Piston ring life evaluation method

Abstract

To provide a method for evaluating the life of a piston ring that can maintain sealing performance over a long operating period even without containing PPS. [Solution] A method for evaluating the lifespan of a piston ring used in a reciprocating compressor includes investigating the correlation between the operating time of the reciprocating compressor and the pressure in a space that is affected by a pressure increase due to leakage of compressed gas through a gap between the piston ring and a cylinder body, determining the operating time when the pressure in the space reaches a predetermined threshold based on the correlation, and evaluating the determined operating time as the lifespan of the piston ring.

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the life of a piston ring. [Background technology]

[0002] Conventionally, in a reciprocating compressor, a piston ring is used to prevent gas leakage from a compression chamber through a gap between an outer periphery of the piston and an inner wall surface of the cylinder. Patent Document 1 describes, as an example of such a piston ring, a piston ring made of a material such as polytetrafluoroethylene (PTFE) or polyphenylene sulfide (PPS). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-49945 Summary of the Invention [Problem to be solved by the invention]

[0004] The present inventors have noticed that when piston rings containing PPS are used in reciprocating compressors for hydrogen stations, the following problem occurs: During the compression of hydrogen gas, the sulfur components of the PPS contained in the piston rings gasify, and the gasified sulfur components may be mixed into the compressed gas, which may then be filled into a fuel cell vehicle (FCV) while containing the sulfur components. In this case, the sulfur components in the gas may adversely affect the normal operation of the fuel cell (for example, reducing power generation efficiency).

[0005] For this reason, it is necessary to avoid using piston rings containing PPS in reciprocating compressors for hydrogen stations, but piston rings that do not contain PPS have a significantly shorter lifespan than piston rings that contain PPS. Therefore, while using piston rings that do not contain PPS can prevent sulfur components from entering the FCV, it becomes difficult to maintain the sealing performance of the piston rings over long operating periods.

[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 is capable of maintaining sealing performance over a long operating period even without containing PPS, a reciprocating compressor including the piston ring, a method for selecting the piston ring, and a method for evaluating the service life of the piston ring. [Means for solving the problem]

[0007] A piston ring according to one aspect of the present invention is a piston ring used in a reciprocating compressor, in which the total amount of polytetrafluoroethylene and one resin of polyether ether ketone and polyimide is 50 mass% or more of the total, the piston ring does not contain polyphenylene sulfide, and the piston ring has a tensile strength in the range of more than 15 MPa and less than 100 MPa.

[0008] The present inventors have conducted extensive research to improve the service life of piston rings that do not contain PPS. As a result, the present inventors have focused on tensile strength, among various properties of piston rings, and have found that by adjusting this within an appropriate range, it is possible to maintain high sealing performance of piston rings for a long period of time even without adding PPS.

[0009] The present invention has been made based on the above-mentioned viewpoints. That is, a piston ring according to one aspect of the present invention has a tensile strength adjusted to a range of more than 15 MPa and less than 100 MPa, and has a significantly improved lifespan compared to piston rings having a tensile strength outside the above range (15 MPa or less or 100 MPa or more). Therefore, by mounting this piston ring on the piston of a reciprocating compressor and using it, it becomes possible to prevent sulfur components derived from PPS from being mixed into the compressed gas and to prevent gas leakage from the compression chamber over a long operating period.

[0010] The piston ring may have a tensile strength of 55 MPa or less.

[0011] This improves the life of the piston ring and prevents a decrease in sealing performance due to a higher tensile strength (harder piston ring) compared to when the pressure is higher than 55 MPa.

[0012] A reciprocating compressor according to another aspect of the present invention is a reciprocating compressor that pressurizes hydrogen gas to a predetermined pressure at a hydrogen station, and includes: a cylinder body having a compression chamber into which hydrogen gas is drawn; a piston that is disposed within the cylinder body and reciprocates within the cylinder body so as to change the volume of the compression chamber; and the piston ring that is attached to the outer periphery of the piston and seals a gap between the outer periphery of the piston and the inner wall surface of the cylinder body.

[0013] This reciprocating compressor uses piston rings that do not contain PPS, preventing sulfur components derived from PPS from being mixed into hydrogen gas. This prevents the sulfur components derived from PPS from adversely affecting the normal operation of the fuel cell installed in the FCV. Furthermore, by adjusting the tensile strength within an appropriate range, the life of the piston rings is improved, making it possible to maintain high sealing performance over long operating periods and effectively suppressing gas leakage from the compression chambers.

