JP7076266B2 - Manufacturing method of sintered oil-impregnated bearing - Google Patents

Description

The present invention relates to a sintered oil-impregnated bearing, and more particularly to a sintered oil-impregnated bearing incorporated in a fluid dynamic pressure bearing device.

The hydrodynamic bearing device is a lubricating oil filled in the radial bearing gap between the outer peripheral surface of the shaft member and the inner peripheral surface of the bearing member by the relative rotation between the bearing member and the shaft member inserted in the inner circumference thereof. The pressure of the bearing is increased, and the shaft member is rotatably and non-contactly supported by this pressure (dynamic action). The fluid dynamic bearing device is suitably used for a spindle motor or the like of an HDD disk drive device because of its excellent rotational accuracy and quietness.

As a bearing member incorporated in a fluid dynamic bearing device, a sintered oil-impregnated bearing formed by impregnating the internal pores of a sintered body with oil may be used. However, since the sintered oil-impregnated bearing has innumerable minute openings on the surface, when the pressure of the lubricating oil filled in the radial bearing gap increases, the inside is formed from the opening on the inner peripheral surface of the sintered oil-impregnated bearing. Lubricating oil may enter the pores and the pressure (oil film strength) of the lubricating oil in the radial bearing gap may decrease. Such a phenomenon is called "dynamic pressure release" and is a problem to be avoided in a fluid dynamic pressure bearing device using a sintered oil-impregnated bearing.

As a means for preventing dynamic pressure release, a method is known in which the inner peripheral surface of the sintered body is subjected to rotational sizing to reduce surface openings (see, for example, Patent Document 1 below).

Further, Patent Document 2 below discloses a method of impregnating pores opened on the surface of a sintered body with a sealing agent (resin) to seal the pores.

Further, in Patent Document 3 below, by using a raw material powder containing a partially diffused alloy powder in which fine copper powder is diffused and adhered around the iron powder, the internal pores of the sintered body are uniformly dispersed and coarse. A method of preventing the formation of pores is shown.

Japanese Unexamined Patent Publication No. 10-306827 Japanese Unexamined Patent Publication No. 2010-6098 Japanese Unexamined Patent Publication No. 2017-150596

However, it cannot be said that the dynamic pressure release can be reliably prevented because the coarse air holes may remain on the bearing surface only by the rotational sizing. Further, when the surface of the sintered body is to be sealed with a sealing agent, a sealing agent and a step of impregnating the sealing agent are required, so that high cost is unavoidable. In addition, the use of special powders such as partial diffusion alloy powders may lead to high material costs.

Therefore, an object of the present invention is to surely prevent dynamic pressure release while suppressing the manufacturing cost.

In order to solve the above problems, the present invention comprises a step of compressing a raw material powder containing 25% by mass or more of copper to form a green compact, and a step of sintering the green compact to obtain a sintered body. A sintered oil-impregnated bearing having a step of compressing the outer peripheral surface of the sintered body with a compression allowance of more than 0 μm and 50 μm or less, and a step of molding a dynamic pressure generating portion on the inner peripheral surface of the sintered body. Provide a manufacturing method.

As described above, in the present invention, before the step of molding the dynamic pressure generating portion on the inner peripheral surface of the sintered body (dynamic pressure groove sizing), the outer peripheral surface of the sintered body is subjected to a minute compression allowance of 50 μm or less. Perform a compression process (light sizing). Due to this light sizing, the copper exposed on the surface (outer peripheral surface) of the sintered body is plastically deformed and enters the coarse air holes on the outer peripheral surface of the sintered body, and the coarse air holes on the surface of the sintered body are reduced. After that, by applying dynamic pressure groove sizing to the sintered body with reduced rough air holes on the surface, the coarse air holes on the outer peripheral surface of the sintered body are further reduced, and the dynamic pressure groove sizing is performed without light sizing. The oil permeability of the sintered body is significantly reduced as compared with the sintered body of the same density.

