Piston rings and piston ring composites

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, in consideration of the environment, hydrogen has been considered for use as a fuel for power generation and automobiles, etc., and the demand for hydrogen is increasing. Incidentally, Patent Document 1 discloses a piston ring that is not used in a compressor that compresses hydrogen gas, but has good heat resistance, friction and wear properties, and sealing properties, and this piston ring is made mainly 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] JP 2007-192242 A [Patent Document 2] Japanese Patent Application Publication No. 11-82741 [Patent Document 3] JP 2023-25840 A [Patent Document 4] JP 2023-25841 A Summary of the Invention [Problem to be solved by the invention]

[0005] In reciprocating compressors for compressing hydrogen gas, which are used at hydrogen stations and the like, oil-free compressors are sometimes required to avoid the inclusion of impurities. In oil-free reciprocating compressors, piston rings are sometimes used in high-temperature environments, so the use of thermoplastic polyimide resins as materials with excellent heat resistance and wear resistance has been considered. However, in Patent Document 1, sliding tests were conducted under oil lubrication, and wear resistance in an oil-free environment was not evaluated. In addition, since wear tests were not conducted in a hydrogen environment, it cannot be said that factors that affect wear properties in a hydrogen environment are suggested. In other words, piston rings mainly composed of thermoplastic polyimide may exhibit wear behavior different from that in air in a hydrogen atmosphere, so it cannot be said that wear tests conducted only in air suggest an index for determining whether or not they can be used in an actual machine as a reciprocating compressor for compressing hydrogen gas. In addition, in Patent Document 2, sliding tests were not conducted in a hydrogen environment, so it cannot be said that factors that affect wear properties 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 problems, and an object of the present invention is to provide a piston ring which can be used in a hydrogen gas compressor in an oil-free environment, is made mainly of a thermoplastic polyimide resin, and 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 for compressing hydrogen gas, the piston ring comprising a thermoplastic polyimide as a main component, Contains carbon fiber as an additive, or Carbon Fiber and Big It contains 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 this case, the piston ring may have a tensile strength of 110 MPa or more and a bending strength of 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] The 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, has a tensile strength lower than a tensile strength of the piston ring, and has a bending strength lower than a bending strength of the piston ring.

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

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

[0015] [Figure 1] FIG. 1 is a cross-sectional view illustrating a reciprocating compressor according to an embodiment. [Diagram 2] FIG. 11 is a cross-sectional view illustrating a part of a reciprocating compressor according to another embodiment. [Diagram 3] FIG. 2 is a schematic diagram showing a sliding test device used for evaluating wear characteristics. [Figure 4] FIG. 2 is a diagram showing the relationship between tensile strength and flexural strength for the examples and comparative examples. [Diagram 5] FIG. 1 is a diagram showing the compressive strength under room temperature and high temperature environments for the examples and comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the 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 a pressure accumulator (not shown), cooled through heat exchange with brine or the like in a precooler (not shown), 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 at hydrogen stations, so 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 that houses 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 a discharge port 58b for discharging the hydrogen gas compressed within this space. The intake port 58a and the discharge port 58b are each provided with a valve (not shown). Of the space within the cylinder portion 58, the space into which the intake port 58a and the discharge port 58b open functions as a compression chamber 60.

[0020] The reciprocating compressor 50 also includes a plurality of piston ring complexes 65 that are attached to the outer peripheral surface of the piston 56 and arranged so as to be in sliding contact with the inner peripheral surface of the cylinder portion 58. By providing the piston ring complexes 65, the compression chamber 60 is separated 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 by a tandem type compressor, may be another compression chamber on the low-pressure side 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 complexes 65, it may be configured to include only one piston ring complex 65. In addition, the seal ring 67 may be omitted as shown in FIG. 2.

[0023] The piston ring 66 is made of a resin containing thermoplastic polyimide (TPI) as a main component and carbon fiber and / or graphite as an additive. This resin may contain polytetrafluoroethylene. This resin has a tensile strength of 90 MPa or more and a bending strength of 150 MPa or more. This makes it strong and less likely to crack. Graphite is added to improve thermal conductivity to prevent deterioration of heat resistance (= 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 tensile strength value measured based on JIS K7161-1 (Plastics - Determination of tensile properties, Part 1: General rules). Also, the "flexural strength" is the flexural strength value measured based on JIS K7171 (Plastics - Determination of flexural properties).

[0027] Since sealing properties are required for the seal ring 67, a resin with lower strength than the resin constituting the piston ring 66 is used. The seal ring 67 deforms during compression (protruding outward and coming into close contact with the inner circumferential surface of the cylinder portion 58), thereby ensuring the sealing properties of the piston ring composite 65. This enables compression within the compression chamber 60. On the other hand, a resin with high strength and low cracking resistance is used for the piston ring 66, which functions as a backup ring. This allows for a long 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. The seal ring 67 may 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 bending 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. EXAMPLES

[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.

[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 bending 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, a resin P2 is used that is different from the resin P1 in composition, tensile strength, and bending strength. The resin P2 is mainly composed of thermoplastic polyimide (TPI), contains carbon fiber and graphite as additives, and does not contain polytetrafluoroethylene.

