JP6548952B2 - Sintered bearing and method of manufacturing the same - Google Patents

Description

  The present invention relates to a sintered bearing and a method of manufacturing the same.

  A sintered bearing is a porous body having innumerable internal pores, and is usually used in the state in which the internal pores are impregnated with a lubricating fluid (for example, lubricating oil). In this case, at the time of relative rotation of the sintered bearing and the shaft inserted in the inner periphery thereof, the lubricating oil held in the internal pores of the sintered bearing bleeds on the inner circumferential surface (bearing surface) of the sintered bearing as the temperature rises. put out. Then, an oil film is formed in the bearing gap between the bearing surface of the sintered bearing and the outer peripheral surface of the shaft by the leaking lubricating oil, and the shaft is supported relatively rotatably.

  For example, in Patent Document 1 below, a copper-iron-based sintered bearing containing iron and copper as a main component is coated with 10% by mass or more and less than 30% by mass of copper with respect to iron powder and has a particle size of 80 The thing which compacted and sintered the copper-coated iron powder made into mesh or less is described.

Patent No. 3613569 Patent No. 5442145

  However, when the sintered bearing to which the technical means of Patent Document 1 is applied is used for a vibration motor which functions as a vibrator of a portable terminal, it is apparent that the bearing surface is worn early and the rotational fluctuation becomes large. became. This is because, in sintered bearings obtained by molding and sintering copper-coated iron powder, the neck strengths of iron phase (iron structure) and copper phase (copper structure) are low, and particles constituting the bearing surface are exfoliated. It is thought that it is easy. Therefore, in order to put the sintered bearing for such use into practical use, it is desirable to improve the bonding strength between the iron structure and the copper structure.

  For example, in the above-mentioned Patent Document 2, a sintered bearing having high wear resistance and high strength can be obtained by using a raw material powder mainly composed of a partial diffusion alloy powder in which iron powder and copper powder are joined by partial diffusion. It is shown to be obtained. Further, in the document, when the raw material powder contains a partial diffusion alloy powder having a large particle diameter, a coarse air hole is easily formed inside the sintered body, and as a result, the required bearing surface resistance It is described that it is preferable to use the partial diffusion alloy powder having an average particle size of 145 mesh or less (average particle size of 106 μm or less) because abrasion properties, radial crushing strength and the like may not be ensured.

  However, in recent years, a further increase in strength is required for a sintered bearing used for a vibration motor or the like, and the sintered bearing as described above may not be able to satisfy the required strength.

  In view of the above-mentioned circumstances, an object of the present invention is to further increase the strength of a copper-iron-based sintered bearing using a partial diffusion alloy powder.

  The present invention made to achieve the above object is a sintered bearing mainly made of an iron structure and a copper structure formed of a partial diffusion alloy powder of iron powder and copper powder, and having a particle diameter of 45 μm or less It has a copper structure formed of the single copper powder, and the ratio of the copper structure formed of the single copper powder is 10% by mass or less.

  Further, the present invention made to achieve the above object comprises the steps of classifying partial diffusion alloy powder of iron powder and copper powder by passing through a sieve, and raw material powder containing classified partial diffusion alloy powder. A method for manufacturing a sintered bearing, comprising the steps of compression molding to form a green compact, and sintering the green compact to form a sintered body, wherein the classification of the raw material powder is performed. Thus, the proportion of the single copper powder dropped from the partial diffusion alloy powder is 10% by mass or less.

  In the present specification, a powder having a particle size equal to or less than a predetermined value means a powder capable of passing through a sieve having an opening of the predetermined value, and a powder having a particle size larger than the predetermined value has an opening It means the powder which remains on the sieve which is the specified value.

  As described above, the sintered bearing is formed of a sintered metal mainly composed of a partial diffusion alloy powder in which a part of the copper powder is diffused in an iron powder, whereby a copper structure after sintering (copper as a main component) High neck strength can be obtained between the target tissue) and the iron tissue (iron-based tissue). Accordingly, it is possible to prevent the copper structure and the iron structure from falling off from the bearing surface, and to improve the wear resistance of the bearing surface. In addition, since the strength of the sintered bearing is enhanced, the bearing surface does not deform following the shape of the inner peripheral surface of the housing even when the sintered bearing is press-fitted and fixed to the inner periphery of the housing, and the height of the bearing surface is high. Accuracy can be improved. Further, since the base of the bearing surface is strengthened, it is possible to suppress the deformation of the bearing surface when the shaft comes in contact with the bearing surface due to vibration or the like.

  As described above, when forming a sintered bearing mainly composed of partial diffusion alloy powder, coarse air holes are less likely to be formed conventionally when partial diffusion alloy powder having a small particle size (does not contain coarse particles) is used. Therefore, it was considered that the wear resistance and the strength of the sintered bearing could be enhanced. However, according to the verification of the present inventors, it has become clear that the use of a partial diffusion alloy powder having a small particle size results in a reduction in strength for the following reasons. That is, in order to obtain a partial diffusion alloy powder having a small particle size, classification by sieving is performed, but at the time of this sieving, a part of the copper powder falls off from the partial diffusion alloy powder and passes through a sieve. The single copper powder is mixed in the partial diffusion alloy powder after classification. For example, after 25 mass% Cu—Fe partial diffusion alloy powder was sieved using a 145 mesh (aperture 106 μm) sieve, its component ratio was confirmed, and it was found that about 40 mass% of Cu was contained. That is, about 15% by mass of single copper powder was mixed in the partially diffused alloy powder after sieving. For this reason, even if a predetermined amount of classified partial diffusion alloy powder is mixed with the raw material powder, the proportion of the partial diffusion alloy powder is actually reduced by the amount of mixing of the single copper powder, so the partial diffusion alloy is The strength improvement effect by using powder is reduced, and as a result, the strength of the sintered bearing is reduced.

  Then, the inventors arrived at the idea that the single copper powder contained in the partial diffusion alloy powder after classification is reduced by enlarging the mesh size of the sieve for classifying the partial diffusion alloy powder. That is, when the mesh size of the sieve is small, a large amount of partial diffusion alloy powder remains on the sieve, so the amount of single copper powder falling off from the partial diffusion alloy powder remaining on the sieve increases, as a result, classification The amount of single copper powder mixed into the later partial diffusion alloy powder is increased. On the other hand, when the mesh size of the sieve is large, the partial diffusion alloy powder remaining on the sieve decreases, so the single copper powder falling off from the partial diffusion alloy powder remaining on the sieve decreases, and as a result, the part after classification The single copper powder mixed in the diffusion alloy powder is reduced. For example, after 25 mass% Cu-Fe partial diffusion alloy powder was sieved using a 100 mesh (150 μm mesh) sieve, its component ratio was confirmed, and it was found that about 30 mass% of Cu was contained. That is, the ratio of the single copper powder mixed in the partial diffusion alloy powder after sieving was suppressed to about 5% by mass. Thus, by using a partial diffusion alloy powder in which the ratio of the single copper powder is small (specifically, 10 mass% or less), the ratio of the single copper powder contained in the raw material powder is reduced. As a result, The proportion of the partial diffusion alloy powder in which the iron powder is strongly bonded is increased, and the strength of the sintered bearing is enhanced.

