JP2008013796A - Immersion tube for treating molten metal and manufacturing method thereof, and vacuum-degassing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an immersion tube and manufacturing method thereof, and a vacuum-degassing method with which regarding to the immersion tube for treating molten metal fitted to a vacuum vessel in the degassing vessel for degassing apparatus performing the degassing treatment in molten metal, the durability thereof is improved and the service life can drastically be prolonged. <P>SOLUTION: The immersion tube for treating molten metal and the manufacturing method thereof, are performed as the followings, that is, a core metal 8 of the immersion tube 5, is a double tube-shape of an inside cylindrical iron plate 8a and an outside cylindrical iron plate 8b and on the inner and the outer circumferences and the bottom part, to the bottom part, to refractory brick 9 or a monolithic refractory 10 is disposed, and in a gap part 11 between the outside cylindrical iron plate 8b and the inside cylindrical iron plate 8a, the monolithic refractory 13 for filling up is filled up, and the monolithic refractory 13 for filling up is filled up and the monolithic refractory 13 for filling up, is ≤30% apparent porosity and ≥5MPa bending strength and a gas introducing tube 14 for flowing cooling gas into the gap part 11 of the core metal 8 is peculiarly disposed . Then, the monolithic refractory 13 for filling up, the refractory as the raw material of that having ≤2mm the maximum grain diameter is used. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a molten metal processing dip tube attached to a vacuum tank of a degassing apparatus for degassing a molten metal, a manufacturing method thereof, and a vacuum degassing method using the dip tube.

  As the metal material is highly purified and upgraded, vacuum degassing is performed in order to remove the impurity gas from the molten metal in the refining process. RH vacuum degassing apparatus and DH vacuum degassing apparatus are typical. In these vacuum degassing apparatuses, a dip tube is provided at the lower part of the vacuum chamber, and after the lower end opening of the dip tube is immersed in the molten metal, the vacuum chamber is depressurized, and the molten metal is sucked into the vacuum chamber to be nitrogen. And gas components such as hydrogen are removed. In the DH degasser, one dip tube is arranged, and in the RH degasser, two dip tubes are arranged.

  The vacuum degassing of the molten steel to which the RH vacuum degassing apparatus is applied will be described with reference to FIG.

  Two dip tubes 5 are disposed below the vacuum chamber 3 of the RH vacuum degassing apparatus. One is an ascending dip tube 5a and the other is a descending dip tube 5b. These dip tubes 5 are immersed in the molten steel 2 in the pan 1, and then the gas in the vacuum chamber 3 is sucked from the exhaust duct 4 provided in the upper portion of the vacuum chamber 3 to reduce the pressure in the vacuum chamber. By reducing the pressure in the vacuum chamber, the molten steel 2 in the ladle is sucked into the vacuum chamber.

  An inert gas blowing nozzle 6 is provided in the inner peripheral portion of the ascending dip tube 5a, and the inert gas is blown into the molten steel in the ascending dip tube 5a. As a result, since the specific gravity of the molten steel in the ascending dip tube 5a is relatively decreased as compared with the molten steel in the descending dip tube 5b, the molten steel in the ascending dip tube rises and the molten steel in the descending dip tube begins to descend. . As a result, the molten steel in the ladle 1 circulates from the ascending dip tube 5a into the vacuum chamber 3 and through the descending dip tube 5b into the ladle 1. Since the surface of the molten steel in the vacuum chamber is in contact with the reduced-pressure atmosphere, the gas component in the molten steel moves to the reduced-pressure atmosphere here, and degassing is performed. While the molten steel circulates, degassing is performed in the vacuum chamber, and the gas component in the molten steel in the ladle is removed.

