JP7024291B2 - Iron-based sintered bearings and iron-based sintered oil-impregnated bearings - Google Patents

Description

The present invention relates to an iron-based sintered oil bearing having a bearing surface that supports the outer peripheral surface of the shaft, and an iron-based sintered oil-impregnated bearing in which the pores thereof are impregnated with lubricating oil.

Conventionally, sintered oil-impregnated bearings made of sintered alloy have been widely used for sliding bearings 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 sintered alloy with pores with lubricating oil, and since self-lubricating property can be imparted by the impregnated lubricating oil, seizure resistance and wear resistance can be imparted. Is good and widely used.

The lubrication theory of sintered oil-impregnated bearings 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 supports the shaft 3 on the inner diameter 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. This flow of lubricating oil lifts the shaft from the inner diameter surface of the bearing to prevent metal contact between the inner diameter 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 diameter surface of the bearing, and the hydraulic pressure distribution 5 on the inner diameter surface of the bearing is as shown in FIG. On the other hand, even if hydraulic 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 diameter 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 the capillary force and returns 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 the disadvantages that it is easily seized and the shaft, which is a mating component, is easily damaged. In particular, when a shaft having no heat treatment and having a low hardness and a bearing containing iron as a main component are used in combination, the above phenomenon becomes remarkable.

Under such circumstances, in Patent Document 1, the overall composition of the sintered alloy is Cu: 2.0 to 9.0%, C: 1.5 to 3.7%, the balance: Fe and the mass ratio. Iron-based sintered bearings made of unavoidable impurities have been proposed. Inside this bearing, a copper phase extending in a direction intersecting the axial direction of the bearing, a graphite phase and pores are contained in an iron alloy phase consisting of 20 to 85% ferrite in terms of area ratio and pearlite in the balance. It shows a dispersed metal structure, and the copper phase is exposed on the bearing surface at an area ratio of 8 to 40%. It is described that this bearing has excellent wear resistance, seizure resistance comparable to that of an iron-copper-based sintered bearing using an iron-copper-based sintered alloy, and resistance to attack on mating parts. ..

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 diameter 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 Has been proposed (Patent Document 2). In this alloy structure, at least one of the free Cu phase and the free Cu—Fe alloy phase is dispersed in the martensite matrix, and the MnS phase is dispersed in an amount of 1.0 to 3.5% by mass. It is characterized by.

Japanese Unexamined Patent Publication No. 2010-077744 Japanese Unexamined Patent Publication No. 2009-155696

As described above, in the sintered oil-impregnated bearing, the lubricating oil drawn out from the pores due to the rotation of the shaft is drawn between the shaft and the inner diameter surface of the bearing as the shaft rotates, and an oil film is formed between the shaft and the inner diameter surface of the bearing. By forming a metal contact between the shaft and the inner diameter surface of the bearing, metal contact is prevented and good lubrication characteristics are exhibited. For this reason, application to various applications is progressing, but application to applications where it is difficult to form a good oil film is not progressing. 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 such as 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 diameter 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. 2 (b), with respect to the inner diameter 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 diameter surface of the bearing is likely to occur.

In these applications, plain bearings whose inner diameter surface is made of a fluororesin such as polytetrafluoroethylene (PTFE) are applied, but soft fluororesins are prone to wear and have problems in durability. be. 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 respect, 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 mating 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 exhibits sliding characteristics by lubricating with a free Cu phase or a Cu—Fe alloy phase and an MnS phase. In this regard, since the MnS phase is formed by the MnS powder added to the raw material powder remaining as it is, the MnS phase is dispersed only at the grain boundaries (powder grain boundaries) between the iron powders. However, since the MnS powder is stable and does not react with other powders, 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.

INDUSTRIAL APPLICABILITY 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 oil-impregnated bearing and a method for manufacturing the same, and an iron-based sintered oil-impregnated bearing in which pores are impregnated with lubricating oil.

