Gas piping

Abstract

To provide gas piping that can be used for introducing an inert gas to an environment where a voltage is applied in a vacuum space.SOLUTION: Gas piping includes: a cylindrical body having an inner surface at which an irregularity part is formed; and a ceramic porous body filled into the cylindrical body.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This specification discloses technology relating to gas piping. [Background technology]

[0002] Patent Document 1 discloses a gas pipe through which high-pressure gas (blow-by gas) passes, and lists rubber, synthetic resin, and metal as materials for the gas pipe. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-135996 Summary of the Invention [Problem to be solved by the invention]

[0004] As disclosed in Patent Document 1, gas pipes are generally made of rubber, synthetic resin, metal, etc. However, these materials are sensitive to heat, and exposure to high temperatures can result in damage or deformation of the gas pipe. Using ceramic gas pipes can reduce damage caused by heat. However, even ceramic gas pipes can sometimes melt when introducing inert gases such as helium gas or argon gas under certain conditions, such as when introducing inert gases into a vacuum environment where a voltage is applied. Therefore, there is a need for gas pipes that can be used to introduce inert gases into a vacuum environment where a voltage is applied. This specification aims to provide a technology for realizing gas pipes that can be used under the above-mentioned specific conditions. [Means for solving the problem]

[0005] The first technique disclosed in this specification may be a gas pipe including a cylindrical body having an uneven portion formed on the inner surface thereof, and a ceramic porous body filled in the cylindrical body.

[0006] A second technique disclosed in this specification is the gas piping of the first technique, wherein the creeping length of the inner surface of the cylindrical body may be 1.08 times or more the piping length of the cylindrical body.

[0007] A third technique disclosed in this specification is the gas pipe of the first or second technique, and the distance between the recesses of the uneven portion may be more than 5 mm and less than 500 mm.

[0008] A fourth technique disclosed in this specification is the gas pipe according to any one of the first to third techniques, wherein the distance between the convex portions of the concave-convex portion may be more than 1 mm and less than 498 mm.

[0009] A fifth technique disclosed in this specification is the gas pipe according to any one of the first to fourth techniques, wherein an average porosity within the cylindrical body may be 15% or more and 60% or less.

[0010] A sixth technique disclosed in this specification is the gas pipe according to any one of the first to fifth techniques, wherein the average particle diameter of the porous body may be 50 mm or more and 600 mm or less.

[0011] The seventh technology disclosed in this specification is a gas pipe according to any one of the first to sixth technologies, wherein the material of the cylindrical body may be primarily composed of at least one selected from silicon oxide, aluminum oxide, and high heat-resistant resin.

[0012] The eighth technology disclosed in this specification is the gas pipe according to any one of the first to seventh technologies, and the material of the porous body may be mainly composed of at least one of silicon oxide and aluminum oxide. [Brief explanation of the drawings]

[0013] [Figure 1] 2 shows a radial cross section of a gas pipe according to a first embodiment. [Figure 2] 1 shows a longitudinal cross section of a gas pipe according to a first embodiment. [Figure 3]1 is a cross-sectional view of a cylindrical body used in the gas piping of the first embodiment. [Figure 4] 10A and 10B are diagrams illustrating the uneven shape of the inner surface of the cylinder. [Figure 5] FIG. 10 shows a diagram for explaining a modified example of the first embodiment. [Figure 6] 10 is a cross-sectional view of a cylindrical body used in a gas pipe according to a second embodiment. [Figure 7] FIG. 10 is a cross-sectional view of a cylindrical body used in the gas piping of the third embodiment. [Figure 8] FIG. 10 is a cross-sectional view of a cylindrical body used in a gas pipe according to a fourth embodiment. [Figure 9] The results of the experimental example are shown below. DETAILED DESCRIPTION OF THE INVENTION

[0014] The gas pipe disclosed herein is suitable for use as a pipe for introducing an inert gas into a vacuum environment where a voltage is applied. The gas pipe includes a cylindrical body and a ceramic porous body filled within the cylindrical body. Because the interior of the cylindrical body is filled with ceramic particles, the gas pipe has a solid structure from a macroscopic perspective. The inner surface of the cylindrical body is uneven. Therefore, the creepage length within the cylindrical body is longer than the pipe length of the cylindrical body. Note that "pipe length" refers to the length of the cylindrical body in the longitudinal direction of the gas pipe (the direction in which the gas flows). Furthermore, "creepage length" refers to the length of the cylindrical body surface in the longitudinal direction of the gas pipe. The gas pipe disclosed herein has unevenness formed on the inner surface (the surface that comes into contact with the gas), so the creepage length within the cylindrical body is longer than the pipe length. Furthermore, the gas pipe disclosed herein can be suitable for use as a pipe for introducing inert gases such as helium gas and argon gas, but can also be used as a pipe for introducing gases such as hydrogen gas, methane gas, and atmospheric air.

