Sintered sliding part and manufacturing method thereof

Abstract

To provide a sintered sliding component capable of improving sliding performance and maintaining the sliding performance for a long period, and a manufacturing method thereof.SOLUTION: A sintered sliding component has a porous sintered component body formed with a sliding surface for slidably supporting a sliding object, and made of a sintered metal. On the sliding surface, a solid lubrication phase containing a solid lubricant and a ground surface on which a large number of pores of the sintered component body are opened are dispersedly formed, where an area ratio of the solid lubrication phase on the sliding surface is 10% or more and 60% or less, and a part of the solid lubrication phase penetrates into the sintered component body.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sintered sliding part such as an oil-impregnated sintered bearing, which can be impregnated with lubricating oil to ensure smooth lubrication, and a method for manufacturing the same. [Background technology]

[0002] Known sintered sliding parts include copper-based bearings, which are relatively soft, made from bronze or brass, iron-based bearings, which contain high strength iron, and iron-copper-based bearings, which are intermediate between the two, and are used according to the sliding speed and the magnitude of the load. For example, copper-based bearings are mainly used for high-speed sliding and low-load specifications, while iron-based bearings are used for low-speed sliding and high-load specifications, and iron-copper-based bearings are used as an intermediate between the two.

[0003] In order to minimize the frictional resistance of such various bearings, an iron-copper based sintered sliding part, as described in Patent Document 1, which contains a solid lubricant as needed, is known. To improve the sliding properties of these iron-copper sintered sliding parts, solid lubricant powder such as graphite or molybdenum disulfide (MoS2) is mixed with the base metal powder and sintered to disperse free graphite, increase the copper content in the surface layer, and support the surface layer with a back metal layer containing a reaction phase such as pearlite, which is a reaction phase between graphite and iron. This provides sintered sliding parts with high strength and improved sliding properties.

[0004] However, in the iron-copper sintered sliding part described in Patent Document 1, when graphite is used as a solid lubricant, a high-strength structure such as cementite is generated by the reaction between iron and graphite during sintering of the metal powder and the solid lubricant powder, and if this high-strength structure is provided in the surface layer, it may damage the sliding object. Also, when MoS2 is used as a solid lubricant, MoS2 is decomposed by the high temperature during sintering, making it difficult to maintain it in the form of MoS2 within the sintered body. Furthermore, adding a solid lubricant to sintering inhibits sintering, reducing the strength and hardness of the bearing. Furthermore, since shafts and other sliding objects are generally made of iron-based materials, if the sintered sliding parts contain iron-based powder, there is a risk of adhesive wear or seizure due to the sliding of like metals (so-called "togane").

[0005] To solve the above-mentioned problems, a method for manufacturing a sintered oil-impregnated bearing is known, for example, as described in Patent Document 2, which involves impregnating a sintered body of metal powder with a solid lubricant to form a solid lubricant-containing metal layer. In the method for manufacturing a sintered oil-impregnated bearing described in Patent Document 2, the bearing body (sintered body) obtained by sintering is sized to form oil holes in the sliding surface having an average pore size larger than the oil holes with the desired average pore size to be exposed on the sliding surface, a metal layer containing solid lubricant is provided on this sliding surface, and the edges of the oil holes are covered with this metal layer containing solid lubricant to form oil holes with the desired average pore size on the sliding surface.

[0006] Furthermore, as a method for forming a low-friction layer made of a fluororesin such as PTFE on a sintered body of metal powder, for example, a method for producing an oil-impregnated sintered bearing is known, as described in Patent Document 3. In the manufacturing method of a sintered oil-impregnated bearing described in Patent Document 3, the surface of the sintered metal is pressed to form it, and then a resin film is formed on the formed surface to form a low-friction layer, and at least some of the surface openings are left in the low-friction layer. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-94167 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-147201 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-249242 Summary of the Invention [Problem to be solved by the invention]

[0008] However, since the solid lubricant-containing metal layer and the low-friction layer formed on the surface both have a layer structure, there is a concern that the solid lubricant-containing metal layer or the low-friction layer will wear out and their durability will decrease if the sliding object slides on them for a long period of time, making it difficult to maintain sliding properties for a long period of time.

[0009] The present invention has been made in view of the above circumstances, and has as its object to provide a sintered sliding component that can improve sliding properties and maintain the sliding properties for a long period of time, and a method for manufacturing the same. [Means for solving the problem]

[0010] The sintered sliding part of the present invention is a sintered sliding part having a porous sintered part body made of sintered metal on which a sliding surface for slidably supporting a sliding object is formed, and the sliding surface is formed with a dispersed solid lubricant phase containing a solid lubricant and a bare surface of the sintered part body on which a large number of pores are opened, the area ratio of the solid lubricant phase to the sliding surface being 10% or more and 60% or less, and a part of the solid lubricant phase has penetrated into the sintered part body.

