Piston ring, piston ring composite and reciprocating compressor

Abstract

To provide a piston ring that is for use in a hydrogen gas compressor in an oil-free environment, contains a thermoplastic polyimide resin as a main component, and is excellent in heat resistance and wear resistance.SOLUTION: A piston ring 66 is a piston ring for use in an oil-free-type reciprocating compressor 50 for compressing hydrogen gas, the piston ring containing thermoplastic polyimide as a main component and carbon fiber and / or graphite as an additive, and having a tensile strength of 90 MPa or more and a bending strength of 150 MPa or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a piston ring used in a reciprocating compressor that compresses hydrogen gas, a piston ring composite, and a reciprocating compressor. [Background technology]

[0002] In recent years, with environmental considerations in mind, the use of hydrogen as a fuel for power generation, automobiles, etc. has been considered, and the demand for hydrogen is increasing. Incidentally, Patent Document 1 discloses a piston ring that is not for use in a compressor that compresses hydrogen gas, but that has good heat resistance, friction and wear properties, and sealing properties, and this piston ring is made primarily of a thermoplastic polyimide resin.

[0003] Patent Document 2 discloses a combination of a piston that reciprocates without lubrication and a compression ring attached to the piston. The compression ring has a composition of 5-15% fluororesin, 3-15% carbon fiber, 5-15% graphite, and the remainder polyimide resin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-192242 [Patent Document 2] Japanese Patent Application Publication No. 11-82741 [Patent Document 3] Japanese Patent Publication No. 2023-25840 [Patent Document 4] Japanese Patent Publication No. 2023-25841 Summary of the Invention [Problem to be solved by the invention]

[0005] Reciprocating compressors for compressing hydrogen gas, such as those used at hydrogen stations, often require oil-free operation to prevent the inclusion of impurities. Because piston rings in oil-free reciprocating compressors are sometimes used in high-temperature environments, the use of thermoplastic polyimide resins has been considered as a material with excellent heat resistance and wear resistance. However, Patent Document 1 conducted a sliding test under oil lubrication and did not evaluate wear resistance in an oil-free environment. Furthermore, since no wear test was conducted in a hydrogen environment, it cannot be said that the factors affecting wear resistance in a hydrogen environment are suggested. In other words, piston rings primarily composed of thermoplastic polyimide may exhibit different wear behavior in a hydrogen atmosphere than in air, so wear tests in air alone cannot be said to provide an indicator for determining whether or not they can be used in an actual reciprocating compressor for compressing hydrogen gas. Furthermore, Patent Document 2 also did not conduct a sliding test in a hydrogen environment, so it cannot be said that the factors affecting wear resistance in a hydrogen environment are suggested. The same is true for Patent Documents 3 and 4.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a piston ring that can be used in a hydrogen gas compressor in an oil-free environment, that is made mainly of a thermoplastic polyimide resin, and that has excellent heat resistance and wear resistance. [Means for solving the problem]

[0007] The piston ring according to the present invention is a piston ring used in an oil-free reciprocating compressor that compresses hydrogen gas, and is composed mainly of thermoplastic polyimide, contains carbon fiber and / or graphite as an additive, and has a tensile strength of 90 MPa or more and a flexural strength of 150 MPa or more.

[0008] The piston ring according to the present invention can improve the heat resistance and wear resistance of the piston ring even when the piston ring is used in an oil-free reciprocating compressor that compresses hydrogen gas, thereby contributing to the efficient supply of hydrogen gas.

[0009] The piston ring may not contain polytetrafluoroethylene, in which case the tensile strength may be 110 MPa or more and the bending strength may be 160 MPa or more.

[0010] In this embodiment, even when the piston ring is used in an oil-free reciprocating compressor that compresses hydrogen gas, the heat resistance can be further improved.

[0011] A piston ring composite according to the present invention includes the piston ring; and a seal ring that is arranged on a high-pressure side of the piston ring and has a tensile strength lower than that of the piston ring and a bending strength lower than that of the piston ring.

[0012] In the piston ring composite according to the present invention, the sealing performance can be improved even when the piston ring is used in an oil-free reciprocating compressor that compresses hydrogen gas.

