JP5085035B2 - Sintered metal material, sintered oil-impregnated bearing, fluid bearing device, and motor - Google Patents

Description

The present invention can be obtained by compression molding a metal powder, sintering to sintered metal material obtained comprises oil-impregnated sintered bearing which is formed of a metal material this, a fluid bearing device having the bearing, and the bearing device Related to the motor .

  Sintered metal materials are used in many other fields including the above-mentioned sintered oil-impregnated bearings. Among them, in the sintered oil-impregnated bearing, along with the relative rotation with the shaft to be supported, the lubricating fluid impregnated inside exudes to the sliding portion with the shaft to form a lubricating film, and through this oil film the shaft And is preferably used in places where particularly high bearing performance and durability are required, such as automobile bearing parts and motor spindles for information equipment.

  Usually, this kind of sintered oil-impregnated bearing was obtained by compression molding a metal powder mainly composed of Cu powder or Fe powder or both into a predetermined shape (mostly cylindrical) and then sintering. It is formed by impregnating a porous body with a fluid such as lubricating oil or lubricating grease (see, for example, Patent Document 1).

On the other hand, the shaft supported for rotation is formed of a high-strength material such as stainless steel (SUS) in consideration of the case where it is used under an axial compressive load action or a moment load action.
Japanese Patent Laid-Open No. 11-182551

  In this type of sintered oil-impregnated bearing, sliding friction with the shaft to be supported is inevitable, so the sliding surface (bearing surface) with the shaft has good slidability and high wear resistance. Is required.

  However, a sintered oil-impregnated bearing formed of the above materials (Cu, Fe powder) shows good results with respect to sliding properties (compatibility) with the shaft, but is always good with respect to wear resistance. Not exclusively. In particular, when the counterpart material is formed of a material having higher hardness (for example, SUS), there is a possibility that the wear of the sintered oil-impregnated bearing may proceed early.

  An object of the present invention is to provide a sintered metal material having improved slidability and wear resistance with respect to a sliding partner material to be supported, and a sintered oil-impregnated bearing formed of the metal material.

In order to solve the above-mentioned problems, the present invention compression-molds mixed metal powder comprising Cu powder, SUS powder, and low melting point metal powder that can be melted at a temperature lower than the sintering temperature that is less than the melting point of Cu powder. After that, the mixed metal powder further includes graphite as a solid lubricant, and provides a sintered metal material in which the upper limit of the amount of graphite is 2.5 wt%. To do. The Cu powder referred to here includes pure Cu powder, Cu alloy powder with other metals, or Cu-coated metal powder in which a Cu coating layer is formed on the surface layer of other metal particles.

  Further, in order to solve the above-mentioned problems, the present invention is formed of a sintered metal material made of the above mixed metal powder, and supports the sliding surface of the shaft to be supported on the inner periphery thereof through a fluid lubricating film. A sintered oil-impregnated bearing provided with a bearing surface is provided.

  Thus, the hardness of the shaping | molding surface (bearing surface of a sintered oil-impregnated bearing) of a sintered metal material improves by mix | blending SUS powder. On the other hand, good slidability (compatibility) of the molding surface (bearing surface) with respect to the sliding counterpart material (shaft) is ensured by blending Cu powder. Therefore, by forming a sintered metal material with the mixed metal powder containing both powders, or forming a sintered oil-impregnated bearing with this sintered metal material, the wear resistance against the sliding counterpart material can be improved. At the same time, it is possible to obtain good sliding characteristics (low friction property, low loss torque property) with respect to the sliding counterpart material.

  Various types of SUS powder can be used. Among them, for example, a SUS powder containing 5 wt% to 16 wt% of Cr is preferably used, and a SUS powder containing 6 wt% to 10 wt% of Cr is more preferable. It can be used. This is because when the content of Cr present in the alloyed state in the SUS powder exceeds 16 wt%, the secondary formability (formability after sintering) of the sintered material or the strength of the sintered material is adversely affected. It is because there is a risk of affecting. Moreover, if the Cr content is less than 5 wt%, the hardness of the SUS powder formed by blending it becomes insufficient, and the effect of improving the wear resistance may not be obtained.

