JP2011033156A - Sintered metal bearing and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sintered metal bearing capable of achieving high resistance to wear and excellent sliding performance while reducing manufacturing cost. <P>SOLUTION: This sintered metal bearing is manufactured by using a material prepared by dispersing Cu system into Fe system and contains the Fe system ten times or more the Cu system by weight ratio, and the Cu system remains as a granular system. This sintered metal bearing is manufactured by compressing and molding raw material powders containing at least, for example, Cu powders and Fe powders ten times or more the Cu powders by weight ratio and then sintering this compressed and molded product at temperature of less than melting point of Cu. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a sintered metal bearing obtained by compressing and then sintering metal powder, and a method for manufacturing the same.

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

  Usually, this type of bearing is, for example, as disclosed in Patent Document 1 below, after compression molding a metal powder mainly composed of Cu powder or Fe powder or both into a predetermined shape (mostly cylindrical). The porous body obtained by sintering is impregnated with a fluid such as lubricating oil or lubricating grease.

  Patent Document 2 below discloses an example of a sintered metal bearing mainly composed of Fe. Specifically, it is an Fe-based sintered sliding member made of Cu-based alloy powder, Cu powder, carbon powder, and Fe powder, and includes a Cu component of 15 to 25 wt%, an Si component of 1 to 5 wt%, and an Sn component of 1 to 1. An Fe-based sintered sliding member composed of 5 wt%, a carbon component of 3 to 10 wt%, and a balance Fe component (55 to 80 wt%) has been proposed. Further, it is disclosed that the sintered sliding member is manufactured by compacting a mixed powder blended so as to have the above weight ratio, and sintering the compact at 1100 to 1150 ° C. .

Japanese Patent Laid-Open No. 11-182551 JP 2001-123253 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. Therefore, the above-mentioned 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. On the other hand, in order to meet the demand for cost reduction, replacement of a relatively expensive Cu powder with a relatively inexpensive Fe powder has been investigated for the raw material powder for the bearing.

  However, as the proportion of Fe powder is increased, the following adverse effects may occur. That is, in order to obtain good slidability with the shaft, the Cu component is indispensable. However, by increasing the proportion of the Fe component, the proportion of the Cu component is relatively reduced, and the desired slidability is achieved. It is difficult to ensure. Moreover, in order to obtain good slidability, high surface accuracy is also required for the sliding surface (bearing surface) with the counterpart material, but when the Fe component occupies most of the bearing, There is a possibility that the predetermined surface accuracy cannot be obtained because the good workability is not reflected.

  In addition, as described in the above-mentioned Patent Document 2, in an Fe-based sintered metal bearing, a temperature relatively close to the melting point of Fe as a main component (1100 ° C. to 1150 ° C.) is usually sintered. Since the temperature is set, sintering is performed at a temperature exceeding the melting point of Cu. In this case, the Cu powder melts and enters the internal pores, and it is difficult to form a bearing surface equivalent to the Fe component. Therefore, in this case, it is difficult to reflect the slidability and workability of the Cu component.

  In view of the above circumstances, it is a technical problem to be solved to provide a sintered metal bearing capable of exhibiting high wear resistance and slidability while being able to be manufactured at low cost.

  The present invention has been made to solve the above problems. That is, the sintered metal bearing according to the present invention is a sintered metal bearing in which a Cu structure is dispersed in an Fe-based structure, and the Fe-based structure is contained in a weight ratio of 10 times or more of the Cu structure. It is characterized by the fact that the texture remains as a granular texture. Here, the “Fe-based structure” includes not only a structure composed only of Fe, but also a structure having Fe as a main component, such as SUS. Further, regarding the Cu structure, it is not necessary that all the Cu structures are granular, and a part thereof may have a non-granular shape by sintering.