[0013] An oil-free reciprocating compressor for compressing hydrogen gas according to the present invention includes the piston ring. [Effects of the Invention]

[0014] As described above, according to the present invention, a piston ring can be obtained which can be used in a hydrogen gas compressor in an oil-free environment, is made primarily of a thermoplastic polyimide resin, and has excellent heat resistance and wear resistance. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view schematically showing a reciprocating compressor according to an embodiment. FIG. [Figure 2] FIG. 10 is a cross-sectional view schematically showing a part of a reciprocating compressor according to another embodiment. [Figure 3] FIG. 1 is a diagram showing a schematic diagram of a sliding test device used to evaluate wear characteristics. [Figure 4]FIG. 1 is a diagram showing the relationship between tensile strength and flexural strength for Examples and Comparative Examples. [Figure 5] FIG. 1 is a diagram showing the compressive strength of Examples and Comparative Examples under room temperature and high temperature environments. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0017] The reciprocating compressor according to this embodiment is used to pressurize hydrogen gas to a predetermined pressure (for example, from 0.7 MPa to 82 MPa) at a hydrogen station. The hydrogen gas compressed by the reciprocating compressor is stored in an accumulator (not shown), cooled in a precooler (not shown) through heat exchange with brine or the like, and then filled into the tank of a fuel cell vehicle by a dispenser (not shown). Note that the reciprocating compressor is not limited to use in hydrogen stations, as long as it is an oil-free compressor used to compress hydrogen gas.

[0018] As shown in FIG. 1, the reciprocating compressor 50 includes a crank mechanism 52, a piston rod 54 driven by the crank mechanism 52, a piston 56 connected to the piston rod 54, and a cylinder portion 58 accommodating the piston 56.

[0019] The cylinder portion 58 is provided with an intake port 58a for drawing hydrogen gas into the space within the cylinder portion 58, and an outlet port 58b for discharging the hydrogen gas compressed within this space. The intake port 58a and the outlet port 58b are each provided with a valve (not shown). The space within the cylinder portion 58 where the intake port 58a and the outlet port 58b open functions as a compression chamber 60.

[0020] The reciprocating compressor 50 also includes a plurality of piston ring assemblies 65 that are attached to the outer peripheral surface of the piston 56 and arranged to slide against the inner peripheral surface of the cylinder portion 58. The provision of the piston ring assemblies 65 separates the compression chamber 60 from other spaces within the cylinder portion 58. This "other space" may be a space that does not function as the compression chamber 60, or, in the case where the reciprocating compressor 50 is configured as a tandem-type compressor, may be another low-pressure compression chamber that compresses hydrogen gas before it is introduced into the compression chamber 60.

[0021] Each piston ring complex 65 has a piston ring 66 and a seal ring 67 arranged on the high-pressure side of the piston ring 66. That is, in each piston ring complex 65, the seal ring 67 is located on the compression chamber 60 side of the piston ring 66.

[0022] Although the reciprocating compressor 50 of the present embodiment includes a plurality of piston ring composites 65, it may also be configured to include only one piston ring composite 65. Furthermore, the seal ring 67 may be omitted as shown in FIG. 2.

[0023] The piston ring 66 is made of a resin primarily composed of thermoplastic polyimide (TPI) with carbon fiber and / or graphite as additives. This resin may also contain polytetrafluoroethylene. This resin has a tensile strength of 90 MPa or more and a flexural strength of 150 MPa or more. This makes it strong and less likely to crack. Graphite is added to improve thermal conductivity and prevent deterioration of heat resistance (i.e., high-temperature strength, etc.) due to frictional heat generation.

[0024] More preferably, the resin constituting the piston ring 66 has a tensile strength of 110 MPa or more and a bending strength of 160 MPa or more. In this case, the resin does not contain polytetrafluoroethylene.

[0025] The seal ring 67 has a tensile strength lower than that of the piston ring 66 and a bending strength lower than that of the piston ring 66 .

[0026] The "tensile strength" referred to here is the value of tensile strength measured in accordance with JIS K7161-1 (Plastics - Determination of tensile properties, Part 1: General rules), and the "flexural strength" is the value of flexural strength measured in accordance with JIS K7171 (Plastics - Determination of flexural properties).

[0027] Because seal ring 67 requires sealing properties, a resin with lower strength than the resin constituting piston ring 66 is used. Seal ring 67 deforms during compression (bulging outward and coming into close contact with the inner circumferential surface of cylinder portion 58), thereby ensuring sealing properties by piston ring composite 65. This enables compression within compression chamber 60. On the other hand, piston ring 66, which functions as a backup ring, is made of a resin with high strength and resistance to cracking. This allows for a longer lifespan.