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 has been found that the use of molybdenum disulfide is useful because it can exhibit good lubrication characteristics even in applications where calcination is likely to occur.
According to one aspect of the present invention, the iron-based sintered bearing has a bearing surface that supports the outer peripheral surface of the shaft, and is made of an iron-based sintered alloy in which pores that can be impregnated with lubricating oil are dispersed. It is a sintered bearing, and the overall composition of the iron-based sintered alloy is Cu: 0.5 to 3%, Mo: 0.3 to 3.3%, C: 1 to 5%, S in terms of mass ratio. : 0.2 to 2.2%, balance: Fe and unavoidable impurities, the density of the iron-based sintered alloy is 5.2 to 7.2 Mg / m ³ , and the metal structure of the iron-based sintered alloy. Has a base in which the pores are dispersed, a copper phase and a graphite phase dispersed in the base, and a sulfide phase which is precipitated and dispersed from at least one of the base and the copper phase, and the base is baynite. The gist is to exhibit one of a single-phase structure, a mixed structure of baynite and pearlite, a mixed structure of baynite and ferrite, and a mixed structure of baynite, pearlite and ferrite.
Further, according to one aspect of the present invention, the iron-based sintered oil-impregnated bearing has the iron-based sintered bearing and the lubricating oil impregnated in the pores of the iron-based sintered bearing.

In the iron-based sintered bearing, the sulfide phase is precipitated and dispersed in the grain boundaries and crystal grains at at least one of the matrix and the copper phase. The sulfide phase is mainly composed of iron sulfide and copper sulfide, and the sulfide phase has an area of 0.9 to 6% of the area of the cross section including pores in the cross section of the iron-based sintered alloy. It is preferable that the iron-based sintered alloy is dispersed so as to be present at a rate. The sulfide phase is granular, and it is preferable that the maximum particle size is 50 μm or less. On the bearing surface, the copper phase and the sulfide phase composed of copper sulfide are preferably dispersed in an area ratio of 5 to 20% with respect to the entire bearing surface in terms of lubrication characteristics. The proportion of bainite in the cross section of the metal structure of the base is preferably 10% or more in terms of area ratio. Further, when the porosity of the bearing surface is 15 to 30% in area ratio, it is suitable for an oil-impregnated bearing.

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 oil-impregnated bearing. It is a schematic diagram explaining the case where a good lubricating oil film is not formed.

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 the 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, has a bearing surface that supports the outer peripheral surface of the shaft, and is composed of an iron-based sintered alloy containing Fe (iron) as a main component. Will be done. The iron-based sintered alloy has pores that can be impregnated with lubricating oil dispersed, and the pores are impregnated with lubricating oil to form a sintered oil-impregnated bearing. 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 or Fe-Mo alloy powder described later, and a base of an iron-based sintered alloy is formed by using a raw material powder containing iron powder or Fe-Mo alloy powder as a main component. .. 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 that constitutes the iron-based sintered bearing is one of the single-phase structure of bainite, the mixed structure of bainite and pearlite, the mixed structure of bainite and ferrite, and the mixed structure of bainite and pearlite and ferrite. It is preferable that it is any one of them. That is, it is preferable that the base exhibits a metal structure containing bainite. Bainite is a tissue element with high mechanical strength because it is hard and has tenacity next to martensite. In the iron-based sintered alloy of the present invention, such bainite is used for the structure of the base to improve the mechanical strength of the iron-based sintered alloy and the wear resistance. Therefore, in the iron-based sintered bearing of the present invention, the ratio of bainite in the metal structure of the base is preferably 10% or more in terms of the area ratio in the cross section of the metal structure. The rest of the substrate may be one or both of pearlite and ferrite.

Ferrite is soft and has good compatibility with the shaft as the mating material, but its mechanical strength is low. 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 bainite single-phase metal structure, a mixed structure of bainite and pearlite, a mixed structure of bainite and ferrite, and bainite, depending on the required characteristics of the iron-based sintered bearing. It may be adjusted according to the blending amount and blending form of graphite and Mo so as to have either a mixed structure of pearlite and ferrite (details will be described later).

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. That is, 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 sintered bearings, such pores are used to impregnate the pores formed in the iron-based sintered alloy with lubricating oil to impart lubricity to the sintered bearing, and its lubricating characteristics are oil-free. Demonstrated for a long time. 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. It becomes impossible to exhibit good lubrication characteristics. On the contrary, 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 machine of the iron-based sintered alloy. The target strength will decrease. From this point of view, the density of the iron-based sintered alloy is preferably 5.2 to 7.2 Mg / m ³ . The density of the iron-based sintered alloy in this range 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 of the metal sintered material specified in Japanese Industrial Standards (JIS) Z2505.

