JP2004211797A - Rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing of long life free from the leakage of grease, having sufficiently low torque property, and provided with both of acoustic life and initial acoustic property. <P>SOLUTION: In this rolling bearing 1, a plurality of rolling elements 13 are rotatably held between an inner ring 10 and an outer ring 11 at approximately equal intervals through a cage 12, and the grease including a diurea compound including a fiber material of fiber length of at least 3 μm as a thickening agent. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００１６】
式中、Ｒ_２は炭酸数６〜１５の芳香族系炭化水素、Ｒ_１、Ｒ_３は脂肪族炭化水素基を表し、同一でも異なっていてもよい。また、Ｒ_１、Ｒ_３は特に炭素数８〜２０の直鎖アルキル基が望ましい。
【００１７】
また、このジウレア化合物は、繊維長が３μｍ以上である長繊維状物を含む。但し、繊維長があまりに大きすぎると、軸受回転時に接触面に入り込んだときの振動が大きくなり、初期音響特性に良い影響を与えない。従って、上限としては２０μｍ以下が望ましい。尚、繊維径は１μｍ未満が適当である。また、この長繊維状物は、増ちょう剤全量の３０重量％以上を占めることが好ましい。３０重量％よりも少ないと、トルク低減効果が十分に発現しない。
【００１８】
上記グリースにおいて、ジウレア化合物の長繊維状物は、透過型電子顕微鏡により６０００倍〜２００００倍の倍率で確認することができる。観察に当たっては、グリースをヘキサンなどの有機溶剤で希釈し、この希釈液をコロジオン膜を貼った銅製メッシュに付着させる。これら一連の観察は、ごく一般的な方法に従って実施すればよい。図２（Ａ）はその顕微鏡写真の一例（実施例１によるグリース組成物）であるが、繊維長が３μｍ以上の長繊維状物が生成していることがわかる。
【００１９】
尚、増ちょう剤量は従来と同様で構わず、グリース全量の５〜２０重量％とすることができる。
【００２０】
また、グリースには、その好ましい特性を損なわない範囲において、上記した基油及び増ちょう剤の他に周知の酸化防止剤、防錆剤、油性剤、極圧添加剤等の添加剤を含有させても良い。これら添加剤は、合計でグリース全量の２０重量％未満とすることが好ましい。
【００２１】
【実施例】
以下に実施例及び比較例を挙げて、本発明を更に説明する。但し、本発明は以下の実施例により何ら制限されるものではない。
【００２２】
（実施例１〜３、比較例１〜４）
表１に示す如く、基油及び増ちょう剤を混合して試験グリースを調製した。また、板状ジウレア及びリチウム石けんを含むグリースは何れも市販品を用いた。そして、試験軸受「呼び番号６９５（内径５ｍｍ、外径１３ｍｍ、幅４ｍｍ、プラスチック保持器付）」に各試験グリースを１０ｍｇ封入し、下記に示す各実験を行い、軸受トルク、グリース漏洩量、ＮＲＲＯ特性を評価した。
【００２３】
【表１】

【００２４】
（実験−１）
図３に示す測定装置３０を用いて軸受トルク試験を行った。この測定装置３０において、上記の試験軸受３１は２個１組で、エアースピンドル３２に連結する軸３３に予圧用ウェーブワッシャ３４を用いて装着される。また、試験軸受３１はエアースピンドル３２とともに水平に置かれ、糸３５を介して荷重変換器３６が吊るされており、この荷重変換器３６の出力がＸ−Ｙレコーダ３７により記録される。試験は、試験軸受３１をアキシアル荷重１４．７Ｎの条件下で２００００ｒｐｍ（外輪回転）で高速回転させ、回転直後のトルクと回転５分後のトルクとを測定し、その上昇率（トルク比）を評価した。結果を図４に示すが、長繊維状物のジウレア化合物を含有するグリースを封入することにより、軸受トルクの上昇を低く抑えられることがわかる。
【００２５】
（実験−２）
実施例１及び比較例３において、４０℃おける動粘度の異なる基油を用いてグリースを調製し、この試験グリースを上記試験軸受に封入し、実験−１と同様の測定装置を用い、同条件にて軸受トルクを測定した。結果を図５に示すが、長繊維状物のジウレア化合物を含有するグリースは、板状のジウレア化合物を含有するグリースに比べて基油の動粘度にかかわらず、軸受トルクが低く抑えられていることがわかる。
【００２６】
（実験−３）
