JP6819696B2 - Iron-based sintered oil-impregnated bearing - Google Patents

Description

The present invention relates to an iron-based sintered oil-impregnated bearing having a bearing surface that supports the outer peripheral surface of the shaft.

Conventionally, a sintered bearing made of a sintered alloy is often used as a slide bearing having a bearing surface that supports the outer peripheral surface of the shaft. Sintered oil-impregnated bearings are made by impregnating the pores of a sintered bearing made of a sintered alloy with pores with lubricating oil, and since self-lubricating property can be imparted by the impregnated lubricating oil, seizure resistance and abrasion resistance. Is good and widely used.

The lubrication theory of a sintered oil-impregnated bearing will be described with reference to FIG. The sintered body constituting the sintered bearing 1 which is the main body of the sintered oil-impregnated bearing is a porous body in which pores are dispersed in a metal matrix, and the pores are impregnated with lubricating oil 2. The sintered bearing is formed in a substantially circular tube or a substantially annular ring, and the shaft 3 is supported on the inner peripheral surface thereof. Here, when the shaft rotates, the lubricating oil impregnated in the pores thermally expands due to the frictional heat with the shaft, and the lubricating oil impregnated in the pores is sucked out by the rotation of the shaft. As shown, the lubricating oil flows from the upper part where the oil pressure is low toward the sliding part which receives the high oil pressure. The flow of the lubricating oil lifts the shaft from the inner peripheral surface of the bearing to prevent metal contact between the inner peripheral surface of the bearing and the shaft. Further, the shaft is offset in the rotational direction by the flow of the lubricating oil that enters between the shaft and the inner peripheral surface of the bearing, and the hydraulic distribution 5 on the inner peripheral surface of the bearing is as shown in FIG. On the other hand, even if flood pressure is generated, the lubricating oil escapes through the pores, so that the lubricating oil circulates in the sintered bearing through the pores and exerts an effective lubricating action on the inner peripheral surface again. When the rotation of the shaft is stopped, the thermally expanded lubricating oil contracts, and the lubricating oil is absorbed into the pores by capillary force to return to the initial state. By repeating this, good lubrication characteristics are exhibited without lubrication for a long period of time.

The shaft supported by the bearing is generally made of an inexpensive iron alloy, and a copper-based sintered bearing to which a copper-based sintered alloy is applied has been widely used for the sintered bearing. In recent years, as the price of copper has soared, there is an increasing need for iron-based sintered bearings using an inexpensive iron-based sintered alloy containing iron as a main component. However, such a bearing containing iron as a main component has a drawback that it is easily seized and the shaft, which is a mating component, is easily damaged. In particular, when a shaft having low hardness that has not been heat-treated and a bearing containing iron as a main component are used in combination, the above phenomenon becomes remarkable.

Under such circumstances, Patent Document 1 has excellent wear resistance, seizure resistance comparable to that of iron-copper-based sintered bearings using iron-copper-based sintered alloys, and mitigation of attacks on mating parts. An iron-based sintered bearing has been proposed as having the above. In this bearing, the overall composition of the sintered alloy is Cu: 2.0 to 9.0%, C: 1.5 to 3.7%, the balance: Fe and unavoidable impurities in terms of mass ratio, and the inside of the bearing. Is a metal structure in which a copper phase extending in a direction intersecting the axial direction of the bearing, a graphite phase and pores are dispersed in an iron alloy phase in which ferrite is 20 to 85% in area ratio and the balance is pearlite. The copper phase is exposed on the bearing surface at an area ratio of 8 to 40%.

Further, as an iron-based sintered alloy for sliding members suitable for use in bearings in which a high surface pressure acts on the inner peripheral surface, the overall composition is C: 0.6 to 1.2% in terms of mass ratio. Cu: 3.5 to 9.0%, Mn: 0.6 to 2.2%, S: 0.4 to 1.3%, balance: Fe and iron-based sintered alloy for sliding members consisting of unavoidable impurities (Patent Document 2) has been proposed, in which at least one of a free Cu phase and a free Cu—Fe alloy phase is dispersed in a martensite matrix, and the MnS phase is 1.0. It is characterized in that it is dispersed in an amount of ~ 3.5% by mass.

