Ladle shroud for metal casting systems

Abstract

The casting system comprises a ladle for holding a certain volume of molten metal, a tundish located downstream of and below the ladle, and a ladle shroud that fluidly connects the ladle to the tundish. The ladle shroud extends along its central axis from an inlet fluidly connected to the ladle to an outlet fluidly connected to the tundish. The ladle shroud defines an internal flow path having a converging section that extends from the inlet to a constriction located downstream of the inlet. The cross-sectional area of ​​the internal flow path, taken in a plane perpendicular to the central axis, decreases along the constriction section to the constriction. The cross-sectional area at the constriction is smaller than the cross-sectional area of ​​the internal flow path anywhere upstream of the constriction, and the constriction is aligned with the baseline level of the molten metal in the tundish.

Description

Related applications

[0001] Cross-reference of related applications This application claims priority to U.S. Patent Application No. 63 / 453,502, filed on 21 March 2023, the entire contents of which are incorporated herein by reference. [Technical Field]

[0002] This disclosure relates, in general, to systems and methods for casting molten metal, and more specifically to ladle shrouds for such casting systems. [Background technology]

[0003] For example, metal casting systems, such as those used to cast steel, typically include a ladle shroud to connect the ladle containing the molten metal to the tundish. The role of the ladle shroud is to protect the molten metal from the atmosphere during transfer from the ladle to the tundish to avoid re-oxidation of the molten metal. The connection between the ladle's slide gate nozzle, or lower nozzle, and the ladle shroud typically involves an overlap between these two parts. Since the pressure field generated within the ladle shroud is negative (i.e., less than 1 atm) at the joint of the lower slide gate nozzle or ladle shroud, air intake typically occurs at this overlap. To avoid this air intake, argon shrouding is used industrially to restrict the entry of air. Typically, a gasket seal is used in which argon is injected through the interior to replace the air. Thus, since gas intake may still be possible, the argon is injected so that a limited amount of air is taken into the molten metal. This can avoid re-oxidation of the molten metal. In other words, since gas ingestion into the falling steel can still occur within a standard ladle shroud, the inert argon bubbles that form within the ladle shroud may help avoid reoxidation of the steel, but they can create a slag open eye (SOE). This upwelling of argon bubbles around the shroud's outlet port can lead to reoxidation of the molten steel, which can then produce alumina inclusions. Therefore, improvement is needed. [Overview of the project]

[0004] In one embodiment, a casting system for casting molten metal is provided, comprising a ladle for holding a certain volume of molten metal, a tundish located downstream of the ladle and below the ladle with respect to the flow of molten metal, and a ladle shroud for fluidly connecting the ladle to the tundish, wherein the ladle shroud extends along a central axis from an inlet fluidly connected to the ladle to an outlet fluidly connected to the tundish, and the ladle shroud defines an internal flow path having a converging section extending from the inlet to a constriction located downstream of the inlet, wherein the cross-sectional area of ​​the internal flow path taken in a plane perpendicular to the central axis decreases along the constriction section, and the cross-sectional area at the constriction is smaller than the cross-sectional area of ​​the internal flow path anywhere upstream of the constriction, and the constriction is aligned with the baseline level of the molten metal in the tundish.

[0005] The casting systems defined above and described herein may also include, in whole or in part, and in any combination of, one or more of the following features:

[0006] In some embodiments, the internal flow path is bounded by the walls of the ladle shroud, which are convex within the convergence section by curving inward toward the central axis.

[0007] In some embodiments, the radius of the wall is approximately 19,000 mm to 20,000 mm.

[0008] In some embodiments, the cross-sectional area decreases monotonically from the entrance to the constricted section.

[0009] In some embodiments, the ladle shroud does not increase the cross-sectional area between the inlet and the constricted portion.

[0010] In some embodiments, the cross-sectional area increases along the divergent section of the ladle shroud, from the constricted section to the outlet.

[0011] In some embodiments, the cross-sectional area increases monotonically from the constriction of the ladle shroud to the outlet.

[0012] In some embodiments, there is no decrease in the cross-sectional area between the constriction and the outlet of the ladle shroud.

[0013] In some embodiments, the casting system does not have an inert gas injection system at the intersection between the ladle shroud and the ladle.

[0014] In some embodiments, the ratio of the cross-sectional area (Aa) at the inlet to the cross-sectional area (Ab) at the constriction is defined by the following formula:

Equation

[0015] In some embodiments, for a ladle shroud having a length of about 1.4 m, the ratio of the cross-sectional area at the inlet to the cross-sectional area at the constriction is about 2.2.

[0016] In some embodiments, the ladle shroud defines at least one opening communicating with the internal flow path at or upstream of the constriction, and at least one opening is fluidly connected to a source of inert gas.

[0017] In some embodiments, at least one opening is fluidly connected to a source of inert gas via one or more of a gas port, a control valve, a gas diffuser, and a casting nozzle.

[0018] In some embodiments, the distance between the inlet and the constriction is in the range of about 10% to 50% of the height of the tundish.

[0019] In some embodiments, the distance is in the range of 10% to 25%.

[0020] In some embodiments, the distance is in the range of 10% to 15%.

[0021] In another aspect, there is provided a method of distributing molten metal to be cast, the method comprising transferring the molten metal from a ladle to a ladle shroud through an inlet of the ladle shroud, the ladle shroud defining an internal flow path; increasing the velocity of the molten metal from the inlet of the ladle shroud through the internal flow path of the ladle shroud to a constriction within the internal flow path of the ladle shroud located downstream of the inlet, the constriction defining a cross-sectional area smaller than the cross-sectional area of the internal flow path anywhere upstream of the constriction; and discharging the molten metal from an outlet of the ladle shroud into a tundish positioned below the ladle, the constriction being substantially aligned with the height of the level of molten metal within the tundish.

[0022] The method described above may include any combination of the following features.

[0023] In some embodiments, increasing the velocity includes flowing the molten metal into a converging section of the internal flow path of the ladle shroud.

[0024] In some embodiments, increasing the velocity includes continuously increasing the velocity from the inlet to the constriction.

[0025] In some embodiments, maintaining the velocity substantially constant includes flowing the molten metal along a region of the converging section of the internal flow path, the region extending from a location proximate the constriction to the constriction.

[0026] In some embodiments, maintaining the velocity substantially constant includes flowing the molten metal along a converging section bounded by a wall that is convex when viewed from the inside of the internal flow path.

[0027] In some embodiments, this method includes reducing the rate of the molten metal before it is output into the tundish.

[0028] In some embodiments, this method includes injecting microbubbles of an inert gas at or upstream of the constriction.