図６に示す装置を用いて、グリースの漏洩試験を行った。図示される装置は、一対の試験軸受５０，５０、シャフト５１、円筒状のハウジング５２、ステータ５３とロータ５４からなるモータ５５で構成される。そして、実施例２、比較例１、比較例４の各試験グリースを試験軸受５０に封入し、アキシアル荷重１４．７Ｎの条件下で２００００ｒｐｍ（外輪回転）で高速回転させ、回転前の軸受重量と所定時間経過後の軸受重量からグリースの漏洩率を求めた。結果を図７に示すが、実施例２の試験グリースを封入した軸受は耐グリース漏洩性に優れることがわかる。
【００２７】
（実験−４）
図８に示す装置を用いて、ＮＲＲＯ特性試験を行った。図示される装置の基本構造は本出願人による特開平９−１７８６１３号公報に示すものであり、ここでは概略を以下に示す。
【００２８】
平行な上板６４と下板６５とを支柱６６、６６により結合して成るフレーム６７を備えており、下板６５には駆動装置６８を支持固定している。この駆動装置６８は試験軸受８１の内輪を、ラジアル方向の位置決めを図った状態で回転駆動するもので、鉛直方向に配置されて図示しないモータにより回転駆動されるスピンドル軸９０と、このスピンドル軸９０を回転自在に支持する静圧気体軸受からなる精密軸受装置１００とから構成される。上板６４には、支持装置６９が支持固定されている。この支持装置６９は、試験軸受８１の外輪を回転しない状態で支持するもので、外輪にアキシアル荷重を付加する機能と、外輪がラジアル方向に円滑に変位する事を許容する機能とを有しており、アキシアル荷重を付与する機能を発揮させるために上板６４の中央部に形成した保持孔７０に、シリンダ部材７１を固定している。シリンダ部材７１の底板部７２に形成した通孔７３には、押圧ロッド７７が昇降のみ自在に（回転不能に）挿通されており、押圧ロッド７７の上端部に固設した鍔部７４の上面と、シリンダ部材７１の中間部に昇降自在に嵌装した受板７５の下面との間には圧縮ばね７６が設けられ、押圧ロッド７７はこの圧縮ばね７６の弾力に見合う力で下方に押圧されている。また、シリンダ部材７１の上端開口部に被着した蓋板２８の中心部にはねじ孔（図示せず）が形成され、このねじ孔に調節ねじ７９を螺合させて受板７５の上下位置を調節するようになっている。また、圧縮ばね７６により押圧ロッド７７に付与されるアキシアル荷重も、調節ねじ７９を回転させることにより調節される。
【００２９】
また、試験軸受８１の外輪がラジアル方向に円滑に変位することを許容するために、支持装置６９の下端部には外輪を抱持するためのホルダ８０が設けられており、このホルダ８０の下面には外輪を抱持するための円形凹孔８１が形成され、上面には直径方向に亙る凸部８２が形成している。更に、押圧ロッド７７の下端部には、係止板８３が固定され、この係止板８３の下面には直径方向に亙る凸部８４が形成されている。そして、ホルダ８０の上面と係止板８３の下面との間に、燒結材料等により造られた多孔質材８５を挟持して、ラジアル方向に亙る変位を許容する静圧気体軸受８６を構成している。また、多孔質材８５に給気口８９を設けて、多孔質材８５内に圧縮空気を送り込み自在としており、圧縮ばね７６によるアキシアル荷重は圧縮空気の膜を介して伝達自在とされている。更に、ホルダ８０の外周面に対向する部分に、非接触式の変位センサ８１が設けられている。
【００３０】
上記の装置を用い、各実施例及び各比較例の各試験グリースを上記試験軸受８１に封入し、アキシアル荷重１４．７Ｎの条件下で１２０００ｒｐｍ（内輪回転）で高速回転させ、非回転同期振れＮＲＲＯを求めた。結果を図９に示すが、長繊維状物のジウレア化合物を含有するグリースを封入することにより、優れたＮＲＲＯ特性が得られることがわかる。
【００３１】
【発明の効果】
以上説明したように、本発明によれば、長繊維状物のジウレア化合物を含有するグリースを封入することにより、十分に低いトルク特性を有し、音響寿命、初期音響特性を兼ね備え、更にグリース漏洩が無く長寿命の転がり軸受が得られる。
【図面の簡単な説明】
【図１】本発明の転がり軸受の一実施形態である玉軸受を示す断面図である。
【図２】（Ａ）実施例１において増ちょう剤として使用したジウレア化合物の電子顕微鏡写真であり、（Ｂ）比較例１のジウレア化合物の電子顕微鏡写真である。
【図３】実験−１及び実験−２において、軸受トルクを測定するために用いた装置を示す概略図である。
【図４】実験−１の測定結果を示すグラフである。
【図５】実験−２の測定結果を示すグラフである。
【図６】実験−３において、グリースの漏洩量を測定するために用いた装置を示す概略図である。
【図７】実験−３の測定結果を示すグラフである。
【図８】実験−４において、ＮＲＲＯ特性を測定するために用いた装置を示す概略図である。
【図９】実験−４の測定結果を示すグラフである。
【符号の説明】
１ 玉軸受
１０ 内輪
１１ 外輪
１２ 保持器
１３ 玉
１４ シール[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a rolling bearing, and more particularly to a rolling bearing having excellent low-torque properties at high-speed rotation and sufficient acoustic durability.
[0002]
[Prior art]
