JP2006316896A - Method for manufacturing oil-impregnated sintered bearing and oil-impregnated sintered bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an oil-impregnated sintered bearing by which occurrence of contamination in use is suppressed, while the longevity of the mold for molding the bearing is increased at low cost. <P>SOLUTION: Material power in which 0.1-1.5 wt.% of graphite is added to metal power M is subjected to a compression molding in a sleeve shape, and then to sintering. The sintered body 15 is axially restrained by top and bottom punches 18, 19 to radially compress by a die 16. The mold 17a in the shape corresponding to dynamic-pressure grooves 8a1, 8a2 for producing hydrodynamic-pressure is pressed on the internal circumferential surface 15a of the sintered body. Thus, the oil-impregnated sintered bearing (bearing sleeve 8) is obtained, in which dynamic-pressure-generating parts including the dynamic-pressure grooves 8a1, 8a2 are formed by plastically deforming the internal circumferential surface 15a. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a sintered oil-impregnated bearing and a sintered oil-impregnated bearing that constitute a hydrodynamic bearing that supports a shaft member in a non-contact manner by a hydrodynamic action of a fluid generated in a bearing gap. Bearing devices equipped with this kind of sintered oil-impregnated bearing include information devices, such as magnetic disk devices such as HDD, optical disk devices such as CD-ROM, CD-R / RW, DVD-ROM / RAM, MD, MO, etc. It is suitable for a spindle motor such as a magneto-optical disk device, a polygon scanner motor of a laser beam printer (LBP), a color wheel of a projector, or an electric device such as a small motor such as an axial fan.

  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.

  For example, in a hydrodynamic bearing device incorporated in a spindle motor of a disk drive device such as an HDD, both the radial bearing portion that supports the shaft member in the radial direction and the thrust bearing portion that supports the axial direction are configured by the hydrodynamic bearing. There is. As a radial bearing part in this type of dynamic pressure bearing device, for example, a plurality of dynamic pressure grooves (inclined grooves) are provided as dynamic pressure generating parts on the inner peripheral surface of a sintered sleeve (sintered oil-impregnated bearing) made of sintered metal. It is known that a radial bearing gap is formed between the surface on which the dynamic pressure generating portion is formed and the outer peripheral surface of the shaft member opposed to the surface where the arrayed region is formed (for example, Patent Document 1). See).

  Usually, this type of sintered oil-impregnated bearing is formed by compressing a metal powder mainly composed of Cu powder or Fe powder or both into a predetermined shape with a corresponding molding die, and sintering the molded body. can get. Moreover, the dynamic pressure groove shape of the inner peripheral surface is formed by inserting a molding rod having a molding die having a shape corresponding to the dynamic pressure groove shape into the outer peripheral surface of the sleeve material (sintered body), and a pair of It is obtained by press-fitting a press-fitting member such as a die into the outer periphery of the sleeve material while pressing the sleeve material in the axial direction with a punch, and pressing the molding die of the forming rod against the inner peripheral surface of the sleeve material (for example, patent Reference 2).

  By the way, in recent years, there is an increasing demand for cost reduction for this kind of sintered oil-impregnated bearing. To meet this demand, for example, means for extending the life of a molding die or a dynamic pressure groove molding die are provided. Proposed.

  As a means for achieving a long service life, for example, there is a method of forming a mold with a material excellent in friction resistance and wear resistance. However, in this method, it is necessary to use an expensive material. Since the material is poor in workability, the processing cost of the mold rises, causing a problem in terms of economy.

  As other means for achieving a longer life, for example, a method of chemically or physically modifying the surface of the mold (see, for example, Patent Document 3), or a method of forming an ultra-hard film on the surface of the mold (For example, refer to Patent Document 4). All of these are effective methods for extending the life of the mold, but the above process requires a great deal of cost, and secondary processing after the process is necessary, so an increase in cost is inevitable. . Alternatively, depending on the mold shape and processing method, the above processing may not be performed.

On the other hand, when the above-described sintered oil-impregnated bearing is used in a hydrodynamic bearing device, considering that the hydrodynamic bearing device is used in an environment that requires precision and high cleanliness such as an HDD, The occurrence of contamination due to sliding wear with the spindle shaft is an event that should be suppressed as much as possible.
JP 2003-239951 A Japanese Patent Laid-Open No. 11-182551 JP 2003-253422 A Japanese Patent Laid-Open No. 7-243046

  An object of the present invention is to provide a method for producing a sintered oil-impregnated bearing which suppresses the occurrence of contamination during use while achieving a long life of a mold for molding this kind of sintered oil-impregnated bearing at a low cost. It is to be.

  In order to solve the above-mentioned problems, the present invention compresses a metal powder into a sleeve shape and sinters it, presses the sintered body obtained thereby, and hydrodynamic pressure action of fluid on the inner peripheral surface thereof When manufacturing a sintered oil-impregnated bearing in which a dynamic pressure generating part is formed by plastically deforming the inner peripheral surface by pressing a mold having a shape corresponding to the dynamic pressure generating part for generating Provided is a method for producing a sintered oil-impregnated bearing, characterized by compacting a metal powder added in an amount of 1.5% to 1.5% by weight.