  Thus, by significantly increasing the proportion of the Fe-based structure as compared with the Cu structure, it is possible to improve the wear resistance and reduce the manufacturing cost. In addition, by leaving the Cu structure as a granular structure, the Cu structure constitutes a bearing surface including a sliding surface together with the Fe-based structure. Can be obtained. Further, it is possible to maintain the surface accuracy of the sliding surface by securing the workability of the sliding surface while increasing the ratio of the Fe component. In addition, the content ratio (10 times) of the Fe-based structure and the Cu structure is the above-mentioned in terms of wear resistance, slidability, and cost by including the Fe-based structure and the Cu structure in this ratio. Based on the inventors' knowledge that all three characteristics are satisfied.

  Here, specifically, the content ratio of the Fe-based structure can be 90% or more by weight ratio. In this case, the content ratio of the Fe-based structure can be increased up to 98% by weight. If it is a sintered metal bearing in which the content ratio of the Fe-based structure is within the above range, it is possible to achieve cost reduction while satisfying the wear resistance and the slidability at the implementation level. .

  Further, the Fe-based structure may be composed of one or both of an Fe structure and a SUS structure, for example. In this case, an Fe structure is preferable if strength or cost is important, and an SUS structure is preferable if corrosion resistance is important.

  Further, the sintered metal bearing according to the above configuration may be provided with a dynamic pressure generating portion for generating a dynamic pressure action of fluid between the shaft to be rotated and supported. Specifically, a dynamic pressure generating portion may be provided on an inner peripheral surface serving as a bearing surface or an axial end surface. Since the bearing according to the present invention adopts a structure in which the Cu structure is left as a granular structure, the Cu structure is also present in the bearing surface layer portion having the bearing surface. For example, uneven shapes such as dynamic pressure grooves are accurately formed. can do.

  Since the sintered metal bearing according to the above configuration is excellent in wear resistance and slidability as described above, it can be suitably used as a fluid dynamic bearing device including this bearing.

  Further, the solution of the above-mentioned problem is a method of manufacturing a sintered metal bearing in which a Cu structure is dispersed in an Fe-based structure, and a Cu powder and an Fe-based powder that is 10 times or more of the Cu powder by weight ratio. It is also achieved by a method for manufacturing a sintered metal bearing, characterized in that at least the raw material powder contained is compression molded, and then the compression molded body is sintered at a temperature lower than the melting point of Cu.

  According to this method, all of the Cu powder in the compression-molded body remains in a granular state without melting, so that the slidability (compatibility with the counterpart material) and workability are ensured at a high level as described above. Can do. Moreover, since it does not need to melt | dissolve at the time of sintering, it can prevent that a new internal pore is formed, or can prevent the expansion of an adjacent internal pore. In any case, it is possible to prevent an increase in the number of internal pores having such a size that allows the lubricating oil to flow as will be described later.

  As the Fe-based powder, Fe-based alloy powder such as Fe powder and SUS powder can be used. Further, in order to enhance the mutual dispersibility of the Fe-based powder and the Cu powder, the Fe-based powder and the Cu powder may be supplied to the raw material powder in an integrated state by partial alloying. In this way, in principle, any Fe-based powder is supplied to the raw material powder integrally with the Cu powder, so that the Fe-based powder or Cu powder is prevented from segregating and a homogeneous sintered body is obtained. Can do.

  In addition, the Cu powder used as one of the raw material powders may have a fine particle size as compared with the Fe-based powder. Here, whether or not “Cu powder has a finer particle size than Fe-based powder” may be evaluated by any of the maximum particle size, average particle size, and median particle size of both powders. Absent. Or you may make it determine the magnitude relationship of both powder particle sizes by the magnitude relationship of the numerical value shown by the 2 or more evaluation criteria among these values. Thus, by using fine Cu powder compared with Fe type powder, the contact area (or contact location) with Fe type powder increases compared with Cu powder which has a particle size equivalent to Fe type powder, for example. Therefore, the strength of the bearing can be ensured even if the proportion of Fe powder is significantly increased (90 wt% or more). In addition, there is a concern about a decrease in fluidity as the powder becomes finer. In the present invention, since the mixing ratio of Cu powder is kept lower than the mixing ratio of Fe-based powder, this kind of problem There is no worry of concern.