  As the mixed metal powder containing Cu powder and SUS powder, those containing 5 wt% to 95 wt% of Cu powder and 5 wt% to 95 wt% of SUS powder are preferable. This is because if the content of the SUS powder is less than 5 wt%, the effect of improving the wear resistance due to the blending of the SUS powder may be insufficient. Moreover, it is because there exists a possibility that favorable slidability (familiarity with a sliding other material) with Cu powder may not be ensured when content of Cu powder is less than 5 wt%.

  As a compound that can be further added to the mixed metal powder containing Cu powder and SUS powder, for example, there is a powder of a low melting point metal (a metal that melts at a temperature equal to or lower than the sintering temperature, including an alloy). This is because by mixing a metal powder that can be melted at a sintering temperature that is usually set below the melting point of Cu powder or SUS powder, the molten (liquid phase) metal is between Cu powder, or Cu, SUS powder. It aims to act as a binder. This makes it possible to increase the mechanical strength of the sintered metal material after sintering or the sintered oil-impregnated bearing.

  The low melting point metal may be any metal that melts at a predetermined sintering temperature (sintering temperature of the sintered oil-impregnated bearing is usually 750 to 1000 ° C.) or less, such as Sn, Zn, Al, P, and the like. A metal or an alloy containing two or more of these can be used. Among them, Sn is particularly preferable because it has an action of alloying with Cu in a liquid phase state and increasing the hardness of the surface of the sintered metal material (the bearing surface of the sintered oil-impregnated bearing).

  When a low melting point metal powder is further blended with the raw metal powder containing Cu powder and SUS powder, the blending ratio is Cu powder: 5 wt% or more and 94.8 wt% or less, SUS powder: 5 wt% or more and 94.8 wt% % Or lower, low melting point metal powder: 0.2 wt% or more and 10 wt% or less.

  Moreover, in order to further improve the sliding characteristics on the sliding surface, a solid lubricant such as graphite can be further blended with the mixed metal powder. However, graphite has a very poor bonding property to a metal powder such as Cu during sintering, and therefore blending graphite may cause a decrease in strength of the sintered body. Therefore, it is necessary to pay attention to the blending amount.

  From the above viewpoint, the upper limit of the amount of graphite was set to 2.5 wt%. By suppressing the blending amount of graphite within this range, it is possible to minimize the decrease in strength of the sintered metal material and the sintered oil-impregnated bearing obtained by sintering them. On the other hand, considering the point that the aggressiveness to the mold during molding is increased by blending SUS powder harder than other metals, the lower limit of the blending amount of graphite is 0.5 wt% or more. preferable. Thereby, the slidability with respect to the metal mold | die at the time of shaping | molding can be improved, and the damage accompanying continuous use of a metal mold can be reduced.

  In this case, the total blending ratio is Cu powder: 5 wt% or more and 94.5 wt% or less, SUS powder: 5 wt% or more and 94.5 wt% or less, and graphite: 0.5 wt% or more and 2.5 wt% or less. Good. Further, when a low melting point metal powder is also blended, the blending ratio is as follows: Cu powder: 5 wt% to 94.3 wt%, SUS powder: 5 wt% to 94.3 wt%, graphite: 0.5 wt% to 2 0.5 wt% or less, low melting point metal powder: 0.2 wt% or more and 10 wt% or less is preferable.

  A sintered oil-impregnated bearing formed of a sintered metal material having the above composition may have a structure in which a dynamic pressure generating portion is formed on a bearing surface provided on the inner periphery thereof. In this case, the sintered oil-impregnated bearing rotatably supports the shaft in a non-contact manner by the dynamic pressure action of the fluid generated in the bearing gap with the shaft to be supported.

  The sintered oil-impregnated bearing can be provided as a fluid bearing device having a sintered oil-impregnated bearing, for example. The hydrodynamic bearing device can also be provided as a motor including the hydrodynamic bearing device.

  As described above, according to the present invention, it is possible to provide a sintered metal material with improved wear resistance and slidability with respect to the shaft to be supported, and a sintered oil-impregnated bearing formed of this metal material.

