JP2006077861A - Shaft member for dynamic pressure type bearing device and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a machining method or a manufacturing method for a shaft member, heightening the dimensional accuracy of a shaft member in this type of dynamic pressure type bearing device and heightening the dimensional accuracy at a low cost. <P>SOLUTION: A shaft blank material 10 integrally having a shaft part 11 and a flange part 12 is formed by forging, and the cylindricity of a part or the whole of the outer peripheral surface 11a of the shaft part 11 is corrected. The shaft part end face 11b of the shaft blank material 10 and the counter-shaft part end face 12b of the flange part 12 are ground taking the surface 13 subjected to correction as a reference, and the outer peripheral surface 10b of the shaft blank material 10 is ground taking both end faces 11b, 12b as a reference. The cylindricity of the radial bearing surface formed on the outer periphery of the shaft part in the thus manufactured shaft member is set to 3 μm or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a shaft member for a hydrodynamic bearing device and a manufacturing method thereof. The hydrodynamic bearing device referred to here is an information device, for example, a magnetic disk device such as an HDD, an optical disk device such as a CD-ROM, CD-R / RW, or DVD-ROM / RAM, or a magneto-optical disk device such as an MD or MO. This is suitable for a spindle motor, a polygon scanner motor of a laser beam printer (LBP), and other small motors.

  In addition to high rotational accuracy, the various motors are required to have high speed, low cost, low noise, and the like. One of the components that determine the required performance is a bearing that supports the spindle of the motor. In recent years, the use of a hydrodynamic bearing having characteristics excellent in the required performance has been studied or actually used. Yes.

A dynamic pressure bearing is a member that rotatably supports a shaft member in a non-contact manner by the dynamic pressure action of lubricating oil generated in a bearing gap, and is used by being incorporated in a spindle motor of a disk-shaped recording medium driving device such as an HDD. The This type of hydrodynamic bearing device is provided with a radial bearing portion that supports the shaft member in a non-contact manner so as to be rotatable in the radial direction, and a thrust bearing portion that supports the shaft member in a non-contact manner so as to be rotatable in the thrust direction. A dynamic pressure generating groove (dynamic pressure groove) is formed on the inner peripheral surface of the bearing sleeve or the outer peripheral surface of the shaft member constituting the bearing portion. Further, both end surfaces of the flange portion of the shaft member constituting the thrust bearing portion, or surfaces facing the flange surface (the end surface of the bearing sleeve, the end surface of the thrust member fixed to the housing, the inner bottom surface of the bottom of the housing, etc.) In addition, a dynamic pressure groove is formed (see, for example, Patent Document 1).
JP 2002-61641 A

  Recently, in order to cope with an increase in information recording density and high-speed rotation in information equipment, the spindle motor for the information equipment has been required to have higher rotational accuracy. Higher rotational accuracy is also required for the hydrodynamic bearing device incorporated in the motor.

  By the way, in order to increase the rotational accuracy of the hydrodynamic bearing device, it is important to manage the radial bearing gap and the thrust bearing gap in which the dynamic pressure is generated with high accuracy. In order to properly manage this gap, high dimensional accuracy is required for the shaft member of the hydrodynamic bearing device involved in the formation of the bearing gaps. On the other hand, it is difficult to increase the precision of existing machining methods because the machining costs are soaring. Therefore, a new machining method that provides both machining accuracy and machining costs for shaft members is provided. Is desired.

  The subject of this invention is improving the dimensional accuracy of the shaft member in this kind of hydrodynamic bearing apparatus.

  Another object of the present invention is to provide a method of machining a shaft member that can increase the dimensional accuracy of the shaft member in this type of hydrodynamic bearing device at low cost.

  In order to solve the above-described problems, the shaft member for a hydrodynamic bearing device according to the present invention includes a shaft portion and a flange portion formed by forging, and a radial bearing surface that faces the radial bearing gap is formed on the outer periphery of the shaft portion. The cylindricity of the radial bearing surface is 3 μm or less. Here, the cylindricity is equal to two cylindrical cylinders (inner surface when the cylindrical body (the surface to be subjected to cylindricity. Here, the radial bearing surface of the shaft portion) is sandwiched between two coaxial geometrically correct cylinders. It is represented by the difference in radius between the two coaxial cylinders when the interval between the tangent cylinder and the circumscribed cylinder) is minimized. The radial bearing surface may be any surface as long as it faces the radial bearing gap that generates the dynamic pressure effect, and it does not matter whether there is a dynamic pressure groove for generating the dynamic pressure effect.