  As described above, according to the present invention, a sintered metal bearing capable of exhibiting high wear resistance and slidability can be manufactured at low cost.

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 equipped 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 one 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. It is a cross-sectional photograph of the sintered metal bearing which concerns on one Embodiment. It is a cross-sectional photograph of the sintered metal bearing which concerns on other embodiment. It is a cross-sectional photograph of the sintered metal bearing which concerns on other embodiment. It is a graph which shows the measurement result of an abrasion test. It is a graph which shows the measurement result of a pressure ring test. It is a graph which shows the measurement result of permeated oil amount.

  The sintered metal bearing according to the present invention is composed mainly of an Fe-based structure and a Cu structure dispersed in the Fe-based structure. Here, the ratio of the Fe-based structure to the whole is 10 times or more of the Cu structure in weight ratio. For example, when the Fe-based structure is included in 90 wt% or more, the bearing is arranged so that the Cu structure is included in 9 wt% or less. The content ratio of each of the Fe-based structure and the Cu structure is set. Here, for example, X3000 manufactured by Hitachi High-Technologies Corporation as SEM and EMAX7021H manufactured by HORIBA, Ltd. as EDS are used, and quantitative analysis of Fe and Cu is performed by elemental analysis. did.

  The Fe-based structure may be either an Fe structure or an Fe-based alloy structure such as SUS, or may include both. In addition, as described above, when the proportion of the entire Fe-based structure is significantly increased (for example, 90 wt% or more), the Fe-based structure is composed of Fe having a relatively low melting point compared to SUS or the like. Is good. This is because a sufficient sintering action can be obtained between the raw material powders (for example, between the Fe powder and the Cu powder) during sintering, and it is easy to ensure the sintering strength.

  The Cu structure constituting the sintered metal structure together with the Fe-based structure is mainly granular. Here, the size of each Cu structure (such as the long width or area of the granular structure) may be generally smaller than that of the Fe structure. Such a structure can be obtained, for example, by using a Cu powder having a finer particle size than that of an Fe-based powder as one of the raw material powders. As described above, since the fine Cu structure is included as compared with the Fe-based structure, the contact area (or contact location) with the Fe-based structure increases. Therefore, the strength of the bearing can be ensured even if the proportion of Fe powder is significantly increased (90 wt% or more). In addition, since the ratio (area or exposed portion) of the Cu structure exposed on the bearing surface such as the bearing surface is increased as compared with that having a Cu structure of the same size as the Fe-based structure, even if the ratio of the structure is small Easy to ensure mobility.

  Further, from the viewpoint of enhancing the slidability of the bearing surface or ensuring the workability of the sintered body, the proportion of the entire Cu structure has never been as high as possible. Can be set relatively small when the size is smaller than that of the Fe-based structure. Specifically, the ratio of the Cu structure to the whole can be set to 1.0 wt% or more and 9.0 wt% or less. When the content of the Cu structure is less than 1.0 wt%, it is difficult to expose the Cu structure on the bearing surface, and even if exposed, good slidability (compatibility) with the counterpart material is obtained. This is because it is difficult to fully demonstrate. In addition, when the Cu structure is included exceeding 9.0 wt%, it is difficult to maintain the ratio of the Fe-based structure in the entire structure to 10 times (90 wt%) or more of the Cu structure. This is because this type of bearing usually contains a predetermined amount of other structures such as Sn structure and graphite in addition to the main Fe-based structure and Cu structure as described later.

