Combination of sliding members, and gas compressor

Abstract

Provided is a combination of sliding members, whereby excellent performance can be maintained by reducing wear, breakage, or the like between two sliding members used without lubrication. The present invention also provides a gas compressor provided with a cylinder and a piston ring composed of such a combination of sliding members, the gas compressor capable of stably implementing a series of operations from gas intake to discharge over a long period of time. In a combination of sliding members obtained by combining a first sliding member and a second sliding member that are used without lubrication, the first sliding member has a hydrogen-containing diamond-like carbon (DLC) film formed thereon, and the second sliding member has a hydrogen-free DLC film or a physical vapor deposition (PVD) film formed thereon. In the gas compressor having the cylinder and the piston ring, the combination of the cylinder and the piston ring is the combination of the abovementioned sliding members.

Description

Sliding member combination and gas compressor

[0001] The present invention relates to a combination of sliding members comprising a first sliding member and a second sliding member used without lubrication, and to a gas compressor having a cylinder and a piston ring for compressing various gases.

[0002] Compressed gases such as air are used in factories across various industries, and in recent years, there has been a growing demand for inert compressed nitrogen gas and clean compressed gases that do not contain oil mist. Furthermore, in the automotive sector, fuel cell vehicles and hydrogen-powered vehicles are expanding, and compressed hydrogen is being supplied to these vehicles at hydrogen refueling stations.

[0003] Compressed gas is produced using a gas compressor equipped with a piston that reciprocates within a cylinder. The gas is introduced into a compression chamber within the cylinder before compression, and then compressed by the piston. The piston is equipped with a piston ring, and for so-called oil-free compressors used without lubrication, PTFE composite materials, mainly composed of PTFE (polytetrafluoroethylene), such as those described in Patent Document 1, are widely used as the piston ring.

[0004] Japanese Patent Application Publication No. 2014-234775

[0005] Incidentally, while PTFE has the advantage of a low coefficient of friction, it also has the problem of high wear. Therefore, when using PTFE or PTFE composite materials, it is necessary to reduce wear while taking advantage of PTFE's low coefficient of friction.

[0006] Furthermore, when two sliding members (i.e., a combination of sliding members) slide against each other, the wear performance varies greatly depending on the mating material. However, while Patent Document 1 states that the cylinder that serves as the mating material for the piston ring is made of metal, the specific material name is not specified, and it cannot be said that the combination with the mating material has been adequately considered.

[0007] This invention has been made in view of the above problems, and aims to provide a combination of sliding members that can reduce wear and damage between two sliding members used without lubrication and maintain excellent performance. Furthermore, this invention aims to provide a gas compressor that includes a cylinder and piston ring made of such a combination of sliding members, and that can stably perform a series of operations from gas intake to discharge over a long period of time.

[0008] To solve the above problems, the present invention provides the following combination of sliding members [1] and [2].

[0009] [1] A combination of sliding members comprising a first sliding member and a second sliding member used without lubrication, wherein the first sliding member is a sliding member on which a DLC film containing hydrogen is formed, and the second sliding member is a sliding member on which a DLC film not containing hydrogen is formed. [2] A combination of sliding members comprising a first sliding member and a second sliding member used without lubrication, wherein the first sliding member is a sliding member on which a DLC film containing hydrogen is formed, and the second sliding member is a sliding member on which a PVD film is formed.

[0010] Furthermore, a preferred embodiment relating to the combination of sliding members of the present invention consists of the configuration shown in [3] below.

[0011] [3] The combination of sliding members according to [2], characterized in that the PVD coating is a Cr-B-N coating or a Cr-B-Ti-V-Mn-Mo-N coating.

[0012] Furthermore, in order to solve the above problems, the present invention provides the gas compressor described in [4] below.

[0013] [4] A gas compressor having a cylinder and a piston ring, or a cylinder liner and a piston ring, characterized in that the combination of the cylinder and the piston ring, or the cylinder liner and the piston ring, is a combination of sliding members described in any one of [1] to [3].

[0014] Furthermore, a preferred embodiment of the gas compressor of the present invention consists of the configurations described in [5] to [7] below.

[0015] [5] The gas compressor according to [4], characterized in that the first sliding member is the cylinder or the cylinder liner, and the second sliding member is the piston ring. [6] The gas compressor according to [4], for compressing air or hydrogen gas. [7] The gas compressor according to [5], for compressing air or hydrogen gas.

[0016] According to the present invention, it is possible to provide a combination of sliding members that can reduce wear and damage between two sliding members used without lubrication, and maintain excellent performance. Furthermore, it is possible to provide a gas compressor equipped with a cylinder and piston ring made up of such a combination of sliding members, which can stably perform a series of operations from gas intake to discharge over a long period of time.