  The degree of cylindricity of the radial bearing surface formed on the outer periphery of the shaft part is particularly accurate for the radial bearing gap formed between the outer periphery of the shaft part and the bearing member (bearing sleeve, housing, etc.) facing the outer periphery of the shaft part. Greatly affects. That is, when the cylindricity is increased, the radial bearing gap is not constant in the circumferential direction or the axial direction, and a portion having a large gap and a portion having a small gap appear remarkably. For this reason, the bearing loss increases at a location where the bearing clearance is small, for example, because the rotational torque of the shaft member increases compared to other locations, and the bearing rigidity decreases at locations where the bearing clearance is large compared to other locations, resulting in shaft runout. Becomes larger. Further, if the gap is not constant in the axial direction, an undesired flow of lubricating fluid in the axial direction occurs, which may adversely affect the proper circulation of the lubricating fluid. From these viewpoints, in the present invention, the cylindricity of the radial bearing surface is regulated to 3 μm or less. According to this, since the variation in the dimension of the radial bearing gap in the circumferential direction or the axial direction is suppressed, the bearing loss can be suppressed and the bearing rigidity can be ensured. Therefore, the radial bearing gap between the shaft member and the bearing member facing the shaft member can be managed with high accuracy, and high rotational accuracy of the bearing device including the shaft member and the bearing member can be realized.

  In this shaft member, it is preferable that the perpendicularity of both end faces of the flange portion and the perpendicularity of the end face of the shaft portion are each 5 μm or less with reference to the radial bearing surface formed on the outer periphery of the shaft portion. Here, the squareness means that the predetermined plane from the geometric plane that is geometrically perpendicular to the reference plane (here, the radial bearing surface) in the combination of the predetermined plane and the reference plane that should be perpendicular. Here, it refers to the magnitude of deviation of the flange end face or shaft end face. If the perpendicularity of the end face of the flange portion is larger than 5 μm, the thrust bearing gap formed between the end face and the opposite face may vary, which may adversely affect the bearing performance such as increased bearing loss. Because there is. If the squareness of the end face of the shaft portion is larger than 5 μm, it becomes difficult to set the thrust bearing gap with high precision, or the reference surface when the shaft end surface grinds the outer peripheral surface of the shaft portion or the end surface of the flange portion. This is because the processing accuracy of these ground surfaces may be reduced.

  The shaft member is formed by forging a shaft portion and a flange portion, and both end surfaces of the shaft member (the end surface of the shaft portion located at both end portions of the shaft member and one end surface of the flange portion) are formed. If the ground surfaces are used, it is possible to perform precision grinding of the outer peripheral surface of the shaft member using these surfaces as reference surfaces. Thereby, the shaft member which has the radial bearing surface which suppressed the value of cylindricity and perpendicularity small can be obtained at low cost. The shaft member can be integrally formed by forging the shaft portion and the flange portion. According to this, the cost can be further reduced.

  If a sloping ridge portion is formed at the corner portion of the shaft portion and the flange portion, it is possible to ensure the escape of the grindstone during grinding of both the outer peripheral surface of the shaft portion and the end surface of the flange portion. Various methods are conceivable as a method for forming the pussies, but from the viewpoint of suppressing the generation of burrs, impurities and the like after processing, it is preferably formed by plastic processing.

  The method of manufacturing a shaft member for a hydrodynamic bearing device according to the present invention includes a step of forming a shaft material integrally having a shaft portion and a flange portion by forging, and a part or all of the cylindricity of the outer peripheral surface of the shaft portion. And a step of correcting. More preferably, a first grinding process is performed on both end faces of the shaft material on the basis of the straightened surface, and then a second grinding process is performed on at least the outer peripheral surface of the shaft material on the basis of the both end faces. It is characterized by.

  Thus, in the present invention, after roughly forming the shaft member and the shaft portion integrated with the shaft portion and the flange portion by forging, the cylindrical degree of the outer peripheral surface of the shaft portion is corrected, so in the first grinding step described later, By using the corrected surface as a reference, highly accurate grinding (width grinding) can be performed.

  In addition, examples of the correction processing of the above-mentioned cylindricity may include rolling processing using, for example, a round die or a flat die, but other than this, drawing, ironing, sizing processing using a split-type press (clamping), etc. Various plastic workings can be used.

  In the first grinding step, grinding is performed on both end surfaces located at both axial ends of the shaft material, specifically, the end surface of the shaft portion and one end surface of the flange portion. At this time, since each end face is ground with reference to the outer peripheral surface of the shaft portion subjected to the correction processing as described above, the squareness and flatness of both end faces of the shaft material can be finished with high accuracy.

  Next, a second grinding process is performed on the outer peripheral surface of the shaft material with reference to both end surfaces of the shaft material subjected to the grinding process. Since both end faces of the shaft material that is the reference surface are finished with high accuracy in the first grinding process, the outer peripheral surface of the shaft material that is the processing target can also be finished with high accuracy. The second grinding process is performed on at least a portion serving as a radial bearing surface in the outer peripheral surface of the shaft material, but can also be performed on the outer peripheral surface of the flange portion. Furthermore, it can also be applied to the other end surface (on the shaft portion side) of the unground flange portion. In the second grinding step, the surfaces to be ground can be finished at a time by using a grindstone having a contour corresponding to the surface to be ground of these shaft materials (total shape grindstone).