[0011] In the present invention, the bare surface remains on the sliding surface, so the solid lubricant phase enhances the lubricating effect, while the base material (bare surface), which is stronger than the solid lubricant phase, supports the load from the sliding object, thereby significantly improving sliding properties. Furthermore, because part of the solid lubricant phase has permeated the sintered part body, even if the surface of the sliding surface is worn by the sliding object, the sliding properties can be prevented from decreasing, and sliding properties can be maintained over the long term. If the area ratio of the solid lubricant phase to the sliding surface is less than 10%, the coefficient of friction becomes large, and if it exceeds 60%, the area of ​​the bare surface becomes small and the solid lubricant phase is easily scraped away by sliding, resulting in an increase in the coefficient of friction and a decrease in load-bearing performance (load-supporting function).

[0012] In a preferred embodiment of the sintered sliding component of the present invention, the roughness Rz (JIS B 0601 2001) of the sliding surface is 5 μm or less. In the above embodiment, even when the roughness of the sliding surface is somewhat large, the unevenness is mainly due to the solid lubricant phase attached to the surface, so the presence of the solid lubricant phase does not significantly reduce the sliding characteristics. On the contrary, conformability is improved, and a good sliding surface can be formed, which may be expected to improve seizure resistance and reduce friction. If the roughness Rz (JIS B 0601 2001) of the sliding surface exceeds 5 μm, excessive wear particles may be generated during the initial break-in period, which may increase the friction of the sliding surface.

[0013] In a preferred embodiment of the sintered sliding part of the present invention, the penetration depth of the solid lubricant phase into the sintered part body is 50 μm or more. If the penetration depth of the solid lubricant phase into the sintered part body is less than 50 μm, it is difficult to improve the sliding properties over a long period of time.

[0014] In a preferred embodiment of the sintered sliding part of the present invention, the solid lubricant phase contains a resin. In the above-described embodiment, the solid lubricant phase contains a resin that is softer than the sintered component body and the sliding object. Therefore, even if the solid lubricant phase wears away due to the sliding of the sliding object, it is possible to prevent the sintered component body and the sliding object from being damaged by the wear powder.

[0015] In a preferred embodiment of the sintered sliding part of the present invention, the main component of the sintered part body is an iron-based metal. In the above embodiment, since the sintered sliding component is mainly composed of an iron-based metal, the strength of the sintered sliding component can be increased and the manufacturing cost can be reduced.

[0016] In a preferred embodiment of the sintered sliding component of the present invention, the solid lubricant contains a substance having cleavage properties or a substance softer than the sliding object. Examples of the cleavable material or material softer than the sliding object include graphite, molybdenum disulfide, calcium fluoride, talc, boron nitride, and graphite fluoride.

[0017] In a preferred embodiment of the sintered sliding part of the present invention, at least a portion of the pores may be impregnated with a lubricating oil. In the above embodiment, since the bare surface with many open pores remains on the sliding surface, the lubricating oil is discharged from these pores as the sliding object slides, thereby further improving the sliding properties of the sintered sliding part. In addition, the solid lubricant in the pores and the lubricating oil impregnated in the pores become cloudy and are supplied to the sliding surface little by little, further improving the sliding properties of the sintered sliding part.

[0018] In a preferred embodiment of the sintered sliding part of the present invention, the solid lubricating phase has lipophilicity. In the above-described embodiment, the solid lubricant phase formed in the sintered component body can prevent the lubricant oil impregnated in the pores from being discharged to the outside.

[0019] The method for producing a sintered sliding part of the present invention is the method for producing the sintered sliding part described above, and includes the following steps: a molding step of filling a raw material powder into a molding die and applying pressure to form a green compact; a sintering step of sintering the green compact to form a sintered part; an impregnation step of impregnating the sintered part with a diluent mixed with a solid lubricant; a heating step of heating the sintered part after the impregnation step to volatilize the liquid content of the diluent; and a sizing step of sizing the sintered part after the heating step to form a sintered part main body.

[0020] In the present invention, the solid lubricant phase is formed after the sintering process, which prevents the solid lubricant from reacting with the metal components constituting the sintered body during sintering to produce a high-strength structure, and prevents the solid lubricant from being decomposed by the high temperatures during sintering, thereby broadening the range of solid lubricant options. Here, if a solid lubricant phase is formed after sizing the sintered body, it becomes difficult to maintain dimensional accuracy and surface roughness due to uneven thickness of the solid lubricant phase adhering to the surface, and the opening diameter of the pores formed on the surface of the sintered body by sizing becomes smaller, making it difficult for the solid lubricant to penetrate into the pores. In contrast, in the present invention, the sizing step is carried out after the impregnation step and the heating step, which makes it easier for the solid lubricant to penetrate into the pores in the impregnation step, and thereby makes it possible to form a solid lubricant phase inside the sintered part body as well.