By the way, as a conventional method for manufacturing a sintered oil-impregnated bearing, dimensional sizing for adjusting the dimensions of the sintered body may be performed before the dynamic pressure groove sizing. This dimensional sizing is intended to compress the sintered body into a predetermined dimensional range when the size of the sintered body deviates significantly from the target value. Specifically, the die for dimensional sizing includes a die 101, a core rod 102, an upper punch 103, and a lower punch 104, as shown in FIG. The inner diameter D2'of the die 101 is the maximum allowable outer diameter of the sintered body. The outer diameter D3'of the core rod is the minimum allowable inner diameter of the sintered body. The axial distance W'between the upper punch 103 and the lower punch 104 is the maximum allowable axial width of the sintered body. By pushing the sintered body 110 into the space partitioned by the die 101, the core rod 102, the upper punch 103, and the lower punch 104 as described above, the dimensions (outer diameter, inner diameter, axial width) of the sintered body 110 can be determined. If any of them exceeds the allowable range, it is molded so as to be within the allowable range.

In this case, for example, as shown in the figure, if the outer diameter D1'of the sintered body 110 before dimensional sizing is smaller than the inner diameter D2' of the die 101, the outer peripheral surface 110d of the sintered body 110 is compressed by the die 101. There is no such thing. As described above, in the dimensional sizing, the outer peripheral surface 110d of the sintered body 110 may not be compressed. On the other hand, in the light sizing of the present invention, the outer peripheral surface of the sintered body is always compressed with a compression allowance larger than 0 μm (preferably a compression allowance of 5 μm or more) regardless of the variation in dimensions for each product. It is different from the conventional dimensional sizing.

By the manufacturing method as described above, a sintered oil-impregnated bearing having reduced coarse air holes on the outer peripheral surface can be obtained. Specifically, it is a sintered oil-impregnated bearing made of a sintered body containing 25% by mass or more of copper and having a dynamic pressure generating portion molded on the inner peripheral surface, and has surface openings on the outer peripheral surface of the sintered body. A sintered oil-impregnated bearing is obtained, wherein the ratio is 2% or more and 15% or less, and the area of each pore opened on the outer peripheral surface of the sintered body is 0.01 mm ² or less.

The oil permeability of the sintered oil-impregnated bearing is, for example, 0.1 g / 10 min or less. The degree of oil flow is determined by applying a predetermined pressure (here, 0.4 MPa) to the oil filled in the inner circumference of the sintered body with the pores opened on both end faces in the axial direction of the sintered body sealed. It is the total weight of the oil exuded from the pores opened on the outer peripheral surface of the sintered body when the sintered body is held for 10 minutes.

The movement of the oil film generated in the radial bearing gap between the sintered oil-impregnated bearing, the shaft member inserted in the inner circumference of the sintered oil-impregnated bearing, and the inner peripheral surface of the sintered oil-impregnated bearing and the outer peripheral surface of the shaft member. The fluid dynamic bearing device provided with the radial bearing portion that supports the shaft member by pressure has excellent bearing rigidity and rotational accuracy because the dynamic pressure release from the inner peripheral surface of the sintered oil-impregnated bearing is suppressed.

As described above, by applying light sizing to the sintered body before the dynamic pressure groove sizing, the oil permeability of the sintered body is reduced and the dynamic pressure is released without the need for sealing treatment or special materials. Can be prevented.

It is sectional drawing of a spindle motor. It is sectional drawing of the fluid dynamic pressure bearing apparatus. It is sectional drawing of the sintered oil-impregnated bearing which concerns on embodiment of this invention. It is a bottom view of the above-mentioned sintered oil-impregnated bearing. (A) and (B) are sectional views showing a light sizing process. (A) is a cross-sectional view of the surface layer of the sintered body before light sizing, and (B) is a cross-sectional view of the surface layer of the sintered body after light sizing. (A) and (B) are sectional views showing a dynamic pressure groove sizing process. It is a graph which shows the test result of the oil permeability degree of a sintered body. It is sectional drawing which shows the conventional dimension sizing process.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

The spindle motor shown in FIG. 1 is used for a disk drive device such as an HDD, and is a fluid dynamic bearing device 1 that rotatably and non-contactly supports the shaft member 2 and a disc hub 3 mounted on the shaft member 2. And a stator coil 4 and a rotor magnet 5 which are opposed to each other through a gap in the radial direction. The stator coil 4 is attached to the casing 6, and the rotor magnet 5 is attached to the disc hub 3. The housing 7 of the fluid dynamic bearing device 1 is mounted on the inner circumference of the casing 6. A predetermined number of discs D such as magnetic disks (two in the illustrated example) are held in the disc hub 3. When the stator coil 4 is energized, an electromagnetic force is generated between the stator coil 4 and the rotor magnet 5, and the electromagnetic force causes the disc hub 3 and the shaft member 2 to rotate together.