JP-A-2010-077744 JP-A-2009-155696

As described above, in the sintered oil-impregnated bearing, the lubricating oil drawn out from the pores by the rotation of the shaft is drawn between the shaft and the inner peripheral surface of the bearing as the shaft rotates, and between the shaft and the inner peripheral surface of the bearing. By forming an oil film on the bearing, metal contact between the shaft and the inner peripheral surface of the bearing is prevented and good lubrication characteristics are exhibited. For this reason, application to various applications is progressing, but its application is not progressing to applications in which it is difficult to form a good oil film. Further improvement of sintered bearings is necessary for further expansion of applications.

In fields where it has been considered difficult to apply such sintered oil-impregnated bearings, for example, paper feed rollers for copiers, head drive motors, and other shafts that rotate in the forward and reverse directions are supported and positive. There are bearings for applications where the drive time for rolling and reversing is short. In such an application, as shown in FIG. 2A, the rotation is stopped before a good lubricating oil film is formed, so that metal contact between the shaft and the inner peripheral surface of the bearing is likely to occur.

Further, in an application as a bearing that supports a rotor shaft that rotates eccentrically with respect to a stator, such as a scroll compressor, as shown in FIG. 2B, with respect to the inner peripheral surface of the bearing. The position of the shaft will move eccentrically. Even in such an application, it is difficult to form a good lubricating oil film, and metal contact between the shaft and the inner peripheral surface of the bearing is likely to occur.

In these applications, plain bearings whose inner peripheral surface is made of a fluororesin such as polytetrafluoroethylene (PTFE) are applied, but soft fluororesins are prone to wear and have a problem in durability. There is. Therefore, even in applications where such metal contact is likely to occur, if a sintered bearing exhibiting good sliding characteristics can be provided, the application of the sintered bearing can be expanded.

In this regard, the iron-based sintered bearing of Patent Document 1 has excellent wear resistance for applications in which a good lubricating oil film can be formed, and has seizure resistance comparable to that of iron-copper-based sintered oil-impregnated bearings. Has the ability to mitigate attacks on partner parts. However, further improvements are needed for applications where metal contact is likely to occur.

On the other hand, the iron-based sintered sliding member of Patent Document 2 is lubricated by a free Cu phase or a Cu—Fe alloy phase and an MnS phase, and exhibits sliding characteristics. In this regard, since the MnS phase is formed by leaving the MnS powder added to the raw material powder as it is, the MnS phase is dispersed only at the grain boundaries (powder grain boundaries) of the iron powders. However, the MnS powder is stable and does not react with other powders, so it does not react with the iron powder forming the matrix, and therefore has poor adhesion to the matrix. Further, since it exists at the grain boundaries of the iron powder and inhibits the bonding between the iron powder particles, the strength of the matrix may decrease.

The present invention achieves further improvement in lubrication characteristics for iron-based sintered oil-impregnated bearings regardless of the method of Patent Document 2 having poor adhesiveness, and has good lubrication characteristics even in applications where metal contact is likely to occur. It is an object of the present invention to provide an iron-based sintered bearing and a method for manufacturing the same.

The present inventors have studied an iron-based sintered bearing that achieves the above object, and metal contact is performed by precipitating and dispersing sulfide in the base of the iron-based sintered alloy constituting the main body of the iron-based sintered bearing. It was found that good lubrication characteristics can be exhibited even in applications where the above is likely to occur.
According to one aspect of the present invention, the iron-based sintered oil-impregnated bearing includes an iron-based sintered bearing having a bearing surface that supports the outer peripheral surface of the shaft and having an iron-based sintered alloy in which pores are dispersed. An iron-based sintered oil-impregnated bearing having the lubricating oil impregnated in the pores, and the overall composition of the iron-based sintered alloy is Cu: 0.5 to 3% and C: 1 to 5 in terms of mass ratio. %, S: 0.3 to 2%, balance: Fe and unavoidable impurities, the density of the iron-based sintered alloy is 5.2 to 7.2 g / cm ³ , and the iron-based sintered alloy is: From a matrix having a metal structure of one of a ferrite structure, a pearlite structure, and a mixed structure of ferrite and pearlite, a copper phase and a graphite phase dispersed in the matrix, and at least one of the matrix and the copper phase. The gist is that it has a sulfide phase that precipitates and disperses.