[0029] In some embodiments, microbubbles are injected through one or more of the following: gas ports, control valves, gas diffusers, and casting nozzles.

[0030] In yet another embodiment, a ladle shroud is provided for fluidly connecting a ladle to a tundish of a casting system, the ladle shroud comprising a wall extending circumferentially around a central axis to define an internal flow path, the wall having an inlet end defining an inlet of the internal flow path and an outlet end defining an outlet of the internal flow path, the internal flow path comprising a converging section extending from the inlet to a constriction located between the inlet and the outlet, the constriction defining a cross-sectional area anywhere upstream of the constriction smaller than the cross-sectional area of ​​the internal flow path, the cross-sectional area of ​​the internal flow path decreasing along the converging section, and a diverging section extending from the constriction to the outlet, the cross-sectional area of ​​the internal flow path increasing along the converging section.

[0031] The ladle shrouds defined above and described herein may also include, in whole or in part, and in any combination of, one or more of the following features:

[0032] In some embodiments, the wall is convex within the convergence section when viewed from inside the internal flow path.

[0033] In some embodiments, the radius of the wall cross-section taken in the convergence section, on a plane containing the central axis, is in the range of approximately 19,000 mm to 20,000 mm.

[0034] In some embodiments, the cross-sectional area decreases monotonically from the entrance to the constricted section.

[0035] In some embodiments, the ratio of the cross-sectional area at the entrance to the cross-sectional area at the constriction is approximately 2.2 for a ladle shroud having a length of approximately 1.4 m.

[0036] In some embodiments, the ladle shroud defines at least one opening in or upstream of a constriction that communicates with an internal flow path, and at least one opening is fluidly connected to a source of inert gas. [Brief explanation of the drawing]

[0037] Please refer to the attached drawing.

[0038] [Figure 1A] This is a schematic diagram of a continuous casting system according to one embodiment, and a cross-sectional view of a ladle shroud according to one embodiment. [Figure 1B] Figure 1A is a schematic side cross-sectional view of the ladle shroud. [Figure 1C] Figure 1B shows a ladle shroud, and Figure 1A shows a cross-sectional view of a tundish used when the system is filled to a steady state level with molten metal. [Figure 1D] This is a cross-sectional view of a ladle shroud according to another embodiment. [Figure 1E] This is a cross-sectional view of a ladle shroud according to yet another embodiment. [Figure 2] This is a flowchart illustrating the steps of a method for distributing molten metal to be cast. [Figure 3A] This shows a computational fluid dynamics (CFD) simulation of steel flow in a traditional sealed inverse tapered ladle shroud at time 0.944 seconds. [Figure 3B] This shows a CFD simulation of steel flow within a traditional sealed inverse tapered ladle shroud at time 14.452 seconds. [Figure 3C]This shows a CFD simulation of steel flow within a traditional sealed inverse tapered ladle shroud at time 29.675 seconds. [Figure 3D] Figure 1B shows a CFD simulation of the steel flow within the ladle shroud at a time of 0.893 seconds. [Figure 3E] Figure 1B shows a CFD simulation of the steel flow within the ladle shroud at time 14.413 seconds. [Figure 3F] Figure 1B shows a CFD simulation of the steel flow within the ladle shroud at time 28.254 seconds. [Figure 4A] This shows a CFD simulation of steel flow within a traditional sealed inverse tapered ladle shroud at time 32.173 seconds. [Figure 4B] This shows a CFD simulation of steel flow within a traditional sealed inverse tapered ladle shroud at time 37.303 seconds. [Figure 4C] This shows a CFD simulation of steel flow within a traditional sealed inverse tapered ladle shroud at time 58.285 seconds. [Figure 4D] Figure 1B shows a CFD simulation of the steel flow within the ladle shroud at time 32.143 seconds. [Figure 4E] Figure 1B shows a CFD simulation of the steel flow within the ladle shroud at a time of 36.964 seconds. [Figure 4F] Figure 1B shows a CFD simulation of the steel flow within the ladle shroud at time 56.553 seconds. [Figure 5A] This shows contour lines of absolute pressure for a traditional sealed inverted tapered ladle shroud, simulated by CFD. [Figure 5B] Figure 1B shows contour lines of the absolute pressure of the ladle shroud, simulated by CFD. [Figure 6A] This shows contour lines of the predicted velocity of a traditional sealed inverse tapered ladle shroud, simulated by CFD. [Figure 6B] Figure 1B shows contour lines of the predicted velocity of the ladle shroud, simulated by CFD. [Figure 7A] This shows the predicted volume fraction contours of steel at time 41.853 seconds, simulated by CFD for a fully sealed traditional inverse tapered ladle shroud. [Figure 7B] This shows contour lines of the predicted absolute pressure at time 41.853 seconds, simulated by CFD for a traditional, unsealed, fully sealed inverted tapered ladle shroud with a 1.2 mm gap. [Figure 8A] The predicted contour lines of the volume fraction of steel at time 42.154 seconds, simulated by CFD after modifying the gap boundary to 1.2 mm to allow air ingress facilitated by negative pressure in a traditional unsealed inverted tapered ladle shroud, are shown. [Figure 8B] This shows contour lines of the predicted absolute pressure at time 42.154 seconds, simulated by CFD after modifying the boundary condition to a 1.2 mm gap to allow air ingress into a traditional inverted tapered ladle shroud. [Figure 9A] The filling of a tundish using a traditional inverted tapered ladle shroud is shown for a full-scale water model at multiple time steps (5 seconds in Figure 9A, 30 seconds in Figure 9B, and 60 seconds in Figure 9C). [Figure 9B] The filling of a tundish using a traditional inverted tapered ladle shroud is shown for a full-scale water model at multiple time steps (5 seconds in Figure 9A, 30 seconds in Figure 9B, and 60 seconds in Figure 9C). [Figure 9C] The filling of a tundish using a traditional inverted tapered ladle shroud is shown for a full-scale water model at multiple time steps (5 seconds in Figure 9A, 30 seconds in Figure 9B, and 60 seconds in Figure 9C). [Figure 10A] The filling of a tundish using the ladle shroud shown in Figure 1B is shown for a full-scale water model at multiple time steps (5 seconds in Figure 10A, 30 seconds in Figure 10B, and 60 seconds in Figure 10C). [Figure 10B] The filling of a tundish using the ladle shroud shown in Figure 1B is shown for a full-scale water model at multiple time steps (5 seconds in Figure 10A, 30 seconds in Figure 10B, and 60 seconds in Figure 10C). [Figure 10C] The filling of a tundish using the ladle shroud shown in Figure 1B is shown for a full-scale water model at multiple time steps (5 seconds in Figure 10A, 30 seconds in Figure 10B, and 60 seconds in Figure 10C). [Modes for carrying out the invention]