As shown in FIG. 2, the fluid dynamic bearing device 1 includes a shaft member 2, a bearing member 8 as a sintered oil-impregnated bearing according to the present embodiment, a housing 7 for holding the bearing member 8 on the inner circumference, and a housing. It has a seal portion 9 provided in the opening at one end in the axial direction of the housing 7, and a lid portion 10 for closing the other end in the axial direction of the housing 7. In the following description, for convenience, the closed side of the housing 7 is referred to as the lower side and the opening side of the housing 7 is referred to as the upper side in the axial direction, but this does not mean that the usage mode of the fluid dynamic bearing device 1 is limited.

The shaft member 2 includes a shaft portion 2a and a flange portion 2b provided at the lower end of the shaft portion 2a. The shaft member 2 is made of a metal material such as stainless steel, and in the present embodiment, the entire shaft member 2 including the shaft portion 2a and the flange portion 2b is integrally formed. The shaft portion 2a and the flange portion 2b can be formed separately.

On the outer peripheral surface of the shaft portion 2a, a cylindrical surface 2a1 formed at two locations separated in the axial direction and an annular recess 2a2 provided between the two cylindrical surfaces 2a1 and having a diameter smaller than that of the cylindrical surface 2a1 are provided. Be done. The cylindrical surface 2a1 functions as a bearing facing surface that faces the bearing surface 8a1 of the inner peripheral surface 8a of the bearing member 8 in the radial direction.

The housing 7 is made of resin or metal and is formed in a cylindrical shape. The outer peripheral surface 8d of the bearing member 8 is fixed to the inner peripheral surface 7a of the housing 7 by an appropriate means such as adhesion or press fitting.

The bearing member 8 has a cylindrical shape, and a radial bearing surface is provided on the inner peripheral surface 8a. In the illustrated example, radial bearing surfaces 8a1 are formed at two locations separated in the axial direction from the inner peripheral surface 8a of the bearing member 8. A dynamic pressure generating portion is formed on each radial bearing surface 8a1, and in the present embodiment, as shown in FIG. 3, dynamic pressure grooves, specifically, dynamic pressure grooves arranged in a herringbone shape are arranged on each radial bearing surface 8a1. Pressure grooves G1 and G2 are provided. The area shown by cross-hatching in the figure indicates a hill portion that rises from the surroundings (the same applies to FIG. 4). The upper dynamic pressure groove G1 has an asymmetrical shape in the axial direction, and the lower dynamic pressure groove G2 has a symmetrical shape in the axial direction. A cylindrical surface 8a2 continuous with the bottom surfaces of the dynamic pressure grooves G1 and G2 is provided in the axially interaxial region of the radial bearing surface 8a1.

Both the upper and lower dynamic pressure grooves G1 and G2 may have axially symmetrical shapes. Further, the upper and lower dynamic pressure grooves G1 and G2 may be made continuous in the axial direction, or one of the upper and lower dynamic pressure grooves G1 and G2 may be omitted. Further, as the dynamic pressure generating part, a dynamic pressure groove having another shape such as a spiral shape, a multi-arc bearing in which a plurality of cylindrical surfaces are combined, or a step bearing in which a plurality of axial grooves are arranged at equal intervals in the circumferential direction, etc. are used. It may be formed.

A thrust bearing surface is provided on the lower end surface 8b of the bearing member 8. A pump-in type spiral-shaped dynamic pressure groove G3 as shown in FIG. 4 is formed on the thrust bearing surface. As the shape of the dynamic pressure groove G3, a herringbone shape, a radial groove shape, or the like may be adopted. Further, the lower end surface 8b of the bearing member 8 may be used as a flat surface, and a dynamic pressure groove may be formed on the upper end surface 2b1 of the flange portion 2b of the shaft member 2.

As shown in FIG. 3, an annular groove 8c1 and a plurality of radial grooves 8c2 provided on the inner diameter side of the annular groove 8c1 are formed on the upper end surface 8c of the bearing member 8. A plurality of axial grooves 8d1 are provided on the outer peripheral surface 8d of the bearing member 8 at equal intervals in the circumferential direction. The space on the outer diameter side of the flange portion 2b of the shaft member 2 communicates with the seal space S through the axial groove 8d1, the annular groove 8c1, the radial groove 8c2, etc., so that the negative pressure in this space can be reduced. Occurrence is prevented. If there is no particular need, the annular groove 8c1 and the radial groove 8c2 may be omitted, and the upper end surface 8c of the bearing member 8 may be a flat surface.