Cu is a component that can form a soft copper phase to improve compatibility with the shaft that is the mating material, and can form copper sulfide with excellent lubricity to improve lubricity. be. When the amount of Cu is scarce, the amount of copper phase dispersed in the substrate is small, and the above effect cannot be sufficiently obtained. 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 of the total composition.

Cu is blended with 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 in the die cavity, the flat copper powder clings to the core rod and the copper powder sticks to the core rod. When this is molded into a bearing, the amount of copper phase exposed on the inner diameter surface of the bearing, which is required to have sliding characteristics, is larger than that inside the bearing. Therefore, even if the amount of Cu in the overall composition is reduced and the amount of Cu inside the bearing is reduced, 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 sulfide phase composed of copper sulfide (described later) can be 5 to 20% of the entire bearing surface in terms of area ratio, and is soft. The sliding characteristics can be further improved by the copper phase and the copper sulfide precipitated from the copper phase. 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 tends to enter 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.

Mo (molybdenum) dissolves in Fe forming a matrix and contributes to strengthening the matrix. In addition, Mo has a function of improving the hardenability of the iron base, and forms bainite in the base structure in the cooling process after sintering to improve the mechanical strength and resistance of the iron-based sintered bearing. Contributes to improvement of wear resistance. If the amount of Mo is small, the above effect will be poor. On the other hand, if the expensive Mo becomes excessive, the cost will increase accordingly. Therefore, the amount of Mo is 0.3 to 3.3% by mass, preferably 0.6 to 3.0% by mass of the total composition.

Mo may be alloyed with iron powder as a main raw material and blended in the form of Fe—Mo alloy powder, or may be blended as molybdenum disulfide. When Fe-Mo alloy powder is used instead of iron powder, Mo is uniformly dispersed throughout, so that the effect of Mo acts uniformly in the matrix, and the matrix structure can be made into a bainite single-phase structure. On the other hand, when Mo is blended using molybdenum disulfide powder, molybdenum disulfide is decomposed into Mo and S in the sintering process, and the generated Mo is diffused into the matrix, and the hardenability of the matrix structure of the portion where Mo is diffused is diffused. To form a bainite phase. Therefore, the portion where the diffusion of Mo is poor becomes pearlite. Therefore, it is possible to adjust the production ratio of bainite by using the compounding form of Mo.

S (sulfur) forms iron sulfide by combining with Fe forming a matrix, and forms copper sulfide when combined with Cu forming a copper phase. 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. Since these sulfides are rich in lubricity, 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. .. In the present invention, the sulfide phase is considered to specifically include all of the above sulfides, that is, sulfides derived from iron sulfide, copper sulfide and unavoidable impurities (manganese sulfide), depending on the situation. , One or more of the above sulfides are present in the metal structure of the sintered alloy as a sulfide phase.

S is introduced by blending with the raw material powder in at least one form of iron sulfide powder and molybdenum disulfide powder. When S added in the form of iron sulfide powder exceeds 988 ° C. in the heating process of the sintering step, a eutectic liquid phase of Fe—S is generated, and liquid phase sintering proceeds and the liquid phase sintering proceeds between the powder particles. Promotes neck growth. On the other hand, when S is introduced in the form of molybdenum disulfide, S generated by decomposition of MoS diffuses into the iron powder in the process of raising the temperature, and when the temperature exceeds 988 ° C, a eutectic liquid phase of Fe—S is generated. Liquid phase sintering progresses and promotes the growth of necks between powder particles. After S is uniformly diffused into the iron matrix from the eutectic liquid phase generated in this way, it is deposited again as iron sulfide particles from the grain boundaries of the matrix and the inside of the crystal grains. Therefore, the iron sulfide particles are uniformly dispersed in the crystal grain boundaries of the matrix and in the crystal grains, and the precipitated iron sulfide particles have high adhesion. Further, a part of S can be diffused into the copper phase and bonded to Cu in the copper phase, so that it can be precipitated as copper sulfide particles in the grain boundaries of the copper phase and in the crystal grains. Therefore, the copper sulfide particles are also precipitated and dispersed in the crystal grain boundaries and crystal grains of the copper phase in this way, and thus have high adhesiveness. Regarding the ease of forming sulfides, Fe and Cu are as easy to form sulfides, and Mo is more difficult to form sulfides than Fe and Cu. Mainly iron sulfide and copper sulfide. The sulfide phase precipitates at at least one of the matrix and the copper phase and is present at the grain boundaries and within the grain.

