JP2018040401A - Slide bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress pressure leakage from a bearing surface to enhance a load capacity, without increase costs, and prevent oil film shortage at a slide part between the bearing surface and an opposite member (shaft) to prevent seizure.SOLUTION: A slide bearing (bearing sleeve 8) has bearing surfaces A, B comprising a green compact where particles 11 are coupled to each other by an oxide film 12 formed on surfaces of the particles 11 of metal powder, and sliding with an opposite member to be supported (shaft member 2) through a lubrication film. On the bearing surfaces A, B, provided are many opening parts 13a where communication with an internal pore 13b is cut off by the oxide film 12.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a sliding bearing that slides with a counterpart material to be supported and a lubricating film.

  Sintered oil-impregnated bearings, which are a kind of sliding bearings, are sometimes used for rotation support bearings of small motors such as HDD spindle motors, polygon scanner motors for laser beam printers, and fan motors for cooling fans. . Sintered oil-impregnated bearings have internal pores impregnated with oil (or grease; the same shall apply hereinafter), and this oil oozes out from the bearing surface to supply oil to the sliding part between the bearing surface and the shaft. Lubricity can be improved.

  However, when the pressure of the oil film in the bearing gap increases, a part of the oil escapes from the bearing surface opening of the sintered oil-impregnated bearing to the outside through the internal pores. It will decline. In order to suppress such pressure loss from the opening of the bearing surface, for example, in Patent Document 1 below, the opening of the bearing surface is sealed by sliding a mold (for example, a mandrel) on the bearing surface. Technology to do is shown.

Japanese Patent No. 3377681

  However, if the bearing surface is sealed by sliding the mold as described above, the bearing surface is likely to be damaged and the quality may be deteriorated. Further, the number of processes and molds for sealing the bearing surface increase, resulting in an increase in cost.

  In addition to the above, as means for suppressing pressure loss from the opening of the bearing surface, for example, the volume of the internal pores can be reduced by increasing the molding pressure of the green compact to increase the density, or molten resin or molten metal There is a method to fill the internal pores by soaking. However, the improvement in density by increasing the compacting pressure of the green compact is limited in terms of press capacity, mold strength, and productivity. Further, sealing with molten resin or molten metal makes it difficult to maintain the accuracy of the bearing surface, and requires a great number of man-hours and increases costs.

  Further, if the bearing surface is smoothed by completely sealing the opening of the bearing surface or forming a sliding bearing with a material having no pores such as molten steel, the oil film pressure can be prevented from decreasing. However, in this case, oil is not supplied from the internal pores, so that the oil in the sliding portion between the bearing surface and the shaft is easily depleted, and there is a possibility that seizure occurs due to contact between the bearing surface and the shaft.

  Therefore, the present invention increases the load capacity by suppressing pressure loss from the bearing surface without increasing the cost, and prevents the lubricating film from being cut off at the sliding portion between the bearing surface and the counterpart material (shaft). The purpose is to prevent seizure.

  In order to solve the above-mentioned problems, the present invention comprises a green compact in which the particles are bonded together by an oxide film formed on the surface of the metal powder particles, and the support material to be supported and the lubricating film interposed therebetween. A sliding bearing having a sliding bearing surface is characterized in that the bearing surface has a large number of openings that are blocked from communicating with internal pores by the oxide coating.

  The slide bearing of the present invention does not sinter the green compact at a high temperature (for example, 850 ° C.) like a general sintered bearing, but heat-treats the green compact at a relatively low temperature (for example, 500 ° C.). In this way, an oxide film is formed on the surface of the metal powder particles constituting the green compact, and the particles are bonded together by this oxide film. In this case, since at least a part of the internal pores of the green compact is filled with the oxide coating, it becomes difficult for oil to escape from the surface of the green compact. The pressure capacity from the surface can be suppressed and the load capacity can be increased.

  Also, the oxide coating does not completely seal the opening of the green compact surface and the bearing surface is not smooth. A large number of openings that are blocked from communication remain. This opening functions as an oil reservoir that holds oil, and the oil held in the opening is supplied to the sliding portion between the bearing surface and the counterpart material, thereby preventing the oil film from being cut off at the sliding portion. . The “internal pores” mean pores formed by particles that are not exposed on the surface of the green compact or an oxide film formed on the surface.

  The sliding bearing preferably has an oil content of 4 vol% or less and a surface opening ratio of the bearing surface of 40% or more. The surface opening ratio is an area ratio of all openings on the bearing surface including not only the opening not communicating with the internal pore as described above but also the opening communicating with the internal pore.

  The sliding bearing preferably has an oil permeability of 0.01 g / 10 min or less. The oil permeability is determined by contacting the oil with the surface of the slide bearing (for example, the inner peripheral surface) and holding the oil under a predetermined pressure (0.4 MPa in this case) for 10 minutes. It is obtained by measuring the total weight of oil that has oozed from the opening on the opposite surface (for example, the outer peripheral surface).