[0014] A method for selecting a piston ring, according to still another aspect of the present invention, is a method for selecting a piston ring to be used in a reciprocating compressor, in which a piston ring containing polytetrafluoroethylene and one resin of polyether ether ketone and polyimide in a total amount of 50 mass % or more, containing no polyphenylene sulfide, and having a tensile strength in a range of more than 15 MPa and less than 100 MPa is selected as a piston ring to be fitted on an outer periphery of a piston.

[0015] This method makes it possible to select a piston ring that does not contain PPS and has an improved lifespan. By fitting this piston ring to a piston and operating a reciprocating compressor, it is possible to prevent sulfur components derived from PPS from being mixed into the compressed gas and to suppress gas leakage from the compression chamber for a long period of time.

[0016] A method for evaluating a life of a piston ring according to yet another aspect of the present invention is a method for evaluating a life of a piston ring used in a reciprocating compressor, comprising the steps of: the reciprocating compressor comprises a cylinder body having a low-stage cylinder and a high-stage cylinder, and a pressurizing unit having a low-stage piston and a high-stage piston, a compression chamber is provided inside the low-stage cylinder, the high-stage cylinder is connected to an upper part of the low-stage cylinder, a high-stage compression chamber is provided inside the high-stage cylinder, the low-stage piston is disposed in the low-stage cylinder, the high-stage piston is connected to an upper part of the low-stage piston, is disposed in the high-stage cylinder, and further comprises a plurality of piston rings attached to an outer periphery of the high-stage piston and sealing a gap between the outer periphery of the high-stage piston and an inner wall surface of the high-stage cylinder, The total operating time of the reciprocating compressor , the outer periphery of the high-stage piston and the inner wall surface of the high-stage cylinder It is subject to pressure buildup due to leakage of compressed gas through the gap between the The suction pressure in the connecting passage connected to the suction side of the compression chamber of the low-stage cylinder Multiple plot data between and Take It is therefore important to investigate these correlations and Suction pressure determining the total operating time when the life of the piston ring reaches a predetermined threshold based on the correlation, and evaluating the determined total operating time as the life of the piston ring.

[0017] This method allows accurate evaluation of the life of piston rings by monitoring the pressure in the space affected by the pressure increase due to leakage of compressed gas, without directly measuring the wear amount of the piston rings. Therefore, unlike when directly measuring the wear amount of the piston rings, there is no need to disassemble the compressor each time, making it possible to easily evaluate the life of the rings. [Effects of the Invention]

[0018] As is clear from the above description, the present invention can provide a piston ring that is capable of maintaining sealing performance over a long operating period even without containing PPS, a reciprocating compressor including the piston ring, a method for selecting the piston ring, and a method for evaluating the service life of the piston ring. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram schematically illustrating a configuration of a reciprocating compressor according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram schematically illustrating the configuration of each compression section in the reciprocating compressor according to the embodiment of the present invention. [Figure 3] 10 is a graph showing the relationship between the operation time of the reciprocating compressor and the rate at which the pressure in the space opposite the compression chamber reaches a threshold value. [Figure 4] 1 is a graph showing the relationship between the tensile strength of a piston ring and the target life achievement rate of the piston ring. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0021] (reciprocating compressor) First, the configuration of a reciprocating compressor 1 (reciprocating compressor) according to this embodiment will be described with reference to FIGS.

[0022] The reciprocating compressor 1 according to this embodiment is used to increase the pressure of hydrogen gas at a hydrogen station to a predetermined pressure (for example, from 0.7 MPa to 82 MPa). The hydrogen gas compressed by the reciprocating compressor 1 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 an FCV as fuel by a dispenser (not shown).

[0023] The reciprocating compressor 1 mainly includes a crankshaft (not shown), a crankcase 20, a first compression section 100 and a second compression section 200 that compress hydrogen gas, a connection section 300, and piston rings 2. The reciprocating compressor 1 according to this embodiment is a five-stage compressor in which five compression chambers are arranged in series, and the first compression section 100 and the second compression section 200 are installed in an orientation in which they extend in the direction of gravity (the vertical direction in FIG. 1). However, the number of stages of the compression chambers is not particularly limited, and the reciprocating compressor 1 may also be installed in an orientation in which the first compression section 100 and the second compression section 200 extend in the horizontal direction. Each component of the reciprocating compressor 1 will be described below.

