JP2010223246A - Sintered metal bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sintered metal bearing having excellent wear resistance and sintering strength. <P>SOLUTION: The sintered metal bearing is provided by compressing and molding material powder including at least Cu powder, SUS powder and pure Fe powder, and then by sintering the compression molding body at a predetermined temperature. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a sintered metal bearing obtained by compression molding metal powder and then sintering.

  Sintered metal bearings are suitably used as sintered oil-impregnated bearings in which internal pores are impregnated with lubricating oil, etc., and have excellent bearing performance and durability such as automotive bearing parts and motor spindles for information equipment. Used in places where sex is required.

  For example, as disclosed in Patent Document 1 below, this type of bearing is formed by compressing a metal powder mainly composed of Cu powder and / or Fe powder or both into a predetermined shape (mostly cylindrical), and then firing it. The porous body obtained by bonding is formed by impregnating a fluid such as lubricating oil or lubricating grease.

  Patent Document 2 below discloses a sintered oil-impregnated bearing obtained by compressing and molding a mixed metal powder containing Cu powder and SUS powder and then sintering.

Japanese Patent Laid-Open No. 11-182551 JP 2006-214003 A

  By the way, recently, as represented by an increase in the capacity of HDDs, for example, in various information equipment motors, the spindle including the information storage medium is increased in weight for the purpose of increasing the amount of information processing. Tend to. For this reason, the sintered metal bearing used by being incorporated in this type of motor for information equipment is required to have higher wear resistance than ever before. From this point of view, it seems that a sintered metal bearing containing SUS powder is effective as disclosed in Patent Document 2 above, but SUS powder is poor in sinterability with other metal powders. Therefore, there is a possibility that sufficient sintering strength cannot be obtained simply by blending SUS powder.

  In view of the above circumstances, in the present specification, it is a technical problem to be solved to provide a sintered metal bearing that has excellent wear resistance and can exhibit high sintering strength.

  The present invention has been made to solve the above problems. That is, the sintered metal bearing according to the present invention is obtained by compression-molding and sintering a raw material powder containing a plurality of metal powders, and has a large number of pores capable of containing oil inside. In the bearing, the raw material powder is characterized in that it contains Cu powder, SUS powder, and pure Fe powder. Here, “pure Fe powder” refers to high-purity iron powder used industrially, and includes, for example, one having a purity of 99% or more.

  In this way, by adding pure Fe powder to Cu powder and SUS powder with excellent sliding characteristics and workability, the excellent wear resistance of SUS powder is expressed in the sintered product. While being possible, a sintered metal bearing having high sintering strength can be obtained by reinforcing the poor sinterability of SUS powder and other powders with pure Fe powder. Particularly in this type of bearing, since it is necessary to leave a large number of pores for oil impregnation inside, there is a situation where the density at the time of compression molding cannot be set so high. By blending pure Fe powder excellent in compressibility, desired sintering strength (for example, indicated by crushing strength) can be obtained while securing a considerable number of internal pores.

  In this case, in order to sufficiently obtain the above effect, at least one of the Cu powder, the SUS powder, and the pure Fe powder may be a powder that occupies the highest ratio among the powders included in the raw material powder. . In that case, the three kinds of the above three kinds of metal powders may be the top three kinds having a high ratio in the raw material powder. Specifically, the content ratios of the Cu powder, the SUS powder, and the pure Fe powder in the raw material powder are respectively Cu powder: 15 wt% to 60 wt%, SUS powder: 10 wt% to 35 wt%, and pure Fe powder: 20 wt. % Or more and 60 wt% or less.

  The raw material powder may further contain a phosphide Fe powder. Usually, phosphatized Fe is brittle compared to pure Fe and should be avoided. When mixed with the raw material powder in a separate powder form from pure Fe powder, the strength of the sintered body and Rather, the wear resistance of the bearing surface can be improved without adversely affecting the rigidity.

  In this case, the content ratios of Cu powder, SUS powder, pure Fe powder, and phosphide Fe powder in the raw material powder are respectively Cu powder: 15 wt% to 60 wt%, SUS powder: 10 wt% to 30 wt%, Pure Fe powder: 20 wt% or more and 60 wt% or less, Phosphorus Fe powder: 0.1 wt% or more and 2.0 wt% or less may be adjusted. Here, the reason why the blending ratio (content ratio) of the phosphide Fe powder is set as described above is as follows. That is, when the content ratio of the phosphatized Fe powder is less than 0.1 wt%, the effect of improving the wear resistance is not sufficiently obtained, and when it exceeds 2.0 wt%, the strength of the sintered body is adversely affected. This is because there is a possibility of influence.

  The raw material powder may further contain a low melting point metal powder. The term “low melting point metal” as used herein means a metal having a melting point that can be melted during sintering. Such a metal powder is melted during liquid sintering to form a liquid phase, whereby Cu powder, SUS. Of the powder and pure Fe powder, it acts as a binder between the same kind powders or between different kinds of powders. Therefore, the bonding strength between the powders can be reinforced to improve the sintering strength. As the low melting point metal powder, for example, a metal powder that reliably melts at the sintering temperature of Cu powder, that is, a metal powder such as Sn, Zn, Al, P, or an alloy powder containing two or more of these can be used. Among these, Sn powder is preferable in view of the hardness after sintering.

  In addition, as described above, if the low melting point metal powder is blended, it is possible to reduce the ratio of the Cu powder that mainly contributes to the sintering action, for example, the content ratio of the Cu powder in the raw material powder, It is also possible to make it smaller than the sum total of the content rate of SUS powder and pure Fe powder. Specifically, the content ratios of Cu powder, SUS powder, pure Fe powder, and low melting point metal powder in the raw material powder are Cu powder: 15 wt% or more and 45 wt% or less, SUS powder: 10 wt% or more and 30 wt% or less, Pure Fe powder: 20 wt% to 60 wt%, low melting point metal powder: 0.5 wt% to 10 wt% may be adjusted.

  Alternatively, when the phosphide Fe powder is further included, the content ratio of each metal powder in the raw material powder is Cu powder: 15 wt% or more and 45 wt% or less, SUS powder: 10 wt% or more and 30 wt% or less, pure Fe powder: It may be adjusted to 20 wt% or more and 60 wt% or less, phosphide Fe powder: 0.1 wt% or more and 2.0 wt% or less, low melting point metal powder: 0.5 wt% or more and 10 wt% or less.