[0039] Referring to Figure 1A, the continuous casting system 100 (or simply the “casting system” 100) includes a ladle 102 that holds a certain volume of molten metal 104, such as molten steel. It will be understood that the continuous casting system 100 described herein may be used to cast any suitable metal, such as steel, aluminum, or cast iron. A ladle shroud 106 fluidly connects the ladle 102 to a tundish 110. Thus, the tundish 110 is located downstream of the ladle 102 with respect to the flow of molten metal 104 within the tundish 110. The tundish 110 is located below the ladle (i.e., at a lower height relative to the ladle, which may be vertically downward) so that gravity acts on the molten metal 104 and drives the flow of molten metal 104 from the ladle 102 to the tundish 110. The ladle shroud 106 has an inlet 106a fluid-connected to the ladle 102 and an outlet 106b fluid-connected to the tundish 110. The ladle shroud 106 also has a constriction 108 downstream of the inlet 106a. As described, the constriction is located below the upper edge of the tundish, between this upper edge and the base of the tundish. More specifically, during steady operation of the system, the constriction 108 is substantially aligned with the height of the molten metal in the tundish and is therefore positioned to be close to it. As used herein, the term “close to” with respect to the position of a structure within the ladle shroud is understood to mean that during steady operation, the constriction is at the same height as the level of the molten metal in the tundish, but is separated by no more than approximately one diameter of the ladle shroud. In some embodiments, the constriction is located at a distance below the upper edge of the tundish, and this distance is in the range of about 10% to about 50% of the tundish height, or more preferably about 10% to about 25%, or about 10% to about 15%. During the casting operation, the constriction may be at the same height as the maximum steel level.

[0040] In the constricted portion 108, the cross-sectional area in the internal passage of the ladle shroud 106 is minimized (i.e., minimized throughout the entire ladle shroud 106). The rationale for the design of the ladle shroud 106 of this disclosure with respect to the molten metal 104 is described below. However, it should be understood that the same rationale applies to other incompressible molten metals. The tundish 110 is in fluid communication with one or more casting “shrouds” 112, also referred to as immersion inlet nozzles (SENs), to supply the molten metal 104 to the mold 114. It will be understood that the SENs 112 may be provided in the same shape as the ladle shroud 106 described herein. More specifically, one or more of the SENs 112 may have a constricted portion inside, like the ladle shroud 106. In certain embodiments, these constricted portions within one or more SENs 112 are similarly positioned, for example, below the upper edge of the mold 114.

[0041] The design of a ladle shroud is based on two fundamental equations: the continuity equation and the energy conservation equation. The continuity equation states that, in the case of steady flow, the mass flow rate of an incompressible liquid such as liquid metal must remain constant between the inflow of the liquid into the ladle shroud and the outflow of the ladle shroud. In the case of a straight-bore ladle shroud, the velocity remains constant, but the steel falls from a higher position "z" to a lower position, and the steel exits the ladle shroud 106 and becomes molten steel in the tundish 110. This means that the molten metal loses some of its potential energy equal to [ρ g L], where L represents the length of the ladle shroud 106. Based on the second equation, a special case of the energy equation, if all terms on the left side of the equation are negligible (i.e., friction losses are negligible, no work is being done by the system, and no heat is being transferred within the system), then the total energy of the system is constant: It must remain the net value at location 1 L1 (which is above location L2),

number

number

[0042] This macroscopic relationship is also equivalent to that estimated through the integration of Euler's differential equation for an ideal incompressible fluid flow system in a steady state. In other words, while pressure, kinetic, and potential energy are interconvertible and can change very well from one place to another, the net energy / mass of the fluid flowing through the system must remain constant at all positions within the flow system, provided the flow is frictionless, incompressible, and isothermal. Here, α represents a correction factor for laminar flow (α=1 / 2) or turbulent flow (α approximately 0.8).

[0043] Alternatively, Bernoulli's equations can be written to be useful for the pressure, velocity, and position (height) items, while the net items remain constant.

number

[0044] As in the equation above, the pressure item

number

number

[0045] Therefore, if the z vector points vertically downward, or if Δz of the molten metal falling from the inlet point to the outlet point at the level of molten steel in the tundish is negative at z=0, this loss of potential energy can only be compensated for by the decrease in pressure energy, assuming the velocity of the steel in the ladle shroud remains constant. Thus, the pressure in the steel flowing through the ladle shroud must also decrease by an equivalent amount as it moves upward from the bottom of the straight ladle shroud towards the inlet of the steel into the ladle shroud. In practice, taking a traditional 1.4-meter-long straight-tube ladle shroud as an example, the decrease in potential energy is -[ρ g L], i.e., -7000 kg / m 3 ×9.81m / sec 2 ×1.4m = -96,138 Pascals, and the pressure outside the ladle shroud at 1 atmosphere is approximately 101,000 Pascals. Therefore, the steel entering its traditional ladle shroud is essentially under pure vacuum, roughly at the joint between the ladle shroud and the slide gate nozzle. There, during the discharge of the steel, it is held under mechanical force (e.g., pressure) and may often be improperly aligned vertically but not fixed. Thus, the gasket sealing it from air ingress can be a source of oxygen from within the air leak, leading to the re-oxidation of the molten steel. This re-oxidation can result in the formation of billions of micron-sized inclusions of alumina (Al2O3), which is detrimental to the casting of the steel.

[0046] Traditional ladle shroud designs recognize this risk of air intrusion and attempt to compensate for it by "overflowing" the connection between the ladle and the ladle shroud with argon gas. However, in some cases, the argon injection flow rate may be insufficient to completely prevent air intrusion. Therefore, air remains for a while after the start of molten steel discharge. Alternatively, if argon is injected at an increased flow rate, for example, about three times the flow rate of the steel, this creates many argon bubbles within the steel flow, and Bernoulli's single-phase flow equation no longer applies. This is also highly undesirable, as the argon bubbles escaping from the ladle shroud interfere with the slag layer protecting the molten steel, thereby generating more inclusions within the tundish itself.