  4 and 5 schematically show cross-sectional views of the structure of the conventional dip tube 5. When the dip tube is used as an ascending dip tube, an inert gas blowing nozzle is disposed on the inner peripheral side of the dip tube, but the inert gas blowing nozzle is not shown here. A metal cylinder called a cored bar 8 is disposed in the center of the dip tube. On the inner peripheral side of the cored bar 8, a refractory brick 9 is disposed in FIG. 4, and an irregular refractory 10b is disposed in FIG. About the outer peripheral side of a metal core, the amorphous refractory 10a is arrange | positioned in FIG. These refractories are held by a refractory receiver or a stud installed on the core 8. The cored bar 8 stably holds the refractory constituting the dip tube 5 and plays an important role in preventing the outside air from entering the vacuum chamber, and deformation of the cored bar 8 must be prevented as much as possible. .

  When performing vacuum refining of molten steel, both the ascending dip tube 5a and the descending dip tube 5b are immersed in the molten steel 2, and the molten steel circulates on the inner peripheral side of the dip tube 5, and most of the outer peripheral side of the dip tube 5 is on the outer peripheral side. It is in contact with the molten steel in the ladle. Therefore, during the operation of vacuum degassing, both the ascending dip tube and the descending dip tube are exposed to high temperatures. On the other hand, when the vacuum degassing is finished, the vacuum tank is not in contact with the molten steel, so that these dip tubes are cooled.

  As a result of repeated heating and cooling of the ascending dip tube and the descending dip tube in this manner, the cored bar 8 embedded in the dip tube 5 is subjected to thermal stress caused by expansion and contraction. As shown in FIG. 5, the lower end of the cored bar 8 is deformed into a trumpet shape. The deformation of the metal core causes a crack 7 in the surrounding refractory, and when the molten steel or slag enters the crack 7 erodes and gradually expands, causing the refractory to peel off. That is, the deformation of the cored bar 8 causes the durability of the dip tube 5 to deteriorate, and various techniques for preventing the deformation of the cored bar 8 have been studied.

In Patent Document 1, a first cored bar as a cored bar of a dip tube and a second cored bar are disposed outside the cored bar, and a filling refractory for filling is filled in a gap between the first cored bar and the second cored bar. Has been disclosed. The filling refractory is made of the same or different material as the forming refractory. Specifically monolithic refractory containing 7-8 wt% of Al ₂ O ₃ of 89-90% by weight and MgO is monolithic refractories have been used to contain Al ₂ O ₃ 90-95 wt% . By adopting a double cored bar in this way and filling the gap with an irregular refractory for filling, the reinforcing effect is enhanced, the durability of the dip tube is improved, and the life can be greatly extended.

  Patent Documents 2 and 3 disclose a dip tube having a structure including an outer cylindrical iron plate, an inner cylindrical iron plate, and a bottom plate, in which a core metal for flowing a cooling gas is incorporated, and the periphery thereof is covered with a refractory. The thing of patent document 2 inserts a metal plate in the clearance gap between an outer peripheral cylindrical iron plate and an inner peripheral cylindrical iron plate, and cools by the radiant heat transfer to the interposer metal plate, and the convective heat transfer from the interposer metal plate. Trying to improve. The one described in Patent Document 3 is provided with a plurality of fins extending in the vertical direction on the side surface of the outer cylindrical iron plate and / or the inner cylindrical iron plate on the flow path side of the cooling gas. The cooling capacity is said to increase.

  Among the varieties that perform RH vacuum degassing, there are varieties that should have a very low nitrogen concentration in the molten steel. On the other hand, in the RH vacuum degassing, when the atmosphere enters the molten metal in the vacuum chamber, the nitrogen in the atmosphere moves into the molten metal, and the nitrogen concentration in the molten metal increases. In the dip tube of the RH vacuum degassing apparatus, there is a path through which the outside air at atmospheric pressure enters the vacuum tank through the refractory. In the dip tube, the outer peripheral side refractory and the inner peripheral side refractory of the core metal are connected by the bottom refractory below the core metal, so that air enters the vacuum chamber via these refractories.