  The raw material powder may further contain graphite. In this case, since graphite acts as a solid lubricant, the sliding surface (bearing surface) of the sintered body or the effect of improving the slidability with the mold at the time of compression molding or secondary processing after sintering. Have.

  The sintered metal bearing according to the present invention may be obtained by sintering at a temperature lower than the melting point of Cu. In the case of the sintered metal bearing thus obtained, the Cu powder in the compression molded body remains in a powdery state without melting, so the Cu structure in the finished product remains as a powdery (granular) structure. Some of them constitute a bearing surface together with a SUS structure, a pure Fe structure and the like. Therefore, good slidability can be obtained with the counterpart material (such as a shaft). Further, it is possible to maintain the workability of the bearing surface and maintain the surface accuracy of the sliding surface while increasing the ratio of the pure Fe component. Such a configuration is used when reinforcing the strength of the sintered body by blending the low melting point metal powder as described above, or when replacing a part of the Cu powder with pure Fe powder to further increase the content ratio of the pure Fe powder. It is more effective when combined.

In the sintered metal bearing according to the present invention, the sintered density may be adjusted within a range of 6.8 g / cm ³ or more and 7.3 g / cm ³ or less. If the bearing has a sintered density (apparent density) adjusted within the above range, it can be used as a sintered oil-impregnated bearing while satisfying the wear resistance, strength, slidability and workability of each metal powder. The internal pores of a certain number or size can be secured and can be suitably supplied particularly as a bearing component for a fluid dynamic bearing device described later.

  Further, the sintered metal bearing according to the above configuration may be one in which a dynamic pressure generating portion for generating a dynamic pressure action of a fluid is formed between the sintered metal bearing and a shaft to be rotatably supported. Specifically, a dynamic pressure generating portion may be formed on an inner peripheral surface serving as a bearing surface or an axial end surface. At this time, as described above, by adopting a configuration in which Cu powder, SUS powder, and pure Fe powder are blended in a balanced manner, for example, uneven shapes such as dynamic pressure grooves can be accurately formed, The slidability or wear resistance in the portion can be improved.

  Since the sintered metal bearing according to the above configuration is excellent in wear resistance, strength, and slidability as described above, it can be used as a fluid dynamic bearing device equipped with this bearing, and in particular, a motor such as an HDD. It can be suitably used for a spindle in which the rotational weight of a shaft to be supported is relatively large, such as a bearing device.

  Further, the solution to the above-mentioned problem is obtained by compressing and sintering a raw material powder containing a plurality of metal powders, and manufacturing a sintered metal bearing having a large number of pores capable of containing oil inside. This method is also achieved by a method of manufacturing a sintered metal bearing, characterized in that a raw material powder containing Cu powder, SUS powder, and pure Fe powder is compression-molded and sintered.

  At this time, for example, in order to enhance the dispersibility of the pure Fe powder and the Cu powder, the pure Fe powder and the Cu powder are supplied to the raw material powder in an integrated state by partial alloying. May be. In this way, since the pure Fe powder and the Cu powder are integrally supplied to the raw material powder, a situation where the pure Fe powder or the Cu powder is segregated can be prevented and a homogeneous sintered body can be obtained.

  As described above, according to the present invention, it is possible to provide a sintered metal bearing that is excellent in wear resistance and can exhibit high sintering strength.

  The sintered metal bearing according to the present invention is formed by compressing and sintering a raw material powder containing Cu metal, SUS powder, and pure Fe powder or these metal powders as main components. Here, the ratio of the Cu powder, the SUS powder, and the pure Fe powder to the whole raw material powder is Cu powder: 15 wt% to 60 wt%, SUS powder: 10 wt% to 35 wt%, pure Fe powder: 20 wt% to 60 wt% The blending ratio of each metal powder is adjusted so as to be not more than%.

  Of the metal powder contained in the raw material powder, the composition and shape of the Cu powder are not particularly limited. Therefore, in addition to pure Cu powder, it is also possible to use Cu powder alloyed with another metal partly or entirely. Further, the production method is not particularly limited, and those produced by various methods such as a reduction method, an atomization method, or an electrolysis method can be used. Although the size of the Cu powder is not particularly limited, for example, when using a powder having a fine particle diameter as compared with SUS powder or pure Fe powder, the blending ratio can be reduced. This is because, as the Cu powder is finer, the contact area with the SUS powder or pure Fe powder increases, so that the strength of the bearing can be secured even with a relatively small amount. In addition, compared to the case where Cu powder of the same size as SUS powder or pure Fe powder is used, the ratio of the Cu structure exposed on the bearing surface of the finished product also increases. This is because it is easy to ensure the mobility.

  Further, regarding the SUS powder contained in the raw material powder, the type (structure) and shape thereof are not particularly limited, and any structure form of austenite, austenite / ferrite, ferrite, or martensite can be used. It is also possible to use SUS powder with. Among these, martensitic SUS powder can be used as a material particularly excellent in mechanical strength and wear resistance. As a typical example of this stainless steel, SUS410 (11.5Cr-13.5Cr) can be mentioned, for example.

  The type, shape, etc. of the pure Fe powder are not particularly limited. For example, various pure Fe powders such as reduced Fe powder, atomized Fe powder, electrolytic Fe powder can be used regardless of the production method. it can.

Further, in addition to the above metal powder, other powders may be included, and an example thereof includes phosphide Fe powder (Fe ₃ P powder). In this case, the phosphide Fe powder is blended for the purpose of improving the wear resistance of the sintered body, and the lower limit of the blending ratio is determined to such an extent that the effect of improving the wear resistance is recognized. The upper limit is set to such an extent that the mechanical properties of the body are not adversely affected. Specifically, when Cu powder, SUS powder, and pure Fe powder are included in the raw material powder at the above ratio, the blending ratio of the phosphide Fe powder is 0.1 wt% or more and 2.0 wt% with respect to the entire raw material powder. % Is adjusted within the range.

