JP2019065323A - Iron-based sintered shaft bearing, and iron-based sintered oil-containing shaft bearing - Google Patents

Abstract

To provide an iron-based sintered shaft bearing exhibiting good lubrication property even in an application easy to generate metal contact.SOLUTION: A whole composition of an iron-based sintered alloy constituting an iron-based sintered shaft bearing consists of, by mass ratio, Cu:0.5 to 3%, C:1 to 5%, S:0.3 to 2%, and the balance: Fe with inevitable impurities. Density of the iron-based sintered alloy is 5.2 to 7.2 Mg/m. The iron-based sintered alloy has a copper phase and a graphite phase dispersed in a matrix of one metal structure of a ferrite structure, a pearlite structure, and a mixed structure of ferrite and pearlite, and a metal structure configuration in which a sulfide phase is deposited from the matrix and/or the copper phase and dispersed.SELECTED DRAWING: Figure 1

Description

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

  Sintered oil-impregnated bearings made of sintered alloy have been widely used in the past for slide bearings having bearing surfaces that support the outer peripheral surface of the shaft. A sintered oil-impregnated bearing is one in which a lubricating oil is impregnated in the pores of a sintered bearing made of sintered alloy having pores, and since it can impart self-lubricity with the impregnated lubricating oil, it has seizure resistance and wear resistance. Are 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 the metal matrix, and the lubricating oil 2 is impregnated in the pores. The sintered bearing is formed in a substantially circular tube or a substantially annular ring, and supports the shaft 3 at its inner diameter surface. 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 by the arrow 4 in FIG. As shown, the lubricating oil flows from the upper portion with low oil pressure toward the sliding portion receiving high oil pressure. This lubricating oil flow lifts the shaft from the bearing inner diameter surface to prevent metal contact between the bearing inner diameter surface and the shaft. In addition, the shaft is biased in the rotational direction by the flow of the lubricating oil entering between the shaft and the bearing inner diameter surface, and the hydraulic pressure distribution 5 on the bearing inner diameter surface is as shown in FIG. On the other hand, even if oil pressure is generated, the lubricating oil escapes through the pores, so 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 stops, the thermally expanded lubricating oil contracts and the lubricating oil is absorbed into the pores by capillary force and returns to the initial state. By repeating this, good lubrication characteristics can be exhibited without oiling for a long 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 as a sintered bearing. In recent years, since the price of copper has risen, the need for an iron-based sintered bearing using an iron-based sintered alloy containing an inexpensive iron as a main component is increasing. However, in the case of such an iron-based bearing, there is a disadvantage that it is easy to seize and to easily damage the shaft which is a mating part. In particular, when a shaft having a low hardness not subjected to heat treatment 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, by mass ratio, Cu: 2.0 to 9.0%, C: 1.5 to 3.7%, balance: Fe and Iron-based sintered bearings made of unavoidable impurities have been proposed. The inside of this bearing has a copper phase extending in a direction intersecting with the axial direction of the bearing, a graphite phase, and pores in an iron alloy phase consisting of 20 to 85% of ferrite and the balance consisting of pearlite in area ratio A dispersed metal structure is shown, and the copper phase is exposed at an area ratio of 8 to 40% on the bearing surface. This bearing is described to have excellent wear resistance and to have seizure resistance and attack relieving ability to counterpart parts comparable to that of iron-copper-based sintered bearing using iron-copper-based sintered alloy. .