[0021] In a preferred embodiment of the method for producing a sintered sliding part of the present invention, the diluent may be mixed with the solid lubricant and a resin binder. In the above-described embodiment, the solid lubricant phase can be formed from a solid lubricant and a resin. Since the resin is softer than the sintered component body and the sliding object, even if the solid lubricant phase is worn away by the sliding of the sliding object, the sintered component body and the sliding object can be prevented from being damaged by the wear powder.

[0022] In a preferred embodiment of the method for producing a sintered sliding part of the present invention, the method further comprises a lubricant oil impregnation step of impregnating the sintered sliding part with a lubricant oil after the sizing step. In the above embodiment, by impregnating the sintered sliding component with lubricating oil, an oil-impregnated sintered sliding component (for example, an oil-impregnated sintered bearing) can be provided.

[0023] In a preferred embodiment of the method for producing a sintered sliding part of the present invention, the impregnation step may involve impregnating the sintered body with the dilute solution mixed with the solid lubricant having a particle size smaller than the opening diameter of the pores on the sliding surface. In the above embodiment, the particle size of the solid lubricant is smaller than the opening diameter of the pores, so the solid lubricant can easily enter the pores. This makes it easier to form a solid lubricant phase in the pores. Furthermore, when the pores are impregnated with lubricating oil, the lubricant mixes with the solid lubricant phase in the pores and is discharged to the sliding surface, further improving sliding properties.

[0024] A preferred embodiment of the method for producing a sintered sliding part of the present invention comprises a blinding step of processing a region of the sintered body other than the region that will become the sliding surface before the impregnation step to blind at least some of the pores. In the above embodiment, when the impregnation step is performed by a dipping method, it is possible to prevent the solid lubricant that forms the solid lubricant phase from entering areas other than the area that becomes the sliding surface, thereby reducing manufacturing costs. [Effects of the Invention]

[0025] According to the present invention, the sliding properties of the sintered sliding part can be improved and the sliding properties can be maintained for a long period of time. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a cross-sectional view of a sintered sliding part (sintered oil-impregnated bearing) according to one embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a cross-sectional SEM image of the sintered oil-impregnated bearing shown in FIG. [Figure 3] FIG. 3 is a partially enlarged view of the cross-sectional SEM image shown in FIG. 2. [Figure 4] 4 is a flowchart showing a method for manufacturing a sintered sliding part according to the embodiment. [Figure 5] 1 is an image obtained by performing elemental analysis on the sliding surface of a sintered oil-impregnated bearing in an example. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0028] [Schematic structure of sintered oil-impregnated bearing] The sintered oil-impregnated bearing 1 of this embodiment corresponds to the sintered sliding part of the present invention, and is a cylindrical bearing made by impregnating a porous bearing body 10 (sintered part body) made of sintered metal with lubricating oil. This sintered oil-impregnated bearing 1 is formed with a bearing hole 11 having a sliding surface 12 that supports the outer peripheral surface of a shaft (not shown) that is to slide, and through which the shaft is inserted. This bearing hole 11 slidably supports the inserted shaft.

[0029] This sintered oil-impregnated bearing 1 is formed from a sintered body of metal powder (for example, metal powder mainly composed of iron-based metal powder), and is therefore formed from a porous body with many pores formed therein. The open porosity (JIS Z 2501 2000) of this sintered oil-impregnated bearing 1 (bearing body 10) is set to 14 vol% to 25 vol%, and the pores of the bearing body 10 are impregnated with lubricating oil. The open porosity is the volume ratio of pores that can be impregnated with a fluid such as lubricating oil relative to the volume of the bearing body 10. This open porosity is expressed as a percentage relative to the volume of the bearing body 10, and is calculated by dividing the volume of oil after complete impregnation by the volume of the bearing body 10 and multiplying the result by 100. In other words, the open porosity is approximately the same as the oil impregnation rate relative to the volume of the bearing body 10.

[0030] The lubricating oil impregnated in these pores expands as the temperature of the bearing body 10 rises as the shaft slides, and leaks out from the numerous pores formed in the sliding surface 12 due to the pumping action of the sliding shaft, which sucks out the lubricating oil from the pores in the bearing body.When the sliding of the shaft stops and the temperature of the sintered oil-impregnated bearing 1 drops, the leaked lubricating oil is drawn into the bearing body 10 and recovered.