  As described above, for example, to set the proportion of the copper structure formed of granular single copper powder having a particle diameter of 45 μm or less (single copper powder dropped off from the partial diffusion alloy powder by sieving) to 10% by mass or less, for example The mesh size of the sieve for classifying the partial diffusion alloy powder may be set to 125 μm or more. The classified partial diffusion alloy powder contains 30% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more of powder having a particle diameter of 106 μm (145 mesh) or more.

As described above, when a partial diffusion alloy powder having a relatively large particle size is used, strength can be improved by increasing the proportion of the partial diffusion alloy powder in the raw material powder, while coarse air holes are formed inside the sintered body. Since it is easily formed, there is a concern that the wear resistance and the strength may be reduced. Therefore, by setting the above-mentioned sintered bearing to a high density (specifically, 7.0 g / cm ³ or more), it is possible to suppress the formation of a coarse air hole and to prevent the strength from being reduced.

  The sintered bearing preferably contains a low melting point material (tin, zinc, phosphorus, etc.) having a melting point lower than that of copper. During sintering, a metal containing a low melting point material (tin powder, zinc alloy powder, phosphorus alloy powder, etc.) wets the surface of copper to promote the diffusion of copper, so that metal particles (copper powder and iron powder, copper powder) And copper powder) can be strengthened. The low melting point substance is preferably compounded relatively relatively (eg, 2 to 3% by mass) in the sintered bearing.

  It is preferable that the above-mentioned sintered bearing has a surface layer formed mainly of flat copper powder disposed substantially parallel to the surface. Since flat copper powder is in the form of a foil, it has the property of adhering to the molding surface of the mold during molding of the raw material powder, so the green compact after molding contains a large amount of copper in the surface layer. Therefore, a surface layer having a high content of copper is formed in the sintered body after sintering (preferably, a copper structure of 60% or more in area ratio is formed on the surface of the surface layer). By thus increasing the copper content in the surface layer, it is possible to improve the initial conformability and the quietness, and the sliding characteristics become excellent. In addition, since the aggressivity to the axis is also reduced, the durable life is improved. In addition, since the copper rich bearing surface which is not easily oxidized is formed, fretting wear of the bearing surface can be prevented.

  For example, in the case where the sintered bearing is ultra thin (for example, having a thickness of 0.5 μm or less), if the particle diameter of the partial diffusion alloy powder is too large, highly accurate forming becomes difficult. Therefore, the particle diameter of the partial diffusion alloy powder is preferably set to 1/2 or less of the minimum thickness of the sintered bearing.

  As described above, in the sintered bearing according to the present invention, the proportion of the partial diffusion alloy powder is increased by setting the proportion of the copper structure formed of granular copper powder with a particle size of 45 μm or less to 10 mass% or less. The copper-iron-based sintered bearing can be further strengthened.

It is a sectional view of a sintering bearing concerning the present invention. It is a principal part schematic sectional drawing of a vibration motor. It is sectional drawing in the AA shown in FIG. It is an enlarged view which shows a partial diffusion alloy powder typically. It is a graph which shows the particle size distribution of partial diffusion alloy powder. The upper part is a side view of flat copper powder, and the lower part is a plan view of flat copper powder. It is a side view showing flat copper powder and scale-like graphite which adhered mutually. It is sectional drawing which shows the formation process of the green compact by a metal mold | die. It is an expanded sectional view of the area | region Q in FIG. It is an enlarged view in the radial direction cross section of a sintering bearing (area P of Drawing 1). It is an enlarged view which shows the iron structure | tissue of FIG. 10, and its periphery tissue. FIG. 12A is an enlarged view for explaining the spheroidization of the flat copper powder, and FIG. 12A shows a state before sintering and FIG. 12B shows a state after sintering. It is an enlarged view which shows notionally the green compact structure before sintering of this invention. It is sectional drawing which shows other embodiment of the sintering bearing concerning this invention. It is sectional drawing which shows other embodiment of the sintering bearing concerning this invention. It is sectional drawing which simplifies and shows the typical structure of a starter. It is a cross-sectional photograph of the test piece which concerns on the comparative example of Table 1. FIG. 6 is a cross-sectional photograph of a test piece according to Example 3 of Table 1; 6 is a cross-sectional photograph of a test piece according to Example 4 in Table 1. It is a figure which shows the deformation amount when a predetermined load (30 N) is applied to each test piece. It is a figure which shows the deformation amount when a predetermined load (50 N) is applied to each test piece. It is a figure which shows the apparent hardness of the copper structure of each test piece. It is a figure which shows the apparent hardness of the iron structure of each test piece.

  Hereinafter, an embodiment of the present invention will be described based on the attached drawings.

  As shown in FIG. 1, the sintered bearing 1 is formed in a cylindrical shape having a bearing surface 1 a on the inner periphery. The sintered bearing 1 of this embodiment is used by impregnating the inner pores of a porous sintered body with a lubricating oil (also referred to as a sintered oil-impregnated bearing). When the shaft 2 made of stainless steel or the like is inserted into the inner periphery of the sintered bearing 1 and the shaft is rotated in that state or the bearing 1 is rotated, the lubricating oil held in the innumerable holes of the sintered bearing 1 Exude to the bearing surface 1a as the temperature rises. An oil film is formed in the bearing gap between the outer peripheral surface of the shaft and the bearing surface 1 a by the leaking lubricating oil, and the shaft 2 is relatively rotatably supported by the bearing 1.

  The sintered bearing 1 shown in FIG. 1 can be used for a vibration motor that functions as a vibrator that reports an incoming call, an e-mail, and the like in a portable terminal such as a mobile phone and a smartphone. In this vibration motor, as shown in FIG. 2, the weight (eccentric weight) W attached to one end of the shaft 2 is rotated by the motor unit 4 to vibrate the housing 3 of the vibration motor and the entire portable terminal. It is configured to generate. FIG. 2 conceptually shows the main part of the vibration motor when two sintered bearings 1 (101, 102) are used. In the illustrated example, the axis 2 of the motor unit 4 is made to project on both sides in the axial direction. Both sides are rotatably supported by sintered bearings 1 (101, 102). The sintered bearing 101 on the weight W side is disposed between the weight W and the motor unit 4, and the sintered bearing 101 on the weight W side is thicker than the sintered bearing 102 on the opposite side of the weight W And it is formed in a large diameter. Each of the two sintered bearings 1 has a bearing surface 1a on the inner periphery, and is fixed to the inner periphery of the housing 3 formed of, for example, a metal material by means such as press fitting.

