JP2002188640A - Manufacturing method for dynamic pressure bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable effective and fine elimination of an oxide film produced by nitriding treatment. SOLUTION: By carrying out a process in which the surface of a stainless material 21' is dipped into nitrate liquid 31, dirt adhering on the surface of the stainless material 21', an oxide film produced by nitriding or the like are removed so as to form a passive film to improve corrosion resistance by simple work and to completely prevent conventional peeling phenomenon of a layer of a mill scale.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a dynamic pressure bearing device in which a shaft member and a bearing member are rotatably supported by a dynamic pressure of a lubricating fluid.

[0002]

2. Description of the Related Art Generally, a hydrodynamic bearing device is configured such that a lubricating fluid is injected between both dynamic pressure surfaces of a shaft member and a bearing member (sleeve) which are arranged opposite to each other, and a dynamic pressure is generated in the lubricating fluid. The shaft member and the bearing member are provided so as to be rotatable relative to each other, and a copper alloy is usually used as the bearing member from the viewpoint of ease of processing and the like. On the other hand, as the shaft member, a stainless steel material, particularly an austenitic stainless steel material, may be used for the reason that the thermal expansion properties of the copper alloy constituting the above-mentioned bearing member are made to match.

At this time, it is desirable to make the surface of the shaft member as hard as possible from the viewpoint of durability and the like.
When the austenitic stainless steel described above is employed, the surface hardness cannot be increased by heat treatment such as quenching. Therefore, in that case, a nitriding treatment is conventionally performed on the surface to form a nitrided layer. The nitriding treatment includes salt bath nitriding, ion nitriding,
Three types of gas nitriding are generally known.

[0004]

However, by any of the above-described nitriding treatments, an oxide film (black scale layer) containing Fe ₃ O ₄ as a main component is formed on the outermost layer of the formed nitrided layer. I will. This oxide film is generally porous, and thus easily peels off. When moisture accumulates in the peeled portion, erosion often proceeds rapidly therefrom. In particular, in a dynamic pressure bearing device, when the peeled oxide film enters a bearing portion having a minute gap (gap), the oxide film becomes a foreign substance, increases wear of the dynamic pressure surface, and reduces the life of the bearing. Become.

[0005] From such a situation, it is conceivable to remove the oxide film formed by the nitriding treatment by cutting or grinding, but in such a case, it takes much time and labor to process the groove and the R surface. This causes a problem that productivity is significantly reduced. In addition, it is conceivable that the processing is efficiently performed by barrel processing. However, the collision of the workpieces easily causes scratches and dents, and the oxide film inside the grooves and holes cannot be removed. There's a problem.

Accordingly, an object of the present invention is to provide a method of manufacturing a dynamic pressure bearing capable of efficiently and satisfactorily removing an oxide film formed by a nitriding treatment.

[0007]

In order to achieve the above object, in the method of manufacturing a dynamic pressure bearing according to the present invention, a step of immersing the surface of the stainless steel material after nitriding in a nitric acid solution is performed. The dirt adhering to the surface and the oxide film formed by the nitriding treatment are completely removed by the dissolving action of nitric acid. Then, a passivation film is formed on the highly purified surface of the stainless steel material by oxidation of chromium or the like, thereby inactivating the surface of the stainless steel material. As a result, the corrosion resistance is improved by a simple operation of dipping in a nitric acid solution, and the conventional peeling phenomenon of the black scale layer is completely prevented.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below. Prior to this, the entire structure of a hard disk drive (HDD) equipped with a hydrodynamic bearing device according to the present invention will be described with reference to the drawings. Keep it.

The entire spindle rotating HDD spindle motor shown in FIG. 2 is composed of a stator set 1 as a fixing member.
And a rotor set 2 as a rotating member assembled to the stator set 1 from above in the figure. The stator set 1 has a fixed frame 11 screwed to a fixed base (not shown). The fixed frame 11 is formed of an aluminum-based metal material to reduce the weight, but is provided with an annular cylindrical body constituting a bearing holding member at a substantially central portion of the fixed frame 11. Bearing holder 12 is integrally formed so as to stand upright.