[0031] [Configuration of sliding surface] The sliding surface 12 is formed by mixing the bare surface of the bearing body 10, where the numerous pores are open, with a solid lubricant phase containing a solid lubricant. This solid lubricant phase is made of a cleavable material or a material softer than the shaft that is the sliding object, and a resin. Specific examples of such materials include graphite, molybdenum disulfide, calcium fluoride, talc, boron nitride, and graphite fluoride, and the solid lubricant is made of at least one of these and a resin. It is preferable that the solid lubricant phase has lipophilicity. If the solid lubricant phase has lipophilicity, it is possible to properly impregnate the pores with lubricating oil and also to prevent the lubricating oil impregnated in the pores from being discharged to the outside. Therefore, even if the solid lubricant is oil-repellent, the solid lubricant phase itself may have lipophilicity by containing a resin. In this specification, lipophilicity refers to the ability to retain lubricating oil within the pores of the bearing body 10 to which the solid lubricant phase is applied. This lipophilicity is determined, for example, by whether or not oil is absorbed into the bearing when a drop of oil is dropped into the bearing without the lubricant impregnated. If the oil is absorbed, it is determined to have lipophilicity and form a ball on the surface, and if the oil is not absorbed, it is determined to have no lipophilicity.

[0032] The solid lubricant phase contains resin because resin is softer than the bearing body 10 and the shaft, and can prevent wear particles generated when the resin-containing solid lubricant phase wears from damaging the body and the shaft. Note that resin does not necessarily have to be contained in the solid lubricant phase, and the solid lubricant phase may be formed solely from a solid lubricant.

[0033] The particle size of the solid lubricant may be smaller than the opening diameter of the pores in the sliding surface 12. For example, if the opening diameter of the pores in the sliding surface 12 is set to 5 μm to 100 μm, the particle size of the solid lubricant used may include particles smaller than that. In other words, the particle size of the solid lubricant may include particles smaller than the opening diameter of the pores, and some particles may be larger than that, or all of the particle size of the solid lubricant may be smaller than the opening diameter of the pores. Therefore, a solid lubricant phase made of the solid lubricant is formed not only on the surface (sliding surface 12) of the bearing body 10 but also inside the pores.

[0034] Such a solid lubricant phase contributes to improving the sliding properties of the sliding surface 12, and is formed on part of the surface of the sliding surface 12 and inside the bearing body 10, as shown in Fig. 2. Specifically, the area ratio of the solid lubricant phase on the sliding surface 12 is 10% or more and 60% or less, and the area other than the solid lubricant phase is the bare surface. For example, in the example shown in Fig. 5, the surface of the sliding surface 12 is the part where the solid lubricant phase is shown in black, and is arranged mixed with the bare surfaces shown in white and gray. If the area ratio of the solid lubricant phase on the sliding surface 12 is less than 10%, the friction coefficient of the sliding surface 12 will be large, and if it exceeds 60%, the area of ​​the bare surface on the sliding surface 12 will be small, and the load-bearing function of the bare surface will be reduced.

[0035] Furthermore, the penetration depth of the solid lubricant phase into the bearing body 10 is preferably 50 μm or more. Specifically, as shown in Fig. 2, the solid lubricant phase is arranged in a dispersed state within the bearing body 10. Fig. 3 is an enlarged SEM image of the area enclosed in a frame in Fig. 2, and the area indicated by the arrow in Fig. 3 is the solid lubricant phase. From Figs. 2 and 3, it can be seen that the solid lubricant phase penetrates into the bearing body 10 within the above range, thereby suppressing a decrease in sliding performance when the sliding surface 12 is worn due to sliding of the shaft. If the penetration depth of the solid lubricant phase into the bearing body 10 is less than 50 μm, it is difficult to maintain slidability for a long period of time.

[0036] On the other hand, the open porosity of the bearing body 10 after the solid lubricant phase is formed is preferably 14 vol% or more and 25 vol% or less. This allows the sintered oil-impregnated bearing 1 to be sufficiently impregnated with lubricant oil, improving sliding properties. Furthermore, by preventing the solid lubricant phase from impregnating the bearing body 10 too much, manufacturing costs can be reduced. If the solid lubricant phase is excessively impregnated into the sintered body and the open porosity of the bearing body 10 falls below 14 vol%, the amount of lubricant oil to be impregnated will be reduced, which may reduce the function of the self-lubricating sintered oil-impregnated bearing 1. In addition, excessive impregnation with the solid lubricant phase may increase manufacturing costs.

[0037] The roughness Rz (JIS B 0601 2001) of the sliding surface 12 on which such a solid lubricant phase is formed is preferably 5 μm or less, more preferably 2 μm or less. Although a small roughness is preferable for a sliding member, in this configuration, some unevenness may occur due to the solid lubricant phase adhering to the surface, but since the solid lubricant phase is the main component, the sliding characteristics are not significantly reduced. If the roughness Rz (JIS B 0601 2001) of the sliding surface 12 exceeds 5 μm, the coefficient of friction of the sliding surface 12 may increase due to the generation of excessive wear particles during the initial break-in period of sliding.