  In this vibration motor, the shaft 2 is driven at a rotational speed of 10000 rpm or more. When the shaft 2 rotates, under the influence of the weight W, the shaft 2 rotates while swinging along the entire surface of the bearing surface 1a. In a sintered bearing for normal use, the shaft 2 rotates while maintaining the eccentricity in the direction of gravity, but in the sintered bearing 1 for a vibration motor, as shown in FIG. The axis 2 is rotated with the center Oa being eccentric not only in the direction of gravity but also in all directions.

  As described above, in the bearing for the vibration motor, the shaft 2 swings over the entire surface of the bearing surface, and the bearing surface is frequently hit by the shaft due to the unbalanced load (the shaft is frequently in sliding contact with the bearing surface) The bearing surface is more susceptible to wear than sintered bearings for normal use. In addition, when the sintered bearing is pressed into the inner periphery of the housing 3, if the bearing surface is deformed even slightly according to the inner peripheral surface shape of the housing, the rotational accuracy of the shaft 2 will be greatly affected. These problems can be solved by using the sintered bearing 1 of the present invention for a vibration motor.

  The sintered bearing 1 described above is formed by filling a raw material powder in which various powders are mixed into a mold, compressing the raw material powder to form a green compact, and sintering the green compact.

  The raw material powder is a mixed powder containing a partial diffusion alloy powder, a flat copper powder, a low melting point metal powder, and a solid lubricant powder as main components. To this mixed powder, various molding assistants, for example, lubricants (metal soap etc.) for improving releasability are added as necessary. Hereinafter, the raw material powder and manufacturing procedure of the first embodiment of the sintered bearing 1 will be described in detail.

[Partial diffusion alloy powder]
As the partial diffusion alloy powder, as shown in FIG. 4, an Fe—Cu partial diffusion alloy powder 11 obtained by bonding a plurality of copper powders 13 partially diffused on the surface of the iron powder 12 is used. The diffusion portion of the partial diffusion alloy powder 11 forms an Fe--Cu alloy. Specifically, as shown in the partial enlarged view in FIG. 4, at the boundary between the iron powder 12 and the copper powder 13, a part of the copper structure (copper atoms 13 a) diffuses into the iron structure and By diffusion of a part of the iron structure (iron atom 12a), it has a crystal structure in which iron atom 12a and copper atom 13a are partially substituted.

  As iron powder 12 which constitutes partial diffusion alloy powder 11, well-known iron powder, such as reduced iron powder and atomized iron powder, can be used, and reduced iron powder is used in this embodiment. The reduced iron powder is also referred to as sponge iron powder because it has a spongy (porous) shape with an irregular shape close to a spherical shape and an internal pore. The iron powder 12 constitutes most of the partial diffusion alloy powder 11.

  In addition, as the copper powder 13 constituting the partial diffusion alloy powder 11, widely used irregularly shaped or dendritic copper powder can be widely used. For example, electrolytic copper powder, atomized copper powder or the like is used. In this embodiment, while having many unevenness on the surface, the particle as a whole has an irregular shape close to a spherical shape, and uses an atomized copper powder excellent in formability. The copper powder 13 is in the form of particles, and is clearly distinguished from the flat copper powder in the form of foil described later. The copper powder 13 has a particle diameter smaller than that of the iron powder 12, and specifically, one having a particle diameter of 45 μm or less, preferably 30 μm or less. The copper powder 13 has a particle diameter of 5 μm or more, preferably 10 μm or more. The proportion of Cu in the partial diffusion alloy powder 11 is 10 to 30% by mass (preferably 22 to 26% by mass).

  As the partial diffusion alloy powder 11, a powder from which coarse particles are excluded by classification using a sieve is used. The mesh size of the sieve is preferably 125 μm (120 mesh) or more, and more preferably 135 μm (110 mesh) or more. In this embodiment, the partial diffusion alloy powder 11 having a particle diameter of 150 μm or less is obtained by classifying using a sieve with an opening of 150 μm (100 mesh). The particle size distribution of the partial diffusion alloy powder before classification often exhibits a normal distribution as shown in FIG. Conventionally, such partial diffusion alloy powder was classified with a sieve (for example, 106 μm) having a relatively small opening, and powder in a hatched area in the drawing was used, but in the present embodiment, Classify with a sieve with a relatively large opening (for example, 150 μm) and use the powder in the area indicated by the scattering points in the figure. The particle size distribution of the partially diffused alloy powder after classification changes rapidly at the boundary of 150 μm, and becomes almost zero at 150 μm or more. Also, the powder after classification contains a relatively large amount of partial diffusion alloy powder having a large particle size, and specifically, 30% by mass of a powder having a particle size of more than 106 μm (powder remaining on a sieve with 106 μm mesh) The above content is preferably 50% by mass or more, more preferably 60% by mass or more, and in the present embodiment, about 65% by mass.

  Thus, by classifying using a sieve having a relatively large opening, the ratio of the single copper powder falling off from the partial diffusion alloy powder by sieving is reduced, and the single copper mixed in the partial diffusion alloy powder after classification Powder can be reduced. Specifically, the ratio of granular single copper powder having a particle diameter of 45 μm or less in the powder after classification (that is, the powder passing through the sieve) is 10% by mass or less, preferably 8% by mass or less, more preferably 5% by mass or less It is assumed.

  Moreover, it is preferable that the powder packing property in a compacting process prevents a fall of the partial diffusion alloy powder 11 except an ultrafine particle. Specifically, it is preferable that the proportion of the powder having a particle diameter of 45 μm (350 mesh) or less contained in the partial diffusion alloy powder 11 be less than 25% by mass.

  The particle size is determined by irradiating a particle group with laser light and calculating the particle size distribution by calculation from the intensity distribution pattern of diffracted and scattered light emitted from the group, and further determining the particle size by laser diffraction scattering method (for example, Shimadzu Corporation) It can be measured by the use of SALD 31000 manufactured by Mfg.

[Flat copper powder]
Flat copper powder is obtained by flattening raw material copper powder made of water atomized powder or the like by crushing or crushing. The flat copper powder is in the form of a foil, and specifically, the aspect ratio L / t of length L and thickness t is 10 or more. In the present embodiment, as the flat copper powder, one having a length L of 20 μm to 80 μm and a thickness t of 0.5 μm to 1.5 μm (aspect ratio L / t = 13.3 to 160) is mainly used. The "length" and "thickness" referred to herein refer to the geometrical maximum dimensions of the individual flat copper powder 15 as shown in FIG. The apparent density of the flat copper powder is 1.0 g / cm ³ or less. With flat copper powder of the above size and apparent density, the adhesion of the flat copper powder to the molding surface of the mold is enhanced, so that a large amount of flat copper powder can be adhered to the molding surface of the mold.

