JP2017078183A - Sintered shaft bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sintered shaft bearing capable of reducing surface pore opening rate of a shaft bearing surface at a lower cost.SOLUTION: A raw material powder containing a copper coated iron powder where iron powder is coated with copper with percentage of 30 wt.% or more and 50 wt.% or less and an electrolytic copper powder of 330 mesh or less is molded and sintered.SELECTED DRAWING: None

Description

  The present invention relates to a sintered bearing.

  Sintered bearings are used with internal holes impregnated with lubricating oil, and with the relative rotation with the shaft to be supported, the lubricating oil impregnated inside exudes to the sliding part with the shaft to form an oil film. The shaft is rotationally supported through this oil film. Such sintered bearings are used as bearings for rotating and supporting small motors such as HDDs, LBP polygon scanner motors, or fan motors because of their high rotational accuracy and quietness.

  As a sintered bearing as described above, by forming a plurality of dynamic pressure generating grooves on the inner peripheral surface of a bearing sleeve made of sintered metal, the lubricating oil is collected in a partial region in the axial direction to increase the oil film rigidity. Those having dynamic pressure generating grooves are known. In this kind of sintered bearings, the oil film formed in the bearing gap is released to the inside of the bearing sleeve through the air holes opened in the bearing surface. In general, rotational sizing is applied to the bearing surface of the sintered bearing before the groove is formed to reduce the hole area ratio of the bearing surface (Patent Document 1).

Japanese Patent No. 3602317

  If rotational sizing is performed on the bearing surface of the sintered bearing as in Patent Document 1, the number of manufacturing processes of the sintered bearing increases, resulting in an increase in manufacturing cost.

  Under such circumstances, an object of the present invention is to provide a sintered bearing capable of reducing the surface area ratio of the bearing surface at a lower cost.

  In order to solve the above problems, the sintered bearing according to the present invention is obtained by coating the surface of iron powder with a copper layer, and the copper-coated iron powder having a copper ratio of 30 wt% or more and 50% wt or less, It is characterized by being formed by sintering raw material powder containing electrolytic copper powder having an average particle size smaller than that of copper-coated iron powder.

  Thus, in the present invention, copper-coated iron powder and electrolytic copper powder (preferably 330 mesh or less) having an average particle size smaller than that of the copper-coated iron powder are used as the raw material powder for the sintered bearing. Accordingly, the gap between the copper-coated iron powders can be filled with the electrolytic copper powder at the stage of the compact. Moreover, since the electrolytic copper powder has a dendritic shape that easily entangles with other particles, the gap between the particles can be reduced. Furthermore, the ratio of copper in the copper-coated iron powder may be increased (copper plating amount of 30 wt or more and 50 wt or less), and there is plenty of soft copper phase around the iron phase after sintering. ing. Therefore, when sizing is performed after sintering, voids are easily crushed due to deformation of the copper phase. As described above, according to the present invention, the pores of the sintered bearing can be miniaturized, and the surface area ratio of each bearing surface can be reduced even if sealing treatment such as rotational sizing is omitted. Is possible.

  The raw material powder is preferably blended with a low melting point metal powder having an average particle size smaller than that of the copper-coated iron powder. The low-melting-point metal powder moves in a liquid phase during sintering and forms pores in the original place. As described above, the low-melting-point metal powder can be formed after sintering by using a low-melting-point metal powder having a small particle size. The pores can be further refined. The ratio of the low melting point metal powder in the raw material powder is preferably 1.0 wt% or more and 3.0 wt% or less.

  The ratio of the electrolytic copper powder in the raw material powder is preferably 10 wt% or more and 45 wt% or less. Further, the iron content in the sintered bearing is preferably 38 wt% or more and 42 wt% or less.