On the inner peripheral wall side of the bearing holder 12,
A bearing sleeve 13 as a fixed bearing member formed in a hollow cylindrical shape is inserted, and is fixed by an adhesive (not shown). The bearing sleeve 13 can be joined to the bearing holder 12 by press fitting or shrink fitting. Such a bearing sleeve 13
Is formed of a copper-based alloy material such as phosphor bronze in order to facilitate processing of a small-diameter bearing hole, and has a coefficient of thermal expansion between a rotating shaft 21 as a shaft member described later. They are set to be almost the same.

A stator core 14 made of a laminated body of electromagnetic steel sheets is fitted on a mounting surface provided on the outer peripheral side wall surface of the bearing holder 12. This stator core 1
A drive coil 15 is wound around each salient pole portion provided in 4.

Further, a rotating shaft 21 constituting the above-mentioned rotor set 2 is rotatably inserted into a bearing hole formed through the bearing sleeve 13 along the central axis.
The rotating shaft 21 is formed of an austenitic stainless material such that the thermal expansion coefficients thereof substantially coincide with the bearing sleeve 13 formed of a copper-based alloy material. Such a rotating shaft 21 is formed by the manufacturing method according to the present invention, and a detailed manufacturing method will be described later.

The dynamic pressure surface formed on the inner peripheral surface of the bearing hole in the bearing sleeve 13 is disposed so as to face the dynamic pressure surface formed on the outer peripheral surface of the rotary shaft 21 in the radial direction. A radial dynamic pressure bearing portion RB is formed in a minute bearing gap space between the two dynamic pressure surfaces. More specifically, the dynamic pressure surface on the bearing sleeve 13 side and the dynamic pressure surface on the rotating shaft 21 side of the radial dynamic pressure bearing portion RB are circumferentially opposed to each other with a small gap of about several μm. In the bearing clearance space consisting of minute clearances,
A predetermined lubricating fluid, such as lubricating oil or magnetic fluid, is injected.

Further, on the dynamic pressure surface on the bearing sleeve 13 side, a radial dynamic pressure generating groove having a shape such as a herringbone shape (not shown) is annularly recessed, for example, divided into two blocks in the axial direction. During rotation, the lubricating fluid is pressurized by the pumping action of the two radial dynamic pressure generating grooves to generate a dynamic pressure, and the dynamic pressure of the lubricating fluid causes the rotary shaft 22 to be described later together with the rotary shaft 21.
Are supported by the shaft while floating in the radial direction.

Further, the radial dynamic pressure bearing portion RB
A capillary seal portion RS is disposed in an opening portion provided at the upper end side in the drawing in the bearing gap space. The capillary seal portion RS has a configuration in which the above-described bearing gap space is gradually enlarged toward the outer side of the bearing (upper side in the figure) by the inclined surface formed on the bearing sleeve 13 or the rotating shaft 21 side. For example, it is formed to have a gap size of 20 μm to 300 μm. In this capillary seal portion RS, the gas-liquid interface of the lubricating fluid described above is located regardless of whether the motor rotates or stops.

On the other hand, a ring-shaped thrust plate 24 is provided on the lower end of the rotary shaft 21 in the figure.
Is fixed. The thrust plate 24 is disposed so as to be accommodated in a cylindrical recess formed in the center portion of the bearing sleeve 13 at the lower end in the drawing, and the thrust plate 24 is disposed in the recess of the bearing sleeve 13. The dynamic pressure surface provided on the upper surface side of the thrust plate 24 in the drawing is disposed so as to be opposed to the dynamic pressure surface on the bearing sleeve 13 side in the axial direction. And
A thrust dynamic pressure bearing portion SBa on the upper side in the figure is formed in a bearing gap space between the dynamic pressure surfaces of the thrust plate 24 and the bearing sleeve 13.

