JP7722968B2 - Method and structure for connecting a reflux pipe and an immersion pipe - Google Patents

Description

The present invention relates to a method and structure for connecting a reflux pipe and an immersion pipe used in a vacuum degassing device for molten steel processing.

A known vacuum degassing apparatus for degassing molten steel is an RH-type vacuum degassing apparatus, which consists of an upper vessel equipped with an inlet for metals and an exhaust port, a lower vessel, two reflux pipes located side by side at the bottom of the lower vessel, and immersion tubes connected to each reflux pipe. This vacuum degassing apparatus submerges two immersion tubes in molten steel (molten metal) contained in a ladle, supplies Ar gas into one of the reflux pipes and immersion tube, which function as an upflow pipe, and introduces the molten steel into the vacuum zone of the lower vessel along with the ascending current of the Ar gas, thereby degassing it. The degassed molten steel is then discharged into the ladle through the other reflux pipe and immersion tube, which function as a downflow pipe. Furthermore, in order to facilitate the connection process, a commonly used method for connecting the reflux tube and immersion tube in such vacuum degassing equipment is to abut and fasten (screw) a flat, doughnut-shaped flange attached to the upper end of the immersion tube against a flat, doughnut-shaped flange attached to the lower end of the reflux tube.

The submerged tube connected to the reflux pipe of such a vacuum degassing device is subject to significant damage from the flow of molten steel during the degassing process and must therefore be periodically replaced. However, the flange at the bottom of the reflux pipe can become curved due to thermal history during use. When the flange of the submerged tube is joined to the curved reflux pipe flange, a gap G can form between the refractory material (firebricks) 55 inside the reflux pipe 51 and the refractory material (firebricks) 59 inside the submerged tube 52, as shown in Figure 7. When a gap G forms between the inside of the reflux pipe 51 and the inside of the submerged tube 52, molten metal can seep in through this gap G during the initial stages of molten steel processing under reduced pressure, potentially damaging the refractory material 55 of the reflux pipe 51, the refractory material 59 of the submerged tube 52, or the steel shell 53 covering the outer periphery of the reflux pipe 51 and the steel shell 56 covering the outer periphery of the submerged tube 52.

To prevent molten metal from entering through the gap between the inside of the reflux pipe and the inside of the submerged pipe, a connection structure between the reflux pipe and the submerged pipe has been proposed, as in Patent Document 1, in which the lower end surface of the reflux pipe's refractory material is positioned above the flange, and the upper end surface of the submerged pipe's refractory material is positioned above the flange.

JP 2015-229800 A

The connection structure between the return flow tube and the submerged tube, such as that described in Patent Document 1, is able to prevent damage to the return flow tube and the submerged tube shell because it is unlikely that molten metal will seep through the gap between the return flow tube refractory and the submerged tube refractory and reach the shell. However, it has the disadvantage that the lower end face of the return flow tube refractory must be positioned above the flange, making it time-consuming to assemble the refractory near the lower end of the return flow tube. Furthermore, with the return flow tube and submerged tube connection structure described in Patent Document 1, unexpected gaps can sometimes form between the refractory protruding above the submerged tube flange and the shell of the return flow tube after connection. Molten metal can seep in through these gaps and damage the refractory of the return flow tube or submerged tube, or the shell of the return flow tube or submerged tube.

The object of the present invention is to provide a method and structure for connecting a reflux tube and an immersion tube that resolves the problems inherent in the conventional methods and structures for connecting a reflux tube and an immersion tube, and that can accurately prevent molten metal from entering through the gap between the inside of the reflux tube and the inside of the immersion tube during the initial stages of molten steel processing under reduced pressure, thereby damaging the refractory or steel shell of the reflux tube or immersion tube.

