JP3734981B2 - Sintered oil-impregnated bearing for spindle motor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sintered oil-impregnated bearing impregnated with a lubricating oil obtained by mixing and emulsifying perfluoropolyether (PFPE) with polyalphaolefin (PAO), polyol ester, or other base oil, and is particularly suitable for a spindle motor. The present invention relates to a sintered oil-impregnated bearing.
[0002]
[Prior art]
Some of so-called fluorine oils such as perfluoropolyether have a property of reacting with a metal surface to form a metal fluoride. The produced metal fluoride has solid lubrication performance, and has a low friction coefficient and excellent sliding characteristics. Further, once the metal fluoride film on the metal surface is formed, it is maintained as it is even if it is put in oil other than fluorine oil, and maintains good sliding characteristics. Therefore, since it is sufficient to supply an amount necessary for the reaction with the metal surface for the generally expensive fluorine oil used for such purposes, it is economical to use an appropriate amount added to an inexpensive base oil. Is desirable.
However, even if the fluorine oil is simply mixed with the base oil, the two are separated into two layers, and a uniform mixture cannot be obtained. When such a mixture is put to practical use, the variation in sliding characteristics is large and excellent. The lubrication effect cannot be obtained.
JP-A-5-240251 describes impregnating sintered oil-impregnated bearings with perfluoropolyether alone or as a mixed oil blended with other lubricants. No specific technology is disclosed for the law.
[0003]
[Problems to be solved by the invention]
The present invention provides a sintered oil-impregnated bearing for spindle motors that is excellent in sliding characteristics by preparing a uniform mixture of fluorine oil and base oil and impregnating the mixture, in view of the prior art as described above. With the goal.
[0004]
As a result of intensive investigations along the above-mentioned purpose, the present inventors have found that a uniform mixture with a base oil can be obtained by using a specific fluorine oil, thereby completing the present invention.
That is, the first aspect of the present invention is a polyalphaolefin, polyol ester, diphenyl ether, diester oil, mineral oil (refined mineral oil), one selected from the group consisting of alkylbenzene and alkylnaphthalene, or a mixture of two or more. The present invention relates to a sintered oil-impregnated bearing for a spindle motor , wherein a bearing member is impregnated with a lubricating oil emulsified by mixing 1 to 30% by volume of perfluoropolyether.
In the second aspect of the present invention, the perfluoropolyether is:
_{CF 3 - [(O-CF} 2 -CF 2) p - (O-CF 2) q] -O-CF 3
(Where p and q are integers from 10 to 200)
The present invention relates to a sintered oil-impregnated bearing for a spindle motor impregnated with a lubricating oil.
According to a third aspect of the present invention, the perfluoropolyether is
_{CF 3 -CF 2 -CF 2 -O- (} CF 2 -CF 2 -O) m -CF 2 -CF 3
(Where m is an integer from 10 to 200)
The present invention relates to a sintered oil-impregnated bearing for a spindle motor impregnated with a lubricating oil.
A fourth aspect of the present invention relates to a sintered oil impregnated bearing for a spindle motor impregnated with a lubricating oil in which at least one fluorine atom of the perfluoropolyether is substituted with a methyl trifluoride group.
According to a fifth aspect of the present invention, there is provided a bearing member in which a bearing portion that slides and supports the rotating shaft is provided at both end portions, and an intermediate swelling portion that does not contact the rotating shaft is provided between both bearing portions. The outer peripheral surface of the bearing is press-fitted into the inner hole of the housing, a gap is formed between the outer peripheral surface of the bearing portion and the inner hole surface of the housing, and an axial groove provided on the outer peripheral surface of the press-fit portion of the bearing member. The present invention relates to a sintered oil-impregnated bearing for a spindle motor, in which a bearing member of a bearing in which a through hole is formed by an inner hole surface of a housing and a housing is impregnated with the lubricating oil.