The bearing member 8 is formed of a sintered body containing 25% by mass or more of copper, and in the present embodiment, it is formed of a sintered body containing 25% by mass or more of copper and iron, respectively. The true density ratio of the bearing member 8 is 85 to 95%. The true density ratio is defined by the following equation. ρ1 is the density of the bearing member, and ρ0 is the density (true density) assuming that the bearing member has no pores.
True density ratio [%] = (ρ1 / ρ0) × 100

Of the outer peripheral surface 8d of the bearing member 8, the surface opening ratio in the cylindrical surface region excluding the axial groove 8d1 is smaller than that of the conventional product in which the outer peripheral surface is not lightly sized (details will be described later). In the present embodiment, the surface opening ratio in the cylindrical surface region of the outer peripheral surface 8d of the bearing member 8 is about the same as the surface opening ratio in the radial bearing surface 8a1 of the bearing member 8, and specifically, 2 to 2. It is 15%.

Almost no coarse air holes are formed in the cylindrical surface region of the outer peripheral surface 8d of the bearing member 8, and the size of the pores opened in the cylindrical surface region of the outer peripheral surface 8d of the bearing member 8 is lightly sized on the outer peripheral surface. It is smaller than the conventional product without bearings. In the present embodiment, the area of each pore opened in the cylindrical surface region of the outer peripheral surface 8d of the bearing member 8 is about the same as the area of each pore on the radial bearing surface 8a1 of the bearing member 8. It is 0.01 mm ² or less.

As shown in FIG. 2, the seal portion 9 projects from the upper end of the housing 7 toward the inner diameter side. In the present embodiment, the seal portion 9 is integrally formed with the housing 7, but the seal portion 9 can be separated from the housing 7. The inner peripheral surface 9a of the seal portion 9 has a tapered shape whose diameter is gradually reduced downward. Between the inner peripheral surface 9a of the seal portion 9 and the outer peripheral surface of the shaft portion 2a, a seal space S having a wedge-shaped cross section is formed in which the radial width is gradually narrowed downward. In addition, while the inner peripheral surface of the seal portion 9 is a cylindrical surface, a tapered surface whose diameter is gradually reduced upward is provided on the outer peripheral surface of the shaft portion 2a, and a seal space S having a wedge-shaped cross section is formed between them. You may. The upper end surface 8c of the bearing member 8 is in contact with the lower end surface 9b of the seal portion 9.

The lid portion 10 is made of a metal such as brass or a resin, and is fixed to the lower end portion of the inner peripheral surface 7a of the housing 7 by an appropriate means such as press fitting or adhesion. As a result, the space inside the housing 7 becomes a closed space open to the atmosphere only in the seal space S. The lid portion 10 can also be formed integrally with the housing 7.

A thrust bearing surface is formed on the end surface 10a of the lid portion 10. For example, a pump-in type spiral-shaped dynamic pressure groove is formed on the thrust bearing surface (not shown). As the shape of the dynamic pressure groove, a herringbone shape, a radial groove shape, or the like may be adopted. Further, the end surface 10a of the lid portion 10 may be used as a flat surface, and a dynamic pressure groove may be formed in the lower end surface 2b2 of the flange portion 2b of the shaft member 2.

Oil is injected into the fluid dynamic pressure bearing device 1 having the above configuration, and an oil level is formed in the seal space S (see FIG. 2). The fluid dynamic pressure bearing device 1 of the present embodiment is a so-called full-fill type in which the space around the inner circumference of the housing 7 (the space on the inner side of the seal space S) is filled with oil including the internal pores of the bearing member 8. Is.

When the shaft member 2 rotates, a radial bearing gap is formed between the radial bearing surface 8a1 on the inner peripheral surface 8a of the bearing member 8 and the outer peripheral surface (cylindrical surface 2a1) of the shaft portion 2a. By increasing the pressure of the oil film in the radial bearing gap, the first radial bearing portion R1 and the second radial bearing portion R2 are configured in which the shaft member 2 non-contactly supports in the radial direction. At the same time, there are thrust bearing gaps between the lower end surface 8b of the bearing member 8 and the upper end surface 2b1 of the flange portion 2b, and between the end surface 10a of the lid portion 10 and the lower end surface 2b2 of the flange portion 2b. Is formed. Then, the pressure of the oil film formed in each thrust bearing gap is increased by the dynamic pressure groove G3 of the lower end surface 8b of the bearing member 8 and the dynamic pressure groove of the end surface 10a of the lid portion 10, thereby causing both thrusts of the shaft member. A first thrust bearing portion T1 and a second thrust bearing portion T2 that are non-contactly supported in the direction are configured.