In the iron-based sintered bearing, the sulfide phase may be precipitated and dispersed in the grain boundaries and grain boundaries of the matrix and the copper phase, and the sulfide is mainly iron sulfide and copper sulfide. You can. Further, in the iron-based sintered bearing, the sulfide phase dispersed in the metal structure is dispersed at an area ratio of 0.9 to 6% with respect to the area of the cross section including the pores when observing the cross section of the metal structure. It is preferable that the sulfide phase is granular and the maximum particle size is 50 μm or less. Further, it is preferable that the copper phase and the copper sulfide phase dispersed on the bearing surface are dispersed at an area ratio of 5 to 20% with respect to the entire bearing surface.

According to the embodiment of the present invention, the iron-based sintered bearing is provided with excellent improvement in lubrication characteristics, and exhibits good lubrication characteristics even in applications where metal contact is likely to occur.

It is a schematic diagram explaining the lubrication action of a sintered bearing. It is a schematic diagram explaining the case where a good lubricating oil film is not formed. It is a drawing substitute photograph which shows an example of the metal structure of the iron-based sintered alloy which comprises the iron-based sintered bearing in this invention.

Hereinafter, the metallographic structure of the iron-based sintered alloy constituting the iron-based sintered bearing, which is the main body of the iron-based sintered oil-impregnated bearing in the present invention, and the basis for specifying numerical values will be described together with the operation of the present invention.

In the present invention, the iron-based sintered bearing, which is the main body of the iron-based sintered oil-impregnated bearing, is composed of an iron-based sintered alloy containing Fe (iron) as a main component. As shown in FIG. 3, the iron-based sintered alloy contains, for example, an iron-based matrix (ferrite phase P1 in FIG. 3), a copper phase P2, a graphite phase P3, and a sulfide phase P4. .. Fe is a component suitable as a main component of an iron-based sintered alloy because it is cheaper than Cu (copper) and has excellent mechanical strength. Fe is introduced in the form of iron powder, and by using a raw material powder containing iron powder as a main component, a base of an iron-based sintered alloy is formed. Pore is dispersed in the base of the iron-based sintered alloy. The pores are generated by the powder metallurgy method, and the voids between the powder particles when the raw material powder is compacted remain in the matrix formed by the bonding of the raw material powder.

The metal structure of the base of the iron-based sintered alloy is one of a ferrite structure, a pearlite structure, and a mixed structure of ferrite and pearlite. Ferrite is soft and has good compatibility with the shaft used as the mating material, but has low mechanical strength. On the other hand, pearlite has a high base hardness and a high mechanical strength, but there is a risk of wearing the shaft that is the mating material. Therefore, the metal structure of the base of the iron-based sintered alloy may be a ferrite single-phase metal structure, a metal structure in which ferrite and pearlite are mixed, or a pearlite single-phase metal structure, depending on the required characteristics of the iron-based sintered bearing. Either.

As described above, since pores are formed in the sintered alloy due to the manufacturing method, the density of the sintered alloy (sintered body density) is lower than the theoretical density. When the density of the sintered alloy is high, the amount of pores is small, and when the density of the sintered alloy is low, the amount of pores is large. In a sintered bearing, by utilizing such pores to impregnate the pores formed in the iron-based sintered alloy with lubricating oil, it exhibits long-term lubrication characteristics without lubrication. In the present invention, when the amount of pores formed in the iron-based sintered alloy constituting the iron-based sintered bearing is small, that is, when the density of the iron-based sintered alloy is high, the amount of the lubricating oil impregnated becomes small, which is good. The lubrication characteristics cannot be exhibited. On the other hand, if the amount of pores formed in the iron-based sintered alloy is excessive, that is, the density of the iron-based sintered alloy is low, the amount of bases of the iron-based sintered alloy decreases, and as a result, the iron-based sintered alloy is mechanically mechanical. The strength will decrease. From this point of view, the density of the iron-based sintered alloy is preferably 5.2 to 7.2 g / cm ³ . The density of this iron-based sintered alloy corresponds to about 10 to 25% in terms of porosity of the iron-based sintered alloy. The density ratio of the sintered body is measured by the sintering density test method for metal sintered materials specified in Japanese Industrial Standards (JIS) Z2505.

