via the communication hole, or (3) when the pressure in the gas phase region 110a is lower than the second threshold value, the inert gas may be supplied from the tundish 102 into the gas phase region 110a via the communication hole. That is, the communication hole may be constantly open between the gas phase region 110a and the atmosphere inside the tundish 102, or may be controlled to open and close by a valve or the like. The size and number of the communication holes are not particularly limited. Incidentally, in the nozzle system 100, for example, when the pressure in the gas phase region 110a inside the long nozzle 110 becomes excessively high, the gas phase region 110a may be opened to the outside air. In this case, however, some device (for example, providing a check valve) is required to prevent the intake of outside air into the long nozzle 110 and the reoxidation of the molten metal 105.

[0044] 1.6 Other Conditions and Configurations In the nozzle system 100, as long as the above-described configurations and ΔH are satisfied, other conditions and configurations are not particularly limited. Hereinafter, an example of other conditions and configurations will be shown.

[0045] 1.6.1 Flow Rate of Molten Metal and Average Residence Time in Tundish The flow rate Q of the molten metal 105 supplied to the long nozzle 110 may be, for example, 8000 cm 3 / s or more, and the average residence time τ of the molten metal 105 in the tundish 102 may be, for example, 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 in which a large flow rate of the molten metal 105 passes through the tundish. Specifically, it is the case where the flow rate Q of the molten metal 105 is 8000 cm 3 / s or more. Further, it is still more useful when the same flow rate is 18000 cm 3 / s or more. The upper limit of the same flow rate is not particularly limited, but continuous casting exceeding 40000 cm 3 / s is not practical. This is 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 purification effect for the molten metal 105. It is considered that when the time is 240 seconds or more, inclusions of about 50 to 100 microns, for example, are more likely to be removed by floating. The upper limit value of the same time is not particularly limited, but it is not practical for the time to exceed 1500 seconds during the 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 becomes too large. Incidentally, the average residence time τ is the ratio V τ (cm 3 ) of the volume V of the tundish 102 to the flow rate Q (cm 3 / s) of the molten metal from the nozzle, and can be calculated as V τ / Q.

[0046] 1.6.2 Weir in the tundish As described above, in the nozzle system 100, it is not necessary to provide a weir having a function of controlling the flow of the molten metal 105 inside the tundish 102. According to the nozzle system 100, it is possible to ensure the residence time of the molten metal 105 inside the tundish 102 without using a weir. Rather, if a weir is installed in the tundish 102, there are problems of forming a stagnant area called a dead zone and reducing the actual tundish capacity, and problems of cost increase.

[0047] 1.6.3 Height Dimension 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 101 side and the liquid surface 105a of the tundish 102, and the immersion depth of the long nozzle 110, and is generally often in the range of 1 m to 2.5 m.

[0048] 1.6.4 Type of Molten Metal In the nozzle system 100, there is no particular limitation on the type of molten metal 105 supplied from the ladle 101 to the tundish 102 via the long nozzle 110. In particular, when the molten metal 105 is molten steel, high effects can be expected from the nozzle system 100. The steel grade of the molten steel is not particularly limited.

[0049] 1.7 Function and Effect As described above, in the nozzle system 100, by controlling the pressure in the gas phase region 110a so that the height ΔH of the secondary meniscus is 0 cm or more and 20 cm or less, it is easy to achieve both the function of forming a bubble plume in the molten metal 105 on the downstream side of the secondary meniscus 110b inside the long nozzle 110 and the function of retaining large bubbles constituting the bubble plume inside the long nozzle 110. Thereby, it is possible to simultaneously achieve the capture and removal of non-metallic inclusions, the reduction of the discharge flow rate of the long nozzle, and the prevention of reoxidation on the molten metal surface around the long nozzle. Also, the gas phase region 110a inside the long nozzle 110 does not become excessively negative in pressure, and the intake of outside air into the long nozzle 110 is also suppressed. As a result, problems such as the problem of bare molten metal and the problem of short circuit as shown in Figure 3 are less likely to occur, and the problem of reoxidation of the molten metal 105 due to the intake of outside air is also less likely to occur, and the cleanliness of the molten metal 105 is likely to increase.