[0024] The crankcase 20 has a box-shaped main body 22 that holds the crankshaft and opens upward in FIG. 1, and a lid portion 24 that has a shape that closes the opening of the main body 22.

[0025] The first compression section 100 has a first reciprocating motion converter 110, a first cylinder body 120, and a first pressurizing section 130. The first reciprocating motion converter 110 is connected to the crankshaft, and reciprocates linearly in a direction perpendicular to the axial direction of the crankshaft (the up-down direction in FIG. 1 ) as the crankshaft rotates.

[0026] The first cylinder body 120 has a first low-stage cylinder 121 and a first high-stage cylinder 124. The inside of the first low-stage cylinder 121 and the first high-stage cylinder 124 is machined into, for example, a cylindrical shape, and a compression chamber into which hydrogen gas is drawn is formed.

[0027] The first low-stage cylinder 121 is connected to the upper part of the lid portion 24. As shown in Fig. 2, the first low-stage cylinder 121 is provided therein with a first compression chamber 121S which is the lowest-stage compression chamber, and a second compression chamber 122S which is a compression chamber one stage higher than the first compression chamber 121S.

[0028] The first high-stage cylinder 124 is connected to an upper portion of the first low-stage cylinder 121. The inner diameter of the first high-stage cylinder 124 is set smaller than the inner diameter of the first low-stage cylinder 121. Inside the first high-stage cylinder 124, a fourth compression chamber 124S is provided, which is a compression chamber two stages higher than the second compression chamber 122S.

[0029] The first pressurizing section 130 has a first low-stage piston 132 and a first high-stage piston 134. The first low-stage piston 132 is formed in a cylindrical shape and is connected to the upper end of the first piston rod 116 of the first reciprocating motion converter section 110. The first low-stage piston 132 is disposed in the first low-stage cylinder 121 and reciprocates up and down within the first low-stage cylinder 121 so as to change the volumes of the first compression chamber 121S and the second compression chamber 122S.

[0030] More specifically, within the first low-stage cylinder 121, the space below the first low-stage piston 132 in FIG. 2 is the first compression chamber 121S, and the space above the first low-stage piston 132 in FIG. 2 is the second compression chamber 122S. In other words, the first compression chamber 121S and the second compression chamber 122S are isolated from each other by the first low-stage piston 132. In the first cylinder body 120, when the first low-stage piston 132 is displaced to one side in the sliding direction (the lower side in FIG. 2), hydrogen gas is compressed within the first compression chamber 121S. On the other hand, when the first low-stage piston 132 is displaced to the other side in the sliding direction (the upper side in FIG. 2), hydrogen gas is compressed within the second compression chamber 122S.

[0031] The first high-stage piston 134 is formed in a cylindrical shape and is connected to the upper part of the first low-stage piston 132. The first high-stage piston 134 is disposed in the first high-stage cylinder 124 and moves up and down within the first high-stage cylinder 124 so as to change the volume of the fourth compression chamber 124S. Specifically, when the first high-stage piston 134 is displaced to the other side in the sliding direction (upward in FIG. 2), it compresses hydrogen gas within the fourth compression chamber 124S.

[0032] Because the first low-stage piston 132 and the first high-stage piston 134 slide in the same direction at the same time, hydrogen gas is compressed simultaneously in the second compression chamber 122S and the fourth compression chamber 124S. Furthermore, because the first compression chamber 121S and the second compression chamber 122S are formed on both sides of the first low-stage piston 132, the suction timing of the first compression chamber 121S is the same as the discharge timing of the second compression chamber 122S, and the discharge timing of the first compression chamber 121S is the same as the suction timing of the second compression chamber 122S.

[0033] The second compression section 200 has a second reciprocating motion converter 210, a second cylinder body 220, and a second pressurizing section 230. The second reciprocating motion converter 210 is connected to the crankshaft with a phase shift of 180 degrees from the first reciprocating motion converter 110, and linearly reciprocates in a direction perpendicular to the axial direction of the crankshaft (the up-down direction in FIG. 1 ) as the crankshaft rotates. Note that the phase shift of the second reciprocating motion converter 210 relative to the first reciprocating motion converter 110 does not need to be strictly 180 degrees, and may be a few degrees to a dozen degrees. The structure of the second reciprocating motion converter 210 is basically the same as the structure of the first reciprocating motion converter 110.

