JP5729875B2 - Dipping tube for vacuum degassing of molten steel - Google Patents

Description

  The present invention relates to a dip tube of a vacuum degassing furnace used when manufacturing high cleanliness steel, and relates to a dip tube provided with a circulation gas pipe for circulating molten steel.

  When manufacturing high cleanliness steel from molten steel after decarbonized by a converter, etc., in a vacuum degassing furnace, immersing a dip pipe consisting of a riser pipe and a downcomer pipe leading to the vacuum furnace part into the molten steel, Degassing is performed by blowing an inert gas from a pipe provided in the riser and circulating the molten steel.

  The dip tube of the vacuum degassing furnace has a basic structure including a cylindrical cored bar made of a heat-resistant metal, a refractory material inside and outside the cored bar, and an inner cylindrical part through which molten steel flows.

  7 shows a vertical cross section of a conventional dip tube attached to a vacuum degassing furnace, FIG. 8 shows a horizontal cross section seen from the line AA in FIG. 7, and FIG. 9 blows a reflux gas in the dip tube. It is the figure which developed the reflux gas piping 5 planarly.

  7 and 8, a refractory brick 2 is fixed and supported by a hardware through an indefinite shape material 3 on the inner and outer circumferences of a cylindrical cored bar 1 arranged at the center position of the dip tube.

  The reflux gas pipe 5 has a plurality of heat-resistant steel pipes inserted into a plurality of holes formed in the refractory brick 2 substantially uniformly along the core 1 inside the dip pipe, and each pipe is arranged. A reflux gas such as argon gas is discharged from the tip into the molten steel.

  The plurality of reflux gas pipes 5 form collecting pipes 6 whose bases are collected in one place from the workability when the dip pipe is set in the vacuum degassing furnace, and are connected to the respective reflux gas pipes 5. It has a structure in which intakes of reflux gas from outside are assembled.

    In a vacuum degassing furnace having such a circulating gas piping structure, in order to efficiently degas molten steel, it is necessary to form a uniform flow of molten steel with the circulating gas. It is necessary to uniformly discharge the gas from the circulating gas piping provided in the respective discharge holes.

  However, in view of this necessity, the conventional dip tube has various problems.

    First, in the collecting pipe structure shown in FIG. 9, in terms of the arrangement of the reflux gas pipe 5, the direction of the discharge hole 5 a changes from 0 ° to 180 ° with respect to the reflux gas intake position. Since the lengths of the respective reflux gas pipes 5 are different, there is a difference in the pressure loss for each of the reflux gas pipes, and a phenomenon in which the discharge amount of the reflux gas varies depending on the position of the discharge hole 5a.

    On the other hand, the temperature of the dip tube during the treatment is exposed to a temperature of 1600 ° C. or higher because the inner and outer circumferences are in contact with the molten steel. Since the reflux gas pipe has a structure embedded in the dip pipe, the temperature of the reflux gas rises as it flows through the pipe. In particular, in the circulating gas piping structure shown in FIG. 9, since the piping length differs for each piping, the amount of heat received during the molten steel processing varies depending on the location. In addition, the ambient temperature difference around the pipe may increase, and with this temperature difference, a difference occurs in the viscosity of the circulating gas discharged from the pipe. A different phenomenon occurs.

  Due to these phenomena, the circulating gas discharge amount differs for each circulating gas pipe constituting the collecting pipe, and this causes the molten steel flow to be turbulent, resulting in uneven flow, which causes uneven damage to the refractory. .

    Various countermeasures have been proposed for this problem. For example, in Patent Document 1, the reflux gas pipe has a double-pipe structure, hydrocarbon gas is blown into the inner cylinder side, and Ar gas serving as heat insulation gas is blown into the outer cylinder side, and the mixing ratio of Ar and propane is adjusted. By doing so, it has been proposed that the reflux gas continuously controls the amount of gas blown from the tuyere between 1 to 4 times to increase the degassing efficiency. However, depending on the type of steel to be refined, there is a concern that hydrogen and carbon in steel will rise. In addition, when the pipe length is different, the amount of heat received during the molten steel process does not change depending on the pipe position, and in the portion where the pipe length is long, the temperature of the reflux gas rises and the gas viscosity may be improved. Concerned.

  In addition, Patent Documents 2, 3 and 4 describe the construction of a heat insulator such as a heat insulating mortar around the iron skin. The effect of equalizing the flow rate of the mixed inert gas cannot be expected.

