JP5132887B2 - Shaft member for hydrodynamic bearing device - Google Patents

Description

  The present invention relates to a shaft member for a hydrodynamic bearing device.

  The dynamic pressure bearing device supports a shaft member in a non-contact manner so as to be relatively rotatable by a dynamic pressure action of a fluid generated in a bearing gap. Recently, a hydrodynamic bearing device, for example, a magnetic disk device such as an HDD, a CD-ROM, a CD-R / RW, a DVD-ROM / RAM, taking advantage of its excellent rotational accuracy, high-speed rotation, quietness, etc. In addition to a spindle motor bearing device mounted on an information device such as an optical disk device such as a magneto-optical disk device such as MD or MO, a polygon scanner motor of a laser beam printer (LBP), a color wheel motor of a projector, or It is used as a bearing device for small motors such as fan motors.

  For example, in a hydrodynamic bearing device incorporated in a spindle motor for HDD, it is known that both a radial bearing portion that supports a shaft member in a radial direction or a thrust bearing portion that supports a shaft direction in a thrust direction are configured by hydrodynamic bearings. Yes. In this case, a dynamic pressure groove as a dynamic pressure generating portion is formed on either the inner peripheral surface of the bearing sleeve or the outer peripheral surface of the shaft member facing the bearing sleeve, and the radial bearing is disposed in the radial bearing gap between both surfaces. The part is often formed. In addition, a dynamic pressure groove is formed on one end surface of the flange portion provided on the shaft member and an end surface of the bearing sleeve facing the flange portion, and a thrust bearing portion is formed in the thrust bearing gap between both surfaces. (See, for example, Patent Document 1).

  The dynamic pressure grooves are formed, for example, in a state of being arranged in a herringbone shape, a spiral shape, or the like on the outer peripheral surface of the shaft member. As a method for forming this type of dynamic pressure groove, for example, cutting (see, for example, Patent Document 2), etching (see, for example, Patent Document 3), and the like are known.

Further, as a method for forming a dynamic pressure groove capable of reducing material costs and processing costs as compared with the above-described cutting and etching, for example, rolling processing is known. In this case, the surface hardness of the material is often improved by performing a predetermined heat treatment after the rolling process (see, for example, Patent Document 4).
JP 2003-239951 A Japanese Patent Laid-Open No. 08-196056 Japanese Patent Laid-Open No. 06-158357 Japanese Patent Laid-Open No. 07-114766

  However, since the heat treatment is usually performed at a high temperature, deformation of the shaft itself is unavoidable, and there is a possibility that the outer peripheral surface accuracy may be distorted. In particular, when a micro-sized and high-precision groove such as a dynamic pressure groove is formed, there is a high possibility that deformation during heat treatment of the shaft will adversely affect the shape accuracy of the dynamic pressure groove. As a result, for example, the depth and shape of the dynamic pressure grooves vary, and there is a possibility that sufficient dynamic pressure action cannot be exhibited. The means disclosed in the above document is merely for the purpose of increasing the surface hardness of the shaft member, and does not take into consideration a decrease in outer peripheral surface accuracy due to deformation during heat treatment.

  An object of the present invention is to provide a shaft member for a hydrodynamic bearing device that has excellent wear resistance and can exhibit a high dynamic pressure action.

In order to solve the above-mentioned problems, the present invention provides a shaft member for a hydrodynamic bearing device in which a concave portion for producing a fluid dynamic pressure action in a bearing gap is formed by rolling, and a surface layer portion of the concave portion formed by rolling. And a nitride layer formed by diffusing and penetrating nitrogen in the shaft member material by nitriding after the rolling is formed in the surface layer portion in the peripheral region of the recess, and the ratio of the thickness of the nitride layer to the outer diameter of the shaft member is 0 .05 set below Rutotomoni, the uppermost layer of the nitride layer in the peripheral region of the recess, the work hardening layer is a layer produced work hardening by barreling after the nitriding treatment is formed by overlapping the nitride layer A shaft member for a hydrodynamic bearing device is provided. Further, the concave portion here means a portion for generating a fluid dynamic pressure action in the bearing gap, for example, an axial groove shape, a circumferential groove shape, an inclined groove shape, a cross groove shape, an axial direction or a circumferential direction. Includes intermittent groove shapes in the direction, depressions (dimples), and the like.

  The nitriding treatment is intended to diffuse and penetrate nitrogen into the material, so the heat treatment temperature at that time is set lower (for example, about 500 to 600 ° C.) than the temperature at the other heat treatment such as quenching and carburizing. can do. Therefore, deformation during heat treatment, specifically deformation due to heating and cooling exceeding the transformation point of the material metal, volume change accompanying changes in the metal structure, etc. is minimized, and the shape accuracy of the recess or surrounding area is minimized. Can be kept high.