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

  FIG. 1 shows a configuration example of a hydrodynamic bearing device (dynamic pressure bearing device) 1 including a sintered oil-impregnated bearing according to an embodiment of the present invention, and a spindle motor for information equipment incorporating the hydrodynamic bearing device 1. It shows conceptually. 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. A stator coil 4 and a rotor magnet 5 are provided to face each other through a gap. 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 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. In addition, the shaft member 2 can also have a hybrid structure of a metal material and a resin material. In this case, the sheath portion including at least the outer peripheral surface 2a1 of the shaft portion 2a is formed of the metal, and the remaining portion (for example, the shaft portion) The core part of the part 2a and the flange part 2b) are formed of resin.

  The housing 7 is injection-molded with a resin composition having LCP, PPS, PEEK or the like as a base resin. For example, as shown in FIG. 2, a cylindrical portion 7 a and a bottom portion 7 b integrally formed at the lower end of the cylindrical portion 7 a Consists of. 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 and the shaft member 2 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 SUS 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 dynamic pressure groove as 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 formation region of the upper dynamic pressure groove 8a1, the dynamic pressure groove 8a1 is formed to be axially asymmetric with respect to the axial center m (the axial center of the upper and lower inclined groove regions). The axial dimension X1 of the upper region is larger than the axial dimension X2 of the lower region.

  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 bearing sleeve 8 is formed by compressing a mixed metal powder containing Cu powder (or Cu alloy) powder, SUS powder, and Sn powder as a low melting point metal powder into a cylindrical shape and sintering it at a predetermined sintering temperature. It is obtained by. In this embodiment, rotational sizing and groove sizing of the inner peripheral surface 8a are further performed, whereby dynamic pressure grooves 8a1, 8c1 and the like are formed on the outer surface of the sintered body. In addition, by performing dimension sizing before rotational sizing and groove sizing, each sizing process in the subsequent process can be performed with high accuracy. In addition, for example, the Sn powder can be coated on the surface of the Cu powder (by using the Sn-coated Cu powder), thereby simplifying the powder mixing step and being uniformly dispersed between the Cu powders during sintering. Since it becomes a state, the binder effect can be further enhanced.

  The size of the Cu powder used as the material of the bearing sleeve 8 is preferably equal to or less than that of the SUS powder. Moreover, the compounding ratio of Cu powder, SUS powder, and Sn powder in this embodiment is Cu powder: 40 wt% to 94.5 wt%, SUS powder: 5 wt% to 50 wt%, Sn powder: 0.5 wt% It is preferably 10 wt% or less. This is because if the blending amount of the SUS powder is less than 5 wt%, the effect of improving the wear resistance by the SUS powder is not sufficient, and if it exceeds 50 wt%, the sizing process after sintering, particularly the dynamic pressure grooves 8a1, 8c1, etc. This is because it becomes difficult to form the groove.

  Further, for the purpose of improving the moldability at the time of compression molding or the sliding property of the finished product, a solid lubricant such as graphite can be further blended with the mixed metal powder. In this case, if the amount of graphite is too large, the graphite hinders the sintering action between the metal powders, which may reduce the strength of the sintered body. Further, when the bearing sleeve 8 (fluid bearing device 1) is used, other metal powder and unbound graphite may be released from the bearing sleeve 8 and mixed into the lubricating oil as contamination. Considering these points, it is preferable to set the upper limit of the amount of graphite to 2.5 wt%.

  On the other hand, if the blending amount of graphite is too small, there is a possibility that an adverse effect on moldability due to blending of SUS powder cannot be covered. In other words, by blending SUS powder with poor sinterability with other metals, the molded body (sintered body) itself becomes brittle, so that the detachment force from the mold that occurs during secondary molding such as sizing, for example, during mold release Etc., the sintered body is easily damaged. In particular, during sizing of the groove, the core rod for forming the dynamic pressure grooves 8a1 and 8a2 is pulled out by expanding the inner peripheral surface 8a due to the spring back of the sintered body. If the bonded body is poor in slidability, a large pulling force (resistance force) acts on the dynamic pressure grooves 8a1, 8a2 or the surrounding area. Therefore, if the sintered body is brittle, defects are easily generated. In this case, the molding accuracy of the dynamic pressure grooves 8a1 and 8a2 may be insufficient, and a sufficient dynamic pressure action may not be exhibited.