  As described above, a part of the graphite added to the metal powder serving as the raw material powder adheres (transfers) to the mold surface when the molding mold is filled. Graphite adhering to the mold surface acts as a lubricant between the compression molded body and the mold when compressing or releasing metal powder, specifically during compression or mold release. The resulting sliding friction is reduced.

  This type of friction reduction effect can be achieved by using a die such as dimension sizing and rotational sizing after sintering, or molding of a dynamic pressure generating part using a molding die (such as a molding rod) having a shape corresponding to the dynamic pressure generating part. If it is a molding process, it can be enjoyed in the same way. That is, in any case, a part of the graphite on the surface of the sintered body adheres to the mold surface, or the graphite exposed on the surface of the sintered body acts as a lubricant with the mold surface as it is. Thus, the above-mentioned friction reducing effect can be obtained.

  The mold surface to which graphite is attached is maintained by continuously supplying graphite from the metal powder added with graphite to the mold surface, thereby reducing the sliding friction generated between the compact and the mold. The state can be sustained. Therefore, by simply adding graphite to the raw material powder (metal powder), it is possible to extend the service life of the mold at low cost without using expensive mold materials or applying surface treatment that increases processing costs. be able to.

  In order to maintain the state of graphite adhering to the mold surface, it is necessary to add a certain amount of graphite, but considering that the excessively added graphite does not contribute to the friction reduction effect, the addition amount is increased so much. do not have to. Rather, due to an increase in the amount of graphite added, there is a possibility that graphite itself that is not involved in sintering is released from the compact and mixed into the lubricating oil, for example, as contamination. Alternatively, the excessive addition of graphite makes the sintering action between the metal powders insufficient, and the bond strength of the sintered body is reduced. For example, when using a hydrodynamic bearing device equipped with such a sintered oil-impregnated bearing, the shaft and Due to the sliding wear, there is a risk that the graphite or metal component of the surface layer part may fall off.

  Therefore, as a result of detailed investigation of the relationship between the mold life and the wear resistance with respect to the amount of graphite added, the present inventors can achieve both the suppression of mold damage and the suppression of contamination as follows. The optimum range of graphite addition was found.

  That is, the amount of graphite added to the metal powder is preferably 0.1 wt% or more and 1.5 wt% or less. By setting the addition amount to 0.1 wt% or more, it is possible to maintain the state in which the graphite adheres to the mold surface and to surely obtain the friction reducing effect at the time of molding (particularly during compression and mold release). In addition, by suppressing the addition amount to 1.5 wt% or less, graphite that does not participate in sintering is liberated from the sintered body, and due to a decrease in the bond strength of the sintered oil-impregnated bearing, graphite and metal due to wear during use. It is possible to make it difficult for a component to fall off. The addition amount of the graphite is more preferably 0.2 wt% or more and 0.8 wt% or less. This can provide a remarkable friction reduction effect and wear of the graphite and metal components when the sintered oil-impregnated bearing is used. Or, it is possible to prevent the dropout as much as possible.

  In order to solve the above problems, the present invention provides a dynamic pressure that is formed by compressing and molding a metal powder into a sleeve shape and then sintering the fluid, and generating a fluid dynamic pressure action on the inner peripheral surface thereof. The generating part is a sintered oil-impregnated bearing formed by plastic deformation by pressing a molding die having a shape corresponding to the dynamic pressure generating part on the inner peripheral surface of the sintered body, and the graphite is 0.1 wt% or more 1 Provided is a sintered oil-impregnated bearing characterized in that it is contained in an amount of 0.5 wt% or less.

  As described above, according to the sintered oil-impregnated bearing containing graphite, for example, when the sintered oil-impregnated bearing is compression-molded, or when various sizing and dynamic pressure generating parts are molded, the graphite is adhered to the mold surface to be used. Sliding friction between the body and the mold can be reduced. Thereby, the mold life can be extended at low cost. In addition, by adding graphite in advance so that the graphite content is 0.1 wt% or more and 1.5 wt% or less, as described above, it is possible to extend the life of the mold and suppress the occurrence of contamination. A compatible sintered oil-impregnated bearing can be obtained.

  As the dynamic pressure generating portion, for example, a region in which a plurality of circular arc surfaces are arranged in the circumferential direction and a region in which a plurality of axial grooves are arranged in the circumferential direction can be considered, but in addition to this, a configuration in which a plurality of inclined grooves are arranged Can be considered. In the molding process of this type of dynamic pressure generating part, it is necessary to suppress the damage of the mold and at the same time suppress the frictional damage on the molded body side, specifically, the frictional damage of the dynamic pressure generating part forming area as much as possible. It becomes. If the addition amount of graphite is increased, the sliding friction with the mold is reduced, so that the friction reducing effect of the dynamic pressure generating region can be enhanced, but on the other hand, the increase in the addition amount of graphite is The bond strength (sinter strength between metal powders) of the sintered body is reduced. For this reason, when using such a sintered oil-impregnated bearing, the dynamic pressure generating portion forming region easily wears with the sliding contact with the shaft, which may reduce the fluid dynamic pressure action of the dynamic pressure generating portion. . Thus, the addition of graphite causes a trade-off between sliding friction with the mold during molding and sliding wear with the shaft during use.