  Patent Document 4 discloses a dip tube in which a gas reservoir that circulates a metal core is embedded in the refractory on the outer peripheral surface of the metal core, and an inert gas is blown into the refractory from the gas reservoir. Patent Document 5 discloses a dip tube that supplies nitrogen gas to an arc-shaped plural breathable refractory material that is positioned outside the core metal and below the molten steel surface. Thereby, it is supposed that the penetration | invasion into the molten steel of the air which made the path | route the immersion refractory of a dip tube can be prevented.

JP 2005-325392 A JP-A-61-253318 Japanese Patent Application Laid-Open No. 2004-256881 Japanese Utility Model Publication No. 62-136556 Japanese Patent Laying-Open No. 2005-200696

  In the method described in Patent Document 1, filling the amorphous refractory for filling in the gap between the cores of the double structure certainly increases the life of the dip tube, but the amorphous refractory for filling is not sufficient. The deformation of the metal core cannot be completely suppressed, and the dip tube cannot be cracked or peeled off due to the deformation.

  In the methods described in Patent Documents 2 and 3, the core bar is cooled, but the structure strength of the core metal itself is not sufficient, and the core metal cannot be prevented from being deformed. Cracks occur in the refractory with the deformation of the gold, and when it is severe, it leads to peeling, and the durability of the dip tube cannot be sufficiently improved.

  The present invention relates to a dip tube for molten metal treatment that is attached to a vacuum tank of a degassing device that performs degassing treatment of molten metal, and the dip tube that can improve the durability and greatly extend the life, and a method for manufacturing the dip tube An object of the present invention is to provide a vacuum degassing method.

That is, the gist of the present invention is as follows.
(1) Molten metal processing dip tube 5 attached to a vacuum tank of a degassing apparatus for degassing molten metal, and the core metal 8 of the dip tube 5 includes an inner cylindrical iron plate 8a and an outer cylindrical iron plate 8b. A refractory brick 9 or an irregular refractory 10 is arranged on the inner and outer periphery and bottom of the cored bar 8, and an irregular refractory is formed in the gap 11 between the outer cylindrical iron plate 8b and the inner cylindrical iron plate 8a of the cored bar 8. (Hereinafter referred to as “filled amorphous refractory 13”), the filled amorphous refractory 13 has an apparent porosity of 30% or less, the bending amorphous refractory 13 has a bending strength of 5 MPa or more, and a core. A molten metal processing dip tube in which a gas introduction tube 14 for flowing a cooling gas through the gap 11 of the gold 8 is provided.
(2) The dip tube for molten metal treatment as described in (1) above, wherein a refractory having a maximum particle size of 2 mm or less is used as a raw material for the filled amorphous refractory 13.
(3) The dip tube for molten metal treatment according to the above (1) or (2), which is a dip tube of an RH vacuum degassing apparatus.
(4) A method of manufacturing a dip tube for molten metal treatment that is attached to a vacuum tank of a degassing device that performs degassing treatment of molten metal, wherein the cored bar 8 of the dip tube 5 includes an inner cylindrical iron plate 8a and an outer cylindrical iron plate 8b. The refractory brick 9 or the irregular refractory 10 is disposed on the inner and outer circumferences and bottom of the cored bar 8, and the largest grain is formed in the gap 11 between the outer cylindrical iron plate 8b and the inner cylindrical iron plate 8a of the cored bar 8. Filled with an amorphous refractory with a diameter of 2 mm or less (hereinafter referred to as “filled amorphous refractory 13”), the apparent porosity of the filled amorphous refractory 13 is 30% or less, and the bending strength of the filled amorphous refractory 13 A method for manufacturing a dip tube for treating molten metal, characterized in that a gas introduction tube 14 for flowing a cooling gas through the gap 11 of the core 8 is provided.
(5) The method for manufacturing a dip tube for molten metal treatment as described in (4) above, wherein the dip tube 5 is a dip tube of an RH vacuum degassing apparatus.
(6) A vacuum degassing method using an RH vacuum degassing apparatus, which uses the dip tube for molten metal treatment described in (3) above, and is inert from the gas introduction tube 14 to the gap 11 of the metal core 8. A vacuum degassing method comprising performing vacuum degassing while supplying a gas.