The sixth aspect of the present invention relates to a sintered oil-impregnated bearing for a spindle motor in which a dynamic pressure groove is provided on the inner peripheral surface of the bearing portion.
A seventh aspect of the present invention relates to a sintered oil-impregnated bearing for a spindle motor whose cross section in a direction perpendicular to the axis of the bearing portion has a three-arc shape.
[0005]
The present invention is described in detail below.
First, in the present invention, as a base oil of a lubricating oil composition, one or more selected from polyalphaolefin (PAO), polyol ester, diphenyl ether, diester oil, mineral oil (refined mineral oil), alkylbenzene, alkylnaphthalene, and the like. A mixture of
As PAO, for example, 1-decene, isobutylene or the like polymerized in the presence of a Lewis acid or the like, or further hydrogenated can be used.
Examples of polyol esters include ester compounds of polycarboxylic alcohols such as neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol and dipentaerythritol and monocarboxylic acids.
As the diester oil, diesters obtained from a linear dibasic acid such as sebacic acid, azelaic acid, and adipic acid and a higher alcohol having a side chain, such as 2-ethylhexyl alcohol, exhibit particularly excellent properties.
Moreover, as refined mineral oil, what refined | purified mainly the petroleum-type lubricating oil fraction by methods, such as distillation, solvent refinement | purification, and hydrorefining, can be used.
Examples of the alkylbenzene include propylbenzene, butylbenzene, dimethylbenzene, and trimethylbezene, and examples of the alkylnaphthalene include methylnaphthalene, ethylnaphthalene, and ethylmethylnaphthalene.
[0006]
In the present invention, it is important to emulsify by mixing perfluoropolyether (PFPE) with the above base oil.
That is, the density of the base oil is about 0.8 to 0.9 g / cm ³ whereas the density of PFPE is remarkably high, 1.8 to 1.9 g / cm ³ , so that both oil layers are easily separated. However, even if the base oil and PFPE are mixed by an ordinary method, it is difficult to obtain a uniform mixture. Therefore, as a result of studying the mixing method, the present inventors can obtain a lubricating oil with excellent performance by blending PFPE into the base oil in the range of 0.1 to 30% by volume and emulsifying. I found.
If the amount of PFPE contained in the emulsion is less than 0.1% by volume, the effect of PFPE will not be exhibited, and if it exceeds 30% by volume, it will be difficult to stabilize the emulsion state due to sedimentation due to the difference in specific gravity. Is unfavorable because it increases.
PFPE is excellent in sliding properties but very expensive, whereas base oil is inferior to PFPE in sliding properties but relatively inexpensive. Therefore, it is desirable from the viewpoint of cost reduction to uniformly disperse a small amount of PFPE in the base oil.
The method for forming the emulsion is as follows.
That is, it is sufficient if emulsification (emulsification) is confirmed after an appropriate amount of PFPE is added to the base oil and stirred. The same can be done by adding base oil into PFPE.
[0007]
As the PFPE used in the present invention, those having a chemical structure of the following formula are preferable. All of these have many ether bonds in one molecule and contain a large amount of oxygen atoms, so they easily bond to the metal surface, and therefore easily form metal fluorides, thus exhibiting excellent sliding characteristics. can do.
_{(1) CF 3 - [(} O-CF 2 -CF 2) p - (O-CF 2) q] -O-CF 3
(Where p and q are integers from 10 to 200)
_{(2) CF 3 -CF 2 -CF} 2 -O- (CF 2 -CF 2 -O) m -CF 2 -CF 3
(Here, m is an integer from 10 to 200.)
