JP2006097826A - Rolling bearing and bearing unit for actuator of hard disk drive device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing for an actuator of a hard disk drive device (HDD) capable of suppressing torque and out gas to low extent and torque hashness and having high performance and to provide a rolling bearing unit for the actuator of the HDD for forming the rolling bearing into a unit. <P>SOLUTION: In this rolling bearing for the actuator for supporting a magnetic head of the HDD to avoid vibration, average surface coarseness of a central line of an inner ring raceway track and an outer ring raceway track is 0.03μm or less, and lubricating oil selected from among perfluoropolyether and its derivative and fluoropolyether and its derivative, preferably, straight chain perfluoropolyether is sealed or applied on an inner ring raceway surface, an outer ring raceway surface, a rolling body, and a cage. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a rolling bearing for an actuator of an HDD incorporated in an actuator (particularly a swing arm) which is a component of a hard disk drive device (hereinafter referred to as “HDD”), or an HDD in which the rolling bearing is accommodated in a housing and unitized. The present invention relates to a rolling bearing unit for an actuator.

  In HDDs, rolling bearings built into actuators are required to have low torque in order to cope with the decrease in output of voice coil motors (VCM) as they become thinner. It tends to shift. On the other hand, HDDs have a higher recording density and higher accuracy, and recently the flying height has become extremely narrow to 100 nm or less. In an HDD having such a small gap, the adhesion of foreign matter on the magnetic disk can be a fatal obstacle.

  However, due to the structure of the HDD, a rolling bearing that supports the swing arm is disposed in the vicinity of the magnetic disk, and lubricating oil may leak from the rolling bearing and fly and accumulate on the magnetic disk. Then, the magnetic oil on the magnetic disk causes the magnetic disk and the magnetic head to be attracted, and the attached lubricating oil causes “fluctuation” to cause a problem that normal reading / writing cannot be performed.

  Even when the lubricating oil itself does not adhere as described above, the lubricating oil is heated by the heat generated by the VCM to generate outgas, and the outgas liquefaction may adhere to the magnetic disk. Various types of chemical contamination (chemical contamination) have the same adverse effects.

As described above, rolling bearings for actuators of HDDs are required to have low torque and low outgas generation and low chemical contamination. Conventionally, the vapor pressure at 25 ° C. is 1.3 × 10 ⁻³ Pa or less. A lubricating oil composition in which a synthetic lubricating oil sealed (see Patent Document 1) is incorporated into an HDD actuator, or a lubricating ether composition in which a fluorinated ether aliphatic diamide compound is added to a side chain perfluoropolyether to lubricate the bearing (patent) It is practiced to use a lubricating oil composition (see Patent Document 3) in which a fluorine-containing organic phosphorus compound is added to perfluoropolyether.

JP 2002-130304 A JP 2001-207186 A JP 2003-27079 A

  However, along with the dramatic increase in recording capacity of HDDs, the track width of magnetic disks has been miniaturized to several μm, and minute torque fluctuations (torque hashness) related to the surface roughness of the bearing raceway are also present. There is a growing concern about poor positioning accuracy.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a high-performance HDD actuator rolling bearing with low torque and low outgas, and reduced torque hashness, and an HDD actuator rolling bearing unit in which the rolling bearing is unitized. is there.

In order to solve the above problems, the present invention provides a rolling bearing and a bearing unit for an actuator of an HDD shown below.
(1) In the rolling bearing of the actuator that vibrates and supports the magnetic head of the HDD, the center line average surface roughness of the inner ring raceway and the outer ring raceway is 0.03 μm or less, and perfluoropolyether and its derivatives, fluoropolyether A rolling bearing for an actuator of an HDD, wherein a lubricating oil selected from the group consisting of derivatives thereof and a lubricant oil is enclosed, or is applied to an inner ring raceway surface, an outer ring raceway surface, a rolling element, and a cage.
(2) The rolling bearing for an actuator of HDD according to (1), wherein the lubricating oil is a linear perfluoropolyether.
(3) A rolling bearing unit for an actuator of HDD, wherein the rolling bearing for an actuator of HDD according to (1) or (2) is housed in a housing.

  According to the present invention, the inner ring raceway and the outer ring raceway are smoothed to have a center line average surface roughness of 0.03 μm or less, and torque hashness can be suppressed. Further, perfluoropolyether and derivatives thereof, A lubricating oil selected from ether and its derivatives is sealed or coated on each surface of the bearing, so that a low-torque, low-outgas, no torque hashness and high-performance HDD actuator rolling bearing and bearing unit are provided. .

  Hereinafter, a rolling bearing for an actuator of an HDD according to the present invention (hereinafter simply referred to as “rolling bearing”) will be described in detail with reference to the drawings.