  The sintered bearing described above is particularly suitable for a sintered bearing with dynamic pressure generating grooves in which a plurality of dynamic pressure generating grooves are formed on the bearing surface. The formation of the dynamic pressure generating groove on the bearing surface can be performed, for example, by pressing a concavo-convex mold against the sintered material during sizing. In this case, the amount of deformation of the material on the bearing surface, particularly the copper phase, Increases (strong sizing). Accordingly, the holes are more easily crushed and the holes can be further miniaturized.

  As described above, in the sintered bearing of the present invention, the pores can be miniaturized. Therefore, even if sealing processing such as rotational sizing is omitted, it is possible to prevent dynamic pressure loss and obtain high oil film rigidity. Therefore, it is possible to reduce the cost of the sintered bearing.

It is sectional drawing of a fluid dynamic pressure bearing apparatus. It is sectional drawing of the sleeve used with the said fluid dynamic pressure bearing apparatus. It is a bottom view of the sleeve used with the said fluid dynamic pressure bearing apparatus. It is a top view of the bottom part used with the said fluid dynamic pressure bearing apparatus. It is sectional drawing which shows a sizing process. It is sectional drawing which shows the structure of a copper covering iron powder roughly.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

  FIG. 1 shows a cross-sectional view of a fluid dynamic bearing device 1 used for rotation support of an HDD or a fan motor. The configuration of the fluid dynamic pressure bearing device 1 described below is merely an example, and the present invention can be similarly applied to the fluid dynamic pressure bearing device 1 having a configuration other than the illustrated example.

  A fluid dynamic pressure bearing device 1 shown in FIG. 1 includes a shaft member 2, a sleeve made of sintered metal (fluid dynamic pressure bearing) 8 in which the shaft member 2 is inserted on the inner periphery, and the sleeve 8 fixed on the inner peripheral surface. The cylindrical housing 7 is mainly provided, a bottom portion 9 that closes the opening portion on the one axial end side of the housing 7, and a seal portion 10 that is disposed on the opening portion on the other axial end side of the housing 7. .

  The shaft member 2 is formed of a metal material such as stainless steel, for example, and includes a shaft portion 2a and a flange portion 2b provided integrally or separately at the lower end of the shaft portion 2a. The outer peripheral surface 2a1 of the shaft portion 2a is a smooth cylindrical surface without irregularities. A clearance portion 2a2 having a slightly smaller diameter than the outer peripheral surface 2a1 is provided at a substantially central portion in the axial direction of the outer peripheral surface 2a1. The flange portion 2b has a disk shape. The upper end surface 2b1 and the lower end surface 2b2 of the flange portion 2b are flat surfaces without unevenness.

  The sleeve 8 is formed of a sintered metal, and is formed of a copper iron-based sintered metal mainly composed of copper and iron. The manufacturing procedure of the sleeve 8 will be described in detail later.

  On the inner peripheral surface 8a of the sleeve 8, radial bearing surfaces 8a1 and 8a2 are provided in two regions separated in the axial direction. On the radial bearing surfaces 8a1 and 8a2, a plurality of dynamic pressure generating grooves G and F as shown in FIG. 2 are formed in a herringbone shape.

  On the upper radial bearing surface 8a1, as the dynamic pressure generating groove G, a first inclined groove G1 and a second inclined groove G2 having different inclination directions are formed apart from each other in the axial direction. When the shaft member 2 rotates, the first inclined groove G1 pushes the lubricating oil in the radial bearing gap downward, and the second inclined groove G2 pushes the lubricating oil in the radial bearing gap upward. In the present embodiment, since the axial dimension L1 of the first inclined groove G1 is larger than the axial dimension L2 of the second inclined groove G2 (L1> L2), the downward pumping force by the first inclined groove G1 is reduced. , Exceeding the upward pumping force by the second inclined groove G2. Accordingly, a pumping force that causes the lubricating oil in the radial bearing gap to flow downward is generated as the entire dynamic pressure generating groove G.

