JP7623872B2 - Sliding materials and fluid machinery - Google Patents

Description

This disclosure relates to sliding materials and fluid machinery.

Reciprocating fluid machines (gas compressors, etc.) are known as fluid machines capable of compressing or expanding gas. Reciprocating fluid machines include normal piston type fluid machines and oscillating piston type fluid machines. The former type of fluid machine has a bearing at the compression/expansion chamber side end of the connecting rod and a piston supported by the bearing so that it can oscillate. The latter type of fluid machine does not have a bearing on the compression/expansion chamber side of the connecting rod and has a piston integrated with the connecting rod. Of these, in oscillating piston type fluid machines, gas is compressed by the piston reciprocating while oscillating within a metal cylinder. The piston has a sliding member that slides on the inner circumferential surface of the cylinder, and examples of the sliding member include a lip ring and a piston ring.

As a technology related to sliding members, Patent Document 1 describes "a piston for a cylinder, characterized in that in a cylinder device consisting of a cylinder and a piston that engages with the inner circumferential surface of the cylinder via a piston ring, the piston ring is formed on the outer circumferential surface of the piston by insert molding using a resin composition whose essential components are 60-80% by weight of polyphenylene sulfide (PPS) resin, 10-30% by weight of fluororesin, 2-10% by weight of spherical filler, and 2-10% by weight of fibrous filler."

Japanese Patent Application Publication No. 3-74681

The details will be described later with reference to the examples, but the technology described in Patent Document 1 leaves room for improvement in terms of wear resistance of the sliding members.
An object of the present disclosure is to provide a sliding member and a fluid machine having excellent wear resistance.

The sliding member of the present disclosure is a sliding member that comes into contact with a sliding surface, and includes a first member that is made of a first material containing a first base resin made of a resin other than a fluororesin and fluororesin particles and rod-shaped particles dispersed in the first base resin, and a second member that is arranged adjacent to the first member along the sliding direction of the sliding member on the sliding surface and that is made of a second base resin made of a fluororesin and a second material that contains a reinforcing agent dispersed in the second base resin. Other solutions will be described later in the description of the embodiment of the invention.

This disclosure provides a sliding member and fluid machinery with excellent wear resistance.

FIG. 2 is a cross-sectional view showing a sliding member of the first embodiment. FIG. FIG. 1A and 1B are diagrams illustrating a transfer film formed during sliding. 1 is a schematic diagram of a fluid machine including a sliding member according to a first embodiment; FIG. 11 is a cross-sectional view showing a sliding member of a second embodiment. FIG. 2 is a diagram illustrating a test method for a friction test. 1 is an energy dispersive X-ray analysis image of the surface of a test piece after a friction test. FIG. 1 is a diagram showing test results of wear volume and friction coefficient obtained in a friction test. FIG. 1 is a graph showing the correlation between the wear amount and friction coefficient obtained in a friction test and the content of fluororesin particles.

Below, a form for implementing the present disclosure (referred to as an embodiment) will be described with reference to the drawings. In the following description of one embodiment, other embodiments that can be applied to the one embodiment will also be described as appropriate. The present disclosure is not limited to the one embodiment below, and different embodiments can be combined with each other, or modified as desired without significantly impairing the effects of the present disclosure. In addition, the same symbols will be used for the same components, and duplicate descriptions will be omitted. Furthermore, components having the same functions will be given the same names. The contents shown are merely schematic, and for the sake of illustration, changes may be made from the actual configuration without significantly impairing the effects of the present disclosure, and some components may be omitted or modified between drawings.

Figure 1 is a cross-sectional view showing a sliding member 12 of the first embodiment. The sliding member 12 contacts a sliding surface 13, which is, for example, an inner wall surface of a metal member 11. In the illustrated example, the sliding member 12 reciprocates (moves up and down) up and down as indicated by the solid arrow while sliding on the sliding surface 13. The sliding member 12 is configured as, for example, a piston 40 (Figure 5). The sliding member 12 includes a first member 12a and a second member 12b.