[0038] [Manufacturing method for sintered oil-impregnated bearings] The production of sintered oil-impregnated bearing 1 includes a molding step (step S11) in which raw material powder is filled into a molding die and pressurized to form a cylindrical green compact, a sintering step (step S12) in which this green compact is sintered to form a sintered body, an impregnation step (step S13) in which the sintered body is impregnated with a diluent mixed with a solid lubricant, a heating step (step S14) in which the sintered body after the impregnation step is heated to volatilize the liquid portion of the diluent, a sizing step (step S15) in which the sintered body after the heating step is sized to form bearing body 10, and a lubricant impregnation step (step S16) in which lubricant is impregnated into bearing body 10 after the sizing step. Each step will be explained below according to the flowchart shown in FIG.

[0039] (molding process) The metal that is the material for the sintered oil-impregnated bearing 1 is not particularly limited, but it is preferable to use an iron-based powder or an iron-copper-based powder as the raw material powder. The iron-based powder is an iron powder whose main component is iron or an iron alloy, and may contain a low-melting-point metal powder whose melting point is below the sintering temperature. In this case, the iron-based powder is a combination of 0.5% to 70% by mass of copper-based powder, 0.5% to 10% by mass of low-melting-point metal powder, and the remainder of the iron-based powder. In iron alloy-based materials, copper may be used as the low-melting-point metal.

[0040] In the molding process, a molding die (not shown) is used, and raw material powder is poured into the space formed by the molding die. A cylindrical upper molding punch is inserted from above to narrow the gap between the lower molding punch and the upper molding punch, and the raw material powder is compressed at 100 MPa to 800 MPa to form a green compact.

[0041] (Sintering process) Next, in the sintering step, the green compact is sintered at a temperature of 600° C. to 1150° C. This sinters the green compact into a sintered body. The holding time at the maximum temperature is preferably 5 to 30 minutes. The open porosity of the sintered body at this stage is 15 to 30 vol%. This open porosity is the volume ratio of pores in the sintered body that can be impregnated with a fluid such as lubricating oil, and is expressed as a percentage of the volume of the sintered body. It is calculated by dividing the volume of oil after complete impregnation by the volume of the sintered body and multiplying the result by 100.

[0042] (Impregnation process) In the impregnation step, the sintered body is impregnated with a dilute solution prepared by diluting at least one solid lubricant, such as graphite, molybdenum disulfide, calcium fluoride, talc, boron nitride, or graphite fluoride, with a solvent and a resin binder. These solid lubricants preferably have lipophilic properties, and their average particle size is preferably smaller than the average opening diameter of pores on the surface of the region of the sintered body that will become the sliding surface 12. Note that the solid lubricant is not limited to the above-mentioned examples, and any solid lubricant may be used as long as it is a cleavable material or a material softer than the sliding object. In this embodiment, for example, 10 mass% of molybdenum disulfide and 10 mass% of an epoxy resin binder are added to an organic solvent and stirred to produce a diluted solution. Then, the sintered body is immersed in the diluted solution for a predetermined time (e.g., 5 to 30 minutes), thereby impregnating the sintered body with the diluted solution. At this time, the particle size of the solid lubricant contains particles smaller than the opening diameter of the pores formed on the surface of the sintered body, so that part of the solid lubricant penetrates into the pores. In order to make the area ratio of the solid lubricant phase on the sliding surface 12 10% to 60%, the roughness Rz (JIS B 0601 2001) of the sliding surface 12 5 μm or less, and the penetration depth of the solid lubricant phase into the bearing body 10 50 μm or more, it is preferable to set the diluted concentration of the solid lubricant and resin binder in the diluted solution to 20 mass% to 30 mass%, and to immerse the sintered body in this diluted solution for 3 seconds to 30 minutes.

[0043] In the above embodiment, the sintered body is impregnated with the diluted solution by immersing it in the diluted solution. However, the present invention is not limited to this. For example, the diluted solution may be impregnated by vapor deposition, painting by spraying, or the like, or by plating bath or the like.

[0044] (Heating process) In the heating step, the sintered body impregnated with the diluent is heated. The heating temperature in this heating step is preferably a temperature at which the solid lubricant does not decompose when heated and at which the liquid component of the diluent can be volatilized. For example, the heating conditions in the heating step are such that the sintered body is kept at 150°C to 250°C for 30 to 120 minutes.

[0045] (Sizing process) In the sizing step, the inner peripheral surface, outer peripheral surface, and both end surfaces of the sintered body are clamped with a correction die (not shown) to correct the size of the sintered body, thereby forming the bearing body 10.

[0046] (lubricating oil impregnation process) Then, the lubricating oil is allowed to permeate the pores of the bearing body 10. In this way, the sintered oil-impregnated bearing 1 is manufactured.