[0017] Figure 1 is a schematic perspective view of the test apparatus (block-on-ring) used to evaluate the sliding properties in <Test 1> and <Test 2>. Figure 2 is a graph showing the results of (Test 1-1) in <Test 1>, showing the "sliding time - friction coefficient" when the rotating piece is made of "gray cast iron" and the fixed piece is made of "hydrogen-free DLC coated material". Figure 3 is a graph showing the results of (Test 1-2) in <Test 1>, showing the "sliding time - friction coefficient" when the rotating piece is made of "gray cast iron" and the fixed piece is made of "Cr-B-N coated material". Figure 4 is a graph showing the results of (Test 1-3) in <Test 1>, showing the "sliding time - friction coefficient" when the rotating piece is made of "gray cast iron" and the fixed piece is made of "PEEK". Figure 5 is a graph showing the results of (Test 1-4) in <Test 1>, showing the "sliding time - friction coefficient" when the rotating piece is made of "gray cast iron" and the fixed piece is made of "PTFE". Figure 6 is a graph showing the results of (Test 1-5) in <Test 1>, showing the "sliding time - friction coefficient" when the rotating piece is made of "Cr plated product" and the fixed piece is made of "hydrogen-free DLC coated product". Figure 7 is a graph showing the results of (Test 1-6) in <Test 1>, showing the "sliding time - friction coefficient" when the rotating piece is made of "Cr plated product" and the fixed piece is made of "Cr-B-N coated product". Figure 8 is a graph showing the results of (Test 1-7) in <Test 1>, showing the "sliding time - friction coefficient" when the rotating piece is made of "Cr plated product" and the fixed piece is made of "PEEK". Figure 9 is a graph showing the results of (Test 1-8) in <Test 1>, and is a graph showing the "sliding time - friction coefficient" when the rotating piece is a "Cr plated product" and the fixed piece is made of "PTFE". Figure 10 is a graph showing the results of (Test 1-9) in <Test 1>, and is a graph showing the "sliding time - friction coefficient" when the rotating piece is a "hydrogen-containing DLC ​​coated product" and the fixed piece is a "hydrogen-free DLC coated product". Figure 11 is a graph showing the results of (Test 1-10) in <Test 1>, and is a graph showing the "sliding time - friction coefficient" when the rotating piece is a "hydrogen-containing DLC ​​coated product" and the fixed piece is a "Cr-B-N coated product".Figure 12 is a graph showing the results of (Test 1-11) in <Test 1>, and is a graph showing the "sliding time - friction coefficient" when the rotating piece is a "hydrogen-containing DLC ​​coated product" and the fixed piece is made of "PEEK". Figure 13 is a graph showing the results of (Test 1-12) in <Test 1>, and is a graph showing the "sliding time - friction coefficient" when the rotating piece is a "hydrogen-containing DLC ​​coated product" and the fixed piece is made of "PTFE". Figure 14 is a graph showing the results of (Test 2-1) in <Test 2>, and is a graph showing the "sliding time - friction coefficient" when the rotating piece is a "hydrogen-containing DLC ​​coated product" and the fixed piece is a "hydrogen-free DLC coated product". Figure 15 is a graph showing the results of (Test 2-2) in <Test 2>, showing the "sliding time - coefficient of friction" when the rotating piece is a "hydrogen-containing DLC ​​coated product" and the fixed piece is a "Cr-B-N coated product". Figure 16 is a graph showing the results of (Test 2-3) in <Test 2>, showing the "sliding time - coefficient of friction" when the rotating piece is a "hydrogen-containing DLC ​​coated product" and the fixed piece is a "Cr-B-Ti-V-Mn-Mo-N coated product". Figure 17 is a schematic perspective view of the test apparatus (ball-on-disk) used to evaluate the sliding properties in <Test 3>. Figure 18 is a graph showing the results of (Test 3-1) in <Test 3>, showing the "sliding time - coefficient of friction" when the test piece is a "Cr-B-N coated product" and the ball is made of "SUJ2". Figure 19 is a graph showing the results of (Test 3-2) in <Test 3>, and is a graph showing the "sliding time - friction coefficient" when the test piece is a "hydrogen-free coated product" and the ball is a "hydrogen-containing DLC ​​coated product". Figure 20 is a graph showing the results of (Test 3-3) in <Test 3>, and is a graph showing the "sliding time - friction coefficient" when the test piece is a "Cr-B-N coated product" and the ball is a "hydrogen-containing DLC ​​coated product". Figure 21 is a schematic cross-sectional view showing an example of the gas compressor of the present invention, and is a diagram showing the intake state. Figure 22 is a diagram showing the compression state of the gas compressor shown in Figure 21. Figure 23 is a diagram showing the discharge state of the gas compressor shown in Figure 21.

[0018] The inventors of this invention have diligently studied sliding materials that can replace the above-mentioned PTFE or PTFE composite materials, as well as combinations of two sliding members, in order to reduce wear and friction and improve durability, and have completed the present invention.

[0019] Embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the embodiments described below, and can be modified and implemented as necessary without departing from the spirit of the invention.

[0020] [1. Combination of sliding members] The present invention relates to a combination of sliding members comprising a first sliding member and a second sliding member used without lubrication.

[0021] <Test 1> To evaluate the sliding properties between the two sliding members, the test apparatus (block-on-ring) shown in Figure 1 was used. As shown in the figure, the first sliding member was the rotating piece 10, and the second sliding member was the fixed piece 1. In an unlubricated and atmospheric (air) environment (under unlubricated conditions), the fixed piece 1 was pressed against the rotating piece 10, which was rotating at a rotational speed of 1 m / s (sec), with a pressing force of 98.1 N, and the sliding continued for 600 seconds (s), during which the change in the coefficient of friction was measured. The maximum value, minimum value, average value, and σ of the coefficient of friction were determined.