  In addition, as an iron-based sintered alloy for a sliding member suitable for use in a bearing in which a high surface pressure acts on the inner diameter surface, the overall composition is, by mass ratio, C: 0.6 to 1.2%, Iron-based sintered alloy for sliding members comprising Cu: 3.5 to 9.0%, Mn: 0.6 to 2.2%, S: 0.4 to 1.3%, balance: Fe and unavoidable impurities Has been proposed (Patent Document 2). In this alloy structure, at least one of the liberated Cu phase and the liberated Cu-Fe alloy phase is dispersed in a martensitic matrix, and the MnS phase is dispersed in an amount of 1.0 to 3.5 mass%. It is characterized by

Unexamined-Japanese-Patent No. 2010-077474 JP, 2009-155696, A

  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 bearing inner diameter surface as the shaft rotates, and an oil film is formed between the shaft and the inner diameter surface of the bearing. By forming the above, metal contact between the shaft and the inner diameter surface of the bearing is prevented, and good lubrication characteristics are exhibited. For this reason, although the application to various uses is advanced, the application is not advanced to the use which is difficult to form a favorable oil film. For further application expansion, further improvement of the sintered bearing is necessary.

  As a field where application of such sintered oil-impregnated bearings has been considered difficult, for example, while supporting forward and reverse rotating shafts such as paper feed rollers of copying machines and head drive motors, etc. There are bearings for applications where the drive time for each roll and reverse is short. In such applications, as shown in FIG. 2 (a), since the rotation is stopped before a good lubricating oil film is formed, 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 the shaft of a rotor that rotates eccentrically with respect to the stator, such as a scroll compressor, as shown in FIG. The position of the shaft moves eccentrically. Even in such applications, 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, a slide bearing in which the inner diameter surface is formed of a fluorine-based resin such as polytetrafluoroethylene (PTFE) is applied, but a soft fluorine-based resin is prone to wear and has a problem with durability. is there. Therefore, the application of the sintered bearing can be expanded if it is possible to provide a sintered bearing that exhibits good sliding characteristics even in applications where such metal contact is likely to occur.

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

  On the other hand, the iron-based sintered sliding member of Patent Document 2 is lubricated by the liberated Cu phase or Cu-Fe alloy phase and the MnS phase to exhibit sliding characteristics. In this regard, since the MnS phase is formed by the remaining MnS powder added to the raw material powder as it is, the MnS phase is dispersed only in grain boundaries (powder grain boundaries) of 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 the adherence to the matrix is poor. Moreover, since it exists in the grain boundary of iron powder and inhibits the binding of iron powder particles, there is a possibility that the strength of the base may be reduced.

  The present invention achieves a further improvement of the lubricating characteristics to an iron-based sintered oil-impregnated bearing regardless of the method of Patent Document 2 having a poor adhesion, and a good lubricating characteristic 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 producing the same, and an iron-based sintered oil-impregnated bearing in which pores are impregnated with a lubricating oil.

The present inventors examined an iron-based sintered bearing that achieves the above object, and deposit and disperse sulfides in the base of an iron-based sintered alloy that constitutes the main body of the iron-based sintered bearing to achieve metal contact. It has been found that it can exhibit good lubricating properties even in applications where is prone to occur, and the use of molybdenum disulfide is useful.
According to one aspect of the present invention, the iron-based sintered bearing comprises an iron-based sintered alloy having a bearing surface that supports the outer peripheral surface of the shaft and in which pores capable of being impregnated with lubricating oil are dispersed. It is a sintered bearing, and the total composition of the iron-based sintered alloy is, by 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, 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 The matrix has a matrix in which the pores are dispersed, a copper phase and a graphite phase dispersed in the matrix, and a sulfide phase precipitated and dispersed from at least one of the matrix and the copper phase, and the matrix is bainite Single phase structure, mixed structure of bainite and perlite, mixed structure of bainite and ferrite, and with bainite and perlite The subject matter is to present a metal structure of one of the mixed structures of ferrite.
Further, according to one aspect of the present invention, the iron-based sintered oil-impregnated bearing is characterized by having the iron-based sintered bearing and a lubricating oil impregnated in pores of the iron-based sintered bearing.

  In the iron-based sintered bearing, the sulfide phase precipitates and disperses in grain boundaries and grains in at least one of the base 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% with respect to 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 preferably granular and has a maximum particle size of 50 μm or less. In 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 lubricating characteristics. The proportion of bainite in the metallographic cross section of the base may be 10% or more in area ratio. Moreover, the porosity of the said bearing surface is suitable as an oil-impregnated bearing as it is 15 to 30% by area ratio.

