JP4454491B2 - Method of manufacturing sleeve for hydrodynamic fluid bearing and sleeve for hydrodynamic fluid bearing - Google Patents

Description

  The present invention relates to a sleeve used for a hydrodynamic bearing and a manufacturing method thereof.

  As a bearing used for a spindle motor of a hard disk device, a hydrodynamic bearing that is superior in rotational accuracy and also quieter than a ball bearing is being used in place of a conventionally used ball bearing. .

  A sleeve using a porous material as a sleeve for rotatably supporting a shaft in a hydrodynamic bearing is disclosed in Patent Document 1 and the like. In FIG. 7, reference numeral 50 denotes a sleeve body formed of a sintered metal having a bearing hole 50a and formed by sintering a metal powder material such as a copper alloy. The sleeve body 50 is integrally inserted and fixed inside a sleeve housing 51 processed with metal or resin, and the sleeve body 50 and the sleeve housing 51 constitute a sleeve. Reference numeral 52 denotes a shaft, which is rotatably fitted to a sleeve body 50 having a bearing hole 50a through a minute gap. The shaft 52 integrally has a large-diameter thrust flange 53 at one end, and the thrust flange 53 is accommodated in a space surrounded by the sleeve body 50, the sleeve housing 51, and the thrust plate 54. The thrust flange 53 is rotatably provided in the sleeve main body 50 through a minute gap in a posture in which both surfaces are sandwiched between the thrust plate 54 and the sleeve main body 50. A sealing washer 65 is disposed above the sleeve body 50 and is fitted in the sleeve housing 51.

  A rotor hub 55 is fixed to the shaft 52, a rotor magnet 56 is fixed to the inner periphery of the large diameter portion of the rotor hub 55, and a motor stator 57 around which a coil 64 is wound so as to face the rotor magnet 56 is attached to the base 58. Yes. Dynamic pressure generating grooves 59A and 59B are provided on the outer peripheral surface of the shaft 52, and dynamic pressure generating grooves are formed on the opposing surface of the thrust flange 53 and the thrust plate 54 and the opposing surface of the thrust flange 53 and the sleeve body 50, respectively. 60A and 60B are provided, and a space between the shaft 52 and the sleeve body 50 facing these dynamic pressure generating grooves 59A, 59B, 60A and 60B and a space in which the thrust flange 53 is disposed are used as a working fluid. Lubricating oil 61 is filled.

  In this hydrodynamic bearing, when the coil 64 is energized, a rotating magnetic field is generated, and the shaft 52, the thrust flange 53, and the rotor magnet 56 begin to rotate integrally with the rotor hub 55. At this time, the dynamic pressure generating grooves 59A, 59B, 60A, 60B generate a pumping pressure in the lubricating oil 61, float and rotate in a non-contact manner. That is, a radial bearing that is rotatably supported with a predetermined gap in the radial direction is formed at the locations of the dynamic pressure generating grooves 59A, 59B, 60A, 60B, and the thrust direction is at the locations of the dynamic pressure generating grooves 60A, 60B. A thrust bearing is formed which is rotatably supported with a predetermined gap therebetween.

Thus, by forming the sleeve body 50 from a sintered metal that is a porous material, there is an advantage that raw material costs can be reduced compared to the case of forming the sleeve body 50 from a simple metal material.
However, the conventional hydrodynamic bearing having the above-described configuration has the following problems.

  The sleeve body 50 formed of sintered metal has a large number of holes therein, and the lubricating oil 61 existing in the holes leaks out of the sleeve body 50 due to a temperature rise inside the bearing. Sometimes. If the outer peripheral surface of the sleeve body 50 is exposed to the outside, the lubricating oil 61 may flow out of the bearing and contaminate the surrounding air.

  Further, since the sleeve body 50 has holes on the surface, the pressure generated in the bearing due to the action of the dynamic pressure generating grooves 59A, 59B, 60A, 60B leaks from the holes on the surface, and the radial bearing As a result, the shaft 52 could not rotate in a non-contact manner and could rub against the sleeve body 50 during rotation.

  Therefore, in this type of hydrodynamic bearing, a sleeve housing 51 that covers the sleeve body 50 from the outer periphery and a sealing washer 65 that covers the sleeve body 50 from above are required, and the lubricating oil 61 is supported by the sleeve housing 51 and the washer 65. It was prevented from flowing out to the outside, and the pressure leaked from the surface holes was minimized. However, since the sleeve housing 51 and the washer 65 are required, the number of parts is increased and the manufacturing cost is increased.

Based on these points, the present applicant has devised a hydrodynamic bearing capable of solving the above-mentioned problems while taking advantage of the use of a sintered metal sleeve as described above.
In this dynamic pressure fluid bearing, as shown in FIG. 8, the entire sleeve 72 fixed to the base 71 is made of sintered metal, and resin, metal, water glass is formed in pores existing on the surface of the sintered metal. The coating layer (sealing agent) 73 having the property of not allowing the lubricating oil 74 to pass through is impregnated and cured to cover.