  Alternatively, in addition to the above powder, a powder made of a metal having a lower melting point than Cu, for example, Sn powder may be included. That is, the raw material powder may include Cu powder and SUS powder, pure Fe powder, phosphide Fe powder, and Sn powder as a low melting point metal powder. This kind of metal powder melts (liquid phase) during sintering and acts as a binder between the above-mentioned same kind of metal powders or between different kinds of metal powders, and contributes to improving the strength of the sintered body (sintered metal bearing). . Therefore, in such a case, the proportion of Cu powder that mainly contributes to the sintering action can be reduced. Specifically, the content ratio of Cu powder and SUS powder, pure Fe powder, phosphide Fe powder, and low melting point metal powder (Sn powder) in the raw material powder is Cu powder: 15 wt% or more and 45 wt% or less, SUS powder : 10 wt% or more and 30 wt% or less, pure Fe powder: 20 wt% or more and 60 wt% or less, phosphide Fe powder: 0.1 wt% or more and 2.0 wt% or less, Sn powder: adjusted to 0.5 wt% or more and 10 wt% or less More preferably, Cu powder: 30 wt% to 45 wt%, SUS powder: 15 wt% to 25 wt%, pure Fe powder: 30 wt% to 50 wt%, phosphide Fe powder: 0.2 wt% to 1 0.0 wt% or less, Sn powder: 1.0 wt% or more and 4.0 wt% or less may be adjusted.

  Further, for the purpose of improving the moldability and releasability during compression molding, or the sliding characteristics of the finished product, the raw material powder may further contain graphite (graphite) powder. In this case, the raw material powder may include Cu powder and SUS powder, pure Fe powder, phosphide Fe powder, low melting point metal powder (Sn powder), and graphite powder. In this case, the content ratio of each powder in the raw material powder is as follows: Cu powder: 15 wt% or more and 45 wt% or less, SUS powder: 10 wt% or more and 30 wt% or less, pure Fe powder: 20 wt% or more and 60 wt% or less, phosphide Fe Powder: 0.1 wt% or more and 2.0 wt% or less, Sn powder: 0.5 wt% or more and 10 wt% or less, Graphite powder: 0.5 wt% or more and 2.5 wt% or less may be adjusted.

  The sintered metal bearing according to the raw material powder composition described above is manufactured by, for example, the following method. That is, after at least three steps of the step (a) of compressing the raw material powder into a predetermined shape, the step (b) of sintering the green compact, and the step (c) of sizing the sintered body. Manufactured.

  First, regarding the compacting step (a), a raw material powder is prepared by mixing Cu powder, SUS powder, and pure Fe powder with a V-type mixer or the like. If necessary, a raw material powder obtained by further mixing various powders such as a phosphide Fe powder, a low melting point metal powder, and graphite may be prepared. Here, the mixing ratio of each powder is set according to the content ratio of each powder in the whole raw material powder described above.

In the case of mixing the phosphide Fe powder in order to enhance the dispersibility of the phosphide Fe powder, by preparing a mixture of phosphide Fe powder beforehand pure Fe powder, the mixed powder (Fe + Fe ₃ P mixed powder) may be mixed with Cu powder or SUS powder. Alternatively, for the same purpose, Cu powder is partially brought into contact with the surface of pure Fe powder in advance, and the contact portion is alloyed (partial alloy body of pure Fe powder and Cu powder). It is also possible to use it as a raw material powder after mixing. Such a technique is particularly effective when fine Cu powder having poor dispersibility (for example, Cu powder having the above exemplified particle diameter) is used.

Next, a molding die having a powder filling space having a shape corresponding to the finished product (for example, the cylindrical shape shown in FIG. 3) is prepared, and the raw material powder is filled in the die and pressed at a predetermined pressure. Then, a green compact having a shape corresponding to the mold is obtained. At this time, the pressing conditions are set so that the density of the green compact is, for example, 6.5 g / cm ³ or more and 7.0 g / cm ³ or less.

  Next, the green compact is heated for a predetermined time at a predetermined sintering temperature, here, a temperature lower than the melting point of Cu (1083 ° C.). Thereby, at least Cu powder and pure Fe powder are mutually sintered, whereby a sintered body composed of a sintered metal structure having at least a Cu structure, a SUS structure, and a pure Fe structure can be obtained. (Sintering step (b)). Here, regarding the sintering temperature, if the sintering temperature is too close to the melting point of Cu, the ratio of the molten Cu powder increases, and the molten Cu structure enters the inside of the bearing. Therefore, the Cu structure can be maintained on the bearing surface. It becomes difficult. Further, if sintering is performed at a low temperature that is too far from the melting point of Cu, sufficient sintering action cannot be expected in the first place. From this viewpoint, the sintering temperature is preferably set within a range of 750 ° C. or more and 1060 ° C. or less, for example.

  By carrying out sizing on the sintered body for the purpose of correcting the size or shape of the sintered body thus obtained (sizing step (c)), a sintered metal bearing is completed. By this sizing, the sintered body is shaped to a size or shape according to the finished product, and the surface area ratio of the bearing surface is adjusted to a predetermined size. In addition, for the purpose of reducing the number of surface apertures and individual opening areas on the inner peripheral surface, it is possible to perform rotational sizing together with or in place of the sizing. According to this sizing, the surface area ratio of the inner peripheral surface is adjusted to be smaller (for example, 10% or less). Therefore, an oil film having a predetermined film thickness can be easily formed on the bearing surface even when it is incorporated into a fluid dynamic pressure bearing device described later.

  Moreover, when using the said sintered metal bearing as a sintered oil impregnation bearing, you may provide an oil impregnation process (d) after this. That is, a sintered oil-impregnated bearing can be manufactured by properly removing the surface lubricating oil after impregnating the internal pores of the sintered metal bearing with a lubricant such as lubricating oil using a vacuum impregnation method or the like. Is possible.

Here, the volume ratio (100-porosity [%]) of the sintered metal bearing is preferably set in accordance with the actual application, for example, 75% to 95% (in terms of porosity, 5% And 25% or less). For example, when the internal pores are impregnated with lubricating oil as used in a fluid dynamic pressure bearing device described later, the lubricating oil can be supplied to the bearing surface (bearing gap) without any delay. In addition, even when the amount of oil decreases as the temperature changes, a relatively large amount of lubricating oil can be held in the internal pores so that the lubricating oil can be supplied to the bearing gap (8 in terms of porosity). % To 18%). Here, the “porosity” refers to the ratio of the total volume of the internal pores per unit volume of the sintered metal bearing, and is specifically calculated by the following equation.
Porosity [%] = 100−Density ratio [%] = {1− (ρ1 / ρ0)} × 100
ρ1: Sintered density of sintered metal bearing (Refer to JIS Z 2501 dry density column for measurement method)
ρ0: True density of a material having the same composition as the sintered metal bearing It has been found that the porosity decreases almost linearly as the density ratio increases. Therefore, the porosity can be obtained by determining the density ratio. it can.