  The bearing surface can be, for example, a smooth cylindrical surface that does not have a dynamic pressure groove or the like. The slide bearing is configured to be a fluid dynamic pressure bearing by facing the outer peripheral surface of the shaft member in which the dynamic pressure groove is formed, or to be a circular bearing by facing the cylindrical outer peripheral surface of the shaft member. be able to.

  A dynamic pressure groove may be formed on the bearing surface. For example, the sliding bearing can be configured to face a smooth outer peripheral surface or end surface of the shaft member to constitute a fluid dynamic pressure bearing.

  The above-mentioned plain bearing can be incorporated into a fluid dynamic bearing device, for example. Specifically, it comprises the above-mentioned slide bearing and a shaft member as the mating member inserted in the inner periphery of the slide bearing, and a radial between the bearing surface of the slide bearing and the outer peripheral surface of the shaft member It is possible to obtain a fluid dynamic bearing device that supports the shaft member in a non-contact manner so as to be relatively rotatable with the pressure of the lubricating film in the bearing gap.

  As described above, in the present invention, by filling at least part of the internal pores of the sliding bearing (green compact) with the oxide film, it is possible to suppress the pressure loss from the bearing surface and increase the load capacity. In addition, since a large number of openings serving as oil reservoirs are provided on the bearing surface of the slide bearing, it is possible to prevent the oil film from being cut off at the sliding portion with the counterpart material and to prevent seizure.

It is sectional drawing of a spindle motor. It is sectional drawing of a fluid dynamic pressure bearing apparatus. It is sectional drawing of the slide bearing (bearing sleeve) which concerns on one Embodiment of this invention. It is a bottom view of the slide bearing. It is sectional drawing in the bearing surface vicinity of the said slide bearing. It is a photograph of the bearing surface of the slide bearing. It is sectional drawing of the forming metal mold | die which performs a compacting process (before shaping | molding). It is sectional drawing of the forming metal mold | die which performs a compacting process (at the time of shaping | molding completion). It is sectional drawing of the forming metal mold | die which performs a compacting process (at the time of mold release). The left figure is a cross-sectional structure diagram of the green compact before heat treatment, the center figure is a cross-sectional structure diagram of the green compact after degreasing, and the right figure is a cross-sectional structure diagram of the green compact after the oxidation treatment. It is a graph showing the relationship between the true density ratio of a green compact, and oil content. It is a graph showing the rotational speed and oil film formation rate of the motor which has the slide bearing which concerns on an Example. It is a graph showing the rotational speed and oil film formation rate of a motor which has a slide bearing concerning a comparative example.

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

  The spindle motor shown in FIG. 1 is used in a disk drive device such as an HDD, and includes a fluid dynamic bearing device 1 that rotatably supports a shaft member 2 in a non-contact manner, and a disk hub 3 mounted on the shaft member 2. And, for example, a stator coil 4 and a rotor magnet 5 that are opposed to each other via a gap in the radial direction. The stator coil 4 is attached to the casing 6, and the rotor magnet 5 is attached to the disk hub 3. The housing 7 of the fluid dynamic bearing device 1 is mounted on the inner periphery of the casing 6. The disk hub 3 holds a predetermined number of disks D such as magnetic disks. When the stator coil 4 is energized, the rotor magnet 5 is rotated by the electromagnetic force between the stator coil 4 and the rotor magnet 5, whereby the disk hub 3 and the shaft member 2 are rotated together.

  As shown in FIG. 2, the fluid dynamic bearing device 1 includes a bearing sleeve 8 as a slide bearing according to an embodiment of the present invention, a shaft member 2 as a counterpart material supported by the bearing sleeve 8, and a bearing sleeve. The housing 7 holds the inner periphery 8, the seal portion 9 is provided at the opening at one axial end of the housing 7, and the thrust bush 10 closes the other axial end of the housing 7. In the example of illustration, the housing 7 and the seal part 9 are comprised by one component. In the following description, for the sake of convenience, the closed side of the housing 7 is referred to as the lower side and the open side of the housing 7 is referred to as the upper side in the axial direction, but this is not intended to limit the usage mode of the fluid dynamic bearing device 1.

  The shaft member 2 includes a shaft portion 2a and a flange portion 2b provided at the lower end of the shaft portion 2a. The shaft member 2 is formed of, for example, metal, and in this embodiment, the entire shaft member 2 including the shaft portion 2a and the flange portion 2b is integrally formed of stainless steel.

  The housing 7 is formed in a cylindrical shape with resin or metal. The outer peripheral surface 8d of the bearing sleeve 8 is fixed to the inner peripheral surface 7a of the housing 7 by an appropriate means such as adhesion or press fitting.