  Further, dynamic pressure generating grooves 75A and 75B of radial bearings are formed on the inner peripheral surface of the sleeve 72. 8, 76 is a shaft, 77 is a thrust flange fixed to the shaft 76, 78 is a thrust plate fixed to the bottom of the sleeve 72, and 79A and 79B are dynamic pressure generating grooves of the thrust bearing.

  According to this configuration, since the entire sleeve 72 is covered with the covering layer 73, the lubricating oil 74 does not leak through the hole of the sleeve 72. For this reason, the sleeve housing 51 and the washer 65 as shown in FIG. It is possible to reduce the number of parts and the manufacturing cost. It is also possible to prevent the pressure generated in the bearing due to the action of the dynamic pressure generating groove from leaking from the surface holes.

The dynamic pressure generating grooves 75A and 75B of the radial bearing are formed by cutting or plastic working by ball rolling.
JP 2003-239949 A

  However, in the hydrodynamic bearing shown in FIG. 8, when the dynamic pressure generating grooves 75A and 75B of the radial bearing are formed on the inner peripheral surface of the sleeve 72 by plastic working such as ball rolling, the dynamic pressure generating grooves of the radial bearing are formed. If the density of the sintered metal on the inner peripheral surface of the sleeve 72 forming 75A and 75B is insufficient, the dynamic pressure generating grooves 75A and 75B cannot be formed in a good shape, and sufficient dynamic pressure cannot be secured. is there.

  Further, since the fixing portion 72a for fixing the thrust plate 78 in the sleeve 72 from the outer peripheral side is thin-walled, the packing density of the sintered metal material to the fixing portion 72a is likely to be low, and when the packing density is low, There was a possibility that the dimensional accuracy of the fixed portion 72a could not be obtained, and the assembling strength of the thrust plate 78 was insufficient.

  The present invention solves the above-mentioned problems, and can reduce the manufacturing cost, and at the same time, can form a good dynamic pressure generating groove, and can ensure sufficient assembly strength with respect to the thrust plate. It is an object of the present invention to provide a manufacturing method that can satisfactorily manufacture a sleeve for a bearing.

In order to solve the above-mentioned problems, a method for manufacturing a hydrodynamic fluid bearing sleeve according to the present invention provides a powder material in an outer mold for primary molding in which a rod-shaped inner mold for primary molding is inserted. filled, primary-molding a primary molding step of molding the compression molded to 1 preform in the axial direction by the upper die contact and under type, inside the inner shape die for the secondary molding of the rod-shaped The primary molded body is inserted into the inserted outer mold for secondary molding, and the inner peripheral portion of the upper or lower mold pressing surface facing the primary molded body is pressed more than the outer peripheral portion. A secondary molded body for a sleeve whose inner peripheral side portion has a higher compression ratio than the outer peripheral side portion is formed by compression molding in the axial direction using the upper and lower molds for secondary molding protruding in the direction. and having a secondary molding step for.

  According to this method, it is possible to satisfactorily produce a secondary molded body for a sleeve whose inner peripheral side portion has a higher compression ratio than the outer peripheral side portion, and therefore the inner peripheral surface having a high density of sintered metal in the sleeve. In addition, it is possible to satisfactorily form the dynamic pressure generating groove for the radial bearing and to secure a sufficient dynamic pressure.

The present invention also provides a hydrodynamic fluid bearing sleeve for forming a sleeve forming body having a stepped recess in which a thrust flange is accommodated and a thrust plate is fitted and fixed on the axially outer side. a method of manufacturing, the shape which the rod-like inner shape type for primary molding a powder material filled in the outer mold for primary molding, which is inserted therein to correspond to the stepped recess A primary molding step in which a primary molded body is molded by compression molding in the axial direction using an upper mold or a lower mold for primary molding provided with one stepped protrusion, and rod-shaped secondary molding inner shape type inserting the primary molded body in the outer mold for secondary molding is inserted into the use, the second stepped protrusion of corresponds to the shape provided in the stepped recess 2. A secondary molded body is manufactured by compression molding in the axial direction using an upper mold or a lower mold for secondary molding. The first stepped convex portion and the second stepped convex portion have dimensions in the axial direction corresponding to the thrust flange housing space of the first stepped convex portion, The axial dimension of the second stepped convex portion corresponding to the thrust flange storage space is small, and the axial dimension of the first stepped convex portion corresponding to the thrust plate storage space is smaller than the axial dimension. The second stepped protrusion with respect to the axial dimension corresponding to the thrust flange storage space of the first stepped protrusion is small. Of the second stepped convex portion with respect to the axial direction dimension of the first stepped convex portion corresponding to the thrust plate accommodating space, rather than the ratio of the axial direction dimension corresponding to the thrust flange accommodating space of the portion. Corresponding to the thrust plate storage space Wherein the ratio of the axial direction dimension is small.