The surface open area ratio may be set according to the actual application. For example, in the case of the fluid dynamic bearing device application, it is preferable to set it to 2% or more and 15% or less. In particular, as will be described later, a dynamic pressure generating portion (an arrangement region of the dynamic pressure grooves 8a1 and 8a2 in FIG. 3) for generating the dynamic pressure action of the lubricating oil is provided on the inner peripheral surface of the sintered metal bearing. For the purpose of preventing the escape of hydraulic pressure, the surface opening ratio of the inner peripheral surface is preferably set to be relatively small (for example, 2% to 10%). Here, “surface opening” means a portion where pores contained in a sintered metal bearing having a porous structure are opened on the outer surface. “Surface open area ratio” refers to the area ratio of surface open area to the unit area of the outer surface, and is measured and evaluated under the following conditions.
[measurement tool]
Metallic microscope: Nikon ECLIPSS ME600
Digital camera: Nikon DXM1200
Photography software: Nikon ACT-1 ver. 1
Image processing software: QUICK GRAIN made by Innotek
[Measurement condition]
Photography: Shutter speed 0.5 seconds Binary threshold: 235

  Since the sintered metal bearing according to the above description is excellent in wear resistance, strength, and slidability, for example, magnetic disk devices such as HDD, CD-ROM, CD-R / RW, DVD-ROM / Bearing devices for spindle motors in optical disk devices such as RAM, magneto-optical disk devices such as MD and MO, or motor bearings such as polygon scanner motors for laser beam printers (LBP), color wheel motors for projectors, fan motors, etc. It is preferably used as a device.

  FIG. 1 shows an example of the above application, and is a cross-sectional view of a fluid dynamic bearing device 1 incorporating a sintered metal bearing 8 according to the present invention, and further a disk of an HDD equipped with this fluid dynamic bearing device 1. The principal part sectional view of a drive motor is shown. This motor includes a fluid dynamic bearing device 1 that rotatably supports a shaft member 2 to which a hub 3 is attached, a stator coil 4 and a rotor magnet 5 that are opposed to each other via a gap in the radial direction, and a bracket 6. . The stator coil 4 is fixed to the bracket 6, and the rotor magnet 5 is fixed to the hub 3. The housing 7 of the fluid dynamic bearing device 1 is fixed to the inner periphery of the bracket 6. As shown in the figure, the hub 3 holds one or a plurality of disks D (two in FIG. 1). In the spindle motor configured as described above, when the stator coil 4 is energized, the rotor magnet 5 is rotated by the exciting force generated between the stator coil 4 and the rotor magnet 5, and accordingly, is held by the hub 3. The disk D rotates together with the shaft member 2.

  FIG. 2 shows a longitudinal sectional view of the fluid dynamic bearing device 1. The fluid dynamic bearing device 1 includes a shaft member 2, a housing 7, a sintered metal bearing 8 fixed to the housing 7 and having the shaft member 2 disposed on the inner periphery, and a lid member that closes one end of the housing 7. 9 and a seal member 10 disposed on the other end opening side of the housing.

  The shaft member 2 includes a shaft portion 2a and a flange portion 2b provided integrally or separately at the lower end of the shaft portion 2a. A radial bearing surface 2a1 is formed on the outer periphery of the shaft portion 2a so as to face the dynamic pressure grooves 8a1 and 8a2 arranged in the inner peripheral surface 8a of the sintered metal bearing 8 to be described later in the radial direction. In this embodiment, the radial bearing surfaces 2a1 are provided at two locations apart in the axial direction. When the shaft portion 2a is inserted through the inner periphery of the sintered metal bearing 8, the radial bearing surfaces 2a1, 2a1 Radial bearing clearances of radial bearing portions R1 and R2 described later are formed between the peripheral surface 8a (see FIG. 2). The shaft member 2 having the above structure can be formed of various metal materials, for example, formed of a steel material such as stainless steel in consideration of strength, rigidity, wear resistance, and the like.

  The housing 7 is formed in a substantially cylindrical shape with a metal material such as brass or a resin material, for example, and has a shape in which both axial ends thereof are opened. The outer peripheral surface 8d of the sintered metal bearing 8 is connected to the inner peripheral surface 7a of the housing 7 by appropriate means such as adhesion (including loose adhesion and press-fit adhesion), press-fitting, and welding (including ultrasonic welding and laser welding). It is fixed with. In addition, a fixing surface 7b that is larger in diameter than the inner peripheral surface 7a and that fixes a lid member 9 to be described later is formed on the lower end side of the inner peripheral surface 7a. When the housing 7 is formed of a resin material, both a thermoplastic resin and a thermosetting resin can be used. For example, if the resin is a thermoplastic resin, a liquid crystal polymer (LCP), polyphenylene sulfide (PPS), poly Crystalline resins represented by ether ether ketone (PEEK), polyacetal (POM), polyamide (PA), etc., polyphenylsulfone (PPSU), polyethersulfone (PES), polyetherimide (PEI), polyamide Amorphous resins such as imide (PAI) can be used. These resin materials can be used alone or in a mixture of two or more.

  In addition, the above resin materials include, as necessary, fibrous fillers such as glass fibers and carbon fibers, whisker-like fillers such as potassium titanate, scaly fillers such as mica, carbon black, graphite, and metal powder. It is also possible to fill (add) one or more kinds of powdery fillers such as organic powders. Of course, the material of the housing 7 is not limited to the resin, and for example, a metal such as a copper alloy or other materials can be adopted. The forming method is not particularly limited, and for example, plastic working such as forging or pressing, or metal injection molding such as MIM can be adopted in addition to cutting.