[Fluid lubricant]
In order to make flat copper powder adhere to the mold molding surface, a fluid lubricant is previously attached to the flat copper powder. The fluid lubricant may be attached to the flat copper powder before filling the raw material powder in the mold, preferably before mixing the raw material powder, and more preferably adhering to the raw copper powder at the stage of crushing the raw copper powder. Let After crushing, the fluid lubricant may be attached to the flat copper powder by, for example, supplying the fluid lubricant to the flat copper powder and stirring the mixture before mixing with other raw material powder. In order to ensure the adhesion amount of the flat copper powder on the molding surface of the mold, the blending ratio of the fluid lubricant to the flat copper powder is 0.1% by weight or more, desirably 0.2% by mass or more. In addition, in order to prevent aggregation due to adhesion of the flat copper powder, the blending ratio of the fluid lubricant to the flat copper powder is 0.8% by weight or less, desirably 0.7% by mass or less. As a fluid lubricant, fatty acids, especially linear saturated fatty acids are preferred. This type of fatty acid is represented by the general formula C _n-1 H _{2 n-1} COOH. As this fatty acid, n is in the range of 12 to 22, and for example, stearic acid can be used as a specific example.

[Low melting point metal powder]
The low melting point metal powder is a metal powder containing a low melting point substance such as tin, zinc and phosphorus, which has a melting point lower than copper and a melting point lower than a sintering temperature. In this embodiment, metal powder having a melting point of 700 ° C. or less, such as tin powder, zinc alloy powder (zinc-copper alloy powder), phosphorus alloy powder (phosphorus-copper alloy powder), etc., is used as the low melting point metal powder. Be done. Among these, tin powder with little transpiration at the time of sintering is preferable. As the low melting point metal powder, it is preferable to use one having a particle diameter smaller than that of the partial diffusion alloy powder 11. In the present embodiment, the particle size of the low melting point metal powder is set to 5 μm to 45 μm. These low melting point metal powders have high wettability to copper. By blending the low melting point metal powder with the raw material powder, at the time of sintering, the low melting point metal powder is first melted to wet the surface of the copper powder, thereby promoting the diffusion of copper into iron. This enhances the bonding strength between the iron particles and the copper particles, and between the copper particles.

[Solid lubricant powder]
Solid lubricant powder is added to reduce friction at the time of metal contact by sliding with the shaft 2, for example, graphite is used. At this time, it is desirable to use flaky graphite powder as the graphite powder so that the adhesion to flat copper powder can be obtained. As solid lubricant powder, in addition to graphite powder, molybdenum disulfide powder can also be used. Molybdenum disulfide powder has a layered crystal structure and exfoliates in a layered manner, so that the adhesion to flat copper powder is obtained in the same manner as flaky graphite.

[Blending ratio]
The compounding ratio of each powder in the raw material powder is 75 to 95 mass% of partial diffusion alloy powder (including granular single copper powder having a particle diameter of 45 μm or less), 5 to 20 mass% of flat copper powder, and low melting point metal powder 0.8 to 6.0% by mass (preferably 2.0 to 3.0% by mass) of (for example, tin powder), 0.3 to 1.0% by mass of solid lubricant powder (for example, graphite powder) Is preferred. Further, the proportion of granular single copper powder having a particle diameter of 45 μm or less mixed in the partial diffusion alloy powder (that is, single copper powder dropped from the partial diffusion alloy powder by sieving) is 10% by mass or less of the whole raw material powder Ru. The reason why each powder is compounded as described above is as follows.

  By setting the proportion of the partial diffusion alloy powder to 75% by mass or more, the strength of the sintered bearing can be sufficiently enhanced. In particular, by using a partial diffusion alloy powder having a small mixing ratio of granular single copper powder having a particle diameter of 45 μm or less, a substantial proportion of the partial diffusion alloy powder can be sufficiently secured. The decrease in strength of the sintered bearing due to Further, in the present embodiment, as described later, the flat copper powder is attached to the mold in layers when the raw material powder is filled in the mold. If the blending ratio of flat copper powder in the raw material powder is less than 8% by weight, the amount of flat copper powder attached to the mold is insufficient, and the effect of the present invention can not be expected. Further, the amount of flat copper powder attached to the mold saturates at about 20% by mass, and even if the compounding amount is further increased, the cost increase due to the use of high cost flat copper powder becomes a problem. If the proportion of the low melting point metal powder is less than 0.8% by mass, the strength of the bearing can not be secured, and if it exceeds 6.0% by mass, the influence of the spheroidization of the flat copper powder can not be ignored. In particular, if the low melting point metal powder is blended at 2.0% by mass or more, the strength of the bearing can be further enhanced. If the proportion of the solid lubricant powder is less than 0.5% by weight, the friction reduction effect on the bearing surface can not be obtained, and if it exceeds 2.0% by mass, the strength is reduced.

[mixture]
It is desirable to perform mixing of each powder described above in two steps. First, as primary mixing, flaky graphite powder and flat copper powder to which a fluid lubricant is previously attached are mixed by a known mixer. Next, as secondary mixing, partial diffusion alloy powder (including granular single copper powder having a particle size of 45 μm or less) and low melting point metal powder are added to and mixed with the primary mixed powder. Flat copper powder is low in apparent density among various raw material powders, so it is difficult to uniformly disperse in the raw material powder. Therefore, if flat copper powder and graphite powder with the same level of apparent density in primary mixing are mixed in advance, it is possible to use flat copper powder 15 and flat copper powder 15 as shown in FIG. The graphite powder 14 adheres to each other and overlaps in layers, increasing the apparent density of the flat copper powder. This makes it possible to uniformly disperse the flat copper powder in the raw material powder at the time of secondary mixing. If a lubricant is separately added at the time of primary mixing, adhesion of the flat copper powder and the graphite powder is further promoted, so it becomes possible to disperse the flat copper powder more uniformly at the time of secondary mixing. As the lubricant to be added here, powdery ones may be used in addition to the same or different fluidic lubricants as the above-mentioned fluid lubricants. For example, since the forming assistant such as the above-mentioned metal soap is generally in the form of powder and has a certain degree of adhesion, it can be promoted from the adhesion of the flat copper powder and the graphite powder.

  The adhesion state of the flat copper powder 15 and the scaly graphite powder 14 shown in FIG. 7 is maintained to some extent even after the secondary mixing, so when the raw material powder is filled in the mold, the flat copper powder on the mold surface A large amount of graphite powder will be attached.

[Molding]
The raw material powder after the secondary mixing is supplied to the mold 20 of the molding machine. As shown in FIG. 8, the mold 20 comprises a core 21, a die 22, an upper punch 23 and a lower punch 24, and the cavities partitioned by these are filled with the raw material powder. When the upper and lower punches 23, 24 are brought close to compress the raw material powder, the raw material powder is formed by the molding surface comprising the outer peripheral surface of the core 21, the inner peripheral surface of the die 22, the end face of the upper punch 23, and the end face of the lower punch 24. A green compact 25 having a cylindrical shape is obtained.

  Among the metal powders in the raw material powder, the apparent density of flat copper powder is the smallest. Moreover, flat copper powder is foil shape which has the said length L and thickness t, and the area of the wide surface per unit weight is large. Therefore, the flat copper powder 15 is susceptible to the adhesive force by the fluid lubricant adhering to the surface, the Coulomb force, etc., and after filling the raw material powder into the mold 20, as shown in FIG. Layer 19 with its wide face directed to the molding surface 20a of the mold 20 and with a plurality of layers (about 1 to 3 layers) overlapped. And adhere to the entire area of the molding surface 20a. At this time, the scaly graphite attached to the flat copper powder 15 is also attached to the molding surface 20a of the mold along with the flat copper powder 15 (illustration of the graphite is omitted in FIG. 9).