  In addition to the above structure, other structures may be included, for example, a metal structure having a melting point lower than that of the Cu structure (for example, a structure made of a low melting point metal such as Sn) may be included. That is, the sintered metal bearing may be composed of an Fe-based structure, a Cu structure, and a low melting point metal structure. Such a metal structure is melted (liquid phase) at the time of sintering, and acts as a binder between Fe-based powders or between Cu powder and Fe-based powders. Therefore, even when the sintering action between the Fe-based powders is insufficient, the bonding force between the powders can be reinforced and the strength of the sintered body (sintered metal bearing) can be improved. The low melting point metal may be any metal that melts at a predetermined sintering temperature (here, a temperature lower than the melting point of Cu), and includes, for example, metals such as Sn, Zn, Al, and P, or two or more thereof. Alloys can be used.

  Further, for the purpose of improving the moldability and mold release property during compression molding or the sliding characteristics of the finished product, the metal structure may further contain a graphite (graphite) structure. In this case, the sintered metal bearing is composed of an Fe-based structure, a Cu structure, a low-melting-point metal structure, and a graphite structure.

The volume ratio (100-porosity [%]) of the sintered metal bearing having the above-described structure is preferably set according to the actual application, for example, 75% to 95% (in terms of porosity). 5% or more and 25% or less). For example, when the internal pore is 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 (for example, 15% to 25%) can be retained in the internal pores so that the amount of lubricating oil can be supplied to the bearing gap. The following should be set. 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: Density of sintered metal bearing (refer to the column of JIS Z 2501 dry density for the measurement method)
ρ0: True density of materials with the same composition as sintered metal bearings Porosity has been found to decrease almost linearly with increasing density ratio, thus obtaining porosity by determining density ratio Can do.

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 a dynamic pressure action of the lubricating oil is provided on the inner peripheral surface of the sintered metal bearing. In this case, it is preferable to set the surface area ratio of the inner peripheral surface to be relatively small (for example, 2% or more and 10% or less) for the purpose of preventing escape of hydraulic pressure. Here, “surface opening” refers to 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]
Photo shooting: Shutter speed 0.5 seconds Binary threshold: 235

  The sintered metal bearing according to the above structure is manufactured by, for example, the following method. That is, a step (a) of compressing a raw material powder containing Fe-based powder and Cu powder into a predetermined shape (a), a step (b) of sintering a green compact, and a step of sizing the sintered body ( It is manufactured through at least three steps of c).

  First, regarding the compacting step (a), a raw material powder in which Cu powder is mixed with Fe-based powder (for example, Fe powder) with a V-type mixer or the like is prepared. Here, for example, an Fe powder having an average particle size of 150 μm or less is used, and a Cu powder having an average particle size of 75 μm or less is used. Further, when mixing the powder, the mixing ratio of each powder is set according to the content ratio of each structure in the finished product. For example, the respective powders are mixed so that the Fe-based powder (the total amount when a plurality of types of Fe-based powders are mixed) is 10 times or more of the Cu powder by weight ratio. Of course, if necessary, a powder obtained by further mixing other types of powder such as Sn powder and graphite powder with the above metal powder may be used as the raw material powder.

  At this time, in order to enhance the dispersibility of the Cu powder, the Cu powder is partially brought into contact with the surface of the Fe powder in advance, and the contact portion is alloyed (part of Fe powder and Cu powder). It is also possible to use an alloy body) as a raw material powder. 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 (for example, a cylindrical shape) according to the finished product is prepared, and the raw material powder is supplied to the filling space 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, 6.0 g / cm ³ or more and 6.8 g / cm ³ or less.

  Next, the green compact is heated for a predetermined time at a temperature lower than the melting point of Cu (1083 ° C.). As a result, at least the Cu powder and the Fe-based powder are sintered with each other, whereby a sintered body made of a sintered metal structure having an Fe-based structure and a Cu structure can be obtained (sintering step (b )). Here, regarding the sintering temperature, if sintering is performed at a temperature that is too close to the melting point of Cu, the proportion of the Cu powder that is actually melted increases, making it difficult to maintain the granular structure of Cu in the finished product. Further, if sintering is performed at a temperature that is too far (low) 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 850 ° C. or higher and 1050 ° C. or lower, 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 even smaller (for example, 10% or less). For this reason, an oil film having a predetermined film thickness can be formed on the bearing surface even when it is incorporated into a fluid dynamic pressure bearing device described later.