  The bearing sleeve 8 has a cylindrical shape, and a radial bearing surface facing the outer peripheral surface 2a1 of the shaft member 2 is provided on the inner peripheral surface 8a. In the illustrated example, radial bearing surfaces A are formed at two locations spaced in the axial direction of the inner peripheral surface 8 a of the bearing sleeve 8. In each radial bearing surface A, dynamic pressure grooves are formed, and in this embodiment, as shown in FIG. 3, dynamic pressure grooves G1, G2 arranged in a herringbone shape are provided in each radial bearing surface A. A region indicated by cross-hatching in the figure indicates a hill raised on the inner diameter side (the same applies to FIG. 4).

  The upper dynamic pressure groove G1 has an asymmetric shape in the axial direction, and the lower dynamic pressure groove G2 has a symmetrical shape in the axial direction. The oil in the radial bearing gap is pushed in the axial direction by the upper dynamic pressure groove G <b> 1 having the axially asymmetric shape, and the oil is forcibly circulated inside the housing 7. In a region between the axial directions of the radial bearing surface A, a cylindrical surface that is continuous with the bottom surfaces of the dynamic pressure grooves G1 and G2 is provided. Note that both the upper and lower dynamic pressure grooves G1, G2 may have an axially symmetrical shape. The upper and lower dynamic pressure grooves G1 and G2 may be continuous in the axial direction, or one or both of the upper and lower dynamic pressure grooves G1 and G2 may be omitted. Further, a spiral dynamic pressure groove or a dynamic pressure groove extending in the axial direction may be formed on the radial bearing surface. Further, the inner circumferential surface 8a (radial bearing surface A) of the bearing sleeve 8 may be a cylindrical surface, and a dynamic pressure groove may be formed on the outer circumferential surface 2a1 of the shaft member 2.

  A thrust bearing surface B facing the upper end surface 2b1 of the flange portion 2b of the shaft member 2 is provided on the lower end surface 8b of the bearing sleeve 8. On the thrust bearing surface B, a pump-in type spiral-shaped dynamic pressure groove G3 as shown in FIG. 4 is formed. In addition, as a shape of the dynamic pressure groove, a herringbone shape, a radiation groove shape, or the like may be adopted. Further, a dynamic pressure groove may be formed on the upper end surface 2b1 of the flange portion 2b of the shaft member 2 with the lower end surface 8b (thrust bearing surface B) of the bearing sleeve 8 as a flat surface.

  As shown in FIG. 3, an annular groove 8c1 and a plurality of radial grooves 8c2 provided on the inner diameter side of the annular groove 8c1 are formed on the upper end surface 8c of the bearing sleeve 8. A plurality of axial grooves 8d1 are provided on the outer peripheral surface 8d of the bearing sleeve 8 at equal intervals in the circumferential direction. The space on the outer diameter side of the flange portion 2b of the shaft member 2 communicates with the seal space S through the axial groove 8d1, the annular groove 8c1, the radial groove 8c2, and the like. Occurrence is prevented. If not particularly necessary, the annular groove 8c1 and the radial groove 8c2 may be omitted, and the upper end surface 8c of the bearing sleeve 8 may be a flat surface.

  The bearing sleeve 8 is a porous oil-impregnated bearing in which oil is impregnated in the internal pores of a metal powder compact. The entire surface of the bearing sleeve 8, including the groove bottom surfaces of the dynamic pressure grooves G1, G2, and G3 and the top and side surfaces of the hills, is a molded surface. The bearing sleeve 8 is not sized, and no sliding mark is formed on the surface of the bearing sleeve 8.

  The bearing sleeve 8 is made of a green compact containing, for example, 95 wt% or more of a single metal. In the present embodiment, as shown in FIG. 5, the bearing sleeve 8 is composed of a green compact composed of iron particles 11 and an oxide coating 12 formed on the surface of the iron particles 11. The iron particles 11 are bonded to each other by an oxide coating 12. Specifically, the oxide coating 12 formed on the surface of each iron particle 11 spreads between the iron particles 11 to form a network, thereby ensuring the strength of the bearing sleeve 8.

  In the bearing sleeve 8, at least a part of the gap (internal pore) between the iron particles 11 is filled with the oxide coating 12, so that the porosity, particularly the porosity communicating with the surface (open porosity) is reduced. Yes. As a result, the oil content of the bearing sleeve 8 is, for example, 4 vol% or less, preferably 2 vol% or less. Further, the oil permeability of the bearing sleeve 8 is set to 0.01 g / 10 min or less, for example.