[0047] Referring to Figure 1B, a ladle shroud 106 is shown that can at least partially mitigate these drawbacks. The ladle shroud 106 is designed to minimize or prevent air from entering the joint by having a design that ensures there is no negative gauge pressure at the slide gate nozzle / ladle joint. Typically, in the case of a traditional shroud of constant diameter that is completely filled with molten metal, ΔP g The gauge pressure at the inlet of the ladle shroud (referred to as point A herein) is equal to -[ρ gh], since, in the absence of air intrusion, the kinetic energy of the steel remains constant within the ladle shroud. Here, "ρ" is the density of the molten metal (in this example, that of the steel, i.e., 7000 kg / m³). 3 ) represents the constant of gravity (9.81 m / s²), where g is the acceleration gravitational constant. 2and h is the height of the ladle shroud above the surface of the liquid molten metal (e.g., steel) in the tundish. As described above, a traditional ladle shroud with a height of 1.4 m is completely filled with liquid molten metal, and although other heights are contemplated, the decrease in potential energy at the level of the molten metal in the tundish (referred to herein as point B) must be compensated by the decrease in pressure energy at point A, so that at point A, a nearly complete vacuum can be generated. To avoid this negative pressure at the nozzle-ladle shroud junction, the pressure at the junction (A) and the pressure at the surface of the molten metal in the tundish (B) should both be at atmospheric pressure. That is, P A =P B =P atm

[0048] To achieve this, the kinetic energy was increased to compensate for the decrease in potential energy at point B relative to point A. The following is an example of the calculation of the diameter (D g ) at point B required for this condition of 0.0P B (gauge pressure relative to atmospheric pressure) of the ladle shroud 106 of the present disclosure. An exemplary inlet velocity of 0.8 m / s was selected, and an exemplary initial diameter (ID) of 50 mm (D A ) was selected. These values are merely exemplary, and it will be understood that the velocity and flow rate can vary greatly depending on different plants and different molten metals. Typically, the inlet velocity is a known variable and can be calculated based on known parameters such as the density of the metal, the inlet diameter of the ladle shroud, the depth of the metal in the ladle, etc. Then, in addition to the continuity equation, the Bernoulli equation is used, which assumes that the total energy in the system, including motion, position, and pressure, remains constant. For the case of P A =P B , the following equation is provided.

Equation

[0049] From the continuity equation, ρA A u A =ρAB u B , or in the case of an incompressible fluid, A B / A A =U A / U B This leads to the conclusion.

[0050]

number

number

[0051] The value of 23 mm is illustrative, and it will be understood that other values ​​are intended and may vary as a function of the cross-sectional area of ​​the ladle shroud 106 at the entrance. Although the ladle shroud is depicted as having a circular cross-sectional area, other shapes such as elliptical, square, or rectangular may be used, for example.

[0052] Therefore, for the reasons stated above, the ladle shroud 106 of the present disclosure preferably has a constriction 108 positioned at point B. The constriction 108 is located below the upper edge of the tundish and is preferably aligned perpendicular to the surface of the molten metal during steady operation of the system (i.e., having the same or the same height) (i.e., aligned with the level of the molten metal in the tundish).

[0053] In some embodiments, as illustrated in Figure 1B, the cross-sectional area of ​​the ladle shroud 106 decreases from the inlet 106a to the constriction 108 along a linearly converging section 107 of the ladle shroud 106. The converging section 107 can generally be described as funnel-shaped or frustoconical. The cross-sectional area can be defined as the flow cross-sectional area along the ladle shroud 106 as it moves downstream from the inlet 106a. This decrease in cross-sectional area increases the velocity of the molten metal in the ladle shroud 106 to compensate for the decrease in potential energy. In some embodiments, the cross-sectional area decreases monotonically from the inlet 106a to the constriction 108. In this specification, the expression “monotonically decreasing” means that the cross-sectional area may decrease or remain constant along a particular portion but never increase. This can decrease at various rates. In some embodiments, the ladle shroud 106 has no increase in the circulating flow region between the inlet 106a and the constriction 108. The ladle shroud 106 may have an inlet section with a constant cross-sectional area extending from the inlet 106a to an intermediate location between the inlet 106a and the constriction 108. As the cross-sectional area begins to converge from this intermediate location, it may converge continuously and uninterruptedly to the constriction 108. In some embodiments, as illustrated in Figure 1B, the cross-sectional area of ​​the converging section 107 decreases linearly from the inlet 106a to the constriction 108. The design of the ladle shroud 106 may allow for pressures above atmospheric pressure to be achieved at the inlet 106a and the constriction 108, so that there may be no negative pressure at the inlet 106a that induces air intrusion. In some embodiments, the pressure at the constriction 108 is about 0.58 atmospheres, and the velocity of the molten metal is about 3.98 m / s. Therefore, in that case, air leads to re-oxidation, while argon is inert, so its sole role is to replace the intrusion of air, thus avoiding the introduction of an argon gas flow. Accordingly, in some embodiments, the casting system of the present disclosure does not have an inert gas injection system at the intersection between the ladle shroud and the ladle. This may be advantageous because the introduction of an inert gas, especially at higher flow rates of the inert gas, can lead to the formation of bubbles in the molten metal.Therefore, the disclosed ladle shroud 106 can limit the formation of bubbles in the molten metal within the ladle shroud. Accordingly, the proposed ladle shroud can be used in conjunction with microbubble generation, either in or over a constricted area, depending on the desired microbubble size.

[0054] Size relationship between cross-sectional areas (A A / A B ) is the entrance (U A This can be determined by the molten material rate at the ) and the height (H) of the distance between the inlet and the constricted section. Therefore, the size relationship between the cross-sectional areas can be calculated using the equations listed above.

[0055] Based on the correlations described above, in some embodiments, the cross-sectional area at the inlet of the ladle shroud 106 is about 2 to about 6 times, preferably about 3 to about 5, or about 4, the cross-sectional area at the constriction 108. To obtain a stable flow within the ladle shroud 106, if the converging section 107 has sections with a constant and non-decreasing cross-sectional area, these non-decreasing areas are preferably up to 20% of the length of the ladle shroud, more preferably less than 10% or less than 5%. The cases described above are examples, and the cross-sectional area ratio should be kept within reasonable limits according to the presented equations.