  According to this method, in the secondary molding step, the portion that becomes the outer periphery of the stepped recess in the sleeve can be compressed at a high compression rate, and more particularly, the portion that fixes the thrust plate from the outer peripheral side can be compressed to a higher degree. This can increase the packing density of the powder material into the thrust flange storage space and the thrust plate mounting location, and can successfully form the mounting recess shape of the thrust plate in the stepped recess. Assembling strength can be sufficiently strong.

In addition, the present invention provides a powder material filled in an outer mold in which a rod-shaped inner mold is inserted, compression-molded in the axial direction by an upper mold and a lower mold, and a stepped recess on the inner peripheral side. a method of manufacturing a sleeve for a hydrodynamic bearing for molding a molded body shape with a, the outer peripheral portion of the stepped recess in the space to be filled with powder material, is filled with fine powder material than elsewhere And compression molding.

  According to this method, since the fine powder material is filled in the outer peripheral portion facing the stepped recess in the space filled with the powder material, that is, the location where the thrust plate in the sleeve is fixed from the outer peripheral side, The packing density of the powder material can be increased, the mounting recess shape of the thrust plate in the stepped recess can be satisfactorily formed, and the assembly strength of the thrust plate can be sufficiently high.

Further, the hydrodynamic bearing sleeve of the present invention is provided at the cylindrical outer peripheral surface, the cylindrical inner peripheral surface into which the shaft is inserted, and the axial end portion, and the inner peripheral portion is more than the outer peripheral portion. also possess a recessed step portion in the axial direction, is composed of a sintered metal material, inner peripheral portion corresponding to the step portion, characterized in that it is a high compression ratio than the outer peripheral portion.

According to this configuration, a secondary molded body for a hydrodynamic fluid bearing sleeve having an inner peripheral portion having a higher compressibility than the outer peripheral portion can be obtained, so that the inner peripheral surface having a high density of sintered metal in the sleeve In addition, it is possible to satisfactorily form the dynamic pressure generating groove for the radial bearing and to secure a sufficient dynamic pressure.

According to the manufacturing method of hydrodynamic sleeve bearing of the present invention, it is possible to produce a molded body as the sleeve by using powder powder materials, while it is possible to reduce the manufacturing cost, in the secondary molding step by the inner peripheral portion near the push surfaces are compressed into the axial direction by using the upper and lower molds for secondary molding projecting in the pressing direction than the outer peripheral portion close to, the inner peripheral side portion outer peripheral side It is possible to manufacture a secondary molded body for a sleeve having a higher compression ratio than the portion, and to satisfactorily form a dynamic pressure generating groove for a radial bearing on the inner peripheral surface where the sintered metal density in the sleeve is high. And sufficient dynamic pressure can be secured, improving reliability.

  Also, the thrust flange storage of the stepped convex portion in the upper mold or the lower mold for the secondary molding with respect to the axial dimension corresponding to the thrust flange storage space of the stepped convex portion in the upper mold or the lower mold for the primary molding. The upper mold for secondary molding with respect to the axial dimension corresponding to the thrust plate housing space of the stepped convex portion in the upper mold or lower mold for primary molding, rather than the ratio of the axial dimension corresponding to the space or Using an upper mold or lower mold for primary molding and an upper mold or lower mold for secondary molding with a small proportion of axial dimension corresponding to the thrust plate storage space of the stepped convex portion in the lower mold, By performing the primary molding step and the secondary molding step, in the secondary molding step, the compression ratio of the portion surrounding the thrust plate storage space from the outer periphery can be increased, and thereby the location where the thrust plate is fixed is increased. Filling with powder material Degree can be increased, and it can be favorably molded mounting recess shape of the thrust plate in the stepped recess, fastening strength of the thrust plate can also obtain a sufficient strength, the reliability is improved.

  Also, filling the powder material at the location where the thrust plate is fixed by filling the outer peripheral part facing the stepped recess in the space filled with the powder material with a finer powder material than other places and compression molding The density can be increased, and the shape of the recessed mounting portion of the thrust plate in the stepped recessed portion can be satisfactorily formed. As a result, sufficient strength can be obtained for assembling the thrust plate, and the reliability is improved.

Further, as a sleeve for a hydrodynamic bearing according to the present invention, a cylindrical outer peripheral surface, a cylindrical inner peripheral surface into which a shaft is inserted, and an axial end portion are provided. have a level difference portion recessed in the axial direction than is composed of a sintered metal material, inner peripheral portion corresponding to the step portion by a higher compression ratio than the outer peripheral portion, baked in the sleeve A dynamic pressure generating groove for a radial bearing can be satisfactorily formed on the inner peripheral surface where the density of the metal is high, and sufficient dynamic pressure can be secured. Further, a portion closer to the inner periphery than the stepped portion on the surface on which the shaft is inserted is used as an application surface of an oil repellent that prevents the working fluid from leaking to the outside, and the surface on the side on which the shaft is inserted The part closer to the outer periphery than the step part can be used as a reference surface at the time of bearing assembly or bearing inspection. Therefore, it is possible to reliably prevent the working fluid from leaking to the outside from the surface coated with the oil repellent agent.