In recent years, in hard disk drive (HDD) spindles, servo motors, and the like, speeding up has been promoted to improve the work efficiency of the apparatus, and low output has been promoted due to demand for reduction in power consumption. For this reason, in a rolling bearing used for a motor bearing or the like, torque characteristics are required as an important function.
[0003]
In a rolling bearing, viscous resistance of grease is known as one of the causes of generation of dynamic friction torque. Therefore, the reduction of the viscous resistance of the grease is an effective means for reducing the dynamic friction torque of the rolling bearing. In order to reduce the viscous resistance of grease, it is effective to reduce the kinematic viscosity of the base oil and the grease consistency. However, reducing the base oil viscosity or reducing the grease consistency causes another problem as described below.
[0004]
That is, in order to reduce the kinetic friction torque, the kinematic viscosity of the base oil is conventionally set in the range of 5 to 200 mm ² / s, but the lower the viscosity, the lower the heat resistance of the base oil. Therefore, synthetic oils such as ester oils, poly-α-olefin oils, and ether oils having relatively high heat resistance are used as the base oil to compensate for the decrease in heat resistance (for example, see Patent Document 1).
[0005]
Also, reducing the consistency of the grease leads to an increase in the amount of the thickener, which is disadvantageous in maintaining a stable lubricating property over a long period of time by relatively reducing the amount of the base oil. In addition, as a thickener, it is common to use a metal soap such as lithium soap or a urea compound. However, in the case of grease using metal soap as a thickener, the shear resistance of the metal soap fiber is weak, so that the grease softens during high-speed or high-temperature rotation and easily leaks. Therefore, grease using this metallic soap as a thickener is difficult to hold a sufficient amount of base oil for lubrication for a long period of time, so that it tends to suffer from poor lubrication and does not have sufficient acoustic durability. On the other hand, a grease using a urea compound has a problem that sufficient torque characteristics and initial sound cannot be obtained.