  On the other hand, as in the present invention, by defining the graphite content (added amount) to be 0.1 wt% or more and 1.5 wt% or less, any of the friction damage during molding and the wear damage during use can be achieved. In addition, the shape of the dynamic pressure generating portion molded with high accuracy can be maintained. As a result, it is possible to exhibit high dynamic pressure bearing performance by suppressing the falling of graphite or the like during use as much as possible, ensuring the cleanliness of the bearing, and suppressing damage to the dynamic pressure generating portion to a small extent. In particular, when forming an inclined groove (dynamic pressure groove) for generating a dynamic pressure action as a dynamic pressure generating portion, the mold for forming the dynamic pressure groove has a larger diameter than other parts. When a rod equipped with a molding die is pulled out of the molded body after forming the dynamic pressure groove, depending on the amount of spring back in the radial direction, the molded dynamic pressure groove region (especially the region between the dynamic pressure grooves) may be damaged. As mentioned above, by defining the optimum addition range of graphite, the mold (molded rod) molded with fine and high precision, and the wear at the time of mold release of the dynamic pressure groove formed thereby are suppressed. This dynamic pressure groove can be formed with high accuracy.

  The sintered oil-impregnated bearing having the above-described configuration can be suitably provided as a hydrodynamic bearing device having the sintered oil-impregnated bearing.

  The hydrodynamic bearing device having the above-described configuration is suitable as a motor equipped with the hydrodynamic bearing device, for example, a magnetic disk drive device such as an HDD, an optical disk drive device such as a CD-ROM or DVD-ROM, or a fan motor. Can be provided.

  As described above, according to the present invention, it is possible to reduce the occurrence of contamination during use of a sintered oil-impregnated bearing while achieving a long life of a mold for molding this kind of sintered oil-impregnated bearing at a low cost. Can do.

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

  FIG. 1 conceptually shows a configuration example of a spindle motor for information equipment incorporating a fluid dynamic bearing device 1 according to an embodiment of the present invention. This spindle motor 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 mounted on the shaft member 2, and a radial direction, for example. The stator coil 4 and the rotor magnet 5 are opposed to each other with a gap therebetween. The stator coil 4 is attached to the outer periphery of the motor bracket 6, and the rotor magnet 5 is attached to the inner periphery of the disk hub 3. The disk hub 3 holds one or a plurality (two in FIG. 1) of a disk-shaped information storage medium (hereinafter simply referred to as a disk) D such as a magnetic disk on its outer periphery. In the spindle motor configured as described above, when the stator coil 4 is energized, the rotor magnet 5 is rotated by an exciting force generated between the stator coil 4 and the rotor magnet 5, and accordingly, the disk hub 3 and the disk are rotated. The disk D held by the hub 3 rotates integrally with the shaft member 2.

  FIG. 2 shows the hydrodynamic bearing device 1. The hydrodynamic bearing device 1 includes a shaft member 2, a housing 7, a bearing sleeve 8 fixed to the housing 7, and a seal member 9 as main components. For convenience of explanation, the bottom 7b side of the housing 7 will be described below, and the side opposite to the bottom 7b will be described as the upper side.

  The shaft member 2 is formed of a metal material such as stainless steel, for example, and includes a shaft portion 2a and a flange portion 2b provided integrally or separately at the lower end of the shaft portion 2a. The shaft member 2 can also have a hybrid structure of a metal material and a resin material. In this case, a portion (upper end portion) including at least a fastening portion of the shaft portion 2a with the disk hub 3 is formed of the metal. The remaining portions (for example, the core portion of the shaft portion 2a and the flange portion 2b) are formed of resin. In order to secure the strength of the flange portion 2b, the flange portion 2b can be made of a resin / metal hybrid structure, and the core portion of the flange portion 2b can be made of metal together with the sheath portion of the shaft portion 2a.

  The housing 7 is injection-molded with a resin composition based on a crystalline resin such as LCP, PPS, PEEK, or a mixture of these crystalline resins with an amorphous resin such as PSU, PES, PEI, etc. As shown in FIG. 2, it is comprised by the side part 7a and the bottom part 7b integrally formed in the lower end of the side part 7a. Examples of the resin composition constituting the housing 7 include fibrous fillers such as glass fibers, whisker-like fillers such as potassium titanate, scaly fillers such as mica, carbon fibers, carbon black, graphite, carbon An appropriate amount of a fibrous or powdery conductive filler such as a nanomaterial or various metal powders can be blended depending on the purpose.