Figure 2 is a cross-sectional view of the first member 12a. The first member 12a is made of a first material, which includes a first base resin 21 made of a resin other than fluororesin, and fluororesin particles 22 and rod-shaped particles 23 dispersed in the first base resin 21. The particles are preferably dispersed evenly throughout the first base resin 21, but may be unevenly distributed in some areas.

The first base resin 21 forms the outer shell of the first member 12a. The first base resin 21 is not particularly limited as long as it is made of a resin other than fluororesin and can function as the sliding member 12, but among them, a resin with excellent heat resistance and a low thermal expansion coefficient is preferable. Specific examples include polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyether sulfone (PES), phenolic resin (PF), polyimide (PI), etc., as well as modified forms of these. The first base resin 21 may be used alone or in any ratio and combination of two or more types.

The first base resin 21 preferably contains at least one of polyphenylene sulfide and polyether ether ketone. By containing these polymers, the heat resistance of the first member 12a can be improved.

When the fluororesin particles 22 slide on the sliding surface 13 (FIG. 1), the fluororesin is transferred to the sliding surface 13, forming a transfer film 14 (FIG. 4) on the sliding surface 13. The constituent material of the fluororesin particles 22 is not particularly limited as long as it is a fluororesin, and examples of the constituent material include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), etc. One type of constituent material of the fluororesin particles 22 may be used alone, or two or more types may be used in any ratio and combination.

The fluororesin particles 22 preferably contain at least one of polytetrafluoroethylene and tetrafluoroethylene-perfluoroalkylvinylether copolymer. The use of these polymers can promote the formation of a transfer film 14 on the sliding surface 13 (Figure 1) caused by the fluororesin particles 22.

The form in which the fluororesin particles 22 are contained is not particularly limited as long as it does not significantly impair the effects of the present disclosure, but for example, they can be in a particulate form (granular form). The particle size of these particles can be, for example, 5 μm or more and 200 μm or less. The particle size can be measured, for example, as an average particle size that can be measured using a laser diffraction particle size distribution measuring device.

The content of the fluororesin particles 22 is not particularly limited as long as it does not significantly impair the effects of the present disclosure, but is preferably 15% by mass or more and 30% by mass or less with respect to the first material. By setting the content in this range, excessive thermal expansion of the first member 12a caused by the fluororesin particles 22 can be suppressed, and the friction coefficient of the first member 12a against the sliding surface 13 (Figure 1) can be reduced. Furthermore, peeling of the transfer film 14 (Figure 4) caused by the fluororesin particles 22 can be suppressed. As a result, the wear resistance of the sliding member 12 can be particularly improved.

The rod-shaped particles 23 improve the strength of the first member 12a against stress, such as tensile stress, due to their rod-shaped form. The rod-shaped particles 23 can be made of any material as long as it does not significantly impair the effects of the present disclosure, but it is preferable for the rod-shaped particles 23 to contain at least one of carbon fiber and glass fiber. By using these fibers, the rod-shaped particles 23 can be made using easily available fibers.

The length and diameter of the rod-shaped particles 23 are not particularly limited as long as they do not significantly impair the effects of the present disclosure, but for example, the length can be, for example, 10 μm or more and 300 μm or less, and the diameter can be, for example, 1 μm or more and 30 μm or less. The length and diameter can be measured values in a cross-sectional microscope photograph of the first member 12a.

The amount of rod-shaped particles 23 contained is not particularly limited as long as it does not significantly impair the effects of the present disclosure, but can be, for example, 5% by mass or more and 20% by mass or less relative to the first material.

However, when the rod-shaped particles 23 contain carbon fibers, the carbon fiber content is preferably 5% by mass or more and 15% by mass or less with respect to the first material. In this way, the strength of the first member 12a against stresses such as shear stress can be improved.

