JP2000304058A - Rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling bearing which can prevent the contamination owing to the evaporation and the scattering of a lubricant, at a low torque and by reducing the torque variation, while preventing a fretting abrasion generated when the lubricant amount is little. SOLUTION: In this rolling bearing (ball bearing 27), an inner ring 29 is provided on the inner periphery of an outer ring 31 plural rolling elements (balls 37) are provided between the inner peripheral surface of the outer ringring 31 and the outer peripheral surface of the inner ring 29, in the circumferential direction, and the system is composed by assembling the inner ring 29 and the outer ring 31 rotatable relatively through the rolling elements 37. In this case, to a space 41 formed between the inner peripheral surface of the outer ring 31, and the outer peripheral surface of the inner ring 29, a lubricant of 0.3 to 3% of the capacity of the space 41 is sealed in.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing suitable for use as, for example, a bearing for a swing arm for a magnetic disk device which slightly swings at a high speed.

[0002]

2. Description of the Related Art A swing arm for a magnetic disk device requires a high-speed, minute swing in order to seek a target track on a magnetic disk with a magnetic head at a high speed and with high accuracy. In order to realize such high-speed and minute swing, a rolling bearing is used for a base swing portion of the swing arm. FIG. 6 is a cross-sectional view of a base end of a swing arm supported by a conventional rolling bearing. A base plate 3 is screwed into a casing 1 of an actuator (for example, a voice coil motor) that performs high-speed, minute swinging, and the lower end of the support shaft 5 is fitted and fixed to one end of the base plate 3. The upper end of the support shaft 5 is screwed to the casing 1 by a screw 6 penetrating the casing 1.

A pair of ball bearings (rolling bearings) 7 are provided on the outer periphery of the support shaft 5 at intervals in the axial direction of the support shaft 5. The ball bearing 7 has an inner ring fixed to the support shaft 5 and an outer ring fixed to the housing 9. A base end of a swing arm 11 is fixed to the outer periphery of the housing 9, and the swing arm 11 is swingably supported by the support shaft 5 via a ball bearing 7. A magnetic head (not shown) is provided at the tip of the swing arm 11. A voice coil section 13 is provided on the outer periphery of the housing 9.
Is provided in a magnetic field formed by a permanent magnet 15 disposed in the housing 9. Therefore, by supplying a predetermined current to the voice coil unit 13 by a magnetic circuit, a turning force is applied, and the swing arm 11 is swung by a predetermined amount.

[0004] In this type of ball bearing 7, a lubricant such as grease is sealed inside for lubrication. Conventionally, the amount of the lubricant to be filled is 10 times the space volume inside the bearing.
About 20% was common.

[0005]

In recent years, with the increase in the density of the magnetic disk device, a narrower space is required between the magnetic head and the magnetic disk.
For this reason, management of contamination (contaminants) becomes more and more important for the reliability of the magnetic disk drive. In particular, since the swing arm is provided close to the surface of the magnetic disk, it is required that the contamination be low. For this reason, a lubricant and a lubricating method with less evaporation and scattering are required for the ball bearing than ever before. On the other hand, the track width of a magnetic disk is becoming increasingly narrower, and a swing arm is required to have faster access to a target track and higher positioning performance. For this reason, the ball bearing supporting the swing arm is required to be free from an increase in torque and a sudden change in torque (torque spike). However, conventional ball bearings for swing arms generally enclose a large amount of grease of 10 to 20% of the internal space volume of the bearing for the purpose of prolonging the service life. Various measures have to be taken to prevent the occurrence of outgassing or the possibility that these may adhere to the surface of the magnetic disk. In addition, when the amount of grease sealed is increased for the purpose of improving the durability and the like, there is a problem that torque fluctuation and torque increase are caused. The present invention has been made in view of the above circumstances, while preventing fretting wear that occurs when the amount of lubricant is small, low torque, little torque fluctuation, and
An object of the present invention is to provide a rolling bearing capable of preventing contamination due to evaporation and scattering of a lubricant.

[0006]

A rolling bearing according to the present invention for attaining the above object has a track surface formed on an inner peripheral surface of an outer ring and an outer peripheral surface of an inner ring, and a plurality of track surfaces are provided between the track surfaces. In the rolling bearing assembled with the rolling elements of
A space formed between the raceway surface of the outer race and the raceway surface of the inner race is filled with a lubricant of 0.3 to 3% of the space volume.