In this embodiment, the sintered metal bearing 8 has a cylindrical shape having a porous structure, and a region where a plurality of dynamic pressure grooves are arranged as a radial dynamic pressure generating portion is formed on the whole or a part of the inner peripheral surface 8a. It is formed. In this embodiment, for example, as shown in FIG. 3, regions where a plurality of dynamic pressure grooves 8a1 and 8a2 having different inclination angles are arranged in a herringbone shape are formed at two locations separated in the axial direction. In this embodiment, the dynamic pressure grooves 8a1 and 8a2 are arranged asymmetrically in the axial direction in order to intentionally create a circulation of lubricating oil inside the bearing. Explaining in the form illustrated in FIG. 3, the arrangement of the dynamic pressure grooves 8a1 above the axial center m (on the seal member 10 side) of the region (so-called band portion 8a3) between the dynamic pressure grooves 8a1 and 8a2 adjacent in the axial direction. the axial dimension X ₁ region is formed to be larger than the axial dimension X ₂ of the lower dynamic pressure grooves 8a2 sequence region. The dynamic pressure groove 8a1 and 8a2 arrangement region located on the lower side of the inner peripheral surface 8a (the side closer to the thrust bearing gap described later) is formed symmetrically in the axial direction with the strip 8a3 at the center in the axial direction as a boundary. .

  As shown in FIG. 4, a region where a plurality of dynamic pressure grooves 8b1 are arranged in a spiral shape is formed as a thrust dynamic pressure generating portion on the entire surface or a partial region of the lower end surface 8b of the sintered metal bearing 8. . This dynamic pressure groove 8b1 arrangement region faces the upper end surface 2b1 of the flange portion 2b in the finished product state, and a thrust bearing of the first thrust bearing portion T1 described later between the upper end surface 2b1 when the shaft member 2 rotates. A gap is formed (see FIG. 2).

  As shown in FIG. 3, an annular groove 8 c 1 having a wedge-shaped cross section is formed at the center position in the radial direction of the upper end surface 8 c of the sintered metal bearing 8. Further, radial grooves 8c2 that connect the annular groove 8c1 and the inner peripheral surface 8a are formed at a plurality of locations in the circumferential direction on the inner peripheral side of the upper end surface 8c from the annular groove 8c1. The annular groove 8c1 and the radial groove 8c2 together with an axial groove 8d1 described later form a lubricating oil circulation path in the bearing internal space, thereby ensuring a smooth lubricating oil supply state.

  A plurality of (for example, three) axial grooves 8d1 extending in the axial direction are formed on the outer peripheral surface 8d of the sintered metal bearing 8. These axial grooves 8d1 are formed at positions spaced apart from each other at equal intervals in the circumferential direction.

  Thus, the dynamic pressure grooves 8a1 and 8a2 arrangement region of the inner peripheral surface 8a is further sintered by performing groove sizing after the sizing and rotation sizing performed in the sizing step (c) described above. It is formed on the inner peripheral surface 8a of the bonded body (sintered metal bearing 8). Specifically, the outer peripheral surface of a molding die (molding rod) having a plurality of convex portions corresponding to the dynamic pressure grooves 8a1 and 8a2 is pressed on the inner peripheral surface of the cylindrical sintered body in the radial direction. The dynamic pressure grooves 8a1 and 8a2 are transferred and molded by pressing and plastically deforming the inner peripheral surface following the mold. At this time, if sintering is performed at a temperature lower than the melting point of Cu, a large number of Cu granular structures remain on the inner peripheral surface of the sintered body, and the moldability of the groove sizing process is ensured well. The Therefore, the dynamic pressure grooves 8a1 and 8a2 or the arrangement region of the dynamic pressure grooves 8a1 and 8a2 can be formed with high accuracy. In particular, the dynamic pressure groove 8a1, 8a2 arrangement region of the shape shown in FIG. 3 is a region between the dynamic pressure grooves 8a1, 8a1 arranged along the circumferential direction on the inner peripheral surface of the sintered body before sizing. The belt 8a3 which is a region between the dynamic pressure grooves 8a1 and 8a2 arranged in the axial direction (both regions shown by cross hatching in FIG. 3) is raised relative to the surroundings to thereby increase the dynamic pressure grooves 8a1 and 8a1. 8a2 is formed. Therefore, the structure in which the Cu structure remains on the inner peripheral surface of the sintered body effectively acts on the formability or forming accuracy of the dynamic pressure grooves 8a1 and 8a2. In the same way, the dynamic pressure groove 8b1 arrangement region of the lower end surface 8b can also be formed at the time of the groove sizing process or dimension sizing.

  The lid member 9 that closes the lower end side of the housing 7 is formed of, for example, a metal material or a resin material, and is fixed to a fixing surface 7 b provided at the inner peripheral lower end of the housing 7. At this time, a known fixing means such as adhesion, press-fitting, welding, or welding can be used for fixing the lid member 9. Of course, the fixing form of the lid member 9 is not limited to the form shown in the figure. For example, a portion that protrudes in a cylindrical shape from the outer peripheral edge to the upper end surface 9 a side is provided, and the outer peripheral surface of this protruding part and the inner peripheral side of the housing 7 are provided. The fixing surface 7b may be fixed, or the inner peripheral surface of the protruding portion and the outer peripheral surface on the lower end side of the housing 7 may be fixed.

  For example, a dynamic pressure groove array region having an array mode similar to that in FIG. 4 (the direction of the spiral is reversed) is formed on the entire upper surface 9a of the lid member 9 or a partial region thereof. In the dynamic pressure groove arrangement region, the finished product state, it faces the lower end surface 2b2 of the flange portion 2b, and a thrust bearing gap of the second thrust bearing portion T2 described later is formed between the lower end surface 2b2 and the shaft member 2 when rotating. Form (see FIG. 2).

  In this embodiment, the sealing member 10 as a sealing means is formed separately from the housing 7, and is fixed to the inner periphery of the upper end of the housing 7 by any means such as press-fitting, bonding, welding, and welding. Here, the seal member 10 is fixed to the housing 7 in a state where the lower end surface of the seal member 10 is in contact with the upper end surface 8 c of the sintered metal bearing 8. The material of the seal member 10 is not particularly limited, and various metal materials or resin materials can be used as long as the material is not likely to cause oil leakage such as a porous material. Or even if it is a porous material, it can be used as the sealing member 10 by sealing the surface which contacts external air by coating etc. Of course, any one of the sealing member 10 and the lid member 9 can be integrally formed of the same material as the housing 7.