  Here, FIGS. 7 to 9 are cross-sectional photographs of sintered metal bearings according to an example of the present invention. All of these cross-sectional photographs were taken using a VE9800 manufactured by Keyence Corporation. The observation magnification was 200 times. In addition, the sintered metal bearing was cut in the axial direction and the cut surface was lapped, and the object to be photographed was observed. FIG. 7 shows cross-sectional photographs in the case of Fe structure: 70 wt%, FIG. 8 in the case of Fe structure: 80 wt%, and FIG. 9 in the case of Fe structure: 90 wt%. In each figure, the lightest gray represents the “Cu structure”, the medium gray represents the “Fe structure”, and the darkest gray (color close to black) represents the “internal pores”. From these figures (photographs), when the Fe structure is 70 wt%, it is not so clear, but when the Fe structure is 90 wt%, the Cu structure remains appropriately dispersed as a granular structure. I can see it. Also, it can be seen from each figure that relatively many fine pores exist compared to each metal structure.

  Since the sintered metal bearing according to the above description is excellent in wear resistance and slidability, for example, magnetic disk devices such as HDD, CD-ROM, CD-R / RW, DVD-ROM / RAM As a bearing device for a spindle motor in a magneto-optical disk device such as an optical disk device such as MD or MO, or a motor bearing device such as a polygon scanner motor of a laser beam printer (LBP), a color wheel motor of a projector, or a fan motor Is preferably used.

  FIG. 1 shows an example of the above-mentioned 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 of an HDD equipped with this fluid dynamic bearing device 1. The principal part sectional drawing of the motor for a disk drive 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 that is fixed to the housing 7 and has the shaft member 2 disposed on the inner periphery, and a lid that closes one end of the housing 7. A member 9 and a seal member 10 disposed on the other end opening side of the housing are provided.

  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 oppose 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 into the inner periphery of the sintered metal bearing 8, the radial bearing surfaces 2a1, 2a1 and Radial bearing gaps of radial bearing portions R1 and R2 described later are formed between the inner 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 appropriately connected to the inner peripheral surface 7a of the housing 7 by, for example, bonding (including loose bonding and press-fitting bonding), press-fitting, welding (including ultrasonic welding and laser welding). Fixed by means. 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, a liquid crystal polymer (LCP), polyphenylene sulfide (PPS), 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.

The sintered metal bearing 8 has a cylindrical shape having a porous structure in this embodiment, and a region in which a plurality of dynamic pressure grooves are arranged as a radial dynamic pressure generating portion on the whole or a part of the inner peripheral surface 8a. 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 8 a 1 above the axial center m (the seal member 10 side) of the region (so-called band portion 8 a 3) between the dynamic pressure grooves 8 a 1 and 8 a 2 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, 8a2 arrangement region located below the inner peripheral surface 8a (the side close to a thrust bearing gap described later) is formed symmetrically in the axial direction with the strip 8a3 at the axial center. .

  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. The 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 8 d 1 extending in the axial direction are formed on the outer peripheral surface 8 d 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.

  As described above, the dynamic pressure grooves 8a1 and 8a2 arrangement region of the inner peripheral surface 8a is subjected to the sizing process (c) in the above-described sizing process and the rotational sizing, and then subjected to the groove sizing process to obtain a sintered body (fired body). It is formed on the inner peripheral surface 8a of the 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. In this case, since many granular structures of Cu remain on the inner peripheral surface of the sintered body, the moldability of the groove sizing process is also good, and the dynamic pressure grooves 8a1, 8a2 or the dynamic pressure grooves 8a1, 8a2 The array region 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 granular structure of Cu remains on the inner peripheral surface of the sintered body effectively acts on the moldability or molding 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.