  From the above viewpoint, it is preferable that the lower limit of the blending amount of graphite is 0.5 wt% or more. Thereby, the slidability with respect to the metal mold | die at the time of shaping | molding can be improved, and damage to a metal mold | die can be reduced. Further, by smoothing the removal of the core rod at the time of releasing in the groove sizing process, the removal force (resistance force) acting on the sintered body, in particular, the dynamic pressure grooves 8a1 and 8a2 and the surrounding area is suppressed to a small level. The molding accuracy of the dynamic pressure grooves 8a1 and 8a2 can be improved. In particular, when the dynamic pressure grooves 8a1 and 8a2 are provided in the bearing sleeve 8 as in this embodiment, the dynamic pressure grooves 8a1 are formed by the graphite entering the gaps (holes) between the metal powders neck-bonded to each other by sintering. , 8a2 can reduce the escape of dynamic pressure. Therefore, bearing performance (bearing rigidity) can be further enhanced.

  In this case, the total blending ratio is Cu powder: 40 wt% or more and 94 wt% or less, SUS powder: 5 wt% or more and 50 wt% or less, Sn powder: 0.5 wt% or more and 10 wt% or less, Graphite: 0.5 wt% or more. It should be 5 wt% or less.

  The temperature during sintering (sintering temperature) is preferably 750 ° C. or higher and 1000 ° C. or lower, and more preferably 800 ° C. or higher and 950 ° C. or lower. This is because when the sintering temperature is less than 750 ° C., the sintering action between the powders is not sufficient, so the strength of the sintered body is reduced. When the sintering temperature exceeds 1000 ° C., for the same reason as described above, that is, during sizing processing This is because there is a risk of disturbing the groove formability.

By forming the sintered body in this way, the roundness of the inner peripheral surface and the outer peripheral surface of the sintered body after sizing, or the groove depth of the dynamic pressure grooves 8a1 and 8c1 can be finished with high accuracy. . Finally, the sintered body is impregnated with lubricating oil (usually after being fixed to the housing 7), thereby completing a bearing sleeve 8 as a sintered oil-impregnated bearing. The density of the bearing sleeve 8 as a finished product is, for example, 7.0 to 7.4 [g / cm ³ ], and the surface opening ratio of the inner peripheral surface is 2 to 10 [vol%]. In this way, by using a mixed metal powder containing a predetermined proportion of Cu powder and SUS powder, a bearing sleeve (sintered) excellent in the slidability and hardness of the bearing surface, or the mechanical strength and workability of the main body. Oil-impregnated bearing) 8 can be obtained.

  In this embodiment, as the SUS powder contained in the mixed metal powder, for example, a powder containing 5 wt% or more and 16 wt% or less of Cr is used. By using SUS powder alloyed with Cr within this range, the wear resistance is improved and the formability after sintering (sizing workability, formability of the dynamic pressure grooves 8a1 and 8c1), and the strength of the sintered body And the bearing sleeve 8 having a higher level. Further, when the bearing sleeve 8 having the dynamic pressure grooves 8a1 and 8a2 is formed as in this embodiment, among the SUS powders containing Cr within the above range, particularly the SUS powder containing 6 wt% or more and 10 wt% or less of Cr. (For example, SUS powder containing 8 wt% Cr) is preferable. By using a SUS powder alloyed with Cr within this range, it is possible to easily adjust the surface opening ratio by rotational sizing while imparting an appropriate hardness to the bearing surface of the bearing sleeve 8, and The workability (formability) of the dynamic pressure grooves 8a1 and 8a2 can be further improved.

  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 cylindrical portion 7 a 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, Fix by means of adhesion, press-fitting, welding, etc. 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 with lubricating oil. At this time, the oil level of the lubricating oil filled in the internal space of the housing 7 (including the internal holes of the bearing sleeve 8) sealed by 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 toward the axial center m of the dynamic pressure grooves 8a1 and 8a2, and the pressure rises. 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 by the dynamic pressure action of the dynamic pressure groove.