  A tapered seal surface 10a is formed on the inner periphery of the seal member 10, and a seal space S is formed between the seal surface 10a and the upper outer peripheral surface of the shaft portion 2a. In a state where the lubricating oil is filled in the fluid dynamic pressure bearing device 1, the oil level of the lubricating oil is always maintained in the seal space S.

  After assembling the above-described components into a form conforming to a predetermined procedure and FIG. 2, the bearing internal space (the area indicated by the dotted pattern in FIG. 2) is filled with lubricating oil, so that the sintered metal bearing 8 The internal pores are impregnated with the lubricating oil, and other spaces (such as radial bearing gaps) are filled with the lubricating oil. Thereby, the fluid dynamic bearing device 1 as a finished product is obtained. As the lubricating oil filled in the fluid dynamic bearing device 1, various oils can be used. However, the lubricating oil provided to the fluid dynamic bearing device 1 for a disk drive device such as an HDD includes Considering temperature changes during use or transportation, ester-based lubricants with excellent low evaporation rate and low viscosity, such as dioctyl sebacate (DOS), dioctyl azelate (DOZ), etc., can be suitably used. is there.

  In the fluid dynamic pressure bearing device 1 having the above-described configuration, when the shaft member 2 rotates, the dynamic pressure grooves 8a1 and 8a2 of the sintered metal bearing 8 are arranged in the radial bearing surfaces 2a1 and 2a1 of the shaft portion 2a and the radial bearing gap. Opposite through. As the shaft member 2 rotates, the lubricating oil is pushed toward the axial center of the dynamic pressure grooves 8a1 and 8a2 in any of the upper and lower dynamic pressure grooves 8a1 and 8a2 arrangement regions, and the pressure rises. Due to the dynamic pressure action of the dynamic pressure grooves 8a1 and 8a2, the first radial bearing portion R1 and the second radial bearing portion R2 that rotatably support the shaft member 2 in the radial direction are separated from each other in the axial direction. Are configured in two places (see FIG. 2 for both).

  Further, in the thrust bearing gap between the dynamic pressure groove 8b1 arrangement region provided on the lower end surface 8b of the sintered metal bearing 8 and the upper end surface 2b1 of the flange portion 2b opposed thereto, and the upper end surface 9a of the lid member 9 An oil film of lubricating oil is formed in the thrust bearing gap between the provided dynamic pressure groove array region and the lower end surface 2b2 of the flange portion 2b facing the region, by the dynamic pressure action of the dynamic pressure groove. The first thrust bearing portion T1 and the second thrust bearing portion T2 that support the shaft member 2 in the thrust direction in a non-contact manner are configured by the pressure of these oil films (see FIG. 2 for both).

  In this case, since the sintered metal bearing 8 has a structure including a lot of SUS structure and pure Fe structure, the hardness of the inner peripheral surface 8a serving as the radial bearing surface is relatively high. Therefore, for example, immediately after the rotation of the shaft member 2 made of SUS, or immediately before the rotation is stopped, the sliding contact between the outer peripheral surface 2a1 of the shaft portion 2a and the inner peripheral surface 8a of the sintered metal bearing 8 opposed thereto is performed. Even if it occurs, the difference in hardness between the two surfaces 2a1 and 8a can be small, and wear between the sintered metal bearing 8 and the shaft portion 2a can be suppressed. In particular, when the hub 3 and the plurality of discs D are mounted on the top of the shaft member 2 as in this embodiment, the center of gravity of the rotating body including the shaft member 2 moves upward, and the moment load increases. Therefore, the shaft member 2 and the sintered metal bearing 8 are easy to contact and slide at the upper part of the bearing, but as described above, the hardness difference between both members 2a and 8 (the hardness difference between both sliding surfaces 2a1 and 8a) is reduced. As a result, such sliding wear can be minimized.

  The upper dynamic pressure grooves 8a1 and 8a2 arranged in the inner peripheral surface 8a of the sintered metal bearing 8 are formed so as to be axially asymmetric with respect to the axial center of the band 8a3. The axial dimension X1 of the upper region is larger than the axial dimension X2 of the lower region. Therefore, when the shaft member 2 rotates, the lubricating oil pull-in force (pumping force) in the upper region is relatively larger than that in the lower region. Then, due to the difference in the pulling force, the lubricating oil that has flowed out downward from the radial bearing gap is in the axial direction of the sintered metal bearing 8 located on the outer diameter side from the thrust bearing gap of the first thrust bearing portion T1. From the groove 8d1 and the axial clearance between the upper end surface 8c and the lower end surface of the seal member 10, the annular groove 8c1 and the radial groove 8c2 are circulated through the path, and are drawn again into the radial bearing clearance of the first radial bearing portion R1. .

  In this way, by configuring the lubricating oil to flow and circulate in the bearing internal space including the radial bearing gap, a phenomenon in which the pressure of the lubricating oil in the internal space becomes a negative pressure locally is prevented. Problems such as generation of bubbles accompanying generation of pressure, leakage of lubricating oil due to generation of bubbles, deterioration of bearing performance, generation of vibration, and the like can be solved. Further, when bubbles are mixed in the lubricating oil for some reason, the bubbles are discharged from the oil surface (gas-liquid interface) of the lubricating oil in the seal space S to the outside air when circulating in the circulation path along with the lubricating oil. Therefore, the bad influence by the bubble is effectively prevented.

  As described above, one application example of the sintered metal bearing 8 according to the present invention has been described. However, it is needless to say that the fluid dynamic bearing device 1 to which this bearing can be applied is not limited to this example.

  For example, as the fluid dynamic pressure bearing device including the sintered metal bearing 8, in the above application example, the thrust bearing portions T1 and T2 are formed on both end surfaces 2b1 and 2b2 side of the flange portion 2b provided at one end of the shaft portion 2a. Although the case where it has a form was demonstrated, it is also possible to vary the axial direction separation distance of these thrust bearing parts T1 and T2. FIG. 5 shows an example thereof. The fluid dynamic bearing device 11 according to FIG. 5 mainly includes a point that two seal spaces S1 and S2 are disposed at both ends of the housing 17, and thrust bearing portions T1 and T2. It has a form different from the fluid dynamic bearing device 1 shown in FIG. 2 in that it is formed at both ends of the sintered metal bearing 18.