[0015] In a gas pipe in which a cylindrical body is filled with a porous body, when the applied voltage in the environment in which an inert gas is introduced becomes high (for example, 30 kV or higher), electrons are accelerated in the gap between the inner surface of the cylindrical body and the porous body, making it easier for discharge to occur. Discharges tend to occur along the inner surface of the cylindrical body. However, the gas pipe disclosed in this specification has unevenness formed on the inner surface of the cylindrical body, ensuring a long creeping length of the inner surface. Therefore, in the gas pipe disclosed in this specification, discharges are less likely to occur along the inner surface of the cylinder. By suppressing the occurrence of discharges, melting of the cylindrical body (gas pipe) can be suppressed, and the durability (lifespan) of the cylindrical body can be improved.

[0016] Furthermore, the gas pipe disclosed in this specification has an uneven portion formed on the inner surface of the cylindrical body, which restricts the movement of the porous body within the cylindrical body and prevents the porous body from coming off the cylindrical body. The concave (or convex) portion of the uneven portion may be formed around the circumference of the cylindrical body (a direction perpendicular to the longitudinal direction). Alternatively, the concave (or convex) portion of the uneven portion may be formed in a spiral shape relative to the longitudinal direction of the cylindrical body.

[0017] The porosity of the gas pipe within the cylindrical body can be adjusted by adjusting the particle size of the porous material, etc. Adjusting the porosity of the cylindrical body allows adjustment of the strength of the gas pipe and the flow path area within the gas pipe (within the cylindrical body). The porosity of the cylindrical body is greater than the porosity of the cylindrical body. Specifically, the average porosity within the cylindrical body is adjusted to 15% or more and 60% or less, and the porosity of the cylindrical body is adjusted to 5% or less. If the average porosity within the cylindrical body is 15% or more, a gas flow path can be reliably secured within the cylindrical body. Furthermore, if the average porosity within the cylindrical body is 60% or less, sufficient strength of the gas pipe can be secured, and a gas pipe with a strength of, for example, 10 MPa or more and 80 MPa can be realized. The gas pipe disclosed in this specification has a strength adjusted to 10 MPa or more and 80 MPa. The average porosity within the cylindrical body can be adjusted based on the pressure loss required for the intended purpose. Adjusting the porosity of the cylindrical body itself to 5% or less can prevent gas within the cylindrical body from passing through the cylindrical body and leaking to the outside (outside the gas pipe).

[0018] The average particle diameter of the porous body may be 50 μm or more and 600 μm or less. If the average particle diameter of the porous body is 50 μm or more, gaps are secured between the particles, and gas flow paths can be reliably secured. Furthermore, if the average particle diameter of the porous body is 600 μm or less, the contact area between the porous bodies and the contact area between the porous body and the inner surface of the cylinder is increased, allowing the two to be stably bonded. The average distance between particles of the porous body (average pore diameter within the cylinder) may be 10 μm or more and 200 μm or less.

[0019] The cylindrical body may be made primarily of silicon oxide, aluminum oxide, a highly heat-resistant resin (e.g., a fluororesin such as PTFE), or a mixture thereof. These materials have high heat resistance and can suppress damage to the gas pipe even when the temperature of the environment into which helium gas is introduced is high. The inner surface of the cylindrical body may be coated with a ceramic material such as alumina or mullite. The porous body may be made primarily of silicon oxide, aluminum oxide, or a mixture thereof. These materials have high heat resistance and high strength, which contribute to improving the strength of the gas pipe. The term "main component" refers to a material that accounts for 50% or more by mass of the constituent materials.

