JP2010156385A - Fluid bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluid bearing device in which corrosion of bearing metal is effectively suppressed. <P>SOLUTION: A passive film (passivation film) 112 is provided on a surface of a sintered body such that the passivation film 112 covers a part of the sintered body which contacts lubricating fluid 17. The lubricating fluid 17 hardly enter into voids 111 of the sintered body because of the passivation film 112. Also, substances for forming a protective film 171 on the surface of the bearing metal or the like are added to ion liquid serving as base oil of the lubricating fluid 17. Therefore, corrosion of the bearing metal is suppressed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lubricant composition that can be used in a fluid bearing device or the like and a fluid bearing device.

  In recent years, along with miniaturization and speeding up of hard disk drives, spindle motors mounted on hard disk drives are required to have a high rotational speed and a long life that can withstand this high speed rotation.

Lubricating fluid is used for the hydrodynamic bearing device in the spindle motor, and the characteristics of the lubricating fluid affect the characteristics (rigidity, current value, life, etc.) of the spindle motor. For example, the evaporation of the lubricating fluid leads to a decrease in the lubricating fluid and changes the characteristics of the spindle motor. Therefore, in order to meet the above-described requirements, it has been proposed to use an ionic liquid instead of the ester oil that has been widely used as a base oil for a lubricating fluid (for example, Patent Document 1).
JP 2005-147394 A

  However, the conventional hydrodynamic bearing device has a problem that the surface of the bearing metal is corroded by using the ionic liquid. When the corrosion occurs, the size of the bearing metal changes or a part of the metal is peeled off, causing a problem such as deterioration in rotational accuracy.

  Then, this invention makes it a subject to provide the hydrodynamic bearing apparatus by which such corrosion was suppressed.

In order to solve the above problems, the present invention provides:
(1) a sleeve having a bearing hole, a shaft disposed in the bearing hole of the sleeve so as to rotate relative to the sleeve, and a gap between the sleeve and the shaft; A hydrodynamic bearing device comprising: an ionic liquid as a lubricant composition comprising a corrosion inhibitor film-forming agent;
(2) The hydrodynamic bearing device according to (1), wherein the lubricant composition includes a corrosion inhibitor and / or a rust inhibitor as the corrosion prevention film forming agent. (3) The sleeve is made of metal sintered. The hydrodynamic bearing device according to the above (1) or (2), which comprises a body and has a passive film on the surface.

  The hydrodynamic bearing device of the present invention has the effect that the corrosion of the bearing metal is effectively suppressed because the lubricant composition contains the corrosion preventing film forming agent.

[1] First Embodiment (1-1) Spindle Motor As an example of the hydrodynamic bearing device of the present invention, a hydrodynamic bearing device in a spindle motor for a hard disk drive will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a spindle motor 1 according to this embodiment.

[Configuration of spindle motor 1]
As shown in FIG. 1, the spindle motor 1 of the present embodiment is a device for rotationally driving a disk-shaped magnetic recording disk 151, and mainly includes a hydrodynamic bearing device 10, a base 18, a stator core 19, And a rotor magnet 20.

  The hydrodynamic bearing device 10 smoothly rotates the rotating side member including the rotor hub 15 around the shaft 12 in a non-contact state with respect to the fixed side member such as the sleeve 11. Since the magnetic recording disk 151 is mounted on the rotor hub 15, the magnetic recording disk 151 rotates about the shaft 12. The configuration of the hydrodynamic bearing device 10 will be described later.

  The base 18 forms a base portion of the hydrodynamic bearing device 10 and the stator core 19. The base 18 is made of a non-magnetic aluminum-based metal material (for example, ADC 12) or a magnetic iron-based metal material (for example, SPCC, SPCD). A sleeve 11 and a stator core 19 are attached to the base 18.

  The stator core 19 is fixed to the base 18, and the outer peripheral portion thereof is disposed at a position facing the inner peripheral portion of the rotor magnet 20 with a predetermined gap. The stator core 19 has a plurality of salient poles formed toward the outer periphery, and coils are wound around the salient poles.