  Through the above procedure, a shaft member having a radial bearing surface with a cylindricity of 3 μm or less, a squareness of both end faces of the flange portion, and a perpendicularity of the end face of the shaft portion of 5 μm or less is manufactured at low cost. Is possible.

  The shaft member for a hydrodynamic bearing device is configured to apply pressure by a hydrodynamic action of a fluid generated in a bearing sleeve in which the shaft member is inserted into the inner periphery and a radial bearing gap between the outer periphery of the shaft portion and the inner periphery of the bearing sleeve. A radial bearing that non-contact-supports the shaft portion in the radial direction, and a non-contact support that supports the flange portion in the thrust direction by generating pressure by the dynamic pressure action of the fluid generated in the thrust bearing gap at one end of the flange portion. A hydrodynamic bearing including a first thrust bearing portion and a second thrust bearing portion that generates pressure by a dynamic pressure action of fluid generated in a thrust bearing gap on the other end side of the flange portion and supports the flange portion in a non-contact manner in the thrust direction. It can be provided as a device.

  In this case, for example, a dynamic pressure groove for generating a dynamic pressure action of fluid is formed on one of the outer peripheral surface of the shaft portion facing the radial bearing gap and the inner peripheral surface of the bearing sleeve facing the outer peripheral surface. It can be asymmetric in the axial direction.

  Moreover, the said dynamic pressure bearing apparatus can also be provided as a motor provided with the dynamic pressure bearing apparatus, the rotor magnet, and the stator coil.

  According to the present invention, the shaft portion outer peripheral surface of the shaft member and the end surface of the flange portion involved in the formation of the radial bearing gap and the thrust bearing gap can be processed with high accuracy and low cost. It is possible to manage each bearing gap of the embedded dynamic pressure bearing device with high accuracy. As a result, high rotational accuracy can be imparted to the dynamic pressure bearing device.

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

  FIG. 2 conceptually shows a configuration example of a spindle motor for information equipment incorporating the fluid dynamic bearing device 1 according to one embodiment of the present invention. This spindle motor for information equipment is used in a disk drive device such as an HDD, and includes a hydrodynamic bearing device 1 that rotatably supports a shaft member 2 in a non-contact manner, a disk hub 3 attached to the shaft member 2, For example, a stator coil 4 and a rotor magnet 5 which are opposed to each other via a gap in the radial direction, and a bracket 6 are provided. The stator coil 4 is attached to the outer periphery of the bracket 6, and the rotor magnet 5 is attached to the inner periphery of the disk hub 3. The bracket 6 has the hydrodynamic bearing device 1 mounted on the inner periphery thereof. The disk hub 3 holds one or more disks D such as magnetic disks on the outer periphery thereof. In this spindle motor for information equipment, when the stator coil 4 is energized, the rotor magnet 5 is rotated by the magnetic force between the stator coil 4 and the rotor magnet 5, and accordingly, the disk hub 3 and the shaft member 2 are integrated. Rotate.

  FIG. 3 shows the hydrodynamic bearing device 1. The hydrodynamic bearing device 1 includes a housing 7 having a bottom portion 7b at one end, a bearing sleeve 8 fixed to the housing 7, and a shaft member 2 inserted into the inner periphery of the bearing sleeve 8 as main components. Is done. For convenience of explanation, the following description will be made with the bottom 7b side of the housing 7 as the lower side and the side opposite the bottom 7b as the upper side.

  As shown in FIG. 3, the housing 7 is located on one end side of the side portion 7a and the side portion 7a formed in a cylindrical shape with a resin material such as LCP, PPS, or PEEK, and is formed of, for example, a metal material. It is comprised by the bottom part 7b. In this embodiment, the bottom portion 7b is formed as a separate body from the side portion 7a, and is retrofitted to the lower inner periphery of the side portion 7a. In the partial annular region of the upper end surface 7b1 of the bottom portion 7b, for example, a spiral dynamic pressure groove is formed as a dynamic pressure generating portion, although illustration is omitted. In this embodiment, the bottom portion 7b is formed separately from the side portion 7a and is fixed to the lower inner periphery of the side portion 7a. However, the bottom portion 7b can be integrally molded with the side portion 7a, for example, with a resin material. . At that time, the dynamic pressure groove provided in the upper end surface 7b1 can be molded simultaneously with the injection molding of the housing 7 composed of the side portion 7a and the bottom portion 7b, thereby eliminating the trouble of separately forming the dynamic pressure groove in the bottom portion 7b. It can be omitted.