[0047] In this embodiment, a bare surface with numerous pores remaining on the sliding surface 12 combines the lubricating action of the solid lubricant phase with the load-bearing action of the bare surface, significantly improving sliding performance. Furthermore, because the solid lubricant phase permeates the bearing body 10, even if the surface of the sliding surface 12 is worn by the sliding object (shaft), a decrease in sliding performance can be suppressed. Furthermore, the solid lubricant in the pores and the lubricating oil impregnated in the pores become turbid and are supplied to the sliding surface 12 little by little, thereby maintaining sliding performance over a long period of time. Furthermore, because the sliding surface 12 has a small roughness Rz and is formed flat without any protruding irregularities, excessive generation of wear powder on the sliding surface 12 can be suppressed, reducing friction on the sliding surface.

[0048] Furthermore, the solid lubricant phase contains a resin that is softer than the bearing body 10 or the sliding object, and the solid lubricant that forms this solid lubricant phase together with the resin contains a substance that has cleavage properties or a substance that is softer than the sliding object (for example, graphite, molybdenum disulfide, calcium fluoride, talc, boron nitride, graphite fluoride, etc.). Therefore, even if the solid lubricant phase wears away due to the sliding of the sliding object, it is possible to prevent the bearing body 10 or the sliding object from being damaged by the wear powder. Furthermore, since the sintered oil-impregnated bearing 1 is mainly composed of an iron-based metal, the strength of the sintered oil-impregnated bearing 1 can be increased and the manufacturing cost can be reduced. Furthermore, because a bare surface with numerous open pores remains on the sliding surface 12, lubricating oil is discharged from these pores as the sliding object slides, further improving the sliding properties of the sintered oil-impregnated bearing 1. In this case, because the solid lubricating phase has lipophilicity, the solid lubricating phase formed within the bearing body 10 can prevent the lubricating oil impregnated in the pores from being discharged to the outside.

[0049] In the manufacturing method of the sintered oil-impregnated bearing 1 of this embodiment, a solid lubricant phase is formed after the sintering step, which prevents the solid lubricant from reacting with the metal components that make up the sintered body during sintering to create a high-strength structure, and prevents the solid lubricant from being decomposed by the high temperatures during sintering, thereby broadening the range of solid lubricant options available. Here, if a solid lubricant phase is formed after sizing the sintered body, it becomes difficult to maintain dimensional accuracy and surface roughness due to uneven thickness of the solid lubricant phase adhering to the surface, and the opening diameter of the pores formed on the surface of the sintered body by sizing becomes smaller, making it difficult for the solid lubricant to penetrate into the pores. In contrast, in this embodiment, the sizing process is carried out after the impregnation process and the heating process, which makes it easier for the solid lubricant to penetrate into the pores in the impregnation process, and thereby makes it possible to form a solid lubricant phase inside the bearing body 10 as well.

[0050] In addition, since the particle size of the solid lubricant is smaller than the opening diameter of the pores, the solid lubricant can easily enter the pores. This makes it easier to form a solid lubricant phase in the pores. Furthermore, because the lubricant is impregnated into the pores, as the shaft slides, the lubricant mixes with the solid lubricant phase in the pores and is discharged to the sliding surface 12, further improving the sliding properties of the sintered oil-impregnated bearing 1.

[0051] The present invention is not limited to the configuration of the above embodiment, and various modifications can be made to the detailed configuration without departing from the spirit of the present invention. For example, in the above embodiment, the impregnation step is performed immediately after the sintering step, but this is not limited to this. For example, a blinding step may be provided in which regions of the sintered body other than those that will become the sliding surfaces 12 (both end faces and the outer peripheral surface of the bearing body 10) are processed before the impregnation step to blind at least some of the pores. This blinding step can prevent the solid lubricant that will become the solid lubricant phase from entering regions other than those that will become the sliding surfaces 12, for example, when the impregnation step is performed by a dipping method, thereby reducing manufacturing costs.

[0052] In the above embodiment, iron-based metal powder is used as the metal powder that forms the base of the sintered oil-impregnated bearing, but the present invention is not limited to this, and various sintered metals may be used.

[0053] In the above embodiment, a dilution liquid consisting of an organic solvent mixed with molybdenum disulfide and a resin binder is used to form the solid lubricant phase, but this is not limiting, and an organic solvent mixed with a resin binder and two or more of the above-mentioned solid lubricants such as graphite, molybdenum disulfide, calcium fluoride, talc, boron nitride, and graphite fluoride may also be used as the dilution liquid. Furthermore, the solid lubricant is not limited to the above-mentioned substances exemplified as solid lubricants, and any solid lubricant may be used as long as it is a substance that has cleavage properties or is softer than the sliding object.