  The present invention relates to a dip tube for molten metal treatment that is attached to a vacuum tank of a degassing apparatus that performs degassing treatment of molten metal, and the dip tube has a double-pipe core metal, and an outer cylindrical iron plate and an inner cylinder of the core metal Filling the gaps in the iron plate with an irregular refractory with an apparent porosity of 30% or less and a bending strength of 5 MPa or more, and flowing cooling gas through the gaps in the cored bar improves the durability and greatly increases the service life. Can be extended to Moreover, air is prevented from entering the vacuum chamber through the dip tube refractory.

  An example of the dip tube of the present invention is schematically shown in cross-sectional views in FIGS.

  Both the dip tube used in the RH vacuum degassing apparatus and the dip tube used in the DH vacuum degassing apparatus have the same basic structure. As shown in FIG. 6, with respect to the rising dip tube 5a of the RH vacuum degassing apparatus, an inert gas blowing nozzle 6 for blowing an inert gas from the inner periphery of the dip tube is arranged. However, an inert gas blowing nozzle is not shown in FIGS. Hereinafter, the ascending dip tube, the descending dip tube of the RH vacuum degassing apparatus, and the dip tube of the DH vacuum degassing apparatus will be described without distinction.

  The dip tube 5 of the present invention is coupled to the vacuum chamber 3 at a flange 12 disposed on the top thereof. The inner cylindrical iron plate 8a and the outer cylindrical iron plate 8b constituting the cored bar 8 are both joined to the flange 12, and both form a double tube shape. Refractory bricks 9 or amorphous refractories 10 are arranged on the inner and outer circumferences and bottom of the cored bar 8. In the example of FIG. 1, a refractory brick 9 is disposed on the inner peripheral side of the cored bar 8, an outer peripheral side indefinite refractory 10 a is disposed on the outer periphery of the cored bar, and a bottom indeterminate refractory 10 c is disposed on the bottom. In the example of FIG. 2, the irregular refractory 10 is disposed on both the inner and outer circumferences and the bottom of the cored bar.

  It is preferable to use a metal (for example, carbon steel, stainless steel, etc.) excellent in heat resistance for both the inner cylindrical iron plate 8a and the outer cylindrical iron plate 8b serving as the cored bar 8. The thickness of these cylindrical iron plates is determined by the diameter of the dip tube, but a thickness of 10 to 20 mm is used. In addition, a stud or brick holding metal is attached by welding to hold the refractory as necessary.

  The gap 11 between the inner cylindrical iron plate 8a and the outer cylindrical iron plate 8b is preferably widened to further increase the strength of the core metal structure. On the other hand, the total thickness of the dip tube 5 is limited, and the outer refractory and inner refractory thicknesses of the core metal ensure the necessary thickness corresponding to the melting damage during use. There is a need. For this reason, the gap between the inner cylindrical iron plate 8a and the outer cylindrical iron plate 8b is also restricted, and specifically, it is preferably in the range of 10 to 40 mm.

  In order to further increase the strength of the structure of the cored bar 8, the ends of the outer cylindrical iron plate 8b and the inner cylindrical iron plate 8a can be fixed to each other by welding with a steel member on the lower end side of the dip tube 5. Round steel can be used as the steel member.

  In the present invention, an irregular refractory is filled in the gap 11 between the outer cylindrical iron plate 8b and the inner cylindrical iron plate 8a, which is a core metal. This amorphous refractory is referred to as “filled amorphous refractory 13”.