[0020] In addition, when the cylindrical body and the porous body are made of ceramics, they may be integrated. Specifically, the inner surface of the cylindrical body and the porous body may be bonded. For example, by filling the interior of a ceramic cylindrical body with a porous body (ceramic particles) of the ceramic material and firing it, a porous body of ceramic particles is formed inside the cylindrical body, and the inner surface of the cylindrical body and the porous body are sintered, thereby integrating the cylindrical body and the porous body. By integrating the cylindrical body and the porous body, it is possible to prevent the porous body from being damaged by the pressure of the gas moving through the gas pipe.

[0021] The creeping length of the inner surface of the cylinder may be 1.08 times or more the piping length of the cylinder. If the "creeping length / piping length" is 1.08 or more, the above-mentioned advantages (suppression of discharge occurrence, suppression of detachment of the porous body) can be reliably obtained. The creeping length of the inner surface of the cylinder may be 1.1 times or more, 2 times or more, 3 times or more, 5 times or more, 10 times or more, 25 times or more, or 50 times or more the piping length of the cylinder. The creeping length of the inner surface of the cylinder may be 50 times or less the piping length of the cylinder. If the "creeping length / piping length" exceeds 50, it becomes difficult to manufacture the cylinder, and the manufacturing yield of the gas piping decreases. If the "creeping length / piping length" is 50 or less, the decrease in manufacturing yield of the gas piping can be suppressed. The creeping length of the inner surface of the cylinder may be 25 times or less, 10 times or less, 5 times or less, or 3 times or less the piping length of the cylinder.

[0022] In the uneven portion formed on the inner surface of the cylinder, the distance between recesses may be more than 5 mm and less than 500 mm. If the distance between recesses is more than 5 mm, the internal porous body can be prevented from coming off. Furthermore, if the distance between recesses is less than 500 mm, a decrease in the manufacturing yield of the gas pipe can be prevented. In the uneven portion formed on the inner surface of the cylinder, the distance between protrusions may be more than 1 mm and less than 498 mm. If the distance between protrusions is more than 1 mm, the internal porous body can be prevented from coming off. Furthermore, if the distance between protrusions is less than 498 mm, a decrease in the manufacturing yield of the gas pipe can be prevented. Furthermore, if the creeping length of the inner surface of the cylinder relative to the piping length of the cylinder (creeping length ratio) is 10 times or less, a decrease in the manufacturing yield of the gas pipe can be further prevented (the gas pipe can be manufactured with a manufacturing yield of 71% or more).

[0023] The shape of the uneven portion (the shape of the recessed portion or the shape of the protruding portion) is not particularly limited, and may be rectangular, triangular, arcuate, or a combination of these shapes. However, from the viewpoint of suppressing a decrease in manufacturing yield, it is preferable that the shape of the uneven portion is rectangular. Although details are omitted, it has been confirmed that gas pipes with rectangular uneven portions have the highest manufacturing yield compared to gas pipes with non-rectangular uneven portions. [Example]

[0024] (First Example) A gas pipe 10 will be described with reference to FIGS. 1 and 2. FIG. 1 shows a radial cross section of the gas pipe 10, and FIG. 2 shows a longitudinal cross section of the gas pipe 10. As shown in FIGS. 1 and 2, a plurality of porous bodies 12 are filled inside a cylindrical body 14. The cylindrical body 14 is made of alumina, has an outer diameter of 30 mm, and a porosity of 1%. The inner surface of the cylindrical body 14 is provided with irregularities consisting of protrusions 16 and recesses 18. A plurality of protrusions 16 and recesses 18 are provided in the longitudinal direction 20 of the cylindrical body 14. Steps 17 are provided between the protrusions 16 and the recesses 18, and the shapes of the protrusions 16 and the recesses 18 are rectangular in the cross section shown in FIG. 2. Note that no irregularities are provided on the outer surface of the cylindrical body 14.

[0025] The distance D1 between the convex portions 16, 16 is 15 mm, and the distance D2 between the concave portions 18, 18 is 20 mm. That is, the cylindrical body 14 has an inner diameter of 15 mm, and multiple concave portions 18, each 2.5 mm deep, are provided at intervals in the longitudinal direction 20. Alternatively, the cylindrical body 14 can be considered to have an inner diameter of 20 mm, and multiple convex portions 16, each 2.5 mm high, are provided at intervals in the longitudinal direction 20. Since the cylindrical body 14 has unevenness on the inner surface but not on the outer surface, the creeping length of the inner surface of the cylindrical body 14 is longer than the piping length L1 of the cylindrical body 14. The creeping length of the inner surface of the cylindrical body 14 is the sum of the length of the surface 16s of the convex portion 16, the length of the surface 17s of the step 17, and the length of the surface 18s of the concave portion 18 in the longitudinal direction 20. In the cylindrical body 14, the creeping length of the inner surface of the cylindrical body 14 is adjusted to be twice the piping length L1. Since the creeping length of the inner surface of the gas pipe 10 is longer than the pipe length L1 of the cylindrical body 14, even if the applied voltage becomes high in the environment in which the inert gas is introduced, the occurrence of discharge within the cylindrical body 14 can be suppressed.