  Further, the depth and hardness of the hardened layer formed by the heat treatment tend to be determined depending on the processing temperature and the processing time regardless of the size of the material. Therefore, if the required surface hardness is maintained while reducing the size of the material, the ratio of the cured layer to the uncured layer inevitably increases. In this case, the material (shaft member) itself becomes fragile to deformation, which may lead to a decrease in durability. On the other hand, in the present invention, a nitride layer by nitriding is formed on the surface layer portion. With nitriding treatment, a very thin hardened layer (nitriding layer) can be formed compared to other heat treatments, so that only the hardness of the surface layer portion is ensured while ensuring the toughness of the shaft member (durability against deformation). Can be improved.

  Further, in this type of nitriding treatment, the nitrided layer depth tends to decrease as the heat treatment temperature decreases, and the hardness tends to increase. Therefore, the nitriding treatment according to the present invention can be said to be a very suitable means when only the surface layer portion of the shaft member as a small component is cured as described above.

  Moreover, in addition to the said nitriding process, barrel processing can also be given after rolling of a recessed part. In this case, at least a part of the surface of the surface layer portion formed of the nitride layer has a processed surface by barrel processing.

  In this way, by performing nitriding treatment and barrel processing after rolling of the recesses, it is possible to avoid deformation caused by heat treatment, and to minimize the deterioration of the shape accuracy of the recesses and the surrounding area, and to perform rolling. A raised portion (a raised portion) formed around the concave portion by processing can be reduced or removed by barrel processing. Accordingly, it is possible to further improve the shape accuracy of the surface of the surrounding region that becomes the concave portion or the bearing surface, and further improve the bearing performance.

  In the case where the surface layer portion of the surrounding region is composed of a nitrided layer obtained by nitriding after rolling, the hardness of the lower layer region of the surface layer portion is preferably 400 Hv or less. With this degree of hardness, it is possible to improve the rolling processability of the recesses, and since the deformation resistance during rolling is small, the service life of the rolling die (die) can be extended.

  The shaft member for a fluid dynamic bearing device having the above-described configuration can be suitably provided as, for example, a fluid dynamic bearing device including the shaft member.

  As described above, according to the present invention, it is possible to provide a shaft member for a hydrodynamic bearing device that has excellent wear resistance and can exhibit a high dynamic pressure action.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a sectional view of a fluid dynamic bearing device 1 according to an embodiment of the present invention. In the figure, a hydrodynamic bearing device 1 includes a shaft member 2 and a bearing member 3 capable of inserting the shaft member 2 into the inner periphery.

  In this embodiment, the bearing member 3 is a bottomed cylindrical body composed of an electroformed part 4 and a molded part 5, and is integrally injection-molded with resin using the electroformed part 4 that is integral with the master or a separate part as an insert part. . The inner peripheral surface 4a of the electroformed portion 4 facing the outer peripheral surface 2a of the shaft member 2 has a perfect circle shape.

  The shaft member 2 has a shaft shape with a constant diameter, and is manufactured from a metal material having relatively high workability (for example, about 200 Hv to 400 Hv in terms of hardness) such as various types of carbon steel, chromium steel, stainless steel, and copper alloy. Is done.

  On the entire or partial region of the outer peripheral surface 2 a of the shaft member 2, a plurality of lubricating oil dynamic pressure effects are generated in the radial bearing gap 6 between the outer peripheral surface 2 a and the inner peripheral surface 4 a of the electroformed part 4. A recess 7 is formed. In this embodiment, the concave portion 7 is composed of an inclined groove 9a and an inclined groove 9b that are continuous or close to each other on one end side in the circumferential direction and are inclined in directions away from each other on the other end side in the circumferential direction. The plurality of recesses 7 having such a shape are arranged at predetermined intervals in the circumferential direction so as to form a so-called herringbone shape. In this case, each concave portion 7 (inclined grooves 9a, 9b) and their surrounding region 8 constitute a dynamic pressure generating portion 10 that generates a dynamic pressure action of the lubricating oil in the radial bearing gap 6. Further, in this embodiment, the dynamic pressure generating section 10 having the above-described configuration is provided at two locations separated vertically in the axial direction.

  One end surface 2b of the shaft member 2 has a substantially spherical shape, and abuts against the upper end surface 4b1 of the bottom 4b of the opposing electroformed portion 4 when the shaft member 2 is inserted into the inner periphery of the bearing member 3.

  Lubricating oil is injected from the air release side of the radial bearing gap 6 between the bearing member 3 and the shaft member 2. Thereby, the hydrodynamic bearing device 1 in which the bearing internal space including the radial bearing gap 6 is filled with the lubricating oil is completed.

  In the hydrodynamic bearing device 1 having the above-described configuration, when the shaft member 2 is relatively rotated, the dynamic pressure generating portions 10 and 10 provided on the outer peripheral surface 2a of the shaft member 2 and the inner peripheral surface of the electroformed portion 4 facing them. The dynamic pressure action of the lubricating oil is generated in the radial bearing gap 6 between 4a and 4a. Thereby, the first radial bearing portion R1 and the second radial bearing portion R2 that support the shaft member 2 so as to be relatively rotatable in the radial direction are formed.