  Hereinafter, a hydrodynamic bearing sleeve and a manufacturing method thereof according to embodiments of the present invention will be described. In this embodiment, a case will be described in which the hydrodynamic bearing and its sleeve are used in a spindle motor of a hard disk device.

  FIG. 1 is a sectional view of a spindle motor, FIG. 2A is a sectional view of a hydrodynamic bearing, and FIG. 2B is a sectional view of a sleeve of the hydrodynamic bearing. For the sake of easy understanding, the following description will be given of the case where the open end of the bearing hole of the sleeve is arranged upward and the closed end is arranged downward as shown in FIGS. Of course, the use of this hydrodynamic bearing is not limited to this arrangement.

  As shown in FIG. 1, a shaft 2 is rotatably inserted into a bearing hole 1a of a sleeve 1, and a radial bearing surface having dynamic pressure generating grooves 3A and 3B made of patterned shallow grooves on the inner peripheral surface of the sleeve 1 is provided. A rotor hub 5 having a rotor magnet 4 on its inner periphery is attached to the upper side of the shaft 2, and a thrust flange 6 is perpendicular to the shaft 2 at the other end (lower side in FIG. 1) of the shaft 2. It is attached integrally. The bearing surface on the lower end side of the thrust flange 6 faces the thrust plate 7, and the thrust plate 7 is fixed to the bottom of the sleeve 1. A dynamic pressure generating groove 8A having a spiral or fishbone pattern is formed on at least one surface of the thrust flange 6 or the thrust plate 7 facing each other, and the upper flat surface portion of the thrust flange 6 and the sleeve 1 face each other. A dynamic pressure generating groove 8B is provided on at least one of the surfaces. The sleeve 1 is fixed to a base 10 together with a motor stator 9 around which a coil 12 is wound. A gap between the shaft 2 and the sleeve 1 and a gap between the thrust flange 6 and the thrust plate 7 are lubricating oil 11 as a working fluid. Is full.

  In particular, as shown in FIGS. 2A and 2B, a stepped portion 1b is formed on the upper surface portion of the sleeve 1 such that a portion closer to the inner periphery is recessed than a portion closer to the outer periphery. An oil repellent 14 for preventing the lubricating oil 11 as a working fluid from leaking to the outside is applied to the inner peripheral portion.

  In addition, a thrust flange 6 is housed in the lower part of the sleeve 1 and a thrust plate 7 is fitted and fixed. Therefore, the sleeve 1 has a step that is recessed in two steps so that the diameter increases toward the bottom. A recess 1c is formed.

  The sleeve 1 is composed of a metal sintered material obtained by molding and sintering a metal powder material. The space (holes) between the metal sintered particles existing on the surface of the sleeve 1 is a sealing agent 13. Further, in this embodiment, the surface of the sleeve 1 is plated to increase the surface hardness, and complete sealing is achieved.

  The operation of the hydrodynamic bearing will be described. When the motor stator 9 is energized, a rotating magnetic field is generated, and the rotor magnet 4 starts rotating together with the rotor hub 5 and the shaft 2. When rotation starts, the dynamic pressure generating grooves 3A, 3B, 8A, 8B generate pumping pressure in the lubricating oil 11, the pressure of the bearing portions (radial bearing portion and thrust bearing portion) increases, and the shaft 2 and thrust flange 6 are sleeves. 1 and the thrust plate 7 are rotated with high accuracy in a non-contact manner with a minute gap. That is, a radial bearing that is rotatably supported with a predetermined gap in the radial direction is formed at the location of the dynamic pressure generating grooves 3A, 3B, and a predetermined gap is provided at the location of the dynamic pressure generating grooves 8A, 8B in the thrust direction. A thrust bearing is formed which is rotatably supported in a state of having. Here, the groove dimensions E and F of the dynamic pressure generating groove 3A are normally asymmetrical herringbone shapes such that E> F, and the groove dimensions G and H of the dynamic pressure generating groove 3B are G = H. In many cases, a symmetrical herringbone shape is used. In some cases, the dynamic pressure generating groove 3A is a symmetric groove and the dynamic pressure generating groove 3B is asymmetric. Thereby, the lubricating oil 11 receives the pumping pressure pushed into the bearing (thrust bearing side) and does not leak to the outside. Although not shown, the rotor hub 5 can fix one or more disks as magnetic recording media, and rotates with these disks (not shown) to record or reproduce electrical signals.