Figure 3 is a cross-sectional view of the second member 12b. The second member 12b is made of a second material, which includes a second base resin 31 made of a fluororesin and a reinforcing agent 32 dispersed in the second base resin 31. The reinforcing agent 32 is preferably dispersed evenly throughout the second base resin 31, but may be unevenly distributed in some areas.

The second base resin 31 forms the outer shell of the second member 12b. The second base resin 31 is not particularly limited as long as it is a fluororesin and does not significantly impair the effects of the present disclosure. For example, the above-mentioned examples of the constituent materials of the fluororesin particles 22 (Figure 2) can be used. The second base resin 31 may be used alone or in any ratio and combination of two or more types.

The second base resin 31 preferably contains polytetrafluoroethylene. By containing polytetrafluoroethylene, it is possible to promote the formation of a transfer film 14 (FIG. 4) on the sliding surface 13 (FIG. 1) together with the fluororesin particles 22 (FIG. 2) in the first member 12a (FIG. 2).

The fluororesin particles 22 (FIG. 1) and the second base resin 31 are preferably made of the same type of fluororesin. In this way, the fluororesin particles 22 and the second base resin 31 can form a transfer film 14 of the same constituent material on the sliding surface 13, facilitating transfer.

The reinforcing agent 32 improves the strength of the second member 12b (particularly the second base resin 31) against stress such as shear stress. The specific material of the reinforcing agent 32 is not particularly limited as long as it does not significantly impair the effects of the present disclosure. The reinforcing agent 32 may be used alone or in any ratio and combination of two or more types.

The reinforcing agent 32 preferably contains at least one of copper, a copper alloy (an alloy mainly composed of copper, such as bronze), or carbon fiber. By using these materials, even if they fall off the second member 12b and get into the sliding surface 13, the occurrence of scratches on the sliding surface 13 can be suppressed because they are soft materials.

The form in which the reinforcing agent 32 is contained is not particularly limited as long as it does not significantly impair the effects of the present disclosure, but it can be, for example, in a particulate form. In addition, the particle size of the reinforcing agent 32 is also not particularly limited as long as it does not significantly impair the effects of the present disclosure, and is optional.

The content of the reinforcing agent 32 is not particularly limited as long as it does not significantly impair the effects of the present disclosure, but can be, for example, 5% by mass or more and 30% by mass or less relative to the second material.

The second material preferably further contains a solid lubricant 33. By containing a solid lubricant, a lubricating film (not shown) is formed on the sliding surface 13 (FIG. 1), thereby reducing friction between the second member 12b and the sliding surface 13, and further improving the wear resistance of the sliding member 12. The solid lubricant 33 may be used alone or in any combination of two or more types in any ratio.

The solid lubricant 33 preferably contains at least one of molybdenum disulfide and spherical carbon. By containing at least one of these, friction between the second member 12b and the sliding surface 13 can be reduced, and wear resistance can be improved, while the strength of the second member 12b against stresses such as shear stress can be improved. For example, in the case of molybdenum disulfide, the weak S-S bonds cause delamination, which results in solid lubrication.

The content of the solid lubricant 33 is not particularly limited as long as it does not significantly impair the effects of the present disclosure, but can be, for example, 1% by mass or more and 15% by mass or less relative to the second material.

Returning to FIG. 1, the second member 12b is disposed adjacent to the first member 12a along the sliding surface 13. The term "adjacent" here means that the first member 12a and the second member 12b do not need to be in contact with each other in the direction of the sliding surface 13 (sliding direction), and any member is permitted to be disposed between the first member 12a and the second member 12b as long as it does not significantly impair the effects of the present disclosure. In the illustrated example, the first member 12a and the second member 12b are in contact with each other in the direction of the sliding surface 13. The first member 12a and the second member 12b are disposed continuously in the circumferential direction of the sliding member 12 along the sliding surface 13.