  Further, at the time of relative rotation of the shaft member 2, one end surface 2b of the shaft member 2 is contact-supported (pivot supported) to the upper end surface 4b1 of the bottom portion 4b. Thereby, the thrust bearing portion T1 that supports the shaft member 2 so as to be relatively rotatable in the thrust direction is formed.

  Hereinafter, an example of the manufacturing process of the shaft member 2 will be described with reference to FIGS.

  In this embodiment, the shaft member 2 includes a rolling process (a) in which the recess 7 is formed by rolling, and a nitriding process in which at least the peripheral region 8 of the recess 7 formed in the rolling process (a) is nitrided. It is formed through the step (b) and the barrel processing step (c) in which the peripheral region 8 is subjected to barrel processing.

(A) Rolling Step FIG. 2 conceptually shows a step of forming the concave portion 7 having the shape shown in FIG. 1 on the outer peripheral surface 11a of the shaft material 11 made of the above material by rolling. Of the pair of rolling dies 12, 13 (in this example, a flat die), a convex portion having a shape corresponding to the concave portion 7 to be transferred and formed on the shaft material 11 is formed on the opposing surface 12a of the first rolling die 12. A mold (not shown) is provided. As shown to Fig.3 (a), in the state before rolling, the outer peripheral surface 11a of the shaft raw material 11 is smooth.

  The shaft material 11 is slid relative to the first rolling die 12 from the state in which the shaft material 11 is held between the rolling dies 12 and 13, so that the shaft material 11 is moved to the first rolling die 12. Press and roll on the convex forming area of the die 12. Thereby, from the 1st rolling die 12 side, the recessed part 7 (dynamic pressure generation part 10) of the shape shown, for example in FIG.

  At this time, as shown in FIG. 3B, a first work-hardened layer 14 a is formed by rolling on the surface layer portion 14 of the recess 7 formed on the outer peripheral surface 11 a of the shaft material 11. In this embodiment, at the same time, a first work-hardened layer 15 a is formed by rolling in a partial region of the surface layer portion 15 in the peripheral region 8 of the recess 7.

  Moreover, the meat which was originally in the recessed part 7 is extruded to circumference | surroundings with rolling. As a result, as shown in FIG. 3 (b), a bulge (bump 16) occurs at a location near the recess 7 in the surrounding region 8.

(B) Nitriding process step After forming the recess 7 on the shaft material 11 by rolling, the shaft material 11 is subjected to nitriding treatment. In this way, nitrogen is diffused and permeated into the surface layer portion 14 of the recess 7 and the surface layer portion 15 of the surrounding region 8, thereby forming a nitride of the material metal and nitrogen in each surface layer portion 14, 15. Is done. Thereby, for example, as shown in FIG. 3C, a nitride layer 14b is formed in the surface layer portion 14 of the recess 7 including the first work hardened layer 14a. Further, a nitride layer 15b is formed on the surface layer portion 15 of the peripheral region 8 including the first work hardened layer 15a. As specific means for the nitriding treatment (including soft nitriding treatment), for example, gas nitriding or plasma nitriding can be used, and as specific means for soft nitriding treatment, for example, gas soft nitriding or salt bath soft nitriding can be used. It is.

  In this case, the thickness of the nitride layer 15b constituting the surface layer portion 15 is very thin, from several μm to several tens of μm. Moreover, the hardness (here surface hardness) is 600Hv-1000Hv. The same applies to the nitride layer 14b.

  In addition, the “nitride layer thickness” here is a relatively easy distinction between the compound layer in which nitrides are mainly present and the diffusion layer in which nitrogen diffuses and penetrates into the base metal. Means the depth (thickness) of the compound layer.

  Since the nitriding treatment is usually performed at a temperature of 500 ° C. to 600 ° C., for example, deformation of the shaft material 11 (shaft member 2) during the heat treatment is much smaller than heat treatment such as quenching or carburizing. Therefore, deformation during heat treatment and the shape variation of the recesses 7 (inclined grooves 9a and 9b) caused by finish grinding are minimized, and the recesses 7 (dynamic pressure generating unit 10) having high dimensional accuracy are made shaft members. 2 can be provided. Therefore, when the shaft member 2 is used by being incorporated in the dynamic pressure bearing device 1 shown in FIG. 1, the dynamic pressure action of the lubricating oil generated in the radial bearing gap 6 can be enhanced. Moreover, since the finish grinding of the outer peripheral surface 11a etc. becomes unnecessary, this process can be skipped and cost reduction can be achieved.

  Further, when the shaft member 2 is rotated, particularly when starting and stopping, the surface 8a of the peripheral region 8 of the recess 7 may be in sliding contact with the inner peripheral surface 4a of the opposing electroformed part 4 as described above. By configuring the surface layer portion 15 of the surrounding region 8 with the nitride layer 15b, the hardness of the surface layer portion 15 including the bearing surface (surface 8a) can be increased. Thereby, the sliding wear of the shaft member 2 can be reduced, in other words, the wear of the concave portion 7 can be suppressed, and a high dynamic pressure action can be stably exhibited over a long period of time.