  On the lower radial bearing surface 8a2, as the dynamic pressure generating groove F, a first inclined groove F1 and a second inclined groove F2 having different inclination directions are formed apart from each other in the axial direction. When the shaft member 2 rotates, the first inclined groove F1 pushes the lubricating oil in the radial bearing gap downward, and the second inclined groove F2 pushes the lubricating oil in the radial bearing gap upward. In the present embodiment, since the axial dimensions of the first inclined groove F1 and the second inclined groove F2 are equal, a pumping force that causes the lubricating oil in the radial bearing gap to flow in the axial direction is generated as the entire dynamic pressure generating groove F. Absent.

  Inclined hill portions G3, G4, F3, and F4 are provided between the circumferential directions of the inclined grooves G1, G2, F1, and F2 of the dynamic pressure grooves G and F, respectively. Further, between the axial direction of the first inclined groove G1 and the second inclined groove G2 of the dynamic pressure groove G and between the axial direction of the first inclined groove F1 and the second inclined groove F2 of the dynamic pressure groove F, Annular hills G5 and F5 are provided. The inclined hill portions G3 and G4 and the annular hill portion G5, and the inclined hill portions F3 and F4 and the annular hill portion F5 (regions indicated by cross-hatching in FIG. 3) are respectively continuous on the same cylindrical surface.

  A cylindrical surface 8a3 is provided between the axial directions of the radial bearing surfaces 8a1 and 8a2. The cylindrical surface 8a3 is continuous on the same cylindrical surface as the second inclined groove G2 of the dynamic pressure groove G and the first inclined groove F1 of the dynamic pressure groove F. The upper end of the first inclined groove G1 of the dynamic pressure groove G reaches the inner peripheral chamfer of the upper end face 8d of the sleeve 8, and the lower end of the second inclined groove F2 of the dynamic pressure groove F is the lower end face 8b of the sleeve 8. Has reached the inner circumference Changfa.

  A thrust bearing surface having a spiral-shaped dynamic pressure groove 8b1 as shown in FIG. 3 is formed on the lower end surface 8b of the sleeve 8. The outer peripheral surface 8c of the sleeve 8 is a smooth cylindrical surface without irregularities. The upper end surface 8d of the sleeve 8 is a flat surface without unevenness. Further, on the outer peripheral surface of the sleeve 8, a communication groove 8 e that opens to the outer peripheral chamfers at both ends in the axial direction is formed.

  The housing 7 has a cylindrical shape with both axial ends open (see FIG. 1). At the lower end of the inner peripheral surface 7 a of the housing 7, a fixing surface 7 b that is larger in diameter than the inner peripheral surface 7 a and that fixes the bottom 9 is provided. The housing 7 is made of resin, for example, and the sleeve 8 is fixed to the inner periphery of the housing 7 by means such as adhesion or press-fitting adhesion.

  The bottom 9 is formed in a disk shape from a metal material or a resin material. A thrust bearing surface having a spiral-shaped dynamic pressure groove 9a1 as shown in FIG. 4 is formed on the upper end surface 9a of the bottom portion 9. The outer peripheral surface 9b of the bottom portion 9 is fixed to the fixing surface 7b of the housing 7 by appropriate means such as bonding, press-fitting, press-fitting with an adhesive interposed, or a combination thereof.

  The seal portion 10 is provided at the upper end opening of the housing 7, and in this embodiment, the seal portion 10 and the housing 7 are integrally formed of resin. The inner peripheral surface 10a of the seal portion 10 has a tapered shape that gradually increases in diameter upward. Between the inner peripheral surface 10a of the seal portion 10 and the outer peripheral surface 2a1 of the shaft portion 2a is formed a wedge-shaped seal space S having a gradually narrowing radial width downward. The lower end surface 10 b of the seal portion 10 is in contact with the upper end surface 8 d of the sleeve 8.