[Patent Document 1]
JP 2000-192973 A
[Problems to be solved by the invention]
The present invention has been made in view of such circumstances, and has an object to provide a long-life rolling bearing having sufficiently low torque characteristics, having both acoustic life and initial acoustic characteristics, and having no grease leakage. And
[0007]
[Means for Solving the Problems]
The present inventors have worked diligently to achieve the above object, and as a result, by enclosing grease containing a thickener containing a diurea compound and containing a long fibrous material, the bearing torque of the rolling bearing can be reduced. It has been found that it can be significantly reduced. The present invention is based on such findings.
[0008]
That is, in order to achieve the above object, the present invention holds a plurality of rolling elements rotatably at substantially equal intervals through a retainer between an inner ring and an outer ring, and has a fiber length of at least 3 μm. A rolling bearing characterized in that grease containing a diurea compound containing a certain fibrous material as a thickener is sealed therein.
[0009]
Since the thickener contained in the grease contains a long fibrous material, it has excellent orientation and flexibility on the sliding surface, and has reduced torque characteristics and NRRO (Non-Repeatable Run-Out) characteristics. Has an effect. Further, since the shear stability of the thickener in the grease is improved, softening and leakage of the grease are prevented, and the base oil is sufficiently retained in the grease even during high-speed rotation. These effects cannot be obtained with a conventional grease using a plate-shaped urea compound as a thickener.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
[0011]
In the present invention, the structure of the rolling bearing itself is not particularly limited, and may be, for example, a ball bearing shown in FIG. As shown in the figure, the ball bearing 1 holds a plurality of balls 13 as rolling elements at a substantially equal interval between an inner ring 10 and an outer ring 11 via a retainer 12 so as to freely roll. The bearing space S formed by the inner ring 10, the outer ring 11 and the balls 13 is filled with a predetermined amount of the following grease and sealed with a seal 14.
[0012]
The base oil used for the grease is not particularly limited, but the following lubricating oils can be suitably used. That is, highly refined mineral oils such as naphthenes and paraffins, synthetic hydrocarbon oils such as poly-α-olefin oils, cooligomers of α-olefins and ethylene, diester oils, polyol ester oils, aromatic ester oils, carbonate esters Lubricating oils having an ester structure, such as oils, and lubricating oils having an ether structure, such as phenyl ether oils and polyalkylene glycol oils, from which C _{12 to} C ₂₀ (di) alkyl chains of diphenyl, triphenyl, and tetraphenyl are derived. Can be used as a base oil. Above all, in consideration of torque characteristics and acoustic durability, synthetic hydrocarbon oil, polyol ester oil, carbonate ester oil, aromatic ester oil, and (di) alkyl polyphenyl ether oil are preferable. Particularly, polyol ester oil and carbonate ester oil are desirable.
[0013]
The kinematic viscosity of the base oil may be the same as the conventional one, and is preferably 5 to 200 mm ² / s at 40 ° C. If it is less than 5 mm ² / s, the high temperature characteristics will be inferior, and if it exceeds 200 mm ² / s, the torque will be too high, and none of the objects of the present invention can be achieved.
[0014]
In the base oil, a diurea compound is used as a thickener. Particularly, a diurea compound represented by the following general formula [I] is preferable.
[0015]
Embedded image

[0016]
In the formula, R ₂ represents an aromatic hydrocarbon having 6 to 15 carbon atoms, and R ₁ and R ₃ represent an aliphatic hydrocarbon group, which may be the same or different. Further, R ₁ and R ₃ are particularly preferably straight-chain alkyl groups having 8 to 20 carbon atoms.
[0017]
The diurea compound includes a long fiber having a fiber length of 3 μm or more. However, if the fiber length is too large, the vibration when entering the contact surface during the rotation of the bearing increases, and does not have a good effect on the initial acoustic characteristics. Therefore, the upper limit is desirably 20 μm or less. The fiber diameter is suitably less than 1 μm. Further, it is preferable that this long fibrous material accounts for 30% by weight or more of the total amount of the thickener. If the amount is less than 30% by weight, the torque reduction effect is not sufficiently exhibited.