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

It is a schematic diagram explaining the lubricating effect of a sintered oil-impregnated bearing. It is a schematic diagram explaining the case where a favorable lubricating oil film is not formed.

  Hereinafter, the metallographic structure of the iron-based sintered alloy that constitutes the iron-based sintered bearing that is the main body of the iron-based sintered oil-impregnated oil bearing of 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, has a bearing surface for supporting the outer peripheral surface of the shaft, and is made of an iron-based sintered alloy mainly composed of Fe (iron). Be done. In the iron-based sintered alloy, pores capable of being impregnated with the lubricating oil are dispersed, and the pores are impregnated with the lubricating oil to form a sintered oil-impregnated bearing. Fe is inexpensive as compared with Cu (copper) and excellent in mechanical strength, and thus is a component suitable as a main component of an iron-based sintered alloy. Fe is introduced in the form of iron powder or an Fe-Mo alloy powder to be described later, and a base of iron-based sintered alloy is formed by using a raw material powder containing iron powder or Fe-Mo alloy powder as a main component. . Pores are dispersed in the base of the iron-based sintered alloy. The pores are generated due to 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 metallographic structure of the base of the iron-based sintered alloy constituting the iron-based sintered bearing is 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 It is good if it is any one of. That is, it is preferable that the base exhibits a metal structure including bainite. Bainite is a structural element with high mechanical strength because it is as hard as martensite and has toughness. In the iron-based sintered alloy of the present invention, such bainite is used for the matrix structure to improve the mechanical strength of the iron-based sintered alloy and to improve the wear resistance. For this reason, in the iron-based sintered bearing of the present invention, the proportion of bainite in the metal structure of the base is preferably 10% or more in area ratio in the metal structure section. The remainder of the matrix may be one or both of pearlite and ferrite.

  Ferrite is soft and has good compatibility with the shaft to be a mating material, but has low mechanical strength. On the other hand, although pearlite has high base hardness and high mechanical strength, there is a possibility that the shaft serving as the mating material may be worn away. For this reason, the base metal structure of the iron-based sintered alloy is the bainite single phase metal structure, the mixed structure of bainite and pearlite, the mixed structure of bainite and ferrite, and the bainite according to the required characteristics of the iron-based sintered bearing. It is good to adjust by the compounding quantity and the compounding form of graphite and Mo so that it may become any of the mixed structure of a pearlite and a ferrite (the detail is mentioned later).

As described above, since the pores resulting from the manufacturing method are formed in the sintered alloy, the density (sintered body density) of the sintered alloy 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, using such pores, the pores formed in the iron-based sintered alloy are impregnated with lubricating oil to impart lubricity to the sintered bearing, and its lubricating properties are oil-free It is exhibited over a long period of time. In the present invention, when the amount of pores formed in the iron-based sintered alloy forming the iron-based sintered bearing is poor, that is, the density of the iron-based sintered alloy is high, the amount of lubricating oil to be impregnated becomes poor. Lubrication characteristics can not be exhibited. Conversely, when 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 the base of the iron-based sintered alloy decreases, and as a result, the machine of the iron-based sintered alloy Strength will be reduced. From this viewpoint, the density of the iron-based sintered alloy may be 5.2 to 7.2 Mg / m ³ . The density of the iron-based sintered alloy in this range corresponds to approximately 10 to 25% in the porosity of the iron-based sintered alloy. In addition, the density ratio of a sintered compact is measured by the sintering density test method of the metal sintering material of prescription | regulation to Japanese Industrial Standard (JIS) Z2505.

  Cu is a component capable of forming a soft copper phase to make the compatibility with the shaft serving as the counterpart good, and forming copper sulfide excellent in lubricity to improve the lubricity. is there. If the amount of Cu is low, the copper phase dispersed in the base decreases, and the above effect can not be sufficiently obtained. On the other hand, if expensive Cu is excessive, the cost increases accordingly. Therefore, the amount of Cu is 0.5 to 3% by mass of the whole composition.