The present invention, as set forth in claim 1, is a method for connecting a reflux pipe and an immersion pipe provided near the lower end of a vacuum degassing apparatus, the reflux pipe having a cylindrical refractory material provided near the lower end thereof, and the immersion pipe having a cylindrical refractory material provided near the upper end thereof, the cylindrical refractory material having an inner diameter smaller than that of the cylindrical refractory material provided near the lower end thereof, the method comprising the steps of: joining the reflux pipe and the immersion pipe in a state in which the lower surface of the cylindrical refractory material near the lower end of the reflux pipe is brought into contact with the upper surface of the cylindrical refractory material near the upper end of the immersion pipe, and the cylindrical refractory material near the upper end of the immersion pipe is arranged concentrically with the cylindrical refractory material near the lower end of the reflux pipe; and a refractory stacking process for stacking amorphous refractory material on the inner surface of a cylindrical refractory material near the lower end of the flow tube so that it is flush with the inner surface of the cylindrical refractory material near the upper end of the immersion tube, wherein the refractory stacking process comprises placing a cylindrical metal connecting auxiliary member having an outer diameter approximately the same as the inner diameter of the cylindrical refractory material near the upper end of the immersion tube inside the cylindrical refractory material near the upper end of the immersion tube, and using the connecting auxiliary member, stacking amorphous refractory material on the inner surface of the cylindrical refractory material near the lower end of the reflux tube, wherein the connecting auxiliary member comprises a truncated cone portion connected to the upper side of a cylindrical portion .

The invention as set forth in claim 2 is characterized in that in the invention as set forth in claim 1, a magnesia-based or magnesia-spinel-based refractory is used as the monolithic refractory.

The invention described in claim 3 is a connection structure for connecting an immersion tube to a reflux tube provided near the lower end of a vacuum degassing apparatus, wherein the reflux tube has a cylindrical refractory material provided near the lower end, and the immersion tube has a cylindrical refractory material provided near the upper end, the cylindrical refractory material having an inner diameter smaller than that of the cylindrical refractory material provided near the lower end of the reflux tube, and the lower surface of the cylindrical refractory material near the lower end of the reflux tube is brought into contact with the upper surface of the cylindrical refractory material near the upper end of the immersion tube, and the cylindrical refractory material near the upper end of the immersion tube is brought into contact with the cylindrical refractory material near the lower end of the reflux tube. The reflux tube and immersion tube are joined in a concentric arrangement around the cylindrical refractory, and amorphous refractory is layered on the inner surface of the cylindrical refractory near the lower end of the reflux tube so that it is flush with the inner surface of the immersion tube.The connection between the reflux tube and the immersion tube is characterized by the fact that a connecting auxiliary member made of metal and having an outer diameter approximately the same as the inner diameter of the cylindrical refractory of the immersion tube, and having a shape consisting of a truncated cone portion connected to the upper part of a cylindrical portion, is disposed inside the connection between the reflux tube and the immersion tube .

According to the method for connecting a reflux tube and a submerged tube described in claim 1, even if the flange of the reflux tube has become distorted due to use, the gap between the inside of the reflux tube and the inside of the submerged tube is sealed with monolithic refractory, effectively preventing damage to the refractory and steel shell caused by molten metal entering through the gap during the early stages of molten steel processing under reduced pressure.

In addition, according to the method of connecting a reflux pipe and an immersion pipe described in claim 1 , a connecting auxiliary member is placed inside a cylindrical refractory material near the upper end of the immersion pipe, and an amorphous refractory material is stacked on the inner surface of the cylindrical refractory material near the lower end of the reflux pipe, making the construction of connecting the reflux pipe and the immersion pipe extremely easy.

According to the method of connecting a reflux tube and an immersion tube described in claim 2 , the gap between the inside of the reflux tube and the inside of the immersion tube is sealed with a highly heat-resistant magnesia-based refractory or a magnesia-spinel-based refractory, making it possible to prevent molten metal from entering through the gap with greater accuracy during the initial stages of molten steel processing under reduced pressure.