[0034] The second cylinder body 220 has a second low-stage cylinder 223 and a second high-stage cylinder 225. The inside of the second low-stage cylinder 223 and the second high-stage cylinder 225 is machined into, for example, a cylindrical shape, and a compression chamber into which hydrogen gas is drawn is formed.

[0035] The second low-stage cylinder 223 is connected to the upper part of the lid portion 24 alongside the first low-stage cylinder 121. As shown in Fig. 2, the second low-stage cylinder 223 is provided therein with a third compression chamber 223S, which is a compression chamber one stage higher than the second compression chamber 122S.

[0036] The second high-stage cylinder 225 is connected to an upper portion of the second low-stage cylinder 223. The inner diameter of the second high-stage cylinder 225 is set smaller than the inner diameter of the second low-stage cylinder 223. Inside the second high-stage cylinder 225, a fifth compression chamber 225S is provided, which is a compression chamber one stage higher than the fourth compression chamber 124S.

[0037] The second pressurizing section 230 has a second low-stage piston 233 and a second high-stage piston 235. The second low-stage piston 233 is formed in a cylindrical shape and is connected to the upper end of the second piston rod 216 of the second reciprocating motion converter section 210. The second low-stage piston 233 is disposed in the second low-stage cylinder 223 and reciprocates up and down within the second low-stage cylinder 223 so as to change the volume of the third compression chamber 223S. The second high-stage piston 235 is formed in a cylindrical shape and is connected to the upper part of the second low-stage piston 233. The second high-stage piston 235 is disposed in the second high-stage cylinder 225 and reciprocates up and down within the second high-stage cylinder 225 so as to change the volume of the fifth compression chamber 225S.

[0038] When the second low-stage piston 233 is displaced to the other side in the sliding direction (upward in FIG. 2), it compresses hydrogen gas in the third compression chamber 223S. When the second high-stage piston 235 is displaced to the other side in the sliding direction (upward in FIG. 2), it compresses hydrogen gas in the fifth compression chamber 225S. Hydrogen gas is compressed simultaneously in the third compression chamber 223S and the fifth compression chamber 225S. As described above, since the phase of the second reciprocating motion converter 210 is shifted by 180 degrees from the phase of the first reciprocating motion converter 110, the second pressurizer 230 compresses hydrogen gas in the third compression chamber 223S and the fifth compression chamber 225S, and at the same time, the first pressurizer 130 compresses hydrogen gas in the first compression chamber 121S.

[0039] The connection part 300 connects the compression chambers in the reciprocating compressor 1. Specifically, the connection part 300 has a first connection flow path 301 connecting the first compression chamber 121S and the second compression chamber 122S, a second connection flow path 302 connecting the second compression chamber 122S and the third compression chamber 223S, a third connection flow path 303 connecting the third compression chamber 223S and the fourth compression chamber 124S, and a fourth connection flow path 304 connecting the fourth compression chamber 124S and the fifth compression chamber 225S. As a result, a hydrogen gas flow path is formed in the reciprocating compressor 1 that continues in this order from the first compression chamber 121S to the second compression chamber 122S, the third compression chamber 223S, the fourth compression chamber 124S, and the fifth compression chamber 225S. The pressure difference between the third compression chamber 223S and the fifth compression chamber 225S is 40 MPa or more and 90 MPa or less, and is, for example, approximately 60 MPa. Also, as shown in FIG. 2, the second connection flow path 302 is provided with a pressure sensor 3 that detects the pressure of the hydrogen gas in the second connection flow path 302.

[0040] When the reciprocating compressor 1 is operating, the hydrogen gas drawn into the first compression chamber 121S is compressed and then drawn into the second compression chamber 122S at the same time that it is discharged from the first compression chamber 121S. The hydrogen gas drawn into the second compression chamber 122S is compressed and then drawn into the third compression chamber 223S at the same time that it is discharged from the second compression chamber 122S. Furthermore, the hydrogen gas in the third compression chamber 223S is drawn into the fourth compression chamber 124S at the same time that it is discharged. The hydrogen gas in the fourth compression chamber 124S is drawn into the fifth compression chamber 225S at the same time that it is discharged.