  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 thereof 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 seal 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 region indicated by the dotted pattern in FIG. 2) is filled with lubricating oil, whereby 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 configured as described above, 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. Opposing through a gap. 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, 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 to this, 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 dynamic pressure groove arrangement region provided on the lower end surface 2b2 of the flange portion 2b facing the dynamic pressure groove arrangement 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 an extremely large Fe-based structure, the hardness of the inner peripheral surface 8a serving as the radial bearing surface is increased. Therefore, for example, immediately after the rotation of the shaft member 2 made of SUS or immediately before the rotation is stopped, contact sliding 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. Even if this 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. However, as described above, the hardness difference between both the members 2a and 8 (the hardness difference between both sliding surfaces 2a1 and 8a) is reduced. By doing so, 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 axially asymmetric with respect to the axial center of the band portion 8a3. The axial dimension X1 in the upper area from the center is larger than the axial dimension X2 in the lower area. 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. The lubricating oil that has flowed downward from the radial bearing gap due to the difference in the pulling force causes the shaft of the sintered metal bearing 8 located on the outer diameter side from the thrust bearing gap of the first thrust bearing portion T1. The circular groove 8c1 and the radial groove 8c2 are circulated from the axial groove between the directional groove 8d1 and the upper end surface 8c and the lower end surface of the seal member 10, and drawn into the radial bearing gap of the first radial bearing portion R1 again. It is.

  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 according to the present invention has been described, but 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 a fluid dynamic pressure bearing device including a 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 of the flange portion 2b provided at one end of the shaft portion 2a. Although the case where it has the form demonstrated 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 on the dynamic pressure groove arrangement region having the shape shown in FIG. 4 (the direction of the spiral is opposite to that in FIG. 3). Have Therefore, 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 the second seal member 20. Is provided between the upper end surface 20a of the metal plate and the lower end surface 18b 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, the sliding wear of the sintered metal bearing 18 due to contact with the shaft member 2 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 increases. 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 in an axial direction, and these sintered metal bearings 8 and 8 are formed by a cylindrical portion 27a, 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 has an asymmetric dynamic pressure groove 8a1, illustrated in FIG. 8a2 is provided, and the lower sintered metal bearing 8 is provided with the symmetrical dynamic pressure grooves 8a1, 8a2 exemplified 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 the excellent bearing performance can be exhibited over a long period of time even when the rotating body weight 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 made 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 outer peripheral surface facing the peripheral 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).

  In the above embodiment, the case where all the dynamic pressure generating portions are provided on the fixed side (the housing 27, the sintered metal bearing 8, the lid member 9, etc.) has been described. (The shaft members 2 and 12, the flange portion 2b, the seal members 19 and 20, etc.) may 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.

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

  Further, in the above embodiment, the lubricating oil is exemplified as the fluid for filling the fluid dynamic pressure bearing devices 1, 11 and 21 and forming a fluid film in the radial bearing gap and the 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 is excellent in 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) formed of a raw material powder containing Fe-based powder and Cu powder in a predetermined ratio and a sintered material formed of a raw material powder of a conventional composition The metal bearing (comparative example) was subjected to a wear test, a crushing test, and a permeated oil amount measurement test, respectively, and a comparative evaluation was performed for each characteristic.