  Further, the present invention is characterized in that the concave portion 7 for generating dynamic pressure is provided on the shaft member 2 side, so that the size of the dynamic pressure bearing device 1 is reduced with the recent miniaturization of information equipment. It is possible to meet this requirement without reducing the workability of the recess 7. As for the shaft member 2 having a shaft diameter of about several millimeters at present, the diameter of the hydrodynamic bearing device 1 can be further reduced. However, as described above, a very thin nitride layer 15b is formed. If possible, the toughness (fatigue resistance) of the shaft member 2 itself can be kept high by minimizing the ratio of the hardened layer (here, the nitrided layer 15b) to the uncured layer of the entire shaft member 2. Specifically, by setting the ratio t / d of the thickness t of the nitride layer 15b to the shaft diameter d of the shaft member 2 to 0.05 or less, the hardness of the surface 8a of the surrounding region 8 serving as the bearing surface is increased. The toughness of the shaft member 2 can be kept high.

  Moreover, in this embodiment, since the shaft raw material 11 (shaft member 2) is formed with the metal material of hardness 400Hv or less, the workability of the recessed part 7 can be improved at the time of rolling. Moreover, since the deformation resistance at the time of rolling is small, the wear accompanying continuous use of the rolling dies 12 and 13 can be minimized, and the service life of the dies 12 and 13 can be extended.

(C) Barrel processing step In this embodiment, after the shaft material 11 is subjected to nitriding treatment, the shaft material 11 is subjected to barrel processing (for example, a centrifugal barrel, a fluid barrel, or a barrel processing combining these). . As a result, the raised portions 16 formed in the surrounding area 8 are removed while being crushed, and the surface 8a of the surrounding area 8 is smoothed, for example, as shown in FIG. At this time, a processed surface (polished surface) by barrel processing is formed in at least a part of the surface 8a of the surrounding region 8 (for example, a region where the raised portion 16 is formed).

  At this time, a medium having a certain size with respect to the size of the shaft member 2 is used from the viewpoint of the effectiveness of barrel processing. Therefore, there is no medium collision on the surface 7a (the bottom surface 7a1 and the inner surface 7a2) of the recess 7, and the medium collides with the surface 8a of the surrounding area 8. As a result, work hardening due to collision with the media occurs in the surface layer portion 15 of the peripheral region 8, and a second work hardened layer 15c by barrel processing is formed in this region (see FIG. 4). In this embodiment, the surface layer portion 15 in the peripheral region 8 is composed of a nitride layer 15b formed by nitriding treatment and a second work hardened layer 15c formed by barrel processing. The second work hardened layer 15c is formed so as to overlap with the outermost layer portion of the nitride layer 15b formed earlier.

  As described above, after nitriding the shaft material 11 (shaft member 2) formed by rolling the recesses 7, the shaft material 11 is subjected to barrel processing, so that the surface layer portion 15 of the surrounding region 8 has the nitride layer 15b and the first layer. Thus, the shaft member 2 having the two work-hardened layers 15c is obtained. Thereby, not only the hardness of the surface 8a of the surrounding area 8 which becomes a bearing surface can be improved, but also the smoothness (flatness) of the surface 8a and the shape accuracy of the recess 7 can be improved. In particular, as in this embodiment, by performing barrel processing after nitriding, the raised portion 16 is removed while minimizing collision marks and deformation on the shaft material 11 and finishing accuracy of the bearing surface (surface 8a). Can be further enhanced.

  Further, as in this embodiment, if the shaft material 11 (the shaft member 2 whose hardness of the lower layer regions of the surface layer portions 14 and 15 is 400 Hv or less) made of a material having a hardness of 400 Hv or less is used, when the recess 7 is rolled. The size of the raised portion 16 formed in the surrounding region 8 is small, and it is easy to form a shape that can be easily removed by barrel processing. Therefore, the finishing accuracy of the bearing surface (surface 8a) can be increased also by this.

  In addition, when the groove-like recess 7 (inclined grooves 9a, 9b) is formed by rolling as in this embodiment, burrs may be generated at the peripheral edge 17 of the recess 7, but a medium having an appropriate size. By performing barrel processing using this, such burrs can be removed, or the peripheral edge 17 of the recess 7 can be appropriately chamfered. Thereby, at the time of relative rotation of the shaft member 2, it is possible to avoid wear of the inner peripheral surface 4a of the electroformed portion 4 serving as a sliding mating surface as much as possible, or avoid damage such as galling, and improve the durability of the bearing. it can.

  As media used for the barrel processing, media made of various materials such as metals, ceramics, and resins can be used. From the viewpoint of forming the second work hardened layer 15c by barrel processing, it is relatively hard. It is recommended to use high-quality metal or ceramic soft media. Further, from the viewpoint of keeping the shape of the concave portion 7 with high accuracy, a medium having a size that does not contact the bottom surface 7a1 of the concave portion 7 is preferable. In addition to spherical media, media having various shapes such as a polygonal shape or a rod shape can be used.