  The rolling bearing of the present invention is not limited in its configuration itself. For example, as shown in FIG. 1, an inner ring 2 having an inner ring raceway 1 on an outer peripheral surface and an outer ring 4 having an outer ring raceway 3 on an inner peripheral surface. A plurality of balls 5 are disposed concentrically between the inner ring raceway 1 and the outer ring raceway 3 so as to be freely rollable by a cage 7, and the gap between the inner ring 2 and the outer ring 4 is sealed with a seal member 6. However, the inner ring raceway 1 and the outer ring raceway 3 are finished to have a centerline average surface roughness of 0.03 μm or less. The center line average roughness value is preferably smaller. With such a finish, torque hashness can be suppressed.

  Also, for lubrication, a lubricating oil selected from perfluoropolyether (PFPE) and its derivatives, fluoropolyether and its derivatives is enclosed, or the inner ring raceway surface, outer ring raceway surface, balls 5 and cage 7 are coated. To do. In the present invention, since it is lubrication with lubricating oil, the torque is lower than that of grease lubrication.

The magnetic disk is coated with a fluoropolymer for wear resistance and slidability. However, each of the above lubricating oils has a lower vapor pressure than the fluoropolymer, and maintains low lubrication performance. Asto gas can be realized. PFPE and its derivatives are
-C _X F _2X -O- (X is an integer of 1 to 4)
Is the main structural unit and preferably has an average molecular weight of 1,000 to 15,000. In consideration of lubrication performance and torque performance, the molecular weight is more preferably 3000 to 13000. Specifically, as the side chain structure of PFPE

As a straight chain structure

Is mentioned. Since the polymer having an average molecular weight of PFPE as described above of 3000 to 13000 has a high viscosity index and a low pour point, good lubricating characteristics can be obtained in a wide temperature range.

  Such PFPEs are also available from the market. For example, DUPONT's Krytox 143, Krytox GPL, Krytox 1500, Solvay Solexis's Fomblin Y Standard, NOK Kryuber's Barrierta J Fluid As the linear structure product, for example, demnum manufactured by Daikin Industries, Ltd. and Fomblin Z manufactured by Solvay Solexis can be suitably used. Among them, PFPE having a linear structure is preferably used because it has a high viscosity index, a pour point is lower than that of a side chain structure, and is excellent in evaporation characteristics and lubrication characteristics.

  Examples of the fluoropolyether derivative include those having a modified structure in which an isocyanate group, a hydroxyl group, a carboxyl group, or an ester group is introduced as a functional group at both terminal groups of a straight chain and a side chain structure. Among these, the hydroxyl group, carboxyl group or ester group modified product shown below is preferable.

Moreover, what combined the functional group of the terminal in different types can also be used. Furthermore, what introduce | transduced the said functional group into one terminal group can also be used. Furthermore, alcohol-modified products as shown below can also be used.
HO— (CH ₂ CH ₂ —O) _n —CH ₂ —CF ₂

  Such fluoropolyethers and derivatives thereof can be obtained from the market, and for example, fomblin Z derivatives from Solvay Solexis, Krytox 157 from DUPONT, and demnum modified types from Daikin Industries, Ltd. can be suitably used.

  These PFPE and derivatives thereof, fluoropolyether and derivatives thereof can be used by mixing those having different average molecular weights or functional groups, and viscosity can be adjusted. Further, by mixing PFPE and a fluoropolyether derivative, the wettability to metal can be improved. However, both or one end of the fluoropolyether derivative is modified with the above functional group. Therefore, the vapor pressure becomes higher than that of PFPE alone. Therefore, when giving top priority to the reduction of ast gas, it is preferable to use PFPE having a linear structure.

  The amount of the lubricating oil applied is preferably 0.1% to 10% of the bearing internal space volume formed by the inner ring, the outer ring and the rolling elements. Furthermore, if considering lubricity and lubricating oil leakage, 0.25% to 5% is preferable. In particular, when the upper limit is exceeded, it is impossible to reduce the torque. Although the application method is not limited, a specified amount of the lubricating oil composition is measured with a micro syringe or plunger pump capable of measuring a very small amount, and discharged onto the rolling element in a state where the inner ring, outer ring, rolling element and cage are assembled. A method of rotating the bearing several times is preferable. Further, in order to prevent leakage of the lubricating oil composition, it is preferable to apply the lubricating oil composition as a thin film, in which case, the bearing is immersed in a diluted lubricating oil diluted with the lubricating oil composition in a solvent, What is necessary is just to wipe off and dry the lubricating oil dilution liquid adhering to the outer surface. Moreover, the wiping work can be omitted by drying after discharging the lubricant dilution liquid onto the rolling elements.