  In this illustrated example, the sintered metal bearing 18 according to the present invention has not only the lower end surface 18b but also the upper end surface 18c provided with the dynamic pressure groove array region having the shape shown in FIG. 4 (the direction of the spiral is opposite to that in FIG. 3). Have. For this reason, the first thrust bearing portion T1 is provided between the lower end surface 19a of the first seal member 19 and the upper end surface 18c of the sintered metal bearing 18, and the second thrust bearing portion T2 is provided on the second seal member 20. It is provided between the upper end surface 20 a and the lower end surface 18 b of the sintered metal bearing 18. The first seal space S1 is formed between the outer peripheral surface 19b of the first seal member 19 fixed to the shaft member 12 and the inner peripheral surface 17a at the upper end of the housing 17 facing the surface. The space S2 is formed between the outer peripheral surface 20b of the second seal member 20 and the inner peripheral surface 17a at the lower end of the housing 17 facing the surface. The radial bearing portions R1 and R2 are respectively formed between the inner peripheral surface 18a provided with the radial dynamic pressure generating portion illustrated in FIG. 3 and the outer peripheral surface 12a of the shaft member 12 facing the inner peripheral surface 18a. This is the same as in the case of the fluid dynamic bearing device 1 shown in FIG.

  In the fluid dynamic pressure bearing device 11 according to this embodiment, the separation distance between the thrust bearing portions T1 and T2 is larger than that of the fluid dynamic pressure bearing device 1 shown in FIG. The load capacity can be improved. Therefore, sliding wear of the sintered metal bearing 8 due to contact with the shaft member 2 is caused even when the weight of the rotating body is increased, such as an increase in the number of disks, as the capacity of information devices such as HDDs is increased. It can be reduced (suppressed).

  FIG. 6 shows a sectional view of a fluid dynamic bearing device 21 according to still another embodiment. In the fluid dynamic pressure bearing device 21 according to the figure, two sintered metal bearings 8 are arranged so as to overlap in the axial direction, and these sintered metal bearings 8 and 8 are composed of a cylindrical portion 27a and a bottom portion 27b. It is fixed to the inner peripheral surface 27a1 of the bottomed cylindrical housing 27. Of the two sintered metal bearings 8 arranged so as to overlap in the axial direction, the upper sintered metal bearing 8 is arranged only on the seal member 10 side in the arrangement of the asymmetric dynamic pressure grooves 8a1, 8a2 illustrated in FIG. A region is provided, and the lower sintered metal bearing 8 is provided with the symmetrical dynamic pressure groove 8a1, 8a2 array region illustrated in FIG. 3 only on the flange portion 2b side. For this reason, the radial bearing portions R1 and R2 are formed at positions that are the most axially separated between the sintered metal bearings 8 and 8.

  As described above, the fluid dynamic bearing device 21 according to FIG. 6 has a larger distance between the radial bearing portions R1 and R2 than the fluid dynamic bearing devices 1 and 11 shown in FIG. 2 and FIG. The load capacity for the moment load of the entire bearing is improved. Therefore, the sliding wear of the sintered metal bearings 8 and 8 can be reduced and excellent bearing performance can be exhibited over a long period of time even when the weight of the rotating body is increased or the rotational speed is increased.

  In the above description, the radial bearing portions R1 and R2 and the thrust bearing portions T1 and T2 are exemplified by the configuration in which the dynamic pressure action of the lubricating oil is generated by the dynamic pressure grooves having a herringbone shape or a spiral shape. The configuration to which the present invention can be applied is not limited to this.

  For example, as the radial bearing portions R1 and R2, although not shown, a so-called step-like dynamic pressure generating portion in which axial grooves are formed at a plurality of locations in the circumferential direction, or a plurality of circular arc surfaces in the circumferential direction. A so-called multi-arc bearing in which wedge-shaped radial gaps (bearing gaps) are formed between the outer peripheral surfaces 2a1 and 12a of the opposing shaft members 2 and 12 may be employed.

  Alternatively, the inner peripheral surfaces 8a and 18a of the sintered metal bearings 8 and 18 serving as radial bearing surfaces are formed into a perfect circular inner peripheral surface without a dynamic pressure groove or an arc surface as a dynamic pressure generating portion. A so-called perfect circle bearing can be constituted by a perfect circular outer peripheral surface facing the surface.

  One or both of the thrust bearing portions T1 and T2 are also 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 configured by a step bearing or a corrugated bearing (having a corrugated waveform such as an end face).

  Moreover, although the above embodiment demonstrated the case where all the dynamic-pressure generation | occurrence | production parts were provided in the fixed side (The housing 27, the sintered metal bearing 8, the cover member 9, etc.), the one part or all part was rotated side ( The shaft members 2 and 12, the flange portion 2b, the seal members 19 and 20, and the like can be provided. Specifically, the outer peripheral surfaces 2a1 and 12a of the shaft members 2 and 12, the both end surfaces 2b1 and 2b2 of the flange portion 2b, or the lower end surface 19a and the upper end surface 20a of the seal members 19 and 20 are described in one or more places. It is possible to provide a dynamic pressure generator.

  Further, in the above embodiment, the configuration in which the shaft members 2 and 12 rotate and are supported by the sintered metal bearings 8 and 18 has been described. The present invention can also be applied to a configuration in which the side rotates and the shaft members 2 and 12 support it. In this case, although not shown, the sintered metal bearings 8 and 18 are bonded and fixed to members disposed on the outside thereof, rotate integrally with the outer member, and are supported by the shaft portion on the fixed side.

  Moreover, in the above embodiment, although the fluid dynamic pressure bearing apparatus 1,11,21 was filled inside and lubricating oil was illustrated as a fluid for forming a fluid film in a radial bearing gap or a thrust bearing gap, In addition, a fluid capable of forming a fluid film, for example, a gas such as air, a fluid lubricant such as a magnetic fluid, or lubricating grease may be used. Of course, since the sintered metal bearing according to the present invention has excellent wear resistance, it can be used as a normal sliding bearing without using any lubricating fluid.

  In order to demonstrate the effect of the present invention, a sintered metal bearing (Example 1) formed of a raw material powder containing Cu powder, SUS powder, and pure Fe-based powder at a predetermined ratio, and a raw material powder of a conventional composition The formed sintered metal bearings (Comparative Examples 1 and 2) were respectively subjected to a pressure ring test and a wear amount measurement test, and subjected to comparative evaluation for each characteristic.