  On the other hand, in the inner region of the layered structure of flat copper powder 15 (the area on the center side of the cavity), the dispersion state of partial diffusion alloy powder 11, flat copper powder 15, low melting metal powder 16 and graphite powder in total It is uniformed. In this inner region, copper powder 13 flat copper powder 15 diffusion bonded to iron powder 12 of partial diffusion alloy powder 11 as copper powder, and granular single copper powder dropped from partial diffusion alloy powder 11 during classification. There is 13 '. The green compact 25 after molding holds the distribution state of each powder almost as it is.

[Sintering]
Thereafter, the green compact 25 is sintered in a sintering furnace. In the present embodiment, the sintering conditions are determined so that the iron structure has a two-phase structure of a ferrite phase and a pearlite phase. Thus, if the iron structure is a two-phase structure of a ferrite phase and a pearlite phase, the hard pearlite phase contributes to the improvement of the wear resistance and suppresses the wear of the bearing surface under high surface pressure to improve the bearing life. It can be done.

  By the diffusion of carbon, the existing proportion of pearlite (γFe) becomes excessive, and when the proportion is equal to or higher than that of ferrite (αFe), the aggression with respect to the axis by pearlite is remarkably increased and the axis is easily worn. In order to prevent this, the pearlite phase (γFe) is suppressed to the extent to be present (dotted) in the grain boundaries of the ferrite phase (αFe) (see FIG. 11). As used herein, “grain boundaries” mean both grain boundaries formed between powder particles, as well as grain boundaries 18 formed in powder particles. Thus, in the case where the iron structure is formed as a dual phase structure of the ferrite phase (αFe) and the pearlite phase (γFe), the proportions of the ferrite phase (αFe) and the pearlite phase (γFe) in the iron structure are the base portion S2 described later. It is desirable to set it as about (alpha) Fe: (gamma) Fe = 80 to 95%: 5 to 20% by the area ratio in arbitrary cross sections. This makes it possible to simultaneously suppress the wear of the shaft 2 and the wear resistance of the bearing surface 1a.

  The growth rate of pearlite depends mainly on the sintering temperature. Therefore, in order to cause the pearlite phase to exist at the grain boundaries of the ferrite phase in the above embodiment, the sintering temperature (atmosphere temperature in the furnace) is set to about 820 ° C. to 900 ° C. and a gas containing carbon as the furnace atmosphere, Sinter using natural gas or endothermic gas (RX gas). As a result, carbon contained in the gas can diffuse into iron during sintering to form a pearlite phase (γFe). C. Sintering at a temperature exceeding 900.degree. C. is not preferable because carbon in the graphite powder reacts with iron to increase the pearlite phase more than necessary. During the sintering, the fluid lubricant, other lubricants, and various forming aids burn inside the sintered body or evaporate from inside the sintered body.

By passing through the above-described sintering step, a porous sintered body can be obtained. The sintered body is sized and further impregnated with lubricating oil or liquid grease by a method such as vacuum impregnation to complete the sintered bearing 1 (sintered oil-impregnated bearing) shown in FIG. The lubricating oil impregnated in the sintered body is retained not only in the pores formed between the particles of the sintered structure but also in the pores of the reduced iron powder of the partial diffusion alloy powder. The lubricant impregnated in the sintered body, kinematic viscosity at 40 ℃ is 30 mm ² / sec or more, 200 mm ² / sec or less being preferred. Depending on the application, the impregnation process of the lubricating oil may be omitted, and the sintered bearing 1 may be used without oil.

  The microstructure in the vicinity of the surface (region P in FIG. 1) of the sintered bearing 1 which has undergone the above manufacturing steps is schematically shown in FIG.

  As shown in FIG. 10, in the sintered bearing 1 of the present invention, the green compact 25 is formed in a state where the flat copper powder 15 is attached in layers to the mold molding surface 20a (see FIG. 8). The surface layer S1 having a copper concentration higher than the other is formed on the entire surface including the bearing surface 1a of the bearing 1 because the powder 15 is sintered. Moreover, the wide surface of the flat copper powder 15 is also attached to the molding surface 20a, and most of the copper structure 31a of the surface layer S1 thins the thickness direction of the surface layer S1 (ie, the surface (bearing surface 1a) (Arranged substantially parallel to)). The thickness of the surface layer S1 corresponds to the thickness of the flat copper powder layer deposited in a layer on the mold molding surface 20a, and is approximately 1 μm to 6 μm. The surface of the surface layer S1 is mainly formed of free graphite 32 (shown in black) in addition to the copper structure 31a, and the remaining portion is an opening of pores and an iron structure described later. Among these, the area of the copper structure 31a is the largest, and specifically, 60% or more of the surface is the copper structure 31a.

  On the other hand, three types of copper structures (31b, 31c, 31d), iron structures 33, free graphite 32, and pores are formed in the inner base portion S2 covered with the surface layer S1. The first copper structure 31 b is formed from the flat copper powder 15 contained in the green compact 25 and has a flat shape corresponding to the flat copper powder. The second copper structure 31 c is formed from the copper powder 13 joined to the iron powder 12 of the partial diffusion alloy powder 11 and is firmly diffusion-bonded to the iron structure 33. The second copper structure 31c plays a role of enhancing the bonding between particles as described later.

  The third copper structure 31 d is formed from granular single copper powder 13 ′ having a particle diameter of 45 μm or less (that is, single copper powder dropped from the partial diffusion alloy powder 11 at the time of classification), It adheres to the iron structure 33 and other copper structures 31b and 31c. The third copper structure 31d may be partially diffused and bonded to the iron powder 12 by sintering, but in comparison with the second copper structure 31c derived from the copper powder 13 diffusion bonded in advance to the iron powder 12 Thus, the alloy formation region (diffusion region) with the iron structure 33 is small. Further, the third copper structure 31 d is completely different in shape from the flat first copper structure 31 b derived from the flat copper powder, and has a shape close to granular. Therefore, in the copper structure of base portion S 2, if the alloy formation region with iron structure 33 is small and approximately granular, the copper structure is a single copper powder 13 ′ dropped from partial diffusion alloy powder 11. It can be determined that the third copper structure 31d is derived from

  In the present embodiment, although a single copper powder is not separately added to the raw material powder, even when such a single copper powder is added, the copper structure is obtained by observing the structure after sintering. It can be determined whether or not it originates from a single copper powder dropped from the partial diffusion alloy powder. That is, usually, the single copper powder added to the raw material powder has a particle size of at least 45 μm, and in many cases, more than 80 μm. On the other hand, the single copper powder dropped from the partial diffusion alloy powder has a particle size of at least 45 μm or less, and usually about 20 μm. Therefore, the size of the copper structure derived from the single copper powder dropped from the partial diffusion alloy powder and the copper structure derived from the single copper powder separately added to the raw material powder are clearly different. Specifically, if the particle size of the single copper powder forming the copper structure is 45 μm or less in an arbitrary cross section of the base portion S2, the copper structure is derived from the single copper powder dropped from the partial diffusion alloy powder. If the particle size of the single copper powder forming the copper structure is larger than 45 μm, it can be determined that the copper structure is derived from the single copper powder separately added to the raw material powder.