Hereinafter, a method for manufacturing the bearing member 8 will be described. The bearing member 8 is mainly manufactured through a raw material powder mixing step, a forming step, a sintering step, a light sizing step, a rotary sizing step, and a dynamic pressure groove sizing step in this order. Hereinafter, each step will be described in detail.

In the raw material powder mixing step, the raw material powder for the bearing member 8 is produced by mixing a plurality of types of powder. The raw material powder includes, for example, an iron-based powder, a copper-based powder, and a low melting point metal powder as metal powder. Various molding lubricants (for example, lubricants for improving releasability), solid lubricants (for example, graphite powder) and the like may be added to the raw material powder, if necessary.

As the iron-based powder, iron alloy powder (for example, stainless steel powder) can be used in addition to iron powder (pure iron powder). As the iron powder, reduced iron powder or atomized iron powder can be used. As the copper-based powder, in addition to copper powder (pure copper powder), copper alloy powder can be used. As the copper powder, electrolytic copper powder or atomized copper powder can be used. As the low melting point metal powder, a powder containing tin, zinc, phosphorus and the like can be used, and in this embodiment, tin powder is used.

The raw material powder contains 25% by mass or more of copper as a metal powder, and for example, iron and copper are contained in an amount of 25% by mass or more, respectively. The metal powder in the raw material powder of the present embodiment contains 25 to 70% by mass of copper powder and 1 to 3% by mass of tin powder, and the balance is iron powder (or iron alloy powder) and unavoidable impurities.

In the forming step, the raw material powder is charged into the cavity of the forming die (not shown) and compressed to obtain a cylindrical compact powder similar to the bearing member 8 shown in FIG. In the forming step, an axial groove 8d1 (see FIG. 3) is formed on the outer peripheral surface of the green compact.

In the sintering step, the green compact is sintered at a predetermined sintering temperature to obtain a sintered body. When various molding lubricants such as fluid lubricants are added to the raw material powder, the molding lubricant volatilizes with sintering.

In the light sizing step, at least the outer peripheral surface 28d of the sintered body 28 is compressed by the light sizing mold 20 shown in FIG. In the present embodiment, as shown in FIG. 5 (A), the core rod 21 is inserted into the inner circumference of the sintered body 28 through a very small gap, and as shown in FIG. 5 (B), the core rod 21 is sintered. The body 28 is pushed downward by the upper punch 22 and press-fitted into the inner circumference of the die 24. As a result, the outer peripheral surface 28d of the sintered body 28 is compressed by the die 24, and the inner peripheral surface 28a of the sintered body 28 is pressed against the cylindrical outer peripheral surface of the core rod 21 and pressed.

The compression allowance of the outer peripheral surface 28d of the sintered body 28 in the light sizing step, that is, the difference between the outer diameter D1 of the sintered body 28 and the inner diameter D2 of the die 24 before the light sizing is the baking in the dynamic pressure groove sizing step described later. It is much smaller than the compression allowance of the outer peripheral surface 28d of the body 28, for example, about 1/5. In the present embodiment, the compression allowance of the outer peripheral surface 28d of the sintered body 28 in the light sizing step is 50 μm or less, preferably 30 μm or less, and more preferably 20 μm or less. Further, in the light sizing step, the outer peripheral surface 28d of the sintered body 28 is always compressed with a compression allowance larger than 0 μm, preferably a compression allowance of 5 μm or more, based on the dimensional tolerance of each product of the sintered body 28. , The inner diameter D2 of the die 24 is set. In FIG. 5, the size of the compression allowance of the outer peripheral surface 28d of the sintered body 28 by the light sizing mold 20 is exaggerated.