(3) In the above item (1), a compound having a structure in which at least one fluorine atom is substituted with a methyl trifluoride group, for example,
_{CF 3 - [(O-CF} (CF 3) -CF 2) p - (O-CF 2) q] -O-CF 3
(Product name: von Brion, made by Augmont)
(4) In the above (2), a structure having at least one fluorine atom substituted with a methyl trifluoride group, for example,
_{CF 3 -CF 2 -CF 2 -O- (} CF (CF 3) -CF 2 -O) m-1 -CF 2 -CF 3
(Product name: Barrierta, manufactured by Kluber; Product name: Krytox, manufactured by DuPont)
[0008]
Next, a structure of a sintered oil-impregnated bearing that is particularly suitable for use by impregnating the lubricating oil will be described. That is, a bearing having the configuration of the following items [1] to [3] and a configuration in which the requirement of the item [4] is added thereto is preferable.
[1] A shaft support surface is provided at both end portions of the inner hole of the bearing member, and an intermediate bulge portion is formed by increasing the inner diameter of the intermediate portion between the two.
[2] The outer peripheral surface of the middle bulging portion of the bearing member is press-fitted into the inner hole of the housing, and a gap is provided between the outer peripheral surface corresponding to the shaft support surface on both ends and the housing inner hole surface. The shape of the housing inner hole is adjusted so as to have the above-described configuration according to the outer shape of the bearing member at the time of modeling the middle swelling portion. Various methods are known for modeling the middle bulge portion, as will be described later.
[3] An axial groove is provided on the outer peripheral surface of the bearing member, and when the bearing member is press-fitted into the inner hole of the housing, an axial through hole is formed in which the groove becomes a vent hole or an oil passage hole.
[0009]
FIGS. 1A to 1C are longitudinal sectional views of various bearing examples of the present invention, and FIGS. 1D to 1F are plan views of these bearings. 1 (d) is a plan view of the bearing of FIG. 1 (a), FIG. 1 (e) is a plan view of the bearing of FIG. 1 (b), and FIG. 1 (f) is a plan view of FIG. ) Is a plan view of the bearing.
In each drawing of FIG. 1, the bearing member 1 is made of a porous powder sintered metal and can be impregnated with a lubricating oil. The bearing member 1 has bearing portions 2 on both sides, and has an intermediate bulge portion 3 in the middle of the inner holes of both bearing portions 2. Further, the bearing member 1 is press-fitted into the inner hole (press-fit surface 7) of the housing 4 on the outer peripheral surface of the middle swelling portion 3, and a gap is formed between the outer periphery of the bearing portion 2 and the inner hole of the housing 4. Has been. Further, a groove 5 is provided in the axial direction on the outer peripheral surface of the press-fitting portion of the bearing member 1, and the groove 5 and the inner hole surface (press-fitting surface 7) of the housing 4 form a through hole 6.
[0010]
In addition to the configurations of the items [1] to [3], it is preferable to add the following requirements.
[4] A dynamic pressure groove is provided on the sliding surface of the inner hole of the bearing portion 2. As the dynamic pressure groove, a spiral, herringbone, inclined, or peripherally closed groove is formed, or a three-arc bearing member is formed.
FIG. 2 is a development view of the sliding surface provided with these dynamic pressure grooves. 2A to 2D show examples of the spiral groove 11a, the herringbone groove 11b, the inclined groove 11c, and the closing groove 11d, respectively.
FIG. 3 is a cross-sectional view showing the shape of the inner hole of the bearing portion 2 of the three-arc bearing member 12, and an imaginary circle is indicated by a dotted line for comparison.
[0011]
The spiral groove, herringbone groove, inclined groove and closing groove can be manufactured by the following method.
For example, a bearing member having a slightly larger inner diameter is fitted to a mandrel having a convex portion on the outer periphery corresponding to a dynamic pressure groove formed on the sliding surface of the bearing member, and the bearing member is pressed against the mandrel in a mold. After forming the groove on the inner peripheral surface, the bearing member is released together with the mandrel, and the bearing member is spring-backed and extracted from the mandrel.