  Lubricating oil is injected into the fluid dynamic bearing device 1 composed of the above components. As a result, the internal space of the fluid dynamic bearing device 1 including the radial bearing gap, the thrust bearing gap, and the internal holes of the sleeve 8 is filled with the lubricating oil. That is, the space on the closed side of the housing 7 with respect to the seal space S is filled with the lubricating oil without interruption, and the oil level is always maintained within the range of the seal space S.

  When the shaft member 2 rotates, a radial bearing gap is formed between the radial bearing surfaces 8a1 and 8a2 (dynamic pressure groove G and F formation region) of the inner peripheral surface 8a of the sleeve 8 and the outer peripheral surface 2a1 of the shaft portion 2a. . Then, the pressure of the oil film in the radial bearing gap is increased by the dynamic pressure grooves G and F, and by this dynamic pressure action, the first radial bearing portion R1 and the second radial bearing portion R2 that rotatably support the shaft portion 2a in a non-contact manner. Is configured.

  At the same time, thrust bearing gaps are formed between the upper end surface 2b1 of the flange portion 2b and the lower end surface 8b of the sleeve 8, and between the lower end surface 2b2 of the flange portion 2b and the upper end surface 9a of the bottom portion 9, respectively. Is done. Then, the pressure of the oil film in the thrust bearing gap is increased by the dynamic pressure grooves 8b1 and 9a1, and by this dynamic pressure action, the first thrust bearing portion T1 and the second thrust bearing portion T1 that support the flange portion 2b rotatably in both thrust directions are contacted. And a thrust bearing portion T2. The lubricating oil circulates in the bearing device from the radial bearing gap via the thrust bearing gap of the first thrust bearing portion T1, the communication groove 8e, and the seal space S by the pumping force generated on the upper radial bearing surface 8a2. .

  The sintered metal sleeve 8 described above is formed by first forming a compact having a smooth cylindrical surface with no dynamic pressure generating groove on the inner peripheral surface, and then sintering the compact to obtain a sintered material. It is manufactured by sizing the sintered material.

  The sizing step is a step of simultaneously performing dimensional correction of the inner peripheral surface, both end surfaces, and outer peripheral surface of the sintered material and molding of the dynamic pressure generating grooves on the inner peripheral surface and the lower end surface of the sintered material, The sizing mold shown in FIG. 5 is used. The sizing die includes a die 11, a core rod 12, a lower punch 13, and an upper punch 14. Formed on the outer peripheral surface of the core rod 12 is a molding portion 12a having a shape corresponding to the concave and convex shape of the radial bearing surfaces 8a1 and 8a2 (the concave and convex shape formed by the dynamic pressure generating groove and the hill portion), and is formed on the end surface 13a of the lower punch 13. A molded portion 13a having a shape corresponding to the uneven shape of the thrust bearing surface is formed.

  By pressing the sintered material 8 ′ with the upper and lower punches 13 and 14 in a state where the sintered material 8 ′ is disposed between the inner periphery of the die 11 and the outer periphery of the core rod, each surface of the sintered material 8 ′ is The die 11 is pressed against the inner peripheral surface of the die 11, the outer peripheral surface of the core rod 12, and the end surfaces of the upper and lower punches 13, 14, and the dimensions of these surfaces are corrected. At this time, the molded portion 12a of the core rod 12 bites into the inner peripheral surface 8a ′ of the sintered material 8 ′, so that the dynamic pressure generating grooves F and G and the hill portions G3 to G5 and F3 to F5 are respectively molded, and the lower punch The 13 forming portions 13a bite into the lower end face 8b ′ of the sintered material 8 ′, thereby forming the dynamic pressure generating groove 8b1 and the hill portion 8b2 (see FIG. 3) between the dynamic pressure generating grooves. Thereafter, when the sintered material 8 ′ is pushed out of the die 11, the sintered material 8 ′ springs back, so that the sintered material 8 ′ is extracted from the core rod 12 without breaking the irregular shape of the inner peripheral surface thereof. Is possible. Then, the sleeve 8 shown in FIG. 2 is completed by impregnating (vacuum impregnating) the lubricant into the sintered material 8 ′ and retaining the lubricant in the holes.