[0050] 2. Continuous Casting Method of Molten Metal The technology of the present disclosure also has an aspect as a method for continuous casting of molten metal. The method for continuous casting of molten metal of the present disclosure is characterized by using the nozzle system 100 of the present disclosure. The continuous casting method of the present disclosure may include, for example, supplying molten metal 105 from the ladle 101 to the tundish 102 through the long nozzle 110 using the nozzle system 100, supplying the molten metal 105 from the tundish 102 to a mold (not shown) through the nozzle 120, and continuously withdrawing a slab from the mold. In the method for continuous casting of molten metal of the present disclosure, general continuous casting conditions may be employed except that the above-described nozzle system 100 is adopted. Alternatively, as described above, the flow rate Q and the average residence time τ may be adjusted so as to be equal to or greater than a predetermined value.

[0051] 3. Supplementary In addition, for the exploration of the above-described various indexes and their appropriate ranges, the experimental apparatus according to Patent No. 6750533 by the applicant of the present application can be utilized. The experimental apparatus is an apparatus that can faithfully reproduce the effects of gravity, inertial force, viscous force, and surface tension acting on the molten metal flow and can accurately reproduce the gas-liquid two-phase flow phenomenon including the buoyancy and rising velocity of bubbles.

Examples

[0052] Hereinafter, the present invention will be further described while showing examples, but the present invention is not limited to the following examples. The present invention can adopt various conditions as long as it does not deviate from the gist and can achieve its object.

[0053] Continuous casting of steel was carried out using the system as shown in FIGS. 1 and 2. Table 1 and Table 2 below show the continuous casting conditions for each of the examples and comparative examples. Table 3 below shows the compositions of the cast slabs employed in the examples and comparative examples. Note that the "steel cleanliness index" in Tables 1 and 2 is the value obtained by analyzing the total amount of oxides in samples of 5 mm square × 50 mm length taken from six locations, namely, the 1 / 4 thickness at the center of the width, 1 / 4 thickness at 1 / 4 width, 1 / 4 thickness at 3 / 4 width, 3 / 4 thickness at the center of the width, 1 / 4 thickness at 1 / 4 width and 3 / 4 thickness, and 3 / 4 thickness at 3 / 4 width in a cast slab solidified to a thickness of 250 mm and a width of 1800 mm, with the value of Comparative Example 3B shown later set as 10 and indexed. The smaller this index, the higher the cleanliness of the molten steel.

[0054]

Table 1

[0055]

Table 2

[0056]

Table 3

[0057] 1. When using Long Nozzle A Continuous casting was carried out using the long nozzle shown in FIG. 4(A). In FIG. 4(A), the length L from the inlet of the long nozzle to the upper end of the enlarged diameter part a is 733 mm, the length L b of the enlarged diameter part is 267 mm, and the length L c from the lower end of the enlarged diameter part to the outlet is 400 mm. In this case, the inner diameters D1, D2, and D3 of the long nozzle shown in FIG. 2 are 130 mm, 130 - 210 mm, and 210 mm respectively, h1 is 540 mm, h2 is 740 mm, and the length L from the inlet (upper end) to the outlet (lower end) of the long nozzle is 1400 mm.

[0058] 1.1 Example 1A In Example 1A of Table 1, while supplying molten steel from the ladle to the tundish through the long nozzle at a predetermined molten steel throughput, Ar as an inert gas was blown into the long nozzle to form a gas phase region and a secondary meniscus in the long nozzle. By adjusting the blowing amount or suction amount (discharge amount) of Ar, the height ΔH of the secondary meniscus was changed from 25 cm to 5 cm, and continuous casting was carried out while maintaining ΔH at 5 cm. (At this time, L2 referred to in FIG. 2 was L2 = ΔH + h1 = 590 mm.)