  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.

  When the rotation of the shaft member 2 starts or stops, contact sliding occurs between the shaft portion outer peripheral surface 2a1 of the shaft member 2 and the inner peripheral surface 8a (radial bearing surface thereof) of the bearing sleeve 8 opposed thereto. Even when the bearing sleeve 8 is made of a mixed metal powder containing Cu powder and SUS powder, the hardness of the radial bearing surface serving as the sliding surface can be increased. As a result, the difference in hardness between the two surfaces 2a1 and 8a is reduced, and the situation where one or both of the bearing sleeve 8 and the shaft portion 2a of the shaft member 2 are in contact with each other and wear is minimized. Can be prevented. In particular, when the disc hub 3 and the disc D are mounted on the upper portion of the shaft member 2 as in this embodiment, a moment load acts on the shaft member 2, and the shaft member 2 and the bearing sleeve 8 contact at the upper end of the bearing. Although it is easy to slide, the sliding wear between the two members 2a and 8 can be suppressed as much as possible by reducing the hardness difference between the two members 2a and 8 (the hardness difference between both sliding surfaces 2a1 and 8a).

  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 cylindrical portion 7a and the bottom portion 7b are integrally molded with the resin as the housing 7. However, for example, although not shown, the cylindrical portion 7a is separated from the bottom portion 7b. It can also be molded with resin. In this case, for example, the seal member 9 can be molded integrally with the cylindrical portion 7a from resin, and according to this, the axial positioning of the bearing sleeve 8 can be performed under the seal portion molded integrally with the cylindrical portion 7a. This can be done by bringing the upper end surface 8b of the bearing sleeve 8 into contact with the end surface.

  Moreover, although the case where the thrust bearing part was provided in the bottom part 7b side of the housing 7 was demonstrated in the above embodiment, for example, it is also possible to provide in the opposite side (opening side of the housing 7) from the bottom part 7b. . In this case, for example, although not shown, a metal (for example, stainless steel) flange portion 2b is formed above the lower end of the shaft portion 2a, and the lower end surface 2b2 of the flange portion 2b is formed on the upper end surface 8b of the bearing sleeve 8. While making it face, a dynamic pressure groove (direction opposite) similar to the dynamic pressure groove 8c1 is formed on the entire upper surface 8b or a partial annular region. Thereby, a thrust bearing gap is formed between both surfaces 8b and 2b2.

  When the rotation of the shaft member 2 is started or stopped, contact sliding occurs between the lower end surface 2b2 of the flange portion 2b and the upper end surface 8b of the bearing sleeve 8 (the region serving as a thrust bearing surface thereof) facing the flange portion 2b. However, in this case as well, the hardness of the upper end surface 8b including the thrust bearing surface can be increased by forming the bearing sleeve 8 with a mixed metal powder containing Cu powder and SUS powder. As a result, the difference in hardness between the two surfaces 2b2 and 8b is reduced, and the situation where one or both of the bearing sleeve 8 and the flange portion 2b of the shaft member 2 wear in contact with each other is worn as much as possible. Can be prevented.

  In the above embodiment, the radial bearing portions R1 and R2 and the thrust bearing portions T1 and T2 are configured to generate the dynamic pressure action of the lubricating fluid by the herringbone shape or spiral shape dynamic pressure grooves. However, the present invention is not limited to this.

  For example, so-called step bearings or multi-arc bearings may be employed as the radial bearing portions R1 and R2.

  FIG. 4 shows an example in which one or both of the radial bearing portions R1 and R2 are constituted by multi-arc bearings. In the same figure, the area | region used as the radial bearing surface of the internal peripheral surface 8a of the bearing sleeve 8 is comprised by several arc surface 8a3 (this figure 3 arc surface). Each arc surface 8a3 is an eccentric arc surface centered at a point offset from the rotation axis O by an equal distance, and is formed at equal intervals in the circumferential direction. An axial separation groove 8a4 is formed between each eccentric arc surface 8a3.