[0022] Furthermore, the presence of abnormal noises during sliding was judged by the tester's hearing, and determined as follows: "○": No abnormal noise... quieter than the operating noise of the test device, at an inaudible level. "△": Medium abnormal noise... a sound is audible, but no vibration is felt when touching the test device. "×": Loud abnormal noise... a sound is clearly audible, and vibration is felt when touching the test device.

[0023] Furthermore, the specific wear amount (mm) can be calculated from the dimensional change before and after sliding. ３ We calculated the value of / Nm.

[0024] For the "first sliding member" which will become the rotating piece 10, the sliding members (A) to (C) below were prepared, and for the "second sliding member" which will become the fixed piece 1, the sliding members (D) to (G) below were prepared.

[0025] (A) "Gray cast iron" ・Material: Gray cast iron (FC250) ・No coating

[0026] (B) "Cr-plated coated product" ・A Cr-plated coating with a thickness of 80 μm is formed on a base material (material: SUJ2) by electroplating ・Coating hardness: HV900

[0027] (C) "Hydrogen-containing DLC coated product" ・A sliding member having a hydrogen-containing DLC coating formed thereon ・A Cr intermediate layer with a thickness of 1.5 μm is formed on a base material (material: equivalent to JIS standard SUJ2), and a DLC coating containing 20 to 30 atomic% of hydrogen (i.e., hydrogen-containing DLC coating) with a thickness of 2 to 5 μm is formed thereon by plasma CVD method ・Coating hardness: Suitable range: HV900 to HV1200 (provided that in this test example, a "hydrogen-containing DLC coated product" with HV1000 is used)

[0028] (D) "Hydrogen-free DLC coated product" ・A sliding member having a DLC coating that does not contain hydrogen (based on film formation conditions, hydrogen is hardly contained, but substantially 0.01 to 7 atomic% of hydrogen is included) formed thereon ・A Cr intermediate layer with a thickness of 0.2 μm is formed on a base material (material: equivalent to JIS standard SUS410J1), and a DLC coating substantially free of hydrogen (i.e., hydrogen-free DLC coating) with a thickness of 5.5 μm is formed thereon by arc ion plating method ・Coating hardness: Suitable range: HV1000 to HV3000 (provided that in this test example, a "hydrogen-free DLC coated product" with HV1300 is used) ・The above-mentioned hydrogen-free DLC coating: the carbon bond sp ２ bond and the carbon bond sp represented by diamond ３ a film in which bonds are mixed ・sp ２ component ratio: 0.05 to 0.8 (provided that sp ２ component ratio refers to the graphite component (sp ２ ) and diamond component (sp ３ ) with respect to the graphite component (sp ２ ), which is [sp ２ / (sp ２ +sp ３ )], which represents the above component ratio.)

[0029] The hydrogen-free DLC film described above, as measured by TEM-EELS which combines transmission electron microscopy (TEM) with electron energy loss spectroscopy (EELS), has sp ２ component ratio preferably in the range of 5% or more and 80% or less. sp ２ If the component ratio is less than 5%, the diamond component (sp ３ ) becomes dominant, so although the film structure is dense, it has low toughness, which is not favorable for forming a hydrogen-free DLC film. sp ２ If the component ratio exceeds 80%, the graphite component (sp ２ ) becomes dominant, which makes it difficult to form a hydrogen-free DLC film and is thus not preferable. Such covalent bond ratio can be measured using an EELS analyzer (Model 863GIF Tridiem, manufactured by Gatan). This measurement can be performed according to the following procedures (a) to (e):

[0030] (a) Measure an EELS spectrum using the EELS analyzer. For the measured EELS spectrum, fit the region before the peak with a linear function and fit the region after the peak with a cubic function, then normalize the peak intensity. (b) Thereafter, the data is compared with diamond data and graphite data, energy calibration is performed by aligning the peak start positions. (c) For the calibrated data, calculate the area within the range of 280 eV to 310 eV. (d) Separate into two peaks within the range of 280 eV to 295 eV (one is the sp ２ peak, and the other is the peak of CH or amorphous carbon), then calculate the peak area around 285 eV. (e) Obtain the area within the range of 280 eV to 310 eV from (c) above, and the peak area around 285 eV from (d) above. For this area ratio, set graphite as 100 and diamond as 0, and obtain the sp ２ component ratio from the relative value. The value obtained in this manner is taken as the sp ２ component ratio.

[0031] (E) "Cr-B-N coated product" - A sliding member on which a PVD coating has been formed, a type of PVD coating in which B is added to Cr-N - A porous columnar crystal structure with a thickness of 5 μm is formed on a base material (material: equivalent to JIS standard SUS410J1), and a PVD coating with a thickness of 15 μm, in which B is added to Cr-N (i.e., a Cr-B-N coating), is formed on it by the PVD method - Coating hardness... Suitable range: HV1600 to HV2000 (however, in this test example, a "Cr-B-N coated product" with HV1800 was used) - PVD coating composition... B: 1 to 3 mass%, N: 34 to 40 mass%, Cr: remainder

[0032] (F) "Made of PTFE" ・Material: PTFE (Polytetrafluoroethylene) ・No coating

[0033] (G) "Made of PEEK" ・Material: PEEK (polyetheretherketone) ・No coating

[0034] Then, two of the above-mentioned sliding materials were combined as appropriate to form the following combinations of sliding members.