  The bearing sleeve 8 is formed in a cylindrical shape with a porous body made of sintered metal, in particular, a sintered metal porous body mainly composed of copper, and is fixed at a predetermined position on the inner peripheral surface 7 c of the housing 7. The

  A dynamic pressure groove as a dynamic pressure generating portion is formed on the entire inner surface 8a of the bearing sleeve 8 or a partial cylindrical surface region. In this embodiment, for example, as shown in FIG. 4, herringbone-shaped dynamic pressure grooves 8 a 1 and 8 a 2 are formed at two locations in the axial direction. The upper dynamic pressure groove 8a1 is formed axially asymmetric with respect to the axial center m (the axial center of the upper and lower inclined groove regions), and the axial dimension X1 of the upper region is lower than the axial center m. It is larger than the axial dimension X2 of the side region.

  For example, a spiral-shaped dynamic pressure groove is formed on the entire lower surface 8b of the bearing sleeve 8 or a partial annular region as a dynamic pressure generating portion, although illustration is omitted.

  As shown in FIG. 3, the sealing member 9 as a sealing means is formed in a ring shape with a soft metal material such as brass, other metal materials, or a resin material, and is press-fitted into the upper inner periphery of the side portion 7a of the housing 7. It is fixed by means such as adhesion. In this embodiment, the inner peripheral surface 9 a of the seal member 9 is formed in a cylindrical shape, and the lower end surface 9 b of the seal member 9 is in contact with the upper end surface 8 c of the bearing sleeve 8.

  As shown in FIG. 1, the shaft member 2 is formed of a metal material such as stainless steel and has a T-shaped cross section integrally including a shaft portion 21 and a flange portion 22 provided at the lower end of the shaft portion 21. On the outer periphery of the shaft portion 21, as shown in FIG. 3, radial bearing surfaces 23a and 23b facing the formation regions of the two dynamic pressure grooves 8a1 and 8a2 formed on the inner peripheral surface 8a of the bearing sleeve 8 are axially arranged. Two places are formed apart from each other. Above one of the radial bearing surfaces 23a, a tapered surface 24 that gradually decreases in diameter toward the tip of the shaft is formed adjacently, and a cylindrical surface 25 that serves as a mounting portion of the disk hub 3 is further formed thereabove. . Between the two radial bearing surfaces 23a, 23b, between the other radial bearing surface 23b and the flange portion 22 and between the tapered surface 24 and the cylindrical surface 25, annular nuisance portions 26, 27, 28 are respectively provided. Is formed.

  Thrust bearing surfaces 22a and 22b are formed on both end surfaces of the flange portion 22 so as to face the dynamic pressure groove regions respectively formed on the lower end surface 8b of the bearing sleeve and the upper end surface 7b1 of the bottom portion 7b.

  Between the taper surface 24 of the shaft portion 21 and the inner peripheral surface 9a of the seal member 9 facing the taper surface 24, an annular seal whose radial dimension gradually increases from the bottom 7b side of the housing 7 upward. A space S is formed. In the hydrodynamic bearing device 1 (see FIG. 3) after completion of assembly, the oil level is within the range of the seal space S.

  In the dynamic pressure bearing device 1 configured as described above, when the shaft member 2 is rotated, the formation regions (two upper and lower portions) of the dynamic pressure grooves 8a1 and 8a2 on the inner periphery of the bearing sleeve 8 are opposed to these regions, respectively. The dynamic pressure of the lubricating oil is generated in the radial bearing gap between the radial bearing surfaces 23a and 23b of the shaft portion 21, and the shaft portion 21 of the shaft member 2 is supported in a non-contact manner so as to be rotatable in the radial direction. As a result, the first radial bearing portion R1 and the second radial bearing portion R2 that support the shaft member 2 in a non-contact manner so as to be rotatable in the radial direction are formed. The first thrust between the dynamic pressure groove region formed on the lower end surface 8b of the bearing sleeve 8 and the thrust bearing surface 22a on the upper side (shaft side) of the flange portion 22 facing the dynamic pressure groove region. The second thrust bearing between the bearing clearance and the dynamic pressure groove region formed in the upper end surface 7b1 of the bottom portion 7b and the thrust bearing surface 22b on the lower side (on the opposite shaft side) of the flange portion 22 facing this surface. The dynamic pressure of the lubricating oil is generated in the gap, and the flange portion 22 of the shaft member 2 is supported in a non-contact manner so as to be rotatable in both thrust directions. Thereby, the 1st thrust bearing part T1 and the 2nd thrust bearing part T2 which support the shaft member 2 in a non-contact manner so as to be rotatable in the thrust direction are formed.

  Hereinafter, the manufacturing method of the shaft member 2 which comprises the said dynamic-pressure bearing apparatus 1 is demonstrated.

  The shaft member 2 is manufactured mainly through two steps of (A) a forming step and (B) a grinding step. In this embodiment, the forging process (A-1) and the straightening process (A-2) are included in the molding process (A), and the width grinding process (B-1) is included in the grinding process (B). And a whole surface grinding process (B-2) and a finish grinding process (B-3).