The three-arc bearing member can be manufactured by an ordinary method of forming using a core rod during powder molding or sizing. The three-arc bearing member is regarded as a deformation of the structure provided with dynamic pressure grooves. For example, in the Lubrication Society of Japan “Lubrication Handbook” (1970) Yokendo Co., Ltd. p.136 or the Bearing and Lubrication Handbook Editorial Board “Bearing and Lubrication Handbook” (1961) Its structure is described.
[0012]
By using the bearing member having the structure as described above, the circulation of the lubricating oil and the cooling effect thereby are promoted, the performance of the lubricating oil itself is more effectively extracted, and a bearing element particularly suitable for high-speed rotation can be obtained. That is, a structure suitable for a small spindle rotating at a relatively high speed can be provided. The configurations of the items [1] to [4] exhibit the following effects, respectively.
[1] The sliding area is relatively small, and the manufacturing accuracy of both the upper and lower shaft support surfaces is improved. Further, since the middle swelling portion can be used as an oil sump, the number of members as a bearing element can be further reduced.
[2] Since the shaft support surface is not deformed when assembled in the housing, the assembly accuracy is good. Further, it is not necessary to insert a mandrel into the shaft support surface during assembly.
[3] Leakage of lubricating oil in the bearing element can be prevented by discharging the thermally expanded air in the gap of the bearing element from the through hole. Further, since the lubricating oil circulates in the bearing element through the through hole, the effect of re-lubrication and cooling is obtained.
[4] By providing the dynamic pressure groove, the lubrication of the sliding surface is further improved by the dynamic pressure action, and the effect appears remarkably at high speed rotation.
[0013]
There are the following methods for modeling the bearing member having the middle swelling portion, and any one of them can be appropriately employed.
(A) Japanese Patent Application Laid-Open No. 10-46212 When a cylindrical sintered body is put into a die and pressed with a punch from above and below using a mandrel thinner than the inner diameter of the sintered body, the diameters at both ends are deformed and reduced, and the mandrel is sized. Done.
(B) Japanese Patent Application Laid-Open No. 2-107705 A mandrel having a large diameter only in the middle in the axial direction is compressed in the same manner as described above, the inner diameter of the sintered body is brought into contact with the mandrel, and the whole mandrel is extracted from the die. At the same time, the bearing member is spring-backed and the mandrel is pulled out.
(C) Japanese Patent Laid-Open No. 63-270918 An outer peripheral intermediate portion of a cylindrical sintered body is cut and formed in an annular shape and compressed in a mold so that the annular groove portion of the sintered body disappears. Is expanded and both ends are sized with mandrels.
(D) The die used in Japanese Patent Laid-Open No. 58-84222 is divided into two in the axial direction, and when integrated, the inner diameter of the intermediate portion increases. When the cylindrical sintered body is compressed in the mold, the sintered body swells toward the large diameter portion of the die hole, and the inner diameter intermediate portion also has a large diameter. The small diameter portions at both ends of the inner diameter are formed by mandrels.
(E) Japanese Patent Application Laid-Open No. 6-233831 A cylindrical sintered body having an inner diameter larger than the mandrel diameter is used, and only both end sides of the sintered body are reduced from the outer peripheral direction.
(F) JP-A-2-8302 uses a sintered body formed by reducing one end of the inner diameter from the middle to the other end, and reducing the end of the larger inner diameter from the outer periphery with a mold during sizing. To do.
(G) Japanese Laid-Open Patent Publication No. 1-242821 A sintered body in which one end side of the inner diameter is smaller than the diameter of the mandrel and formed from the intermediate portion to the other end is used. A large-diameter portion that creates a gap is provided. During sizing, the small diameter portion of the inner hole is expanded by the mandrel, the other end side is reduced in diameter by the die to the mandrel side, and the intermediate portion of the bearing member is expanded so as to fill the gap with the die.
[0014]
As the sintered alloy for the bearing member, a bronze-based material or an iron-copper-based material containing 40% or more of iron is preferable. The latter is suitable when wear resistance is particularly necessary and is low in cost.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Specific embodiments of the present invention will be described with reference to the following examples.