[0026] The porous body 12 is formed by firing alumina particles and glass. The average particle diameter of the alumina particles that make up the porous body 12 is 257 μm. Voids are provided between the porous bodies 12, 12, and the average porosity within the cylindrical body 14 is 35%. The porous body 12 is also filled within the recesses 18. The gas pipe 10 is formed by filling the raw materials (alumina particles and glass) of the porous body 12 into an unfired cylindrical body 14 and then firing it at 1100 to 1300°C in an air atmosphere. The firing sinters the porous bodies 12, 12 to each other and also sinters the cylindrical body 14 and the porous body 12. The presence of the sintered porous body 12 within the recesses 18 prevents the porous body 12 from coming off the cylindrical body 14.

[0027] The uneven shape inside the cylindrical body 14 will be described with reference to FIGS. 3 and 4. FIG. 3 is a cross-sectional view of the cylindrical body 14, and corresponds to the gas pipe 10 shown in FIG. 2 with the porous body 12 removed. FIG. 4 shows the direction in which the convex portions 16 (concave portions 18) are formed. As shown in FIGS. 3 and 4, the convex portions 16 (concave portions 18) are formed around the circumference of the cylindrical body 14 at intervals in the longitudinal direction of the cylindrical body 14. Therefore, a ring-shaped concave portion 18 exists between adjacent ring-shaped convex portions 16, 16 in the longitudinal direction of the cylindrical body 14. Similarly, a ring-shaped convex portion 16 exists between adjacent ring-shaped concave portions 18, 18 in the longitudinal direction of the cylindrical body 14.

[0028] FIG. 5 shows the direction in which the convex portions 16 (concave portions 18) are formed on the cylindrical body 14a. The cylindrical body 14a is a modified example of the cylindrical body 14. In the cylindrical body 14a, the convex portions 16 (concave portions 18) are formed in a spiral shape along the longitudinal direction of the cylindrical body 14a. Even in this configuration, when a cross section of the cylindrical body 14a (the cross section of the cylindrical body 14a shown in FIG. 3) is observed, a concave portion 18 is present between adjacent convex portions 16, 16 in the longitudinal direction of the cylindrical body 14a, and a convex portion 16 is present between adjacent concave portions 18, 18. Even when the gas pipe 10 is fabricated using the cylindrical body 14a instead of the cylindrical body 14, the creeping length of the inner surface of the cylindrical body 14a is longer than the pipe length of the cylindrical body 14a. Furthermore, the presence of the sintered porous body 12 in the concave portions 18 can prevent the porous body 12 from coming off the cylindrical body 14a. Therefore, the gas pipe 10 can be produced by using the cylindrical body 14a instead of the cylindrical body 14.

[0029] Second to fourth embodiments (cylindrical bodies 114, 214, and 314) will be described below with reference to Figs. 6 to 8. The cylindrical bodies 114, 214, and 314 are modified versions of the cylindrical body 14, and descriptions of structures that are substantially the same as those of the cylindrical body 14 may be omitted by assigning the same reference number or reference numbers with the same last two digits as those assigned to the cylindrical body 14. Note that the creeping length of the inner surface of each of the cylindrical bodies 114, 214, and 314 described below is greater than the piping length of the cylindrical bodies 114, 214, and 314. Any of the cylindrical bodies 114, 214, and 314 can be used in place of the cylindrical body 14 to produce the gas pipe 10.

[0030] (Second Example) 6, in cylindrical body 114, convex portions 116 are arc-shaped. In the case of cylindrical body 114, the creeping length of the inner surface of cylindrical body 114 is the total length of the length of surfaces 116s of convex portions 116 and the length of surfaces 18s of concave portions 18 in longitudinal direction 20. Note that in cylindrical body 114 as well, convex portions 116 (concave portions 18) may be formed in a spiral shape along the longitudinal direction of cylindrical body 114.