  Moreover, in this embodiment, the inner peripheral surface of the bearing member 3 that forms the radial bearing gap 6 between the shaft member 2 and the recess 7 (the inclined grooves 9a and 9b) formed by rolling is formed on the electroformed portion 4. Since the inner peripheral surface 4a is formed, the inner peripheral surface 4a can be formed with high accuracy, whereby the radial bearing gap 6 can be set to be narrower. Rather, depending on the required bearing performance, if the width of the radial bearing gap 6 is small and can be managed with high accuracy, it is necessary to arrange a plurality of recesses 7 in a complicated shape (herringbone shape, etc.). There is no. For example, even in a dynamic pressure generating portion constituted by a recess 7 having a simple shape (a shape that can be more easily processed) such as an axial groove 22 to be described later and a dimple 32, a high dynamic pressure action is applied to the radial bearing gap. It becomes possible to bring

  As mentioned above, although one embodiment of the present invention was described, the present invention is not limited to this embodiment and can adopt other configurations. Hereinafter, the other structure of this invention is demonstrated based on FIGS.

  In the above embodiment, the concave portion 7 is constituted by the inclined groove 9a and the inclined groove 9b, and the case where the concave portions 7 having such a shape are arranged in a herringbone shape is exemplified. For example, as shown in FIG. The axial groove 22 as the recess 7 can also be formed on the outer peripheral surface 21 a of the shaft member 21. In this case, the plurality of axial grooves 22 are formed at predetermined intervals in the circumferential direction as shown in FIG. These axial grooves 22 and the surrounding area 23 constitute a dynamic pressure generating portion 24. Therefore, although not shown, the shaft member 21 is inserted into the inner periphery of the bearing member 3 shown in FIG. 1 and the shaft member 21 is rotated relative to the bearing member 3 so that it is filled with lubricating oil. The dynamic pressure of the lubricating oil is generated by the dynamic pressure generating portion 24 in the radial bearing gap, thereby forming a radial bearing portion that supports the shaft member 21 in a non-contact manner in the radial direction with respect to the bearing member 3.

  The shaft member 21 having the axial groove 22 is formed through (a) rolling process, (b) nitriding process, and (c) barrel processing process, as in the above embodiment. As a result, for example, as shown in FIG. 6A, a nitride layer 25b is formed on the surface layer portion 25 of the axial groove 22 by nitriding. Further, a nitride layer 26b is formed by nitriding treatment on the surface layer portion 26 of the peripheral region 23 of the axial groove 22, and a second work hardened layer by barrel processing is formed on the outermost layer portion of the surface layer portion 26 including the surface 23a. 26c is formed. A processed surface by barrel processing is formed on the surface 23a.

  Also in this embodiment, bearing layers are provided by providing nitrided layers 25b and 26b by nitriding treatment on the surface layer portion 25 of the axial groove 22 formed by rolling and the surface layer portion 26 of the peripheral region 23 of the axial groove 22, respectively. It is possible to improve the hardness of the surface 23a of the surrounding region 23 to be a surface. Further, by performing barrel treatment in addition to nitriding treatment, the surface accuracy of the surface 23a of the surrounding region 23 can be improved. Accordingly, it is possible to obtain the shaft member 21 for a hydrodynamic bearing device having both high bearing performance and wear resistance.

  As the axial groove 22 that can be formed, as shown in FIG. 6A, in addition to the curved surface 22a having a cross-sectional arc shape that protrudes toward the center in the axial direction, for example, as shown in FIG. 6B. In addition, an axial groove 22 configured by a plane 22b whose cross-sectional shape is a chord with respect to the arc of the outer peripheral surface 21a is conceivable. Alternatively, as shown in FIG. 6C, an axial groove 22 having a configuration in which rising portions 22c are provided at both ends in the circumferential direction of the flat surface 22b so that a step is formed between the flat surface 22b and the outer peripheral surface 21a. Alternatively, as shown in FIG. 6 (d), there is an axial groove 22 composed of a curved surface 22d having a constant groove depth in the axial direction and the circumferential direction and a convex shape toward the outer diameter side. It can be formed.

  The number of the axial grooves 22 formed on the outer periphery of the shaft member 21 is preferably 3 or more in consideration of the dynamic pressure action of the lubricating oil. For the same reason, the circumferential angle α indicating the circumferential width of the axial groove 22 is preferably 10 ° to 60 °, and the groove depth h1 of the axial groove 22 is preferably 2 μm to 20 μm. Further, when viewed from both sides of low torque and high rigidity, the ratio of the total area of the axial groove 22 to the total area of the surface 23a of the peripheral region 23 (if the axial length of the axial groove 22 is uniform) The area ratio is {α / (360 ° −α)}.) Is preferably 15% to 70%.