  The surface of the bearing sleeve 8 is not completely sealed and smoothed by the oxide coating 12, and the surface of the bearing sleeve 8, particularly the radial bearing surface A and the thrust bearing surface B, has a large number of openings. 13a (a minute recess) is formed. The many openings 13a communicate with the internal pores 13b (the pores 13b formed by the iron particles 11 not exposed on the surface of the bearing sleeve 8 or the oxide coating 12 formed on the surface thereof). 12 is blocked. That is, before the oxide film 12 is formed, the internal pores 13b and the opening 13a are communicated with each other. However, when the oxide film 12 is divided, any surface (for example, the inner peripheral surface 8a) is formed. ) Is formed in the opening 13a only. The inner side of the opening 13 a is closed with the oxide film 12. The numerous openings 13a function as an oil reservoir that holds oil. Each bearing surface A, B of the bearing sleeve 8 is also provided with an opening 13c communicating with the internal pore 13b. At least a part of the opening 13c is in communication with the other surface (for example, the outer peripheral surface 8d) of the bearing sleeve 8.

  The surface opening ratios of the bearing sleeve 8 on the radial bearing surface A and the thrust bearing surface B are each 40% or more. The surface aperture ratios of the bearing surfaces A and B are measured by analyzing captured images of the bearing surfaces A and B. FIG. 6 is an enlarged photograph of the inner peripheral surface 8a (radial bearing surface A) of the bearing sleeve 8, and the region shown in black is the opening 13a or 13c. By calculating the ratio of black areas (openings 13a and 13c) in this image, the surface aperture ratio is obtained. In addition, the straight line shown by FIG. 6 is a boundary of a dynamic pressure groove and a hill part.

  The seal portion 9 protrudes from the upper end of the housing 7 toward the inner diameter side. In the present embodiment, the seal portion 9 is formed integrally with the housing 7. The inner peripheral surface 9a of the seal portion 9 has a tapered shape that is gradually reduced in diameter toward the lower side. Between the inner peripheral surface 9a of the seal portion 9 and the outer peripheral surface 2a1 of the shaft portion 2a, a wedge-shaped seal space S is formed in which the radial width is gradually narrowed downward (see FIG. 2). In addition, while the inner peripheral surface of the seal portion 9 is a cylindrical surface, a tapered surface that gradually decreases in diameter upward is provided on the outer peripheral surface of the shaft portion 2a, and a wedge-shaped seal space S is formed therebetween. May be.

  The thrust bush 10 is made of, for example, a metal material (brass or the like) or a resin material, and is fixed to the lower end portion of the inner peripheral surface 7a of the housing 7 by an appropriate means such as press fitting or adhesion. A thrust bearing surface C is formed on the end surface 10 a of the thrust bush 10. On this thrust bearing surface C, for example, a pump-in type spiral dynamic pressure groove is formed (not shown). In addition, as a shape of the dynamic pressure groove, a herringbone shape, a radiation groove shape, or the like may be adopted. Alternatively, the end surface 10a (thrust bearing surface C) of the thrust bush 10 may be a flat surface, and a dynamic pressure groove may be formed on the lower end surface 2b2 of the flange portion 2b of the shaft member 2.

  Oil (or grease) is injected into the fluid dynamic bearing device 1 having the above configuration. In the present embodiment, the inner circumferential space of the housing 7 is filled with oil including the internal pores of the bearing sleeve 8, and an oil surface is formed in the seal space S.

  When the shaft member 2 rotates, the bearing surfaces provided on the bearing sleeve 8 and the thrust bush 10 and the shaft member 2 slide through the oil film. Specifically, a radial bearing gap is formed between the radial bearing surface A of the inner peripheral surface 8a of the bearing sleeve 8 and the outer peripheral surface 2a1 of the shaft portion 2a, and the dynamic pressure grooves G1 and G2 provided on the radial bearing surface A are used. By increasing the pressure of the oil film in the radial bearing gap, the first radial bearing portion R1 and the second radial bearing portion R2 that support the shaft member 2 in a non-contact manner in the radial direction are configured. At the same time, between the lower end surface 8b (thrust bearing surface B) of the bearing sleeve 8 and the upper end surface 2b1 of the flange portion 2b, and below the end surface 10a (thrust bearing surface C) of the thrust bush 10 and the flange portion 2b. Thrust bearing gaps are formed between the side end faces 2b2 and the pressure of the oil film in the thrust bearing gaps is increased by the dynamic pressure grooves provided on the thrust bearing faces B and C. A first thrust bearing portion T1 and a second thrust bearing portion T2 that are supported in a non-contact manner in the direction are configured.

  At this time, when the internal pores of the bearing sleeve 8 are filled with the oxide film 12 and the oil content of the bearing sleeve 8 is 4 vol% or less, the pressure of the oil film in the bearing gap is increased. However, the intrusion of oil from the surface of the bearing sleeve 8 (particularly the radial bearing surface A and the thrust bearing surface B) can be suppressed. Thereby, since the pressure drop of the oil film of a bearing gap is suppressed, the load capacity of radial bearing part R1, R2 and thrust bearing part T1, T2 can be raised.