  In the conventional manufacturing process of a sintered bearing, the inner peripheral surface 8a ′ of the sintered material 8 ′ is subjected to a sealing process such as rotational sizing (a step of pressing a rotating jig against the inner peripheral surface 8a ′) and the inner peripheral surface 8a ′. In general, the sizing step shown in FIG. 5 is performed after the surface area ratio of the surface 8a ′ is reduced. On the other hand, in the present invention, this sealing treatment step is omitted. For this reason, there is no sliding trace of the jig on the radial bearing surfaces 8a1 and 8a2 of the sleeve 8. The composition of the sintered material 8 'is improved in order to reduce the surface hole area ratio necessary for realizing the omission of the sealing process. Hereinafter, the composition of the improved sintered material 8a 'will be described in detail.

  As the raw material powder of the sintered material 8 ′, a mixture of copper-coated iron powder, copper simple powder, and low melting point metal simple powder (low melting point metal powder) is used.

  As shown in FIG. 6, the copper-coated iron powder is a powder obtained by performing copper plating on the iron powder 20 and covering the periphery of the iron powder 20 with a copper layer 21. The ratio of copper in the copper-coated iron powder is preferably about 30 wt% to 50 wt%. By covering the iron powder 20 with a large amount of copper 21 in this way, the copper layer can be prevented from peeling off from the iron powder even when performing strong sizing shown in FIG. As the iron powder used for copper-coated iron, it is preferable to use a powder of 200 mesh or less, specifically, a powder that has passed through a sieve when sieved with a sieve of 200 mesh (aperture 75 μm).

  As the iron powder 20 constituting the copper-coated iron powder, known powders such as reduced iron powder and atomized iron powder can be widely used, but the reduction is porous and has an irregular shape as compared with the atomized iron powder. It is preferable to use iron powder. By using irregularly shaped reduced iron powder, the copper-coated iron powder also becomes irregularly shaped. Therefore, the copper-coated iron powders can be intertwined closely in the state of a compact, thereby making it possible to refine the pores after sintering.

  Moreover, as the copper simple powder, electrolytic copper powder having a dendritic shape is used. As the electrolytic copper powder, a powder having a particle size of 330 mesh or less, specifically, a powder that has passed through a sieve when sieved with a 330 mesh sieve (aperture 45 μm) is used. When compared with the average particle size (for example, measured by laser diffraction / scattering method), the particle size of the electrolytic copper powder is smaller than that of the copper-coated iron powder. By using electrolytic copper powder having a small particle diameter in this way, electrolytic copper powder enters the gaps between the copper-coated iron powders, and thus the pores after sintering can be miniaturized.

  Theoretically, pores can be refined by simply reducing the particle size of the copper-coated iron powder without blending the single copper powder into the raw material powder. However, in this case, the apparent density of the copper-coated iron powder is lowered and the fluidity is lowered, so that it is difficult to smoothly fill the raw material powder into the molding die at the time of molding the compact. On the other hand, as described above, using copper-coated iron powder with a large particle size as a base powder, and adding electrolytic copper powder with a small particle size to this, ensuring the fluidity of the entire raw material powder, It becomes possible to make the pores finer. From the above viewpoint, the blending ratio of the electrolytic copper powder in the raw material powder is preferably 10 wt% or more and 45 wt% or less (more preferably 30 wt% or more and 40 wt% or less).

  The single powder of the low melting point metal is added as a binder during sintering. As this simple substance powder, a metal powder having a melting point of 700 ° C. or less, for example, a powder of tin, zinc, phosphorus or the like is used. In this embodiment, among these, tin powder that is easy to diffuse into copper and iron and that can be easily used as a single powder, particularly atomized tin powder, is used. The low melting point metal powder moves in a liquid phase during sintering and forms vacancies in the original place. From the viewpoint of refining the vacancies, the low melting point metal powder has a small particle size. Specifically, it is preferable that 94% or more of the particles have a particle size of 330 mesh or less. Further, the blending amount of the low melting point metal powder in the raw material powder is desirably about 1 to 3 wt%.