  Cu is added to the raw material powder in the form of copper powder. As the copper powder, it is preferable to use flat or foil-like copper powder. When a 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 adheres to the core rod, When this is formed into a bearing, the amount of copper phase exposed to the bearing inner diameter surface where the sliding characteristics are required is increased as compared with the inside of the bearing. Therefore, even if the amount of Cu in the entire composition is reduced to reduce the amount of Cu inside the bearing, the amount of copper phase exposed on the bearing inner diameter surface can be maintained at the required amount. In this regard, the total appropriate amount of the copper phase dispersed in the bearing inner diameter surface and the sulfide phase (described later) constituted by copper sulfide can be 5 to 20% of the whole bearing surface in area ratio, and it is soft The sliding properties can be further improved by copper sulfide and copper sulfide precipitated from the copper phase. As the flat copper powder, one having a particle diameter of about 20 to 150 μm can be suitably used. Copper powder having a small particle size is likely to enter the interstices between iron particles, and excessive copper powder is less likely to be ubiquitous around the core rod. The ratio of particle diameter to thickness is preferably about 2.5 to 20.

  Mo (molybdenum) is dissolved in Fe forming the matrix to contribute to the strengthening of the matrix. In addition, Mo has a function to improve the hardenability of iron base, and bainite is formed in the base structure in the cooling process after sintering to improve the mechanical strength and resistance of iron-based sintered bearing. It contributes to the improvement of wear resistance. If the amount of Mo is poor, the above effects become poor. On the other hand, when expensive Mo becomes excessive, the cost increases accordingly. Therefore, the Mo content is 0.3 to 3.3% by mass, preferably 0.6 to 3.0% by mass, based on the total composition.

  Mo may be alloyed into iron powder which is a main raw material, and may be mix | blended in the form of Fe-Mo alloy powder, or you may mix | blend as molybdenum disulfide. When Fe-Mo alloy powder is used instead of iron powder, Mo disperses uniformly throughout, so the effect of Mo acts uniformly in the matrix, and the matrix structure can be bainite single phase texture. On the other hand, when Mo is compounded using molybdenum disulfide powder, Mo formed by the decomposition of molybdenum disulfide into Mo and S during the sintering process diffuses into the matrix, and the hardenability of the matrix structure of the portion where Mo is diffused Improve to form a bainite phase. Therefore, the part where the diffusion of Mo is poor becomes pearlite. Therefore, it is possible to adjust the production rate of bainite by using the combination form of Mo.

  S (sulfur) combines with base-forming Fe to form iron sulfide, and combines with Cu forming a copper phase to form copper sulfide. In addition, the iron powder which is a main raw material contains very trace amount (1 mass% or less) of Mn as an unavoidable impurity originating in a manufacturing method. For this reason, manganese sulfide can also be dispersed to a small extent. Since these sulfides are rich in lubricity, precipitation and dispersion of such sulfides in a matrix can form a matrix that exhibits excellent lubricating properties even under sliding conditions in which metal contact is likely to occur. . In the present invention, it is considered that the sulfide phase may specifically include all the above-mentioned sulfides, that is, iron sulfide, copper sulfide and sulfide derived from unavoidable impurities (manganese sulfide), depending on the situation. And one or more of the above sulfides exist in the metal structure of the sintered alloy as a sulfide phase.