  The thing of patent document 1 arrange | positions the 1st metal core as a metal core of a dip tube, and the 2nd metal core on the outer side, and fills the clearance gap between a 1st metal core and a 2nd metal core, and is an irregular-shaped fireproof for filling. Although the material was filled, the deformation of the core metal could not be completely prevented, and the durability of the dip tube could not be sufficiently improved. In particular, molten steel and slag infiltration into cracks were major problems.

  As the amorphous refractory, a refractory having a particle size distribution in which the maximum particle size is more than 2 mm is usually used. The thing of patent document 1 does not designate the particle size distribution of the amorphous refractory to be used. When an irregular refractory having a particle size distribution generally used in Patent Document 1 is filled in the gap between the first core and the second core, the apparent porosity of the filled refractory is about 40%. It is considered that the apparent porosity was high. It was clarified that the reason why the life of the dip tube described in Patent Document 1 was not sufficiently extended was that the apparent porosity of the filled amorphous refractory was too high.

  Therefore, in the present invention, when the apparent porosity of the filled amorphous refractory 13 is 30% or less and the refractory has a dense structure, the strength of the cored bar 8 as a structure can be improved, and the dip tube 5 It was possible to exert a great effect on improving the life of the product. The apparent porosity of the filled amorphous refractory 13 was measured by the method prescribed in JIS R 2205 (Measurement method of apparent porosity, water absorption rate and specific gravity of refractory bricks).

  In order to ensure an apparent porosity of 30% or less by filling an irregular refractory into such a gap, the gap 11 is a narrow gap of about 10 to 40 mm. It is effective to set the maximum particle size of the irregular refractory to 2 mm or less.

  Further, it has been clarified that the bending strength of the filled amorphous refractory 13 needs to be 5 MPa or more in order to ensure the structure strength of the cored bar 8. The bending strength measurement of the filled amorphous refractory 13 was performed by applying a filled amorphous refractory in a 40 × 40 × 160 mm mold. The test piece was measured by a three-point bending test method defined in JIS R2553 (castable refractory bending test method).

  The bending strength when the irregularly shaped refractory (usually larger than 2 mm) that is normally used is filled into the gap 11 of the cored bar and molded is at most about 3 to 4 MPa. This is because the apparent porosity exceeds 30% and the denseness of the filled amorphous refractory 13 is insufficient. In order to set the bending strength to 5 MPa or more, an irregular refractory having a maximum particle size of 2 mm or less may be used, and it may be densely packed so that the apparent porosity is 30% or less.

  When constructing the filled amorphous refractory 13, a refractory material having a maximum particle size of 2 mm or less is kneaded with arbitrary water to construct the kneaded product. Although the construction method is not particularly limited, it can be constructed by a casting method or a stamp method. Although the refractory raw material is not particularly limited, it is composed of raw materials such as alumina, magnesia, and spinel, and an amorphous refractory containing 80 to 90% by mass of alumina can be used.

  The dip tube 5 of the present invention further includes a gas introduction tube 14 for flowing a cooling gas in the gap 11 of the core 8, and supplies an inert gas from the gas introduction tube 14 to the gap 11 of the core. The vacuum degassing is performed. The gas introduction pipe 14 is disposed in the dip pipe from near the flange, and supplies an inert gas to the gap between the inner cylindrical iron plate 8a and the outer cylindrical iron plate 8b.

  The dip tubes described in Patent Documents 2 and 3 also flow cooling gas between the outer cylindrical iron plate and the inner cylindrical iron plate that constitute the core metal. However, since the thing of patent documents 2 and 3 does not fill the amorphous refractory between the outer cylindrical iron plate and the inner cylindrical iron plate, the strength as a core metal structure cannot be secured sufficiently. Therefore, even though the cored bar is cooled, deformation of the cored bar cannot be prevented, and cracking occurs in the refractory with the deformation of the cored bar. The durability could not be improved sufficiently.