Here, NC100.24 manufactured by Heganes Co., Ltd. as Fe powder, CE-15 manufactured by Fukuda Metal Foil Co., Ltd. as Cu powder, and Daido Special Steel Co., Ltd. as SUS powder are used as test materials. ) DAP410L manufactured by) was used. 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 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 were set so that the density of the green compact was 6.5 to 6.9 [g / cm ³ ]. The sintering temperature of the example was 1050 ° C., and the sintering temperature of the comparative example was 870 ° C. Table 1 shows the compositions of the comparative example, the example, and the raw material powders. The particle size distribution of each powder is as shown in Tables 2-6.
The finished product dimensions of the test piece as a finished product were set to φ (outer diameter) 7.5 mm × t (axial width) 10 mm in both the examples and the comparative examples in the case of a wear test described later. In the pressure ring test and the measurement test of the permeated oil amount, φ (outer diameter) 7.5 mm × φ (inner diameter) 4 mm × t (axial width) 10 mm in both the examples and the comparative examples. Moreover, the number of test pieces was set to 5 in each of the examples and comparative examples.

Here, the abrasion test was performed using the above test piece under the following test conditions.
Opposite test piece Material: SUS420J2
Dimensions: φ (outer diameter) 40 mm x t (axial width) 4 mm
Peripheral speed: 50 m / min
Surface pressure: 1.3 MPa
Lubricating oil: Ester oil (viscosity: 12mm ² / s)
Test time: 3hrs

  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.

In the permeated oil measurement test, lubricating oil is supplied from the tank to the inner periphery of the test piece (sintered metal bearing) that is not impregnated with lubricating oil, and an appropriate air pressure is applied to the inner periphery of the test piece. It was performed by applying a predetermined time (4 atm, 10 minutes) and measuring the amount of lubricating oil leaked to the outside from the outer peripheral surface of the test piece. The lubricating oil used was ester oil (12 mm ² / s).

FIG. 10 shows the measurement result of the wear test, FIG. 11 shows the measurement result of the pressure ring test, and FIG. 12 shows the measurement result of the permeated oil amount. As shown in FIG. 10, when the ratio of the Fe-based structure to the whole is 10 times or more of the Cu structure by weight (Example), the amount of wear is greatly reduced compared to the previous composition (Comparative Example). The effect was seen. Further, from the results shown in FIG. 11, even when the proportion of the Fe-based structure is significantly increased compared to that of the Cu structure (Example), the crushing strength at the same level as the previous composition (Comparative Example) is shown. I understand that. Furthermore, from the results shown in FIG. 12, the composition (Example) having excellent wear resistance and crushing strength as described above, but also the amount of permeated oil (lubricant permeability) was compared with the previous composition (Comparative Example). It can be seen that the same level of performance is exhibited.

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 circumference Surfaces 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 (9)

  A sintered metal bearing in which a Cu structure is dispersed in an Fe-based structure, wherein the Fe-based structure is contained in a weight ratio of 10 times or more of the Cu structure, and the Cu structure remains as a granular structure. Sintered metal bearing.   The sintered metal bearing according to claim 1, wherein the content ratio of the Fe-based structure is 90% or more by weight.   The sintered metal bearing according to claim 2, wherein the content ratio of the Fe-based structure is 98% or less by weight.   The sintered metal bearing according to claim 1, wherein the Fe-based structure is composed of one or both of an Fe structure and a SUS structure.   The sintered metal bearing according to claim 1, wherein a dynamic pressure generating portion for generating a dynamic pressure action of fluid is provided between the shaft to be rotatably supported.   A fluid dynamic bearing device comprising the sintered metal bearing according to claim 1. A method of manufacturing a sintered metal bearing in which a Cu structure is dispersed in an Fe-based structure,
A raw material powder containing at least a Cu powder and an Fe-based powder at least 10 times the weight of the Cu powder in a weight ratio is compression-molded, and then the compact is sintered at a temperature lower than the melting point of Cu. A method for manufacturing a sintered metal bearing.   The manufacturing method of the sintered metal bearing according to claim 7, wherein the Fe-based powder and the Cu powder are used as the raw material powder in an integrated state by partial alloying.   The method for manufacturing a sintered metal bearing according to claim 7, wherein the Cu powder has a finer particle diameter than that of the Fe-based powder.