Compositions: ceramic – Ceramic compositions – Refractory
Reexamination Certificate
2001-05-16
2002-11-05
Marcantoni, Paul (Department: 1755)
Compositions: ceramic
Ceramic compositions
Refractory
C501S104000
Reexamination Certificate
active
06475940
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wear resistant member for electronic equipment in which deficiency due to static electricity is lessened, and a bearing and spindle motor therewith.
2. Description of the Related Art
In recent years, magnetic recording devices such as hard disk drives (HDDS) and floppy disk drives (FDDs), optical disk devices such as CD-ROMs and DVDs, and various kinds of game machines have made a remarkable development. In electronic equipment, usually a rotational driver such as spindle motor rotates a rotation axis with high speed, thereby facilitating various kinds of disks mounted to this rotation axis to function.
So far, for bearing member supporting such rotation axis, in particular, for bearing balls, metal such as bearing steel or the like has been used. However, metal such as bearing steel or the like is poor in wear resistance. Accordingly, in the field requiring a high speed rotation of more than 5000 rpm such as for instance electronic equipment, due to an increase of fluctuation of life, there are problems that reliable rotational drive cannot be provided.
In order to overcome such deficiencies, recently for the bearing balls, ceramics such as silicon nitride sintered body has been employed (cf. Japanese Patent Laid-Open Application No. JP-A 2000-314426). Among the ceramics, the silicon nitride sintered body is excellent in sliding properties and has excellent wear resistance. Accordingly, even when rotating at high speeds, mechanically reliable rotational drive can be provided.
However, a silicon nitride bearing ball is electrically an insulator. Accordingly, there occur a problem that static electricity generated when rotating at high speeds can be skillfully guided neither to the rotation axis consisting of metallic material such as bearing steel or the like nor to bearing member other than the bearing ball such as ball receiver. Thus, when without successfully dissipating to build up unnecessarily the static electricity in the bearing and periphery components, in a recording device using magnetic signals such as for instance HDD, an adverse affect may be caused on a recording medium. As a result, there are concerns that the content recorded in the HDD may be lost, and furthermore the electronic equipment itself may be destroyed.
Furthermore, portable personal computers, electronic notebooks, various kinds of mobile products and so on have been downsized year by year, accordingly for the HDDs therefor, demands for larger storage capacity and smaller size have become stronger year by year. In order to come up to such demands, for instance in the HDDs, rotation of still higher speed has been studied, and in the future, the high speed rotation of approximately 10000 rpm or more is expected to be realized. It is the bearing configured of the rotation axis, a bearing ball and a ball receiver that supports such high speed rotation, excess pressure being essentially concentrated on the bearing balls.
In addition to this, when rotating at high speeds, due to sliding of the bearing ball, a large amount of heat is liberated. At that time, silicon nitride is largely different in linear expansion coefficient from that of bearing steel (for instance SUSJ2) that constitutes the rotation axis and ball receiver. Accordingly, there occur such problems that due to the deformation caused by thermal expansion of the metal member, noise or unusual sound is generated, or due to thermal strain caused by thermal expansion, non-synchronized deflection is generated. Also from such viewpoints, the existing silicon nitride bearing ball cannot sufficiently come up to the longer time high speed rotation.
To the problems caused due to the high speed rotation as mentioned above, a bearing that employs a bearing ball consisting of a zirconium oxide sintered body of which linear expansion coefficient is close to that of metal is proposed (Japanese Patent Laid-Open Application No. JP-A 11-223220). The zirconium oxide sintered body, while, in addition to the above, being superior to the silicon nitride sintered body in fracture toughness, is an electrical insulator similarly with the silicon nitride bearing ball. Accordingly, when rotating at high speeds, there is similarly accumulated static electricity. It cannot be overcome that based on the static electricity, there occur various problems.
A conductive zirconium oxide sintered body of which specific resistance is approximately 10
−5
&OHgr;·m is known (cf. Japanese Patent Publication Gazette Nos. JP-B2 1-24747 and JP-B2 3-51667). To such conductive zirconium oxide sintered body that is mainly used in cutting tools and electrical resistance heating elements, a large amount of conductivity enhancer such as carbides or the like is added to improve conductivity (low specific resistance). In the zirconium oxide sintered body wherein a large amount of the conductivity enhancer is added, while the specific resistance itself becomes lower, the conductivity enhancer that are excessively added tend to coagulate themselves. This causes to lower mechanical strength and sliding properties of the zirconium oxide sintered body.
For instance, as in the case of bearing balls, in the use always exposed to repetition fatigue of compressive stress and/or tensile stress, when the aforementioned agglomerated particle exists in a large amount, cracks tend to start therefrom. As a result, the sliding properties are largely deteriorated. Accordingly, the conductive zirconium oxide sintered body such as mentioned in the above publications is far from applying in the wear resistant member such as bearing balls. The above publications, not assuming the application of the conductive zirconium oxide sintered body in the sliding member, give the conductivity only to make use electric discharge machining.
In Japanese Patent Laid-Open Application No. JP-A 8-296649, it is disclosed that ceramic material having volume resistivity of 10
4
&OHgr;·m or less is used in a dynamic pressure bearing having a spiral groove that generates a dynamic pressure effect. However, there are used ceramic materials such as sintered bodies essentially consisting of conductive ceramics such as SiC, TiC, TiN, and TiB
2
, and composite sintered bodies between Al
2
O
3
and TiC, and ZrO
2
and NiO. There is not disclosed any of ceramic material that has characteristics intrinsic to the zirconium oxide sintered body.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a wear resistant member for electronic equipment that can realize a stable high speed rotation when applied in the bearing ball or the like, in addition can prevent unnecessarily excessive static electricity from accumulating. Furthermore, another object is to provide a bearing and spindle motor that, by the use of such wear resistant member for electronic equipment, enable to realize higher performance and higher reliability of the electronic equipment such as magnetic recording device such as HDDs and optical disk device such as DVDs.
The wear resistant member for electronic equipment of the present invention comprises a zirconium oxide sintered body of which specific resistance is in the range from 1 to 10
5
&OHgr;·m. In the wear resistant member for electronic equipment of the present invention, the zirconium oxide sintered body comprises a conductivity enhancer of which specific resistance is 10
−5
&OHgr;·m or less.
In the wear resistant member for electronic equipment of the present invention, the conductivity enhancer contained in the zirconium oxide sintered body is preferable to be at least one kind selected from carbides and nitrides of elements of 4A, 5A, 6A and 7A groups in the periodic table, silicon and boron. In particular, at least one kind of carbide selected from tantalum (Ta), niobium (Nb), chromium (Cr), tungsten (W), molybdenum (Mo), titanium (Ti), zirconium (Zr), hafnium (Hf), manganese (Mn) and silicon (Si) carbides is preferably used.
Furthermore, in the wear resistant member for electronic
Fukuda Yoshiyuki
Ikeda Isao
Komatsu Michiyasu
Takao Minoru
Takenami Yukihiro
Foley & Lardner
Marcantoni Paul
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