  In the first place, when the cooling gas is made to flow through the gap between the cores of the double tube structure, if the gap is filled with an irregular refractory, it is impossible to flow a sufficient amount of gas for cooling. It was thought to be. This is especially true when the filled amorphous refractory is packed densely so that the apparent porosity of the filled amorphous refractory is 30% or less. However, even if the apparent porosity is 30% or less, there are pores in the filled amorphous refractory. In addition, as shown in FIG. 3 (b), a gap 16 is formed between the outer and inner cylindrical iron plates and the filled amorphous refractory material by heating and cooling that is received by using the dip tube for degassing the molten metal. Further, as shown in FIG. 3C, a crack 15 may occur in the filled amorphous refractory 13. The inert gas blown into the gap 11 of the double tube structure from the vicinity of the upper end of the core metal through these pores, gaps 16 and cracks 15 moves as a gas flow 17 between the filled amorphous refractory 13, It was found that it propagated from the lower end of the cored bar 8 into the refractory constituting the bottom of the dip tube and was finally discharged out of the dip tube. Then, it is confirmed that the life of the dip tube is improved by flowing a cooling gas through the gap 11 of the cored bar having a double tube structure, and the cooling effect by the cooling gas is surely effective. It is clear.

  The present invention has been made on the basis of the above knowledge, and after filling the gap 11 of the double-bar structure cored bar 11 with an amorphous refractory, an inert gas is further allowed to flow into the internal space, thereby forming an amorphous refractory. By improving the strength of the cored bar structure by filling and reducing the temperature of the cored bar during vacuum degassing due to the cooling effect by flowing gas, the deformation prevention effect of the cored bar is dramatically improved. And succeeded in greatly improving the durability of the dip tube.

  Conventionally, as described in Patent Document 1, just filling the internal space of a double-pipe cored bar with an indeterminate refractory does not provide sufficient resistance to erosion and infiltration, and sufficient dip tube durability. Cannot be improved. In particular, molten steel and slag infiltration into cracks were major problems. On the other hand, as a result of flowing the cooling gas into the inner space of the double-bar structure core metal in the present invention, the effect of preventing the intrusion of the molten steel and slag into the pores and cracks is also exhibited. .

As an inert gas to be used, it is preferable to use Ar gas. Further, the flow rate of the inert gas is determined by the apparent porosity of the amorphous refractory used and the shape of the dip tube, and is not particularly limited. In the case of the dip tube of the RH vacuum degassing apparatus in which the diameter of the core metal is 1070 mm and the gap between the inner cylindrical iron plate and the outer cylindrical iron plate is about 16 mm, the flow rate can be set to about 0.5 to ³ Nm ³ / min.

  The inert gas introduced from the gas introduction pipe 14 into the gap 11 of the cored bar 8 is introduced from the lower end of the cored bar 8 into the bottom refractory of the dip pipe. Therefore, even if air enters from the atmosphere contact portion of the refractory on the outer periphery side of the core metal of the dip tube 5, it is blocked by the inert gas filled in the bottom refractory and reaches the refractory on the inner periphery side of the core metal Can not do it. For this reason, since nitrogen in the atmosphere does not reach the molten steel in the decompression section, it is possible to prevent the molten steel from being absorbed during vacuum degassing. Since it is not necessary to provide a special mechanism for preventing nitrogen absorption during the vacuum degassing process as described in Patent Documents 4 and 5, it is possible to melt ultra-low nitrogen steel at low cost.

  The dip tube 5 of the present invention can exhibit an effect when it is a dip tube of an RH vacuum degassing apparatus. This is because the RH vacuum degassing apparatus is most frequently used as a vacuum degassing apparatus for molten steel.