The gap between the inner peripheral surface 28a of the sintered body 28 and the outer peripheral surface of the core rod 21 is set as small as possible. Specifically, when the outer peripheral surface 28d of the sintered body 28 is compressed by the inner peripheral surface of the die 24, the inner peripheral surface 28a of the sintered body 28 is taken into consideration based on the dimensional tolerance of each product of the sintered body 28. The outer diameter D3 of the core rod 21 is set so that is always pressed against the outer peripheral surface of the core rod 21 and pressed. In addition, the inner circumference of the sintered body 28 is set only when the outer diameter D3 of the core rod 21 is set to the allowable minimum outer diameter of the sintered body 28 and the inner diameter of the sintered body 28 is smaller than the outer diameter D3 of the core rod 21. The surface 28a may be pressed by the outer peripheral surface of the core rod 21.

In the present embodiment, the sintered body 28 is pressed from both sides in the axial direction by the upper punch 22 and the lower punch 23. Specifically, based on the dimensional tolerance of each product of the sintered body 28, the upper punch 22 and the lower punch 23 always press the sintered body 28 from both sides in the axial direction when the light sizing is completed. The axial distance W between the punch 22 and the lower punch 23 is set. Only when the axial spacing W of the upper and lower punches 22 and 23 is set to the allowable minimum axial width of the sintered body 28 and the axial width of the sintered body 28 is larger than the axial width of the upper and lower punches 22 and 23. In addition, the sintered body 28 may be pressed from both sides in the axial direction by the upper and lower punches 22 and 23.

As described above, by pressing the sintered body 28 from all directions of the outer peripheral side, the inner peripheral side, and both sides in the axial direction, the volume (apparent volume) of the sintered body 28 is reduced. This volume reduction is absorbed by the internal pores of the sintered body 28.

As shown in FIG. 6A, iron powder 11 and copper powder 12 are exposed on the surface (outer peripheral surface 28d) of the sintered body 28 before light sizing, and relatively large pores (coarse air pores P) are exposed. Is formed. Then, by lightly sizing the sintered body 28 and compressing the outer peripheral surface 28d with a minute compression allowance, as shown in FIG. 6B, the copper powder 12 exposed on the outer peripheral surface 28d of the sintered body 28 Plasticly flows and enters the crude atmosphere pore P. In this way, the coarse air pores opened in the outer peripheral surface 28d of the sintered body 28 are reduced, so that the surface opening ratio in the outer peripheral surface 28d and the area of each pore opened in the outer peripheral surface 28d are reduced. The chain line in FIGS. 6A and 6B represents the surface (outer peripheral surface 28d) of the sintered body 28 after light sizing.

In the rotary sizing step, a jig (sizing pin) is pressed against the inner peripheral surface of the sintered body with a tightening margin, and in this state, the jig is rotated along the circumferential direction of the inner peripheral surface of the sintered body (not shown). ). As a result, the material of the surface layer on the inner peripheral surface of the sintered body is rolled by a jig, the pores on the inner peripheral surface are crushed, the surface opening rate on the inner peripheral surface, and the pores opened on the inner peripheral surface. Area is reduced.

In the dynamic pressure groove sizing step, the dynamic pressure groove is formed on the inner peripheral surface 28a of the sintered body 28 by the dynamic pressure groove sizing mold 30 shown in FIG. Specifically, as shown in FIG. 7A, the core rod 31 is inserted into the inner circumference of the sintered body 28 through a very small gap, and the axial width of the sintered body 28 is set to the upper and lower punches 32. Restrain at 33. While maintaining this state, as shown in FIG. 7B, the sintered body 28 is press-fitted into the inner circumference of the die 34. As a result, the sintered body 28 is pressed from the outer periphery, and the inner peripheral surface 28a of the sintered body 28 is pressed against the molding die 31a formed on the outer peripheral surface of the core rod 31 and is pressed against the inner peripheral surface 28a of the sintered body 28. The shape of the molding die 31a is transferred to form the dynamic pressure grooves G1 and G2 (see FIG. 3). After that, the sintered body 28, the core rod 31, and the upper and lower punches 32, 33 are raised, and the sintered body 28 and the core rod 31 are taken out from the inner circumference of the die 34. At this time, the inner peripheral surface 28a of the sintered body 28 is expanded in diameter by the spring back, and is peeled off from the molding mold 31a on the outer peripheral surface of the core rod 31. Then, the core rod 31 is pulled out from the inner circumference of the sintered body 28.