(1) Mixing of raw materials (a) Example of bronze type: copper powder + 10% tin powder (b) Example of iron copper type: Select from the following ranges according to applications.
Iron powder: 40-80%
Copper powder: 20-60%
Tin powder: 4-10% of copper
(2) Powder compaction Using an ordinary mold, powder molding is performed into a cylindrical shape to produce a bearing member.
(3) Sintering In the case of the bronze and iron copper systems, sintering is performed at 750 ° C. in a reducing atmosphere of ammonia decomposition gas.
(4) Sizing of the middle swelling portion (d) Performed by the method described in JP-A-58-84222. As described above, the die to be used is divided into two in the axial direction, and when integrated, the inner diameter of the intermediate portion is increased. When the cylindrical sintered body is compressed in the mold, the sintered body swells toward the large diameter portion of the die hole, and the inner diameter intermediate portion also has a large diameter. Moreover, the small diameter part of the both ends of an internal diameter is formed with a mandrel. During this sizing, for example, three longitudinal grooves are formed in the large-diameter portion on the outer periphery of the bearing member.
In addition, if the middle bulge part is shaped by another method, the outer shape of the bearing member may be different from that of this method, and the shape of the longitudinal groove and the housing inner hole described later is manufactured according to the outer shape of the bearing member. .
(5) Formation of dynamic pressure groove When the dynamic pressure groove is formed by the spring back method described above, the surface of the core rod is slightly thinner than the inner diameter of the bearing portion of the sized bearing member formed in (4) above. A convex portion corresponding to the groove shape pattern is formed by an electrolytic corrosion method or the like. When a core rod is mounted on a sized bearing member, the outer periphery or end face side of the bearing member is pressed and deformed in the mold, and the bearing member is in close contact with the groove and engraved with the groove, and the bearing member is released together with the core rod. The bearing rod can spring back and the core rod can be removed.
FIG. 4 is a partial perspective view of a core rod for forming a herringbone dynamic pressure groove. A large number of ridges 14 corresponding to the pattern of the dynamic pressure grooves are formed on the surface of the core rod 13.
The three-arc bearing member can be formed by the process (4).
(6) Impregnation of lubricating oil A lubricating oil made by mixing 0.1 to 30% by volume of PFPE with a base oil such as a polyol ester is vacuum impregnated at ordinary temperature by an ordinary method. When the viscosity is high, vacuum impregnation may be performed in a state where the viscosity is lowered by heating. The emulsified oil has another effect of suppressing foaming during impregnation, and PFPE functions as an antifoaming agent.
(7) Fabrication of the housing Since the plain inner shape of the housing is easier to fabricate, the bearing member preferably has a large diameter portion on the outside as shown in FIG. The housing is formed by cutting a molten bar or using powder metallurgy.
(8) Push the bearing member into the press-fitting housing of the bearing member and press-fit it. Since the press-fitting portion of the bearing member is intermediate between the two bearing portions and the inner diameter of the bearing sliding portion is not affected by the press-fitting, it is not necessary to use a centering mandrel during press-fitting. However, when the bearing member having the middle swelling portion is long, it is preferable to press-fit using a mandrel in order to reduce the distortion of the shaft center as much as possible.
(9) Preferred application example The sintered oil-impregnated bearing of the present invention is a spindle motor for a CD-ROM drive (rotational speed when used: about 2,000 to 11,000 rpm), MD (mini disk), LBP (laser) Beam printers), spindle bearings such as cooling fans for ICs, and other applications as bearings for small high-speed rotating equipment.
FIG. 5 is a longitudinal sectional view showing an example of a spindle motor for a CD-ROM drive.