[0056] In some embodiments, the constriction 108 is located at the outlet 106b, as illustrated in Figure 1A. However, in preferred embodiments, as illustrated in Figures 1B and 1C, the ladle shroud 106 has a diverging section 109 (e.g., an inverse taper) downstream of the constriction 108. The diverging section 109 may be omitted in some embodiments. In the disclosed embodiments, the diverging section 109 allows the pressure of the molten steel to return to above the ambient pressure while reducing the outlet velocity of the molten metal to about 1 m / s. This may allow the molten metal to flow smoothly into the tundish 110 under steady operation. In such embodiments, the cross-sectional area increases along the diverging section 109 of the ladle shroud 106 from the constriction 108 to the outlet 106b. In some embodiments, the cross-sectional area increases monotonically from the constriction 108 to the outlet 106b of the ladle shroud 106. In some embodiments, the ladle shroud does not experience a reduction in cross-sectional area between the constriction 108 and the outlet 106b. The purpose of the divergence section 109 is to slow the outlet velocity of the molten metal 104 entering the tundish 110 under steady-state operating conditions. In some embodiments, the diameter of the outlet 106b is equal to or smaller than the diameter of the inlet 106a. In some embodiments, the cross-sectional area of ​​the ladle shroud 106 at the outlet 106b defined by the divergence section 109 is larger than that of the ladle shroud 106 at the inlet 106a. In the disclosed embodiments, the divergence angle defined by the divergence section 109 is approximately 11 degrees. In summary, the purpose of the divergence section 109 is to increase the pressure and slow the outlet velocity of the molten metal 104 entering the tundish 110 under steady-state operating conditions, thereby enabling smoother ladle transfer during continuous casting operations. The disclosed ladle shroud also differs from conventional ladle shroud designs in that it can prevent slag from being dragged into the ladle shroud during non-immersion ladle shroud transitions.

[0057] Referring to Figure 1C, a portion of the casting system 101 having a ladle shroud 106 with an divergence section 109 is shown. During operation, the tundish 110 is generally filled with molten metal 104. During steady-state operation of the casting system, the molten metal fills the tundish 110 up to a baseline level 116. This may also be referred to as the steady-state level of the molten metal. The casting operation takes place over a period of time, and it is expected that the molten metal ejected from the tundish 110 will be replenished by new molten metal flowing into the tundish 110 through the ladle shroud 106. Therefore, an unstable state may occur during the initial filling phase when the level of molten metal in the tundish 110 increases from 0 (i.e., at the base of the tundish 110) to the baseline level 116. However, once this baseline level 116 is reached, the operation is in a steady state where the level of molten metal in the tundish 110 remains substantially aligned with the baseline level 116. Furthermore, there is a layer of slag on top of the molten metal. The baseline level 116 corresponds to the upper surface of the molten metal, which can be defined as the interface between the molten metal and the slag layer. The constriction 108 is substantially aligned with this baseline level 116. The constriction 108 may be located below the upper edge of the tundish at a distance corresponding to 10% to 50%, more preferably 10% to 25% or 10% to 15%, of the total height of the tundish 110 measured from the upper edge to the base of the tundish. In other words, as can be seen in Figure 1C, in some embodiments, the constriction 108 is aligned with the baseline level of the molten metal in the tundish when the tundish is filled. During operation, the baseline level remains substantially constant because the molten metal 104 is replenished from the ladle shroud 106 as it flows out of the tundish 110 and casts. Generally, when referring to the "level" or "baseline level" of molten metal, it means the level (i.e., height) in a steady state during continuous casting operation.

[0058] Referring further to Figure 1B, in some embodiments, an inert gas such as argon may be injected from a gas source S into or near the constriction 108 of the ladle shroud 106. In some embodiments, the gas may be injected into or near the inlet of the ladle shroud through a preferred opening defined therethrough. One or more openings 106c may be defined through the ladle shroud 106 through which the gas can reach the internal flow path of the ladle shroud 106. The injection of gas through the openings 106c is performed here in the constriction 108. Alternatively, the gas may be injected from slightly upstream of the constriction 108 (e.g., about 10% of the height of the ladle shroud) to slightly downstream of the constriction 108 (e.g., about 10% of the height of the ladle shroud). The gas is injected where the velocity of the molten metal is high (e.g., about 1.5 m / sec or more). When a bubble comes into contact with the molten metal, the molten metal applies shear stress to the bubble, thereby bursting the formed bubble. This can create microbubbles that adhere to inclusions, thereby causing such inclusions to float on the surface of the molten metal. This can make it possible to cast parts while avoiding these inclusions in the final steel product. These inclusions are typically oxides, fragments of the tundish 110 (e.g., dirt), etc. In some embodiments, gas injection may be omitted.

[0059] Gas bubbles injected into one or more openings 106c may have a diameter of approximately 0.5 mm. These bubbles may adhere to inclusions of similar size, allowing them to float to the surface and subsequently be removed. The openings 106c may be fluidly connected to a source of inert gas (e.g., argon) via one or more of the following: gas ports, control valves, gas diffusers, and casting nozzles.

[0060] Referring to Figure 1D, another embodiment of the ladle shroud is shown. In the embodiment shown, the ladle shroud has a converging section 207 which is convex when viewed from inside the internal flow channel defined by the converging section 207. In other words, the converging section 207 is bounded by a wall that extends circumferentially around the central axis A1 of the internal flow channel, and the wall is convex when viewed from inside the internal flow channel. The wall may be said to curve inward toward the central axis A1. The wall may appear to create a gently curved surface that protrudes into the internal flow channel.

[0061] By making the convergence section 207 convex, the length of the high-velocity region of the fluid flowing through the convergence section 207 along the central axis A1 is increased. Thus, greater flexibility can be provided when selecting the location of one or more openings 106c (Figure 1B). Thus, one or more openings 106c may be located upstream of the constriction 108. That is, due to the convex shape, the inert gas can be injected upstream of the constriction 108. The radius of curvature R1 of the wall bordering the flow path of the convergence section 207 may be about 19000 mm to about 20000 mm, preferably about 19221 mm. These radius values ​​can be calculated using different distance values ​​of h to approximate the area ratio defined by the equation described above. The convex surface defined by the average angle between the chord joining the inlet and the throat, and the rate of change of the cross section due to the distance below the inlet 106a, corresponds to an average angle of about 2 degrees between the linear convergence (chord) and the convex convergence. In this configuration, the radius is constant. In some alternative embodiments, the radius may vary along the converging section 207. The diameter of the flow path in the constricted section 108 may be about 23 mm. The angle defined between the central axis A1 and the wall bordering the flow path in the converging section 207 may range from about 1 degree to about 6 degrees. The convex shape may also increase the initial stability of the injection and avoid impurity pores in the ladle shroud, thereby preventing blowback. A convex shape with a radius in the range of about 19,000 mm to about 20,000 mm may be beneficial for the injection of molten metal.

[0062] As used herein, "radius" will be understood to refer to the radius of the wall of the ladle shroud in a cross-section of the wall taken on a plane containing the central axis A1. In other words, the wall defining the internal flow path is viewed as a curve in a cross-section on a plane containing the central axis A1. The radius refers to the radius of that curve.

