# US 2010/0166343 A1 · Shaft member for fluid dynamic bearing device

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- Number: US 2010/0166343 A1
- Document ID: US20100166343A1
- Status: Published application
- Kind: A1
- Application number: 12/160,654
- Filed: 2006-12-26
- Published: 2010-07-01
- Earliest claimed: 2006-01-19
- Assignees: Ntn Corporation
- Inventors: Kenji Hibi; Yasuhiro Yamamoto
- Web page: https://patentgrep.com/patent/US20100166343A1

## CPC

- F16C 33/12: Structural composition; Use of special materials or surface treatments, e.g. for rust-proofing
- F16C 17/02: for radial load only
- F16C 17/026: {with helical grooves in the bearing surface to generate hydrodynamic pressure, e.g. herringbone grooves}
- F16C 33/107: {Grooves for generating pressure}
- F16C 33/14: Special methods of manufacture; Running-in
- F16C 2204/60: Ferrous alloys, e.g. steel alloys
- F16C 2220/40: by deformation without removing material
- F16C 2220/44: by rolling
- F16C 2220/60: by removing material, e.g. machining
- F16C 2220/70: by grinding
- F16C 2223/14: with nitriding
- F16C: SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS

## Abstract

Provided is a shaft member for a fluid dynamic bearing device, which is excellent in wear resistance and which can exert a high dynamic pressure effect. A shaft material (11) is rolled to form a recess (7) for causing a dynamic pressure effect of a lubricating oil in a radial bearing clearance (6). In this case, in a surface layer portion (14) of the recess (7) to be formed in an outer peripheral surface (11a) of the shaft material (11), a first hardened layer (14a) is formed by rolling. At the same time, also in a surface layer portion (15) of a surrounding region (8) of the recess (7), a first hardened layer (15a) is formed by rolling at a partial region thereof. After the recess (7) is formed by the rolling, barreling is applied to the shaft material (11). As a result, an outermost surface layer portion of the surface layer portion (15) is formed with a second hardened layer (15b) by the barreling. A hardness of the second hardened layer (15b) formed in the surrounding region (8) is higher by 50 Hv or more and 200 Hv or less than that of the first hardened layer (14a) formed in the recess (7).

## Claims

### Claim 1

A shaft member for a fluid dynamic bearing device, the shaft comprising:
a recess for causing a dynamic pressure effect of a fluid in a bearing clearance, which is formed thereon by rolling;
a first hardened layer formed in a surface layer portion of the recess by the rolling; and
a second hardened layer formed in a surface layer portion of a surrounding region of the recess,
wherein a hardness of the second hardened layer is higher by 50 Hv or more and 200 Hv or less than a hardness of the first hardened layer formed in the recess.

### Claim 2 (depends on 1)

A shaft member for a fluid dynamic bearing device according to claim 1, wherein the second hardened layer is obtained by performing barreling.

### Claim 3 (depends on 2)

A shaft member for a fluid dynamic bearing device according to claim 2, wherein the barreling is performed by using a medium having a size that prevents the medium from being brought into contact with a bottom surface of the recess.

### Claim 4

A shaft member for a fluid dynamic bearing device, comprising a recess for causing a dynamic pressure effect of a fluid in a bearing clearance, which is formed thereon by rolling, wherein a surface layer portion in a surrounding region of the recess comprises a nitride layer formed by nitriding after the rolling.

### Claim 5 (depends on 4)

A shaft member for a fluid dynamic bearing device according to claim 4, wherein at least a partial region of a surface of the surface layer portion has a surface processed by barreling.

### Claim 6 (depends on 4)

A shaft member for a fluid dynamic bearing device according to claim 4, wherein a hardness of a lower layer region of the surface layer portion is equal to or less than 400 Hv.

### Claim 7 (depends on 1, 2, 3, 4, 5, 6)

A fluid dynamic bearing device comprising the shaft member for a fluid dynamic bearing device according to any one of claims 1 to 6.