  FIG. 11 is an enlarged view of the iron structure 33 after sintering and the surrounding structure shown in FIG. As shown in FIG. 11, tin as a low melting point metal (low melting point substance) is first melted at the time of sintering and diffused to copper powder 13 constituting partial diffusion alloy powder 11 (see FIG. 4), and bronze phase 34 (Cu-Sn) is formed. Diffusion to iron particles and other copper particles proceeds by this bronze phase 34, and iron particles and copper particles or copper particles are strongly bonded to each other. Further, among the individual partial diffusion alloy powders 11, a part of the copper powder 13 diffuses and the molten tin also diffuses into the part where the Fe-Cu alloy is formed, and the Fe-Cu-Sn alloy (alloy phase 17) ) Is formed. The combination of the bronze phase 34 and the alloy phase 17 forms a second copper structure 31c. Thus, since a part of the second copper structure 31 c is diffused to the iron structure 33, high neck strength can be obtained between the second copper structure 31 c and the iron structure 33. Note that, in FIG. 11, the ferrite phase (αFe), the pearlite phase (γFe), and the like are expressed by light and shade of color. Specifically, the color is increased in the order of ferrite phase (αFe) → bronze phase 34 → alloy phase 17 (Fe—Cu—Sn alloy) → perlite phase (γFe).

  When the normal iron powder 19 is used instead of the partial diffusion alloy powder 11, a part of the low melting point metal powder 16 is present between the flat copper powder 15 and the normal iron powder 19 as shown in FIG. It will be done. When sintering is performed in this state, the flat copper powder 15 is drawn into the low melting metal powder 16 by the surface tension of the molten low melting metal powder 16 and is rounded using the low melting metal powder 16 as a core. Cause problems of When the spheroidization of the flat copper powder 15 is left, the area of the copper structure 31a (see FIG. 10) in the surface layer S1 is reduced, which greatly affects the slidability of the bearing surface 1a.

  On the other hand, in the present invention, as shown in FIG. 13, since the partial diffusion alloy powder 11 in which substantially the entire periphery of the iron powder 12 is covered with the copper powder 13 is used as the raw material powder A large number of copper powders 13 will be present in the vicinity of. In this case, the low melting point metal powder 16 melted along with the sintering diffuses into the copper powder 13 of the partial diffusion alloy powder 11 prior to the flat copper powder 15. Particularly in the early stage of sintering, this phenomenon is promoted because the fluid lubricant remains on the surface of the flat copper powder 15. Thereby, the influence of low melting point metal powder 16 on flat copper powder 15 of surface layer S1 can be suppressed (even if low melting metal powder 16 is present immediately below flat copper powder 15, flat copper powder The surface tension acting on 15 is reduced). Therefore, the spheroidization of the flat copper powder 15 in the surface layer can be suppressed, and the proportion of the copper structure in the bearing surface including the bearing surface 1a can be increased to obtain good sliding characteristics. In order to take advantage of the above features, it is preferable not to add single iron powder to the raw material powder as much as possible. That is, it is preferable that the iron structure 33 be all derived from the partial diffusion alloy powder.

  As described above, in the present invention, since the spheroidization of the flat copper powder 15 in the surface layer S1 can be avoided, the blending ratio of the low melting point metal powder 16 in the bearing can be increased. That is, in the conventional technical common sense, in order to suppress the influence of the spheroidization of the flat copper powder 15, the blending ratio of the low melting point metal powder 16 to the flat copper powder 15 should be suppressed to less than 10% by mass. According to the invention, this proportion can be increased to 10% by weight to 30% by weight. Moreover, the compounding ratio of the low melting point metal powder 16 is made into 5 mass%-10 mass% with respect to all the copper in a bearing. Since the effect of promoting the diffusion of the copper powder to the iron powder is further enhanced by increasing the proportion of the low melting point metal powder 16 as described above, the strength of the sintered bearing 1 is enhanced.

  From the above configuration, the area ratio of the copper structure to the iron structure can be made 60% or more over the entire surface of the surface layer S1 including the bearing surface 1a, and the copper rich bearing surface 1a hard to be oxidized is stably obtained. be able to. Further, even if the surface layer S1 wears, a copper structure 31c derived from the copper powder 13 attached to the partial diffusion alloy powder 11 appears on the bearing surface 1a. Therefore, even when the sintered bearing 1 is used for a vibration motor, it is possible to prevent fretting wear of the bearing surface 1a. In addition, sliding characteristics of the bearing surface 1a including initial conformability and quietness can be improved.

  On the other hand, the base portion S2 on the inner side of the surface layer S1 has a hard structure having a lower copper content and a higher iron content than the surface layer S1. Specifically, in the base portion S2, the content of Fe is the largest, and the content of Cu is 20 to 40% by mass. As described above, since the iron content in the base portion S2 that occupies most of the bearing 1 is increased, the amount of copper used in the entire bearing 1 can be reduced, and cost reduction can be achieved. In addition, the strength of the entire bearing can be enhanced because the iron content is high.

  In particular, in the present embodiment, high neck strength is obtained between the copper structure 31 c derived from the partial diffusion alloy powder 11 and the iron structure 33. Therefore, it is possible to prevent the copper structure and the iron structure from falling off from the bearing surface 1a, and to improve the wear resistance of the bearing surface. Further, since the bearing strength (specifically, the radial crushing strength) can be enhanced, even when the sintered bearing 1 is press-fitted and fixed to the inner periphery of the housing 3 as shown in FIG. It is possible to stably maintain the roundness and the cylindricity of the bearing surface 1a even after attachment without deformation according to the peripheral surface shape. Therefore, after the sintered bearing 1 is press-fitted and fixed to the inner periphery of the housing 3, desired roundness (for example, sizing) is not additionally performed to finish the bearing surface 1a to an appropriate shape and accuracy. For example, a roundness of 3 μm or less can be secured. Further, even when the shaft 2 contacts the bearing surface 1a, deformation of the bearing surface 1a can be prevented.

  Furthermore, in the present invention, when classifying the partial diffusion alloy powder 11, the proportion of the single copper powder contained in the partial diffusion alloy powder 11 after classification is 10% by mass by using a sieve having a relatively large opening. It was made to be the following. Thereby, the ratio of the single copper powder unintentionally contained in the raw material powder is reduced, and as a result, the ratio of the partial diffusion alloy powder in the raw material powder can be increased, so the strength of the sintered bearing is enhanced. Specifically, a radial crushing strength of 350 MPa or more can be obtained.