Next, a method for manufacturing the sleeve according to the embodiment of the present invention will be described with reference to FIGS.
First, for example, a metal powder material containing, for example, iron or copper is prepared, and this metal powder material can be moved in the axial direction along with the rod-shaped inner mold 21 for primary molding (in this embodiment) A cylindrical die-shaped outer mold 23 is filled with a lower die 22 that can be moved up and down (filling step S1). At this time, after filling the metal powder material having a normal roughness, the metal powder material finer than this is filled in the portion near the upper outer periphery. In addition, the place where this fine metal powder material is filled is the part which makes the outer periphery of the stepped recessed part 1c of the sleeve 1, and its vicinity part finally. Further, in this embodiment, the sleeve 1 is configured to be molded in an upside down posture, but the present invention is not limited to this.

  Second, using the upper mold 24 and the lower mold 22 for primary molding, the metal powder material filled in the molding space is compression-molded in the axial direction to form the primary molded body 18 (first 1 molding step S2). In this case, as shown in FIG. 4 (a), the lower die 22 that is formed by pressing the portion that finally becomes the upper side of the sleeve 1 has a press surface 22a formed substantially flat. It is done. On the other hand, as shown in FIG. 2 (b), a stepped concave portion 1a must be formed at a location that finally becomes the lower side of the sleeve 1, and the lower surface side is formed so as to substantially correspond to this. On the pressing surface of the upper die 24, a stepped convex portion 24 a is formed that protrudes in two steps substantially corresponding to the stepped concave portion 1 a of the sleeve 1.

  Thirdly, the primary molded body 18 is sintered (sintering step S3), and fourthly, an inner mold 31 and an outer mold 33 arranged at predetermined positions, and an upper mold 34 and a lower mold that can be raised and lowered. In the mold for secondary molding consisting of 32, the sintered body is placed and pressed, so that the inner and outer peripheral surface portions and both end surface portions are simultaneously sized (secondary molding) (second molding step S4). ). Here, as shown in FIG. 4 (b), the lower mold 32 for secondary molding has a shape in which a portion closer to the inner periphery of the pressing surface (press surface) protrudes in the pressing direction than a portion closer to the outer periphery. Yes. For example, the protrusion amount d of the protrusion 32a is preferably 0.2 mm or less. In this embodiment, as shown in FIG. 4B, the inner peripheral surface protrudes into a right cylindrical shape.

  Thereby, in this 2nd shaping | molding process S4, only the protrusion of the protrusion part 32a of the inner peripheral part in the lower mold | type 32 for secondary shaping | molding WHEREIN: An inner peripheral side part is a higher compression rate compared with an outer peripheral side part. Compressed. Therefore, it is possible to satisfactorily manufacture the sleeve secondary molded body 19 whose inner peripheral side portion has a higher compression ratio than the outer peripheral side portion, and to form dynamic pressure generating grooves 3A and 3B for radial bearings, which will be described later. In this step, the dynamic pressure generating grooves 3A and 3B for the radial bearing can be satisfactorily formed on the inner peripheral surface where the density of the sintered metal in the sleeve 1 is high, and sufficient dynamic pressure can be secured.

  Further, a stepped convex portion 34a is formed on the press surface of the upper mold 34 for secondary molding. This stepped convex portion 34a is substantially final as shown in FIG. The size corresponds to the stepped recess 1 a of the sleeve 1. Here, the axial direction dimension of the stepped convex portions 24a, 34a of the upper dies 24, 34 corresponds to the storage space of the thrust flange 6 of the stepped convex portion 24a of the upper mold 24 for primary molding. The axial dimension a corresponding to the storage space of the thrust flange 6 of the stepped protrusion 34a of the upper mold 34 for secondary molding is smaller than the direction dimension A, and the step of the upper mold 24 for primary molding is reduced. The axial dimension b corresponding to the storage space of the thrust plate 7 of the stepped convex portion 34a of the upper mold 34 for secondary molding than the axial dimension B corresponding to the storage space of the thrust plate 7 of the convex part 24a. Is set to be small. Further, the thrust flange 6 of the stepped convex portion 34a in the upper mold 34 for secondary molding with respect to the axial dimension A corresponding to the thrust flange 6 storage space of the stepped convex portion 24a in the upper mold 24 for primary molding. The ratio C1 (= a / A) of the axial dimension a corresponding to the storage space is, for example, about 96% (when the axial dimension a is 1.23 mm), and the upper mold 24 for primary molding. The axial dimension b corresponding to the thrust plate 7 storage space of the stepped convex portion 34a in the upper mold 34 for secondary molding with respect to the axial dimension B corresponding to the thrust plate 7 storage space of the stepped convex portion 24a in FIG. The ratio C2 (= b / B) is, for example, about 93% (when the axial dimension b is 1.6 mm), and is set so that the ratio C2 is smaller than the ratio C1. .