(A) Forming step (A-1) Forging process First, a rod-shaped metal material such as stainless steel, which is a material of the shaft member 2 to be molded, is cold-forged, and as shown in FIG. A shaft material 10 having a T-shaped cross section integrally having the flange portion 12 is formed. As the cold forging method, any one of indentation, upsetting, heading, or a combination thereof can be used. In the illustrated example, the outer peripheral surface 11a of the shaft portion 11 after the forging process has a different diameter shape with the tapered surface 14 interposed, but the tapered surface 14 may be omitted and formed into a uniform diameter over the entire length.

  In this way, if the shaft material 10 is formed by forging, the waste of the material can be eliminated without generating a cutting allowance as compared with the case where the similar shaft material 10 is formed by cutting or the like. Moreover, since it is a press work, the cycle time per shaft material 10 can be increased, and the productivity can be improved.

(A-2) Straightening Next, plastic working for straightening the cylindricity is performed on the shaft outer peripheral surface 11a of the shaft material 10 after forging. Thereby, the cylindricity of the surface 13 subjected to the correction processing in the shaft outer peripheral surface 11a of the shaft material 10 is improved within a required range (for example, 10 μm or less). At this time, for example, as shown in FIGS. 6A and 6B, a rolling process using a round die 34, a flat die 35, or the like can be adopted as the cylindrical degree correction process. Various processing methods such as squeezing and ironing, or sizing processing using a split-type press (pinching) can be employed. In addition to performing the straightening process over the entire length of the outer peripheral surface of the shaft portion 11, it can also be performed on only a part thereof. In the case where only a part is corrected, the processing region includes at least regions that become the radial bearing surfaces 23 a and 23 b of the shaft member 2.

(B) Grinding Step (B-1) Width Grinding Process The shaft end face 11b and the opposite end face 12b (see FIG. 5) of the flange 12 which are both end faces of the shaft material 10 that has undergone the straightening process are used as the shaft section. Grinding is performed with reference to the surface 13 of the outer peripheral surface 11a that has been subjected to the correction processing (first grinding step). For example, as shown in FIGS. 7A and 7B, the grinding device 40 used in this grinding process includes a carrier 41 that holds a plurality of shaft materials 10 as workpieces, and a shaft material 10 that is held by the carriers 41. A shaft end face 11b and a pair of grindstones 42, 42 for grinding the opposite end face 12b of the flange portion 12 are provided.

  As shown in the drawing, a plurality of notches 43 are provided at equal pitches in the circumferential direction in a partial region in the circumferential direction of the outer peripheral edge of the carrier 41. The shaft material 10 is accommodated in the notch 43 in a state in which the straightened surface 13 is in angular contact with the inner surface 43 a of the notch 43. The straightened surface 13 of the shaft material 10 protrudes slightly from the outer peripheral surface of the carrier 41, and a belt 44 is stretched on the outer diameter side of the carrier so as to constrain the protruding portion of the shaft material 10 from the outer diameter side. Has been. A pair of grindstones 42 and 42 are coaxially arranged at predetermined intervals on both ends in the axial direction of the carrier 41 of the shaft material 10 accommodated in the notch 43 so that the end surfaces (grinding surfaces) thereof face each other.

  As the carrier 41 rotates, the shaft material 10 is sequentially put into the notch 43 from a fixed position. The thrown shaft material 10 traverses from the outer diameter end to the inner diameter end on the end faces of the rotating grindstones 42 and 42 in a state where the dropping from the notch 43 is restrained by the belt 44. Along with this, both end surfaces of the shaft material 10, in other words, the shaft portion end surface 11 b and the opposite end surface 12 b of the flange portion 12 are ground by the end surfaces of the grindstones 42 and 42. At this time, since the straightened surface 13 of the shaft material 10 is supported by the carrier 41 and the straightened surface 13 has a high degree of cylindricity, the rotational axis of the grindstone 42 and the ground surface of the grindstone 42 are in advance. If the straight angle of the shaft and the parallelism between the rotational axis of the grindstone 42 and the rotational axis of the carrier 41 are managed with high accuracy, the both end surfaces 11b of the shaft material 10 are based on the straightened surface 13 as a reference. 12b can be finished with high accuracy, and the value of the squareness with respect to the straightened surface 13 can be kept small. Moreover, the axial direction width | variety (full length including the flange part 12) of the shaft raw material 10 is finished to a predetermined dimension.

(B-2) Whole surface grinding Next, grinding of the outer peripheral surface 10b of the shaft material 10 and the shaft portion side end surface 12a of the flange portion 12 is performed on the basis of both end faces 11b and 12b of the ground shaft material (second grinding) Process). A grinding apparatus 50 used in this grinding process performs plunge grinding with a grindstone 53 while pressing a backing plate 54 and a pressure plate 55 against both end surfaces of the shaft material 10 as shown in FIG. The straightened surface 13 of the shaft material 10 is rotatably supported by the shoe 52.