  The rotor magnet 20 has an annular shape, is fixed to the inner peripheral surface of the hanging cylindrical portion from the flange portion of the rotor hub 15, and constitutes a magnetic circuit together with the stator core 19 around which the coil is wound.

[Configuration of Fluid Bearing Device 10]
As shown in FIG. 2, the hydrodynamic bearing device 10 according to the present embodiment includes a sleeve 11, a shaft 12, a flange 13, a thrust plate 14, a rotor hub 15, a sleeve cap 16, and a lubricating fluid 17. I have.

The sleeve 11 has a bearing hole 11a and a communication passage 11b that communicates the open end side and the closed end side of the bearing hole 11a. Details of the sleeve 11 will be described later.
As shown in FIG. 2, the shaft 12 is rotatable in the bearing hole 11 a of the sleeve 11 so as to form a first gap G <b> 1 between the inner peripheral surface of the bearing hole 11 a and the outer peripheral surface of the shaft 12. It is inserted in the state. Dynamic pressure generating grooves 11 c and 11 d are formed on at least one of the outer peripheral surface of the shaft 12 or the inner peripheral surface of the bearing hole 11 a of the sleeve 11. A flange 13 is fixed to the lower end portion of the shaft 12 at a substantially right angle with high accuracy.

  The flange 13 is disposed at the lower end portion of the shaft 12 so that the angle formed by the shaft 12 and the flange 13 is substantially perpendicular and the upper end surface of the flange 13 faces the sleeve 11. Further, the flange 13 is disposed so as to form a gap between the sleeve 11 and the flange 13, and this gap is continuous from the first gap G1 described above.

  Further, the flange 13 is arranged so that the lower end surface thereof faces the thrust plate 14 and forms a gap between the flange 13 and the thrust plate 14, and this gap is formed between the sleeve 11 and the flange. It continues from the gap between 13. Further, the gap between the flange 13 and the thrust plate 14 continues to the communication path 11b.

  A dynamic pressure generating groove 11e is formed on at least one of the surface of the sleeve 11 facing the flange 13 and the surface of the flange 13 facing the sleeve 11. Further, a dynamic pressure generating groove 14 a is formed on at least one of the surface of the flange 13 facing the thrust plate 14 and the surface of the thrust plate 14 facing the flange 13. Only one of the dynamic pressure generating grooves 11e and 14a may be provided.

  A rotor magnet 20 (described later) is fixed to the rotor hub 15 at a position facing the stator core 19, and a magnetic recording disk 151 such as a magnetic disk or an optical disk is attached as necessary. The rotor hub 15 includes a boss portion 15 a that protrudes toward the sleeve 11.

  The sleeve cap 16 has a central hole 16 a and is fixed to the upper end surface of the sleeve 11. The sleeve cap 16 is disposed so as to form a second gap G <b> 2 between the upper surface of the sleeve 11. The second gap G2 is continuous from the first gap G1 to the communication path 11b. The above-described boss portion 15a and shaft 12 have outer peripheral surfaces facing the inner peripheral surface of the central hole 16a, and a third gap G3 is formed between the outer peripheral surface and the inner peripheral surface of the central hole 16a. To be arranged. The third gap G3 communicates with the first gap G1 and the second gap. Although the third gap G3 is open to the atmosphere, the lubricating fluid 17 is held in the hydrodynamic bearing device 10 by its own surface tension.

  The lubricating fluid 17 is filled in the bearing gap including the first to third gaps G1 to G3 shown in FIG. When the rotation of the rotation side member including the shaft 12 is started, the lubricating fluid 17 flows into the dynamic pressure generation grooves 11c, 11d, 11e and the like to generate dynamic pressure, and the radial dynamic pressure generation groove Circulation force is generated by 11c and 11d being formed asymmetrically and circulates in the hydrodynamic bearing device 10 along the direction of the arrow in the figure.

  Stainless steel is the most suitable material for the shaft 12. Stainless steel is effective because it has higher hardness and can suppress the amount of wear compared to other metals. More preferably, it is martensitic stainless steel.