  FIG. 5 illustrates a configuration in which a plurality of axial grooves 22 extending in the axial direction over the entire region where the radial bearing portion is to be formed (dynamic pressure generating portion 24) are arranged in parallel in the circumferential direction. In addition to this, for example, as shown in FIG. 7, a configuration in which the axial grooves 22 are intermittently provided in the axial direction can be adopted. The other configuration is the same as that in the case where the axial groove 22 extending over the entire axial length of the dynamic pressure generating portion 24 is provided, and the description thereof is omitted.

  In the above-described embodiment, the inclined grooves 9a and 9b and the axial groove 22 are exemplified as the concave portion 7, but it is of course possible to form the concave portion 7 having a shape other than the groove. FIG. 8A shows an example thereof, and a plurality of dimples 32 as the recesses 7 are dispersed and arranged in a partial region of the outer peripheral surface 31 a of the shaft member 31. In this case, the dynamic pressure generating portion 34 is configured by the plurality of dimples 32 and their surrounding regions 33. Therefore, although not shown, the shaft member 31 is inserted into the inner periphery of the bearing member 3 shown in FIG. 1 and the shaft member 31 is rotated relative to the bearing member 3 to be filled with lubricating oil. Thus, a dynamic pressure action of the lubricating oil by the dynamic pressure generating portion 34 occurs in the radial bearing gap, thereby forming a radial bearing portion that supports the shaft member 31 in a non-contact manner in the radial direction with respect to the bearing member 3.

  The shaft member 31 having the dimples 32 is formed through (a) rolling process, (b) nitriding process, and (c) barrel processing process, as in the above embodiment. As a result, for example, as shown in FIG. 8B, a nitride layer 35b is formed on the surface layer portion 35 of the dimple 32 by nitriding. Further, a nitride layer 36b by nitriding is formed on the surface layer portion 36 of the peripheral region 33 of the dimple 32, and a second work hardened layer 36c by barrel processing is formed on the outermost layer portion of the surface layer portion 36 including the surface 33a. It is formed. A processed surface by barrel processing is formed on the surface 33a.

  Also in this embodiment, the surface layer portion 35 of the dimple 32 formed by rolling and the surface layer portion 36 of the peripheral region 33 of the dimple 32 are provided with nitrided layers 35b and 36b by nitriding treatment, respectively, so that the periphery serving as the bearing surface is obtained. The hardness of the surface 33a of the region 33 can be improved. Further, by performing barrel processing in addition to nitriding treatment, the surface accuracy of the surface 33a of the surrounding region 33 can be increased. Therefore, it is possible to obtain the shaft member 31 for a hydrodynamic bearing device having both high bearing performance and wear resistance.

  As the size of the dimple 32, for example, as shown in FIG. 8C, the ratio a / d of the width a in the major axis direction of the dimple 32 to the shaft diameter d is 0.1 or more and 0.4 or less. Is preferred. Moreover, it is preferable that the depth h2 of the dimple 32 is, for example, about 1 to 10 times the width of the radial bearing gap that the outer peripheral surface 31a of the shaft member 31 faces. With dimples 32 of this size, unlike the conventional dimples provided on the shaft member, it is possible to configure a dynamic pressure generating portion 34 that generates a high dynamic pressure action, and even when the radial bearing gap width is small. It works effectively as an oil sump. Further, from the viewpoint of lowering the torque and increasing the rigidity, the ratio of the total area of the dimple 32 forming region to the total area of the surface 33a of the peripheral region 33 is preferably 10% to 70%. Further, as the shape of the dimple 32, for example, the ratio a / b of the major axis width a to the minor axis width b is preferably in the range of 1.0 (perfect circle shape) to 2.0, In particular, even the dimple 32 having a shape outside the above range can be formed without any problem.

  In the above embodiment, the inclined grooves 9a and 9b, the axial grooves 22, the dimples 32, and the like are exemplified as the recesses 7. However, the present invention produces a dynamic pressure action of lubricating oil in the bearing gap such as the radial bearing gap 6. Therefore, the present invention can be applied to the concave portion 7 having a shape other than the above as long as it is a concave portion.

  Moreover, in the said embodiment, irrespective of the specific shape of the recessed part 7, although the case where (b) nitriding treatment was performed to the shaft raw material 11 after rolling and (c) barrel processing was performed after that was illustrated, this order It is not necessary to be limited to. For example, after forming the concave portion 7 by rolling, it is possible to perform processing in the order of (c) barrel processing and (b) nitriding treatment. In addition, depending on the material of the shaft material 11 (shaft member 2) to be used, (a) the raised portion 16 generated during the rolling process may not have a size (height) that requires removal. In such a case, it is possible to omit the (c) barrel processing step.

  The shaft member for a hydrodynamic bearing device and the hydrodynamic bearing device including the shaft member described above can be used by being incorporated in a spindle motor for information equipment, for example. A configuration example in which the dynamic pressure bearing device shaft member 31 is applied to the motor spindle will be described below with reference to FIG. In addition, about the site | part and member which make the structure and effect | action same as embodiment shown in FIGS. 1-8, the same reference number is attached | subjected and duplication description is abbreviate | omitted.