Cu is a component capable of forming a soft copper phase to improve compatibility with a shaft as a mating material, and forming copper sulfide having excellent lubricity to improve lubricity. is there. If the amount of Cu is poor, the copper phase dispersed in the matrix will be poor, and the above effect will be poor. On the other hand, if the expensive Cu is excessive, the cost will increase accordingly. Therefore, the amount of Cu is set to 0.5 to 3% by mass.

Cu is added in the raw material powder in the form of copper powder. As the copper powder, it is preferable to use a flat or foil-shaped copper powder. When flat copper powder is used as the Cu raw material, when the raw material powder falls into the die cavity, the flat copper powder clings to the core rod, and the copper powder sticks to the core rod. The amount of copper phase exposed on the inner diameter surface of the bearing, which requires sliding characteristics, is larger than that inside the bearing. Therefore, even if the amount of Cu inside the bearing is reduced to reduce the amount of Cu in the overall composition, the amount of copper phase exposed on the inner diameter surface of the bearing can be maintained at a required amount. In this regard, the total appropriate amount of the copper phase dispersed on the inner diameter surface of the bearing and the copper sulfide phase described later can be 5 to 20% of the inner diameter surface in terms of area ratio, and the sulfide precipitated from the soft copper phase and the copper phase. With copper, the sliding characteristics can be further improved. As the flat copper powder, those having a particle size of about 20 to 150 μm can be preferably used. Copper powder with a small particle size easily enters the gaps between iron particles, and excessive copper powder is less likely to be ubiquitous around the core rod. The ratio of the particle size to the thickness is preferably about 2.5 to 20.

S (sulfur) combines with Fe forming a matrix to form iron sulfide, and also combines with Cu forming a copper phase to form copper sulfide. The iron powder, which is the main raw material, contains a very small amount (1% by mass or less) of Mn as an unavoidable impurity due to the production method. Therefore, manganese sulfide can also be dispersed in a small part. These sulfides are highly lubricious, and by precipitating and dispersing such sulfides in the matrix, it is possible to form a matrix that exhibits excellent lubrication characteristics even under sliding conditions where metal contact is likely to occur. ..

S is added to the raw material powder by adding it in the form of iron sulfide powder. When S added in the form of iron sulfide exceeds 988 ° C. in the temperature raising process of the sintering step, a eutectic liquid phase of Fe-S is generated, and liquid phase sintering proceeds to cause a neck between powder particles. Promote growth. Further, after S is uniformly diffused into the iron matrix from this eutectic liquid phase, it is precipitated again as iron sulfide particles from the grain boundaries of the matrix and inside the crystal grains. Therefore, the iron sulfide particles are uniformly dispersed in the grain boundaries of the matrix and in the crystal grains, whereby the adhesiveness of the iron sulfide particles can be enhanced. Further, a part of S may diffuse into the copper phase, combine with Cu in the copper phase, and precipitate as copper sulfide particles in the grain boundaries of the copper phase and in the crystal grains. Copper sulfide particles are also highly adherent because they are precipitated and dispersed in the crystal grain boundaries and crystal grains of the copper phase in this way.

When the amount of S is poor, the amount of sulfide dispersed in the matrix is poor, and the lubrication characteristics are poor. If the amount of S is excessive, the amount of precipitated sulfide is excessive and the strength of the matrix is lowered, and as a result, the mechanical strength of the iron-based sintered alloy constituting the iron-based sintered bearing is lowered. .. For this reason, the amount of S may be 0.3 to 2% by mass. At this time, the sulfide phase in the metal structure of the cross section of the iron-based sintered alloy is 0.9 to 6% in terms of the area ratio with respect to the area of the cross section including the pores when observing the cross section of the metal structure.