The first member 12a and the second member 12b are arranged so that the second member 12b is sandwiched between at least two of the first members 12a. In this way, even if the second base resin 31 (FIG. 3) in the second member 12b thermally expands, the second member 12b is sandwiched between the first members 12a, so that the deformation of the entire sliding member 12 due to thermal expansion can be kept within the design tolerance. At the same time, a transfer film 14 (FIG. 4) can be formed on the sliding surface 13, improving the wear resistance of the sliding member 12. In the illustrated example, two first members 12a are provided, and when three or more first members 12a are provided, the second member 12b may be disposed between any two of the first members 12a.

Figure 4 is a diagram illustrating the transfer film 14 formed during sliding. When the sliding member 12 slides on the sliding surface 13, a transfer film 14 made of fluororesin is formed on the sliding surface 13.

The thermal expansion coefficient of the fluororesin particles 22 (Fig. 2) and the fluororesin that constitutes the second base resin 31 (Fig. 3) is relatively large. For this reason, if the sliding member 12 were made up of only the first member 12a or only the second member 12b, there is a possibility that deformation, uneven wear, etc. may occur, especially in a high-temperature friction environment. A specific example of a high-temperature friction environment is the vicinity of the compression/expansion chamber 44 (Fig. 5) in a fluid machine 100 (Fig. 5) such as a rocking piston type reciprocating gas compressor.

The sliding member 12 is composed of a first member 12a including a first base resin 21 (FIG. 2) having fluororesin particles 22 dispersed therein, and a second member 12b including a second base resin 31 made of fluororesin. The first base resin 21 made of a resin other than fluororesin has a high friction coefficient depending on the constituent material, and the transfer film 14 formed on the sliding surface 13 may peel off due to the second base resin 31. Therefore, by dispersing fluororesin particles 22 in the first base resin 21, the friction coefficient of the first member 12a on the sliding surface 13 can be reduced, peeling of the transfer film 14 can be suppressed, and wear resistance can be improved.

On the other hand, when only the first member 12a is used, the fluororesin capable of forming the transfer film 14 is derived only from the fluororesin particles 22, so there is still room for improvement in the degree of formation of the transfer film 14. Therefore, by using the second member 12b, which includes the second base resin 31 made of fluororesin, in addition to the first member 12a, the formation of the transfer film 14 can be promoted, and the friction coefficient can be reduced and abrasion resistance can be improved.

In addition, in the sliding member 12, the first member 12a and the second member 12b mutually assist in the formation of a transfer film 14 (Fig. 4) on the metal member 11, suppressing wear. In addition, the materials other than fluororesin contained in the first base resin 21 and the second base resin 31, respectively (rod-shaped particles 23 (Fig. 2), reinforcing agent 32 (Fig. 3), and solid lubricant 33 (Fig. 3)), improve toughness or slipperiness. This improves the wear resistance of the first member 12a and the second member 12b.

In addition, the presence of the first material, the second material, the fluororesin particles 22 (FIG. 2), the rod-shaped particles 23, the reinforcing agent 32, and the solid lubricant 33 in the sliding member 12 can be confirmed, for example, as follows. That is, for example, the surface or crushed matter of the first member 12a or the second member 12b can be easily identified by performing surface observation and chemical analysis using an optical microscope, energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy, infrared spectroscopy, etc.

Returning to FIG. 1, the metal member 11 can be composed of transition metals such as iron, nickel, molybdenum, chromium, titanium, copper, and light metals such as aluminum, silicon, and magnesium. Specifically, the metal member 11 can be composed of aluminum-based materials such as aluminum and aluminum alloys, copper-based materials such as copper and copper alloys, titanium-based materials such as titanium and titanium alloys, and iron-based materials such as iron and iron-nickel alloys.

The metal member 11 is, for example, a metal material with an untreated surface, but a surface treatment may be applied to the surface of the metal material. In this case, the sliding member 12 comes into contact with and slides on the surface-treated surface. That is, the surface of the metal member 11 may be formed by the metal elements that constitute the metal member 11, or may be formed by a surface treatment applied on the metal member 11.