In this rolling bearing, a lubricant is filled in a space formed between the raceway surface of the outer ring and the raceway surface of the inner ring, and the amount of the lubricant is 0.3 to 3% of the space volume.
As a result, there is no excess or deficiency of the lubricant, and the fretting wear and damage to the raceway surface and the rolling elements, which are likely to occur when the amount of the filled lubricant is 0.3% or less, are eliminated. Evaporation and scattering of the lubricant and increase and fluctuation of the torque which are likely to occur when the content is 3% or more are eliminated. Therefore, if the rolling bearing according to the present invention is used as a bearing for a swing arm for a magnetic disk drive, high-speed and high-precision operation of the swing arm can be achieved with less contamination.

In the rolling bearing according to the present invention, a seal member for closing an annular gap in the space opened at both end surfaces of the outer ring and the inner ring is fixed to one of the outer ring and the inner ring. Is also good.

In this rolling bearing, the annular gap of the space opened at both end surfaces of the outer ring and the inner ring is sealed by a seal member, thereby preventing foreign matter from entering the bearing from the outside and being sealed in the space. Evaporation or scattering of the lubricated lubricant to the outside is prevented. As a result, the life of the rolling bearing can be prolonged, and contamination due to evaporation and scattering of the lubricant can be reduced.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the rolling bearing according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional view of a swinging part of a swing arm for a magnetic disk device provided with a rolling bearing according to the present invention, and FIG. 2 is an enlarged view of a main part of the rolling bearing shown in FIG.

A lower end of a support shaft 23 is fixed in a casing 21 of an actuator (for example, a voice coil motor) which performs high-speed and minute swinging. The upper end of the support shaft 23 is screwed to the casing 21 by a screw 25 penetrating the casing 21. Be worn.

A pair of ball bearings (rolling bearings) 27 are provided on the outer periphery of the support shaft 23 in the axial direction of the support shaft 23. In the ball bearing 27, the inner ring 29 is press-fitted and fixed to the support shaft 23, and the outer ring 31 is press-fitted and fixed to the housing 33.
A base end of a swing arm (not shown) is fixed to the outer periphery of the housing 33, and the swing arm is swingably supported by the support shaft 23 via a ball bearing 27.

As shown in FIG. 2, the outer race 31 of the ball bearing 27
Of the inner race 29 and the outer peripheral surface of the inner ring 29 have raceway surfaces 35 and 36, respectively.
Are formed. A plurality of balls 37 as rolling elements are interposed between the raceway surfaces 35 and 36 in the circumferential direction. An annular retainer 39 is mounted between the outer race 31 and the inner race 29 to rotatably hold the rolling element. That is, the outer race 31 and the inner race 29 are relatively rotatably mounted via the balls 37.

The inner peripheral surface of the outer race 31 of the ball bearing 27 and the inner race 29
A space 41 accommodating the ball 37 and the retainer 39 is formed between the ball 41 and the outer peripheral surface. The "space" here refers to a space between the inner peripheral surface of the outer ring and the outer peripheral surface of the inner ring, in a region surrounded by the seal member, excluding the volume of the balls and the retainer. In the case of a bearing without a seal member, a state in which the seal member is provided is assumed, and it is considered within a virtual region surrounded by the seal member in that state. The space 41 is filled with oil or grease as a lubricant. As will be described later, when the amount of the lubricant is 0.3% or less of the volume of the space 41, early fretting wear and damage to the raceway surface and the rolling elements are likely to occur. Has been verified. Further, it has been confirmed by experiments by the inventors that when the amount of the filled lubricant is 3% or more of the volume of the space 41, evaporation, scattering, increase in torque, and fluctuation are likely to occur.

Therefore, the space 41 of the ball bearing 27 according to the present embodiment is filled with a lubricant of 0.3 to 3% of the space volume. Further, it has been confirmed that it is more preferable that the upper limit of the filling amount be 2% or less in order to keep outgassing low.

As the lubricant, urea-based grease, fluorine-based grease, ester-based oil, fluorine-based oil, etc., which cause less oozing, are preferred. In order to keep outgas low, it is preferable to use fluorine-based grease or fluorine-based oil having high affinity.

A lubricant such as grease or oil is previously injected and sealed into at least one of the raceway surfaces of the ball 37 and the inner ring 29, the raceway surface of the ball 37 and the outer ring 31, and the sliding surface of the ball 37 and the pocket surface of the retainer 39. Is done. This is because the lubricant is transferred to the entire surface by the initial rotation or swing, so that the lubricant can be distributed over the entire sliding surface if it is injected into at least one place.