[0041] (Piston rings) Next, the piston ring 2 will be described in detail. The piston ring 2 is an annular part that is attached to the outer periphery of each piston (first low-stage piston 132, first high-stage piston 134, second low-stage piston 233, second high-stage piston 235) and seals the gap between the outer periphery of the piston and the inner wall surface of the cylinder body (first low-stage cylinder 121, first high-stage cylinder 124, second low-stage cylinder 223, second high-stage cylinder 225). Attaching the piston ring 2 can suppress gas leakage from each compression chamber. The piston ring 2 is attached in a groove (not shown) that is formed in an annular shape along the outer periphery of each piston.

[0042] 2, a plurality of piston rings 2 are attached to the outer periphery of the second high-stage piston 235, and the plurality of piston rings 2 seal the gap between the outer periphery of the second high-stage piston 235 and the inner wall surface of the second high-stage cylinder 225, thereby suppressing leakage of hydrogen gas from the fifth compression chamber 225S to the third compression chamber 223S and the second connecting flow path 302. Piston rings 2 are also attached to the outer peripheries of the other pistons (the first low-stage piston 132, the first high-stage piston 134, and the second low-stage piston 233), thereby suppressing leakage of hydrogen gas from each compression chamber (the second compression chamber 122S, the third compression chamber 223S, and the fourth compression chamber 124S). Note that the number of piston rings 2 attached to each piston is not particularly limited, but in this embodiment, approximately 20 piston rings 2 are attached to the second high-stage piston 235.

[0043] The piston ring 2 is one in which the total amount of polytetrafluoroethylene (PTFE) and polyether ether ketone (PEEK) is 50% by mass or more of the total, and does not contain polyphenylene sulfide (PPS). Alternatively, the piston ring 2 may be one in which the total amount of PTFE and polyimide (PI) is 50% by mass or more of the total, and does not contain PPS. "PTFE and PEEK" or "PTFE and PI" is the "base resin" of the piston ring 2.

[0044] In this way, by using the piston ring 2 that does not contain PPS, it is possible to prevent sulfur components derived from PPS from being mixed into the compressed gas (hydrogen gas). This prevents sulfur components from being mixed into the FCV when filling it with fuel (hydrogen gas), and prevents the sulfur components from affecting the normal operation of the fuel cell.

[0045] While piston rings that do not contain PPS typically have a significantly reduced seal life, the piston ring 2 according to this embodiment has a tensile strength adjusted to an appropriate range, which makes it possible to suppress the intrusion of sulfur components into hydrogen gas and to suppress a reduction in seal life. Specifically, the piston ring 2 according to this embodiment has a tensile strength greater than 15 MPa and less than 100 MPa. This makes it possible to suppress the intrusion of sulfur components into the FCV and to extend the seal life compared to a case where the tensile strength is outside the above range. As a result, sufficient sealing performance can be maintained even during long-term operation of the reciprocating compressor 1, making it possible to suppress gas leakage from each compression chamber. The tensile strength of the piston ring 2 is preferably 55 MPa or less, more preferably 45 MPa or more, and more preferably 44.8 MPa or more and 55 MPa or less.

[0046] The piston ring 2 is a commercially available product, and its "tensile strength (tensile strength)" is a nominal value listed in a piston ring catalog, etc. However, the "tensile strength (tensile strength)" may be a value measured based on JIS K7161 (Plastics - Test methods for tensile properties, Part 1: General rules).

[0047] In addition to the base resin, the piston ring 2 may further contain additives such as carbon fiber and graphite. Carbon fiber includes PAN (polyacrylonitrile) and pitch types. Graphite includes artificial graphite and natural graphite. However, these additives are not essential components of the piston ring of the present invention and may not be included.

[0048] (How to select piston rings) Next, a method for selecting a piston ring according to an embodiment of the present invention will be described.

[0049] The method for selecting piston rings according to this embodiment is a method for selecting piston rings to be mounted on each piston (first low-stage piston 132, first high-stage piston 134, second low-stage piston 233, second high-stage piston 235) before manufacturing the reciprocating compressor 1 described above.