[0063] The disclosed configuration of the ladle shroud can provide a single-phase flow system because virtually no gas can be introduced at the inlet. The disclosed ladle shroud can also reduce turbulence.

[0064] In an alternative embodiment, one or more openings 106c include a plurality of openings defined by porous plugs located in or adjacent to the constriction 108, where “adjacent” means that the porous plugs may be located in a region where the velocity of the molten steel is at least about 90% of the maximum velocity of the molten steel in the ladle shroud, similar to the openings 106c.

[0065] Referring to Figure 1E, another embodiment of the converging section of the ladle shroud is shown at 307. In this configuration, the wall defining the converging section 307 is concave when viewed from within the internal flow path. Such a configuration can significantly reduce the length along the central axis A1 of the high-velocity zone within the internal flow path. When the wall is concave, its radius R2 can be about 8000 mm to about 9000 mm, preferably about 8735 mm, for the same diameter of 23 mm at the constriction 108.

[0066] Argon may be injected where the velocity of the molten metal is high (e.g., greater than or equal to about 1.5 m / s). When the injecting gas comes into contact with the molten metal, the molten metal exerts shear stress on the formed bubbles. This can generate microbubbles that enter the molten steel as it exits the tundish. There, they can float up so that they are absorbed into the overlying slag, acting as sites for the incorporation and / or adhesion of alumina inclusions, or alumina inclusion aggregates, or silicate droplets. Furthermore, these microbubbles are very small (about 500 microns in diameter) and cannot break the slag layer to form SOEs (slag open eyes), but are large enough not to enter the exit port, into the mold below. A similar design system may be envisioned for SEN (immersion inlet nozzle) systems. The disclosed ladle shroud design may also be used for direct cooling casting (DC casting) of aluminum slabs.

[0067] This can result in a significant reduction in smaller-sized inclusions that may not be removed in typical steel casting operations. These inclusions are typically alumina oxides, refractory fragments, silicates, etc. However, in some embodiments, gas injection can be completely omitted using this new design for the ladle shroud.

[0068] Referring to Figure 2, for example, a method 200 for distributing molten metal to be cast is provided using the casting system 100 of Figure 1A. The molten metal is received through the inlet of the ladle shroud (202). The velocity of the molten metal increases downward from the inlet 106a of the ladle shroud 106 to the constriction 108 (204). The molten metal is ejected into the tundish 110 from the outlet 106b of the ladle shroud 106 (208), where the constriction 108 is substantially aligned with the steady-state operating level of the molten metal in the tundish. From the tundish, the molten metal can then be poured into various molds. In this specification, the expression “substantially” includes a variation of plus or minus 10% in the length of the ladle shroud 106.

[0069] As described above, the velocity of the molten metal can be increased by flowing the molten metal into the converging section of the ladle shroud (e.g., the converging section 107 of the ladle shroud 106 in Figure 1B). Increasing the velocity may involve continuously increasing the velocity from the inlet to the constriction. This can be achieved in the exemplary ladle shroud described above, which has a monotonically decreasing circulating flow region.

[0070] Optionally, the velocity of the molten metal is reduced before ejecting the molten metal into the tundish (206). This is done to reduce the velocity at which the molten metal jet enters the tundish and to reduce the scattering of molten metal within the tundish. This can help avoid turbulence and bubble formation within the tundish. This can be done by directing the molten metal into the diverting section 109, as illustrated in Figures 1B-1C.

[0071] As demonstrated in the following sections of examples, the intrusion of air can first lead to the oxidation of molten aluminum in the molten steel, creating many solid Al2O3 (alumina) inclusions. Any inclusions or aggregates remaining in the molten steel will impair the properties of the solid steel being cast. The ladle shroud of this disclosure has been found to overcome these limitations of conventional ladle shrouds. [Examples]

[0072] The ladle shroud of this disclosure was compared to a conventional ladle shroud design using computational fluid dynamics (CFD) ANSYS Fluent code v19.0 to determine whether the experimentally identified shortcomings described above are overcome by this ladle shroud. A conventional inverse tapered ladle shroud (initial ID 50 mm and final ID 75 mm) was used as a comparison point for the ladle shroud of this disclosure (initial ID 50 mm, ID 23 mm at point B, and final ID 50 mm). This comparison was performed during the injection phase and quasi-steady operation to compare the flow behavior of the steel in the two designs. Standard k-ε turbulence and fluid volume (VOF) models were used to model the turbulent fluid flow and steel / gas phase interaction. In both cases, molten steel at 1600°C was used as the primary phase.

[0073] At the start of injection, both ladle shrouds were filled with air. Transient state calculations were then performed to track the interface behavior during system filling before they eventually reached their steady-state operating levels. In both cases, the inlet velocity was specified as 0.8 m / s. Figures 3A–3F and 4A–4F present predicted contour lines of the volume fraction of steel at different times for both ladle shrouds on a transverse center plane for 2D visualization. As shown in Figures 3A–3C, in the inverted tapered ladle shroud design, a falling flow is formed, and due to divergence ID, it can be observed that this ladle shroud is not filled with steel. This leads to re-oxidation of the steel. With respect to the ladle shroud design of this disclosure, in Figure 3E, it can be observed that at 14.4 seconds, the ladle shroud is virtually completely filled with steel, avoiding any mixing with the initial air in the system. At 29.7 seconds, in Figure 3C, it can be observed that in the case of the inverted tapered design, two-phase turbulence is generated in the system. Large bubbles generated in the steel will cause re-oxidation of the molten steel. In contrast, Figure 3F shows that in this design, it is single-phase and turbulent at 28.3 seconds. Figures 4A-4F present the predicted results over longer time periods. In the case of the inverse taper design (Figures 4A-4C), we observe how multiphase turbulence persists until the “box section” is completely filled with steel. Along the length of the shroud, at 37.3 seconds, bubbles detrimental to the steel are generated. Using the design of this disclosure (Figures 4D-4F), a stationary flow is achieved through the filling of the “box section” with steel without mixing of gas and liquid. This is a significant advantage in that no inclusions are generated due to contact between the refined steel and air. Figures 5A-5B present predicted absolute pressure contours for both designs under steady-state operating conditions. As expected, in the case of the inverse taper design in Figure 5A, negative pressure (less than 1 atm) is predicted at the upper and lower nozzle-ladle shroud joints of the system. This will generate air inflow if a complete seal is not achieved at that joint. Figures 6A and 6B show the predicted velocity contours for both designs under steady-state operation.The velocity field results show that a high velocity of molten steel (3 m / sec) is achieved in the "constriction section" of this design, which can be used to generate microbubbles for subsequent cleaning. Moreover, in both cases, the velocity of the steel leaving the ladle shroud and reaching the tank or tundish is approximately 1.2 m / sec, meaning that using this ladle shroud design can be expected to have no impact on casting speed and productivity. A CFD comparison of the ladle shroud design of this disclosure with a traditional reverse taper design demonstrates the advantages and innovations of this design.

