Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
1999-02-04
2001-01-16
Marmor, Charles A. (Department: 3681)
Bearings
Rotary bearing
Antifriction bearing
Reexamination Certificate
active
06174089
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to rolling bearings, for example, a rolling bearing suitable for use with spindles of hard disk drives (HDDs), small-sized spindles for dental handpieces and the like.
Conventionally, as this type of rolling bearing, there has been available a rolling bearing comprising inner and outer rings made of bearing steel, and balls made of silicon nitride. Because the balls are made of silicon nitride, this bearing is advantageous in being capable of high-speed rotation and free from replenishment of grease for a long time.
However, in the conventional bearing as described above, although the intervals for replenishment of grease during high-speed rotation can be prolonged, that is, prolonged life of grease can be achieved, there has been a problem that increased vibrations and noise would be involved, as compared with bearings made fully of bearing steel, because the contact surface pressure between bearing steel and silicon nitride is higher than the contact surface pressure of bearings in which the inner and outer rings and the balls are both made of bearing steel.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a rolling bearing which is capable of reducing vibrations and noise while satisfying the requirements of high-speed rotation and prolonged life of grease.
In order to achieve the above object, the present invention provides raceway rings, and rolling elements which are formed of a ceramic material whose major component is zirconia and which has a Young's modulus not more than 250 GPa.
According to this invention, the rolling elements are formed of the ceramic material whose major component is zirconia and which has a Young's modulus of 250 GPa or lower. Therefore, because of the low Young's modulus of the rolling element, the contact surface pressure between the rolling elements and the raceway rings becomes lower. As a result, this rolling bearing can be greatly reduced in vibrations and noise. Consequently, the rolling bearing has advantages of low vibrations and low noise in addition to the capability of high-speed rotation and prolonged life of grease.
In an embodiment, the ceramic material of the rolling elements is sintered by hot isostatic pressing (hereinafter, abbreviated as HIP).
In this embodiment, the rolling elements made of a ceramic material whose major component is zirconia are sintered by HIP, and this results in a compact sintered body having almost no pores. Accordingly, by using these rolling elements, the rolling bearing becomes small in vibrations, low in noise and yet good at durability (high in fatigue strength)
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patent: 5967670 (1999-10-01), Gabelli et al.
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“Ceramic Materials Physical, Mechanical, Thermal And Electrical Properties Reference Chart”, By Ferro-Ceramic Grinding Inc., http://ferroceramic.com/tables/t-17.htm., Apr. 2000.
Young's Modulus, Flexural Strength And Fracture Of Yttria-Stabilized Zirconia Versus Temperature, Adams et al., Journal Of American Ceramic Society, vol. 80, Apr. 1997.
“Advanced Ceramics Get Tough On Costs”, Materials Engineering, pp. 20-22, ISSN 0025-5319, Apr. 1992.
Hattori Tomoya
Kitamura Kazuhisa
Takebayashi Hiroaki
Koyo Seiko Co. Ltd.
Marmor Charles A.
Pang Roger
Wenderoth , Lind & Ponack, L.L.P.
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