[0035] (Test 1-1... Rotating piece 10: Gray cast iron, Fixed piece 1: Hydrogen-free DLC coated product) In the test apparatus shown in Figure 1, the rotating piece 10 was made of "gray cast iron" and the fixed piece 1 was made of "hydrogen-free DLC coated product" to perform a sliding performance test. Figure 2 shows a graph of the change in the coefficient of friction with respect to sliding time (s). Also, specific wear amount (mm) ３ Table 1 summarizes the friction coefficient (in Nm), its maximum, minimum, average, and σ values, the abnormal noise determination, and the compatibility determination of the two sliding members, which is an overall judgment based on these results.

[0036] Furthermore, the "compatibility judgment" was determined by comprehensively considering these results, with "○" indicating good compatibility between the two sliding members and "×" indicating poor compatibility between the two sliding members (the same applies hereafter).

[0037]

[0038] (Test 1-2... Rotating piece 10: Gray cast iron, Fixed piece 1: Cr-B-N coated) In the test apparatus shown in Figure 1, the rotating piece 10 was made of "gray cast iron" and the fixed piece 1 was made of "Cr-B-N coated" to perform a sliding performance test. Figure 3 shows a graph illustrating the change in the coefficient of friction with respect to sliding time (s). Also, specific wear amount (mm) ３ Table 2 summarizes the friction coefficient (in Nm), its maximum, minimum, average, and σ values, the abnormal noise determination, and the compatibility determination of the two sliding members, which is an overall judgment based on these results.

[0039]

[0040] (Test 1-3... Rotating piece 10: Gray cast iron, Fixed piece 1: PEEK) The rotating piece 10 of the test apparatus in Figure 1 was made of "gray cast iron" and the fixed piece 1 was made of "PEEK" to perform a sliding performance test. Figure 4 shows a graph of the change in the coefficient of friction with respect to sliding time (s). Also, specific wear amount (mm) ３ Table 3 summarizes the friction coefficient (in Nm), its maximum, minimum, average, and σ values, the abnormal noise determination, and the compatibility determination of the two sliding members, which is an overall judgment based on these results.

[0041]

[0042] (Test 1-4... Rotating piece 10: Gray cast iron, Fixed piece 1: PTFE) In the test apparatus shown in Figure 1, the rotating piece 10 was made of "gray cast iron" and the fixed piece 1 was made of "PTFE" to conduct a sliding performance test. Figure 5 shows a graph illustrating the change in the coefficient of friction with respect to sliding time (s). Also, specific wear amount (mm) ３ Table 4 summarizes the friction coefficient (in Nm), its maximum, minimum, average, and σ values, the abnormal noise determination, and the compatibility determination of the two sliding members, which is an overall judgment based on these results.

[0043]

[0044] (Test 1-5... Rotating piece 10: Cr-plated product, Fixed piece 1: Hydrogen-free DLC-coated product) In the test apparatus shown in Figure 1, the rotating piece 10 was a "Cr-plated product" and the fixed piece 1 was a "Hydrogen-free DLC-coated product" to perform a sliding performance test. Figure 6 shows a graph of the change in the coefficient of friction with respect to sliding time (s). Also, specific wear amount (mm)３ Table 5 summarizes the friction coefficient (in Nm), its maximum, minimum, average, and σ values, the abnormal noise determination, and the compatibility determination of the two sliding members, which is an overall judgment based on these results.

[0045]

[0046] (Test 1-6... Rotating piece 10: Cr-plated product, Fixed piece 1: Cr-B-N coated product) In the test apparatus shown in Figure 1, the rotating piece 10 was a "Cr-plated product" and the fixed piece 1 was a "Cr-B-N coated product" to perform a sliding performance test. Figure 7 shows a graph of the change in the coefficient of friction with respect to sliding time (s). Also, specific wear amount (mm) ３ Table 6 summarizes the friction coefficient (in Nm), its maximum, minimum, average, and σ values, the abnormal noise determination, and the compatibility determination of the two sliding members, which is an overall judgment based on these results.

[0047]

[0048] (Test 1-7... Rotating piece 10: Cr plated, Fixed piece 1: PEEK) The rotating piece 10 of the test apparatus in Figure 1 was made of "Cr plated material" and the fixed piece 1 was made of "PEEK" to perform a sliding performance test. Figure 8 shows a graph of the change in the coefficient of friction with respect to sliding time (s). Also, specific wear amount (mm) ３ Table 7 summarizes the friction coefficient (in Nm), its maximum, minimum, average, and σ values, the abnormal noise determination, and the compatibility determination of the two sliding members, which is an overall judgment based on these results.

[0049]

[0050] (Test 1-8... Rotating piece 10: Cr-plated, Fixed piece 1: PTFE) In the test apparatus shown in Figure 1, the rotating piece 10 was made of "Cr-plated material" and the fixed piece 1 was made of "PTFE" to conduct a sliding performance test. Figure 9 shows a graph of the change in the coefficient of friction with respect to sliding time (s). Also, specific wear amount (mm) ３ Table 8 summarizes the friction coefficient (in Nm), its maximum, minimum, average, and σ values, the abnormal noise determination, and the compatibility determination of the two sliding members, which is an overall judgment based on these results.