  The sleeve 11 is preferably made of a material such as copper alloy, iron alloy, stainless steel, ceramics, or resin. Furthermore, copper alloy, iron alloy, and stainless steel, which have higher wear resistance and workability and are low in cost, are more preferable. Surface modification may be performed on a part or all of the sleeve material by plating, physical vapor deposition, chemical vapor deposition, diffusion coating, or the like. Moreover, a metal sintered body can be used for the sleeve material from the viewpoint of cost.

The case where a sintered body is used for the sleeve 11 will be described with reference to FIG. FIG. 3 is a cross-sectional view around the first gap G1 in the hydrodynamic bearing device 10.
The sintered body is a compacted metal sintered body in which the iron component is 80% by weight or more, preferably 95% by weight or more of the whole. The sintered body is a porous body having a plurality of pores 111 and having a volume density of 98% or more.

  The metal constituting the sintered body includes iron, copper, aluminum, titanium, and chromium, and alloys thereof. Among them, iron, aluminum, titanium, and chromium that can form a passive film on the surface thereof. And alloys thereof are preferred. As the metal constituting the sintered body, a metal having a close passivity and an ionization tendency with the metal constituting the shaft 12 is particularly selected from the viewpoint of preventing corrosion. That is, in this embodiment, since the shaft 12 is made of stainless steel, iron is used as the metal constituting the sintered body. However, the sintered body is constructed in accordance with the change of the metal constituting the shaft 12. The metal can also be changed.

In the present embodiment, a passive film (passive film) 112 is formed on the surface of the sintered body. The thickness of the coating 112 is preferably 2 to 15 micrometers, and the pores 111 on the surface of the sintered body are filled with the coating 112. As a method for forming the film 112, a conventionally known metal oxidation method can be suitably used. When the sintered body is iron, an example of the coating 112 is a triiron tetroxide (Fe ₃ O ₄ ) coating. The triiron tetroxide (Fe ₃ O ₄ ) film is formed by various oxidation treatments such as steam treatment at 400 ° C. to 700 ° C., for example.

  The film 112 is provided so as to cover at least the inner peripheral surface of the bearing hole 11a, and is preferably provided also on the surfaces constituting the communication path 11b, the second gap G2, and the third gap G3. In other words, the coating 112 is preferably provided so as to cover a portion of the sintered body that contacts the lubricating fluid 17.

  The holes 111 are gaps formed between the sintered particles and are connected to each other. Therefore, when a passive film is not formed, the ionic liquid tends to enter from the surface of the sintered body to the inside. As shown in FIG. 3, since the surface is covered with the coating 112, the lubricating fluid 17 is unlikely to enter the pores 111 of the sintered body.

[Lubricating fluid 17]
As the lubricating fluid 17, a lubricant composition containing an ionic liquid as a base oil and containing a corrosion prevention film forming agent is used.

(Base oil)
An ionic liquid is an ionic substance that is liquid at room temperature and is composed of cations and anions. Ionic liquids are also called room temperature molten salts.

  The “base oil” means a substance that is a main component of the lubricant composition and imparts lubricity to the lubricant composition. Therefore, generally, the content of the base oil in the entire lubricant composition is set to 50% by weight or more. In particular, the content of the ionic liquid in the entire lubricant composition can be set to 80% by weight or more, 90% by weight or more, or 95% by weight or more.

  As described above, the ionic liquid is a liquid at room temperature, but more specifically, an ionic liquid having a melting point of 0 ° C. or lower is preferable. Among these, an ionic liquid having a melting point of about 0 to −60 ° C. is more preferable. The melting point is measured using a differential scanning calorimeter (DSC).

An ionic liquid may be used individually by 1 type, and may be used in combination of 2 or more type.
The composition of the ionic liquid, for example, the contained anions and cations, the concentration of each ion, and the like are not particularly limited. Examples of the cation that can be used include imidazolium, pyrazolium, pyrrolidinium, pyridinium, piperidinium, phosphonium, sulfonium, and ammonium. The anions include Cl ⁻ , Br ⁻ , I ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , [SCN] ⁻ , [C _n F _{2n + 1} SO ₃ ] ⁻ , [(C _n F _{2n + 1} SO _2). ) ₂ N] ⁻ , [p-CH ₃ C ₆ H ₄ SO ₂ ] ⁻ , [C _n H _{2n + 1} SO ₃ ] ⁻ , [C _n H _{2n + 1} OSO ₃ ] ⁻ , [C _n H _{2n + 1} CO ₂ ] ⁻ , [C _n F _{2n + 1} CO ₂ ] ⁻ , [N (CN) ₂ ] ⁻ , [C (CN) ₃ ] ⁻ , and [(C _n H _{2n + 1} ) ₂ PO ₄ ] ^-, and the like.