  Thus, the axial dimension A corresponding to the storage space of the thrust flange 6 and the axial dimension B corresponding to the storage space of the thrust plate 7 of the stepped convex portion 24a of the upper mold 24 for primary molding. The axial dimension a corresponding to the storage space of the thrust flange 6 of the stepped convex portion 34a of the upper mold 34 for secondary molding and the thrust of the stepped convex portion 34a of the upper mold 34 for secondary molding. Since the axial dimension b corresponding to the storage space of the plate 7 is set to be small, when the pressing is performed in the secondary molding, the outer peripheral portion of the thrust flange 6 in the sleeve 1 is finally formed. The portion 19a and the portion 19b forming the outer peripheral portion of the thrust plate 7 in the sleeve 1 (that is, the outer peripheral portion of the stepped concave portion 1a of the sleeve 1) can be molded while being compressed. Made high packing density of the metal powder material to the outer peripheral portion of the stepped recess 1a of over Bed 1 (2 preform 19), it is possible to improve the strength of this portion. Further, as described above, since this portion is filled with a fine metal powder material, this can further increase the packing density of the metal powder material and improve the strength of this portion.

  Moreover, the axial center dimension A, a corresponding to the thrust flange 6 storage space between the stepped convex portion 24a of the upper mold 24 for primary molding and the stepped convex portion 34a of the upper mold 34 for secondary molding. Since the ratio C2 (= b / B) of the axial dimensions B and b corresponding to the thrust plate 7 storage space is set to be smaller than the ratio C1 (= a / A), the secondary forming step , The portion 19b of the sleeve 1 (secondary molded body 19) where the thrust plate 7 is fixed from the outer peripheral side can be compressed at a higher compression ratio, and the mounting recess shape of the thrust plate 7 in the stepped recess 1a of the sleeve 1 can be compressed. Can be formed satisfactorily, the packing density of the assembly location of the thrust plate 7 can be further increased, the assembly strength of the thrust plate 7 can be sufficiently increased, and the reliability is improved.

  After that, fifthly, the secondary molded body 19 is put in a sealing agent 13 containing resin, polymer, metal, water glass or the like and impregnated on the surface, and if necessary, the pressure is lowered to the inside. And (6) the sealing agent 13 is hardened by a curing process (sealing agent curing step S6).

  Seventh, the dynamic pressure generating grooves 3A and 3B are processed on the inner peripheral surface of the bearing hole 1a of the sleeve 1 (inner peripheral surface dynamic pressure groove processing step S7). The dynamic pressure generating grooves 3A and 3B are processed by rolling using balls as disclosed in, for example, Japanese Patent Publication No. 3-68768. At this time, as described above, the secondary molded body 19 for the sleeve in which the inner peripheral side portion has a higher compression ratio than the outer peripheral side portion is manufactured, and the sintered metal density in the sleeve 1 is increased to the inner peripheral surface. Since the dynamic pressure generating grooves 3A and 3B for the radial bearing are formed, the dynamic pressure generating grooves 3A and 3B for the radial bearing can be formed satisfactorily, and the rolling accuracy of the dynamic pressure generating grooves 3A and 3B can be increased. Can be improved. This step is necessary when the dynamic pressure generating grooves 3A and 3B are processed on the inner peripheral surface of the bearing hole 1a of the sleeve 1, but instead, the dynamic pressure generating grooves 3A are formed on the outer peripheral surface of the shaft 2. , 3B is processed, this step is unnecessary.

Eighth, after the inner peripheral surface of the bearing hole 1a of the sleeve 1 is inspected (inner diameter inspection step S8), ninthly, it is cleaned (cleaning step S9).
Thereby, the hole on the surface of the sintered sleeve 1 is sealed, and the sleeve 1 having the bearing hole 1a of good quality is obtained.

  Finally, the surface of the sleeve 1 is plated with nickel phosphorus or the like (plating step S10), and the inner peripheral surface of the bearing hole 1a of the sleeve 1 is inspected (inner diameter inspection step S11), thereby completing the sleeve 1. To do. By thus plating the surface of the sleeve 1 with nickel phosphorous or the like, the holes on the surface of the sleeve 1 can be more completely sealed and the hardness of the surface of the sleeve 1 can be increased. For example, when high manganese chrome steel or stainless steel is used as the shaft 2, good sliding and wear resistance with the shaft 2 can be exhibited, and a long-life hydrodynamic bearing can be configured.

  After the sleeve 1 is manufactured in this way, when the lube repellant 14 is applied to a portion closer to the inner periphery than the step portion 1b of the sleeve 1 and used as a hydrodynamic fluid bearing, the lubricating oil 11 as a working fluid is Prevent leakage to the outside.