  The grindstone 53 is a general-purpose grindstone provided with a grinding surface 56 corresponding to the outer peripheral surface shape of the shaft member 2 as a finished product. The grinding surface 56 includes a cylindrical grinding portion 56a that grinds the outer peripheral surface 11a over the entire axial length of the shaft portion 11 and the outer peripheral surface 12c of the flange portion 12, and a surface grinding portion 56b that grinds the shaft portion side end surface 12a of the flange portion 12. And. In the illustrated grindstone 53, as the cylindrical grinding portion 56a, the portions 56a1 and 56a2 for grinding the regions corresponding to the radial bearing surfaces 23a and 23b of the shaft member 2, the portion 56a3 for grinding the region corresponding to the tapered surface 24, and the cylindrical surface 25, a portion 56 a 4 for grinding the region corresponding to 25, portions 56 a 5 to 56 a 7 for grinding each of the portions 26 to 28, and a portion 56 a 8 for grinding the outer peripheral surface 12 c of the flange portion 12.

  The grinding process in the grinding apparatus 50 having the above-described configuration is performed in the following procedure. First, in a state where the shaft material 10 and the grindstone 53 are rotated, the grindstone 53 is sent in an oblique direction (in the direction of arrow 1 in the figure), and the surface grinding portion 56b of the grindstone 53 is placed on the flange portion shaft side end surface 12a of the shaft material 10. Pressing and grinding mainly the shaft side end face 12a. Thereby, the shaft part side end surface 12a in the flange part 22 of the shaft member 2 is ground. Next, the grindstone 53 is fed in a direction orthogonal to the rotational axis of the shaft blank 10 (in the direction of arrow 2 in the figure), and the grindstone 53 is placed on the outer circumferential surface 11 a of the shaft portion 11 and the outer circumferential surface 12 c of the flange portion 12. The cylindrical grinding portion 56a is pressed to grind the surfaces 11a and 12c. Thus, of the outer peripheral surface of the shaft portion 21 of the shaft member 2, the regions 13 a and 13 b corresponding to the radial bearing surfaces 23 a and 23 b of the shaft material 10, the tapered surface 24, the region 15 corresponding to the cylindrical surface 25, and the flange portion 22. The outer peripheral surface 22c is ground, and further each of the pussies 26 to 28 are formed. In the grinding, for example, as shown in FIG. 9, it is preferable to perform grinding while measuring the remaining grinding allowance with a measurement gauge 57.

  In this second grinding step, since the perpendicularity of the both end faces 11b and 12b of the shaft blank 10 is determined in advance by width grinding, each surface to be ground can be ground with high precision. .

(B-3) Finish grinding (B-2) Radial bearing surface 23a of shaft member 2 among the surfaces ground by the whole surface grinding.
The final finish grinding is performed on the regions 13a, 13b, and 15 corresponding to the cylinder surface 25b. The grinding apparatus used for this grinding process is a cylindrical grinder shown in FIG. 10 that performs plunge grinding with the grindstone 63 while rotating the shaft material 10 held between the backing plate 64 and the pressure plate 65. The shaft material 10 is rotatably supported by the shoe 62. The grinding surface 63a of the grindstone 63 includes a first cylindrical grinding portion 63a1 for grinding the regions 13a and 13b corresponding to the radial bearing surfaces 23a and 23b, and a second cylindrical grinding portion for grinding the region 15 corresponding to the cylindrical surface 25. 63a2.

  In the grinding device 60 having the above-described configuration, by feeding the rotating grindstone 63 in the radial direction, the regions 13a, 13b, and 15 corresponding to the radial bearing surfaces 23a and 23b and the cylindrical surface 25 are ground, respectively. Finished with final surface accuracy. In this embodiment, both the region corresponding to the radial bearing surfaces 23a and 23b and the region corresponding to the cylindrical surface 25 are finish-ground, but the grinding of the region corresponding to the cylindrical surface 25 can be omitted.

  After passing through the forming step (A) and the grinding step (B), the shaft member 2 shown in FIG. 1 is completed by performing heat treatment and cleaning treatment as necessary.

  In the case of the shaft member 2 manufactured by the above-described manufacturing method, the cylindrical degree of the radial bearing surfaces 23a and 23b formed on the outer periphery of the shaft portion 21 can be finished to, for example, 3 μm or less (preferably 1.5 μm or less). As a result, for example, the radial bearing gap formed between the inner periphery of the bearing sleeve 8 in the hydrodynamic bearing device 1 can be suppressed within a predetermined range in the circumferential direction or the axial direction, and the radial bearing gap can be reduced. An adverse effect on bearing performance due to variations can be avoided. Therefore, the radial bearing gap can be managed with high accuracy, and the rotational accuracy of this type of hydrodynamic bearing device can be maintained at a high level. In the present embodiment, since the finish grinding process (see FIG. 10) is performed not only on the radial bearing surfaces 23a and 23b but also on the region corresponding to the cylindrical surface 25, the cylindrical surface 25 is also finished to the above-described cylindricity. . Therefore, the attachment accuracy when attaching a member such as the disk hub 3 to the shaft member 2 is increased, which can contribute to improvement of motor performance.