According to the connection structure between the reflux pipe and the submerged pipe described in claim 3 , even if the flange of the reflux pipe has become distorted due to use, the gap between the inside of the reflux pipe and the inside of the submerged pipe is blocked by the monolithic refractory, making it possible to effectively prevent damage to the refractory and steel shell caused by molten metal entering through the gap during the initial stage of molten steel processing under reduced pressure.

FIG. 2 is an explanatory diagram (vertical cross-sectional view) showing a vacuum degassing device. 1A and 1B are explanatory diagrams showing a circulation tube (a is a vertical cross-sectional view, and b is a cross-sectional view taken along line AA in a). 1 is an explanatory diagram showing an immersion tube (a is a vertical cross-sectional view, and b is a cross-sectional view taken along line BB in a). FIG. 10 is an explanatory diagram (vertical cross-sectional view) showing how an immersion tube is connected to a reflux tube. 10A and 10B are explanatory views showing a connection auxiliary member (FIG. 10A is a vertical cross-sectional view, and FIG. 10B is a plan view). An explanatory diagram showing the connection structure between the reflux pipe and the immersion pipe (a is a vertical cross-sectional view, b is an enlarged view of part C in a, and c is a cross-sectional view along line D-D in a). FIG. 1 is an explanatory diagram (vertical cross-sectional view) showing a conventional connection structure between a reflux pipe and an immersion pipe.

Below, one embodiment of the method and structure for connecting a reflux tube and an immersion tube according to the present invention will be described in detail with reference to the drawings.

<Structure of reflux tube>
FIG. 1 shows a vacuum degassing apparatus for removing gas components from molten steel. Two reflux pipes 1, 1 are installed vertically side by side at the bottom of the lower vessel of the vacuum degassing apparatus M. FIG. 2 shows the reflux pipe 1, which is composed of a cylindrical refractory brick stack 5 formed by assembling a large number of refractory bricks, a shell 3 covering the outer periphery of the refractory brick stack 5, and castable refractory filling the gap between the refractory brick stack 5 and the shell 3. As shown in FIG. 2(b), the refractory brick stack 5 is formed by concentrically stacking flat cylindrical bodies 5a, 5b, 5c, etc., each of which is made up of a large number of refractory bricks 11, 11, etc. assembled in a doughnut shape (bonded together with castable refractory). The shell 3 has a flattened cylindrical lower end, and a doughnut-shaped flange 4 is integrally formed at the lower edge.

<Structure of reflux tube>
Figure 3 shows the submerged pipe 2 connected to the reflux pipe 1. The submerged pipe 2 is composed of a refractory brick assembly 9 formed by integrally assembling a number of refractory bricks 11, 11..., a cylindrical shell 6 covering the periphery of the refractory brick assembly 9, and a castable refractory 8 formed to fill the gap between the refractory brick assembly 9 and the shell 6 and to cover the periphery of the shell 6 and the underside of the refractory brick assembly 9. As shown in Figure 3(b), the refractory brick assembly 9 is formed into a thick cylindrical shape by assembling a number of vertically elongated, approximately rectangular refractory bricks 11, 11... (bonded together with the castable refractory). Meanwhile, a doughnut-shaped flange 7 is integrally formed on the upper edge of the shell 6.

<Method of connecting the reflux tube and the immersion tube>
Figure 4 shows how a new submerged tube 2 is connected (attached) to the reflux tube 1 installed near the lower end of the vacuum degassing apparatus M as described above. When connecting the reflux tube 1 and the submerged tube 2, first, as shown in Figure 4(a), the inner wall of the lowest cylindrical body 5a of the refractory brick stack 5 made of refractory bricks stacked inside the steel shell 3 of the reflux tube 1 is ground (polished) by a certain thickness. Then, the inner diameter of the lowest cylindrical body 5a is made larger by a certain length (approximately 20 to 200 mm) than the inner diameter of the upper cylindrical body 5b. Here, the method employed is to first form the stacked firebrick body 5, and then grind the inner wall of the lowest cylindrical body 5a of the stacked firebrick body 5 by a certain thickness. However, it is also possible to previously form a cylindrical body 5a with an inner diameter larger than the inner diameters of the upper cylindrical bodies 5b and 5c (i.e., a cylindrical body 5a thinner than the cylindrical bodies 5b and 5c), and then set the cylindrical body 5a with the larger inner diameter in position a.