The sulfide is preferably dispersed in the metal structure in granular form. Further, if the size of the precipitated sulfide particles is coarse, the locations where the sulfide particles are present are unevenly distributed, and in the locations where the presence of the sulfide particles is scarce, wear, adhesion, etc. are likely to occur during metal contact. It is preferable that the particles are dispersed as particles having a maximum particle diameter of 50 μm or less.

C (carbon) is imparted in the form of graphite powder to form a graphite phase and impart lubricity to the iron-based sintered alloy. Further, when the matrix is composed of a single-phase structure of pearlite or a mixed structure of ferrite and pearlite, a part of C diffuses into Fe powder particles constituting the matrix and dissolves to form pearlite. Contributes to improving the mechanical strength of the base. The graphite phase is formed by the graphite powder particles remaining in the iron-based sintered alloy in an undiffused state. Therefore, the graphite phase will be dispersed in the pores.

When the amount of C is poor, the amount of graphite phase dispersed in the iron-based sintered alloy is poor, and the lubrication characteristics are poor. On the other hand, if the amount of C is excessive, the amount of the graphite phase to be dispersed becomes excessive, and the strength of the matrix is lowered. As a result, the mechanical strength of the iron-based sintered alloy constituting the main body of the iron-based sintered bearing is reduced. Will decrease. Therefore, the amount of C is set to 1 to 5% by mass. It is preferable to use graphite powder having an average particle size of about 40 to 80 μm in terms of diffusion to a matrix, sliding characteristics, and the like.

From the above, in a preferred embodiment of the present invention, the iron-based sintered alloy constituting the iron-based sintered bearing has an overall composition of Cu: 0.5 to 3% and C: 1 to 5% in terms of mass ratio. , S: 0.3 to 2%, balance: Fe and unavoidable impurities, the pore ratio of the iron-based sintered alloy is 10 to 25%, and the metal structure of the iron-based sintered alloy is the ferrite structure. It is one of a pearlite structure and a mixed structure of ferrite and pearlite. The copper phase and graphite phase are dispersed in the matrix, and the sulfide phase is precipitated and dispersed from the matrix and / or the copper phase. It exhibits a metallic structure.

The area ratio of the sulfide phase is based on an image obtained by observing the cross section or surface of an iron-based sintered bearing (iron-based sintered alloy) with a metallurgical microscope, an electron probe microanalyzer (EPMA), or the like. , Mitani Shoji Co., Ltd. Can be measured using image analysis software such as WinROOF.

In the method for producing an iron-based sintered bearing in the present invention, copper powder, graphite powder, and iron sulfide powder are added to iron powder as the raw material powder of the iron-based sintered alloy constituting the iron-based sintered bearing. Mix and use a mixed powder prepared to have a composition of Cu: 0.5 to 3%, C: 1 to 5%, S: 0.3 to 2%, balance: Fe and unavoidable impurities in terms of mass ratio. be able to.

The method for manufacturing an iron-based sintered bearing is a step of molding the above-mentioned raw material powder into a bearing shape, that is, a shape of a substantially circular tube or a substantially annular ring having an inner diameter surface that slides on a shaft, and the obtained molding. It has a step of sintering the body. In the molding process, by setting the molding pressure of the raw material powder to 250 to 650 MPa, the iron-based sintered bearing is provided so that the density of the iron-based sintered alloy after sintering becomes 5.2 to 7.2 g / cm ^3. Can be manufactured.

In the sintering step, if the sintering temperature is too low, iron sulfide does not melt and sulfide cannot be precipitated and dispersed in the base of the iron-based sintered alloy. Therefore, the sintering temperature is preferably 990 ° C. or higher. .. Further, if the sintering temperature is too high, graphite diffuses to the matrix and the residual graphite phase becomes scarce, and the copper powder melts and the copper phase becomes scarce. Therefore, the sintering temperature should be 1080 ° C. or lower. .. Since S easily reacts with hydrogen and oxygen, if the sintering atmosphere is an oxidizing gas, the S component introduced into the raw material powder is separated and the amount of S in the iron-based sintered alloy decreases. , The sintering atmosphere needs to be a non-oxidizing atmosphere. Further, it is preferable to use an atmosphere having a low dew point.
In the present invention, the method for manufacturing an iron-based sintered oil-impregnated bearing includes a step of preparing an iron-based sintered bearing according to the above-mentioned manufacturing method for an iron-based sintered bearing and impregnating the iron-based sintered bearing with lubricating oil. It has an impregnation step, and if necessary, the iron-based sintered bearing before impregnation may be subjected to final compression processing such as sizing and coining. The lubricating oil can be appropriately selected and used from various lubricating oils in consideration of the application and operating environment. For example, one type or a combination of two or more types of mineral oil, synthetic hydrocarbon oil, ester oil, etc. is used. You can do it.