[0051]

[0052] (Test 1-9... Rotating piece 10: Hydrogen-containing DLC ​​coated product, Fixed piece 1: Hydrogen-free DLC coated product) In the test apparatus shown in Figure 1, the rotating piece 10 was made of a "hydrogen-containing DLC ​​coated product" and the fixed piece 1 was made of a "hydrogen-free DLC coated product" to perform a sliding performance test. Figure 10 shows a graph of the change in the coefficient of friction with respect to sliding time (s). Also, specific wear amount (mm) ３ Table 9 summarizes the friction coefficient (in Nm), its maximum, minimum, average, and σ values, the abnormal noise determination, and the compatibility determination of the two sliding members, which is an overall judgment based on these results.

[0053]

[0054] (Test 1-10... Rotating piece 10: Hydrogen-containing DLC ​​coated product, Fixed piece 1: Cr-B-N coated product) In the test apparatus shown in Figure 1, the rotating piece 10 was made of "hydrogen-containing DLC ​​coated product" and the fixed piece 1 was made of "Cr-B-N coated product" to perform a sliding performance test. Figure 11 shows a graph illustrating the change in the coefficient of friction with respect to sliding time (s). Also, specific wear amount (mm) ３ Table 10 summarizes the friction coefficient (in Nm), its maximum, minimum, average, and σ values, the abnormal noise determination, and the compatibility determination of the two sliding members, which is an overall judgment based on these results.

[0055]

[0056] (Test 1-11... Rotating piece 10: Hydrogen-containing DLC ​​coated product, Fixed piece 1: PEEK) A sliding performance test was conducted using the rotating piece 10 of the test apparatus in Figure 1 as a "hydrogen-containing DLC ​​coated product" and the fixed piece 1 as "PEEK". Figure 12 shows a graph of the change in the coefficient of friction with respect to sliding time (s). Also, specific wear amount (mm) ３ Table 11 summarizes the friction coefficient (in Nm), its maximum, minimum, average, and σ values, the abnormal noise determination, and the compatibility determination of the two sliding members, which is an overall judgment based on these results.

[0057]

[0058] (Test 1-12... Rotating piece 10: Hydrogen-containing DLC ​​coated product, Fixed piece 1: Made of PTFE) In the test apparatus shown in Figure 1, the rotating piece 10 was made of "hydrogen-containing DLC ​​coated product" and the fixed piece 1 was made of "PTFE" to conduct a sliding performance test. Figure 13 shows a graph illustrating the change in the coefficient of friction with respect to sliding time (s). Also, specific wear amount (mm) ３ Table 12 summarizes the friction coefficient (in Nm), its maximum, minimum, average, and σ values, the abnormal noise determination, and the compatibility determination of the two sliding members, which is an overall judgment based on these results.

[0059]

[0060] The results of (Test 1-1) to (Test 1-12) can be summarized for each of the 10 rotating pieces as follows.

[0061] <When the rotating piece 10 (first sliding member) is made of gray cast iron>

[0062] <When the rotating piece 10 (first sliding member) is a "Cr-plated product">

[0063] <When the rotating piece 10 (first sliding member) is a "hydrogen-containing DLC ​​coated product">

[0064] Based on the results in Tables 13 to 15 above, if "PEEK" or "PTFE" is used as one of the sliding members (the second sliding member), the amount of wear is excessive regardless of which sliding member is used as the other sliding member (the first sliding member) in the pair. Therefore, it can be said that it is undesirable to use either of these materials as one of the sliding members when forming a combination of sliding members.

[0065] Similarly, if "gray cast iron" is used as one of the sliding members (the first sliding member), the amount of wear will be excessive regardless of which sliding member is used as the other sliding member (the second sliding member) in the pair. Therefore, it can be said that it is undesirable as one of the sliding members when forming a combination of sliding members.

[0066] Furthermore, if a "Cr-plated product" is used as one of the sliding members (the first sliding member), it is preferable to combine it with a "hydrogen-free DLC-coated product" as the other sliding member (the second sliding member) (see Table 14).

[0067] Furthermore, when using a "hydrogen-containing DLC ​​coated product" as one of the sliding members (the first sliding member), it is preferable to combine it with a "hydrogen-free DLC coated product" or a "Cr-B-N coated product" as the other sliding member (the second sliding member). In particular, since the "hydrogen-containing DLC ​​coated product" has a similar coefficient of friction but significantly less specific wear, it is preferable to combine it with a "Cr-B-N coated product" rather than a "hydrogen-free DLC coated product" (see Table 15).

[0068] Furthermore, in the "hydrogen-free DLC coated products," "Cr-B-N coated products," and "hydrogen-containing DLC ​​coated products," the base material is always metal, but there are no restrictions on the type of metal. Also, there are no restrictions on the amount of Cr, N, or B added in the coating of the "Cr-B-N coated products," nor on the hydrogen content in the coating of the "hydrogen-containing DLC ​​coated products."