  By inserting the shaft portion 2a of the shaft member 2 into the inner peripheral surface 8a of the bearing sleeve 8, the eccentric arc surface 8a3 and the separation groove 8a4 of the bearing sleeve 8 and the perfect circular outer peripheral surface 2a1 of the shaft portion 2a are interposed. The radial bearing gaps of the first and second radial bearing portions R1 and R2 are respectively formed. In the radial bearing gap, a region formed by the eccentric arc surface 8a3 and the perfect circular outer peripheral surface 2a1 is a wedge-shaped gap 8a5 in which the gap width is gradually reduced in the circumferential direction. The reduction direction of the wedge-shaped gap 8a5 coincides with the rotation direction of the shaft member 2.

  FIG. 5 shows another embodiment of the multi-arc bearing constituting the first and second radial bearing portions R1 and R2. In this embodiment, in the configuration shown in FIG. 4, the predetermined region θ on the minimum gap side of each eccentric arc surface 8 a 3 is configured by concentric arcs with the rotation axis O as the center. Accordingly, the radial bearing gap (minimum gap) 8a6 in each predetermined region θ is constant. The multi-arc bearing having such a configuration may be referred to as a tapered flat bearing.

  In FIG. 6, a region that becomes a radial bearing surface of the inner peripheral surface 8 a of the bearing sleeve 8 is formed by three arc surfaces 8 a 7, and the centers of the three arc surfaces 8 a 7 are offset from the rotation axis O by an equal distance. Yes. In each region defined by the three eccentric arc surfaces 8a7, the radial bearing gap 8a8 has a shape that is gradually reduced with respect to both circumferential directions.

  The multi-arc bearings of the first and second radial bearing portions R1 and R2 described above are all so-called three-arc bearings, but are not limited thereto, so-called four-arc bearings, five-arc bearings, and more than six arcs. You may employ | adopt the multi-arc bearing comprised by the several circular arc surface. In addition to the configuration in which the two radial bearing portions are provided apart in the axial direction as in the radial bearing portions R1 and R2, one radial bearing portion extends over the upper and lower regions of the inner peripheral surface 8a of the bearing sleeve 8. It is good also as a structure which provided.

  One or both of the thrust bearing portions T1 and T2, for example, are not shown in the figure, but a plurality of radial groove-shaped dynamic pressure grooves are provided at predetermined intervals in the circumferential direction in a region serving as a thrust bearing surface. It can also be constituted by a step bearing, a so-called corrugated bearing (the corrugated step mold) or the like.

  Moreover, although the radial bearing part R1 and R2 and the thrust bearing part T1 and T2 were comprised by the dynamic pressure bearing in the above embodiment, it can also comprise by bearings other than this. For example, the inner peripheral surface 8a of the bearing sleeve 8 serving as a radial bearing surface is a perfect circular inner peripheral surface not provided with the dynamic pressure groove 8a1 or the circular arc surface 8a3 as a dynamic pressure generating portion, and the shaft portion opposed to the inner peripheral surface A so-called perfect circle bearing can be constituted by the perfect circular outer peripheral surface 2a1 of 2a.

  In the case of a perfect circle bearing, the preferable mixing ratio of Cu powder is 30 wt% or more and 80 wt% or less. Here, the lower limit is set to 30 wt%, as compared to the bearing sleeve 8 in which the dynamic pressure groove 8a1 as the dynamic pressure generating portion is formed on the inner peripheral surface, the perfectly circular inner peripheral surface slides at the time of contact sliding. This is because the moving area is large and the loss torque at the start of rotation (when stopped) increases.

  The perfect circle bearing is not limited to the hydrodynamic bearing device 1 and can be used as a bearing component for, for example, a small motor or an office machine.

  Further, in the above embodiment, the lubricating oil is exemplified as the fluid that fills the inside of the hydrodynamic bearing device 1 and forms a lubricating film in the radial bearing gap or the thrust bearing gap. A fluid capable of forming a lubricating film, for example, a gas such as air, a fluid lubricant such as a magnetic fluid, or lubricating grease may be used.