As a sealing method when the lubricant is oil, a dipping method in which the oil is applied thinly can be adopted. Further, so-called oil plating may be performed. Further, a lubricant application method for forming a coating or a thin film may be used.

As the material of the ball 37, ordinary bearing steel or stainless steel is used. In the case of micro-oscillation (tracking) with random seek in a range of about 30 degrees as in the case of a swing arm bearing, even if a bearing steel or stainless steel is used for the ball material, the amount of the filled lubricant is limited. It has been confirmed that if the volume is in the range of 0.3 to 3%, there is no practical problem in the durability performance of the random seek (fretting wear does not occur over several hundred million times). In applications where the durability performance of a certain area seek is important, it is more preferable to use a ceramic ball having a high hardness as the ball material in order to reduce fretting wear.

As a method of fixing the inner ring 29 of the ball bearing 27, the support shaft 23 of the outer ring 31, and the housing 33 to the housing 33, the inner ring 29 is press-fitted while being vibrated, the resonance frequency is measured on the outer ring 31 side, and preload control is performed. A so-called resonance press-fitting method is used. This press-fitting method is a more preferable fixing method from the viewpoint of taking measures against contamination of the magnetic disk surface due to the outgassing of the adhesive and the advantage that the resonance (rigidity) can be kept constant. The inner ring 29 and the outer ring 31 of the ball bearing 27 may be fixed to the support shaft 23 and the housing 33 by bonding.

Further, in order to reduce outgassing and bleeding of the lubricant, both sides of the ball bearing 27 are provided with sealing members 43.
Is preferably sealed. Seal member 43
Is fixed to one of the outer ring 31 and the inner ring 29,
And the annular gap 4 of the space 41 opened at both end surfaces of the inner ring 29
5 is sealed. Since there is no influence on the outgas, the seal member 43 is provided with the inner seal 43 shown in FIG.
A one-sided seal without a may be used.

In the ball bearing 27 configured as described above, a lubricant is filled in a space 41 formed between the inner peripheral surface of the outer ring 31 and the outer peripheral surface of the inner ring 29, and the amount of the filled lubricant is 0, which is the space volume. By setting the amount to be 3 to 3%, the fretting wear and the damage to the raceway surface and the rolling elements, which are likely to occur when the amount of the lubricant is 0.3% or less, are eliminated, and the amount of the lubricant is reduced. Evaporation and scattering of the lubricant and increase and fluctuation of the torque which are likely to occur when the content is 3% or more are eliminated.

The annular gap 45 of the space 41 opened at both end surfaces of the outer ring 31 and the inner ring 29 is sealed by a seal member 43 to prevent foreign substances from entering the bearing from the outside, and to prevent the space 41 from entering. Evaporation and scattering of the lubricant sealed in the outside are prevented. As a result, the life of the ball bearing 27 is extended, and contamination due to evaporation and scattering of the lubricant is reduced.

Therefore, according to the above-described ball bearing 27, it is possible to prevent fretting wear at an early stage, to eliminate evaporation and scattering of lubricant, and to increase or fluctuate torque. This has the effect of realizing high-speed and high-precision operation.

In the above embodiment, the case where the rolling bearing is the ball bearing 27 has been described as an example. However, the rolling bearing according to the present invention has the same effect as described above even when used in a roller bearing. is there.

[0026]

Next, results of a swing durability test performed on the rolling bearing of the present invention will be described. FIG. 3 shows a swing endurance test apparatus 50 using the voice coil motor used in this test. In this swing endurance test apparatus 50, an outer ring of a test bearing 53 is fixed to an inner peripheral surface of a housing 52 to which a voice coil motor 51 is attached, and an inner ring of a test rolling bearing 53 is fixed to a support shaft 55. A rotary encoder 56 for detecting a rotation angle is attached to the housing 52. Voice coil motor 51
Is of the same type as that used in the magnetic disk drive, is driven by a drive unit 58 based on an operation signal from a computer 57, and swings the outer ring of a test rolling bearing 53 through a housing 52. . Then, the change with time of the torque (drive current) in the repeated swing drive is measured, and the result is displayed on the monitor 59.

Generally, when fretting wear occurs in the rolling bearing, torque fluctuation starts to occur, and when the wear further progresses, the torque fluctuation increases. When this rolling bearing is applied to a magnetic disk drive, this wear eventually causes a positioning control error.