[0059] 1.2 Example 2A In Example 2A of Table 1, while supplying molten steel from the ladle to the tundish through the long nozzle at a predetermined molten steel throughput, Ar as an inert gas was blown into the long nozzle to form a gas phase region and a secondary meniscus in the long nozzle. By adjusting the blowing amount or suction amount (discharge amount) of Ar, the height ΔH of the secondary meniscus was changed from -5 cm to 0 cm, and continuous casting was carried out while maintaining ΔH at 0 cm. (At this time, L2 referred to in FIG. 2 was L2 = ΔH + h1 = 540 mm.)

[0060] 1.3 Example 3A In Example 3A of Table 1, while supplying molten steel from the ladle to the tundish through the long nozzle at a predetermined molten steel throughput, Ar as an inert gas was blown into the long nozzle to form a gas phase region and a secondary meniscus in the long nozzle, and continuous casting was carried out while maintaining the height ΔH of the secondary meniscus at 10 cm. (At this time, L2 referred to in FIG. 2 was L2 = ΔH + h1 = 640 mm.)

[0061] 1.4 Example 4A In Example 4A of Table 1, while supplying molten steel from the ladle to the tundish through the long nozzle at a predetermined molten steel throughput, Ar as an inert gas was blown into the long nozzle to form a gas phase region and a secondary meniscus in the long nozzle. By adjusting the blowing amount or suction amount (discharge amount) of Ar, the height ΔH of the secondary meniscus, which was 30 cm, was changed to 5 cm, and then continuous casting was performed while maintaining ΔH at 5 cm. (At this time, L2 referred to in FIG. 2 was L2 = ΔH + h1 = 590 mm).

[0062] 1.5 Comparative Example 1A In Comparative Example 1A of Table 1, while supplying molten steel from the ladle to the tundish through the long nozzle at a predetermined molten steel throughput, Ar as an inert gas was blown into the long nozzle to form a gas phase region and a secondary meniscus in the long nozzle, and continuous casting was performed while maintaining the height ΔH of the secondary meniscus at -5 cm. (At this time, L2 referred to in FIG. 2 was L2 = ΔH + h1 = 490 mm).

[0063] 1.6 Comparative Example 2A In Comparative Example 2A of Table 1, while supplying molten steel from the ladle to the tundish through the long nozzle at a predetermined molten steel throughput, Ar as an inert gas was blown into the long nozzle to form a gas phase region and a secondary meniscus in the long nozzle. By adjusting the blowing amount or suction amount (discharge amount) of Ar, the height ΔH of the secondary meniscus, which was 50 cm, was changed to 25 cm, and then continuous casting was performed while maintaining ΔH at 25 cm. (At this time, L2 referred to in FIG. 2 was L2 = ΔH + h1 = 790 mm).

[0064] 1.7 Comparative Example 3A In Comparative Example 3A of Table 1, molten steel was supplied from the ladle to the tundish through the long nozzle at a predetermined molten steel throughput, and Ar as an inert gas was blown into the long nozzle to form a gas phase region and a secondary meniscus in the long nozzle. Continuous casting was carried out while maintaining the secondary meniscus height ΔH at 25 cm (at this time, L2 referred to in FIG. 2 was L2 = ΔH + h1 = 790 mm).

[0065] 2. When using Long Nozzle B Continuous casting was carried out using the long nozzle shown in FIG. 4(B). In FIG. 4(B), the length L from the inlet of the long nozzle to the upper end of the enlarged diameter portion d was 733 mm, and the length L from the upper end of the enlarged diameter portion to the outlet e was 667 mm. In this case, the inner diameters D1, D2, and D3 of the long nozzle shown in FIG. 2 were 130 mm, 130 - 210 mm, and 210 mm respectively, h1 was 540 mm, h2 was 740 mm, and the length L from the inlet (upper end) to the outlet (lower end) of the long nozzle was 1400 mm.