JP 2000-45013 A JP 7-224319 A JP 2001-33174 A JP 2010-168600 A

  Here, in the present invention, in order to form a uniform molten steel flow in the dip pipe of the vacuum degassing apparatus, in the circulatory gas piping structure of the dip pipe of the vacuum degassing apparatus, the circulating gas from each of the circulated gas pipes It is an object of the present invention to provide a dip tube for a vacuum degassing apparatus capable of making the discharge amount uniform and preventing the occurrence of non-uniform damage to the refractory due to the turbulence of the flowing molten steel flow.

  The present invention pays attention to the fact that the recirculation gas flow discharged from the recirculation gas piping is affected by the pressure loss difference accompanying the length of the recirculation gas piping and the change in the viscosity of the discharge gas flow due to the heat from the molten metal. And completed.

  That is, the feature of the present invention is to suppress the gas flow rate difference due to the pressure loss due to the difference in the pipe length of the reflux gas pipe in the dip pipe of the vacuum degassing furnace, and to further enhance the heat insulation function in the discharge hole of the reflux gas pipe, Thus, by preventing an increase in the temperature of the reflux gas by preventing the temperature of the reflux gas in the reflux gas pipe from increasing, the gas flow rate balance of each of the reflux gas pipes is achieved.

  The first means of the recirculation gas flow rate difference suppressing means accompanying the pressure loss of the recirculation gas is a heat insulation of the recirculation gas pipe having a short pipe length in a dip pipe having a structure in which the recirculation gas is blown into a different length depending on the position of the recirculation gas discharge hole. This is that the heat insulation of the reflux gas pipe having a long pipe length is increased rather than the performance.

  Specifically, in the dip pipe of the present invention, in the dip pipe having a structure in which the length of the reflux gas pipe is different due to the position of the discharge hole of the reflux gas, the reflux gas pipe arranged at a position far from the collecting pipe. And heat insulation around the discharge hole. Depending on the dip tube, there is a case where a heat insulating material is applied to either the inner cylinder side or the outer cylinder side between the core metal and the refractory material for the purpose of suppressing thermal expansion and deformation of the core metal. Even in this case, the heat insulation around the circulating gas pipe and the circulating gas discharge hole arranged at a position far from the collecting pipe is strengthened. Therefore, it is desirable to use a member having a lower thermal conductivity for heat insulation around the circulating gas pipe and the circulating gas discharge hole arranged at a position far from the collecting pipe.

  As a method of strengthening the heat insulation around the reflux gas pipe and the reflux gas discharge hole arranged at a position far from the collecting pipe, it is also possible to apply a heat insulating material directly to the reflux gas pipe or wrap a heat insulation tape. . Moreover, you may use the heat insulation castable, mortar, heat insulation wool, and heat insulation sheet which use hollow particles, such as a silica and an alumina, as a heat insulating material.

  The second means of the circulating gas flow rate difference suppressing means is a pipe length longer than the inner cross-sectional area of the reflux gas pipe having a short pipe length in a dip pipe having a structure in which the pipe length for blowing the reflux gas differs depending on the position of the reflux gas discharge hole. Increase the inner cross-sectional area of the long reflux gas pipe.

  Specifically, pipes with a large inner diameter cross-section are used for reflux gas pipes with a long pipe length, and pipes with a smaller inner diameter cross-section are used for pipes with a short pipe length and with a smaller inner diameter cross-section. The pressure loss due to the long length is reduced, and the difference in the flow rate of the recirculation gas from that of the short pipe length is suppressed to make the recirculation gas flow uniform.

The third means of the recirculation gas flow rate difference suppression means is to recirculate so that the distance from the inner cylinder side discharge hole position of the dip tube to the molten metal surface position of the molten metal existing on the outer tube side of the dip tube is minimized. Gas piping was arranged. This minimizes the heat reception from the molten metal present on the outer cylinder side in the dip tube to the reflux gas piping, thereby suppressing the annual increase of the reflux gas and reducing the difference in the reflux gas flow rate with the piping having a short piping length. Make the reflux gas flow uniform.

  The fourth means of the recirculation gas flow rate difference suppressing means is that the length of the recirculation gas pipe is such that the pressure loss difference of each pipe from the pipe former blow-in part to the discharge hole is within 10%. When the immersion pipe of the device is immersed in the molten metal, the distance from the molten metal surface level on the outer cylinder side of the immersion pipe to the height position of the discharge hole inside the immersion pipe is minimized. Install piping. As a result, the difference in pressure loss due to the difference in pipe length is reduced, and the heat flow from the molten metal present on the outer cylinder side in the dip pipe to the reflux gas pipe is minimized, so that Suppresses the increase in gas viscosity and suppresses the effect on the reflux gas flow rate.