Here, 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 Heganess Co., Ltd. as pure Fe powder. NC100.24 manufactured by PNG60 manufactured by Heganess Co., Ltd. was used as the phosphatized Fe powder. In this experiment, Sn powder and graphite powder as a low melting point metal were used as raw material powder, Sn-At-W350 manufactured by Fukuda Metal Foil Industry Co., Ltd. was used for Sn powder, and Japanese graphite was used for graphite powder. ECB-250 manufactured by Kogyo Co., Ltd. was used. Molding conditions (pressing force) were set so that the density of the green compact was 6.5 to 7.0 [g / cm ³ ]. The sintering temperature of the example was 1050 ° C., and the sintering temperature of the comparative example was 870 ° C. Examples and Comparative Examples, and the composition of each raw material powder are as shown in Table 1 below. The finished product dimensions of the test piece (sintered metal bearing) as a finished product were φ (inner diameter) 4 mm × φ (outer diameter) 7.5 mm × t (axial width) 12.4 mm in both the examples and comparative examples. . Moreover, the number of test pieces was set to 5 in each of the examples and comparative examples.

  The measurement test of the crushing strength was carried out in accordance with JIS Z 2507 in both Examples and Comparative Examples using the above test pieces.

The wear amount measurement test was also carried out using a Sabang type wear tester in both the Examples and Comparative Examples using the above test pieces. The test conditions at that time are as follows.
Mating material: SUS420J2
Peripheral speed: 50m / min
Surface pressure: 1.3 MPa
Lubricant: Ester oil (12 mm ² / s)
Test time: 3hrs

Table 2 below shows the measurement results of the crushing test and the wear test, respectively. All values are shown as relative values with reference to Comparative Example 1 (the measured value of Comparative Example 1 is 1).

  First, regarding wear resistance, in the case of a sintered metal bearing (Example 1) containing SUS powder and pure Fe powder as a raw material powder, it is almost the same as a sintered metal bearing containing only SUS powder (Comparative Example 2). It was confirmed that the same amount of wear (wear depth, wear scar area) was exhibited. Further, as regards the crushing strength, it was confirmed that a high value equivalent to or higher than that of a sintered metal bearing (Comparative Example 1) mainly containing Cu powder and Fe powder and not containing SUS powder was confirmed. Furthermore, also regarding the linear expansion coefficient, it was confirmed that the sintered metal bearing which concerns on Example 1 shows the smallest value. From the above results, it was confirmed that the sintered metal bearing according to the present invention is excellent in wear resistance and can exhibit high sintered strength.

1 is a sectional view of a fluid dynamic pressure bearing device incorporating a sintered metal bearing according to an embodiment of the present invention, and a spindle motor provided with the fluid dynamic pressure bearing device. It is sectional drawing of a fluid dynamic pressure bearing apparatus. It is sectional drawing of the sintered metal bearing which concerns on this invention. It is a top view of a sintered metal bearing. It is sectional drawing of the fluid dynamic pressure bearing apparatus which concerns on another form. It is sectional drawing of the fluid dynamic pressure bearing apparatus which concerns on another form.

DESCRIPTION OF SYMBOLS 1,11,21 Fluid dynamic pressure bearing apparatus 2,12 Shaft member 2a Shaft part 2b Flange part 3 Hub 4 Stator coil 5 Rotor magnet 6 Bracket 7, 17, 27 Housing 8, 18 Sintered metal bearing 8a, 18a Inner peripheral surface 8a1, 8a2 Dynamic pressure grooves 8b, 18b Lower end surface 8b1 Dynamic pressure grooves 8c, 18c Upper end surface 8d Outer peripheral surface 8d1 Axial groove 9 Lid member 10, 19, 20 Seal member R1, R2 Radial bearing portion T1, T2 Thrust bearing portion S1 , S2 Seal space

Claims (12)

In a sintered metal bearing which is obtained by compression molding and sintering a raw material powder containing a plurality of metal powders, and having a large number of pores capable of containing oil inside,
A sintered metal bearing, wherein the raw material powder includes Cu powder, SUS powder, and pure Fe powder.   The content ratios of Cu powder, SUS powder, and pure Fe powder in the raw material powder are respectively Cu powder: 15 wt% to 60 wt%, SUS powder: 10 wt% to 35 wt%, pure Fe powder: 20 wt% to 60 wt% The sintered metal bearing according to claim 1, wherein the sintered metal bearing is adjusted.   The sintered metal bearing according to claim 1, wherein the raw material powder further contains a phosphide Fe powder.   The content ratios of Cu powder, SUS powder, pure Fe powder, and phosphide Fe powder in the raw material powder are respectively Cu powder: 15 wt% to 60 wt%, SUS powder: 10 wt% to 30 wt%, pure Fe powder: 20 wt% The sintered metal bearing according to claim 3, wherein the sintered metal bearing is adjusted to not less than 60% and not more than 60 wt% and phosphide Fe powder: not less than 0.1 wt% and not more than 2.0 wt%.   The sintered metal bearing according to any one of claims 1 to 4, wherein the raw material powder further contains a low melting point metal powder.   The sintered metal bearing according to claim 5, wherein the low melting point metal powder is Sn powder.   The content ratios of Cu powder, SUS powder, pure Fe powder, and low melting point metal powder in the raw material powder are respectively Cu powder: 15 wt% or more and 45 wt% or less, SUS powder: 10 wt% or more and 30 wt% or less, pure Fe powder: 20 wt% The sintered metal bearing according to claim 5, wherein the sintered metal bearing is adjusted to a low melting point metal powder: 0.5 wt% or more and 10 wt% or less.   The sintered metal bearing according to claim 1, wherein the raw material powder further contains graphite.   The sintered metal bearing according to any one of claims 1 to 8, obtained by sintering at a temperature lower than the melting point of Cu. The sintered metal bearing according to any one of claims 1 to 9, wherein a sintered density is adjusted within a range of 6.8 g / cm ³ or more and 7.3 g / cm ³ or less.   The sintered metal bearing according to any one of claims 1 to 10, wherein a dynamic pressure generating portion for generating a dynamic pressure action of a fluid is formed between the shaft to be rotatably supported.   A fluid dynamic bearing device comprising the sintered metal bearing according to claim 1.

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