[0069] Furthermore, in the "hydrogen-free DLC coated product," "Cr-B-N coated product," and "hydrogen-containing DLC ​​coated product," the film quality differs depending on the material of the coating, and the optimal film thickness also differs. For each coating, if the coating is too thin, there may be areas where the coating has not been formed, or the durability may be insufficient. Conversely, if the coating is too thick, it may be difficult to form the coating, or the coating may be damaged or peeled off due to the shear force applied during sliding. Specifically, the film thickness of the "hydrogen-free DLC coated product" is preferably 1 μm or more, and more preferably 4 μm or more. In the "Cr-B-N coated product," the film thickness is preferably 5 μm or more, and more preferably 10 to 25 μm. In the "hydrogen-containing DLC ​​coated product," the film thickness is preferably 0.5 μm or more, and more preferably 2 μm or more. From this, it can be said that while it is difficult to create thick films for "hydrogen-free DLC coated products" and "hydrogen-containing DLC ​​coated products," it is easy to create thick films for "Cr-B-N coated products," which is advantageous in terms of durability.

[0070] Furthermore, each coating may be modified to form a base layer or to roughen the surface of the base material.

[0071] Based on the results of <Test 1>, it can be said that any of the following combinations of sliding members (1) to (3) are preferable: (1) A combination of a sliding member with a Cr plating film (i.e., a Cr-plated product) and a sliding member with a hydrogen-free DLC film (i.e., a hydrogen-free DLC film product) (2) A combination of a sliding member with a hydrogen-containing DLC ​​film (i.e., a hydrogen-containing DLC ​​film product) and a sliding member with a hydrogen-free DLC film (i.e., a hydrogen-free DLC film product) (3) A combination of a sliding member with a hydrogen-containing DLC ​​film (i.e., a hydrogen-containing DLC ​​film product) and a sliding member with a Cr-B-N film (i.e., a Cr-B-N film product)

[0072] <Test 2> In <Test 1> above, the sliding performance was evaluated over a relatively short period of 600 seconds (s). In <Test 2>, the test was conducted over a longer period of 7 hours (i.e., 25,200 seconds) to evaluate the durability of the sliding performance.

[0073] The test apparatus and test conditions used in <Test 2> were the same as those in <Test 1>, except for the sliding time. Specifically, as shown in Figure 1, the first sliding member was a rotating piece 10 and the second sliding member was a fixed piece 1. The fixed piece 1 was pressed against the rotating piece 10, which was rotating at a rotational speed of 1 m / s (sec), with a pressing force of 98.1 N in an unlubricated atmospheric (air) environment (under unlubricated conditions), and the sliding continued for 7 hours (i.e., 25,200 seconds), during which the change in the coefficient of friction was measured.

[0074] (Test 2-1... Rotating piece 10: Hydrogen-containing DLC ​​coated product, Fixed piece 1: Hydrogen-free DLC coated product) In the test apparatus shown in Figure 1, the rotating piece 10 was made of a "hydrogen-containing DLC ​​coated product" and the fixed piece 1 was made of a "hydrogen-free DLC coated product" to perform a sliding performance test. Details of the "hydrogen-containing DLC ​​coated product" and the "hydrogen-free DLC coated product" are the same as those described in "(C) 'Hydrogen-containing DLC ​​coated product'" and "(D) 'Hydrogen-free DLC coated product'" in <Test 1> above, so the explanation is omitted. Figure 14 shows a graph of the change in the coefficient of friction with respect to the sliding time (s). From the results in Figure 14, it can be seen that although a change in the coefficient of friction is observed up to about 3000 seconds from the start of the sliding test, the coefficient of friction remains low and stable thereafter, indicating excellent durability of the sliding performance.

[0075] (Test 2-2... Rotating piece 10: Hydrogen-containing DLC ​​coated product, Fixed piece 1: Cr-B-N coated product) The rotating piece 10 of the test apparatus in Figure 1 was a "hydrogen-containing DLC ​​coated product," and the fixed piece 1 was a sliding member with a PVD coating formed on it, a type of PVD coating in which B is added to Cr-N, and a sliding performance test was conducted. Details of the "hydrogen-containing DLC ​​coated product" and the "Cr-B-N coated product" are the same as those described in "(C) "Hydrogen-containing DLC ​​coated product"" and "(E) "Cr-B-N coated product"" in <Test 1>, respectively, so the explanation is omitted. Figure 15 shows a graph showing the change in the coefficient of friction with respect to sliding time (s). From the results in Figure 15, it can be seen that the coefficient of friction remained low and stable from the beginning of the sliding test, indicating excellent durability of the sliding performance.

[0076] (Test 2-3... Rotating piece 10: Hydrogen-containing DLC ​​coated product, Fixed piece 1: Cr-B-Ti-V-Mn-Mo-N coated product) The rotating piece 10 of the test apparatus in Figure 1 was a "hydrogen-containing DLC ​​coated product," and the fixed piece 1 was a sliding member with a PVD coating formed on it, a type of PVD coating in which B is added to Cr-N, called a "Cr-B-Ti-V-Mn-Mo-N coated product," and a sliding performance test was conducted. Details of the "hydrogen-containing DLC ​​coated product" are the same as those in "(C) "Hydrogen-containing DLC ​​coated product"" in <Test 1> above, so the explanation is omitted. Details of the "Cr-B-Ti-V-Mn-Mo-N coated product" are as follows. (H) "Cr-B-Ti-V-Mn-Mo-N coated product" - A sliding member on which a PVD coating has been formed, which is a type of PVD coating in which B is added to Cr-N. - A porous columnar crystal structure with a thickness of 5 μm is formed on a base material (material: equivalent to JIS standard SUS410J1), and a PVD coating with a thickness of 15 μm is formed on it by the PVD method, in which B, Ti, V, Mn and Mo are added to Cr-N (i.e., a Cr-B-Ti-V-Mn-Mo-N coating). - Coating hardness... Preferred range: HV1550 to HV1950 (however, in this test example, a "Cr-B-Ti-V-Mn-Mo-N coated product" with HV1750 is used). PVD coating composition: B: 0.1-1.5 mass%, Ti: 0.05-1.5 mass%, V: 0.05-1.0 mass%, Mn: 0.01-2 mass%, Mo: 0.01-2 mass%, N: 30-40 mass%, Cr: remainder. Figure 16 shows a graph illustrating the change in the coefficient of friction with respect to sliding time (s). From the results in Figure 16, it can be seen that the coefficient of friction remained low and stable from the beginning of the sliding test in Figure 15, indicating excellent durability of the sliding performance.