  Further, according to the above manufacturing method, the perpendicularity of both end faces (thrust bearing surfaces) 22a and 22b of the flange portion 22 and the shaft end surface 21b with respect to the radial bearing surfaces 23a and 23b formed on the outer periphery of the shaft portion 21. It is also possible to mold the shaft member 2 having a squareness of 5 μm or less. Among these, the thrust bearing surfaces 22a and 22b formed on both end surfaces of the flange portion 22 are thrust bearings between opposing surfaces (the lower end surface 8b of the bearing sleeve 8 and the upper end surface 7b1 of the bottom portion 7b of the housing 7). Since the gap is formed, the variation in the thrust bearing gap can be suppressed by reducing the squareness value. Further, the end surface 21b of the shaft portion not only serves as a reference surface for grinding the outer peripheral surface of the shaft portion 21 and the upper end surface (the thrust bearing surface 22a side) of the flange portion 22, but also when setting the thrust bearing clearance. It also becomes the reference plane. Therefore, by suppressing the squareness value of the shaft end face 21b to be small, not only the ground surface but also the thrust bearing gap can be managed with high accuracy.

  In the above description, in the overall grinding process shown in FIG. 9, the cylindrical grinding of the outer peripheral surface 10 b of the shaft material 10 and the surface grinding of the shaft portion side end surface 12 a of the flange portion 12 are performed by the common grindstone 53. However, it is also possible to perform both in separate steps using separate whetstones.

  Moreover, although the above description illustrated the case where the rugged portions 26 to 28 of the shaft member 2 are formed by the entire surface grinding (B-2) shown in FIG. 9, these murky portions 26 to 28 are illustrated in FIG. 6. Plastic processing (for example, roll forming) can be performed simultaneously with the correction processing shown in (a) and (b). In this case, in particular, by forming the corner portion 27 between the shaft portion 21 and the flange portion 22 in an inclined manner as shown in FIG. 11, in the entire surface grinding process (see FIG. 9), the flange portion 12 It can be made to function as relief of the grindstone 53 at the time of grinding the shaft part side end surface 12a and the shaft part outer peripheral surface 11a simultaneously.

  Moreover, although the radial bearing surfaces 23a and 23b and the thrust bearing surfaces 22a and 22b of the shaft member 2 are all smooth surfaces without dynamic pressure grooves in the above embodiment, the dynamic pressure is applied to these bearing surfaces. Grooves can also be formed. In this case, the radial dynamic pressure groove can be formed by rolling or forging before the entire surface grinding shown in FIG. 9, and the thrust dynamic pressure groove can be formed by pressing or forging.

  Moreover, in the above embodiment, as the dynamic pressure bearings constituting the radial bearing portions R1 and R2 and the thrust bearing portions T1 and T2, for example, a dynamic pressure generating portion including a herringbone shape or a spiral shape dynamic pressure groove is used. Although the bearing is illustrated, the configuration of the dynamic pressure generating unit is not limited to this. As the radial bearing portions R1 and R2, for example, multi-arc bearings, step bearings, taper bearings, taper flat bearings, etc. can be used. As the thrust bearing portions T1 and T2, step pocket bearings, taper pocket bearings, taper・ Flat bearings can also be used.

  Moreover, in the above embodiment, the inside of the hydrodynamic bearing device 1 is filled, and the radial bearing gap between the bearing sleeve 8 and the shaft member 2 and the thrust between the bearing sleeve 8 and the housing 7 and the shaft member 2 are filled. Although the lubricating oil is exemplified as the fluid that causes the dynamic pressure action in the bearing gap, it is not particularly limited to this fluid. A fluid capable of generating a dynamic pressure action in each bearing gap having the dynamic pressure grooves, for example, a gas such as air, or a fluid lubricant such as a magnetic fluid may be used.