[0031] (Third Example) 7, in cylindrical body 214, convex portion 216 has a triangular shape. In the case of cylindrical body 214, the creeping length of the inner surface of cylindrical body 214 is the total length of the length of surface (triangular slope) 216s of convex portion 216 in longitudinal direction 20 and the length of surface 18s of concave portion 18. Note that in cylindrical body 214 as well, convex portion 216 (concave portion 18) may be formed in a spiral shape along the longitudinal direction of cylindrical body 214.

[0032] (Fourth Example) As shown in FIG. 8 , in the cylindrical body 314, the convex portion 316 includes a thin-walled portion 315 and a thick-walled portion 317. The thickness of the thick-walled portion 317 is greater than the thickness of the thin-walled portion 315 in the longitudinal direction 20. The thick-walled portion 317 is provided closer to the tip of the convex portion 316 than the thin-walled portion 315. The thick-walled portion 317 protrudes in one direction in the longitudinal direction 20 relative to the thin-walled portion 315. Specifically, the thick-walled portion protrudes toward the upstream side of the gas pipe 10 relative to the thin-walled portion 315. Although not shown, when the gas pipe 10 is manufactured using the cylindrical body 314, the thick-walled portion 317 bites into the porous body 12 in the longitudinal direction 20, which further prevents the porous body 12 from coming off the cylindrical body 314 (see FIG. 2 for comparison). In the case of the cylindrical body 314, the creeping length of the inner surface of the cylindrical body 314 is the total length of the length of the surface 315s of the thin-walled portion 315 in the longitudinal direction 20, the length of the surface 317s of the thick-walled portion 313, and the length of the surface 18s of the recess 18. Note that in the cylindrical body 314 as well, the protrusion 316 (recess 18) may be formed in a spiral shape along the longitudinal direction of the cylindrical body 314.

[0033] (Experimental example) The gas pipe 10 was fabricated using a cylindrical body 14 (with a rectangular convex portion) with a different creepage length ratio, and a discharge test was carried out. 3 A voltage of 0 to 25 kV was applied to the end of the gas pipe 10 (the end on the gas discharge side) with the gas flowing at 15 / min. In the discharge test, if no discharge occurred at 25 kV, it was rated "A", if discharge occurred at 15 to 25 kV, it was rated "B", if discharge occurred at 5 to 14 kV, it was rated "C", and if discharge occurred at less than 5 kV, it was rated "D". In the discharge test, ratings of "A" to "C" are considered pass levels. The results are shown in Figure 9.

[0034] As shown in Fig. 9, it was confirmed that the larger the creepage length ratio (the longer the creepage length of the inner surface of the cylindrical body 14 relative to the piping length of the cylindrical body 14), the less likely discharge occurs. Specifically, it was confirmed that if the creepage length ratio was 1.05 or more (Samples 13 to 22), it was at an acceptable level. It was also confirmed that if the creepage length ratio was 1.08 or more, particularly good discharge resistance was obtained.

[0035] Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The claimed technology includes various modifications and variations of the specific examples exemplified above. Furthermore, the technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives alone is technically useful. [Explanation of symbols]

[0036] 10: Gas piping 12: Porous material 14: Cylinder

Claims

1. a cylindrical body having an uneven portion formed on its inner surface; a ceramic porous body filled in the cylindrical body, The uneven portion is a gas pipe formed by recesses and protrusions that run around the circumferential direction of the inner surface of the cylindrical body, or by recesses and protrusions that are spirally formed along the longitudinal direction of the inner surface of the cylindrical body.

2. 2. The gas pipe according to claim 1, wherein the creeping length of the inner surface of the cylindrical body is 1.08 to 100 times the piping length of the cylindrical body.

3. 3. The gas pipe according to claim 1, wherein the average porosity within the cylindrical body is 15% or more and 60% or less.

4. 3. The gas pipe according to claim 1, wherein the porous body has an average particle size of 50 μm or more and 600 μm or less.

5. 3. The gas pipe according to claim 1, wherein the cylindrical body is made of a material containing at least one material selected from the group consisting of silicon oxide, aluminum oxide, and highly heat-resistant resin as a main component.

6. 3. The gas pipe according to claim 1, wherein the porous body is made of a material containing at least one of silicon oxide and aluminum oxide as a main component.

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