  S is introduced by being mixed with the raw material powder in the form of at least one of iron sulfide powder and molybdenum disulfide powder. When S in the form of iron sulfide powder exceeds 988 ° C. in the temperature rising process of the sintering step, a eutectic liquid phase of Fe-S is generated, and liquid phase sintering proceeds to cause powder particles to separate. Promote the growth of the neck. 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 temperature rising process, and when it exceeds 988 ° C., a eutectic liquid phase of Fe-S is generated, Liquid phase sintering proceeds to promote the growth of necks between powder particles. After S uniformly diffuses into the iron matrix from the eutectic liquid phase thus generated, iron sulfide particles are precipitated again from the grain boundaries of the matrix and within the crystal grains. Therefore, the iron sulfide particles are uniformly dispersed in the grain boundaries and grains of the matrix, and the fixing properties of the precipitated iron sulfide particles are high. In addition, it is possible that a part of S diffuses into the copper phase and bonds with Cu in the copper phase, whereby copper sulfide particles can be precipitated in grain boundaries and grains of the copper phase. Accordingly, the copper sulfide particles are also deposited and dispersed in the grain boundaries and grains of the copper phase as described above, and therefore, the copper sulfide particles have high adhesion. In addition, since Fe and Cu easily form sulfides to the same extent as Mo and sulfide is more difficult to form sulfides than Fe and Cu, sulfides dispersed in a matrix are: Mainly iron sulfide and copper sulfide. The sulfide phase precipitates in at least one of the matrix and the copper phase, and is present in grain boundaries and grains.

  If the amount of S is low, the amount of sulfide dispersed in the base is reduced, resulting in insufficient lubricating properties. When the amount of S is excessive, the amount of precipitated sulfide is excessive to reduce the strength of the base, and as a result, the mechanical strength of the iron-based sintered alloy constituting the iron-based sintered bearing is reduced. . From such a thing, the amount of S should be 0.2 to 2.2% by mass, preferably 0.4 to 2.0% by mass of the whole composition. At such a ratio, the sulfide phase in the metal structure of the iron-based sintered alloy is 0.9 to 6% in area ratio to the area of the cross section including the pores when the metal structure cross section is observed.

  The sulfide is preferably dispersed in the form of particles in the metal structure. In addition, when the size of the precipitated sulfide particles is coarse, the location where the sulfide particles are present is unevenly distributed, and wear, adhesion, and the like are likely to occur at the time of metal contact at locations where the presence of sulfide particles is poor. Therefore, it is preferable that the sulfide phase be 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 non-diffused state in the iron-based sintered alloy. For this reason, 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. In addition, a part of the graphite powder diffuses into Fe powder particles constituting the matrix to form a solid solution, thereby forming pearlite and contributing to the improvement of the mechanical strength of the matrix. This produces a base exhibiting a single phase structure of pearlite or a mixed structure of ferrite and pearlite.

  If the amount of C is low, the amount of the graphite phase dispersed in the iron-based sintered alloy is reduced, and the lubricating characteristics are degraded. On the other hand, when the amount of C is excessive, the amount of dispersed graphite phase becomes excessive, and the strength of the base is lowered. 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. Use of a graphite powder having an average particle diameter of about 40 to 80 μm is preferable in terms of diffusion to a base, sliding characteristics, and the like.

  From the above, in the preferred embodiment of the present invention, the overall composition of the iron-based sintered alloy that constitutes the iron-based sintered bearing is, by mass ratio, Cu: 0.5 to 3%, Mo: 0.3 to It consists of 3.3%, C: 1 to 5%, S: 0.2 to 2.2%, balance: Fe and unavoidable impurities, and the porosity of the iron-based sintered alloy is 10 to 25%. The iron-based sintered alloy has a metallographic structure in which pores, a copper phase and a graphite phase are dispersed in a matrix, and a sulfide phase is precipitated and dispersed from the matrix and / or the copper phase, and the matrix is bainite single It exhibits a phase structure, a mixed structure of bainite and perlite, a mixed structure of bainite and ferrite, and a metal structure of one of a mixed structure of bainite, perlite and ferrite.

  The area ratio of the sulfide phase is based on an image obtained by observing a cross section or surface of an iron-based sintered bearing (iron-based sintered alloy) with a metallographic microscope, an electron probe micro analyzer (EPMA), or the like. Measurement can be performed using image analysis software such as WinROOF manufactured by Mitani Corporation.