  Next, as shown in FIG. 5 (a), the sleeve 1 is placed on the platform 40 in such a posture that the stepped portion 1b is downward, and the shaft in which the thrust flange 6 is fixed to the bearing hole 1a of the sleeve. 2 is inserted, and the thrust plate 7 is fitted into the stepped recess 1 a of the sleeve 1. Thereafter, in order to inspect the mounting posture of the thrust plate 7 with respect to the sleeve 1, the position detection sensor 41 (in FIG. 5B) detects the position of the thrust plate 7 every 90 degrees in the circumferential direction. The detection sensor 41 for detecting each position in contact with each part is shown.) Even if it is detected by contacting with a plurality of locations on the thrust plate 7 (without contacting with a laser or the like) (Good) Check.

  Here, as shown in FIGS. 5 (a) and 5 (b), in these assembling steps and inspection steps, the sleeve 1 is mounted using a surface 1d that is flatter than the stepped portion 1b as a reference surface. Since it can be placed on the table 40, the application surface of the oil repellent 14 that is closer to the inner periphery than the stepped portion 1 b does not contact the table 40. Therefore, at this time, it is possible to prevent the problem that the oil repellent 14 comes into contact with the mounting table 40 and the like and the oil repellent 14 can be removed. As a result, the oil repellent function is not deteriorated and lubrication as a working fluid is achieved. It is possible to reliably prevent the oil 11 from leaking from the coated surface of the oil repellent agent 14 to the outside, and the reliability as the hydrodynamic bearing is improved. That is, if the entire surface on the open end side of the sleeve 1 is simply a flat shape, the oil repellent 14 is not removed when the sleeve 1 is placed on the mounting table 40, but this does not occur.

  In the above-described embodiment, the shape of the portion of the sleeve 1 where the stepped portion 1b is provided is described as the case where the inner peripheral surface protrudes into a right cylindrical shape. 6 (a) to 6 (c), the sleeve 1 is formed with a step portion 1b recessed in a tapered or curved shape using a lower mold 32 having a protruding portion 32a protruding in a tapered or curved shape. Even in this case, the same effect can be obtained.

  In the above-described embodiment, the case where the step 1b of the sleeve 1 is upward and the stepped recess 1c is downward is described in the primary molding process or the secondary molding process. The upper mold and the lower mold may be formed so that the upper mold and the lower mold are reversed. In this case, the upper mold has a stepped portion and the lower mold has a stepped convex portion. What has this may be used.

  The manufacturing method and the hydrodynamic bearing sleeve of the present invention can be applied to various hydrodynamic bearings. The hydrodynamic bearing is particularly suitable as a spindle motor for a disk drive device, a reel drive device, a capstan drive device, a drum drive device, etc., but is not limited thereto.

Sectional drawing of the spindle motor provided with the hydrodynamic fluid bearing which concerns on embodiment of this invention (A) is a sectional view of the hydrodynamic bearing, (b) is a cross sectional view of a sleeve for the hydrodynamic bearing. Flow chart showing the manufacturing process of the sleeve for the hydrodynamic bearing (A) is sectional drawing which shows the state at the time of the primary shaping | molding of the sleeve for same dynamic pressure fluid bearings, (b) is sectional drawing which shows the state at the time of the secondary shaping | molding of the sleeve (A) is a figure which shows the state at the time of assembling | attaching a shaft etc. to the sleeve for same dynamic pressure fluid bearings, (b) is a figure which shows the state at the time of the inspection after an assembly | attachment. (A) is sectional drawing which shows the state at the time of the secondary shaping | molding of the sleeve which concerns on other embodiment of this invention, (b), (c) is a figure which respectively shows another lower mold | type. Cross section of a conventional hydrodynamic bearing Cross section of other conventional hydrodynamic bearings

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sleeve 1a Bearing hole 1b Step part 1c Stepped recessed part 2 Shaft 3A, 3B Dynamic pressure generating groove 6 Thrust flange 7 Thrust plate 8A, 8B Dynamic pressure generating groove 11 Lubricating oil (working fluid)
13 Sealing agent 14 Oil repellent 18 Primary molded body 19 Secondary molded body 21 Inner mold (for primary molding)
22 Lower mold (for primary molding)
22a Press surface 23 Outline die (for primary molding)
24 Upper mold (for primary molding)
24a Stepped convex portion 31 Inner shape mold (for secondary molding)
32 Lower mold (for secondary molding)
32a Protrusion 33 External type (for secondary molding)
34 Upper mold (for secondary molding)
34a Convex with step 40 Platform

Claims (15)