[0018]
In the grease, the long fibrous material of the diurea compound can be confirmed by a transmission electron microscope at a magnification of 6,000 to 20,000 times. In the observation, the grease is diluted with an organic solvent such as hexane, and the diluted solution is attached to a copper mesh on which a collodion film is attached. These series of observations may be performed according to a very general method. FIG. 2 (A) is an example of the micrograph (the grease composition according to Example 1), and it can be seen that a long fibrous material having a fiber length of 3 μm or more is formed.
[0019]
The amount of the thickener may be the same as the conventional one, and may be 5 to 20% by weight of the total amount of grease.
[0020]
In addition, the grease contains additives such as a known antioxidant, a rust inhibitor, an oil agent, and an extreme pressure additive in addition to the base oil and the thickener described above, as long as the preferable properties are not impaired. May be. It is preferable that these additives make up less than 20% by weight of the total amount of the grease.
[0021]
【Example】
Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples. However, the present invention is not limited at all by the following examples.
[0022]
(Examples 1-3, Comparative Examples 1-4)
As shown in Table 1, a base oil and a thickener were mixed to prepare a test grease. Greases containing tabular diurea and lithium soap were all commercially available. Then, 10 mg of each test grease was sealed in the test bearing “No. 695 (inner diameter 5 mm, outer diameter 13 mm, width 4 mm, with plastic retainer)”, and the following experiments were performed to determine the bearing torque, grease leakage, NRRO The properties were evaluated.
[0023]
[Table 1]

[0024]
(Experiment-1)
A bearing torque test was performed using the measuring device 30 shown in FIG. In the measuring device 30, the test bearings 31 are mounted in pairs of two using a preload wave washer 34 on a shaft 33 connected to an air spindle 32. The test bearing 31 is placed horizontally with the air spindle 32, and a load converter 36 is suspended via a thread 35. The output of the load converter 36 is recorded by an XY recorder 37. In the test, the test bearing 31 was rotated at a high speed of 20,000 rpm (outer ring rotation) under the condition of an axial load of 14.7 N, the torque immediately after the rotation and the torque 5 minutes after the rotation were measured, and the rate of increase (torque ratio) was measured. evaluated. The results are shown in FIG. 4, and it can be seen that the increase in bearing torque can be suppressed to a low level by enclosing grease containing a long fiber-like diurea compound.
[0025]
(Experiment-2)
In Example 1 and Comparative Example 3, grease was prepared using base oils having different kinematic viscosities at 40 ° C., and the test grease was sealed in the test bearing. The bearing torque was measured at. The results are shown in FIG. 5. The grease containing the long fiber-like diurea compound has a low bearing torque, regardless of the kinematic viscosity of the base oil, as compared to the grease containing the plate-like diurea compound. You can see that.
[0026]
(Experiment-3)
A grease leakage test was performed using the apparatus shown in FIG. The illustrated device is composed of a pair of test bearings 50, 50, a shaft 51, a cylindrical housing 52, and a motor 55 including a stator 53 and a rotor 54. Then, each test grease of Example 2, Comparative Example 1, and Comparative Example 4 was sealed in a test bearing 50 and rotated at a high speed of 20,000 rpm (outer ring rotation) under the condition of an axial load of 14.7 N to obtain a bearing weight before rotation. The grease leakage rate was determined from the weight of the bearing after a predetermined time. The results are shown in FIG. 7, which shows that the bearing in which the test grease of Example 2 is sealed has excellent grease leakage resistance.
[0027]
(Experiment-4)
An NRRO characteristic test was performed using the apparatus shown in FIG. The basic structure of the illustrated apparatus is shown in Japanese Patent Application Laid-Open No. Hei 9-178613 by the present applicant, and the outline is shown below.