In the dynamic pressure groove sizing step, since it is necessary to press the inner peripheral surface 28a of the sintered body 28 against the outer peripheral surface of the core rod 31, the compression allowance of the outer peripheral surface 28d of the sintered body 28 by the dynamic pressure groove sizing mold 30, that is, The difference between the outer diameter D4 of the sintered body 28 and the inner diameter D5 of the die 34 before the dynamic pressure groove sizing is set to a value larger than the compression allowance of the outer peripheral surface 28d of the sintered body 28 in the light sizing mold 20. For example, it is set to 100 to 200 μm. In FIG. 7, the size of the compression allowance of the outer peripheral surface 28d of the sintered body 28 by the dynamic pressure groove sizing mold 30 is exaggerated.

As described above, in the light sizing step, the outer peripheral surface 28d of the sintered body 28 is compressed with a minute compression allowance to reduce the coarse air pores, and then the sintered body 28 has a dynamic pressure groove due to a relatively large compression allowance. By applying the sizing, the coarse air holes opened in the outer peripheral surface 28d of the sintered body 28 are further reduced. As a result, the oil permeability of the sintered body 28 is significantly reduced (for example, 35% or more) as compared with the sintered body that has been subjected to dynamic pressure groove sizing without light sizing, for example, 0.1 g / 10 min or less. It is said that.

When the internal pores of the sintered body 28 formed in this way are impregnated with lubricating oil by a method such as vacuum impregnation, the bearing member 8 shown in FIG. 1 is completed.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the fluid dynamic bearing device 1 having a so-called full-fill structure in which the internal space of the housing 7 is filled with lubricating oil is shown, but the present invention is not limited to this, and the internal space of the housing 7 is filled with lubricating oil. The present invention may be applied to a fluid dynamic bearing device having a partial fill structure provided with unfilled voids (not shown).

Further, in the above embodiment, the case where the shaft member 2 is on the rotating side and the housing 7 and the bearing member 8 are on the fixed side is shown. On the contrary, the shaft member 2 is on the fixed side, the housing 7 and the bearing member. 8 may be the rotation side.

Further, in the above embodiment, the case where the fluid dynamic bearing device 1 is applied to the spindle motor of a disk drive device such as an HDD is shown, but the present invention is not limited to this, for example, a polygon scanner motor of a laser beam printer or an electronic device. The fluid dynamic bearing device according to the present invention can also be applied to the cooling fan motor and the like.

In order to confirm the effect of the present invention, test pieces (Examples 1 to 3) prepared by the production method (with light sizing) of the above-described embodiment using three types of raw material powders made of different materials, and the above-mentioned Among the manufacturing methods of the above embodiment, test pieces (Comparative Examples 1 to 3) in which the light sizing step was omitted were prepared, and the oil permeability of each test piece was evaluated. The compression allowance of the outer peripheral surface of the sintered body in the light sizing was 20 μm, and the compression allowance of the outer peripheral surface of the sintered body in the dynamic pressure groove sizing was 200 μm. The composition, true density ratio, and oil permeability of each test piece are shown in Table 1 and FIG. 8 below.

As shown in Table 1 and FIG. 8, the light sizing example had a significantly (35% or more) reduction in oil permeability as compared with the comparative example having the same composition without the light sizing. From the above, it was confirmed that applying light sizing is extremely effective in reducing the degree of oil flow and, in turn, suppressing dynamic pressure release.

1 Fluid dynamic bearing device 2 Shaft member 7 Housing 8 Bearing member (sintered oil-impregnated bearing)
9 Seal part 10 Lid part 11 Iron powder 12 Copper powder 20 Light sizing mold 21 Core rod 22 Upper punch 23 Lower punch 24 Die 28 Sintered body 30 Dynamic pressure groove Sizing mold G1, G2, G3 Dynamic pressure groove (dynamic pressure generation) Department)
P Coarse atmosphere hole R1, R2 Radial bearing part T1, T2 Thrust bearing part S Seal space

Claims (2)

A step of compressing a raw material powder containing 25% by mass or more of copper to form a green compact, a step of sintering the green compact to obtain a sintered body, and a step of sintering the sintered body on the outer peripheral side and the inner peripheral side. And , by pressing from all directions on both sides in the axial direction, the outer peripheral surface of the sintered body is always compressed with a compression margin of more than 0 μm and 50 μm or less regardless of the variation in dimensions for each product, and the sintering. A method for manufacturing a sintered oil-impregnated bearing, which comprises a step of molding a dynamic pressure generating portion on the inner peripheral surface of the body. The method for manufacturing a sintered oil-impregnated bearing according to claim 1 , wherein the compression allowance is 5 μm or more.

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