  In conventional copper-iron sintered bearings, alloyed copper powder (for example, bronze powder) in which copper and a low melting point metal are alloyed may be used as the copper powder. Since the powder is generally hard and hardly deformed, gaps are easily generated between the particles when the compact is formed, and the pores after sintering become a factor. Further, even in the sizing process shown in FIG. 5, since the sintered bronze structure is hard, it is difficult to crush the pores even when a pressing force is applied. On the other hand, such a problem can be prevented by using each single powder as the copper component and the low melting point metal component as described above and reducing the particle size of each single powder.

  In the raw material powder described above, the composition and blending amount of various powders are such that the iron content is 38 wt% to 42 wt%, the low melting point metal content is 1 wt% to 3.0 wt%, and the balance is copper. Adjusted.

  The raw material powder described above is supplied to the mold after adding various molding aids, for example, a lubricant for improving releasability, if necessary. A raw material powder is compression-molded with a molding die to produce a cylindrical compact, and then sintered to obtain a sintered material 8 'shown in FIG. The sintering temperature is set to a temperature not lower than the melting point of the low melting point metal and not higher than the melting point of copper, specifically about 800 ° C. to 900 ° C. During sintering, the tin powder first becomes a liquid phase to wet the copper layer of the copper-coated iron powder and the surface of the electrolytic copper powder. Thereby, copper sintering is promoted, copper and tin diffuse into the iron particles, and the iron particles and the copper layer of the copper-coated iron powder are firmly bonded. Moreover, the tin powder which became a liquid phase during sintering plays the role of a binder, and copper covering iron powder, electrolytic copper powder, copper covering iron powder, and electrolytic copper powder are couple | bonded.

  The metal structure of the sleeve 8 (after sizing) is mainly formed of an iron phase and two types of copper phases. Among these, the iron phase and one copper phase (the first copper phase) are derived from the copper-coated iron powder, and, like the copper-coated iron powder shown in FIG. It is a covered form. The other copper phase (second copper phase) is a structure derived from the electrolytic copper powder, and at least a part thereof has a dendritic form. A lot of fine pores are formed around the cupric phase because the electrolytic copper powder has an irregular dendritic form (in contrast to the electrolytic copper powder, it has a more spherical shape). When close atomized copper powder is used, fine pores are not formed around it).

  Moreover, since there is much quantity of the copper layer 21 in copper covering iron powder, peeling from the iron phase of the 1st copper phase accompanying sizing can be suppressed. Accordingly, almost the entire surface of the sleeve 8 after sizing (the right side in the figure) is covered with the cuprous phase derived from the copper-coated iron powder (some surfaces are formed of the cupric phase derived from the electrolytic copper powder). ) Specifically, 90% or more of the surface of the sleeve 8 is formed of the first and second copper phases. As described above, according to the present invention, since almost the entire surface of the sleeve 8 is covered with the copper phases 31 and 32, the aggressiveness of the bearing surface with respect to the outer peripheral surface of the shaft 2 can be reduced, and high sliding is achieved. It becomes possible to ensure the sex.

  In the present invention, as described above, copper-coated iron powder and electrolytic copper powder having an average particle size smaller than that of the copper-coated iron powder are used as the raw material powder of the sintered material 8 ′ constituting the sleeve 8. Yes. Accordingly, the gap between the copper-coated iron powders can be filled with the electrolytic copper powder at the stage of the compact. Moreover, since the electrolytic copper powder has a dendritic shape that easily entangles with other particles, the gap between the particles can be reduced. Furthermore, the ratio of copper in the copper-coated iron powder may be increased (copper plating amount of 30 wt or more and 50 wt or less), and soft copper phases 31 and 32 are formed around the iron phase 30 after sintering. Exists in abundance. Therefore, when the sizing shown in FIG. 5 is performed after sintering, the voids are easily crushed due to the deformation of the copper phases 31 and 32.