[0066] 2.1 Example 1B In Example 1B of Table 2, molten steel was supplied from the ladle to the tundish through the long nozzle at a predetermined molten steel throughput, and Ar as an inert gas was blown into the long nozzle to form a gas phase region and a secondary meniscus in the long nozzle. By adjusting the blowing amount or suction amount (discharge amount) of Ar, the secondary meniscus height ΔH, which was originally 30 cm, was changed to 10 cm, and then continuous casting was carried out while maintaining ΔH at 10 cm (at this time, L2 referred to in FIG. 2 was L2 = ΔH + h1 = 640 mm).

[0067] 2.2 Example 2B In Example 2B of Table 2, while supplying molten steel from the ladle to the tundish through the long nozzle at a predetermined molten steel throughput, Ar as an inert gas was blown into the long nozzle to form a gas phase region and a secondary meniscus in the long nozzle. By adjusting the blowing amount or suction amount (discharge amount) of Ar, the height ΔH of the secondary meniscus, which was 25 cm, was changed to 15 cm, and then continuous casting was carried out while maintaining ΔH at 15 cm. (At this time, L2 referred to in Fig. 2 was L2 = ΔH + h1 = 690 mm).

[0068] 2.3 Example 3B In Example 3B of Table 2, while supplying molten steel from the ladle to the tundish through the long nozzle at a predetermined molten steel throughput, Ar as an inert gas was blown into the long nozzle to form a gas phase region and a secondary meniscus in the long nozzle, and continuous casting was carried out while maintaining the height ΔH of the secondary meniscus at 10 cm. (At this time, L2 referred to in Fig. 2 was L2 = ΔH + h1 = 640 mm).

[0069] 2.4 Example 4B In Example 4B of Table 2, while supplying molten steel from the ladle to the tundish through the long nozzle at a predetermined molten steel throughput, Ar as an inert gas was blown into the long nozzle to form a gas phase region and a secondary meniscus in the long nozzle. By adjusting the blowing amount or suction amount (discharge amount) of Ar, the height ΔH of the secondary meniscus, which was -10 cm, was changed to 5 cm, and then continuous casting was carried out while maintaining ΔH at 5 cm. (At this time, L2 referred to in Fig. 2 was L2 = ΔH + h1 = 590 mm).

[0070] 2.5 Comparative Example 1B In Comparative Example 1B of Table 2, while supplying molten steel from the ladle to the tundish through the long nozzle at a predetermined molten steel throughput, Ar as an inert gas was blown into the long nozzle to form a gas phase region and a secondary meniscus in the long nozzle. By adjusting the blowing amount or suction amount (discharge amount) of Ar, the height ΔH of the secondary meniscus was changed from -10 cm to -5 cm, and continuous casting was performed while maintaining ΔH at -5 cm. (At this time, L2 referred to in FIG. 2 was L2 = ΔH + h1 = 490 mm).

[0071] 2.6 Comparative Example 2B In Comparative Example 2B of Table 2, while supplying molten steel from the ladle to the tundish through the long nozzle at a predetermined molten steel throughput, Ar as an inert gas was blown into the long nozzle to form a gas phase region and a secondary meniscus in the long nozzle. By adjusting the blowing amount or suction amount (discharge amount) of Ar, the height ΔH of the secondary meniscus was changed from 35 cm to 25 cm, and continuous casting was performed while maintaining ΔH at 25 cm. (At this time, L2 referred to in FIG. 2 was L2 = ΔH + h1 = 790 mm).

[0072] 2.7 Comparative Example 3B In Comparative Example 3B of Table 2, while supplying molten steel from the ladle to the tundish through the long nozzle at a predetermined molten steel throughput, Ar as an inert gas was blown into the long nozzle to form a gas phase region and a secondary meniscus in the long nozzle. By adjusting the blowing amount or suction amount (discharge amount) of Ar, the height ΔH of the secondary meniscus was changed from 25 cm to -10 cm, and continuous casting was performed while maintaining ΔH at -10 cm. (At this time, L2 referred to in FIG. 2 was L2 = ΔH + h1 = 440 mm).