When the amount of S is poor, the amount of sulfide dispersed in the substrate decreases, and the lubrication characteristics become insufficient. 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. .. Therefore, the amount of S is preferably 0.2 to 2.2% by mass, preferably 0.4 to 2.0% by mass of the total composition. At such a ratio, the sulfide phase in the metal structure 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 a granular manner. Further, when 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 at the time of metal contact. Therefore, the sulfide phase is preferably dispersed as particles having a maximum particle size of 50 μm or less.

C (carbon) is compounded in the form of graphite powder. 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 is dispersed in the pores of the iron-based sintered alloy. The graphite phase imparts lubricity to the iron-based sintered alloy. Further, a part of the graphite powder diffuses and dissolves in the Fe powder particles constituting the matrix to form pearlite, which contributes to the improvement of the mechanical strength of the matrix. This creates a matrix showing a single-phase structure of pearlite or a mixed structure of ferrite and pearlite.

When the amount of C is poor, the amount of the graphite phase dispersed in the iron-based sintered alloy decreases, and the lubrication characteristics deteriorate. 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 decreases. As a result, the mechanical strength of the iron-based sintered alloy constituting the iron-based sintered bearing is reduced. Therefore, the amount of C is preferably 1 to 5% by mass of the total composition. It is preferable to use graphite powder having an average particle size of about 40 to 80 μm in terms of diffusion to a substrate, 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 Mo: 0.3 to mass ratio. It is composed of 3.3%, C: 1 to 5%, S: 0.2 to 2.2%, the balance: Fe and unavoidable impurities, and the pore ratio of the iron-based sintered alloy is 10 to 25%. The iron-based sintered alloy has a metal structure in which pores, a copper phase and a graphite phase are dispersed in the matrix, and a sulfide phase is precipitated and dispersed from the matrix and / or the copper phase, and the matrix is bainite simple. It exhibits a phase structure, a mixed structure of bainite and pearlite, a mixed structure of bainite and ferrite, and a metal structure of one of a mixed structure of bainite, pearlite and ferrite.

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, electron probe microanalyzer (EPMA), or the like. , Can be measured using image analysis software such as WinROOF manufactured by Mitani Shoji Co., Ltd.

In the method for manufacturing an iron-based sintered bearing in the present invention, as the raw material powder of the iron-based sintered alloy constituting the iron-based sintered bearing, iron powder or Fe-Mo alloy powder, copper powder, graphite powder, and At least one kind of sulfide powder of iron sulfide powder and molybdenum disulfide powder is added and mixed, and by mass ratio, Cu: 0.5 to 3%, Mo: 0.3 to 3.3%, C: 1 to 1 to A mixed powder prepared to have a composition of 5%, S: 0.2 to 2.2%, balance: Fe and unavoidable impurities can be used.

The method for manufacturing an iron-based sintered bearing includes a molding step of forming the above-mentioned raw material powder into a bearing shape (net 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. It has a sintering step of sintering the obtained molded product. 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 Mg / m ³ . Can be manufactured.

In the sintering step, if the sintering temperature is too low, iron sulfide does not melt and sulfide cannot be dispersed and precipitated in the base of the iron-based sintered alloy, so the sintering temperature should be 990 ° C or higher. .. Further, if the sintering temperature is too high, graphite diffuses to the matrix and the residual graphite phase decreases, and the copper powder melts and the residual copper phase becomes scarce. Therefore, the sintering temperature should be 1080 ° C. or lower. Is. It should be noted that S easily reacts with hydrogen and oxygen, and 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 sintered 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, bainite is generated by the quenching effect of molybdenum, so that it is not necessary to perform quenching treatment in particular.

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 from various lubricating oils in consideration of the application and operating environment, and is used, for example, one type or a combination of two or more types from mineral oil, synthetic hydrocarbon oil, ester oil and the like. You can do it.