  The bearing surfaces A and B of the bearing sleeve 8 are provided with a large number of openings 13a (see FIG. 5). The opening 13a is a minute recess in which communication with the internal pore 13b is blocked by the oxide film 12, and serves as an oil reservoir for holding oil. When the shaft member 2 rotates, the oil retained in the opening 13a is supplied to the bearing gap, thereby preventing the oil film from being cut in the bearing gap and preventing seizure due to contact between the bearing sleeve 8 and the shaft member 2. be able to.

  Here, a manufacturing method of the above-described sliding bearing (bearing sleeve 8) will be described. The bearing sleeve 8 is manufactured through a dusting process, a degreasing process, an oxidation process, and an oil impregnation process. Hereinafter, each process will be described in detail.

(1) Compacting step The compacting step is a step of obtaining a cylindrical compact by supplying raw material powder to a mold and compression molding. The method of the compacting process is not particularly limited, and other than uniaxial pressure molding, molding by a multi-axis CNC press can be applied.

  The raw material powder mainly contains metal powder such as iron powder and copper powder. Iron powder can be used regardless of the production method, and for example, atomized powder or reduced powder can be used. Copper powder can also be used regardless of a manufacturing method, for example, electrolytic powder, atomized powder, and reduced powder can be used. In addition, it is also possible to use an alloy powder whose main component is iron or copper (for example, prealloyed pre-alloy powder, partially diffusion alloyed partial diffusion alloy powder). In order to increase strength and improve lubricity, low melting point metal powders such as Sn and Zn, and carbon-based powders such as graphite and carbon black may be added to the raw material powder.

  However, the metal powder contained in the raw material powder preferably contains 95 wt% or more of a single kind of metal powder, and more preferably consists of only a single metal powder. This is because, if the metal type is different, the thickness of the oxide film formed on the surface of the particle, the adhesion to the base material, and the like are different, so that dimensional accuracy and bearing characteristics may not be satisfied. In addition, as long as dimensional accuracy and bearing characteristics are satisfied, a plurality of types of metal powders may be mixed.

  A molding lubricant may be added to the raw material powder in order to ensure lubrication between the raw material powder and the mold in the subsequent compacting step, or between the raw material powders. As the molding lubricant, metal soap or amide wax can be used. The molding lubricant is mixed with the raw material powder as a powder, and a solution in which the above-mentioned molding lubricant is dispersed in a solvent is sprayed or immersed in a metal powder to volatilize and remove the solvent component. A molding lubricant may be coated on the surface of the metal powder.

  In the present embodiment, the raw material powder consists only of pure iron powder (reduced iron powder) and a molding lubricant. The molding lubricant is contained in an amount of 0.1 to 1 wt%, preferably 0.3 to 0.6 wt%, based on pure iron powder.

  The compacting process is performed using a forming mold shown in FIG. The forming mold includes a die 21, a core rod 22, an upper punch 23 and a lower punch 24. On the outer peripheral surface of the core rod 22, molding dies 22a and 22b having shapes corresponding to the dynamic pressure grooves G1 and G2 are provided. On the upper surface of the lower punch 24, a molding die 24a having a shape corresponding to the dynamic pressure groove G3 is provided. In addition, although illustration is omitted, a molding die having a shape corresponding to the axial groove 8d1 is provided on the inner peripheral surface of the die 21, and an annular groove 8c1 and a radial groove 8c2 are formed on the lower surface of the upper punch 23. A mold having a corresponding shape is provided.

  First, as shown in FIG. 7, a raw material powder M is filled into a cavity defined by a die 21, a core rod 22, and a lower punch 24. Next, as shown in FIG. 8, the upper punch 23 is lowered to compress the raw material powder M to form a green compact 8 '. At the same time, the dynamic pressure grooves G1 and G2 are formed on the inner peripheral surface of the green compact 8 ′ by the molds 22a and 22b of the core rod 22, and the green compact 8 ′ by the mold 24a of the lower punch 24. A dynamic pressure groove G3 is formed on the lower end surface of the lower surface.

  Thereafter, as shown in FIG. 9, the green compact 8 'is discharged from the inner periphery of the die 21, so that the force directed to the inner diameter applied to the green compact 8' is released, and the green compact 8 'is spring-loaded. Back occurs. As a result, the inner peripheral surface of the green compact 8 ′ increases in diameter, and the green compact 8 ′ is released from the molds 22 a and 22 b of the core rod 22.

Usually, in a sintered part, the higher the density, the higher the strength. However, as in this embodiment, in the case of increasing the strength by subjecting the green compact to oxidation treatment, if the density of the green compact is too high, an oxidizing gas such as air cannot penetrate into the green compact. Since the formation of the oxide film is limited to the very surface layer of the green compact, although the strength is improved, it is not preferable. In view of this point, the green density is 7.2 g / cm ³ or less (true density ratio 91% or less), preferably 7.0 g / cm ³ or less (true density ratio 89% or less).