[0073] 3. Results From the results shown in Tables 1 and 2, it can be seen that by controlling the pressure in the gas phase region within the long nozzle so that the height ΔH of the secondary meniscus is 0 cm or more and 20 cm or less regardless of the shape of the long nozzle, the cleanliness of the steel in the slab obtained after continuous casting is improved compared to the case where the control is such that ΔH is less than 0 cm or more than 20 cm. That is, by controlling ΔH to be 0 cm or more, it is considered that the function of forming a bubble plume in the molten steel on the downstream side of the secondary meniscus inside the long nozzle and the function of retaining large bubbles constituting the bubble plume inside the long nozzle could be made compatible. As a result, the capture and removal of non-metallic inclusions, the reduction of the discharge flow rate from the long nozzle, and the prevention of reoxidation on the molten steel surface around the long nozzle can be simultaneously achieved. Also, if ΔH is 20 cm or less, it is considered that the gas phase region inside the long nozzle does not become excessively negative in pressure and the intake of outside air into the long nozzle is also suppressed. As a result, problems such as the problem of exposed molten steel in the tundish and the problem of short circuit are less likely to occur, and also the problem of reoxidation of the molten steel due to the intake of outside air is less likely to occur, and it is considered that the cleanliness of the steel is improved.

Explanation of Signs

[0074] 100 Nozzle system 101 Ladle 101a Bottom surface 101b Side wall 102 Tundish 102a Bottom surface 102b Side wall 102c Lid 105 Molten metal 110 Long nozzle 110x Inlet 110y Outlet 110a Gas phase region 110b Secondary meniscus 110c Enlarged diameter part 111 Collector nozzle 112 Flow rate adjustment mechanism (sliding nozzle) 112a Slide plate 113 Inert gas supply mechanism 120 Nozzle

Claims

1. A nozzle system for supplying molten metal from a ladle to a tundish through a long nozzle, wherein the long nozzle is a cylindrical single-hole nozzle having an inlet on the ladle side which is the upstream side, an outlet on the tundish side which is the downstream side, and extending downward from the upstream side to the downstream side, wherein 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, wherein an inert gas is supplied from the outside to the inside of the long nozzle, and a gas phase region containing the inert gas and a secondary meniscus of the molten metal exist inside the long nozzle, wherein the distance h1 from the liquid level of the molten metal in the tundish to the outlet of the long nozzle is 100 mm or more and 600 mm or less, the distance h2 from the outlet of the long nozzle to the bottom surface of the tundish is 200 mm or more and 900 mm or less, and the ratio h1 / h2 of h1 to h2 is 0.2 or more and 1.0 or less, wherein the pressure of the gas phase region is controlled so that the secondary meniscus height ΔH defined by the following formula (1) is 0 cm or more and 20 cm or less, Nozzle system. ΔH = (P Ｔ - P Ｌ ) / (ρ・g) …(1) Here, P Ｔ is the atmospheric pressure in the tundish, P Ｌ 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.

2. When the pressure of the gas phase region is higher than a first threshold value, the amount of the inert gas supplied to the gas phase region is decreased so that the pressure of the gas phase region is decreased, wherein the first threshold value is the pressure at which ΔH becomes 0 cm, The nozzle system according to claim 1.

3. When the pressure of the gas phase region is lower than a second threshold value, the amount of the inert gas supplied to the gas phase region is increased so that the pressure of the gas phase region is increased, wherein the second threshold value is the pressure at which ΔH becomes 20 cm, The nozzle system according to claim 1 or 2.

4. The long nozzle has at least one communication hole, wherein the gas phase region inside the long nozzle and the atmosphere inside the tundish are configured to be communicable with each other through the communication hole, The nozzle system according to any one of claims 1 to 3.

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

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