There are two types of rocking modes: fixed area seek and random seek. In the case of a constant area seek with a small swing angle, the position of the rolling element does not move from a specific minute area, which is a severe condition for a fretting durability test, but since a random seek is performed in a magnetic disk device, Here, a test by random seek was performed. The test conditions of the random seek swing durability test are described below. (1) Test bearing: ball bearing for swing arm (bearing inner diameter 6.35 mm, bearing outer diameter 9.525 mm, width 3.15 m)
m) (2) Number of oscillations: hundreds of thousands to hundreds of millions (3) Oscillation angle: random seek of 26 to 1 degree (4) Oscillation frequency: 30 Hz (5) Atmospheric temperature: normal temperature (25 ° C.) )

FIG. 4 shows the change of the torque value with respect to the swing angle when the ball bearing is swung. FIG. 4A shows an initial state, and FIG. 4B shows a state in which a torque fluctuation occurs when the usage limit is reached. As shown in FIG. 4, in the initial state, a substantially constant torque value is exhibited at each swing angle regardless of the swing direction, and the torque value linearly changes according to the change in the swing angle. . However, when the usage limit is reached, the torque value differs depending on the swinging direction, and a change in the torque value due to the swing angle swells, and the torque fluctuation increases.

Next, the results of a swing endurance test of rolling bearings having different amounts of lubricating oil will be described. FIG. 5 summarizes the results of the swing durability test. The horizontal axis in the figure is the space volume ratio of the amount of the filled lubricant, and the vertical axis is the number of seeks in which torque fluctuation occurs (left axis) and the amount of outgas generated (right axis). The results for each case are shown. Here, outgas measurement conditions are shown below. (1) Test bearing: ball bearing for swing arm (bearing inner diameter 6.35 mm, bearing outer diameter 9.525 mm, width 3.15 mm) (2) Measuring instrument: gas chromatograph mass spectrometer (GC
-MS) (3) Measurement temperature: 70 ° C (4) Measurement time: 3 hours

According to the test results shown in FIG. 5, when the space volume ratio of the amount of the filled lubricant is 0.3% or more, the number of seeks until a torque fluctuation occurs is at a level that does not cause any practical problem. On the other hand, if it is less than 0.3%, torque fluctuation occurs with a small number of seeks, which causes a practical problem. Further, the outgas generation amount is 10 ³ [ng] when the space volume ratio of the amount of the filled lubricant is 3% or less.
The trace amount is as follows. On the other hand, if it is more than 3%, the amount of outgas generated increases, causing a practical problem. From the above, it was confirmed that by setting the space volume ratio of the amount of the filled lubricant to 0.3 to 3%, the amount of outgas generated can be suppressed without causing torque fluctuation. That is, by setting the above range, it is possible to prevent early fretting wear and prevent evaporation and scattering of the lubricant and increase or fluctuation of the torque.

[0032]

As described above in detail, the rolling bearing according to the present invention seals the lubricant in the space formed between the raceway surface of the outer ring and the raceway surface of the inner ring, and reduces the amount of the lubricant. Since the volume is set to 0.3 to 3% of the space volume, it is possible to prevent early fretting wear that occurs when the amount of the filled lubricant is 0.3% or less, and to occur when the amount of the filled lubricant is 3% or more. Evaporation and scattering of lubricant, and increase and fluctuation of torque can be eliminated. As a result, when used as a bearing of a swing arm for a magnetic disk drive, high-speed and high-precision operation of the swing arm can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of a swinging part of a swing arm for a magnetic disk drive provided with a rolling bearing according to the present invention.

FIG. 2 is an enlarged view of a main part of the rolling bearing shown in FIG.

FIG. 3 is a diagram showing a swing endurance test apparatus using a voice coil motor.

FIG. 4 is a diagram showing a change in torque value with respect to a swing angle when a ball bearing is swung.

FIG. 5 is a diagram showing the results of a swing durability test.

FIG. 6 is a sectional view of a swinging portion of a conventional swing arm for a magnetic disk drive provided with a rolling bearing.

[Explanation of symbols]

 27 Ball bearing (rolling bearing) 29 Inner ring 31 Outer ring 37 Ball (rolling element) 41 Space

Claims (1)

[Claims] 1. A rolling bearing in which a raceway surface is formed on each of an inner peripheral surface of an outer ring and an outer peripheral surface of an inner ring, and a plurality of rolling elements are interposed between the raceway surfaces to be assembled. A rolling bearing, characterized in that 0.3 to 3% of a space volume of a lubricant is sealed in a space formed between a surface and a raceway surface of the inner ring.