[0028] The seal ring 67 is made of a resin containing thermoplastic polyimide (TPI) as a main component and polytetrafluoroethylene and carbon fiber as additives. Note that the seal ring 67 may also be made of a resin containing polytetrafluoroethylene as a main component.

[0029] The piston ring 66 of this embodiment is made of a resin containing thermoplastic polyimide (TPI) as a main component and carbon fiber and / or graphite as an additive, and has a tensile strength of 90 MPa or more and a flexural strength of 150 MPa or more. Therefore, even when the piston ring 66 is used in an oil-free reciprocating compressor 50 that compresses hydrogen gas, the heat resistance and wear resistance of the piston ring 66 can be improved. [Example]

[0030] Tests were conducted to confirm that the piston ring 66 of this embodiment has wear resistance and high-temperature properties even in a hydrogen gas atmosphere, and the results will be described below.

[0031] First, the wear characteristics were evaluated using test pieces made of the resins of Examples 1-1, 1-2, 2-1, 2-2, 3-1, and 3-2 and Comparative Examples 1-1 and 1-2.

[0032] In Examples 1-1 and 1-2, resin P1 having the same composition, tensile strength, and flexural strength is used. Resin P1 is mainly composed of thermoplastic polyimide (TPI), contains carbon fiber and graphite as additives, and does not contain polytetrafluoroethylene.

[0033] In Examples 2-1 and 2-2, resin P2 is used, which has a different composition, tensile strength, and flexural strength from resin P1. Resin P2 is mainly composed of thermoplastic polyimide (TPI), contains carbon fiber and graphite as additives, and does not contain polytetrafluoroethylene.

[0034] Examples 3-1 and 3-2 use a resin P3 that differs from resins P1 and P2 in composition, tensile strength, and flexural strength. Resin P3 is primarily composed of thermoplastic polyimide (TPI), and contains carbon fiber and graphite as additives, as well as polytetrafluoroethylene (PTFE).

[0035] Comparative Examples 1-1 and 1-2 use a resin P4 that differs from resins P1, P2, and P3 in composition, tensile strength, and flexural strength. Resin P4 is primarily composed of thermoplastic polyimide (TPI) and contains carbon fiber and graphite as additives. Resin P4 also contains polytetrafluoroethylene (PTFE) as an additive. As described below, resin P4 in Comparative Examples 1-1 and 1-2 has inferior tensile strength and flexural strength to resins P1, P2, and P3 in Examples 1-1, 1-2, 2-1, 2-2, 3-1, and 3-2.

[0036] The tensile properties were determined by measuring the tensile strength based on JIS K7161-1 (Plastics - Determination of tensile properties, Part 1: General rules), and the flexural properties were determined by measuring the flexural strength based on JIS K7171 (Plastics - Determination of flexural properties).

[0037] The wear characteristics were evaluated using a sliding tester shown in Figure 3. The sliding tester is a pin-on-disk type sliding tester with a chamber 1 configured to allow hydrogen gas to be introduced. The chamber 1 is equipped with a gas inlet 2 for introducing hydrogen gas and a gas outlet 3 for discharging gas from the chamber 1. The chamber 1 contains a fixing unit 8 for fixing a test specimen 7 and a rotating table 4 to which a metal plate 5 is attached with fixing screws 6 and which rotates the metal plate 5. The test specimen 7 attached to the fixing unit 8 is pressed against the metal plate 5 by a pressing mechanism 15. The pressing mechanism 15 includes a pressure application rod 10 that is oscillatably mounted around a fulcrum 11, a weight 13 attached to the base end of the pressure application rod 10 via a wire 12, and a fixing unit 8 attached to the tip of the pressure application rod 10. A load cell 9 is attached to the pressure application rod 10.

[0038] The test piece 7 is fixed to the fixing part 8 of the pressure application rod 10. The test piece 7 fixed to the fixing part 8 is pressed against the metal plate 5 with a predetermined load by the weight of the weight 13. In this state, the turntable 4 rotates the metal plate 5 at a predetermined rotation speed, causing the test piece 7 to slide against the metal plate 5 at a predetermined speed.

[0039] The test piece 7 was machined into a pin shape with a diameter of 5.0 mm and a length of 10.0 mm, and the surface roughness Ra of the sliding surface was adjusted to 1.0 μm or less. The metal plate 5 was machined into a disk shape from chromium molybdenum steel (SCM435), and the surface roughness Ra was adjusted to 0.2 μm.