[First Example]
Using reduced iron powder, flat copper powder, molybdenum disulfide powder, and graphite powder, and using the raw material powder added and mixed 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 1 to 21. In addition, in order to perform the following measurements, a plurality of sintered bearing samples were prepared for each sample number.

For these bearing samples, the density of the iron-based sintered alloy 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, for the bearing sample of each sample number, the friction coefficient on the inner diameter surface of the sintered oil-impregnated 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 the bearing attached to the housing with a gap, and the shaft was rotated with a vertical load 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.

Further, a wear test was performed using a bearing sample of each sample number impregnated with lubricating oil in the same manner as described above. In the wear test, under the same conditions as the measurement of the friction coefficient described above, the shaft is inserted into the bearing sample attached to the housing, a load is applied to the housing, and the shaft is rotated for 120 minutes at the sliding position of the bearing surface. The amount of wear was measured. In the measurement of the amount of wear, the inner diameter in the vertical direction including the sliding position of the shaft was measured in advance for each bearing sample before the test, and the measurement was performed again after the test to calculate the amount of wear as the amount of fluctuation before and after the test. The results are shown in Table 1.

By comparing the bearing samples of sample numbers 1 to 7 in Table 1, the influence of the amount of Cu can be investigated. From Table 1, the bearing sample of sample No. 1 containing no Cu has a large value of friction coefficient because a soft copper phase is not formed. In the bearing sample of sample number 2 in which the amount of Cu added is 0.5% by mass, a soft copper phase is formed and the friction coefficient is reduced to 0.25. It can also be seen that the coefficient of friction decreases as the amount of Cu increases. However, as the amount of Cu added increases, the annular strength decreases, and in sample number 7 exceeding 3% by mass, the annular strength becomes less than 150 MPa and the amount of wear also exceeds 20 μm. 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 a bearing having a Cu content of 0.5 to 3% by mass can be used even under sliding conditions in which it is difficult to form a good lubricating oil film.

On the other hand, the influence of the amount of C can be investigated by comparing the bearing samples of sample numbers 3, 16 to 21. The bearing sample of sample number 16 in which the amount of C is 0.5% by mass has a large value of friction coefficient because the graphite phase is scarce. In the bearing sample of sample number 17 in which the amount of C added is 1% by mass, a sufficient amount of graphite phase is formed and the friction coefficient is reduced to 0.24. Further, it can be seen that the coefficient of friction decreases as the amount of C increases. However, 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, and the value of the amount of wear also increases to a value close to 20 μm. do. 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 a bearing having a C content of 0.5 to 5% by mass can be used even under sliding conditions in which it is difficult to form a good lubricating oil film.

Further, by comparing the bearing samples of sample numbers 3, 08 to 15, the influence of the amount of S can be investigated. In the bearing sample of sample number 8 which does not contain S, since the sulfide phase is not formed, the friction coefficient and the amount of wear are large values. On the other hand, in the bearing sample of sample number 9 having an S amount of 0.2% by mass, a sulfide phase is formed, the friction coefficient is reduced to 0.25, and the wear amount is also reduced to 16 μm. Considering the values of sample numbers 3, 10 to 13, it is clear that the friction coefficient and the amount of wear decrease as the amount of S increases, and the coefficient of friction and the amount of wear are reduced when the proportion of S is 0.2% by mass or more. The amount is preferable because it shows a low value. However, 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 2.2% by mass, the annular strength decreases to 120 MPa. From these facts, it can be seen 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 0.2 to 2.2% by mass. Preferably, the raw material powder is prepared so that the amount of S is 0.4 to 2.0% by mass. Corresponding to the above results, it is clear that the Mo amount is preferably in the range of 0.3 to 3.3% by mass, and preferably in the range of 0.6 to 3.0% by mass. This result shows that bearings with an S amount of 0.2 to 2.2% by mass and a Mo amount of 0.3 to 3.3% by mass are compatible even under sliding conditions where it is difficult to form a good lubricating oil film. Show that it is possible.