Further, a counter plate 16 made of a disk-shaped member having a relatively large diameter is arranged so as to be close to the lower dynamic pressure surface of the thrust plate 24 in the figure. The counter plate 16 is mounted so as to close the lower end side opening portion of the bearing sleeve 13 and is fixed by an adhesive 17, and has a dynamic pressure surface provided on the upper surface side of the counter plate 16 in the drawing. The lower thrust dynamic pressure bearing portion S shown in the drawing is provided in the close opposing gap portion between the above thrust plate 24 and the lower dynamic pressure surface in the drawing.
Bb is formed.

As described above, the two dynamic pressure surfaces on the thrust plate 24 side forming a set of thrust dynamic pressure bearing portions SBa, SBb disposed adjacent to each other in the axial direction, the bearing sleeve 13 and the counter opposed thereto. The two dynamic pressure surfaces on the plate 16 side are axially opposed to each other with a small gap of several μm therebetween, and the above-mentioned radial dynamic pressure bearing portion R
The same lubricating fluid is filled so as to continue from B, and the lubricating fluid is axially continuous via the outer peripheral passage of the thrust plate 24. Further, on at least one side of the dynamic pressure surface of the thrust plate 24 and the dynamic pressure surfaces of the bearing sleeve 13 and the counter plate 16, a dynamic pressure generating groove having a shape such as a herringbone shape (not shown) is formed, for example, in a radial direction. The lubricating fluid is pressurized by the pumping action of the thrust dynamic pressure generating groove to generate a dynamic pressure when rotating, and the dynamic pressure of the lubricating fluid causes The rotating shaft 21 and the rotating hub 22 are axially supported in the thrust direction.

On the other hand, the rotor set 2 is
Is formed of a substantially cup-shaped member made of an aluminum-based metal or an iron-based alloy so as to mount a recording medium disk such as a magnetic disk (not shown). Partly provided joint holes,
The rotary shaft 21 is integrally joined to the upper end in the figure by press fitting or shrink fitting. The rotating hub 22
Has a substantially cylindrical body 22a on which a recording medium disk is mounted on an outer peripheral portion, and is provided on a disk mounting surface 22b provided so as to project radially outward from the body 22a. , A recording medium disk not shown is placed.

Further, on the inner peripheral wall side of the body portion 22a,
An annular drive magnet 23 is attached. The annular driving magnet 23 is arranged in proximity to the outer peripheral end face of the salient pole portion of the stator core 14 so as to annularly face the above.

Here, as described above, the rotating shaft 21
Is formed of an austenitic stainless steel so that the thermal expansion coefficients thereof substantially correspond to that of the bearing sleeve 13 formed of a copper-based alloy. In the present embodiment, the austenitic stainless steel is used. As a material,
SUS303 is adopted and is manufactured through the following steps.

That is, in manufacturing the rotating shaft 21 as described above, first, the surface of the stainless steel blank material after the stainless steel material is processed into a required shape is subjected to nitriding treatment. The nitriding treatment at this time is to form a nitrided layer by performing a so-called nitriding treatment on the surface of the stainless steel blank material.
In this embodiment, the salt bath nitriding with cyanide is carried out at 60.
By performing the process at 0 ° C., a nitride layer having a depth of about 10 μm and an outermost surface layer hardness (Hv) of 1100 is obtained. Then, by such a nitriding treatment, an oxide film (black scale layer) of about 0.05 μm is formed on the surface.
As the nitriding treatment in this case, any of ion nitriding and gas nitriding may be used in addition to the above-described salt bath nitriding.

Next, as shown in FIG. 1, for example, a step of immersing the surface of the stainless steel blank material 21 ′ after the above-mentioned nitriding treatment in a nitric acid solution 31 is performed. Such nitric acid treatment is performed, for example, in a suitable tank 32 at a concentration of 20%.
% Nitric acid solution 31 is stored, and the stainless blank material 21 ′ is stored in the stored nitric acid solution 31 by 50%.
By immersion at 10 ° C. for 10 minutes, dissolution is performed over a depth of about 0.1 μm, and as a result, the oxide film (black scale layer) formed on the surface in the above-described nitriding treatment is completely removed.