After grinding the inner wall of the lowest cylindrical body 5a inside the reflux pipe 1 as described above, the submerged tube 2 is concentrically joined to the underside of the reflux pipe 1 (joining process). That is, the underside of the flange 4 of the reflux pipe 1 is abutted against the flange 7 of the submerged tube 2, and the flanges 4, 7 are fastened together (for example, by screwing them together with bolts and nuts). By joining the submerged tube 2 to the underside of the reflux pipe 1 in this way, a cylindrical cavity C is formed inside the reflux pipe 1 and the submerged tube 2.

Next, the auxiliary connecting member 21 is inserted into the hollow portion C. Figure 5 shows the auxiliary connecting member 21, which is integrally formed into a cylindrical shape from metal (iron, etc.). The lower portion (cylindrical portion 22) of the auxiliary connecting member 21 has an outer diameter approximately the same as the inner diameter of the immersion tube 2, while the upper portion is formed into a truncated cone shape with a gradually decreasing diameter from bottom to top. The outer surface of the truncated cone portion 23 is inclined at approximately 30° with respect to the vertical plane. When inserting the auxiliary connecting member 21 into the hollow portion C, as shown in Figure 4(b), the auxiliary connecting member 21 is positioned so that the boundary line B between the cylindrical portion 22 and the truncated cone portion 23 of the auxiliary connecting member 21 is located inside the lowest cylindrical body 5a of the reflux tube 1. The auxiliary connecting member 21 is then fixed (adhered) to the immersion tube 2.

After inserting the auxiliary connection member 21 into the hollow portion C of the reflux tube 1 and the submerged tube 2 as described above, as shown in Figure 4(c), a castable refractory (magnesia-based or magnesia-spinel-based refractory (castable)) 10 is poured into the gap between the inner wall of the lowest cylindrical body 5a of the reflux tube 1 and the truncated cone-shaped portion 23 of the auxiliary connection member 21 (the castable refractory layering process). The connecting process is then completed by allowing the castable refractory 10 to fully harden. Note that, as described above, a synthetic resin tube or the like can be suitably used when pouring the castable refractory 10 into the gap between the inner wall of the lowest cylindrical body 5a of the reflux tube 1 and the truncated cone-shaped portion 23 of the auxiliary connection member 21.

Figure 6 shows the state in which the reflux tube 1 and the submerged tube 2 are connected. Due to use, distortion has occurred in the flange 4 of the reflux tube 1, creating a gap between the flange 4 and the flange 7 of the submerged tube 2. This has resulted in a gap G between the underside of the lowest cylindrical body 5a of the reflux tube 1 and the upper surface of the refractory brick assembly 9 of the submerged tube 2. However, this gap G is blocked by castable refractory 10 poured into the gap between the inner wall of the lowest cylindrical body 5a of the reflux tube 1 and the truncated cone-shaped portion 23 of the connecting support member 21. As shown in Figure 6(b), the castable refractory 10 has penetrated into the gap G between the underside of the lowest cylindrical body 5a of the reflux tube 1 and the upper surface of the refractory brick assembly 9 of the submerged tube 2.