The bearing member 1 is press-fitted into the inner hole of the housing 4 fixed to the base 21, and the lower end of the shaft 22 inserted into the bearing member 1 is rotatably supported by the thrust receiving plate 8. The disk holding jig 23, the rotating plate 24 and the rotor 25 are fixed to the upper end of the shaft 22, and rotate at high speed by the magnetic force of the permanent magnet 26 provided inside the rotor and the electromagnetic coil 27 provided on the outer periphery of the housing 4. .
[0016]
【The invention's effect】
The lubricating oil emulsified by mixing the base oil and perfluoropolyether used in the present invention forms a metal fluoride film on the metal surface and exhibits excellent sliding properties. By impregnating the bearing member of the bearing having a specific configuration with such a lubricating oil, it is possible to provide a sintered impregnated bearing suitable for a high-speed rotating small spindle motor or the like.
[Brief description of the drawings]
1 (a) to 1 (c) are longitudinal sectional views of embodiments of various bearings of the present invention, and FIGS. 1 (d) to (f) are plan views thereof.
FIG. 2 is a development view of a sliding surface of an inner hole in which various dynamic pressure grooves are provided in the bearing portion of the bearing member. FIGS. 2A to 2D are a spiral groove, a herringbone groove, and an inclined groove, respectively. An example of a closed groove is shown.
FIG. 3 is a cross-sectional view of a three-arc bearing member.
FIG. 4 is a partial perspective view of a core rod used for forming a herringbone groove as a dynamic pressure groove.
FIG. 5 is a longitudinal sectional view of an embodiment of a spindle motor for a CD-ROM drive.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Bearing member 2 Bearing part 3 Medium swelling part 4 Housing 5 Groove 6 Through-hole 7 Press-fit surface 8 Thrust receiving plate 11a Spiral groove 11b Herringbone groove 11c Inclination groove 11d Closure groove 12 Three-arc bearing member 13 Core rod 14 Protrusion 21 Base 22 Shaft 23 Disc holding jig 24 Rotating plate 25 Rotor 26 Permanent magnet 27 Electromagnetic coil

Claims (7)

0.1 to 30% by volume of one or more mixtures selected from the group consisting of polyalphaolefin (PAO), polyol ester, diphenyl ether, diester oil, mineral oil (refined mineral oil), alkylbenzene and alkylnaphthalene. A sintered oil-impregnated bearing for a spindle motor , wherein a bearing member is impregnated with a lubricating oil emulsified by mixing fluoropolyether (PFPE). Said perfluoropolyethers, CF ₃ - In _{- [(O-CF 2)} q (O-CF 2 -CF 2) p] -O-CF 3 ( where, p and q are from 10 to 200 integer) The sintered oil impregnated bearing for spindle motors according to claim 1. Claim wherein the _{perfluoropolyether, CF 3 -CF 2 -CF 2 -O-} (CF 2 -CF 2 -O) m -CF 2 -CF 3 ( where, m is from 10 integers 200) is 1. A sintered oil-impregnated bearing for spindle motors according to 1. The sintered oil-impregnated bearing for a spindle motor according to claim 2 or 3, which is a compound in which at least one fluorine atom of the perfluoropolyether is substituted with a methyl trifluoride group.   A bearing member that slides and supports the rotating shaft at both ends and an intermediate swelling portion that does not contact the rotating shaft between the bearing portions is provided on the outer peripheral surface of the inner swelling portion of the housing. A gap formed between the outer peripheral surface of the bearing portion and the inner hole surface of the housing, and an axial groove provided on the outer peripheral surface of the press-fit portion of the bearing member, and an inner hole surface of the housing. The sintered oil-impregnated bearing for a spindle motor according to any one of claims 1 to 4, wherein the lubricating oil is impregnated in a bearing member of a bearing in which a through hole is formed.   The sintered oil-impregnated bearing for spindle motor according to claim 5, wherein a dynamic pressure groove is provided on an inner peripheral surface of the bearing portion.   The sintered oil-impregnated bearing for a spindle motor according to claim 5, wherein a cross section in a direction perpendicular to the axis of the bearing portion has a three-arc shape.

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