[0074] The process following this air intake case is similar to the simulation performed for the simplified case. Therefore, the contour lines of the volume fraction of steel during the filling phase are virtually identical, since the argon flow generally only slightly affects the velocity field. Figure 7A depicts the contour lines of the volume fraction of steel at 41.853 seconds, showing that the ladle shroud is virtually filled with molten steel, with some bubbles present along the inner sidewall of the ladle shroud. The corresponding contour lines of absolute pressure, Figure 7B, present the negative pressure field at the top, where the absolute pressure at the top is in the range of 0.416–0.582 atm, which is very similar to the CFD results already presented in Figure 5A.

[0075] The simulation was stopped at 41.853 seconds to modify the boundary conditions to allow air leakage through a 1.2 mm gap between the slide gate nozzle and the ladle shroud. Figures 8A-8B show the predicted contour lines of the volume fraction of steel and absolute pressure at 42.154 seconds, 0.301 seconds after the boundary conditions were modified. This dramatic change can be seen in Figure 8A, where the contour line of the volume fraction of steel indicates a zone near the wall of the ladle shroud, where the volume fraction of steel is equal to 0 (blue) and the volume fraction of air is equal to 1. Compared to the previous Figure 7A, a rapid influx of air occurred in just 0.3 seconds, or 300 milliseconds.

[0076] After the boundary conditions changed, the absolute pressure contour lines changed from Figure 7B to Figure 8B in 0.301 seconds. As the system was then "opened" to atmospheric pressure (1 atm), the predicted values ​​within the ladle shroud changed to an absolute pressure of 1 atm, almost along its entire height.

[0077] These calculations demonstrate that the pressure difference between the ladle shroud and the atmosphere generates significant air inflow into the system unless a complete seal between the mating parts (between the lower nozzle and the ladle shroud) is sufficiently achieved. This impairs the quality of the molten steel by allowing air to enter the ladle shroud, leading to a high reoxidation rate of molten aluminum in the deoxidized steel and a large amount of alumina particles (inclusions). In addition, the previous results are quantified by demonstrating the possibility of air intake within the ladle shroud through mathematical modeling.

[0078] A preliminary full-scale water modeling experiment was conducted to verify the behavior of the current ladle shroud design compared to an inverse taper design (Figures 9A-9C and 10A-10C). These figures show the behavior of this ladle shroud (Figures 10A-10C) compared to an inverse taper design used in the industry (standard, Figures 9A-9C). Note that the traditional shroud is gradually filled with liquid and forms a large bubble flow after 60 seconds, whereas this ladle shroud does not release bubbles from its outlet port after 60 seconds of filling (see Figures 10A-10C in particular). Microbubble formation was achieved at a maximum of approximately 0.5 liters / minute using a small gas inlet in the constricted section. These microbubbles differ significantly from the much larger bubbles emitted from the traditional ladle shroud. The two different sizes of bubbles have a significant impact on either degrading the quality of the molten steel in a traditional ladle shroud, or improving the steel quality by allowing smaller inclusions to adhere to the microbubble surface and providing the necessary support for them to reach the upper slag layer where they are absorbed. Faster cross-flow fluid velocities lead to a reduction in bubble radius.

[0079] Therefore, in certain embodiments, the design of this ladle shroud can substantially limit, if not substantially eliminate, all inclusions formed by the reoxidation of the metal during the transfer of molten metal from the ladle to the tundish. The design of this ladle shroud also allows for the controlled generation / injection of gas microbubbles during the transfer of molten metal from the ladle to the tundish through a single slot or porous media gas injection, which can lead to the elimination of small inclusions less than 50 micrometers in diameter that are not removed using current ladle shroud techniques.

[0080] In multiphase flow visualization, these results did not include chemical interactions. However, it is known that when molten steel is in contact with air, it tends to reoxidize during the tundish filling phase. This is exacerbated by the divergence design of the ladle shroud, which effectively reduces the rate of incoming steel but compromises the quality of the steel.

[0081] In the case of a tightly sealed ladle shroud, a negative absolute pressure was predicted at the lower nozzle-ladle shroud junction. Otherwise, if leakage is present, this generates an inward flow of air in the absence of effective argon sealing. This shows that for the cases simulated and quantified and modeled herein, it is possible to have an instantaneous air intake flow of 314.75 L / min.

[0082] During steady-state operation, the two-phase flow (steel-argon) generates bubbles approximately 20 mm in diameter, which exit the ladle shroud, disturb the slag layer, create slag open eyes (SOE), and introduce slag inclusions.

[0083] The ladle shroud of this disclosure can prevent air from entering the inlet (connection to the slide gate) of the ladle shroud by ensuring a positive gauge pressure (pressure greater than 1 atm). It can prevent the formation of large air or argon gas bubbles in the diameter size range (5-100 mm) inside, and promotes slag mixing in the tundish. It can promote a stationary single-phase flow inside, enabling the generation and integrity of argon microbubbles while preventing gas-liquid (multiphase) turbulence during initial and steady-state casting operations. An inert gas such as argon can be injected into liquid metal (steel) in a cross-flow at high speeds (greater than 1 m / s) to create a dispersed cloud of microbubbles (diameter size 400-1000 microns). The disclosed ladle shroud allows for pressure and volume-controlled lateral injection of argon at the ladle shroud inlet, preventing air ingress that may result in oxidation of the molten steel, accommodating the input static pressure of the steel, and compensating for potential pressure fluctuations during casting, such as steel leakage or welding of external steel components.

[0084] In the context of this disclosure, the expression "approximately" means a variation of plus or minus 20%.

[0085] The embodiments described herein provide non-limiting examples of possible implementations of the Art. Those skilled in the art will recognize, upon consideration of this disclosure, that modifications may be made to the embodiments described herein without departing from the scope of the Art. For example, the inclusions in the divergent section 109 are optional, and the converging section may converge monotonically or have one or more regions with a constant cross-sectional area. While the ladle shroud is described herein in the context of its use in a continuous casting system, such as the type used for steel casting, it will be understood that the casting system and the ladle shroud can be used in casting systems for other metals (e.g., aluminum), and in other metal casting systems, such as bottom-injection ingot casting. Further modifications may be implemented by those skilled in the art in consideration of this disclosure, and such modifications will remain within the scope of the Art.