  The present invention relates to argon gas in a recirculation gas pipe disposed at a position far from the collecting pipe by reinforcing the heat insulation of the recirculating gas pipe disposed at a position far from the collecting pipe, or at a position close to the discharge hole. By preventing the temperature of the reflux gas such as gas from rising, the viscosity of the reflux gas is prevented from increasing, and the circulation gas flow balance of the reflux gas piping arranged in the dip pipe is balanced to make the discharge amount of the reflux gas uniform. It was possible.

  As a result, the circulating gas flow discharged from the plurality of gas discharge holes that open to the inner peripheral surface of the dip tube is made uniform, and the formation of drift is eliminated, resulting in uneven wear of the refractory formed around the periphery. Occurrence can be eliminated.

It is a vertical sectional view of a dip tube attached to the vacuum degassing furnace of the present invention. It is the horizontal cross section seen from the BB line of FIG. It is the figure which developed the reflux gas piping of the dip tube of Example 1 in the shape of a plane. It is the figure which developed the reflux gas piping of the dip tube of Example 2 in the shape of a plane. It is the figure which expand | deployed the reflux gas piping of the dip tube of Example 3 planarly. It is the figure which expand | deployed the reflux gas piping of the dip tube of Example 4 planarly. The longitudinal cross-section of the reflux gas piping part in the riser pipe of the conventional RH furnace is shown. It is a horizontal sectional view along the AA line of FIG. It is the figure which developed the recirculation gas piping of the dip tube of Drawing 8 in the shape of a plane. It is an experimental apparatus assuming the dip tube of the present invention. It is an experimental apparatus assuming the dip tube of the present invention.

  FIG. 1 shows a vertical cross section of a dip tube of a vacuum degassing furnace of the present invention, and FIG. 2 shows a horizontal cross section seen from the line BB in FIG.

  As with the conventional dip tube shown in FIGS. 8 and 9, the dip tube of the vacuum degassing furnace is provided with refractory bricks 2 on the inner and outer circumferences of the cylindrical cored bar 1 arranged at the center position of the dip tube. 3 is fixed and supported. The reflux gas pipe 5 is provided with a plurality of heat-resistant steel pipes inserted into a plurality of holes formed in the refractory brick 2 substantially uniformly along the core 1 inside the dip pipe, A circulating gas such as argon gas is discharged into the molten steel from a discharge port 5a at the tip of the gas pipe 5.

  The plurality of reflux gas pipes 5 form a collecting pipe 6 whose bases are collected at one place, and the reflux gas is supplied from the outside to each of the reflux gas pipes 5 through the collecting pipe 6.

  The cored bar 1 used in the dip tube of the present invention is a cylindrical member made of a heat-resistant metal and usually has a substantially circular cross-sectional shape, but can also be formed in an elliptical shape or a polygonal shape. Also, a double tube structure may be used. A fixed refractory material may be used for a part or all of at least one of the inner periphery and the outer periphery of the core metal 1.

  It is preferable that a stud is joined to the core metal 1 outward. This stud is formed by using a metal round bar, square bar, plate or corrugated member such as steel or alloy steel. In order to effectively support the refractory material by the stud, a shape that generates a large contact resistance with the refractory material is desirable. For example, a bent or branched shape such as a V shape, a T shape, an L shape, or a Y shape. It can be. Moreover, it is preferable to provide a plurality of studs so that they are widely dispersed on the surface of the cored bar, so that the refractory material can be supported over a wide area.

  In addition, it is possible to support a refractory material like a stud by joining a metal mesh such as a lath metal mesh to the core metal in the dip tube.

  Furthermore, the circulating gas piping used for the dip tube of the present invention uses a member made of a heat-resistant metal such as steel, stainless steel, alloy steel or the like. In consideration of gas leakage, it is desirable to use a carbon steel pipe for piping or a carbon steel pipe for pressure piping.

  The refractory material used for the dip tube of the present invention is constructed and arranged on the inside and outside of the cored bar. As the refractory material, a known refractory material material can be used, for example, magnesia, magnesia-chromium, magnesia-carbon, magnesia-alumina, magnesia-alumina-zirconia, magnesia-alumina-titania, Refractory materials such as magnesia-spinel, alumina-chromium, alumina-carbon, alumina-magnesia-carbon, alumina-spinel-carbon, magnesia-alumina-carbon, etc. can be used.