A powder material is filled in an outer mold for primary molding in which a rod-shaped inner mold for primary molding is inserted, and compression molding is performed in the axial direction by an upper mold and a lower mold for primary molding. A primary molding step of molding the primary molded body,
The primary molded body is inserted into an outer mold for secondary molding in which a rod-shaped inner mold for secondary molding is inserted, and the upper mold or the lower mold facing the primary molded body is pressed. The inner peripheral part of the surface is compression-molded in the axial direction using the upper mold and the lower mold for secondary molding protruding in the pressing direction from the outer peripheral part, and the inner peripheral part is more than the outer peripheral part. A method for producing a hydrodynamic fluid bearing sleeve, comprising: a secondary molding step of producing a secondary molded body for a sleeve having a high compression ratio. Wherein one of the upper mold or the lower mold for primary molding is its pressing surface is flat, et al, hydrodynamic bearing of claim 1, one end surface is formed flat Rana said primary molded member For manufacturing a sleeve.   The portion near the inner periphery of the pressing surface of the upper mold or the lower mold for secondary molding that protrudes in the pressing direction from the portion near the outer periphery of the upper mold or the lower mold is a flat surface of the primary molded body. The manufacturing method of the sleeve for hydrodynamic fluid bearings of Claim 2 which opposes and opposes. A method of manufacturing a hydrodynamic fluid bearing sleeve, wherein a thrust flange is accommodated and a forming body for a sleeve having a stepped concave portion is formed to which a thrust plate is fitted and fixed on the outer side in the axial direction. ,
The powder material is filled in the outer shape die for primary molding, which is inserted into a rod-like inner shape type for primary molding, a first stepped convex portion having a shape that corresponds to the stepped recess A primary molding step in which a primary molded body is molded by compression molding in the axial direction using an upper mold or a lower mold for primary molding provided;
Rod of the primary molded body is inserted into the outer mold for secondary molding to the inner shape type is inserted into for secondary molding, the second with the stage of shape that corresponds to the stepped recess A secondary molding step of producing a secondary molded body by compression molding in the axial direction using an upper mold or a lower mold for secondary molding provided with convex portions,
The first stepped protrusion and the second stepped protrusion are:
The axial dimension corresponding to the thrust flange accommodating space of the second stepped convex portion is smaller than the axial dimension corresponding to the thrust flange accommodating space of the first stepped convex portion,
The axial dimension corresponding to the thrust plate storage space of the second stepped convex portion is smaller than the axial dimension corresponding to the thrust plate storage space of the first stepped convex portion,
The ratio of the axial dimension of the second stepped protrusion corresponding to the thrust flange storage space to the axial dimension of the first stepped protrusion corresponding to the thrust flange storage space is greater than the ratio of the axial dimension of the second stepped protrusion corresponding to the thrust flange storage space. For hydrodynamic bearings, the ratio of the axial dimension of the second stepped convex portion corresponding to the thrust plate storage space to the axial dimension of the first stepped convex portion corresponding to the thrust plate storage space is small. A method for manufacturing a sleeve. A molded body having a shape having a stepped recess on the inner peripheral side, filled with a powder material in an outer mold in which a rod-shaped inner mold is inserted, and compression molded in the axial direction by an upper mold and a lower mold A method for manufacturing a hydrodynamic bearing sleeve for molding
A method for manufacturing a hydrodynamic bearing sleeve, wherein a powder material finer than other places is filled in an outer peripheral portion of the stepped recess in a space filled with the powder material and compressed.   The method for producing a sleeve for a hydrodynamic bearing according to any one of claims 1 to 5, further comprising a sealing treatment step of sealing pores existing on the surface of the secondary compact.   The method for manufacturing a sleeve for a hydrodynamic fluid bearing according to claim 6, wherein, in the sealing treatment step, the hole is impregnated with a sealing agent that does not allow the working fluid of the hydrodynamic fluid bearing to pass through and hardened.   A spindle motor equipped with a hydrodynamic bearing sleeve manufactured by the manufacturing method according to claim 1. A cylindrical outer peripheral surface;
A cylindrical inner peripheral surface into which the shaft is inserted;
Provided at the end in the axial direction, the inner peripheral portion has a stepped portion recessed in the axial direction than the outer peripheral portion,
A sleeve for a hydrodynamic bearing, which is made of a sintered metal material, and has an inner peripheral side portion corresponding to the stepped portion having a higher compressibility than the outer peripheral side portion. The sleeve for a hydrodynamic bearing according to claim 9, further comprising a stepped recess on one end side of which a thrust plate is inserted and fixed facing the shaft.   The hydrodynamic fluid bearing sleeve according to claim 9 or 10, wherein the shaft projects in an axial direction from the stepped portion.   The sleeve for a hydrodynamic bearing according to any one of claims 9 to 11, wherein a hole existing on a surface of the sleeve for the hydrodynamic bearing is sealed. The sleeve for a hydrodynamic bearing according to claim 12 , wherein the hole is impregnated with a sealing agent that does not allow the working fluid of the hydrodynamic bearing to pass through and cured.   A spindle motor on which the hydrodynamic bearing sleeve according to claim 9 is mounted.   A hard disk device on which the spindle motor according to claim 8 is mounted.

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