It is a side view of the shaft member for fluid dynamic bearing devices concerning one embodiment of the present invention. It is sectional drawing of the spindle motor for information devices incorporating the dynamic pressure bearing apparatus provided with the shaft member. It is a longitudinal cross-sectional view of a fluid dynamic bearing device. It is a longitudinal cross-sectional view of a bearing sleeve. It is a side view of the shaft raw material shape | molded by the forging process. It is a figure which shows an example of a correction process, (a) is the schematic of the rolling process by a round die, (b) is the schematic of the rolling process by a flat die. (A) is the schematic which shows an example of the grinding apparatus which concerns on the width grinding process of a shaft raw material, (b) is an enlarged view of the notch periphery of the carrier holding a shaft raw material. It is a partial cross section figure showing an example of a grinding device concerning the above-mentioned width grinding process. It is the schematic which shows an example of the grinding device which concerns on the shaft material whole surface grinding process. It is the schematic which shows an example of the grinding apparatus which concerns on the grinding finishing process of a shaft raw material. It is an expanded sectional view of the corner | angular part periphery of the axial part and flange part of a shaft member.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dynamic pressure bearing apparatus 2 Shaft member 3 Disc hub 4 Stator coil 5 Rotor magnet 7 Housing 8 Bearing sleeve 10 Shaft material 10b Outer peripheral surface 11 Shaft corresponding area (shaft portion)
11a Outer peripheral surface 12 Flange part corresponding area (flange part)
12a Shaft side end surface 12b Countershaft side end surface 13 Straightening surface 21 Shaft portion 22 Flange portion 22a Thrust bearing surface 22b Thrust bearing surface 23a Radial bearing surface 23b Radial bearing surface 24 Tapered surface 25 Cylindrical surfaces 26, 27, 28 Nusumi portion 34 Round die 35 Flat die 40 Grinding device 41 Carrier 42 Grinding stone 43 Notch 43a Inner surface 50, 60 Grinding device 51, 61 Rotating support member 52, 62 Support member 53 Grinding stone 54, 64 Backing plate 55, 65 Pressure plate 56 Grinding surface 63 Grinding wheel 63a Grinding surface R1, R2 Radial bearing part T1, T2 Thrust bearing part

Claims (14)

Each is provided with a shaft portion and a flange portion formed by forging, and a radial bearing surface facing the radial bearing gap is formed on the outer periphery of the shaft portion,
A shaft member for a hydrodynamic bearing device, wherein a cylindrical degree of the radial bearing surface is 3 μm or less.   2. The shaft member for a hydrodynamic bearing device according to claim 1, wherein the squareness of both end faces of the flange portion and the squareness of the end face of the shaft portion are each 5 μm or less with respect to the radial bearing surface.   The shaft member for a hydrodynamic bearing device according to claim 1, wherein the shaft portion and the flange portion are integrally formed by forging.   The shaft member for a hydrodynamic bearing device according to claim 1, wherein both end surfaces of the shaft member are ground surfaces.   The shaft member for a hydrodynamic bearing device according to claim 1, wherein an inclined ridge portion is formed at a corner portion between the shaft portion and the flange portion.   The shaft member for a hydrodynamic bearing device according to any one of claims 1 to 5, a bearing sleeve into which the shaft member is inserted into an inner periphery, and a radial bearing gap between an outer periphery of the shaft portion and an inner periphery of the bearing sleeve A radial bearing that generates non-contact support in the radial direction by generating pressure by the dynamic pressure of the fluid generated in the fluid, and a flange that generates pressure by the dynamic pressure of the fluid generated in the thrust bearing gap at one end of the flange A first thrust bearing portion that supports the contact portion in the thrust direction in a non-contact manner and a second thrust bearing portion that contacts the flange portion in the thrust direction by generating pressure by the dynamic pressure action of the fluid generated in the thrust bearing gap at the other end of the flange portion. A hydrodynamic bearing device comprising a thrust bearing portion.   A dynamic pressure groove for generating a dynamic pressure action of fluid is formed asymmetrically in the axial direction on either the outer peripheral surface of the shaft part facing the radial bearing gap or the inner peripheral surface of the bearing sleeve facing this outer peripheral surface. The hydrodynamic bearing device according to claim 6.   A motor comprising the hydrodynamic bearing device according to claim 6, a rotor magnet, and a stator coil.   Manufacture of a shaft member for a hydrodynamic bearing device including a step of forming a shaft material integrally having a shaft portion and a flange portion by forging, and a step of correcting part or all of the cylindricity of the outer peripheral surface of the shaft portion Method.   The method for manufacturing a shaft member for a hydrodynamic bearing device according to claim 9, wherein the straightening step is performed by rolling.   The first grinding process is performed on both end faces of the shaft material on the basis of the straightened surface, and the second grinding process is performed on at least the outer peripheral surface of the shaft material on the basis of the both end faces. Of manufacturing a shaft member for a hydrodynamic bearing device.   The method for manufacturing a shaft member for a hydrodynamic bearing device according to claim 11, wherein the first grinding is performed on one end surface of the flange portion and the end surface of the shaft portion.   The method for manufacturing a shaft member for a hydrodynamic bearing device according to claim 11 or 12, wherein the second grinding is performed on at least a portion of the shaft material that becomes a radial bearing surface facing a radial bearing gap on an outer periphery of the shaft portion.   The method for manufacturing a shaft member for a hydrodynamic bearing device according to claim 13, wherein the other end face of the flange portion is further ground in the second grinding process.

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