The surface treatment formed on the surface of the metal member 11 is, for example, a surface coating artificially applied to the metal material, a natural oxide film, etc. The natural oxide film is, for example, aluminum oxide when the metal member 11 is aluminum, and iron oxide when the metal member 11 is iron. The surface coating is formed, for example, by a chemical vapor deposition (CVD) method, a physical vapor deposition (PVD) method, plating treatment, carburization treatment, etc., and is composed of a material containing at least one of aluminum, chromium, iron, phosphorus, nickel, and zinc. Specific examples include anodizing, aluminum plating, chromium plating, iron plating, nickel plating, zinc plating, etc.

Figure 5 is a schematic diagram of a fluid machine 100 equipped with a sliding member 12 of the first embodiment. In the illustrated example, the fluid machine 100 is a reciprocating gas compressor of a rocking piston type. The fluid machine 100 exhibits particularly significant effects when there is not enough lubricating oil, etc., present on the inner wall surface 411 (an example of the sliding surface 13 (Figure 1)) and used in an oil-less manner, or when there is no lubricating oil at all and used in an oil-free manner. However, lubricating oil, grease, etc. may be present on the inner wall surface 411.

The fluid machine 100 includes a cylinder 41 (an example of a metal member 11 (FIG. 1)) and a piston 40 that reciprocates (moves up and down in the illustrated example) inside the cylinder 41. The piston 40 includes a sliding member 12 that slides on the inner wall surface 411 of the cylinder 41, and the sliding member 12 is composed of a piston body 42 (an example of a first member 12a (FIG. 1)) and a piston ring 43 (an example of a second member 12b (FIG. 1)). The piston ring 43 is, for example, annular, and is fitted into an annular groove (not shown) formed on the outer circumferential side surface of the disk-shaped piston body 42.

The space above the piston 40 in the cylinder 41 is provided with a compression/expansion chamber 44, which is a working space for compressing or expanding gas. The upper end of the cylinder 41 is closed by a partition plate 45, which has an intake port 45a and an exhaust port 45b. The intake port 45a and the exhaust port 45b are provided with an intake valve 45c and an exhaust valve 45d, which are connected to pipes (not shown).

The operating principle of gas compression will be explained. The piston 40 is integral with the connecting rod 46. As the crankshaft 47 rotates, the piston 40 moves up and down, sucking gas into the compression/expansion chamber 44 through the intake port 45a, where the gas is compressed. The compressed gas is discharged to the outside through the exhaust port 45b and collected by piping (not shown).

The piston 40 is a separate part from the connecting rod 46 that supports the piston 40. As the piston 40 moves up and down, the piston 40, which is formed of the sliding member 12 in the illustrated example, slides on the inner wall surface 411 of the cylinder 41 by point contact. The connecting rod 46 may be made of metal or resin.

A coating may be formed on the inner wall surface 411 of the cylinder 41 by surface treatment of the metal member 11. For example, the inner circumferential surface of the cylinder 41 may be left as it is with a natural oxide film formed thereon, or may be anodized or the like. Also, it is not necessary to form a coating on the inner circumferential surface of the cylinder 41.

The sliding member 12 may be used in mechanical devices that require good sliding properties, such as analytical devices, vacuum devices, and space-related equipment, in addition to the fluid machine 100 shown in FIG. 5.

Figure 6 is a cross-sectional view showing a sliding member 121 of the second embodiment. The sliding member 121 is similar to the sliding member 12 (Figure 1) except that the arrangement order of the first member 12a and the second member 12b is different.

In the sliding member 121, the first member 12a and the second member 12b are arranged so that the first member 12a is sandwiched between at least two second members 12b. By arranging them in this manner, the transfer film 14 (Figure 4) can be formed starting from the multiple second members 12b, which have a fluororesin base material, and the formation of the transfer film 14 (Figure 4) can be promoted.

Example 1
The first member 12a (FIG. 2) was produced from a first material including PPS as the first base resin 21 (FIG. 2), PTFE as the fluororesin particles 22 (FIG. 2), and carbon fiber as the rod-shaped particles 23 (FIG. 2). The fluororesin particles 22 and the rod-shaped particles 23 were dispersed throughout the first base resin 21. The content of the fluororesin particles 22 was 15% by mass relative to the first material. The content of the rod-shaped particles 23 was 10% by mass relative to the first material. The length and diameter of the rod-shaped particles 23 were 100 μm and 8 μm, respectively, as the average length and diameter measured by the above method.

The second member 12b (Fig. 3) was made from a second material containing PTFE as the second base resin 31 (Fig. 3), bronze as the reinforcing agent 32 (Fig. 3), and molybdenum disulfide and spherical carbon as the solid lubricant 33 (Fig. 3). The reinforcing agent 32 and the solid lubricant 33 were dispersed throughout the second base resin 31. The content of the reinforcing agent 32 was 10 mass% relative to the second material. The content of the molybdenum disulfide was 5 mass% relative to the second material. The content of the spherical carbon was 10 mass% relative to the second material. Therefore, in Example 1, the total amount of the solid lubricant 33 composed of molybdenum disulfide and spherical carbon used was 15 mass% relative to the second material.

Figure 7 is a diagram explaining the test method of the friction test. The sliding member 12 of Example 1 was produced so that the produced first member 12a and second member 12b were arranged on the sliding surface 13. The sliding member 12 was produced so that the first member 12a surrounded the second member 12b. The height H1 of the first member 12a in the vertical direction of the paper was 10 mm, and the width W1 in the horizontal direction of the paper was 10 mm. The height H2 of the second member 12b in the vertical direction of the paper was 5 mm, and the width W2 in the horizontal direction of the paper was 4 mm. The lengths (not shown) of the first member 12a and the second member 12b in the front depth direction of the paper were both shorter than the vertical length of the test piece 15 described below. The area ratio of the first member 12a to the second member 12b on the sliding surface 13 was 6:4.

The sliding member 12 was brought into contact with a test piece 15 made of an aluminum alloy plate (20 mm long (direction from the front of the paper, not shown), 43 mm wide W3, and 3 mm thick H3) with an anodized surface serving as the sliding surface 13, and was moved back and forth in the left-right direction of the paper. The conditions for the friction test were: contact pressure between the sliding member 12 and the test piece 15: 3 MPa, friction speed: 0.4 m/s, distance per reciprocation: 20 mm, surface temperature of the test piece 15 (temperature of the sliding surface 13): 110°C. The total amount of wear when sliding was performed for a specified time in the friction test, and the friction coefficient during sliding for the specified time were measured. The results of the friction test will be described later with reference to Figures 8 to 10.

<Comparative Example 1>
A sliding member of Comparative Example 1 was produced and subjected to a friction test in the same manner as in Example 1, except that the sliding member did not contain the fluororesin particles 22 (FIG. 2) and the rod-shaped particles 23 (FIG. 2). The results of the friction test will be described later with reference to FIGS. 8 to 10.

<Comparative Example 2>
A sliding member of Comparative Example 2 was produced in the same manner as in Example 1, except that the second member 12b was not provided, and a friction test was conducted. The results of the friction test will be described later with reference to Figs. 8 to 10. The sliding member of Comparative Example 2 corresponds to the technology described in Patent Document 1.

The materials used to make the sliding members in Example 1, Comparative Example 1, and Comparative Example 2 are shown in Table 1 below. "〇" indicates that the material was used, and "-" indicates that the material was not used.

Figure 8 shows energy dispersive X-ray analysis images (EDX) of the test piece surface after the friction test. The EDX-Al image shows the presence of aluminum on the test piece surface, and the EDX-F image shows the presence of fluorine on the test piece surface. There are almost no white areas in the EDX-Al image of Example 1, indicating that there is no aluminum on the surface. On the other hand, there are white areas in the EDX-F image of Example 1, indicating that there is fluorine on the surface. Therefore, it is believed that a transfer film 14 (Figure 4) containing fluorine was formed on the surface of the test piece, which resulted in almost no detection of aluminum, the constituent material of the test piece.

On the other hand, the EDX-Al images of Comparative Examples 1 and 2 show white areas, indicating the presence of aluminum on the surface of the test piece, whereas the EDX-F images of Comparative Examples 1 and 2 show no white areas, indicating the absence of fluorine on the surface. Therefore, it is believed that almost no fluorine-containing transfer film 14 (Figure 4) was formed on the surface of the test piece, and most of the aluminum that constitutes the test piece was exposed as is.

These results are believed to be the result of containing fluororesin in both the first member 12a and the second member 12b. That is, it is believed that the transfer film 14 can be formed by providing the first member 12a and the second member 12b, as in the sliding member 12 according to the present disclosure. However, when, for example, fluororesin particles 22 are not used, as in Comparative Example 1, the transfer film 14 formed by the second member 12b is peeled off by the first member 12a, as described above, and it is believed that the transfer film 14 is unlikely to remain. In addition, as in Comparative Example 2, since the second base resin 31, which is a fluororesin, is not used, it is difficult to form the transfer film 14, and it can be seen that there is room for improvement in the degree of formation of the transfer film 14.

Figure 9 shows the test results of the wear amount (bar graph) and friction coefficient (plot) obtained in the friction test. Figure 9 shows the total wear amount when sliding for a specified time in the friction test shown in Figure 7, and the average friction coefficient during sliding for the specified time. Note that to make the results easier to understand, the wear amount is expressed as a relative value when Comparative Example 2 is set to 100.

The coefficient of friction of Example 1 was lower than those of Comparative Example 1 and Comparative Example 2. This is believed to be due to the formation of the transfer film 14 (FIG. 4), as described with reference to FIG. 8. The lower coefficient of friction is believed to have made it easier for the sliding member 12 to slide, reducing the amount of wear. For this reason, the sliding member 12 of the present disclosure exhibits excellent wear resistance.

On the other hand, when comparing Example 1 with Comparative Examples 1 and 2, the wear amount and friction coefficient of Comparative Examples 1 and 2 were both higher than that of Example 1. This is thought to be because in Comparative Example 1, which does not contain fluororesin particles 22, even if a transfer film 14 is formed, it is peeled off by the first member 12a, resulting in a large wear amount and friction coefficient. Also, in Comparative Example 2, which does not have the second member 12b, it is difficult to form the transfer film 14 in the first place, resulting in a large wear amount and friction coefficient.

In addition, in the case of Comparative Examples 1 and 2, if the friction coefficient is reduced, the slipperiness improves. However, if, for example, a decrease in the strength of the material against shear stress, excessive thermal expansion, etc., occurs at the same time, the amount of wear increases as a result. Therefore, the wear coefficient is one element for reducing the amount of wear, and simply reducing the friction coefficient does not necessarily reduce the amount of wear. For this reason, although the friction coefficient was smaller in Comparative Example 2, it is believed that the amount of wear was greater in Comparative Example 2. Therefore, in Example 1, the friction coefficient was reduced to make it easier to slip, and further, it is believed that the amount of wear could be reduced because, for example, a decrease in strength and excessive thermal expansion of the first member 12a and the second member 12b (both in FIG. 7) could be suppressed.

Figure 10 shows the correlation between the amount of wear (circle plots) and coefficient of friction (diamond plots) obtained in the friction test, and the content of fluororesin particles 22 (Figure 2). The results shown in Figure 10 were obtained by simulating the friction test in Figure 7, and were performed under the same conditions as in Example 1, except that the content of fluororesin particles 22 (PTFE) in the first material was changed. The amount of wear is expressed as a relative value when the value when the amount of fluororesin particles 22 is 70% by mass is taken as 100.