  The manufacturing method of the dip tube for molten metal processing attached to the vacuum tank of the degassing apparatus for degassing the molten metal according to the present invention is such that the core metal 8 of the dip tube 5 is composed of an inner cylindrical iron plate 8a and an outer cylindrical iron plate 8b. It has a heavy pipe shape, and refractory bricks 9 or amorphous refractories 10 are arranged on the inner and outer circumferences and bottom of the cored bar 8, and the maximum particle size is 2 mm in the gap 11 between the outer cylindrical iron plate 8b and the inner cylindrical iron plate 8a of the cored bar 8. The following amorphous refractory is filled, the apparent porosity of the filled amorphous refractory 13 is 30% or less, the bending strength of the filled amorphous refractory 13 is 5 MPa or more, and a cooling gas is provided in the gap 11 of the core metal 8. By providing the gas introduction pipe 14 for flowing the gas, the effects as described above can be exhibited.

  Also in this case, the effect can be exhibited in the case of a dip tube of an RH vacuum degassing apparatus.

  In the vacuum degassing method using the RH vacuum degassing apparatus of the present invention, an inert gas is supplied from the gas introduction pipe 14 to the gap 11 of the metal core using the molten metal processing dip pipe 5 of the present invention. While performing vacuum degassing, the life of the dip tube 5 is significantly improved, and nitrogen intrusion from the atmosphere during the vacuum degassing treatment is prevented, and extremely low nitrogen steel can be melted.

  In the dip tube of the RH vacuum degassing apparatus for vacuum degassing treatment of 300 tons of molten steel, the present invention was applied using the dip tube 5 having the shape shown in FIG. The outer diameter of the dip tube is 1370 mm, the inner diameter is 750 mm, and the length is 750 mm. The core 8 has a diameter of 1070 mm and a length of 520 mm.

  In the present invention example and the comparative example in which the core metal 8 has a double tube structure, the thickness of the outer cylindrical iron plate 8b and the inner cylindrical iron plate 8a is 12 mm, and the gap between them is 16 mm. In the conventional example, the cored bar has a single tube structure with a thickness of 12 mm. A magnesia-carbon brick was used as the inner peripheral side refractory of the core metal, and an alumina-spinel amorphous refractory was applied as the outer peripheral and bottom refractories of the core metal.

  In the present invention example and the comparative example, the gap portion 11 of the core metal having a double tube structure was filled with an irregular refractory. Table 1 shows the chemical composition and maximum particle size of the filled amorphous refractory 13. As the construction method, the vibration casting method was adopted. In order to measure the physical properties of the amorphous refractory after filling, it was constructed in a 16 × 16 × 16 mm mold and used as a sample. The apparent porosity is measured according to JIS R 2205 (Measurement method of apparent porosity, water absorption and specific gravity of refractory bricks), and the bending strength is specified in JIS R2553 (bend test method of castable refractories). Measured by the method. In order to investigate the physical properties at the temperature during use, the physical properties after firing at 1500 ° C. × 3 hours were measured.

  The measurement results are shown in Table 1. In each of Invention Examples 1 to 4, since a refractory having a maximum particle size of 2 mm or less was used as the filled amorphous refractory 13, the apparent porosity was 30% or less, and the bending strength was 5 MPa or more. In Comparative Examples 1 and 2, since a refractory having a maximum particle size of more than 2 mm was used as the filled amorphous refractory material, the apparent porosity exceeded 30% and the bending strength was less than 5 MPa. In Comparative Example 3, since the raw material was an irregular refractory having a maximum particle size of 10.0 mm, it could not be filled in the gap portion of the cored bar.

In the present invention example and the comparative example, the gas introduction tube 14 was disposed near the flange 12 of the dip tube 5, and Ar gas was allowed to flow through the gap 11 of the cored bar. The Ar gas flow rate was ³ Nm ³ / min.

  Using the dip tubes shown in Examples 1 to 4 of the present invention, Comparative Examples 1 and 2 and Conventional Example 1 in Table 1, the vacuum degassing treatment of the molten steel was performed by an RH vacuum degassing apparatus. The number of heats used until the end of the life of the dip tube for some reason was counted. Table 1 shows the life of the dip tube of each example and the reason for reaching the life.

  In each of Invention Examples 1 to 4, the dip tube life exceeded 150 charges, and a good life could be realized. The lifetime factors were all due to spontaneous melting of the refractory around the dip tube.