[0040] The pressing load of the test piece 7 against the metal plate 5 was 9.66 MPa, and the chamber 1 was filled with hydrogen gas. The test was carried out at room temperature with a sliding speed of 2.0 m / s and a sliding distance of 20,000 m. The wear amount (mm 3 ) and the wear amount per unit load and unit distance is calculated as the specific wear amount (mm 3 / N·m).

[0041] The test results of the tensile properties, bending properties and abrasion properties of resins P1 to P3 of Examples 1-1, 1-2, 2-1, 2-2, 3-1 and 3-2 and Comparative Examples 1-1 and 1-2 are shown in Table 1 below.

[0042] [Table 1]

[0043] Next, the high-temperature properties of the test piece 7 were evaluated based on the compression properties at room temperature (23°C) and at a high temperature (150°C) in the atmosphere. Note that, since testing in a high-temperature hydrogen gas atmosphere involves danger, the evaluation was performed in air.

[0044] Test piece 7 (pin shape, φ5.0, length 10.0 mm) was subjected to a compression fracture test at a test speed of 1 mm / min using a universal testing machine at room temperature (23°C) and high temperature (150°C). The maximum stress obtained from the stress (load) and strain (crosshead displacement of the testing machine) diagram obtained in this test was defined as the compressive strength.

[0045] The test results of high temperature characteristics at room temperature (23°C) in air conducted on test pieces 7 made of the resins of Examples 1-3, 1-4, 1-5, 2-3, 2-4, 2-5, 3-3, 3-4, 3-5 and Comparative Examples 1-3, 1-4, 1-5 are shown in Table 2 below.

[0046] In Examples 1-3, 1-4, and 1-5, the same resin P1 as in Examples 1-1 and 1-2 is used. In Examples 2-3, 2-4, and 2-5, the same resin P2 as in Examples 2-1 and 2-2 is used. In Examples 3-3, 3-4, and 3-5, the same resin P3 as in Examples 3-1 and 3-2 is used. In Comparative Examples 1-3, 1-4, and 1-5, the same resin P4 as in Comparative Examples 1-1 and 1-2 is used.

[0047] [Table 2]

[0048] The test results of high temperature property tests at high temperature (150°C) conducted on test pieces 7 made of the resins of Examples 1-6, 1-7, 1-8, 2-6, 2-7, 2-8, 3-6, 3-7, 3-8 and Comparative Examples 1-6, 1-7, 1-8 are shown in Table 3 below.

[0049] In Examples 1-6, 1-7, and 1-8, resin P1 having the same composition as in Examples 1-1 and 1-2 is used. In Examples 2-6, 2-7, and 2-8, resin P2 having the same composition as in Examples 2-1 and 2-2 is used. In Examples 3-6, 3-7, and 3-8, resin P3 having the same composition as in Examples 3-1 and 3-2 is used. In Comparative Examples 1-6, 1-7, and 1-8, resin P4 having the same composition as in Comparative Examples 1-1 and 1-2 is used.

[0050] [Table 3]

[0051] As shown in Table 1, Comparative Examples 1-1 and 1-2 had larger wear rates and specific wear rates than Examples 1-1, 1-2, 2-1, 2-2, 3-1, and 3-2. That is, as shown in FIG. 4, the resins of Examples 1-1, 1-2, 2-1, 2-2, 3-1, and 3-2 had tensile strengths of 90 MPa or more and flexural strengths of 150 MPa or more, while the resins of Comparative Examples 1-1 and 1-2 had lower tensile strengths and flexural strengths. These results demonstrate that wear characteristics in a hydrogen gas atmosphere can be improved by selecting a resin that contains thermoplastic polyimide (TPI) as the main component and carbon fiber and / or graphite as an additive, as well as a resin that has a tensile strength of 90 MPa or more and a flexural strength of 150 MPa or more.

[0052] FIG. 5 is a diagram plotting the compressive strength values ​​of Examples 1-3, 1-4, 1-5, 2-3, 2-4, 2-5, 3-3, 3-4, 3-5 and Examples 1-6, 1-7, 1-8, 2-6, 2-7, 2-8, 3-6, 3-7, 3-8, and Comparative Examples 1-3, 1-4, 1-5 and Comparative Examples 1-6, 1-7, 1-8 based on Tables 2 and 3.