On the other hand, if the powder density is too low, chipping or cracking may occur during handling (the rattra value is large), and there is a concern that the interparticle distance is too long to form an oxide film between the particles. In view of this point, the green density should be 5.8 g / cm ³ or more (true density ratio 74% or more), preferably 6.0 g / cm ³ or more (true density ratio 76% or more). In particular, in order to fill the internal pores with an oxide film and reduce the oil content of the green compact to 4 vol% or less, the green density is 6.3 g / cm ³ or more (true density ratio is 80% or more), preferably 6 0.7 g / cm ³ or more (true density ratio 85% or more). In addition, the measurement of a compacting density is based on the dimension measuring method. Further, since the density of the green compact hardly changes even after the subsequent degreasing process and oxidation process, the preferable range of the green compact density is a preferable range of the density of the bearing sleeve 8.

(2) Degreasing process The degreasing process is a process in which the green compact is heated to remove (dewax) the molding lubricant contained in the green compact. The degreasing step is performed at a temperature higher than the decomposition temperature of the molding lubricant and lower than the below-described oxidation step, and is heated, for example, at 300 to 400 ° C. for 60 to 120 minutes. As shown in the left diagram of FIG. 10, the green compact 8 ′ before degreasing is provided with a molding lubricant 14 in the gaps between the iron particles 11, but by performing a degreasing step, FIG. As shown in the center view, the molding lubricant 14 disappears, and a green compact 8 ′ composed only of iron particles 11 is obtained.

  In a conventional sintered bearing manufacturing process, since the green compact is held at a high temperature in the sintering process, the lubricant component contained in the green compact is decomposed and is not included in the sintered product. However, when the present invention is applied, the lubricant component may remain depending on the density of the green compact, the oxidation treatment temperature, and the holding time. Therefore, it is desirable to take a technique in which a degreasing process for decomposing and removing the lubricant component is provided in advance prior to the oxidation process, and the oxidation process is continuously performed in the same atmosphere after the degreasing process. However, it has been confirmed that high strength can be achieved even if an oxidation treatment is carried out while containing a molding lubricant without providing a degreasing step. In addition, the degreasing step may be performed in an atmosphere (for example, an inert gas, a reducing gas, or in a vacuum) different from the oxidation step using a separate heating device.

(3) Oxidation step In the oxidation step, the green compact is heated in an oxidizing atmosphere. Thereby, as shown to the right figure of FIG. 10, the oxide film 12 is produced | generated on the surface of each particle | grains 11 of a metal powder (iron powder), and particle | grains 11 are couple | bonded through this oxide film 12, The strength of the green compact 8 ′ is increased. Specifically, the oxide film formed on the surface of each particle of the metal powder by the oxidation process spreads between the iron particles 11 to form a network, thereby bonding by sintering at a high temperature as in the past. Instead of the force, the green compact 8 'is strengthened. Further, in this embodiment, not all particles of iron powder as a main component are bonded via an oxide film, but some particles are directly in contact with each other without an oxide film and fused. doing.

  Generation of the oxide film 12 fills at least a part of the internal pores of the green compact 8 ′. At this time, at least a part of the opening on the surface of the green compact 8 ′ is blocked from communicating with the internal pores 13 b by the oxide coating 12. As a result, a large number of openings 13a whose inner side is closed with the oxide film 12 are formed on the surface of the green compact 8 '(see FIG. 5).

  The processing conditions (heating temperature, heating time, heating atmosphere) of the above-described oxidation treatment are such that the strength required for a dynamic pressure bearing is imparted to the green compact 8 ′, and the green compact 8 is formed by the oxide coating 12. The oil content of 'is set to 4 vol% or less and the surface opening ratio is 40% or more. Specifically, the heating temperature in the oxidation step of the present embodiment is set to 400 ° C. or higher, preferably 450 ° C. or higher. Further, if the heating temperature is too high, the dimensional change of the green compact becomes large, so the heating temperature is set to 600 ° C. or lower, preferably 550 ° C. or lower. The heating time is appropriately set in the range of 5 minutes to 2 hours, for example, 10 to 20 minutes. The green compact that has undergone the oxidation step has a strength required for the slide bearing, specifically, a crushing strength of 120 MPa or more, and preferably 150 MPa or more.

  The heating atmosphere is an oxidizing atmosphere in order to promote positive oxidation. However, since the generation rate of the oxide film is too high in the water vapor atmosphere, it is preferable to use an oxidizing atmosphere in which the generation rate of the oxide film is lower than that of the water vapor atmosphere. Specifically, it is preferable to heat in an atmosphere of air or oxygen, or an oxidizing gas in which an inert gas such as nitrogen or argon is mixed. By performing oxidation treatment in these oxidizing gases, particularly in an air atmosphere, the oxide film formed on the surface of the green compact can be suppressed, so that a reduction in the surface roughness of the green compact can be suppressed. Further, in order to obtain a strength that can be used as a slide bearing (for example, a crushing strength of 120 MPa or more), the oxygen fraction in the heating atmosphere is preferably 2 vol% or more.