<Function of the vacuum degassing device>
In the vacuum degassing apparatus M, in which the submerged pipes 2, 2 are connected below the reflux pipes 1, 1 as described above, the lower ends of the submerged pipes 2, 2 are immersed in the molten metal (molten steel) in a ladle (not shown). One of the reflux pipes 1 functions as an uprising pipe together with the submerged pipe 2, and the other reflux pipe 1 functions as a downcomer pipe together with the submerged pipe 2. When a vacuum is created inside the apparatus and an inert gas such as argon gas is blown into the uprising pipes (one of the reflux pipes 1 and submerged pipe 2) via piping (not shown), the molten metal in the ladle is drawn into the lower vessel and rises inside the uprising pipe, then descends inside the downcomer pipes (the other reflux pipe 1 and submerged pipe 2) and returns to the ladle to be refluxed. During this reflux process, the molten metal is degassed, and the gas is discharged to the outside.

In the connection structure between the reflux pipe 1 and the submerged pipe 2 described above, the gap G between the inside of the reflux pipe 1 and the inside of the submerged pipe 2 (the gap between the lower surface of the refractory brick stack 5 of the reflux pipe 1 and the upper surface of the refractory brick combination 9 of the submerged pipe) is blocked by the monolithic refractory material 10, so molten metal does not enter the gap G when the vacuum degassing device M is in use as described above. Furthermore, the connection auxiliary member 21 in the connection structure between the reflux pipe 1 and the submerged pipe 2 described above dissolves and disappears in the molten metal within a very short time while the vacuum degassing device M is in use, so the connection auxiliary member 21 does not obstruct the flow of molten metal flowing inside the upflow pipe and downflow pipe.

<Effects of the connection method and connection structure between the reflux tube and the immersion tube>
The above-mentioned method of connecting the reflux pipe 1 and the immersion pipe 2 is such that the reflux pipe 1 has a cylindrical refractory material (firebrick stack 5) at its lower end, and the immersion pipe 2 has a cylindrical refractory material (firebrick combination 9) at its upper end which has an inner diameter smaller than that of the cylindrical refractory material (cylindrical body 5a) at its lower end. The above-mentioned method of connecting the reflux tube 1 and the immersion tube 2 includes a joining process in which the lower surface of the cylindrical body 5a at the lower end of the reflux tube 1 is abutted against the upper surface of the refractory brick combination 9 at the upper end of the immersion tube 2, and the refractory brick combination 9 at the upper end of the immersion tube 2 is arranged concentrically with the cylindrical body 5a at the lower end of the reflux tube 1, and a refractory stacking process in which amorphous refractory 10 is stacked on the inner surface of the cylindrical body 5a at the lower end of the reflux tube 1 so that it is flush with the inner surface of the refractory brick combination 9 at the upper end of the immersion tube 2.

Therefore, with this connection method, even if the flange 4 of the reflux pipe 1 has become distorted due to use, the gap G between the inside of the reflux pipe 1 and the inside of the submerged pipe 2 is sealed by the monolithic refractory 10, effectively preventing damage to the refractory materials (such as the refractory brick stack 5 and refractory brick combination 9), the steel shell 3 of the reflux pipe 1, and the steel shell 6 of the submerged pipe 2 caused by molten metal entering through the gap G during the initial stages of molten steel processing under reduced pressure.

In addition, the above-mentioned method of connecting the reflux pipe 1 and the submerged pipe 2 involves placing a cylindrical metal connecting auxiliary member 21, the outer diameter of which is approximately the same as the inner diameter of the refractory brick combination 9, inside the refractory brick combination 9 at the upper end of the submerged pipe 2, and then using this connecting auxiliary member 21 to stack monolithic refractory material 10 on the inner surface (inner wall surface) of the cylindrical body 5a at the lower end of the reflux pipe 1. This makes it extremely easy to connect the reflux pipe 1 and the submerged pipe 2.

Furthermore, the above-mentioned method of connecting the reflux tube 1 and the submerged tube 2 uses a magnesia-based or magnesia-spinel-based refractory (castable) as the monolithic refractory 10. Therefore, the gap G between the inside of the reflux tube 1 and the inside of the submerged tube 2 (the gap G between the bottom surface of the refractory brick stack 5 of the reflux tube 1 and the top surface of the refractory brick combination 9 of the submerged tube 2) is blocked by the highly heat-resistant magnesia-based or magnesia-spinel-based refractory. This makes it possible to more accurately prevent molten metal from entering through the gap G between the inside of the reflux tube 1 and the inside of the submerged tube 2 during the initial stages of molten steel processing under reduced pressure.