  For example, although not shown, a region in which a plurality of dynamic pressure grooves are arranged in a spiral shape is formed on the entire upper surface 7b1 of the bottom 7b or a partial annular region as a thrust dynamic pressure generating portion. This dynamic pressure groove forming region faces the lower end surface 2b2 of the flange portion 2b, and forms a thrust bearing gap of the second thrust bearing portion T2 between the lower end surface 2b2 when the shaft member 2 rotates (see FIG. 2). reference). This dynamic pressure groove is formed at the same time as the housing 7 by machining the groove mold for forming the dynamic pressure groove in a required part of the mold for molding the housing 7 (the part for molding the upper end surface 7b1). Can do. Further, a step portion 7d that engages with the lower end surface 8c of the bearing sleeve 8 and performs axial positioning is integrally formed at a position that is separated from the upper end surface 7b1 in the axial direction by a predetermined dimension.

  The bearing sleeve 8 is made of a sintered metal porous body mainly composed of Cu or Cu alloy and is formed in a cylindrical shape, and is fixed to the inner peripheral surface 7 c of the housing 7. The bearing sleeve 8 constitutes a sintered oil-impregnated bearing by filling the internal holes with lubricating oil as will be described later.

  A radial dynamic pressure generating portion is formed on the entire inner surface 8a of the bearing sleeve 8 or a partial cylindrical region. In this embodiment, for example, as shown in FIG. 3A, two regions having a plurality of dynamic pressure grooves 8a1 and 8a2 arranged in a herringbone shape are formed apart from each other in the axial direction.

  In the entire or part of the annular region of the lower end surface 8c of the bearing sleeve 8, there is a region where a plurality of dynamic pressure grooves 8c1 are arranged in a spiral shape as a thrust dynamic pressure generating portion, for example, as shown in FIG. It is formed.

  The seal member 9 is formed in an annular shape with, for example, a resin material or a metal material, and is disposed on the inner periphery of the upper end portion of the side portion 7a of the housing 7. An inner peripheral surface 9a of the seal member 9 is opposed to a tapered surface 2a2 provided on the outer periphery of the shaft portion 2a via a predetermined seal space S. The tapered surface 2a2 of the shaft portion 2a is gradually reduced in diameter toward the upper side (outside of the housing 7), and also functions as a capillary force seal and a centrifugal force seal when the shaft member 2 rotates.

  After the shaft member 2 and the bearing sleeve 8 are inserted into the inner periphery of the housing 7 and the bearing sleeve 8 is positioned in the axial direction by the step portion 7d, the bearing sleeve 8 is placed on the inner peripheral surface 7c of the housing 7, for example, It is fixed by means such as adhesion (including loose adhesion and adhesion with press fitting), press fitting, and welding (including ultrasonic welding). The seal member 9 is fixed to the inner peripheral surface 7 c of the housing 7 with the lower end surface 9 b abutting against the upper end surface 8 b of the bearing sleeve 8. Then, the assembly of the hydrodynamic bearing device 1 is completed by filling the internal space of the housing 7 including the internal holes of the bearing sleeve 8 with lubricating oil. At this time, the oil level of the lubricating oil filled in the internal space of the housing 7 sealed with the seal member 9 is maintained within the range of the seal space S.

  When the shaft member 2 rotates, a region (a region where the dynamic pressure grooves 8a1 and 8a2 are formed in the upper and lower portions) of the inner peripheral surface 8a of the bearing sleeve 8 is a radial bearing gap between the outer peripheral surface 2a1 of the shaft portion 2a. Opposite through. As the shaft member 2 rotates, the lubricating oil in the radial bearing gap is pushed into the axial center of each of the dynamic pressure grooves 8a1 and 8a2, and the pressure rises. By such a dynamic pressure action of the dynamic pressure groove, the first radial bearing portion R1 and the second radial bearing portion R2 that support the shaft portion 2a in a non-contact manner are configured.

  At the same time, the thrust bearing gap between the upper end surface 2b1 of the flange portion 2b and the lower end surface 8c (dynamic pressure groove 8c1 formation region) of the bearing sleeve 8 facing the flange portion 2b, and the lower end surface 2b2 of the flange portion 2b and Oil films of lubricating oil are respectively formed in the thrust bearing gaps between the opposed bottom portion 7b and the upper end surface 7b1 (dynamic pressure groove forming region) by the dynamic pressure action of the dynamic pressure grooves. The pressure of these oil films forms a first thrust bearing portion T1 and a second thrust bearing portion T2 that support the flange portion 2b in a non-contact manner so as to be rotatable in both thrust directions.

  Hereinafter, a method for manufacturing a sintered oil-impregnated bearing (bearing sleeve 8) according to an embodiment of the present invention will be described.

  FIG. 4 conceptually shows a process of compression molding metal powder M, which is a raw material of the sintered oil-impregnated bearing (bearing sleeve 8), into a predetermined shape (in this embodiment, the cylindrical shape shown in FIG. 3). The molding apparatus in this embodiment includes a die 11 for molding a location corresponding to the outer peripheral surface of the sintered oil-impregnated bearing after completion, a core rod 12 for molding a location corresponding to the inner peripheral surface, and a location corresponding to the lower end surface. The lower punch 13 to be formed and the upper punch 14 to form a portion corresponding to the upper end surface are configured as main elements.