The iron oxide film formed on the surface of the iron powder is a mixed phase of two or more of Fe ₃ O ₄ , Fe ₂ O ₃ , and FeO. The ratio of these oxide coatings varies depending on the material and processing conditions.

  Strengthening by the oxidation process described above is a material (iron-based, copper-based, iron-copper-based, iron, copper, or a mixture of both of them in various proportions used in conventional general sintered members. Alternatively, it can be applied to a green compact of copper-iron. However, it is preferable that the metal powder consists of only a single type (for example, iron powder) because the thickness of the oxide film and the adhesion with the particles can be made uniform.

  Since the oxidation process described above has a lower processing temperature than the conventional sintering process at a high temperature, the dimensional change of the green compact before and after the process is small. For this reason, a decrease in the dimensional accuracy of the green compact, particularly the dimensional accuracy (groove depth, etc.) of the dynamic pressure groove can be suppressed, and the required accuracy can be satisfied without sizing. By omitting the sizing process in this manner, the manufacturing process of the bearing can be shortened, the cost can be reduced, and the design of the bearing and the forming mold can be facilitated.

  The above oxidation step can be applied regardless of the shape and size of the green compact. Moreover, since the surface of the green compact which performed the oxidation process is covered with an oxide film, a rust prevention effect is high and a rust prevention process is unnecessary depending on the case. In addition, since the processing temperature of the oxidation process is relatively low, an additive that denatures and decomposes at a temperature exceeding this processing temperature (for example, a material having slidability and lubricity) is added to enhance the functionality of the product. It is also possible to plan.

(4) Oil impregnation step The oil impregnation step is a step in which lubricating oil is impregnated into the internal pores of the green compact subjected to oxidation treatment. Specifically, after the green compact is immersed in oil under a reduced pressure environment, the pressure is returned to atmospheric pressure, so that the oil enters the internal pores from the opening on the surface of the green compact. Thus, the bearing sleeve 8 according to this embodiment is completed. Note that the oil impregnation step may be omitted, and a green compact that is not impregnated with oil may be used as the bearing sleeve 8. In this case, after the fluid dynamic pressure bearing device 1 is assembled using the bearing sleeve 8 in the dry state, the internal pores of the bearing sleeve 8 are filled when oil is filled into the internal space of the fluid dynamic pressure bearing device 1 by vacuum impregnation or the like. Is impregnated with oil.

  The embodiment of the present invention is not limited to the above. For example, in the above embodiment, the bearing sleeve 8 is provided with both the radial bearing surface and the thrust bearing surface. However, the present invention is not limited to this, and only one of the radial bearing surface or the thrust bearing surface is provided. The present invention may be applied to a slide bearing. For example, a sliding bearing according to the present invention may be applied as the thrust bush 10 described above.

  Further, in the above embodiment, the case where the dynamic pressure groove is formed in the bearing sleeve 8 is shown, but the present invention is not limited to this. For example, a perfect circle bearing may be configured with both the inner peripheral surface 8a of the bearing sleeve 8 and the outer peripheral surface 2a1 of the shaft member 2 as cylindrical surfaces. In this case, a dynamic pressure is generated in the oil film in the bearing gap between the bearing sleeve 8 and the shaft member 2 due to the swing of the shaft member 2, and a fluid dynamic pressure bearing that supports the shaft in a floating manner is configured by this dynamic pressure. Such a fluid dynamic pressure bearing is applied when supporting a shaft that rotates at a relatively high speed, but is not limited to this, and a counterpart material that rotates at a relatively low speed or a counterpart material that swings or linearly moves. The slide bearing of the present invention can also be applied as a bearing that is slidably supported via a lubricating film.

  In the above-described embodiment, the housing 7 and the seal portion 9 are configured as a single component, and the thrust bush 10 is formed as a separate component. However, the present invention is not limited thereto. For example, the housing 7 and the thrust bush 10 are configured as a single component. The seal portion 9 may be a separate body. Alternatively, the housing 7, the seal portion 9, and the thrust bush 10 may be separated.

  In the above embodiment, the fluid dynamic pressure bearing device having a full-fill structure in which the oil surface is formed only at one place (in the seal space S) is shown. The slide bearing according to the present invention may be incorporated in the fluid dynamic bearing device.

  In the above embodiment, the case where the sliding bearing (bearing sleeve 8) is fixed and the mating member (shaft member 2) rotates is shown. On the contrary, the mating member is fixed and the sliding bearing is fixed. It may be rotated. The slide bearing according to the present invention can be used by being incorporated not only in a spindle motor for a disk drive device such as an HDD but also in a fan motor for a cooling fan or a polygon scanner motor for a laser beam printer.