In addition, the above-mentioned method of connecting the reflux tube 1 and the submerged tube 2 uses a connecting auxiliary member 21 having a shape in which a truncated cone-shaped portion 23 is connected to the upper side of a cylindrical portion 22. This makes it very easy to pour the monolithic refractory 10 into the gap S between the inner wall of the cylindrical body 5a at the lowest position of the reflux tube 1 and the truncated cone-shaped portion 23 of the connecting auxiliary member 21.

Meanwhile, the connection structure between the reflux tube 1 and the submerged tube 2 described above is such that the reflux tube 1 has a cylindrical body 5a near its lower end, and the submerged tube 2 has a refractory brick assembly 9 near its upper end, the inner diameter of which is smaller than that of the cylindrical body 5a near the lower end of the reflux tube 1. The reflux tube 1 and the submerged tube 2 are joined in such a manner that the lower surface of the cylindrical body 5a near the lower end of the reflux tube 1 abuts against the upper surface of the refractory brick assembly 9 near the upper end of the submerged tube 2, and the refractory brick assembly 9 near the upper end of the submerged tube 2 is concentrically positioned relative to the cylindrical body 5a near the lower end of the reflux tube 1. A castable refractory material 10 is layered on the inner surface of the cylindrical body 5a near the lower end of the reflux tube 1 so that it is flush with the inner surface of the submerged tube 2.

Therefore, with this connection structure, even though the flange 4 of the reflux pipe 1 becomes distorted during use, forming a gap G between the inside of the reflux pipe 1 and the inside of the submerged pipe 2, this gap G is blocked by the monolithic refractory 10, effectively preventing damage to the refractory (firebrick stacks 5 and refractory brick assemblies 9) and the steel shell 3 of the reflux pipe 1 and the steel shell 6 of the submerged pipe 2 caused by molten metal entering through the gap G during the initial stages of molten steel processing under reduced pressure.

<Example of changing the dip tube>
The immersion pipe of the present invention is not limited to the above-described embodiment, and the material, shape, structure, size, and other configurations of the reflux pipe (iron shell, refractory brick stack, flange) and the immersion pipe (iron shell, refractory brick combination, monolithic refractory material) can be appropriately modified as needed within the scope of the present invention.

For example, the immersion pipe used in the connection method and connection structure of the present invention is not limited to having a refractory brick assembly formed into a thick cylindrical shape by assembling a large number of approximately rectangular parallelepiped refractory bricks, as in the above embodiment, but may also have a refractory brick assembly formed integrally into a thick cylindrical shape. Furthermore, the immersion pipe is not limited to having a single layer of refractory brick assembly, as in the above embodiment, but may also have a refractory brick assembly stacked in multiple layers.

Furthermore, the connection method and connection structure between the reflux tube and the submerged tube according to the present invention is not limited to the use of a magnesia-based or magnesia-spinel-based refractory (castable) as the monolithic refractory filling the gap between the inner wall of the lowest cylindrical body of the reflux tube and the upper truncated cone-shaped portion of the connecting support member, as in the above embodiment; it is also possible to use alumina-based or magnesia-chromium-based refractories (castable, etc.) as the monolithic refractory.

Furthermore, the connection method and structure for connecting the reflux tube and immersion tube according to the present invention are not limited to those using a connection auxiliary member consisting of a truncated cone-shaped portion attached to the upper side of a cylindrical portion, as in the above embodiment, but may also use a simple cylindrical connection auxiliary member. In addition, the connection method for connecting the reflux tube and immersion tube according to the present invention is not limited to those using a connection auxiliary member inserted into the interior of the immersion tube joined to the reflux tube, as in the above embodiment, but may also involve joining an immersion tube with a connection auxiliary member inserted into it in advance to the reflux tube.