  Hereinafter, embodiments of the dip tube structure of the present invention will be described by way of examples.

  In this embodiment, in the dip pipe having a structure in which the length of the reflux gas pipe for blowing the reflux gas differs depending on the position of the reflux gas discharge hole, the reflux gas pipe having a longer pipe length than the heat insulation of the reflux gas pipe portion having a shorter pipe length. It is the example which increased the heat insulation of the piping part by the side of this discharge hole.

  FIG. 3 is a diagram in which the reflux gas pipe 5 of the dip tube of the present embodiment is developed in a planar shape. FIG. 9 is a horizontal development view corresponding to FIG. 9 showing the arrangement of the discharge pipe at the tip of the reflux gas pipe when the conventional RH riser pipe is viewed from the inner surface. In the development view, the length of each pipe is It depends on the arrangement position of the collecting pipe 6.

  In the development view of the pipe in FIG. 3, the heat insulation of each of the reflux gas pipes 5 from both ends having a long pipe length from the collecting pipe 6 was reinforced. Specifically, for the refractory brick 2 at the same position, the heat insulating sheet 4 was attached to the back surface of the brick 2 on the inner cylinder side and the back surface of the brick 2 positioned on the outer cylinder side.

  As shown in FIGS. 2 and 3, the position of the brick to which the heat insulating sheet 4 is attached corresponds to 1/2 of the facing side of the collecting pipe 6. The heat insulation of the reflux gas pipe 5 located at the site was reinforced.

  In this embodiment, in the dip pipe having a structure in which the length of the reflux gas pipe is different depending on the position of the reflux gas discharge hole, the discharge gas side of the reflux gas pipe having a longer pipe length than the heat insulation of the reflux gas pipe portion having a shorter pipe length. It is the example which increased the heat insulation of the piping part.

  FIG. 4 is a diagram in which the reflux gas pipe of the dip tube of the present embodiment is developed in a planar shape, and the length of each reflux gas pipe 5 varies depending on the arrangement position of the collecting pipe 6. The heat insulating material 4 was wound around each of the five pipes having long pipe lengths from the collecting pipe 6 to strengthen the heat insulation.

  As a method of strengthening the heat insulation around the reflux gas pipe and the reflux gas discharge hole arranged at a position far from the collecting pipe in this way, it is possible to apply a heat insulating material directly to the reflux gas pipe or to wrap a heat insulation tape. Is possible. Moreover, you may use the heat insulation castable, mortar, heat insulation wool, and heat insulation sheet which use hollow particles, such as a silica and an alumina, as a heat insulating material.

  In this embodiment, in the dip tube having a structure in which the length of the reflux gas pipe is different depending on the position of the reflux gas discharge hole, the inner cross-sectional area of the reflux gas pipe having a longer pipe length than the inner cross-sectional area of the reflux gas pipe having a shorter pipe length. This is an example in which

  FIG. 5 is a diagram in which the reflux gas piping of the dip tube of the present embodiment is developed in a planar shape, and the length of each piping varies depending on the arrangement position of the collecting tube 6.

  JIS SGP6A is used for the recirculation gas pipe 8 arranged in the range of 90 ° to the left and right from the concentration tube side, with the collecting tube side position being 0 °, and the recirculation gas located in the range of 90 ° to 270 ° from the concentration tube side. JIS SGP8A was used for the piping 7.

  Regarding the inner diameter of the reflux gas pipe, it is desirable to select an appropriate pipe in consideration of the balance between the pressure loss due to the difference in the pipe length and the flow rate decrease due to the increase in gas viscosity accompanying the temperature rise of the reflux gas during refining. Considering the cost of the member to be used, it is desirable to use a ready-made member, but if it is not available, it can be used in combination with the above-described heat insulation technology for the piping part.

  In this embodiment, the reflux gas piping is arranged so that the distance from the position of the discharge hole on the inner cylinder side of the dip tube to the molten metal surface position on the outer cylinder side of the dip tube is the shortest. .

  FIG. 6 is a diagram in which the reflux gas pipe 5 of the dip pipe of the present embodiment is developed in a planar shape, and the length of each pipe varies depending on the arrangement position of the collecting pipe 6.