  FIG. 9 shows a cross-sectional view of the motor 40 incorporating the dynamic pressure bearing device 41. The motor 40 is used as a spindle motor for a disk drive device such as an HDD, and is mounted on the shaft member 31 and a dynamic pressure bearing device 41 that rotatably supports the shaft member 31 in a non-contact manner. A rotor (disk hub) 42, a stator coil 43 and a rotor magnet 44 that are opposed to each other with a gap in the radial direction, for example, and a bracket 45 are provided. The stator coil 43 is attached to the outer periphery of the bracket 45, and the rotor magnet 44 is attached to the inner periphery of the disk hub 42. The disk hub 42 holds one or a plurality of disks D such as magnetic disks (two in FIG. 9). When the stator coil 43 is energized, the rotor magnet 44 is rotated by electromagnetic force between the stator coil 43 and the rotor magnet 44, whereby the disc D held by the disc hub 42 and the disc hub 42 is integrated with the shaft member 31. Rotate to.

  In this embodiment, the hydrodynamic bearing device 41 includes a bearing member 46 and a shaft member 31 inserted into the inner periphery of the bearing member 46. The bearing member 46 includes a bottomed cylindrical electroformed portion 47 having one end opened, and a molded portion 48 formed integrally with the electroformed portion 47. The bearing member 46 is injection-molded integrally with the molding part 48 with resin using, for example, an electroformed part 47 that is integral with or separate from the master as an insert part.

  As shown in FIG. 9, a plurality of dimples 32 as the recesses 7 are formed on the outer peripheral surface 31 a of the shaft member 31. Further, the one end surface 31b of the shaft member 31 has a spherical shape, and abuts against the upper end surface 47b1 of the bottom 47b of the electroformed portion 47 facing the shaft member 31 when the shaft member 31 is inserted into the inner periphery of the bearing member 46. An annular groove 31c is formed in an end region of the outer peripheral surface 31a of the shaft member 31 which is a fixed region of the disk hub 42. The shaft member 31 having the annular groove 31c is formed integrally with the disc hub 42 by, for example, molding using the shaft member 31 as an insert part. In this case, the annular groove 31 c acts as a retaining for the shaft member 31 of the disk hub 42. Since the other configuration conforms to the description in the above embodiment, the description is omitted.

  The shaft member 31 configured as described above is inserted into the inner periphery of the bearing member 46, and lubricating oil is injected into the internal space of the bearing member 46. Thereby, the dimple 32 formed in the gap space between the inner peripheral surface 47a of the electroformed portion 47 and the upper end surface 47b1 of the bottom portion 47b and the outer peripheral surface 31a of the shaft member 31 opposed thereto is formed. The hydrodynamic bearing device 41 in which the bearing internal space is filled with lubricating oil is completed.

  In the dynamic pressure bearing device 41 configured as described above, when the shaft member 31 rotates, the dynamic pressure generating portion 34 formed on the outer peripheral surface 31 a of the shaft member 31 is connected to the inner peripheral surface (the electroformed portion 47 of the electroformed portion 47). A radial bearing gap 49 is formed between the inner circumference 47a). As the shaft member 31 rotates, the lubricating oil in the radial bearing gap 49 produces a dynamic pressure action by the dynamic pressure generating portion 34, and the pressure rises. Thus, a radial bearing portion R11 that supports the shaft member 31 so as to be rotatable in the radial direction is formed. At the same time, a thrust bearing portion T11 that supports the shaft member 31 rotatably in the thrust direction is formed between the one end surface 31b of the shaft member 31 and the upper end surface 47b1 of the electroformed portion 47 opposed thereto.

  As described above, in the hydrodynamic bearing device 1 according to this embodiment, sliding wear between the shaft member 31 and the bearing member 46 can be reduced. Accordingly, it is possible to avoid the situation where the dynamic pressure action generated in the radial bearing gap 49 due to wear of the dimple 32 provided on the shaft member 31 or the surrounding area 33 is reduced as much as possible, and to exhibit stable bearing performance over a long period of time. Is possible.

  In addition, by providing the dynamic pressure generating portion 34 (the concave portion 7 for generating the dynamic pressure action) on the shaft member 31 side, machining (particularly, compared to the case where the dynamic pressure generating portion 34 is provided on the bearing member 46 side) Nitriding or barrel processing) is easy. For this reason, it is possible to easily meet the demand for downsizing the motor.

  In the above embodiment, the case where the bearing members 3 and 46 are constituted by the electroformed parts 4 and 47 and the resin molded parts 5 and 48 is exemplified, but it is not particularly limited to this structure. For example, instead of the electroformed parts 4 and 47, a sleeve member made of sintered metal can be used to constitute the bearing member. Further, it is possible to integrally form the bearing members 3 and 47 with a metal material, or to integrally form the bearing members 3 and 47 with a resin composition having improved slidability and wear resistance. Alternatively, the bracket 45, which is a member on the motor 40 side, can be integrally formed of the same material (metal or resin) as the bearing member 46.