[0054] In the above embodiment, the sintered sliding part is an oil-impregnated sintered bearing impregnated with lubricating oil, but the present invention is not limited to this and also includes a dry sintered bearing. In this case, the lubricating oil impregnation step may be omitted. Furthermore, in order to provide a sintered oil-impregnated bearing having properties that are compatible with the conditions of use, the metal materials used (the blend of metal powders) and various conditions in the manufacturing process may be changed as appropriate. Furthermore, the shape of the sintered sliding part is not limited to a bearing shape, and any shape is possible as long as it has a sliding surface capable of supporting a sliding object. [Example]

[0055] The results of tests conducted to demonstrate the effects of the present invention will be described below. In Examples 1 to 7 and Comparative Examples 1 and 2, an iron-copper powder containing a mixture of iron, copper, tin, and the like was used as the raw material powder. The raw material powder, consisting of iron and copper, was prepared by mixing 48% by mass of iron powder, 2% by mass of tin powder, and the remainder being copper powder. The raw material powder was then compressed at 300 MPa in the compacting step to form a green compact, and sintered at 900°C in the sintering step to form a sintered body. The area ratio, penetration depth, and sliding surface roughness of the solid lubricant phase were adjusted by setting the dilution concentration of the diluent used in the solid lubricant phase imparting step to 20% by mass to 30% by mass and the immersion time to 3 seconds to 30 minutes. In Examples 1, 3, and 5, 10 mass% molybdenum disulfide and 10 mass% epoxy resin binder were added to an organic solvent and stirred to produce a diluted solution. The sintered body was then immersed in the diluted solution for 30 minutes to impregnate the sintered body with the diluted solution, and the sintered body was then heated at 200°C for 60 minutes to volatilize the liquid content of the diluted solution, forming a solid lubricant layer on the sliding surface and inside the sample. After sizing, a sintered bearing with a bearing body diameter of 16 mm and a bearing bore diameter of 8 mm was formed. The sintered bearing was then impregnated with ISO grade VG68 mineral oil (kinematic viscosity of 68 cst at 40°C) to form an oil-impregnated sintered bearing (hereinafter referred to as the sample). In Example 2, the sintered body in Example 1 was immersed in the diluted solution for 15 minutes, and a sample was prepared in the same manner as in Example 1. In Examples 4 and 7, the diluted solution was prepared by adding 15 mass% of molybdenum disulfide and 15 mass% of an epoxy resin binder to an organic solvent and stirring, and the remaining steps were the same as in Example 1. In Example 6, a sample was prepared in the same manner as in Example 1, except that the immersion time in the diluted solution was 3 seconds.

[0056] On the other hand, in Comparative Example 1, sizing was performed immediately after the sintering step to form a sintered bearing of the above shape. In Comparative Example 2, the same diluent as in Example 4 was used, and the sintered body was immersed in the diluent for 30 minutes to impregnate the sintered body with the diluent. After that, the sintered body was heated at 200°C for 60 minutes, and then immersed in the diluent for another 30 minutes, and then heated at 200°C for 60 minutes. The remaining steps were the same as in Example 1 to form a sample. The surface thickness of the solid lubricant layer, penetration depth, area ratio of the solid lubricant layer on the sliding surface, roughness Rz (JIS B 0601 2001), oil content (open porosity), friction coefficient, and durability of each sample are shown in Table 1.

[0057] (surface thickness measurement) The surface thickness of the solid lubricant layer was calculated by subtracting the inner diameter of the sintered compact before the solid lubricant layer was formed from the inner diameter of the sample on which the solid lubricant layer was formed, specifically, (inner diameter of the sample on which the solid lubricant layer was formed - inner diameter of the solid lubricant layer) / 2.

[0058] (Measurement of penetration depth) The penetration depth of the solid lubricant phase was determined by cutting each sample along the axial direction and observing the cross section of the inner surface side with a scanning electron microscope (SEM). Because the solid lubricant phase uses molybdenum disulfide (MoS2) as the solid lubricant, the penetration depth was confirmed by mapping Mo and S as extracted elements.

[0059] (Area ratio measurement) Each sample (sintered oil-impregnated bearing) was cut in two along the axial direction, and elemental analysis of the sliding surface of the sample was performed using an SEM at one random location. Mo and S were mapped as extracted elements, and the image was binarized using image processing software (see Figure 5). The area in which Mo and S elements were detected was expressed as a ratio to the area of ​​the entire image, which was used to determine the area ratio.

[0060] (Measurement of roughness Rz (JIS B 0601 2001)) Roughness Rz (JIS B 0601 2001) was measured using a roughness meter (SE700 manufactured by Kosaka Laboratory Co., Ltd.) Palpation was performed using a chisel-type stylus with a radius of 1 mm to minimize the influence of pores on the measurement values.

[0061] (Oil content measurement) The oil content was measured according to JIS Z 2501.