  As described above, according to the present invention, the hole 33 of the sleeve 8 can be miniaturized. By reducing the size of the air holes 33, the surface area ratio of each bearing surface can be reduced even if a sealing process such as rotational sizing is omitted. Therefore, it is possible to prevent so-called dynamic pressure loss and maintain high oil film rigidity. Such effects include the other finer measures already described, that is, use of a single powder not alloyed with copper powder as the low melting point metal powder, use of a small melting point metal powder as the low melting point metal powder, It can be further strengthened by adopting any one measure of using reduced iron powder as the iron powder of the copper-coated iron powder, or by appropriately combining two or more measures.

  In order to confirm the effect of pore miniaturization according to the present invention, the following confirmation test was performed.

  In this confirmation test, three types shown in Table 1 below were used as the copper-coated iron powder to be blended with the raw material powder. The particle size of the iron powder used for any copper-coated iron powder is -200 mesh.

  These three types of copper-coated iron powder were mixed with -330mesh electrolytic copper powder and -330mesh atomized tin powder (94% or more) at the above ratio to obtain a raw material powder, which had an inner diameter of φ1.5 (mm), The oil permeability of a sintered body obtained by molding into a cylindrical shape having an outer diameter of φ3 (mm) and a length of 3.3 (mm) and sintering was measured. Prior to the measurement of oil permeability, sealing treatment such as rotation sizing on the bearing surface is not performed. The oil permeability is defined as the weight of the lubricating oil permeated in 10 minutes when both ends of the sleeve are sealed and the lubricating oil is pumped from the inner peripheral surface side to the outer diameter side at 0.4 MPa.

  The measurement result of the oil permeability was 0.03 g / 10 min or less in any of the examples. As a result, it was confirmed that the surface porosity of the sintered body can be reduced to a practically sufficient level even if the rotational sizing is omitted. Is about 0.01 g / 10 min). In particular, in the case of Example 2 and Example 3 in which reduced iron powder is used as the iron powder of the copper-coated iron powder, the value of oil permeability becomes smaller, and the same degree of passage as that of an existing sleeve subjected to rotational sizing is achieved. It was also confirmed that oiliness was obtained.

DESCRIPTION OF SYMBOLS 1 Fluid dynamic pressure bearing apparatus 2 Shaft member 7 Housing 8 Sleeve (sintered bearing)
8a Inner peripheral surface (bearing surface)
8 'Sintered material 20 Iron powder 21 Copper layer

Claims (8)

The surface of the iron powder is coated with a copper layer, and includes a copper-coated iron powder having a copper ratio of 30 wt% or more and 50% wt or less, and an electrolytic copper powder having an average particle size smaller than the copper-coated iron powder. A sintered bearing formed by sintering raw material powder.   The sintered bearing according to claim 1, wherein the bearing surface is not sealed.   The sintered bearing according to claim 1 or 2, wherein a low melting point metal powder having an average particle size smaller than that of the copper-coated iron powder is blended with the raw material powder.   The sintered bearing according to claim 3, wherein a ratio of the low melting point metal powder in the raw material powder is 1.0 wt% or more and 3.0 wt% or less.   The sintered bearing according to any one of claims 1 to 4, wherein a ratio of the electrolytic copper powder in the raw material powder is 10 wt% or more and 45 wt% or less.   The sintered bearing according to any one of claims 1 to 5, wherein the iron content is 38 wt% or more and 42 wt% or less.   The sintered bearing according to any one of claims 1 to 6, wherein the electrolytic copper powder is 330 mesh or less.   The sintered bearing according to any one of claims 1 to 7, wherein a plurality of dynamic pressure generating grooves are formed on the bearing surface.

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