  As in the present invention, an inner ring raceway surface and an outer ring raceway surface have a center line average surface roughness of 0.03 μm or less, and a lubricating oil selected from PFPE and derivatives thereof, fluoropolyether and derivatives thereof, preferably linear PFPE is used. Rolling bearings that are encapsulated or oiled on the inner ring raceway surface, outer ring raceway surface, rolling elements, and cage can achieve higher durability, lower torque, lower torque hashness, and lower outgas than conventional ones, and incorporate this rolling bearing. Thus, a highly reliable and high performance HDD actuator can be provided.

  Moreover, the rolling bearing of this invention can also be unitized. FIG. 2 is a cross-sectional view showing an example of the bearing unit. A pair of rolling bearings 8 of the present invention can be used, and an outer ring can be mounted on the housing 9 and an inner ring can be mounted on the shaft 10 to form a bearing unit.

Hereinafter, the present invention will be clarified by examples and comparative examples.
(Examples 1 to 3, Comparative Example 1)
Lubricating oil compositions were prepared with the formulations shown in Table 1. Further, using a rolling bearing “SMR74 (outer diameter 7 mm, inner diameter 4 mm, width 2 mm)” manufactured by NSK, the inner ring raceway surface and the outer ring raceway surface are processed to have a bearing centerline average surface roughness of 0.030 μm. A. In addition, the inner ring raceway surface and the outer ring raceway surface of the bearing were processed into a bearing center line average surface roughness of 0.050 μm to obtain a test bearing B.

  And the following test was done using said lubricating oil composition, the test bearing A, and the test bearing B. FIG.

(1) Torque hashness evaluation test In the test bearing A or the test bearing B, the lubricating oil composition of Example 1 is sealed so as to be approximately 3% of the bearing internal space volume, and the bearing inner ring is rotated at a low speed (rotation). The torque of the bearing outer ring was measured. The measurement results for the test bearing A are shown in FIG. 3, and the measurement results for the test bearing B are shown in FIG.

(2) Outgas test Head lubricant mass analysis gas chromatograph (GCMS) was used to determine the amount of gas generated when each lubricating oil composition was sealed in test bearing A at about 3% of the internal volume of the bearing and heated at 85 ° C for 1 hour. ). The evaluation criteria are “◎” for a gas generation amount of 500 ng or less, “◯” for 501 to 1000 ng, “Δ” for 1001 to 1500 ng, “x” for 1501 ng or more, and “◎”, “○” and “△”. Pass, “x” was rejected. The results are shown in Table 1.

(3) Fretting durability evaluation The lubricating oil composition of Example 1 was sealed in the test bearing A while changing the amount of sealing, and a fretting durability test was performed. As test conditions, torque fluctuations were observed over time at an oscillation angle of 8 ° and a frequency of 90 Hz, and the number of times that torque fluctuations appeared in the vicinity of ± 4 ° was defined as the fretting durability. 20 million times or more was accepted. The results are shown in FIG.

  From the above test results, it is understood that the torque hashness can be suppressed by setting the inner ring raceway surface and the outer ring raceway surface to a bearing center line average surface roughness of 0.030 μm or less. Moreover, it turns out that the lubricating oil used by this invention has few outgases and high fretting durability. Further, it can be seen that 0.1 to 10% of the bearing internal space volume is appropriate for the amount of the lubricating oil enclosed.

It is sectional drawing which shows an example of the rolling bearing for actuators of HDD of this invention. It is sectional drawing which shows an example of the rolling bearing unit for actuators of HDD. It is a graph which shows the measurement result of the torque hashness of the test bearing A. It is a graph which shows the measurement result of the torque hashness of the test bearing B. It is a graph which shows the relationship between lubricating oil enclosure amount and the frequency of fretting durability.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inner ring raceway 2 Inner ring 3 Outer ring raceway 4 Outer ring 5 Ball 6 Seal member 7 Cage 8 Rolling bearing 9 Housing 10 Shaft

Claims (3)

In the rolling bearing of the actuator that vibrates and supports the magnetic head of the hard disk drive device,
Centerline average surface roughness of inner ring raceway and outer ring raceway is 0.03 μm or less, and a lubricating oil selected from perfluoropolyether and derivatives thereof, fluoropolyether and derivatives thereof is enclosed, or inner ring raceway surface and outer ring A rolling bearing for an actuator of a hard disk drive device, characterized in that the raceway surface, rolling elements and cage are oiled.   2. A rolling bearing for an actuator of a hard disk drive device according to claim 1, wherein the lubricating oil is a linear perfluoropolyether.   3. A rolling bearing unit for an actuator of a hard disk drive device, wherein the rolling bearing for an actuator of the hard disk drive device according to claim 1 or 2 is housed in a housing.

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