[0077] Based on the results of <Test 2>, it can be said that any of the following combinations of sliding members (4) to (6) are particularly preferred. (4) A combination of a sliding member with a hydrogen-containing DLC ​​coating (i.e., a hydrogen-containing DLC ​​coated product) and a sliding member with a hydrogen-free DLC coating (i.e., a hydrogen-free DLC coated product) (5) A sliding member with a hydrogen-containing DLC ​​coating (i.e., a hydrogen-containing DLC ​​coated product) and a sliding member with a Cr-N-B coating (i.e., a sliding member with a PVD coating, where the PVD coating is a coating in which B is added to Cr-N / Cr-B-N coated product) (6) A sliding member having a hydrogen-containing DLC ​​coating (i.e., a hydrogen-containing DLC ​​coated product) and a sliding member having a Cr-B-Ti-V-Mn-Mo-N coating (i.e., a sliding member having a PVD coating, wherein the PVD coating is a coating in which B is added to Cr-N / a Cr-B-Ti-V-Mn-Mo-N coated product)

[0078] <Test 3> In <Test 1> and <Test 2> above, the sliding performance was verified without lubrication and in an atmospheric environment, but in <Test 3>, the sliding performance was verified without lubrication and in a hydrogen (H) environment. ２ The sliding performance in the atmosphere was verified. The test apparatus (ball-on-disk) shown in Figure 17 was used for the test. As shown in the figure, a test piece 52 was fixed on the surface of the disk 50, and with a load applied by a weight 55, a ball 60 made of JIS standard SUJ2 was placed on the surface of the test piece 52, and hydrogen gas was sprayed onto the surface of the test piece 52 from a gas nozzle 65 while the test piece 52 was rotated together with the disk 50, and the change in the coefficient of friction with respect to the rotation time of the disk 50, i.e., the sliding time (s), was measured.

[0079] Also, hydrogen gas (H) is released from the gas nozzle 65. ２ Without spraying (the substance), the change in the coefficient of friction with respect to the sliding time (s) of the test piece 52 in an atmospheric environment was also measured.

[0080] Three combinations of test specimen 52 and ball 60 were prepared: (Test 3-1) to (Test 3-3). (Test 3-1: Test specimen 52: Cr-B-N coated product, ball 60: SUJ2) (Test 3-2: Test specimen 52: Hydrogen-free DLC coated product, ball 60: Hydrogen-containing DLC ​​coated product) (Test 3-3: Test specimen 52: Cr-B-N coated product, ball 60: Hydrogen-containing DLC ​​coated product)

[0081] The materials used for each test specimen in (Test 3-1) to (Test 3-3) described above are the same as those described in <Test 1> above.

[0082] Furthermore, the load applied by the weight 55 was set to 3N in (Test 3-1) and 5N in (Test 3-2) and (Test 3-3) respectively. In addition, in all of (Test 3-1) to (Test 3-3), the rotational speed of the disk 50 was set to a linear velocity of 754 mm / s, and the test time was set to 6 minutes and 40 seconds (i.e., 400 seconds). These tests were conducted by supplying hydrogen gas (H) from the gas nozzle 65. ２ The experiment was conducted in two scenarios: one where hydrogen gas was injected (i.e., under a hydrogen atmosphere) and one where hydrogen gas was not injected (i.e., under an atmospheric atmosphere).

[0083] The change in the coefficient of friction with respect to sliding time (s) in (Test 3-1) is shown in Figure 18, the change in the coefficient of friction with respect to sliding time (s) in (Test 3-2) is shown in Figure 19, and the change in the coefficient of friction with respect to sliding time (s) in (Test 3-3) is shown in Figure 20, all of which are graphed.

[0084] As can be seen by comparing the results in Figures 18 to 20, the combination of test piece 52 and ball 60 in (Test 3-2) and (Test 3-3), which satisfy the provisions of the present invention, exhibits excellent sliding performance not only in the absence of lubrication and hydrogen gas injection (i.e., in an atmospheric environment without lubrication) but also in the absence of lubrication and hydrogen gas injection (i.e., in a hydrogen atmosphere without lubrication).