  In order to confirm the effect of the present invention, the following tests were conducted.

(1) Relationship between oil content and true density ratio After degreasing and oxidizing a plurality of green compacts with different densities to create multiple types of cylindrical test pieces, the oil content of each test piece was measured. . The test piece (green compact after the oxidation treatment) has the same configuration as the sliding bearing (bearing sleeve 8) of the above embodiment, and is composed of iron particles and an oxide film formed on the surface thereof. The oil content is measured according to JIS Z 2501: 2000.

  In FIG. 11, the measurement result of the oil content of each test piece is shown. According to this figure, even if the true density ratio is about 80%, the oil content is less than half (for example, 4 vol% or less) with respect to 10 vol% which is the lower limit value of the oil content of a general sintered oil-impregnated bearing. Further, when the true density ratio is 85% or more, the oil content is almost 0 vol% (2 vol% or less). From the above, it has been clarified that the oil content can be sufficiently suppressed by degreasing and oxidizing the green compact.

(2) Oil film formation rate The green compact made of iron powder and molding lubricant was subjected to degreasing and oxidation treatments to produce a slide bearing according to the example. The plain bearing of the example has the same configuration as the bearing sleeve 8 (see FIGS. 3 and 4) of the above embodiment, the crushing strength is 150 MPa or more, the oil content is 4 vol% or less, the surface opening of the bearing surface The rate is 40% or more. On the other hand, a conventional plain bearing made of sintered copper-based metal was used as a comparative example. The plain bearing of the comparative example has the same shape as the bearing sleeve 8 of the above embodiment, but the manufacturing method is different from the examples. Specifically, after forming a cylindrical green compact without a dynamic pressure groove, this is sintered to obtain a sintered body, and the dynamic pressure groove is formed by sizing the sintered body. Thereafter, the inner peripheral surface of the sintered body was subjected to sealing treatment by rotational sizing.

  The oil bearing formation rate was measured by incorporating the slide bearings of Examples and Comparative Examples into motors and measuring the energization amount between the shaft and the slide bearing while rotating each motor. Specifically, in a normal temperature (25 ° C.) environment, while rotating the motor at 2000 r / min, the shaft is held upright in the vertical direction, and the shaft is swung between the vertical direction and the horizontal direction. This state was repeated alternately every 2 seconds, and the oil film formation rate at this time was measured.

  As shown in FIG. 13, in the motor using the slide bearing of the comparative example, it can be seen that the oil film formation rate is lowered when swinging, and the shaft and the slide bearing are in contact with each other. On the other hand, as shown in FIG. 12, in the motor using the slide bearing of the example, the oil film formation rate was always 100% both in the upright state and in the swinging state. Therefore, it was confirmed that by using the slide bearing of the example, the load capacity is improved and the contact between the shaft and the slide bearing can be prevented.

DESCRIPTION OF SYMBOLS 1 Fluid dynamic pressure bearing apparatus 2 Shaft member 8 Bearing sleeve (slide bearing)
8 'Compact 11 Iron particle 12 Oxide coating 13a Opening 13b Internal pore 14 Molding lubricant A Radial bearing surface B, C Thrust bearing surface G1, G2 (Radial) dynamic pressure groove G3 (Thrust) dynamic pressure groove R1 , R2 Radial bearing part T1, T2 Thrust bearing part S Seal space

Claims (7)

In a slide bearing having a bearing surface that slides through a lubricating film and a counterpart material to be supported, which consists of a green compact in which the particles are bonded together by an oxide film formed on the surface of the metal powder particles,
A slide bearing having a large number of openings on the bearing surface, the communication with internal pores being blocked by the oxide coating. Oil content is 4 vol% or less,
The plain bearing according to claim 1, wherein a surface opening ratio of the bearing surface is 40% or more.   The sliding bearing according to claim 1 or 2, wherein the oil permeability is 0.01 g / 10 min or less.   The plain bearing according to any one of claims 1 to 3, wherein the bearing surface is a smooth cylindrical surface.   The sliding bearing according to any one of claims 1 to 3, wherein a dynamic pressure groove is molded on the bearing surface.   A slide bearing according to any one of claims 1 to 5, and a shaft member as the mating member inserted in an inner periphery of the slide bearing, and a bearing surface of the slide bearing and an outer periphery of the shaft member A fluid dynamic pressure bearing device that supports the shaft member in a non-contact manner so as to be relatively rotatable with a pressure of a lubricating film in a radial bearing gap with a surface. The fluid dynamic pressure bearing device according to claim 6, a rotor magnet provided on a rotating side among the sliding bearing and the shaft member, and a stator provided on a fixed side among the sliding bearing and the shaft member. A motor with a coil.