[0062] (Measurement of coefficient of friction) A shaft made of S45C was inserted into the bearing hole of each sample, with the axial direction perpendicular to the direction of gravity, and the shaft was rotated to evaluate the friction coefficient of each sample. Run-in and measurement were performed at room temperature, with a load of 3 MPa on the shaft and a rotation speed of 100 m / min. The friction coefficient was measured at the point where the friction stabilized after run-in. The friction coefficient was calculated by measuring the torque generated in the bearing as a load using a load cell (UT-1K manufactured by MinebeaMitsumi Inc.), and then converting the distance from the measurement position to obtain the friction coefficient.

[0063] (Durability evaluation) Durability was evaluated for each sample with the oil content shown in Table 1, by running it continuously for 150 hours at room temperature, with a surface pressure on the shaft of 3 MPa and a sliding speed (rotational speed) of 100 m / min. In this evaluation, if the operation stopped due to seizure or the generation of wear powder, it was judged as "stopped," and if the operation continued for 150 hours, it was judged as "no abnormality." The evaluation results are shown in Table 1.

[0064] [Table 1]

[0065] As shown in Table 1, in Examples 1 to 7, in which the lubricating phase was dispersed on the sliding surface and part of the lubricating phase penetrated into the interior, the friction coefficient was low at 0.125 or less, demonstrating improved sliding properties. Furthermore, the samples of Examples 1 to 7 showed no abnormalities even after 150 hours of continuous operation, demonstrating that they maintained high sliding properties. Among these, Examples 1, 3, and 5 had an area ratio of the solid lubricating phase on the sliding surface of 10% to 60%, a penetration depth of the solid lubricating phase into the sintered component body (bearing body) of 50 μm or more, and a sliding surface roughness Rz (JIS B 0601 2001) of 5 μm or less. Therefore, the friction coefficient was particularly small at 0.089 or less, demonstrating further improved sliding properties.

[0066] On the other hand, in Comparative Example 1, since no solid lubricant phase was formed, the friction coefficient was high at 0.153, and sliding properties could not be improved. Furthermore, since no solid lubricant phase was formed in Comparative Example 1, the surface seized after 3 hours of operation, and operation was stopped. Furthermore, in Comparative Example 2, since a solid lubricant phase was formed over the entire sliding surface, there was an insufficient supply of lubricant to the sliding surface, and the shaft was supported only by the solid lubricant phase with low strength. This resulted in the generation of excessive wear particles, resulting in a high friction coefficient of 0.193, and sliding properties could not be improved. Furthermore, wear progressed rapidly on the sliding surface, and wear particles accumulated after 25 hours of operation, causing operation to be stopped. [Explanation of symbols]

[0067] 1 Sintered oil-impregnated bearing 10 Bearing body (sintered body, sintered part body) 11 Bearing hole 12 Sliding surface

Claims

1. A sintered sliding component having a porous sintered component body made of sintered metal on which a sliding surface for slidably supporting a sliding object is formed, a solid lubricant phase containing a solid lubricant and a bare surface of the sintered component body having a large number of open pores are dispersed on the sliding surface, the area ratio of the solid lubricant phase to the sliding surface is 10% or more and 60% or less, the solid lubricant contains particles smaller than the opening diameter of the pores, and a portion of the solid lubricant phase penetrates into the sintered component body; the penetration depth of the solid lubricant phase into the sintered component body is 50 μm or more; The open porosity is 14 vol% or more and 25 vol% or less, A sintered sliding part, characterized in that at least some of the pores are impregnated with lubricating oil.

2. A sintered sliding part according to claim 1, characterized in that the roughness Rz (JIS B 0601 2001) of the sliding surface is 5 μm or less.

3. 2. The sintered sliding part according to claim 1, wherein the solid lubricant phase contains a resin.

4. 4. The sintered sliding part according to claim 1, wherein the main component of the sintered part body is an iron-based metal.

5. 5. The sintered sliding part according to claim 1, wherein the solid lubricant contains a substance having cleavage properties or a substance softer than the sliding object.

6. 2. The sintered sliding part according to claim 1, wherein the solid lubricant phase has lipophilicity.

7. A method for producing a sintered sliding part according to any one of claims 1 to 5, a sintering step of sintering the green compact to form a sintered body having an open porosity of 15 vol % or more and 30 vol % or less; an impregnation step of impregnating the sintered body with a diluent mixed with a solid lubricant containing particles smaller than the opening diameter of pores on the surface that will become the sliding surface of the sintered body; a heating step of heating the sintered body after the impregnation step to volatilize the liquid content of the diluent; a sizing step of sizing the sintered body after the heating step to form a sintered part main body; and a lubricant impregnation step of impregnating the sintered body with a lubricant after the sizing step.

8. 8. The method for producing a sintered sliding part according to claim 7, wherein the dilution liquid is mixed with the solid lubricant and a resin binder.

9. 9. The method for producing a sintered sliding part according to claim 7, further comprising a blinding step of processing a region of the sintered body other than a region that will become the sliding surface, to blind at least some of the pores, before the impregnation step.

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