  The core rod 12 is inserted into the inner periphery of the die 11, and its tip is located above the upper end surface of the die 11. The upper end portion of the lower punch 13 is inserted into the inner periphery of the die 11, and the axial filling amount of the metal powder M is a predetermined value depending on the axial interval from the upper end surface 13 a of the lower punch 13 to the upper end surface of the die 11. Set to

  The metal powder M to be filled is based on the above metal powder, for example, Cu powder or Cu alloy powder, or a mixture of these with Fe powder, and graphite is added to the base metal powder in an amount of 0.1 wt% or more. What added 0.5 wt% or less is used.

  The mold region (cavity) filled with the metal powder M is defined by the inner peripheral surface 11a of the die 11, the outer peripheral surface 12a of the core rod 12, and the upper end surface 13a of the lower punch 13. Is filled with a predetermined amount of metal powder M. At this time, some of the graphite contained in the metal powder M adheres to the inner peripheral surface 11 a of the die 11, the outer peripheral surface 12 a of the core rod 12, and the upper end surface 13 a of the lower punch 13, which serve as a molding surface.

  From the state shown in FIG. 4, first, the upper punch 14 is lowered, and the lower end surface 14a is pressed against the metal powder M being filled. Then, as shown in FIG. 5, the upper punch 14 is further lowered from the position where the lower end surface 14a is pressed (broken line position in the figure), and the metal powder M is compressed from the upper side in the axial direction. Thus, the metal powder M filled in the cavity is compressed in the axial direction in a state in which the radial direction is constrained, and is formed into a compression-molded body Ma having a shape as shown in FIG. 6, for example.

  At this time, the metal powder M compressed in the axial direction by the upper punch 14 and the inner peripheral surface 11a of the die 11 or the outer peripheral surface 12a of the core rod 12 cause sliding friction in the axial direction. At the time, the graphite adhering to the inner peripheral surface 11a of the die 11 and the outer peripheral surface 12a of the core rod 12 reduces the sliding friction between them (between the metal powder M and the inner peripheral surface 11a or the outer peripheral surface 12a).

  Thereafter, as shown in FIG. 6, the core rod 12 and the upper and lower punches 13 and 14 are raised together (relatively moved upward with respect to the die 11), and the upper end surface 13 a of the lower punch 13 is positioned above the die 11. It is raised to the same height as the end face or a position slightly higher than the upper end face. From this position, only the upper punch 14 is raised, and the core rod 12 is lowered, and the core rod 12 is pulled out from the compression molded body Ma. At this time, the sliding adhesion between the outer peripheral surface of the compression molded body Ma is reduced by the graphite adhering to the inner peripheral surface 11a of the die 11, and the compression molded body is performed by the graphite adhering to the outer peripheral surface 12a of the core rod 12. Sliding friction with the inner peripheral surface of Ma is reduced. Therefore, the compression molding body Ma is released from the die 11 and the compression molding body Ma is released from the core rod 12 in a state where the frictional damage of the molding die (die 11 and core rod 12) is suppressed to a small level. be able to.

  A sintered compact is obtained by sintering the compression-molded body Ma formed by the above process at a predetermined sintering temperature. At this time, by setting the graphite content in the sintered body to 1.5 wt% or less, during sintering, the sintering action between the metal powders other than graphite not involved in the sintering is performed without delay, A sintered body having sufficient sintering strength can be obtained. With such a sintered body, when used as a sintered oil-impregnated bearing (bearing sleeve 8), the graphite or metal component of the surface portion of the sintered oil-impregnated bearing is not affected by sliding contact with the shaft member 2, for example. It is possible to prevent as much as possible the situation of falling off due to wear and mixing in the lubricating oil. Thereby, the cleanliness of the hydrodynamic bearing device 1 or the motor including the same can be secured, and the motor can be used stably over a long period of time.

  Although not shown in the figure, the outer periphery and the axial width of the sintered body are corrected to appropriate dimensions by subjecting the sintered body to dimensional sizing and rotational sizing. Also in this case, by attaching graphite on the surface of the sintered body to the surface of the mold used for each sizing, the friction reducing effect of the sizing mold can be obtained as in the case of the compression molding.

  For example, dynamic pressure grooves 8a1 and 8a2 shown in FIG. 3 are molded on the inner peripheral surface of the sintered body that has undergone the sizing process. Hereinafter, an example of the dynamic pressure groove molding process (dynamic pressure groove sizing) for the sintered body 15 will be described with reference to FIGS. In addition, when sizing is not particularly necessary, or when sizing of the sintered body 15 is performed at the same time as forming the dynamic pressure groove in the dynamic pressure groove forming step described later, either of the above sizing or rotational sizing is performed. Alternatively, both can be omitted.

  In the dynamic pressure groove forming step, the dynamic pressure grooves 8a1 and 8a2 are formed on the inner peripheral surface 15a of the sintered body 15 by pressing a forming die having a shape corresponding to the formation region of the finished dynamic pressure grooves 8a1 and 8a2. This is a step of simultaneously molding other regions (regions indicated by cross-hatching in FIG. 3A).