  In order to demonstrate the effect of the present invention, a sintered metal material (practical product) formed of a mixed metal powder containing Cu powder and SUS powder, and a metal powder of a conventional composition (mixed powder of Cu powder and Fe powder) Each of the sintered metal materials (comparative products) formed in (1) was subjected to a wear test, and the wear resistance was evaluated and compared.

  As test materials, CE-15 manufactured by Fukuda Metal Foil Powder Co., Ltd. was used as Cu powder, DAP410L manufactured by Daido Steel Co., Ltd. as SUS powder, and NC100. 24 were used. In addition, Sn-At-W350 manufactured by Fukuda Metal Foil Powder Co., Ltd. is used for Sn powder as a low melting point metal powder, and ECB-250 manufactured by Nippon Graphite Industry Co., Ltd. is used as graphite as a solid lubricant. Using. The sintering temperature of the test piece (sintered metal material) was 870 ° C. for both the comparative product and the implementation product. The composition of each of the mixed metal powders of the comparative product and the practical product is as shown in FIG. Further, the particle size distribution of each powder is as shown in FIG.

The abrasion test was performed under the following conditions for both the comparative product and the implementation product.
Specimen size: 7.5mm outer diameter x 10mm axial width
Counter specimen Material: SUS420J2
Dimensions: 40mm outer diameter x 4mm axial width
Peripheral speed: 50 m / min
Surface pressure: 1.3 MPa
Lubricating oil; ester oil (12 mm ² / s)
Test time: 3 hrs

  FIG. 9 shows the wear test results. As shown in the figure, remarkable wear was confirmed in the sintered metal material (comparative product) not containing SUS powder. On the other hand, the wear amount (wear depth, wear scar area) in the sintered metal material (practical product) formed of metal powder containing SUS powder is very small compared to the conventional composition product (comparative product). It was a thing. From this, it was confirmed that the sintered metal material according to the present invention significantly reduces the amount of wear.

1 is a cross-sectional view of a spindle motor for information equipment incorporating a hydrodynamic 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 sectional drawing which shows the other structural example of a radial bearing part. It is sectional drawing which shows the other structural example of a radial bearing part. It is sectional drawing which shows the other structural example of a radial bearing part. It is a figure which shows a composition of test piece material. It is a figure which shows the particle size distribution of powder. It is a figure which shows an abrasion test result.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fluid bearing apparatus 2 Shaft member 3 Disc hub 4 Stator coil 5 Rotor magnet 6 Bracket 7 Housing 8 Bearing sleeve (sintered oil-impregnated bearing)
8a1, 8a2 Dynamic pressure groove 8c1 Dynamic pressure groove 9 Seal member S Seal space R1, R2 Radial bearing portion T1, T2 Thrust bearing portion

Claims (8)

It was obtained by compressing and then sintering a mixed metal powder containing Cu powder, SUS powder, and a low melting point metal powder that can be melted at a temperature lower than the sintering temperature that is less than the melting point of the Cu powder. And
The mixed metal powder further includes graphite as a solid lubricant, and is a sintered metal material in which the upper limit of the amount of graphite is 2.5 wt% . Sintered metal material according to claim 1, wherein the lower limit of the amount of the graphite was 0.5 wt%. The mixed metal powder, and 5 wt% or more 94.3 wt% or less of the Cu powder, and 5 wt% or more 94.3 wt% or less of the SUS powder, 0.2 wt% or more to 10wt% of the low melting point metal powder The sintered metal material according to claim 2 , comprising:   The sintered metal material according to claim 1, wherein the SUS powder contains 5 wt% or more and 16 wt% or less of Cr. A sintered body formed of the sintered metal material according to any one of claims 1 to 4 , wherein a bearing surface for supporting a sliding surface of a shaft to be supported through a fluid lubricating film is provided on an inner periphery thereof. Oil-impregnated bearing. The sintered oil-impregnated bearing according to claim 5, wherein a dynamic pressure generating portion is formed on the bearing surface. A hydrodynamic bearing device comprising the sintered oil-impregnated bearing according to claim 5 . A motor comprising the hydrodynamic bearing device according to claim 7 .

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