The method and structure for connecting a reflux tube and an immersion tube according to the present invention has the excellent effects described above, and can therefore be suitably used as a method and structure for connecting a reflux tube and an immersion tube in a vacuum degassing apparatus when replacing an immersion tube after it has been used for a certain period of time with a new one.

REFRACTORY TUBE 2 IMMERSION TUBE 4 FLANGE 5 FIREFRACTORY BRICK LAYERED BODY 5a, 5b, 5c CYLINDRICAL BODY 7 FLANGE 8 MODIFIED REFRACTORY 9 FIREFRACTORY BRICK BODY 11 FIREFRACTORY BRICK 21 AUXILIARY CONNECTION MEMBER 22 CYLINDRICAL PORTION 23 FRUSTRATE OF CONCENTRATES M VACUUM DEGASIFICATION APPARATUS

Claims (3)

A method for connecting a reflux pipe and a dip pipe provided at the lower end of a vacuum degassing apparatus, comprising:
The reflux tube has a cylindrical refractory material at the bottom end,
The immersion tube has a cylindrical refractory member at its upper end, the cylindrical refractory member having an inner diameter smaller than that of the cylindrical refractory member at the lower end of the reflux tube,
a joining step of joining the reflux tube and the submerged tube in a state in which the lower surface of the cylindrical refractory material at the lower end of the reflux tube and the upper surface of the cylindrical refractory material at the upper end of the submerged tube are brought into contact with each other, and the cylindrical refractory material at the upper end of the submerged tube is arranged concentrically with the cylindrical refractory material at the lower end of the reflux tube;
and a refractory layering step of layering a monolithic refractory on an inner peripheral surface of a cylindrical refractory at the lower end of the reflux tube so as to be flush with an inner peripheral surface of a cylindrical refractory at the upper end of the immersion tube,
The refractory layering step is a step of placing a cylindrical metal connecting auxiliary member having an outer diameter substantially the same as the inner diameter of the cylindrical refractory at the upper end of the immersion tube inside the cylindrical refractory at the upper end of the immersion tube, and using the connecting auxiliary member, stacking the monolithic refractory on the inner peripheral surface of the cylindrical refractory at the lower end of the reflux tube, and
A method for connecting a reflux pipe and an immersion pipe, characterized in that the connection auxiliary member comprises a cylindrical portion and a truncated cone portion connected to the upper side of the cylindrical portion . The method for connecting a reflux tube and an immersion tube described in claim 1, characterized in that a magnesia-based or magnesia-spinel-based refractory is used as the monolithic refractory. A connection structure for connecting a dip tube to a reflux pipe provided at the lower end of a vacuum degassing apparatus,
The reflux tube has a cylindrical refractory material at the bottom end,
The immersion tube has a cylindrical refractory member at its upper end, the cylindrical refractory member having an inner diameter smaller than that of the cylindrical refractory member at the lower end of the reflux tube,
The reflux tube and the immersion tube are joined in a state in which the lower surface of the cylindrical refractory material at the lower end of the reflux tube is in contact with the upper surface of the cylindrical refractory material at the upper end of the immersion tube, and the cylindrical refractory material at the upper end of the immersion tube is concentrically arranged with the cylindrical refractory material at the lower end of the reflux tube,
A monolithic refractory material is laminated on the inner surface of the cylindrical refractory material at the lower end of the reflux tube so as to be flush with the inner surface of the immersion tube, and
A connection structure between a reflux pipe and an immersion pipe, characterized in that a connection auxiliary member made of metal and having an outer diameter approximately the same as the inner diameter of the cylindrical refractory material of the immersion pipe, and having a shape consisting of a truncated cone portion connected to the upper part of a cylindrical portion, is disposed inside the connection portion between the reflux pipe and the immersion pipe.