[0034] In Examples 3-1 and 3-2, a resin P3 is used which has a composition, tensile strength, and bending strength different from those of resins P1 and P2. Resin P3 is mainly composed of thermoplastic polyimide (TPI), contains carbon fiber and graphite as additives, and contains polytetrafluoroethylene (PTFE) as an additive.

[0035] In Comparative Examples 1-1 and 1-2, resin P4 is used, which has a composition, tensile strength, and bending strength different from those of resins P1, P2, and P3. Resin P4 is mainly composed of thermoplastic polyimide (TPI) and contains carbon fiber and graphite as additives. Resin P4 contains polytetrafluoroethylene (PTFE) as an additive. Resin P4 according to Comparative Examples 1-1 and 1-2 has a tensile strength and bending strength inferior to those of resins P1, P2, and P3 according to Examples 1-1, 1-2, 2-1, 2-2, 3-1, and 3-2, as described later.

[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 by measurements using a sliding tester shown in FIG. 3. The sliding tester is a pin-on-disk type sliding tester, and has a chamber 1 configured to be able to introduce hydrogen gas. The chamber 1 is provided with a gas inlet 2 for introducing hydrogen gas and a gas outlet 3 for discharging gas from the chamber 1. The chamber 1 is provided with a fixing part 8 for fixing the test piece 7, and a rotating table 4 to which a metal plate 5 is attached by a fixing screw 6 and which rotates the metal plate 5. The test piece 7 attached to the fixing part 8 is pressed against the metal plate 5 by a pressing mechanism 15. The pressing mechanism 15 has a pressure application rod 10 that is provided so as to be swingable around a fulcrum part 11, a weight 13 attached to the base end of the pressure application rod 10 via a wire 12, and a fixing part 8 provided at 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, so that the test piece 7 slides 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 was adjusted so that the surface roughness Ra of the sliding surface was 1.0 μm or less. The metal plate 5 was machined into a disk shape from chromium molybdenum steel (SCM435), and was adjusted so that the surface roughness Ra was 0.2 μm.

[0040] The pressing load of the test piece 7 against the metal plate 5 was 9.66 MPa, the chamber 1 was filled with hydrogen gas, the sliding speed was 2.0 m / s, the sliding distance was 20,000 m, and the test was performed at room temperature. The wear amount (mm 3 ) and the amount of wear 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 is dangerous, the evaluation was performed in air.

[0044] A compression fracture test was performed on test piece 7 (pin shape with diameter 5.0 mm and length 10.0 mm) using a universal testing machine at room temperature (23°C) and high temperature (150°C) at a test speed of 1 mm / min. 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 results of tests on 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 results of tests on high temperature characteristics 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, the wear amount and specific wear amount of Comparative Examples 1-1 and 1-2 are larger than those of 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 have a tensile strength of 90 MPa or more and a bending strength of 150 MPa or more, while the resins of Comparative Examples 1-1 and 1-2 have a tensile strength and bending strength lower than those. From this result, it can be understood that the 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 bending strength of 150 MPa or more.

[0052] FIG. 5 is a plot of compressive strength values ​​based on Tables 2 and 3 for 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.

[0053] In FIG. 5, the linear approximation LA of Examples 1-3, 1-4, 1-5 and Examples 1-6, 1-7, 1-8 for resin P1 is shown. The linear approximation LB of Examples 2-3, 2-4, 2-5 and Examples 2-6, 2-7, 2-8 for resin P2 is shown. The linear approximation LC of Examples 3-3, 3-4, 3-5 and 3-6, 3-7, 3-8 for resin P3 is shown. The linear approximation LD of Comparative Examples 1-3, 1-4, 1-5 and Comparative Examples 1-6, 1-7, 1-8 for resin P4 is shown.

[0054] In a room temperature (23°C) environment and a high temperature (150°C) environment, 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, 3-8 are higher than those of Comparative Examples 1-3, 1-4, 1-5 and Comparative Examples 1-6, 1-7, 1-8. This shows that by selecting a resin so that the tensile strength is 90 MPa or more and the bending strength is 150 MPa or more, it is possible to obtain excellent high temperature properties.

[0055] In particular, since the slope of the linear approximation LA is smaller than those of the other linear approximations LB2 to LD, it is considered that resin P1 used in Examples 1-3, 1-4, 1-5 and Examples 1-6, 1-7, and 1-8 (i.e., resin 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 and not restrictive in all respects. 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 complex may be formed 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 complex, 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 piston ring used in an oil-free reciprocating compressor that compresses hydrogen gas, The thermoplastic polyimide is a main component, and carbon fiber is contained as an additive, or carbon fiber and graphite are contained as additives, A piston ring having a tensile strength of 90 MPa or more and a bending strength of 150 MPa or more.

2. Does not contain polytetrafluoroethylene 2. The piston ring according to claim 1, having a tensile strength of 110 MPa or more and a bending strength of 160 MPa or more.

3. The piston ring according to claim 2, 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 piston ring composite body comprising:

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