  In addition, since the sintered bearing of the vibration motor mounted on the portable terminal as in this embodiment has an extremely thin thickness (for example, 500 μm or less), the forming accuracy is increased if the particle diameter of the partial diffusion alloy powder is too large. It can be difficult to secure. Therefore, the particle diameter of the partial diffusion alloy powder is preferably 1/2 or less of the minimum thickness of the sintered bearing, and more preferably 1/3 or less. Based on the above findings, the strength of the sintered bearing can be enhanced by using the partial diffusion alloy powder classified with a sieve having a relatively large opening within the range satisfying such conditions.

  In addition, since free graphite is deposited over the entire surface including the bearing surface 1a, and in addition, flaky graphite is attached to the mold molding surface 20a in a manner associated with the flat copper powder 15, the graphite in the surface layer S1 is The content is higher than the content of graphite in the base portion S2. Therefore, the friction of the bearing surface 1a can be reduced, and the durability of the bearing 1 can be increased.

  Hereinafter, although other embodiments of the present invention are described, it explains focusing on a point which is different from the above-mentioned embodiment, and overlapping explanation is omitted about the same composition as the above-mentioned embodiment.

  In the sintered bearing according to the first embodiment described above, flat copper powder is mixed with the raw material powder to form a surface layer having a higher percentage of copper than the base portion S2, but flat copper powder is shown. It is also possible to use Cu-Fe partial diffusion alloy powder, low melting point metal powder, and raw material powder containing a solid lubricant as a main component without containing Cu. In this case, the sintered bearing has an approximately uniform composition throughout. Also in this sintered bearing, since a partial diffusion alloy powder classified with a sieve having a relatively large opening is used similarly to the above embodiment, granular single copper powder having a particle diameter of 45 μm or less (partial diffusion alloy powder 10% by mass or less of the copper structure formed of the copper powder dropped off from the above. That is, in the sintered bearing according to the present invention, most of the copper structure (for example, 85% by mass or more) in at least the inside (for example, 10 μm or more from the surface) regardless of the presence or absence of the surface layer S1 formed of flat copper powder. Is derived from partial diffusion alloy powder.

  Further, in the first embodiment described above, the iron structure is a two-layer structure of a ferrite phase and a pearlite phase, but the pearlite phase (γFe) is a hard structure (HV 300 or more) and is aggressive to the other material Depending on the conditions of use of the bearing, the wear of the shaft 2 may progress. In order to prevent this, all of the iron structure 33 can be formed of a ferrite phase (αFe).

  As described above, in order to form the entire iron structure 33 in the ferrite phase, the sintering atmosphere is a carbon-free gas atmosphere (hydrogen gas, nitrogen gas, argon gas, etc.) or vacuum. By these measures, in the raw material powder, no reaction between carbon and iron occurs, and therefore the iron structure after sintering becomes all soft (HV 200 or less) ferrite phase (αFe). With such a configuration, even if the surface layer S1 wears and the iron structure 33 of the base portion S2 appears on the surface, the bearing surface 1a can be softened and the aggression with respect to the shaft 2 can be weakened. .

  Further, as shown in FIG. 14, tapered surfaces 1 b 1 and 1 b 2 having a large diameter at the opening side are formed on both sides in the axial direction of the cylindrical surface bearing surface 1 a of the sintered bearing 1 having the surface layer S 1 and the base portion S 2. It can also be done. By forming the tapered surfaces 1b1 and 1b2 at both ends in the axial direction of the sintered bearing 1 in this manner, the outer peripheral surface of the shaft 2 locally contacts the end of the sintered bearing 1 even when the shaft 2 is bent. Contact can be prevented, and local wear of the bearing surface 1a due to stress concentration, reduction in bearing strength, occurrence of abnormal noise, and the like can be prevented.

  Further, as shown in FIG. 15, a tapered surface 1b1 having a large diameter at the opening side can be formed only on one side of the cylindrical bearing surface 1a of the sintered bearing 1 in the axial direction. It is possible to obtain the same effects as those of the embodiment shown in FIG. The sintered bearing 1 shown in FIGS. 14 and 15 can be used, for example, as a drive mechanism for a power window of a car or a drive mechanism for a power seat.

  The above-described sintered bearing 1 can be applied not only to a vibration motor but also to, for example, a starter for an automobile. FIG. 16 schematically shows a typical configuration of a starter ST used for starting an automobile engine. The starter ST mainly includes a housing 3, a motor unit 4 having a motor shaft 2a, a reduction gear 5 having an output shaft 2b, an overrunning clutch 6 having an output shaft 2c, a pinion gear 7, a shift lever 8 and an electromagnetic switch 9. Be a component. The shift lever 8 is rotatable about a fulcrum O, and the tip thereof is disposed behind (on the input side) the overrunning clutch 6. The overrunning clutch 6 is a one-way clutch, and the output shaft 2b of the reduction gear 5 is slidably connected in the axial direction via a spline or the like on the input side thereof. A pinion gear 7 is attached to an output shaft 2c of the overrunning clutch 6, and the overrunning clutch 6 is movable in the axial direction integrally with the output shaft 2c and the pinion gear 7.

  When the ignition is turned on, the motor unit 4 is driven, and the torque of the motor shaft 2 a is transmitted to the pinion gear 7 via the reduction gear 5 and the overrunning clutch 6. Further, the electromagnetic switch 9 is turned on to apply rotational force in the direction of the arrow to the shift lever 8, and the overrunning clutch 6 and the pinion gear 7 integrally advance. As a result, the pinion gear 7 meshes with the ring gear 10 coupled to the crankshaft, and the torque of the motor unit 4 is transmitted to the crankshaft to start the engine. After the engine is started, the electromagnetic switch 9 is turned off, the overrunning clutch 6 and the pinion gear 7 are retracted, and the pinion gear 7 is separated from the ring gear 10. The engine torque immediately after the start of the engine is interrupted by the overrunning clutch 6 and therefore is not transmitted to the motor unit 4.

  The sintered bearing 1 is press-fitted and fixed to the inner periphery of the housing 3 etc. of the starter ST described above, and supports the various shafts 2 (2a to 2c) in the starter ST (in FIG. 16, the motor shaft 2a and the overrunning clutch The case where the output shaft 2c of 6 is supported by the sintered bearing 1 is illustrated). Although not shown in detail, the sintered bearing 1 can also be used to support the gears of the reduction gear 5. For example, when the reduction gear 5 is constituted by a planetary gear mechanism, the planetary gear is rotatably supported on the shaft by press-fitting the sintered bearing 1 of the present invention on the inner periphery of the planetary gear rotating with respect to the shaft. can do.

  In addition, if one or both of single iron powder and single copper powder are added to the raw material powder, the ratio of iron structure and copper structure in the sintered bearing can be freely changed. However, from the viewpoint of enhancing the strength, it is preferable not to mix single iron powder or single copper powder, and to form iron structure and copper structure in a sintered bearing as much as possible by partial diffusion alloy powder.