In the correlation between the blending ratio and the sliding characteristics, as described above, for the copper powder and the graphite powder, the annular strength decreases and the wear amount increases as the blending ratio increases. On the other hand, for molybdenum disulfide powder, the annular strength decreases as the blending ratio increases, but the amount of wear does not increase, but conversely decreases. This is an effect caused by the introduction of Mo, which dissolves in Fe and contributes to the strengthening of the base, improves the hardenability of the iron base and forms the bainite phase. It is considered that the toughness is imparted to the material and the wear resistance is improved. In this respect, the amount of wear is relatively large in the iron-based sintered oil-impregnated bearing obtained when the raw material powder is blended so that the amount of S is the same by using iron sulfide powder instead of molybdenum disulfide powder. It has been confirmed by that. For example, in an iron-based sintered bearing (using 3.3% by mass of iron sulfide powder instead of molybdenum disulfide powder) having the same overall composition as sample number 3 except that it does not contain Mo, baynite is seen in the metal structure. However, the measured value of the amount of wear in the above-mentioned wear test was about 19 μm.

For the iron-based sintered bearings of sample numbers 3, 8, 9 and 15, the cross section of the bearing was observed using an electron probe microanalyzer, the area of the bainite structure was measured based on the observed image, and the bainite structure in the substrate was measured. The area ratio was calculated. In the measurement, image analysis software (WinROOF, manufactured by Mitani Corporation) was used. As a result, the ratio of the bainite phase was 0% in the sample number 8 containing no molybdenum, and the ratio of the bainite phase increased from 3% to 40% in the order of sample number 9, sample number 3, and sample number 15. Was there. In addition, the parts other than the bainite structure of the base were all composed of ferrite and pearlite.

[Second Example]
Using the raw material powder of sample No. 3 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, friction coefficient and wear amount 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. 3 of the first example.

By comparing sample numbers 3, 22 to 29 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 Mg / m 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 Mg / m ³ . The amount of wear decreases as the density decreases, and in order to suppress the amount of wear to about 20 μm or less, it is necessary to mold to a density of 5.2 Mg / m ³ or more. 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 Mg / m ³ . This result shows that it is possible to cope with sliding conditions where it is difficult to form a good lubricating oil film.

The iron-based sintered bearing of the present invention has the tenacity of the base, and when used as an iron-based sintered oil-impregnated bearing impregnated with lubricating oil, it is difficult to form a good lubricating oil film and metal contact is likely to occur. Good lubrication characteristics can be exhibited even under sliding conditions. 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 where the drive time for forward rotation and reverse rotation is 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.

1 Sintered bearing 2 Lubricating oil 3 Shaft 5 Hydraulic distribution

Claims (6)

An iron-based sintered bearing composed of an iron-based sintered alloy having a bearing surface that supports the outer peripheral surface of the shaft and having pores impregnated with lubricating oil dispersed, and the overall composition of the iron-based sintered alloy. However, in terms of mass ratio, Cu: 0.5 to 3%, Mo: 0.3 to 3.3%, C: 1 to 5%, S: 0.2 to 2.2%, balance: Fe and unavoidable impurities. Consists of
The density of the iron-based sintered alloy is 5.2 to 7.2 Mg / m ³ , and the metal structure of the iron-based sintered alloy consists of a base in which the pores are dispersed and a copper phase and graphite dispersed in the base. It has a phase and a sulfide phase that precipitates and disperses from at least one of the matrix and the copper phase.
The base is an iron-based sintered bearing exhibiting a single-phase structure of bainite, a mixed structure of bainite and pearlite, a mixed structure of bainite and ferrite, and a mixed structure of bainite, pearlite and ferrite. The iron-based sintered bearing according to claim 1, wherein the sulfide phase is precipitated and dispersed in crystal grain boundaries and crystal grains at at least one of the matrix and the copper phase. The iron-based sintered bearing according to claim 1 or 2, wherein the sulfide phase is composed of iron sulfide and copper sulfide. The sulfide phase is dispersed in the iron-based sintered alloy so that it is present in the cross section of the iron-based sintered alloy at an area ratio of 0.9 to 6% with respect to the area of the cross section including pores. The iron-based sintered bearing according to any one of claims 1 to 3. The iron-based sintered bearing according to any one of claims 1 to 4 , wherein the bearing surface has a porosity of 10 to 25 % in terms of area ratio. An iron-based sintered oil-impregnated bearing comprising the iron-based sintered bearing according to any one of claims 1 to 5 and a lubricating oil impregnated in the pores of the iron-based sintered bearing.

Images