  The processing apparatus used in the dynamic pressure groove forming process of this embodiment includes a die 16 for press-fitting an outer peripheral surface 15b of a cylindrical sintered body 15 and an inner peripheral surface of the sintered body 15 as shown in FIG. The core rod 17 for forming 15a and the upper punch 18 and the lower punch 19 that restrain both end faces of the sintered body 15 from the vertical direction (axial direction) are configured as main elements.

  On the outer periphery of the core rod 17, for example, as shown in FIG. 8, an uneven mold 17 a corresponding to the formation region of the finished dynamic pressure grooves 8 a 1 and 8 a 2 is provided. The depth H of the convex and concave portions of the molding die 17a is approximately the same as the depth of the dynamic pressure grooves 8a1 and 8a2 to be molded. In general, the depth of the convex and concave portions is about several μm to several tens of μm, which is very small compared to the dimensions of the other components. However, in FIG. 8 and FIGS. Therefore, the depth is exaggerated.

  On the outer periphery of the core rod 17, an upper punch 18 is slidably inserted in the vertical direction, and the upper punch 18 moves up and down integrally with the core rod 17. Both can be moved up and down by a common drive source or by independent drive sources. The die 16 is driven up and down independently of the core rod 17 and the upper punch 18 by driving means (not shown). The lower punch 19 is fixed to a stationary member (for example, a pedestal) of the apparatus.

  In the initial state shown in FIG. 7, the die 16 is in the axially lower position with respect to the sintered body 15, and the core rod 17 and the upper punch 18 are in the axially upper position. A lower punch 19 is slidably inserted into the forming hole of the die 16, and the tip of the lower punch 19 protrudes from the upper end of the forming hole of the die 16. The sintered body 15 that is a workpiece is disposed on the upper end surface of the lower punch 19.

  As shown in FIG. 8, the core rod 17 and the upper punch 18 are lowered integrally from the initial state, and the core rod 17 is inserted into the inner periphery of the sintered body 15. Press against the end face. As a result, the sintered body 15 is supported (restrained) from both sides in the axial direction by the upper and lower punches 18 and 19, and the facing distance between the contact end surfaces of the upper and lower punches 18 and 19 with the sintered body 15 is managed to a predetermined value. The The molding die 17a of the core rod 17 is disposed at an axial position on the inner peripheral surface 15a of the sintered body 15 that opposes the region where the dynamic pressure grooves 8a1 and 8a2 are to be formed.

  At this time, an inner diameter gap G exists between the inner peripheral surface 15 a of the sintered body 15 and the convex portion of the molding die 17 a of the core rod 17. Further, a press-fitting allowance P that is the same as the inner diameter gap G or slightly larger than the inner diameter gap G exists between the outer peripheral surface 15b of the sintered body 15 and the inner peripheral surface 16a of the die 16 (both in FIG. 8). reference).

  Next, as shown in FIG. 9, the die 16 is raised while maintaining the axial restraint state, and the sintered body 15 is press-fitted into a molding hole formed on the inner periphery. As a result, the sintered body 15 is deformed by receiving a pressing force from the die 16 and the upper and lower punches 18 and 19, and is sized in the radial direction. Along with this, the inner peripheral surface 15a of the sintered body 15 is pressed against the molding die 17a of the core rod 17, and the surface layer portion from the inner peripheral surface 15a to a predetermined depth causes plastic deformation and bites into the molding die 17a. Thereby, the uneven shape of the molding die 17a is transferred to the inner peripheral surface 15a of the sintered body 15, and both the dynamic pressure grooves 8a1 and 8a2 and the other region (cross-hatching region in FIG. 3A) are molded at the same time. The At this time, the surface of the sintered body 15 is applied to the molding die 17a of the core rod 17 pressed against the inner peripheral surface 15a of the sintered body 15 and the inner peripheral surface 16a of the die 16 pressing the outer peripheral surface 15b of the sintered body 15. Of graphite adheres.

  After the above steps are completed, as shown in FIG. 10, the die 16 is lowered while the axially restrained state by the upper and lower punches 18 and 19 is maintained, the sintered body 15 is removed from the die 16, and the radial compression is performed. Release power. At this time, the die 16 is pulled out (released) with the graphite adhering to the inner peripheral surface 16a of the die 16 being reduced in sliding friction with the outer peripheral surface 15b of the sintered body 15. Further, with release from the die 16, a radial spring back occurs in the sintered body 15, and the core rod 17 can be extracted from the sintered body 15. Next, the upper punch 18 and the core rod 17 are raised together to release the axially restrained state of the sintered body 15. When the upper punch 18 and the core rod 17 reach the initial position (the position shown in FIG. 7), the upper punch 18 is stopped, while the core rod 17 is continuously raised, whereby the core rod 17 is pulled out from the sintered body 15. The sintered body 15 is released. Thereby, the bearing sleeve 8 as a finished product is formed, and the sintered oil-impregnated bearing is completed by impregnating it with the lubricating oil.