  In the method of producing an iron-based sintered bearing according to the present invention, copper powder, graphite powder, and iron powder or Fe-Mo alloy powder may be used as a raw material powder of an iron-based sintered alloy that constitutes the iron-based sintered bearing. At least one sulfide powder of iron sulfide powder and molybdenum disulfide powder is added and mixed, and Cu: 0.5 to 3%, Mo: 0.3 to 3.3%, C: 1 by mass ratio The mixed powder prepared to the composition which consists of 5%, S: 0.2 to 2.2%, remainder: Fe and an unavoidable impurity can be used.

A method of manufacturing an iron-based sintered bearing includes the step of forming the above-mentioned raw material powder into a bearing shape (net shape), that is, a substantially circular pipe or a substantially annular shape having an inner diameter surface sliding with a shaft And a sintering step of sintering the obtained compact. In the forming step, by setting the forming pressure of the raw material powder to 250 to 650 MPa, the iron-based sintered bearing is made so that the density of the iron-based sintered alloy after sintering is 5.2 to 7.2 Mg / m ^3. It can be manufactured.

  In the sintering step, if the sintering temperature is too low, the iron sulfide will not melt and it will not be possible to disperse and precipitate the sulfide in the iron-based sintered alloy matrix, so the sintering temperature should be 990 ° C or higher . If the sintering temperature is too high, the graphite diffuses to the matrix and the remaining graphite phase decreases, and the copper powder melts and the remaining copper phase becomes scarce, so the sintering temperature is suitably 1080 ° C. or less It is. 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 desorbed to reduce the amount of S in the iron-based sintered alloy. The sintering atmosphere needs to be a non-oxidative atmosphere. Further, it is preferable to use an atmosphere having a low dew point. In the present invention, since the hardening effect by molybdenum produces bainite, it is not necessary to carry out the hardening treatment.

  In the present invention, the method for producing an iron-based sintered oil-impregnated bearing comprises the steps of preparing an iron-based sintered bearing according to the method for producing an iron-based sintered bearing as described above, and impregnating the iron-based sintered bearing with a lubricating oil. The iron-based sintered bearing prior to impregnation may be subjected to final compression processing such as sizing and coining, if necessary. The lubricating oil can be appropriately selected and used from various lubricating oils in consideration of the application and the operating environment. For example, mineral oil, synthetic hydrocarbon oil, ester oil and the like are used in combination of one or more kinds. It is good.

[First embodiment]
Using a raw material powder prepared by adding reduced iron powder, flat copper powder, molybdenum disulfide powder, and graphite powder and mixed at a ratio shown in Table 1, outer diameter 16 mm, inner diameter 10 mm at a molding pressure of 300 MPa Then, 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 measurement, several sintered bearing samples were produced about each sample number.

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

  Further, with respect to the bearing samples of each sample number, the radial crushing strength of each bearing sample was measured by the radial crushing strength test method defined in Japanese Industrial Standard (JIS) Z2507. The results are shown in Table 1 together.

  Furthermore, for the bearing samples of each sample number, the friction coefficient at the inner diameter surface of the sintered oil-impregnated bearing was measured. The measurement of the coefficient of friction attached the shaft made of carbon steel S45C to the rotating shaft of the leveled motor. The shaft was inserted into the bearing attached to the housing with a gap, and the shaft was rotated while a load in the vertical direction 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 shown together in Table 1.