(Corrosion prevention film forming agent)
As shown in FIG. 3, the corrosion preventing film forming agent forms a protective film 171 on the surface of the bearing metal (sleeve 11, shaft 12, sleeve cap 16). The bearing metal is a metal member in contact with the lubricating fluid 17, and specifically includes the sleeve 11, the shaft 12, the flange 13, the thrust plate 14, the rotor hub 15, the sleeve cap 16, and the like. Examples of the corrosion prevention film forming agent include a corrosion inhibitor, a rust inhibitor, and the like. Specifically, a benzotriazole compound, an imidazole compound, a benzimidazole compound, a dimercaptothiazole compound, a succinic acid compound, Metal soaps, ester compounds, sulfonate compounds, phosphite compounds, amines and the like can be mentioned. The corrosion preventing film forming agent can protect the bearing metal from corrosion by forming a protective film on the surface of the bearing metal.

Moreover, a corrosion inhibitor film-forming agent may be used alone or in combination of two or more.
The addition amount of the corrosion preventing film forming agent in the entire lubricant composition is appropriately set according to the kind of the corrosion preventing film forming agent, the characteristics of the ionic liquid, and the like. The addition amount of the corrosion-preventing film forming agent is preferably 0.01% by weight to 10% by weight, more preferably 0.1% by weight to 5% by weight in the entire lubricant composition.

(Other ingredients)
The lubricant composition may contain further additives. Such additives include, for example, antioxidants, metal deactivators, oily agents, extreme pressure agents, friction modifiers, antiwear agents, viscosity index improvers, pour point depressants, defoamers, hydrolysis Examples thereof include an inhibitor, an antistatic agent, a conductivity imparting agent, and a cleaning dispersant.

  In the lubricant composition of the present invention, the additive amount of the additive is not particularly limited, but is, for example, 10% by weight or less, preferably 5% by weight or less, more preferably, based on the entire lubricant composition. May be 2% by weight or less.

(Characteristics of entire lubricant composition)
The lubricant composition is preferably liquid at a low temperature (0 ° C. or lower). That is, the melting point and the freezing point of the lubricant composition are preferably 0 ° C. or lower, and more preferably −20 ° C. or lower. As described above, when the melting point is −20 ° C. or less, when the lubricant composition is used in a hydrodynamic bearing device, a rapid increase in the torque of the bearing in a low temperature environment can be prevented.

(Manufacture of lubricant composition)
The lubricant composition of the present invention can be produced by mixing an ionic liquid, a corrosion-preventing film forming agent, and other additives by a conventional method.

(1-2) Operation of Spindle Motor 1 As shown in FIG. 1, when the stator core 19 is energized, a rotating magnetic field is generated between the rotor magnet 20 and the stator core 19, and the rotor magnet 20 is connected to the shaft 12. , The rotation is started together with the flange 13 and the rotor hub 15. When the shaft 12 starts rotating, the lubricating fluid 17 gathers in the dynamic pressure generating grooves 11c to 11e and 14a, so that the shaft 12 rotates in a non-contact manner with respect to the sleeve 11 while floating in the lubricating fluid 17. The lubricating fluid 17 circulates between the communication path 11b and the gaps G1 and G2.

  As is clear from the above description, the sleeve 11 is a stationary member, and the shaft 12 and the flange 13 are rotating members.

(1-3) Magnetic Recording / Reproducing Device The spindle motor 1 described above can be applied to a magnetic recording / reproducing device. FIG. 4 is a cross-sectional view showing the configuration of the magnetic recording / reproducing apparatus 150 according to this embodiment.