  Depending on the amount of springback in the radial direction of the sintered body 15 when the core rod 17 is pulled out, the outer peripheral surface of the core rod 17 (particularly the molding die 17a) and the inner peripheral surface 15a of the sintered body 15 (particularly the dynamic pressure grooves 8a1, A considerable amount of sliding friction may occur with the 8a2 forming region). On the other hand, as in the present embodiment, by using a metal powder to which graphite is added in an amount of 0.1 wt% or more and 1.5 wt% or less as the material of the sintered body 15, the mold 17 a and the dynamic pressure can be obtained. The sliding friction with the groove region is reduced as much as possible. Thereby, the frictional damage of the molding die 17a for the dynamic pressure grooves 8a1 and 8a2 is reduced, and the shape of the dynamic pressure grooves 8a1 and 8a2 molded by the molding die 17a can be maintained with high accuracy. Further, by setting the upper limit of the graphite addition amount to 1.5 wt%, a decrease in the bonding strength of the sintered body 15 is suppressed as much as possible, and the sintered body 15 is used during the sliding friction or when used as a sintered oil-impregnated bearing. It is possible to suppress damage to the formation regions of the dynamic pressure grooves 8a1 and 8a2. Therefore, by preventing the falling of graphite during use as much as possible to ensure the cleanliness of the bearing and minimizing the damage to the dynamic pressure grooves 8a1 and 8a2, high dynamic pressure bearing performance is demonstrated over a long period of time. It becomes possible to do.

  Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment.

  In the above embodiment, the case where a region in which a plurality of dynamic pressure grooves are arranged in a herringbone shape is formed on the inner peripheral surface 8a of the sintered oil-impregnated bearing (bearing sleeve 8) to be formed has been described. The present invention is not limited to the above configuration, and can be similarly applied to a dynamic pressure generating unit having another configuration.

  For example, as a dynamic pressure generating portion molded on the inner peripheral surface 8a, although not shown, axial grooves are formed at a plurality of locations in the circumferential direction, and between the outer peripheral surface 2a1 of the opposing shaft portion 2a. The present invention can be applied to a so-called step bearing in which a radial gap (bearing gap) that changes in a so-called step shape is formed. Alternatively, the present invention is applied to a so-called multi-arc bearing in which a plurality of arc surfaces are arranged in the circumferential direction and a wedge-shaped radial clearance (bearing clearance) is formed between the opposing shaft outer peripheral surfaces 2a1. Can be applied. As a result, the sliding friction of the mold is reduced and the occurrence of contamination during use is suppressed, thereby achieving both a longer life of the mold and ensuring the cleanliness of the hydrodynamic bearing and the motor equipped with the same. can do.

  For example, as shown in FIG. 2, these dynamic pressure generating portions can be provided at two or more locations separated in the axial direction. In this case, these dynamic pressure generating portions are generated in a region between the dynamic pressure generating portions separated in the axial direction. It can also be set as the structure which provided the escape part larger diameter than the internal diameter of a part. For example, although the illustration of the relief portion is omitted, a mold portion having a shape corresponding to the relief portion (larger diameter than other portions) is provided on the outer periphery of the core rod that forms the dynamic pressure generating portion. It is possible to form on the inner peripheral surface of the power sintered body simultaneously with the formation of the dynamic pressure generating portion.

  Moreover, although the above embodiment demonstrated the case where compression molding of the metal powder M was performed by lowering only the upper punch 14 in a state where the axial position of the lower punch 13 was fixed, the upper punch 14 was lowered. Then, after the metal powder M is compressed, it is also possible to raise the lower punch 13 with the upper punch 14 held in the axial position at the time of compression and compress the metal powder M from both axial ends.

  Further, in the above embodiment, the dynamic pressure groove forming for the sintered body 15 is press-fitted into the outer periphery of the sintered body 15 while the sintered body 15 is restrained in the axial direction by the upper and lower punches 18 and 19. However, the present invention is not limited to this, and other methods can be adopted. For example, although illustration is omitted, the upper and lower punches 18 and 19 are relatively brought close to each other in a state where a die having an inner diameter larger than the outer diameter of the sintered body 15 is arranged on the outer periphery of the sintered body 15. The inner peripheral surface 15a may be pressed against the mold 17a of the core rod 17 by pressing from both ends in the direction.

  Further, in the above embodiment, the lubricating oil is exemplified as the fluid that fills the inside of the hydrodynamic bearing device 1 and causes the hydrodynamic action in the radial bearing gap or the thrust bearing gap. It is also possible to use a fluid capable of generating a dynamic pressure in the gas, for example, a gas such as air, a fluid lubricant such as a magnetic fluid, or a lubricating grease.