  In addition, a wear test was conducted using a bearing sample of each sample number impregnated with lubricating oil as described above. In the wear test, the shaft is inserted into the bearing sample attached to the housing under the same conditions as the measurement of the coefficient of friction described above to load the housing and rotate the shaft 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, for each bearing sample, the inner diameter in the vertical direction including the sliding position of the shaft was measured in advance before the test, measured again after the test, and the amount of wear was calculated 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 examined. From Table 1, the bearing sample of Sample No. 1 not containing Cu has a large value of coefficient of friction because a soft copper phase is not formed. In the bearing sample of sample No. 2 in which the additive amount of Cu is 0.5% by mass, a soft copper phase is formed, and the friction coefficient is reduced to 0.25. Also, it can be seen that the coefficient of friction decreases as the amount of Cu increases. However, as the added amount of Cu increases, the radial crushing strength decreases, and in sample No. 7 exceeding 3% by mass, the radial crushing strength becomes less than 150 MPa, and the wear amount also exceeds 20 μm. From these facts, it was confirmed that good sliding characteristics can be obtained when the amount of Cu is in the range of 0.5 to 3% by mass. This result indicates that a bearing having a Cu content of 0.5 to 3% by mass is compatible 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 No. 16 in which the amount of C is 0.5% by mass has a large value of the coefficient of friction because the graphite phase is poor. In the bearing sample of sample No. 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. Also, it can be seen that the coefficient of friction decreases as the amount of C increases. However, as the amount of C increases, the radial crushing strength decreases, and for the bearing sample of sample No. 21 whose C amount exceeds 5% by mass, the radial crushing 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 properties and high mechanical properties can be obtained when the amount of C is in the range 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 coped with even under sliding conditions in which it is difficult to form a good lubricating oil film.

  Moreover, the influence of S amount can be investigated by comparing the bearing sample of sample numbers 3, 08-15. The bearing sample of sample No. 8 which does not contain S has large values of friction coefficient and amount of wear because a sulfide phase is not formed. On the other hand, in the bearing sample of sample No. 9 in which the S content is 0.2% by mass, a sulfide phase is formed, the friction coefficient is lowered to 0.25, and the wear amount is also reduced to 16 μm. It is clear that the coefficient of friction and the amount of wear decrease as the amount of S increases, considering the values of sample numbers 3, 10 to 13, and the coefficient of friction and the wear when the ratio of S is 0.2% by mass or more The amount is preferable because it shows a low value. However, the radial crushing strength decreases as the amount of S increases, and the radial crushing strength decreases to 120 MPa in the bearing sample of the sample No. 15 in which the amount of S exceeds 2.2 mass%. From these facts, it is understood that an iron-based sintered oil-impregnated bearing having good sliding characteristics and high mechanical characteristics can be obtained when the amount of S is in the range of 0.2 to 2.2% by mass. Preferably, the raw material powder may be prepared such that the amount of S is 0.4 to 2.0% by mass. It is clear that the range of 0.3-3.3 mass% is suitable also about Mo amount corresponding to said result, and the range of 0.6-3.0 mass% is preferable. This result indicates that bearings with an S content of 0.2 to 2.2 mass% and an Mo content of 0.3 to 3.3 mass% are compatible even under sliding conditions in which it is difficult to form a good lubricating oil film. Indicates that it is possible.

  In the correlation between the blending ratio and the sliding property, as described above, with respect to the copper powder and the graphite powder, as the blending ratio increases, the radial crushing strength decreases and the wear amount increases. On the other hand, in the case of molybdenum disulfide powder, the radial crushing strength similarly decreases with the increase of the blending ratio, but the wear amount does not increase but conversely decreases. This is an effect caused by the introduction of Mo. Mo forms a solid solution in Fe to contribute to the strengthening of the matrix and improves the hardenability of the iron matrix to form a bainite phase, thereby the matrix Persistence is given to it and it is thought that abrasion resistance improves. In this point, the amount of wear relatively increases in the iron-based sintered oil-impregnated bearings obtained when raw material powders are blended so that the amount of S is the same using iron sulfide powder instead of molybdenum disulfide powder It has been confirmed by. For example, in an iron-based sintered bearing having the same overall composition as sample No. 3 except that it does not contain Mo (using 3.3 mass% of iron sulfide powder instead of molybdenum disulfide powder), bainite appears in the metal structure The measured value of the amount of wear in the above-mentioned wear test was about 19 μm.

  For iron-based sintered bearings of sample numbers 3, 8, 9 and 15, the cross section of the bearing is observed using an electron beam microanalyzer, the area of the bainite structure is measured based on the observation image, and the bainite structure in the base is The area ratio was calculated. In the measurement, image analysis software (WinROOF, manufactured by Mitani Corporation) was used. As a result, the proportion of the bainite phase is 0% in sample No. 8 not containing molybdenum, and the proportion of the bainite phase in the order of sample No. 9, sample No. 3 and sample No. 15 increases from 3% to 40%. It was Also, all parts other than the bainite structure of the base were composed of ferrite and pearlite.