  In the present embodiment, the arrangement is made so that the positional relationship between the recirculation gas discharge hole position b shown in FIG. 6 and the molten metal surface position a on the outer cylinder side when the dip tube is immersed in the molten metal is the shortest. .

  For example, in the case of a dip tube that is vertically immersed in the molten metal, the outer tube side is formed by connecting the piping from the discharge hole position to be perpendicular to the molten metal surface so that the reflux gas piping is as short as the position where the molten metal exists. The heat received from the molten metal was minimized.

  In this piping method, it is also possible to use a reflux gas pipe having an appropriate inner cross-sectional area according to the pipe length, or to insulate the discharge hole side of the long reflux gas pipe.

  The length of the reflux gas pipe is preferably set so that the difference in pressure loss between the respective reflux gas pipes at room temperature (20 ° C.) is 10% or less.

  If the difference in pressure loss at room temperature (20 ° C) exceeds 10%, when the temperature of the reflux gas pipe rises during refining, the pressure loss increases further because the temperature of the reflux gas received by the pipe length is different. It is because it will do.

[Experimental example]
The mode of the circulating gas discharged from the discharge hole of the pipe having a short pipe length and the pipe having a long pipe length arranged on the collecting pipe side was examined by an assumed experiment.

  10 and 11 are experimental devices. In the apparatus, the pressure-adjusted gas is discharged to each piping pipe through the flow meter 10 and the gas header 12. Each discharge pipe was provided with flow meters 13A and 13B so that the gas flow rate of each pipe could be read.

  The pipes from the flow meters 13A and 13B to the test pipes in each electric furnace were connected using JIS SCH6A pipes and used for the test.

  As piping pipes, JIS SGP6A, two types of 600 mm and 2300 mm corresponding to the length of the reflux gas piping, and one type of piping of JIS SGP8A length 2300 mm were prepared in total of three types. A pipe having a length of 600 mm is assumed to be a pipe having a short pipe length arranged on the collecting pipe side, and a pipe having a length of 2300 mm is assumed to be a pipe having a long pipe length arranged on the opposite surface of the collecting pipe.

  These pipes were wound in a spiral shape with a diameter of 100 mm so that they could be inserted into the electric furnace 14. The hot experiment was carried out in an air atmosphere using a silico unit heating type box-type electric furnace 14.

    In the test for confirming the effect of heat insulation, the heat insulation sheet 16 was applied to a pipe having a long pipe length. As a method of performing heat insulation on the pipe, the heat insulation sheet 16 was prepared by preparing a heat insulation sheet (trade name: SC paper) having a thickness of 2 mm so as to cover the piping in the electric furnace.

  In each of the apparatus that did not insulate the pipes and the apparatus that had insulation, the ambient temperature was measured at room temperature (room temperature 20 ° C.) and the electric furnace temperature 800 ° C.

  The hot measurement atmosphere temperature of 800 ° C. is derived from the temperature of the cored bar immediately after using the RH dip tube for 10 heats by thermal calculation, and this temperature is adopted in the experiment. The furnace for the experiment was heated at 100 ° C. per hour and held at 800 ° C.

  Degreasing, dehumidification, and pressure adjustment were performed using air as the blowing gas. The air pressure was a constant pressure supply of 294 KPa, and the flow rate was read when the float of the flowmeter was stable and the furnace temperature was stable.

  The gas flow rate value of the short pipe equivalent SGP6A 600 mm long pipe in the experiment at each temperature was taken as 100, and the gas flow value of 2300 mm length of each of the long pipe equivalent SGP6A and SGP8A was indexed to confirm the flow rate difference from the short pipe. Further, as a comparative example, the flow rate during the same heating to a homogeneous pipe not subjected to heat insulation treatment was measured. The results are shown in Table 1.

In both the examples and the comparative examples, there was a difference in the flow rate between the SGP6A 600 mm length pipe and the SGP6A 2300 mm pipe at room temperature. This is due to the pressure loss due to the different pipe lengths.
On the other hand, the flow rate of the SGP8A 2300 mm long pipe was the same value as SGP6A.

  Next, in the case of the comparative example, the difference in the flow rate between the 600 mm length pipe and the 2300 mm pipe was further increased in the gas flow rate difference under the 800 ° C. atmosphere. This is because the pipe length is different and there is a pressure loss. In addition, the 2300 mm length pipe receives heat while the gas moves through the pipe, and the viscosity of the gas increases, resulting in an increase in pressure loss. is there.