Claims

1. A casting system for casting molten metal, A ladle for holding a certain volume of the molten metal, A tundish located downstream of the ladle and below the ladle with respect to the flow of the molten metal, A casting system comprising: a ladle shroud for fluidly connecting the ladle to the tundish, wherein the ladle shroud extends along a central axis from an inlet fluidly connected to the ladle to an outlet fluidly connected to the tundish, the ladle shroud defines an internal flow path having a converging section extending from the inlet to a constriction located downstream of the inlet, the cross-sectional area of ​​the internal flow path taken in a plane perpendicular to the central axis decreases along the constriction section to the constriction, the cross-sectional area at the constriction is smaller anywhere upstream of the constriction than the cross-sectional area of ​​the internal flow path, and the constriction is aligned with the baseline level of the molten metal in the tundish.

2. The casting system according to claim 1, wherein the internal flow path is bounded by the wall of the ladle shroud, and the wall is convex within the convergence section by curving inward toward the central axis.

3. The casting system according to claim 2, wherein the radius of the wall is approximately 19,000 mm to 20,000 mm.

4. The casting system according to any one of claims 1 to 3, wherein the cross-sectional area decreases monotonically from the entrance to the constricted portion.

5. The casting system according to any one of claims 1 to 4, wherein the ladle shroud does not increase the cross-sectional area between the inlet and the constricted portion.

6. The casting system according to any one of claims 1 to 5, wherein the cross-sectional area increases along the divergent section of the ladle shroud from the constricted portion of the ladle shroud to the outlet.

7. The casting system according to claim 6, wherein the cross-sectional area increases monotonically from the constricted portion of the ladle shroud to the outlet.

8. The casting system according to claim 6 or 7, wherein the ladle shroud does not reduce the cross-sectional area between the constricted portion and the outlet.

9. The casting system according to any one of claims 1 to 8, wherein the casting system does not have an inert gas injection system at the intersection between the ladle shroud and the ladle.

10. The ratio of the cross-sectional area (Aa) at the entrance to the cross-sectional area (Ab) at the constricted portion is defined by the following formula: [Math 1] In the formula, g is the gravitational constant, H is the distance between the entrance and the constricted portion, and u Ａ The casting system according to any one of claims 1 to 9, wherein is the rate at which the molten metal is injected into the inlet of the ladle shroud.

11. The casting system according to any one of claims 1 to 10, wherein the ratio of the cross-sectional area at the inlet to the cross-sectional area at the constricted portion is approximately 2.2 in the case of the ladle shroud having a length of approximately 1.4 m.

12. The casting system according to any one of claims 1 to 11, wherein the ladle shroud defines at least one opening in or upstream of the constricted portion that communicates with the internal flow path, and the at least one opening is fluidly connected to a source of inert gas.

13. The casting according to claim 12, wherein the at least one opening is fluidly connected to the source of the inert gas via one or more of the gas port, control valve, gas diffuser, and casting nozzle.

14. The casting system according to any one of claims 1 to 13, wherein the distance between the inlet and the constricted portion is in the range of approximately 10% to 50% of the height of the tundish.

15. The casting system according to claim 14, wherein the distance is in the range of 10% to 25%.

16. The casting system according to claim 15, wherein the distance is in the range of 10% to 15%.

17. A method for distributing molten metal to be cast, The transfer of the molten metal from the ladle to the ladle shroud via the inlet of the ladle shroud, wherein the ladle shroud defines an internal flow path, and the transfer is performed. Increasing the velocity of the molten metal through the ladle shroud, from the inlet of the ladle shroud to a constricted portion in the internal flow path of the ladle shroud located downstream of the inlet, such that the constricted portion defines a cross-sectional area smaller than the cross-sectional area of ​​the internal flow path anywhere upstream of the constricted portion. A method comprising discharging the molten metal from the outlet of the ladle shroud into a tundish positioned below the ladle, wherein the constriction is substantially aligned with the height of the molten metal level in the tundish.

18. The method according to claim 17, wherein the increase in the velocity includes causing the molten metal to flow into the converging section of the internal flow path of the ladle shroud.

19. The method according to claim 17 or 18, wherein the increase in the speed includes continuously increasing the speed from the inlet to the constricted portion.

20. The method according to claim 18 or 19, comprising maintaining the velocity substantially constant along a region of the convergence section of the internal flow path, wherein the region extends from a location adjacent to the constriction to the constriction.

21. The method according to claim 20, wherein maintaining the velocity substantially constant involves flowing the molten metal along the convergence section, which is bounded by a wall that is convex when viewed from inside the internal flow path.

22. The method according to any one of claims 17 to 21, comprising reducing the rate of the molten metal before outputting the molten metal into the tundish.

23. The method according to any one of claims 17 to 21, comprising injecting microbubbles of an inert gas in or upstream of the constricted portion.

24. The method according to claim 23, wherein the microbubbles are injected through one or more of a gas port, a control valve, a gas diffuser, and a casting nozzle.

25. A ladle shroud for fluid connection of a ladle to a tundish of a casting system, wherein the ladle shroud comprises, The internal flow path is defined by a wall that extends circumferentially around a central axis, the wall having an inlet end that defines the entrance to the internal flow path and an outlet end that defines the exit to the internal flow path, and the internal flow path is A converging section extending from the inlet to a constricted section located between the inlet and the outlet, wherein the constricted section defines a cross-sectional area smaller than the cross-sectional area of ​​the internal flow path anywhere upstream of the constricted section, and the cross-sectional area of ​​the internal flow path decreases along the converging section, A ladle shroud having a diverging section extending from the constricted portion to the outlet, wherein the cross-sectional area of ​​the internal flow path increases along the converging section.

26. The ladle shroud according to claim 25, wherein the wall is convex within the convergence section when viewed from inside the internal flow path.

27. The ladle shroud according to claim 26, wherein the radius of the cross-section of the wall taken in the convergence section, on the plane including the central axis, is in the range of approximately 19,000 mm to 20,000 mm.

28. The ladle shroud according to any one of claims 25 to 27, wherein the cross-sectional area decreases monotonically from the inlet to the constricted portion.

29. The ladle shroud according to any one of claims 25 to 28, wherein the ratio of the cross-sectional area at the inlet to the cross-sectional area at the constricted portion is approximately 2.2 in the case of the ladle shroud having a length of approximately 1.4 m.

30. The ladle shroud according to any one of claims 25 to 29, wherein the ladle shroud defines at least one opening in or upstream of the constricted portion that communicates with the internal flow path, and the at least one opening is fluidly connected to a source of inert gas.

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