After the nitric acid treatment, the surface is washed with pure water to remove the nitric acid adhering to the surface, and then dried to form a passive film chemically and electrically stopped. To form an inactive, stable state.

Further, the remaining nitride layer 9.9 μm after the nitric acid treatment is polished for 4.9 μm,
Finally, a surface hardness (Hv) of 650 after polishing is obtained by forming a nitride layer of 5 μm.

As described above, in the present embodiment, the surface of the stainless steel blank material after the nitriding treatment is treated with the nitric acid solution 31.
By performing the step of immersion in the inside, dirt adhering to the surface and an oxide film generated by the nitriding treatment are removed by being dissolved by the nitric acid solution 31. A passivation film such as a chromium oxide film is formed on the surface of a stainless steel material that has been cleaned. As a result, the surface of the stainless steel blank material is inactivated and maintained in a stable state. That is, in the present embodiment, the corrosion resistance of the rotating shaft 21 made of stainless steel is improved by a simple operation of dipping in a nitric acid solution, and the peeling phenomenon of the black scale layer as in the related art is completely prevented. It has become.

Although the embodiments of the present invention made by the inventor have been specifically described above, the present invention is not limited to the above-described embodiments, and can be variously modified without departing from the gist thereof. Needless to say.

For example, in the above-described embodiment, the rotating shaft (shaft member) is subjected to nitric acid treatment using a stainless steel material, but the bearing member side is subjected to the same nitric acid treatment using a stainless steel material. Is also possible.

[0029]

As described above, in the method of manufacturing a dynamic pressure bearing according to the present invention, the step of immersing the surface of the stainless steel material after nitriding in a nitric acid solution is carried out, so that the dirt adhered to the surface can be reduced. A passivation film is formed by removing the oxide film and the like generated by the nitriding treatment.The simple work of dipping in nitric acid aims to improve the corrosion resistance and eliminate the conventional peeling phenomenon of the black scale layer. Since it is completely prevented, the oxide film generated by the nitriding treatment can be efficiently and satisfactorily removed, and the reliability of the hydrodynamic bearing device can be improved at low cost.

[Brief description of the drawings]

FIG. 1 is a schematic side view illustrating an apparatus structure for performing a method of manufacturing a shaft member according to an embodiment of the present invention.

FIG. 2 is an HDD provided with the dynamic pressure bearing device according to the present invention.
FIG. 3 is an explanatory longitudinal sectional view showing a structural example of a motor for a (hard disk drive).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Stator set 2 Rotor set 13 Bearing sleeve (bearing member) 16 Counter plate 21 Rotary shaft (shaft member) 21 'Stainless steel material (blank material) 22 Rotating hub 24 Thrust plate RB Radial dynamic pressure bearing part SB Thrust dynamic pressure bearing part 31 Nitric acid solution 32 tanks

Claims (4)

[Claims] 1. A dynamic pressure bearing device in which a shaft member and a bearing member are opposed to each other so as to be relatively rotatable, and a dynamic pressure generating means is formed on at least one side of an opposing surface of the shaft member and the bearing member. A method of forming at least one of the shaft member or the bearing member from a stainless material, and performing a nitriding treatment on the material surface after processing the stainless material into a required shape; Dipping the surface of the stainless steel material in the nitric acid solution after the nitriding treatment. 2. A method of forming the shaft member from an austenitic stainless steel material, wherein an oxide film formed on the surface of the stainless steel material by the nitriding treatment is removed with nitric acid to form a passive film. 2. The method for manufacturing a hydrodynamic bearing device according to claim 1, wherein: 3. The method according to claim 2, wherein an oxide film of chromium is formed as the passive film. 4. The method according to claim 1, wherein a copper alloy having a thermal expansion coefficient substantially equal to that of the shaft member is used as the bearing member, and a groove is formed in an inner peripheral surface of the bearing member as the dynamic pressure generating means. The method for manufacturing a dynamic pressure bearing device according to claim 1, wherein: