This application is a U.S. National Stage Application of International Application No. PCT/JP2017/041336, filed on Nov. 16, 2017, which claims priority to Japanese Application No. 2016-224316, filed on Nov. 17, 2016. The entire disclosures of the above applications are incorporated herein by reference.
The present invention relates to a sliding member.
To improve characteristics of a sliding surface, a sliding material with a resin coating layer is known, in which PTFE, graphite, and MoS2 are used as additives in a binder resin (refer to JP 2002-310345 and JP 2008-56750).
In the technology disclosed in JP 2002-310345 and JP 2008-56750, a problem exists in that a solid lubricant is liable to fall off or cleave under a high-load state, as a result of which the sliding surface becomes rougher. When the sliding surface becomes rough, formation of an oil film is impeded, particularly where an amount of oil present is low, or in a dry environment where a supply of lubricating oil is insufficient. Under such circumstances, abrasion and seizure resistance decreases.
The present invention provides a technique for improving wear and seizure resistance under a high load state in an environment where a supply of lubricating oil supply is insufficient.
The present invention provides a resin composition including: a binder resin made of a thermosetting resin; an additive dispersed in the binder resin, wherein the additive includes PTFE (polytetrafluoroethylene), and at least one of graphite and MoS2, where an average particle size of each of the additive is less than 10 μm, and an average particle size of the PTFE is larger than the average particle size of graphite and MoS2.
The binder resin may include at least one of Polyamide-imide and Polyimide.
The binder resin may be Polyamide-imide.
A content of the binder resin may be 50 to 80 vol %.
A content of the PTFE is higher than a content of the MoS2.
The content of the MoS2 is 0 to 10 vol %.
The additive may include a hard particle.
The present invention further provides a sliding member including: a basic material; and a coating layer made of the resin composition.
According to the present invention, wear and seizure resistance can be improved under a high load state in an environment where a supply of lubricating oil is insufficient.
Coating layer 32 is formed to improve the characteristics of the sliding surface of swash plate 3. Coating layer 32 is made of a resin composition. The resin composition includes a binder resin and an additive dispersed in the binder resin. The binder resin is made of, for example, a thermosetting resin. At least one of polyamideimide (PAI), polyamide (PA), and polyimide (PI), epoxy, and phenol is used as the thermosetting resin, for example. Among these, the binder resin preferably includes at least one of PAI and PI. For example, the content of the binder resin in the resin composition is preferably 50 to 80 vol %. More preferably, the content of the binder resin is more than 60 vol %. More preferably, the upper limit of the content of the binder resin is 75 vol %.
A solid lubricant is used as the additive. The solid lubricant is added to improve lubricating properties, in other words, to reduce a coefficient of friction. For example, the resin composition includes 20 to 50 vol % of solid lubricant in total. PTFE (polytetrafluoroethylene) is used as the solid lubricant. Furthermore, this resin composition includes, in addition to PTFE, at least one of graphite (Gr) and MoS2. The content of MoS2 is preferably less than the content of PTFE. For example, the content of PTFE 10 to 30 vol %, and more preferably 15 to 25 vol %. The content of MoS2 is 0 to 10 vol %, preferably 0 to 4 vol % (that is, MoS2 may not be included). The content of graphite is preferably 0 to 20 vol %, more preferably 10 to 20 vol %. Moreover, it is preferable that the content of MoS2 is less than the content of graphite.
The average particle diameter of the additive added to the binder resin is preferably less than 10 μm, and more preferably, equal to or less than 5 μm, in order to enhance the smoothness of the sliding surface and to assist the formation of an oil film. Here, the average particle diameter means the 50% diameter (median diameter) in the distribution of the sphere equivalent diameter obtained by the laser diffraction method in the state of the raw material before mixing with the binder resin. When the average particle diameter of the additive is less than 10 μm, the sliding surface is maintained smooth, in contrast to where the average particle diameter of the additive is equal to or less than 10 μm, and as a result formation of an oil film is enhanced. Therefore, transition from boundary lubrication to mixed lubrication or fluid lubrication is facilitated, and enhanced lubrication is easily obtained even under severe conditions such as low oil content and high load.
The average particle size of PTFE is preferably larger than either the average particle size of graphite or the average particle size of MoS2. The inventors of the present invention hypothesize that by using PTFE having an average particle diameter larger than that of graphite and MoS2, the PTFE is stretched on the sliding surface to cover the graphite or MoS2, whereby smoothness of the sliding surface is easily maintained.
The resin composition may further include hard particles as the additive. As the hard particle, at least one of an oxide, a nitride, a carbide, and a sulfide is used, for example. The average particle size of the hard particles is preferably less than 10 μm, and more preferably smaller than the average particle size of PTFE.
Coating layer 33 is also formed using the same resin composition as coating layer 32. In the substrate 31, the surface that acts as the sliding surface, that is, the surface on which coating layer 32 is formed and the surface on which coating layer 33 is formed are substantially flat. The surface of the substrate 31 may be roughened to enhance the adhesion to coating layer 32. In addition, an intermediate layer may be formed between the substrate 31 and coating layer 32.
The present invention is not limited to the above embodiment and various modifications can be applied to the embodiment. For example, the sliding member having a coating layer formed using the resin composition according to the present embodiment is not limited to a swash plate for a compressor. The sliding member may be a shoe for a compressor, or a half bearing, a bush, or a thrust washer used in an engine.
The present inventors manufactured test pieces of the sliding member under various conditions. The present inventors evaluated their characteristics. Cast iron was used as the base material of the sliding member. The base material was processed to have the shape of the swash plate shown in
First, the abrasion resistance test was performed on the test pieces of the above three experiment examples. The test conditions of the abrasion resistance test were as follows.
The present inventor observed the sliding surface of the test pieces after the test, and confirmed whether the coating layer was worn or not. Although abrasion occurred in Experiment Example 3, no abrasion was found in Experiment Examples 1 and 2. Thus, compared with Experiment Example 3, Experiment Examples 1 and 2 showed improved wear resistance.
Furthermore, the present inventors performed a seizure resistance test on the test pieces of Experiment Examples 1 and 2. The test conditions of the seizure resistance test were as follows.
Furthermore, the present inventors performed a sliding test on the test pieces of Experiment Examples 1 and 2, and measured the surface roughness of the sliding surface before and after the test using a surface roughness meter (SP81B manufactured by Kosaka Laboratory). Further, the surface was observed with an electron microscope. The test conditions of the sliding test were the same as those of the seizure resistance test described above.
Number | Date | Country | Kind |
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JP2016-224316 | Nov 2016 | JP | national |
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PCT/JP2017/041336 | 11/16/2017 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2018/092856 | 5/24/2018 | WO | A |
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