[0050] Specifically, the piston ring 2 according to the present embodiment described above, i.e., the piston ring containing PTFE and one of PEEK and PI resins as a base resin, not containing PPS, and having a tensile strength in the range of more than 15 MPa and less than 100 MPa, is selected as the piston ring to be fitted to the outer periphery of each piston in the manufacturing process of the reciprocating compressor 1.

[0051] (Piston ring life evaluation method) Next, a method for evaluating the life of a piston ring according to this embodiment will be described.

[0052] In the reciprocating compressor 1 according to the present embodiment described above, as wear of the piston ring 2 attached to the second high-stage piston 235 progresses, an increasing amount of hydrogen gas leaks from the fifth compression chamber 225S to the third compression chamber 223S through a gap between the outer periphery of the second high-stage piston 235 and the inner wall surface of the second high-stage cylinder 225. This exceeds the hydrogen gas processing capacity of the third compression chamber 223S, and as a result, the pressure of the hydrogen gas in the second connection passage 302 (hereinafter also referred to as the "third stage suction pressure") rises. In the piston ring life evaluation method according to the present embodiment, the third stage suction pressure is continuously monitored by the pressure sensor 3 during operation of the reciprocating compressor 1, thereby evaluating the life of the piston ring 2 attached to the second high-stage piston 235, as described below.

[0053] First, we investigate the correlation between the operation time of the reciprocating compressor 1 and the third stage suction pressure. Specifically, we continue to operate the reciprocating compressor 1 for a predetermined period of time, and during that time, we continue to measure the third stage suction pressure using the pressure sensor 3.

[0054] The third stage suction pressure is the pressure in the space affected by the pressure increase due to leakage of compressed gas through the gap between the piston ring 2 and the second high-stage cylinder 225, that is, the pressure in the second connecting passage 302.

[0055] As a result, a graph showing the relationship between the operating period (horizontal axis) of the reciprocating compressor 1 and the third-stage suction pressure (vertical axis) is obtained, as shown in Fig. 3. The horizontal axis of the graph represents the total operating time of the reciprocating compressor 1 divided by 5 hours (the specified daily operating time of a hydrogen station). The vertical axis of the graph represents the ratio (lifetime arrival rate (%)) of the actual measured value of the third-stage suction pressure to the threshold value of the third-stage suction pressure (the value of the third-stage suction pressure when the life of the piston ring 2 is considered to have arrived). In addition, (1) in the graph is a regression line calculated by the least squares method based on the plot data. Note that (1) may be a regression curve instead of a regression line.

[0056] Next, the operating time of the reciprocating compressor 1 when the third stage suction pressure reaches a predetermined threshold, that is, when the life arrival rate, which is the vertical axis value of the graph in Fig. 3, reaches 100(%), is determined based on the above correlation, and the determined operating time is evaluated as the life of the piston ring 2. Specifically, the x value (x value at point P1 in Fig. 3) when 100(%) is substituted as the y value into the equation showing the regression line (1) in Fig. 3 is estimated as the life of the piston ring 2. [Example]

[0057] The life of each of the piston rings in Examples 1 and 2 and Comparative Examples 1 to 5 in Table 1 below was evaluated in accordance with the piston ring life evaluation method according to the above embodiment. In each of Examples 1 and 2 and Comparative Examples 1 to 5, 20 of the same piston rings were mounted on the second high-stage piston 235.

[0058] The materials and tensile strengths (MPa) of the piston rings of Examples 1 and 2 and Comparative Examples 1 to 5 are shown in Table 1 below. In Table 1, a circle indicates that the corresponding material was contained in the piston ring, and an x ​​indicates that the corresponding material was not contained in the piston ring. In Example 1, the total amount of PTFE and PI was 50% by mass or more of the total, and in Example 2, the total amount of PTFE and PEEK was 50% by mass or more of the total. "CF" means carbon fiber, "GP" means graphite, and "TPI" means thermoplastic polyimide. The "target life achievement rate (%)" is the value (%) obtained by dividing the operating period obtained from the regression line when the life achievement rate of each piston ring is set to 100% by the operating period obtained from the regression line when the life achievement rate of the piston ring of Comparative Example 1 is set to 100%, and multiplying the result by 100. FIG. 4 is a graph based on the data in Table 1, showing the relationship between the tensile strength (horizontal axis) and the target life achievement rate (vertical axis) of each piston ring.