[First Example]
Using the raw material powder prepared by preparing reduced iron powder, flat copper powder, iron sulfide powder, and graphite powder, and adding and mixing them at the ratios shown in Table 1, the outer diameter is 16 mm and the inner diameter is 10 mm at a molding pressure of 300 MPa. It was formed into a circular tube shape with a height of 10 mm and sintered at 1000 ° C. in a non-oxidizing gas atmosphere to prepare bearing samples of sample numbers 01 to 20. For each sample number, a plurality of sintered bearing samples were prepared for the following measurements.

For these bearing samples, the density of iron-based sintered alloys measured by the sintering density test method for metal sintered materials specified in Japanese Industrial Standards (JIS) Z2505 is in the range of 5.6 to 6.0 Mg / m ³ . Met.

Further, for the bearing sample of each sample number, the annular strength of each bearing sample was measured by the annular strength test method specified in Japanese Industrial Standards (JIS) Z2507. The results are also shown in Table 1.

Further, the bearing sample of each sample number was impregnated with lubricating oil (mineral oil viscosity grade ISO VG56), and the friction coefficient on the inner diameter surface of the sintered-containing bearing was measured. For the measurement of the coefficient of friction, a shaft made of carbon steel S45C was attached to the rotating shaft of the horizontal motor. This shaft was inserted into a bearing attached to the housing with a gap, and the shaft was rotated while a vertical load was applied to the housing. In this test, the ambient temperature was maintained at 25 ° C., the rotation speed of the shaft was set to 500 rpm, and the load surface pressure was set to 0.3 MPa. These results are also shown in Table 1.

By comparing the bearing samples of sample numbers 01 to 07 in Table 1, the influence of the amount of Cu can be investigated. From Table 1, the bearing sample of sample number 01 containing no Cu has a large coefficient of friction because a soft copper phase is not formed. On the other hand, in the bearing sample of sample number 02 in which the amount of Cu added is 0.5% by mass, a soft copper phase is formed and the friction coefficient can be reduced to 0.25. It can also be seen that the coefficient of friction decreases as the amount of Cu increases. From these facts, it was confirmed that good sliding characteristics can be obtained in the range of Cu amount of 0.5 to 3% by mass. This result indicates that it is possible to cope with sliding conditions in which it is difficult to form a good lubricating oil film.

By comparing the bearing samples of sample numbers 03 and 08 to 15 in Table 1, the effect of the amount of S can be investigated. From Table 1, the bearing sample of sample number 08 not containing S has a large friction coefficient because the sulfide phase is not formed. On the other hand, in the bearing sample of sample number 09 in which the amount of S added is 0.3% by mass, a sulfide phase is formed and the friction coefficient can be reduced to 0.25. It can also be seen that the coefficient of friction decreases as the amount of S increases. On the other hand, as the amount of S increases, the annular strength decreases, and in the bearing sample of sample number 15 in which the amount of S exceeds 2% by mass, the annular strength decreases to 120 MPa. From these facts, it was confirmed that an iron-based sintered oil-impregnated bearing having good sliding characteristics and high mechanical characteristics can be obtained in the range of S amount of 0.3 to 2% by mass. This result indicates that it is possible to cope with sliding conditions in which it is difficult to form a good lubricating oil film.