  In the above description, the present invention is applied to a perfect circular bearing in which the bearing surface 1a has a perfect circular shape, but the present invention is not limited to the perfect circular bearing, and the outer periphery of the bearing surface 1a and the shaft 2 The present invention can be similarly applied to a fluid dynamic pressure bearing provided with dynamic pressure generating parts such as herringbone grooves and spiral grooves on the surface. Moreover, in this embodiment, although the case where the axis | shaft 2 was rotated was demonstrated, it can be used for the application which rotates the bearing 1 conversely to this. Furthermore, although the vibration motor and the starter for motor vehicles etc. which are used for a portable terminal were illustrated as a use, the use of sintering bearing 1 concerning the present invention is not limited to these, and it is widely applied to other uses besides illustration. It is possible.

  Also, when compacting the green compact 25, the so-called warm compaction method of compacting the green compact 25 in a state where at least one of the molding die 20 and the raw material powder is heated; A mold lubrication molding method may be employed in which the green compact 25 is compression molded in a state where a lubricant is applied to the molding surface. By adopting such a method, the green compact 25 can be formed with higher accuracy.

  The following tests were conducted to confirm the effects of the present invention.

  Cylindrical test pieces (comparative examples and examples 1 to 4) were manufactured using mixed powder containing Cu-Fe partial diffusion alloy powder, flat copper powder, tin powder, and graphite powder as main components. The specifications of each test piece are shown in Table 1 below.

  As Cu-Fe partial diffusion alloy powder, two different particle sizes were prepared. Specifically, those classified using a sieve of 145 mesh (opening 106 μm) and those classified using a sieve of 100 mesh (opening 150 μm) were prepared.

  The comparative example used the partial diffusion alloy powder classified using the sieve of 145 mesh, and Examples 1-4 used the partial diffusion alloy powder classified using the sieve of 100 mesh. Example 2 was produced using the raw material powder which added single iron powder to Example 1 further. Example 3 was produced using the raw material powder which increased the amount of tin powder to Example 1 further. Example 4 made sintering temperature higher than Examples 1-3, and was made into 910 degreeC or more.

  As a result, as shown in Table 1, the radial crushing strength of Examples 1 to 4 using the partial diffusion alloy powder having a large particle diameter is smaller than that of the comparative example using the partial diffusion alloy powder having a small particle diameter. It was confirmed that the pressure was higher, specifically 350 MPa or more. It is considered that this is because the single copper powder dropped off from the partial diffusion alloy powder is reduced by increasing the mesh size of the sieve, and the proportion of the partial diffusion alloy powder in the sintered bearing is increased.

  Moreover, it was confirmed by increasing the ratio of tin powder like Example 3 and 4 that the radial crushing strength is still higher than the case where iron powder is increased like Example 2. Furthermore, by setting the sintering temperature to 910 ° C. or higher as in Example 4, the radial crushing strength is significantly higher than the case where the sintering temperature is set to less than 910 ° C. as in Examples 1 to 3. Was confirmed.

  FIG. 17 is a cross-sectional photograph of the comparative example, FIG. 18 is a cross-sectional photograph of the third embodiment, and FIG. 19 is a cross-sectional photograph of the fourth embodiment. In each photograph, the whitish area shows a copper structure, and the blackish area shows an iron structure. From these photographs, it can be seen that the example shown in FIG. 18 and FIG. 19 has a smaller percentage of the copper structure as compared with the comparative example shown in FIG. This is considered to be because the single copper powder dropped off from the partial diffusion alloy powder was reduced by increasing the mesh size of the sieve.

  Further, in FIGS. 20 and 21, the amount of deformation when a predetermined load (30 N in FIG. 20 and 50 N in FIG. 21) is applied to each test piece (comparative example 1 and examples 1 and 2) is shown in FIG. The ratio to the amount of deformation is shown. From these figures, it is confirmed that the amount of deformation is smaller in the example using the partial diffusion alloy powder having a large particle size than the comparative example using the partial diffusion alloy powder having a small particle size. The

  Moreover, the ratio of the apparent hardness of the copper structure of each test piece is shown in FIG. 22, and the ratio of the apparent hardness of the iron structure of each test piece is shown in FIG. From these figures, it is confirmed that Example 4 in which the partial diffusion alloy powder having a large particle size is used and the sintering temperature is higher than 910 ° C. has high hardness of copper structure and iron structure. The

1 Sintered bearing 1a Bearing surface 2 Axis 11 Partial diffusion alloy powder 12 Iron powder 13 Copper powder 13 'Single copper powder 14 Graphite powder 15 Flat copper powder 16 Low melting point metal powder 17 Alloy phase 18 Grain boundary 19 Iron powder 31 (31a ~ 31d) Copper structure 32 Free graphite 33 Iron structure 34 Bronze phase S1 Surface layer S2 Base

Claims (9)

A sintered bearing mainly composed of an iron structure and a copper structure formed of a partial diffusion alloy powder of iron powder and copper powder, and containing 25 to 45% by mass of copper ,
In a copper tissue formed alone copper powder having a particle diameter of 10μm or more 45μm or less granular, the proportion of elemental copper powder in the formed copper tissue Ri der 10 wt% or less, the radial crushing strength not less than 350MPa A sintered bearing characterized by being   The sintered bearing according to claim 1, wherein the partial diffusion alloy powder contains 30% by mass or more of powder having a particle size of more than 106 μm. The sintered bearing according to claim 1, wherein the density is 7.0 g / cm ³ or more.   The sintered bearing according to any one of claims 1 to 3, which contains 2 to 3% by mass of a low melting material having a melting point lower than that of copper.   The sintered bearing according to any one of claims 1 to 4, having a surface layer formed mainly of flat copper powder disposed substantially parallel to the surface. Having a surface layer mainly formed of flat copper powder disposed substantially parallel to the surface,
2 to 3 mass% of tin,
The sintered bearing according to any one of claims 1 to 3, wherein a bronze phase and an alloy phase consisting of iron, copper and tin are formed on the surface of the iron structure. The sintered bearing according to any one of claims 1 to 6 , wherein the particle diameter of the partial diffusion alloy powder is 1/2 or less of the minimum thickness of the sintered bearing. The sintered bearing according to any one of claims 1 to 7 , which is used for a vibration motor. The partial diffusion alloy powder particle size 10μm or 45μm or less of the copper powder is diffused adhered around the iron powder, a step of classifying by mesh opening to pass over a sieve 125 [mu] m, the classification portion diffused alloy powder 75 Sintering comprising: compacting raw material powder containing mass% or more to form a green compact; and sintering the green compact to form a sintered body containing 25 to 45 mass% of copper A method of manufacturing a bearing,
Wherein among the raw material powder, sintering, wherein the proportion of elemental copper powder was dropped off from the partial diffusion alloy powder by the classifying is Ri der 10 wt% or less, the radial crushing strength of the sintered body is not less than 350MPa Bearing manufacturing method.