[0085] [2. Gas Compressor] The present invention also relates to a gas compressor in which a cylinder and a piston ring, or a cylinder liner and a piston ring, are combinations of the above-mentioned sliding members. There are no restrictions on the type of gas compressor or the configuration of the device, and for example, the gas compressor 100 shown in Figures 21 to 23 can be exemplified. Figure 21 is a diagram showing the intake state of the gas compressor, Figure 22 is a diagram showing the compression state of the gas compressor, and Figure 23 is a diagram showing the discharge state of the gas compressor.

[0086] The gas compressor 100 includes a bottomed cylindrical cylinder 111, a piston 112 inserted into the cylinder 111, and a drive device (not shown) that reciprocates the piston 112 in the axial direction of the cylinder 111. A connecting rod 121 is connected to the piston 112, and the piston 112 is connected to the drive device (not shown) via the connecting rod 121 and a crankshaft (not shown).

[0087] Near the bottom 111a of the cylinder 111, an air intake port 115 and an exhaust port 116 are provided, and an air intake valve 117 and an exhaust valve 118, which are configured to be openable and closable, are attached to the air intake port 115 and the exhaust port 116, respectively.

[0088] Multiple piston rings 113a to 113e (five in the example shown) are attached to the piston 112 between it and the inner circumferential surface of the cylinder 111, and these piston rings 113a to 113e constitute a piston ring group 114. The piston ring group 114 slides against the inner circumferential surface of the cylinder 111. As the piston 112 reciprocates, each of the piston rings 113a to 113e slides against the inner circumferential surface of the cylinder 111.

[0089] In the gas compressor 100 configured in this way, as shown in Figure 21, when the piston 112 is lowered to the bottom dead center, the intake valve 117 is opened and the exhaust valve 118 is closed, and gas 119 is supplied into the cylinder through the supply port 115.

[0090] Next, as shown in Figure 22, when the piston 112 is raised, both the intake valve 117 and the exhaust valve 118 close, and the pressure of the gas 119 inside the cylinder increases.

[0091] Then, as shown in Figure 23, when the piston 112 is raised further to reach top dead center, the exhaust valve 118 is opened and the compressed gas 119 is discharged through the exhaust port 116.

[0092] In the present invention, by applying the cylinder 111 (or its inner wall surface) and the piston rings 113a to 113e to the sliding members in the preferred combination described above, a series of operations from intake to discharge of gas 119 can be performed stably over a long period of time. In addition, in the present invention, for example, a cylinder liner (not shown) used by being inserted inside a cylinder block and the piston rings 113a to 113e may be applied to the sliding members in the preferred combination described above.

[0093] Furthermore, hydrogen-free DLC and PVD are deposited by arc ion plating, making it difficult to deposit them on the inner surface of a cylinder. In contrast, hydrogen-containing DLC ​​deposited by CVD is less affected by shape factors because it is deposited using gas. Therefore, it is preferable that the first sliding member is a cylinder and the second sliding member is a piston ring.

[0094] In this embodiment, materials commonly used for piston rings can be used. For example, martensitic stainless steel, austenitic stainless steel, chromium manganese steel, chromium vanadium steel, silicon chromium steel, spring steel, 10Cr steel, 8Cr steel, etc. can be used.

[0095] Furthermore, as can be understood from the results of <Test 3> above, the gas compressor of the present invention is used without lubrication and is useful for compressing air or hydrogen gas, and can be suitably used, for example, as a hydrogen gas compressor in a hydrogen station.

[0096] Furthermore, the term "hydrogen gas" as used in this specification refers to 100% H ２Furthermore, it may also be a gas containing 50% or more by volume of hydrogen, or a mixed gas mainly composed of hydrogen and containing hydrocarbon gases, etc.

[0097] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to these examples. It is clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these will naturally also fall within the technical scope of the present invention. Furthermore, the components of the above embodiments may be combined in any way without departing from the spirit of the invention.

[0098] This application is based on Japanese Patent Application No. 2025-030595 filed on February 27, 2025, and its contents are incorporated herein by reference.

[0099] 1 Fixed piece 10 Rotating piece 50 Disc 52 Test piece 55 Weight 60 Ball 65 Gas nozzle 100 Gas compressor 111 Cylinder 112 Piston 113a-113e Piston ring 114 Piston ring group

Claims

1. A combination of sliding members comprising a first sliding member and a second sliding member used without lubrication, characterized in that the first sliding member is a sliding member having a DLC coating containing hydrogen, and the second sliding member is a sliding member having a DLC coating that does not contain hydrogen.

2. A combination of sliding members comprising a first sliding member and a second sliding member used without lubrication, characterized in that the first sliding member is a sliding member on which a DLC film containing hydrogen is formed, and the second sliding member is a sliding member on which a PVD film is formed.

3. The combination of sliding members according to claim 2, characterized in that the PVD coating is a Cr-B-N coating or a Cr-B-Ti-V-Mn-Mo-N coating.

4. A gas compressor having a cylinder and a piston ring, or a cylinder liner and a piston ring, characterized in that the combination of the cylinder and the piston ring, or the cylinder liner and the piston ring, is a combination of sliding members as described in any one of claims 1 to 3.

5. The gas compressor according to claim 4, characterized in that the first sliding member is the cylinder or the cylinder liner, and the second sliding member is the piston ring.

6. The gas compressor according to claim 4, for compressing air or hydrogen gas.

7. The gas compressor according to claim 5, for compressing air or hydrogen gas.

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