  In Comparative Examples 1 and 2 and Conventional Example 1, the refractory was peeled off at the lower end of the dip tube and had a short life of 70 charges or less. In both cases, deformation of the metal core was observed.

It is sectional drawing which shows the dip tube of this invention. It is sectional drawing which shows the dip tube of this invention. It is a figure which shows the condition of the filling irregular shape refractory of the clearance gap part of a metal core, (a) is the condition immediately after filling, (b) is a clearance gap produced between an inner and an outer cylindrical iron plate, and a filling irregular shape refractory. (C) is a figure which shows the condition where the crack was produced in the filling amorphous refractory. It is sectional drawing which shows the condition where the crack produced in the refractory which comprises a dip tube. It is sectional drawing which shows the condition where the crack produced in the refractory which comprises a dip tube. It is a schematic sectional drawing which shows the whole RH vacuum degassing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ladle 2 Molten steel 3 Vacuum tank 4 Exhaust duct 5 Immersion pipe 5a Ascending dip pipe 5b Descent dip pipe 6 Inert gas blowing nozzle 7 Crack 8 Core metal 8a Inner cylindrical iron plate 8b Outer cylindrical iron plate 9 Fireproof brick 10 Amorphous refractory 10a Peripheral side irregular refractory 10b Inner peripheral side irregular refractory 10c Bottom irregular refractory 11 Crevice 12 Flange 13 Filled irregular refractory 14 Gas introduction pipe 15 Crack 16 Crevice 17 Gas flow

Claims (6)

  A dip tube for molten metal treatment that is attached to a vacuum tank of a degassing device for degassing molten metal, and the core metal of the dip tube has a double tube shape of an inner cylindrical iron plate and an outer cylindrical iron plate, Refractory bricks or amorphous refractories are arranged on the inner and outer circumferences and bottom of the steel plate, and an irregular refractory is filled in the gap between the outer cylindrical iron plate and the inner cylindrical iron plate of the core metal (hereinafter referred to as “filled amorphous refractory”). The filled amorphous refractory has an apparent porosity of 30% or less, the filled amorphous refractory has a bending strength of 5 MPa or more, and a gas introduction pipe for flowing a cooling gas through the gap of the cored bar is provided. A dip tube for molten metal treatment characterized by being provided.   The dip tube for molten metal treatment according to claim 1, wherein a refractory having a maximum particle size of 2 mm or less is used as a raw material for the filled amorphous refractory.   The dip tube for molten metal treatment according to claim 1 or 2, wherein the dip tube is a dip tube of an RH vacuum degassing apparatus.   A method for manufacturing a dip tube for molten metal treatment that is attached to a vacuum tank of a degassing device for degassing molten metal, wherein the core metal of the dip tube has a double tube shape of an inner cylindrical iron plate and an outer cylindrical iron plate , Refractory bricks or amorphous refractories are placed on the inner and outer circumferences and bottom of the core metal, and the gap between the outer cylindrical iron plate and the inner cylindrical iron plate of the core metal is filled with an irregular refractory having a maximum particle size of 2 mm or less (hereinafter “ Filled amorphous refractory "), the apparent porosity of the filled amorphous refractory is 30% or less, the bending strength of the filled amorphous refractory is 5 MPa or more, and a cooling gas is introduced into the gap between the metal cores. A method for producing a dip tube for treating molten metal, characterized in that a gas introduction tube for flowing is provided.   The said dip tube is a dip tube of RH vacuum degassing apparatus, The manufacturing method of the dip tube for molten metal processing of Claim 4 characterized by the above-mentioned.   A vacuum degassing method using an RH vacuum degassing apparatus, wherein a vacuum degassing is performed while supplying an inert gas from a gas introduction pipe to a gap portion of a metal core using the molten metal processing dip pipe according to claim 3. A vacuum degassing method comprising performing a gas.

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