  In order to demonstrate the effect of the present invention, the influence on the frictional force between the molded body and the mold at the time of mold release in the molding process was evaluated when the addition amount of graphite was changed. Specifically, using a raw powder obtained by adding 0 wt% to 5 wt% of graphite to a metal powder based on Cu and Fe, a tablet-shaped (φ20 mm × L20 mm) compact is manufactured by the floating die method. The frictional force at the time of mold release (the frictional force between the molded body and the die; hereinafter referred to as the slide resistance force) was measured. In addition, the raw material powder having the above composition is molded into actual product dimensions (φ7.5 mm × φ4.0 mm × L9.2 mm), and dimensioned sizing is performed on the molded body, and the mold life with respect to the amount of graphite added The correlation was investigated. Further, the correlation between the amount of wear of the compact and the amount of graphite added was examined. The abrasion test was performed on a molded body having the above dimensions (φ7.5 mm × φ4.0 mm × L9.2 mm) at a surface pressure of 0.3 MPa, a speed of 50 m / min, and a test time of 500 hours. The amount of wear at this time was evaluated by the reduction amount [mg] of the molded body weight after the test relative to the weight of the molded body before the test.

  FIG. 11 shows the results of the friction force measurement test. From the figure, the slide resistance is almost unchanged from 0 wt% to 0.05 wt% of the graphite addition, while the slide resistance increases as the addition amount increases from 0.1 wt% to 1.5 wt%. Decrease. When the addition amount exceeds 1.5 wt%, the slide resistance shows a constant value with almost no decrease.

  12 and 13 show the results of the mold life and sizing life test. From the figure, in both cases, a certain correlation was found between the life of the molding die and the sizing die and the amount of graphite added, and a high correlation was also obtained between the sliding resistance force. From this, it can be seen that the effect of reducing the sliding resistance by adding graphite greatly contributes to the extension of the life of the mold.

  FIG. 14 shows the results of the wear test. From the figure, the amount of weight reduction of the compact increases as the amount of graphite added increases. If it is 1.5 wt% or less, the rate of decrease is relatively gradual, but if it exceeds 1.5 wt%, the rate of decrease in the weight of the molded product increases significantly. From this, it is estimated that the amount of contamination generated increases significantly at 1.5 wt%.

1 is a cross-sectional view of a spindle motor for information equipment incorporating a fluid dynamic bearing device according to an embodiment of the present invention. It is sectional drawing of a hydrodynamic bearing apparatus. 2A is a longitudinal sectional view of the bearing sleeve, and FIG. It is a figure which shows notionally the compression molding process of the bearing sleeve used as a sintered oil-impregnated bearing. It is a figure which shows notionally the compression molding process of a bearing sleeve. It is a figure which shows notionally the compression molding process of a bearing sleeve. It is a figure which shows notionally the process of die-molding a dynamic-pressure generation | occurrence | production part on the internal peripheral surface of a bearing sleeve. It is a figure which shows notionally the process of die-molding a dynamic-pressure generation | occurrence | production part on the internal peripheral surface of a bearing sleeve. It is a figure which shows notionally the process of die-molding a dynamic-pressure generation | occurrence | production part on the internal peripheral surface of a bearing sleeve. It is a figure which shows notionally the process of die-molding a dynamic-pressure generation | occurrence | production part on the internal peripheral surface of a bearing sleeve. It is a figure which shows the result of a friction force measurement test. It is a figure which shows the result of a shaping die lifetime measurement test. It is a figure which shows the result of a sizing metal mold | die lifetime measurement test. It is a figure which shows the result of an abrasion test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dynamic pressure bearing apparatus 2 Shaft member 3 Disc hub 4 Stator coil 5 Rotor magnet 6 Motor bracket 7 Housing 8 Bearing sleeve (sintered oil-impregnated bearing)
8a Inner peripheral surfaces 8a1, 8a2 Dynamic pressure groove 9 Seal member 11 Die 12 Core rod 13 Lower punch 14 Upper punch 15 Sintered body 15a Inner peripheral surface 16 Die 17 Core rod 17a Mold 18 Lower punch 19 Upper punch M Metal powder Ma Compression molding Body R1, R2 Radial bearing part T1, T2 Thrust bearing part

Claims (5)

The metal powder is compressed into a sleeve shape and then sintered, and the resulting sintered body is pressed to correspond to a dynamic pressure generating portion for generating a dynamic pressure action of fluid on the inner peripheral surface. When manufacturing a sintered oil-impregnated bearing in which a dynamic pressure generating portion is formed by plastically deforming the inner peripheral surface by pressing a shape-shaped mold,
A method for producing a sintered oil-impregnated bearing, comprising compacting a metal powder to which graphite is added in an amount of 0.1 wt% to 1.5 wt%. A dynamic pressure generating part for generating a fluid dynamic pressure action on the inner peripheral surface of the metal powder is formed on the inner peripheral surface of the sintered body by compressing the metal powder into a sleeve shape and then sintering it. A sintered oil-impregnated bearing formed by plastic deformation by pressing a mold having a shape corresponding to the pressure generating part,
A sintered oil-impregnated bearing comprising 0.1 wt% or more and 1.5 wt% or less of graphite.   The sintered oil-impregnated bearing according to claim 2, wherein a plurality of inclined grooves are arranged as the dynamic pressure generating portion.   A hydrodynamic bearing device comprising the sintered oil-impregnated bearing according to claim 2.   A motor comprising the hydrodynamic bearing device according to claim 4.

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