[0059] [Table 1]

[0060] Based on the results shown in Table 1 and FIG. 4, the following can be considered.

[0061] First, in Comparative Example 3, in which the base resin was PTFE as in Comparative Example 1 and no PPS was added, the piston ring life was significantly worse than in Comparative Example 1. In Comparative Example 2, the base resin was PTFE + PEEK to increase the strength of the piston ring, but the ring life was not improved. The reason for this is thought to be that in Comparative Example 2, the tensile strength of the piston ring was 100 MPa or more (103 MPa), and the high PEEK content made the piston ring too hard, making it impossible to ensure sufficient sealing performance. In Comparative Examples 4 and 5, the tensile strength of the piston ring was 100 MPa or more (195 MPa, 140 MPa), as in Comparative Example 2, and the ring life was not improved.

[0062] In contrast, in Example 1, in which the base resin was PTFE+PI and the tensile strength was in the range of more than 15 MPa and less than 100 MPa (44.8 MPa), and in Example 2, in which the base resin was PTFE+PEEK and the tensile strength was in the range of more than 15 MPa and less than 100 MPa (55 MPa), the rate of decrease in life relative to Comparative Example 1 was smaller than in Comparative Examples 2 to 5 (the target life achievement rate was higher than in Comparative Examples 2 to 5). From the above, it was revealed that the piston ring of the present invention can achieve a desired seal life even without containing PPS. It was also found that by using tensile strength as an index, it is possible to compare the predicted life of multiple types of piston rings.

[0063] The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as limiting. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0064] Here, other embodiments of the present invention will be described.

[0065] In the above embodiment, the reciprocating compressor 1 having multiple stages (five stages) of compression chambers has been described. However, the reciprocating compressor of the present invention can also be applied to a single-stage reciprocating compressor having only one compression chamber.

[0066] In the above embodiment, the case of evaluating the life of the piston ring 2 attached to the second high-stage piston 235 has been described, but the life of piston rings attached to other pistons can also be evaluated in a similar manner. Specifically, the life of the piston ring attached to the first low-stage piston 132 can be evaluated based on the pressure in the space affected by the pressure increase due to leakage of compressed gas through the gap between the piston ring and the first low-stage cylinder 121, the life of the piston ring attached to the first high-stage piston 134 can be evaluated based on the pressure in the space affected by the pressure increase due to leakage of compressed gas through the gap between the piston ring and the first high-stage cylinder 124, and the life of the piston ring attached to the second low-stage piston 233 can be evaluated based on the pressure in the space affected by the pressure increase due to leakage of compressed gas through the gap between the piston ring and the second low-stage cylinder 223. [Explanation of symbols]

[0067] 1 Reciprocating compressor 2 piston rings 120 First cylinder body 121S First Compression Chamber 122S Second compression chamber 124S 4th compression chamber 132 First low-stage piston 134 First high-stage piston 220 Second cylinder body 223S 3rd compression chamber 225S 5th compression chamber 233 Second low-stage piston 235 Second high-stage piston

Claims

[Claim 1] A method for evaluating the life of a piston ring used in a reciprocating compressor, comprising: The reciprocating compressor is a cylinder body having a low-stage cylinder and a high-stage cylinder; a pressurizing unit having a low-stage piston and a high-stage piston; Equipped with A compression chamber is provided inside the low-stage cylinder, the high-stage cylinder is connected to an upper portion of the low-stage cylinder; A high-stage compression chamber is provided inside the high-stage cylinder, the low-stage piston is disposed within the low-stage cylinder; the high-stage piston is connected to an upper portion of the low-stage piston and is disposed within the high-stage cylinder; The high-stage piston further includes a plurality of piston rings attached to an outer periphery of the high-stage piston and sealing a gap between the outer periphery of the high-stage piston and an inner wall surface of the high-stage cylinder, The method comprises: Obtaining a plurality of plot data between the total operating time of the reciprocating compressor and the suction pressure in a connecting flow passage connected to the suction side of the compression chamber of the low-stage cylinder, which is affected by a pressure increase due to leakage of compressed gas through a gap between the outer periphery of the high-stage piston and the inner wall surface of the high-stage cylinder, and investigating the correlation therebetween; determining, based on the correlation, the total operating time when the suction pressure reaches a predetermined threshold value, and evaluating the determined total operating time as a life of the piston ring.

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