The effect of the amount of C can be investigated by comparing the bearing samples of sample numbers 03 and 16 to 21 in Table 1. From Table 1, the bearing sample of sample No. 16 having a C amount of 0.5% by mass has a large friction coefficient because the graphite phase is scarce. On the other hand, in the bearing sample of sample No. 17 in which the amount of C added was 1% by mass, a sufficient amount of graphite phase was formed, and the friction coefficient could be reduced to 0.24. It can also be seen that the coefficient of friction decreases as the amount of C increases. On the other hand, as the amount of C increases, the annular strength decreases, and in the bearing sample of sample number 21 in which the amount of C exceeds 5% by mass, the annular strength decreases to 140 MPa. From these facts, it was confirmed that an iron-based sintered oil-impregnated bearing having good sliding characteristics and high mechanical characteristics can be obtained in the range of C content of 0.5 to 5% by mass. This result indicates that it is possible to cope with sliding conditions in which it is difficult to form a good lubricating oil film.

[Second Example]
Using the raw material powder of sample number 03 of the first example, molding was performed by changing the molding pressure, and sintering was performed under the same sintering conditions as in the first example to prepare bearing samples of sample numbers 22 to 29. did. For these bearing samples, the density, annular strength, and friction coefficient of the iron-based sintered alloy of each bearing sample were measured in the same manner as in the first embodiment. Table 2 shows these results and the results of Sample No. 03 of the first example.

By comparing sample numbers 03 and 22 to 27 in Table 2, the influence of the density of the iron-based sintered alloy can be investigated. The coefficient of friction can be reduced to 0.25 or less in the range of density 5.0 to 7.2 g / cm ³ . It can be seen that as the porosity increases, the contact area between the bearing and the shaft decreases and the friction coefficient decreases. On the other hand, the annular strength decreases as the density decreases, and decreases to 150 MPa in the sample of sample number 22 having a density of 5.0 g / cm ³ . From this, it was confirmed that an iron-based sintered oil-impregnated bearing having good sliding characteristics and high mechanical characteristics can be obtained in the range of density of 5.2 to 7.2 g / cm ³ . This result indicates that it is possible to cope with sliding conditions in which it is difficult to form a good lubricating oil film.

The iron-based sintered oil-impregnated bearing in the present invention is difficult to form a good lubricating oil film, and can exhibit good lubricating characteristics even under sliding conditions where metal contact is likely to occur. It supports a shaft that rotates in the forward and reverse directions, such as a paper feed roller for a copying machine and a head drive motor, and is suitable as a bearing for applications in which the drive times for forward rotation and reverse rotation are short. It is suitable for bearings that support the shaft of a rotor that rotates eccentrically with respect to the stator, such as a type compressor.

Claims (6)

An iron-based sintered oil-impregnated bearing having a bearing surface that supports the outer peripheral surface of the shaft and having an iron-based sintered alloy in which pores are dispersed and a lubricating oil impregnated in the pores. And
The overall composition of the iron-based sintered alloy is composed of Cu: 0.5 to 3%, C: 1 to 5%, S: 0.3 to 2%, the balance: Fe and unavoidable impurities in terms of mass ratio.
The density of the iron-based sintered alloy is 5.2 to 7.2 g / cm ³ .
The iron-based sintered alloy has a matrix having one metal structure of a ferrite structure, a pearlite structure, and a mixed structure of ferrite and pearlite, a copper phase and a graphite phase dispersed in the matrix, and the matrix. An iron-based sintered oil-impregnated bearing having a sulfide phase that precipitates and disperses from at least one of the copper phases. The iron-based sintered oil-impregnated bearing according to claim 1, wherein the sulfide phase is precipitated and dispersed in the grain boundaries and grain boundaries of the matrix and the copper phase. The iron-based sintered oil-impregnated bearing according to claim 1 or 2, wherein the sulfide is mainly iron sulfide and copper sulfide. In the metal structure, the sulfide phase is dispersed in the metal structure at an area ratio of 0.9 to 6% with respect to the area of the cross section including pores when observing the cross section of the metal structure. The iron-based sintered oil-impregnated bearing according to any one of 3. The iron-based sintered oil-impregnated bearing according to any one of claims 1 to 4, wherein the sulfide phase is granular with a maximum particle size of 50 μm or less. The iron-based sintered oil-containing oil according to any one of claims 1 to 5, wherein the copper phase and the copper sulfide phase dispersed on the bearing surface are dispersed at an area ratio of 5 to 20% with respect to the entire bearing surface. bearing.