The amount of wear was particularly low when the content was in the range of 15% by mass or more and 30% by mass or less. Therefore, particularly high wear resistance was shown when the content was in this range. On the other hand, when the content was less than 15% by mass or more than 30% by mass, the amount of wear tended to increase.

The friction coefficient showed a nearly constant value when the content was 15 mass% or more. This means that if the content was 15 mass% or more, a transfer film 14 (Figure 4) with good slipperiness was formed on the test piece. Therefore, from the results in Figure 10, it was found that the content of the fluororesin particles 22 is preferably 15 mass% or more and 30 mass% or less with respect to the first material.

As described above, by applying the sliding member 12 according to the present disclosure to the piston 40, which is a sliding part of a oscillating piston system in, for example, a reciprocating gas compressor, the wear resistance of the piston 40 can be improved. This can extend the life of the piston 40, and for example, the maintenance cycle of the reciprocating gas compressor can be extended.

REFERENCE SIGNS LIST 100 Fluid machine 11 Metal member 12 Sliding member 12a First member 12b Second member 13 Sliding surface 14 Transfer film 15 Test piece 21 First base resin 22 Fluorine resin particles 23 Rod-shaped particles 31 Second base resin 32 Reinforcing agent 33 Solid lubricant 40 Piston 41 Cylinder 411 Inner wall surface 42 Piston body 43 Piston ring 44 Compression/expansion chamber 45 Partition plate 45a Intake port 45b Outlet port 45c Intake valve 45d Outlet valve 46 Connecting rod 47 Crankshaft

Claims (14)

A sliding member that contacts a sliding surface,
The sliding member is
A first member made of a first material including a first base resin made of a resin other than a fluororesin and fluororesin particles and rod-shaped particles dispersed in the first base resin;
a second member disposed adjacent to the first member along a sliding direction of the sliding member on the sliding surface, the second member being made of a second material including a second base resin made of a fluororesin and a reinforcing agent dispersed in the second base resin. 2. The sliding member according to claim 1, wherein the first base resin contains at least one of polyphenylene sulfide and polyether ether ketone. 3. The sliding member according to claim 1, wherein the fluororesin particles contain at least one of polytetrafluoroethylene and a tetrafluoroethylene-perfluoroalkylvinyl ether copolymer. 3. The sliding member according to claim 1, wherein the rod-shaped particles contain at least one of carbon fibers and glass fibers. 3. The sliding member according to claim 1, wherein the second base resin contains polytetrafluoroethylene. 3. The sliding member according to claim 1, wherein the reinforcing agent contains at least one of copper, a copper alloy, and a carbon fiber. The sliding member according to claim 1 or 2, wherein the second material further includes a solid lubricant. 8. The sliding member according to claim 7, wherein the solid lubricant contains at least one of molybdenum disulfide and spherical carbon. The sliding member according to claim 1 or 2, wherein the first member and the second member are arranged such that the second member is sandwiched between at least two of the first members. The sliding member according to claim 1 or 2, wherein the first member and the second member are arranged such that the first member is sandwiched between at least two of the second members. 3. The sliding member according to claim 1, wherein the fluororesin particles and the second base resin are made of the same type of fluororesin. 3. The sliding member according to claim 1, wherein a content of the fluororesin particles in the first material is 15% by mass or more and 30% by mass or less. The rod-shaped particles include carbon fibers,
The sliding member according to claim 12, wherein a content of the carbon fiber is 5% by mass or more and 15% by mass or less with respect to the first material. A cylinder;
a piston having a sliding member that slides on an inner wall surface of the cylinder;
The sliding member is
A first member made of a first material including a first base resin made of a resin other than a fluororesin and fluororesin particles and rod-shaped particles dispersed in the first base resin;
a second member that is arranged adjacent to the first member along a sliding direction of the sliding member on the inner wall surface, the second member being made of a second material including a second base resin made of a fluororesin and a reinforcing agent dispersed in the second base resin.

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