[0028]
A frame 67 is provided by connecting a parallel upper plate 64 and lower plate 65 with columns 66, 66, and a driving device 68 is supported and fixed to the lower plate 65. The drive device 68 is configured to rotationally drive the inner ring of the test bearing 81 in a state of positioning in the radial direction. The drive device 68 is disposed vertically and is driven to rotate by a motor (not shown). And a precision bearing device 100 composed of a static pressure gas bearing for rotatably supporting the bearing. A support device 69 is supported and fixed to the upper plate 64. The support device 69 supports the outer ring of the test bearing 81 without rotating, and has a function of applying an axial load to the outer ring and a function of allowing the outer ring to be smoothly displaced in the radial direction. In addition, a cylinder member 71 is fixed to a holding hole 70 formed in a central portion of the upper plate 64 so as to exert a function of applying an axial load. A pressing rod 77 is inserted through a through hole 73 formed in a bottom plate 72 of the cylinder member 71 so as to be able to move up and down only (non-rotatably), and is provided with an upper surface of a flange 74 fixed to an upper end of the pressing rod 77. A compression spring 76 is provided between the cylinder plate 71 and the lower surface of a receiving plate 75 which is fitted to the intermediate portion of the cylinder member 71 so as to be able to move up and down. The pressing rod 77 is pressed downward by a force corresponding to the elasticity of the compression spring 76. I have. A screw hole (not shown) is formed at the center of the cover plate 28 attached to the upper end opening of the cylinder member 71, and an adjusting screw 79 is screwed into the screw hole to adjust the vertical position of the receiving plate 75. Is adjusted. The axial load applied to the pressing rod 77 by the compression spring 76 is also adjusted by rotating the adjusting screw 79.
[0029]
Further, in order to allow the outer ring of the test bearing 81 to be smoothly displaced in the radial direction, a holder 80 for holding the outer ring is provided at the lower end of the support device 69. Has a circular concave hole 81 for holding the outer ring, and a convex portion 82 extending in a diametric direction is formed on the upper surface. Further, a locking plate 83 is fixed to the lower end of the pressing rod 77, and a projection 84 extending in the diametric direction is formed on the lower surface of the locking plate 83. Then, a porous material 85 made of a sintering material or the like is sandwiched between the upper surface of the holder 80 and the lower surface of the locking plate 83 to form a hydrostatic gas bearing 86 that allows displacement in the radial direction. ing. An air supply port 89 is provided in the porous material 85 so that compressed air can be sent into the porous material 85, and the axial load of the compression spring 76 can be transmitted through a compressed air film. Further, a non-contact type displacement sensor 81 is provided at a portion facing the outer peripheral surface of the holder 80.
[0030]
Using the above-described apparatus, each test grease of each example and each comparative example was sealed in the test bearing 81, and was rotated at a high speed of 12000 rpm (inner ring rotation) under the condition of an axial load of 14.7 N. I asked. The results are shown in FIG. 9, and it is understood that excellent NRRO characteristics can be obtained by enclosing the grease containing the diurea compound as a long fiber.
[0031]
【The invention's effect】
As described above, according to the present invention, by enclosing grease containing a diurea compound as a long fibrous material, it has sufficiently low torque characteristics, has both acoustic life and initial acoustic characteristics, and further has grease leakage. And a long life rolling bearing can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a ball bearing which is one embodiment of a rolling bearing of the present invention.
2A is an electron micrograph of a diurea compound used as a thickener in Example 1, and FIG. 2B is an electron micrograph of a diurea compound of Comparative Example 1.
FIG. 3 is a schematic diagram showing an apparatus used for measuring bearing torque in Experiment-1 and Experiment-2.
FIG. 4 is a graph showing measurement results of Experiment-1.
FIG. 5 is a graph showing measurement results of Experiment-2.
FIG. 6 is a schematic view showing an apparatus used for measuring a grease leakage amount in Experiment-3.
FIG. 7 is a graph showing measurement results of Experiment-3.
FIG. 8 is a schematic diagram showing an apparatus used for measuring NRRO characteristics in Experiment-4.
FIG. 9 is a graph showing measurement results of Experiment-4.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ball bearing 10 Inner ring 11 Outer ring 12 Cage 13 Ball 14 Seal

Claims (1)

A plurality of rolling elements are rotatably held at substantially equal intervals via a retainer between the inner ring and the outer ring, and a diurea compound containing a fibrous material having a fiber length of at least 3 μm is contained as a thickener. A rolling bearing characterized by being filled with grease.

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