[0053] Figure 5 shows the linear approximations LA for Examples 1-3, 1-4, 1-5, and 1-6, 1-7, and 1-8 for Resin P1. It shows the linear approximations LB for Examples 2-3, 2-4, 2-5, and 2-6, 2-7, and 2-8 for Resin P2. It shows the linear approximations LC for Examples 3-3, 3-4, 3-5, and 3-6, 3-7, and 3-8 for Resin P3. It shows the linear approximations LD for Comparative Examples 1-3, 1-4, 1-5, and 1-6, 1-7, and 1-8 for Resin P4.

[0054] In both room temperature (23°C) and high temperature (150°C) environments, the compressive strengths of Examples 1-3, 1-4, 1-5, 2-3, 2-4, 2-5, 3-3, 3-4, 3-5 and Examples 1-6, 1-7, 1-8, 2-6, 2-7, 2-8, 3-6, 3-7, and 3-8 are higher than the compressive strengths of Comparative Examples 1-3, 1-4, 1-5 and Comparative Examples 1-6, 1-7, and 1-8. This shows that by selecting a resin so that the tensile strength is 90 MPa or more and the flexural strength is 150 MPa or more, excellent high-temperature properties can also be achieved.

[0055] In particular, since the slope of the linear approximation LA is smaller than that of the other linear approximations LB2 to LD, it is considered that the resin P1 used in Examples 1-3, 1-4, 1-5 and 1-6, 1-7, and 1-8 (i.e., having a tensile strength of 110 MPa or more and 130 MPa or less, and a flexural strength of 160 MPa or more and 180 MPa or less) has superior high-temperature properties.

[0056] It should be noted that the embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The present invention is not limited to the above-described embodiments, and various modifications and improvements are possible without departing from the spirit of the present invention. For example, each piston ring 66 in this embodiment is made of a resin having a tensile strength of 90 MPa or more and a bending strength of 150 MPa or more, and a seal ring 67 is superimposed thereon. Alternatively, a piston ring composite may be constructed by superimposing two or more (typically two) piston rings 66 made of any of the resins P1 to P3 according to the examples. Furthermore, in this piston ring composite, a seal ring 67 may be further superimposed on the piston ring 66. [Explanation of symbols]

[0057] 50: Reciprocating compressor 56: Piston 65: Piston ring complex 66: Piston ring 67: Seal ring

Claims

1. A method for using a piston ring, the piston ring containing thermoplastic polyimide as a main component and containing carbon fiber as an additive, or containing carbon fiber and graphite as additives, and having a tensile strength of 90 MPa or more and a flexural strength of 150 MPa or more, in an oil-free reciprocating compressor that compresses hydrogen gas.

2. 2. A method for using a piston ring according to claim 1, wherein the piston ring does not contain polytetrafluoroethylene and has a tensile strength of 110 MPa or more and a bending strength of 160 MPa or more, and is used in the reciprocating compressor.

3. a piston ring containing thermoplastic polyimide as a main component and carbon fiber as an additive, or containing carbon fiber and graphite as additives, and having a tensile strength of 90 MPa or more and a bending strength of 150 MPa or more; a seal ring disposed on a high-pressure side of the piston ring, the seal ring having a tensile strength lower than that of the piston ring and a bending strength lower than that of the piston ring; A method for using the piston ring composite in an oil-free reciprocating compressor that compresses hydrogen gas, comprising:

4. An oil-free reciprocating compressor for compressing hydrogen gas, A reciprocating compressor using a piston ring that contains thermoplastic polyimide as a main component and carbon fiber as an additive, or contains carbon fiber and graphite as additives, and has a tensile strength of 90 MPa or more and a bending strength of 150 MPa or more.

5. 5. The reciprocating compressor according to claim 4, wherein the piston ring does not contain polytetrafluoroethylene and has a tensile strength of 110 MPa or more and a bending strength of 160 MPa or more.

6. An oil-free reciprocating compressor for compressing hydrogen gas, a piston ring containing thermoplastic polyimide as a main component and carbon fiber as an additive, or containing carbon fiber and graphite as additives, and having a tensile strength of 90 MPa or more and a bending strength of 150 MPa or more; a seal ring disposed on a high-pressure side of the piston ring, the seal ring having a tensile strength lower than that of the piston ring and a bending strength lower than that of the piston ring; A reciprocating compressor using a piston ring composite comprising:

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