As shown in FIG. 4, the magnetic recording / reproducing apparatus 150 includes a spindle motor 1, a recording disk 151, and a recording head 152.
The magnetic recording disk 151 is mounted on a disk mounting portion of the rotor hub 15. For example, a disk-shaped clamper having spring property in the axial direction (not shown) is set on a tapping screw (not shown), and the central portion of the shaft 12 is set. By screwing the tapping screw into the provided screw tap portion, the tapping screw is pressed down in the axial direction and is held between the clamper and the disk mounting portion of the rotor hub 15.

  The recording head 152 reads information on the magnetic recording disk 151 and writes information. The recording head 152 only needs to be capable of at least one of reading and writing.

  In addition, the magnetic recording / reproducing apparatus 150 includes an arm that supports the recording head 152, an arm driving unit that moves the arm, and arranges the recording head 152 at a predetermined position of the magnetic recording disk 151.

[2] Other Embodiments Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the invention.

(A)
In the above embodiment, the so-called flange type hydrodynamic bearing device 10 in which the flange 13 is attached to the shaft 12 has been described as an example. However, the present invention is not limited to this.

  For example, in FIG. 2, the present invention may be applied to a so-called flangeless type hydrodynamic bearing device in which there is no flange 13 with respect to the shaft 12 and the lower end surface of the shaft 12 is a bearing surface.

(B)
In the above-described embodiment, the rotation-side member including the shaft 12 and the rotor hub 15 is described as an example of the shaft-rotation type hydrodynamic bearing device 10 that rotates with respect to the fixed-side member including the sleeve 11. However, the present invention is not limited to this.

  For example, even if the fixed-side member including the shaft is filled with the lubricating fluid according to the embodiment of the present invention in the fixed-shaft type hydrodynamic bearing device in which the rotating-side member including the sleeve and the rotor hub rotates. Good.

(C)
In the above embodiment, the configuration of the hydrodynamic bearing device 10 that circulates the lubricating fluid 17 along the circulation path including the communication path 11b formed in the sleeve 11 has been described as an example. However, the present invention is not limited to this.

  For example, a lubricating fluid according to an embodiment of the present invention may be filled into a non-circulating fluid bearing device having no communication path in the sleeve.

(D)
The hydrodynamic bearing device and the spindle motor can be applied to a magnetic recording / reproducing apparatus that records / reproduces information on / from a recording disk by the recording head 152. May be.

  Furthermore, the present invention may be applied to a hydrodynamic bearing device included in a spindle motor that rotates a cooling fan mounted on a CPU as an information processing device.

  The hydrodynamic bearing device of the present invention can be suitably used for a spindle motor for a hard disk drive because the bearing metal is hardly corroded.

A sectional view of a spindle motor concerning one embodiment of the present invention. The partial expanded sectional view which shows the structure of the hydrodynamic bearing apparatus mounted in the said spindle motor. FIG. 3 is a cross-sectional view around the first gap G1 in the hydrodynamic bearing device 10; Sectional drawing which shows the structure of the magnetic recording / reproducing apparatus carrying the said hydrodynamic bearing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Spindle motor 10 Fluid bearing apparatus 11 Sleeve 11a Bearing hole 11b Communication path 11c, 11d, 11e Dynamic pressure generating groove 12 Shaft 13 Flange 14 Thrust plate 14a Dynamic pressure generating groove 15 Rotor hub 16 Sleeve cap 16a Center hole 17 Lubricating fluid 18 Base 19 Stator core 20 Rotor magnet 111 Hole 112 Film 150 Magnetic recording / reproducing device 151 Magnetic recording disk 152 Recording head 171 Protective films G1-G3 Gap

Claims (3)

A sleeve having a bearing hole;
A shaft arranged to rotate relative to the sleeve in a bearing hole of the sleeve;
A lubricant composition that is disposed in a gap between the sleeve and the shaft and includes an ionic liquid as a base oil and a corrosion-preventing film forming agent;
A hydrodynamic bearing device comprising:   The hydrodynamic bearing device according to claim 1, wherein the lubricant composition includes a corrosion inhibitor and / or a rust inhibitor as the corrosion prevention film forming agent. The hydrodynamic bearing device according to claim 1, wherein the sleeve is made of a metal sintered body and has a passive film on a surface thereof.

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