  1 and FIG. 9 exemplify the case where the thrust bearing portions T1 and T11 are so-called pivot bearings, the present invention is a dynamic structure constituted by a concave portion such as a dynamic pressure groove and its surrounding region. The present invention can also be applied to a dynamic pressure bearing that supports the shaft member 2 in a thrust direction in a non-contact manner at the pressure generating portion. In this case, although not shown in the drawing, the shaft member 2 is provided with a flange portion that projects to the outer diameter side of the shaft member 2, for example, and a dynamic pressure generating recess such as an inclined groove or dimple is rolled on the end surface of the flange portion. The hardness of the surface (surface of the peripheral area of the recess) that becomes the thrust bearing surface can be increased by forming and then performing nitriding.

  In the above embodiment, the lubricating oil is exemplified as the fluid that fills the inside of the hydrodynamic bearing devices 1 and 41 and generates the hydrodynamic action in the radial bearing gap or the like. A fluid capable of generating a pressure action, for example, a gas such as air, a fluid lubricant such as a magnetic fluid, or a lubricating grease may be used.

1 is a cross-sectional view of a fluid dynamic bearing device according to an embodiment of the present invention. It is a figure which shows notionally the process of rolling a recessed part in the shaft member for dynamic-pressure bearing apparatuses. (A) is a cross-sectional view of the surface layer near the outer peripheral surface of the shaft member before rolling, (b) is a cross-sectional view of the surface of the concave portion after rolling and its peripheral region, (c) is a concave portion after nitriding treatment FIG. 6 is a cross-sectional view of the vicinity of the surface layer portion of the surrounding area. It is sectional drawing of the surface layer part vicinity of the recessed part after a barrel process, and its peripheral region. (A) is a side view of the shaft member which concerns on other embodiment of this invention, (b) is an axis orthogonal sectional view of a shaft member. (A) is an expanded sectional view which shows one shape of the axial direction groove | channel formed in the shaft member, (b)-(d) is an expanded sectional view in which all show the other shape of an axial direction groove | channel. It is a side view of the shaft member concerning other embodiments of the present invention. (A) is a side view of the shaft member which concerns on other embodiment, (b) is an enlarged view which shows the cross-sectional shape of the dimple formed in the shaft member, (c) is an enlarged view which shows the planar shape of a dimple. It is sectional drawing which shows notionally the example of 1 structure of the motor for information devices incorporating the hydrodynamic bearing apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dynamic pressure bearing apparatus 2 Shaft member 3 Bearing member 4 Electroformed part 5 Molding part 6 Radial bearing gap 7 Recess 8 Surrounding area 8a Surface 9a, 9b Inclined groove 10 Dynamic pressure generating part 11 Shaft material 12, 13 Rolling die 14 Surface layer Part (concave)
14b Nitrided layer (concave)
15 Surface layer (surrounding area)
15b Nitride layer (surrounding area)
15c 2nd work hardening layer (surrounding area)
21, 31 Shaft member 22 Axial groove 32 Dimple 23, 33 Surrounding region 24, 34 Dynamic pressure generating portion 25, 35 Surface layer portion 25b Nitride layer 26, 36 Surface layer portion 26b, 36b Nitride layer 26c, 36c Second work hardening layer 40 Motor 41 Dynamic pressure bearing device 42 Disc hub 43 Stator coil 44 Rotor magnet 46 Bearing member 49 Radial bearing gaps R1, R2, R11 Radial bearing portion T1, T11 Thrust bearing portion

Claims (4)

In the shaft member for the hydrodynamic bearing device in which the concave portion for generating the hydrodynamic action of the fluid in the bearing gap is formed by rolling,
In the surface layer portion of the concave portion formed by the rolling and the surface layer portion in the peripheral region of the concave portion, a nitride layer formed by diffusing and penetrating nitrogen into the material of the shaft member is formed by the nitriding treatment after the rolling , Rutotomoni set to the ratio of the thickness of the nitride layer is 0.05 or less with respect to the outer diameter of said shaft member,
A motion hardened layer, which is a layer that has undergone work hardening by barrel processing after nitriding treatment , is formed on the outermost layer portion of the nitride layer in the peripheral region of the recess so as to overlap the nitride layer. Shaft member for pressure bearing devices.   The shaft member for a hydrodynamic bearing device according to claim 1, wherein at least a part of the surface layer portion has a processed surface by barrel processing.   2. The shaft member for a hydrodynamic bearing device according to claim 1, wherein the hardness of the lower layer region of the surface layer portion in the surface layer portion of the recess and the peripheral region of the recess is 400 Hv or less.   A fluid dynamic bearing device comprising the shaft member for a fluid dynamic bearing device according to claim 1.