  Similarly, in an experiment under an atmosphere of 800 ° C., there was no difference between the flow rate of the SGP6A 600 mm length pipe and the gas flow rate of the SGP8A 2300 mm length pipe. This is because the 2300 mm long pipe has a large cross-sectional area of the SGP8A pipe, so even if the gas viscosity increases due to the rise in pipe temperature, the increase in pressure loss is smaller than that of the 600 mm long pipe. It is thought that the difference has become smaller.

  Similarly, in an experiment under an atmosphere at 800 ° C., the difference between the flow rate of the SGP6A 600 mm long pipe and the gas flow rate of the 2300 mm long pipe with heat insulation was reduced. This is thought to be due to the fact that the 2300 mm long pipe is insulated, which suppresses the temperature rise of the gas passing through the pipe and further suppresses the increase in gas viscosity, thereby preventing an increase in pressure loss.

  In a dip tube with a structure in which the length of the pipe that blows in the reflux gas differs depending on the position of the reflux gas discharge hole, the inner cross-sectional area of the reflux gas pipe having a longer pipe length is made larger than the inner cross-sectional area of the reflux gas pipe having a shorter pipe length. Therefore, even if the gas viscosity increases and the flow rate decreases as the piping temperature rises, the difference between the gas flow rate of the recirculating gas piping with a short piping length is reduced, and the uniform flow rate is balanced. To.

  By suppressing the temperature rise of the reflux gas such as argon gas in the pipe of the collecting pipe, the viscosity of the reflux gas is prevented from increasing, and the reflux gas flow balance of the reflux gas pipe section of the dip pipe with different pipe length is balanced and uniform To discharge properly.

1: Metal core 2: Refractory brick 3: Indeterminate refractory 4: Thermal insulation material 5: Recirculation gas pipe 5a: Recirculation gas discharge hole 6: Collecting pipe 7: Recirculation gas pipe (SGP8A) 8: Recirculation gas pipe (SGP6A)
9: Pressure gauge 10: Original gas flow meter
11: Valve 12: Gas header 13: Flow meter 14: Electric furnace 15: Recirculation gas piping for test 16: Thermal insulation sheet a: Molten metal position during immersion b: Recirculation gas discharge hole position

Claims (4)

A refractory material is arranged on the inner and outer circumferences of a cylindrical metal core made of a heat-resistant metal disposed on the outer circumference of the inner cylinder for circulating the molten steel, and inert gas is supplied to the molten steel circulating in the inner cylinder. A collecting pipe is formed at the base of a plurality of reflux gas pipes for discharging, and the inner cylinder is substantially uniformly along the core metal through the refractory material through the reflux gas discharge holes at the tips of the plurality of reflux gas pipes In the dip pipe of the vacuum degassing apparatus established on the inner surface of the part, the dip pipe having a structure in which the length of the reflux gas pipe is different depending on the position of the reflux gas discharge hole,
The vacuum degassing apparatus is characterized in that the heat insulation of the pipe part on the discharge hole side of the long-circulation gas pipe is increased than the heat insulation of the pipe part on the discharge hole side of the short-circulation gas pipe. Immersion tube. A refractory material is arranged on the inner and outer circumferences of a cylindrical metal core made of a heat-resistant metal disposed on the outer circumference of the inner cylinder for circulating the molten steel, and inert gas is supplied to the molten steel circulating in the inner cylinder. A collecting pipe is formed at the base of a plurality of reflux gas pipes for discharging, and the inner cylinder is substantially uniformly along the core metal through the refractory material through the reflux gas discharge holes at the tips of the plurality of reflux gas pipes In the dip pipe of the vacuum degassing apparatus established on the inner surface of the part, the dip pipe having a structure in which the length of the reflux gas pipe is different depending on the position of the reflux gas discharge hole,
A dip tube for a vacuum degassing apparatus, wherein the inner cross-sectional area of a long-circulation gas pipe is larger than the inner cross-sectional area of a short-circulation gas pipe.   When the immersion pipe of the vacuum degassing device is immersed in the molten metal, the height of the molten metal surface on the outer cylinder side of the immersion pipe and the height of the reflux gas discharge hole at the tip of the reflux gas pipe The dip tube of the vacuum degassing apparatus according to claim 1 or 2, wherein the reflux gas discharge holes are arranged so that the distance is the shortest.   4. The vacuum according to claim 2, wherein the length of the reflux gas pipe is such that the pressure loss difference of each pipe from the pipe former blowing portion to the reflux gas discharge hole is within 10%. Degassing device dip tube.

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