Second Embodiment
Using the raw material powder of sample No. 3 of the first embodiment, molding is performed at different molding pressures, and sintering is performed under the same sintering conditions as in the first example to produce bearing samples of sample Nos. 22 to 29 did. With respect to these bearing samples, the density, radial crushing strength, friction coefficient and amount of wear of the iron-based sintered alloy of each bearing sample were measured in the same manner as in the first embodiment. These results and the results for sample No. 3 of the first example are shown in Table 2 together.

By comparing sample numbers 3 and 22 to 29 in Table 2, the influence of the density of the iron-based sintered alloy can be examined. The coefficient of friction can be reduced to 0.25 or less in the density range of 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 coefficient of friction decreases. On the other hand, the radial crushing strength decreases as the density decreases, and decreases to 150 MPa in the sample of sample No. 22 whose density is 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 properties and high mechanical properties can be obtained in the density of 5.2 to 7.2 Mg / m ³ . This result shows 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 bearing of the present invention has the toughness of a base, and when it is impregnated with lubricating oil and used as an iron-based sintered oil-impregnated bearing, it is difficult to form a good lubricating oil film and metal contact tends to occur. Even under sliding conditions, good lubricating characteristics can be exhibited. It is suitable as a bearing for applications that support forward and reverse rotating shafts, such as paper feed rollers for copying machines and head drive motors, and have short forward and reverse drive times, and scrolls. It is suitable for a bearing or the like that supports the shaft of a rotor that rotates eccentrically with respect to the stator, such as a compressor.

1 Sintered bearing 2 Lubricant 3 axis 5 Oil pressure distribution

Claims (9)

An iron-based sintered bearing constituted of an iron-based sintered alloy having a bearing surface for supporting an outer peripheral surface of a shaft and in which pores capable of being impregnated with lubricating oil are dispersed,
The overall composition of the iron-based sintered alloy is, by 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 inevitable impurities,
The density of the iron-based sintered alloy is 5.2 to 7.2 Mg / m ³ ,
The metal structure of the iron-based sintered alloy includes a matrix in which the pores are dispersed, a copper phase and a graphite phase dispersed in the matrix, and a sulfide phase dispersed from at least one of the matrix and the copper phase and dispersed. Have
The base is an iron-based sintered bearing exhibiting a single phase structure of bainite, a mixed structure of bainite and perlite, a mixed structure of bainite and ferrite, and a metal structure of one of a mixed structure of bainite, perlite and ferrite.   The iron-based sintered bearing according to claim 1, wherein the sulfide phase precipitates and disperses in grain boundaries and grains in at least one of the base and the copper phase.   The iron-based sintered bearing according to claim 1 or 2, wherein the sulfide phase is mainly composed of iron sulfide and copper sulfide.   The sulfide phase is dispersed in the iron-based sintered alloy so as to be present at an area ratio of 0.9 to 6% with respect to the area of the cross section including pores in the cross section of the iron-based sintered alloy 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 sulfide phase is granular and has a maximum particle size of 50 μm or less.   The copper phase and the sulfide phase constituted by copper sulfide in the bearing surface are dispersed at an area ratio of 5 to 20% with respect to the entire bearing surface. Iron-based sintered bearing described.   The iron-based sintered bearing according to any one of claims 1 to 6, wherein the proportion of bainite in the metallographic cross section of the base is 10% or more in area ratio.   The iron-based sintered bearing according to any one of claims 1 to 7, wherein the porosity of the bearing surface is 15 to 30% in area ratio.   An iron-based sintered oil-retaining bearing having the iron-based sintered bearing according to any one of claims 1 to 8 and a lubricating oil impregnated in pores of the iron-based sintered bearing.