Ball bearing

Details Ball bearing Ball bearing

1998-07-28

2001-08-28

Yee, Deborah (Department: 1742)

Metal treatment

Stock

Ferrous

C148S906000, C384S492000, C384S609000, C384S613000, C384S912000

Reexamination Certificate

active

06280537

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a rolling bearing, and more particularly to a rolling bearing suitably used for, for example, information instruments such as a hard disc device (HDD), a video tape recorder (VTR), a laser printer, etc.
BACKGROUND OF THE INVENTION
Hitherto, as, for example, a roller bearing for supporting a spindle motor of hard disc devices, a roller bearing wherein the bearing ring and rolling element are formed with a ball bearing steel, etc., has become the main current.
In the above-described hard disc device, to prevent the occurrence of writing errors and reading errors, the improvement of the acoustic characteristics such as vibrations, noises, etc., has been required.
Also, because these information instruments are frequently placed near users at a relatively calm place in an office, a home, etc., it is strongly desired to reduce the generation of noises, particularly, having the frequency of the audible range of a human.
Under such circumstances, to quiet a rolling bearing for supporting spindle motor, it has been carried out to reduce the shape errors of each constituting element as small as possible, such as, for example, to improve the out of roundness of inner and outer rings and to equalize the sizes of all rolling elements used.
In addition, when the constituting elements of a rolling bearing are composed of a ball bearing steel, generally a heat treatment such as hardening, tempering, etc., is applied to the elements to control such that the residual austenite amount becomes about 10%.
Now, in the above-described conventional counterplan, there is a definite limit and thus further improvement has become necessary. Also, under the circumstance that the lubricating condition is severe, a rolling bearing is liable to generate heat as well as fine impressions, cracks, peelings, etc., are liable to form on the rolling elements and the bearing rings, whereby the caustic characteristics such as vibrations, noises, etc., are reduced.
Also, as the result of investigations, it has been confirmed that one of the causes of generating noises of a rolling bearing is the fine scratches formed on, in particular, rolling elements. On the other hand, recently, there are rolling elements formed with a ceramic material which is hard to be scratched. When the rolling element is formed with a ceramic material, the generation of noises by scratches can be restrained as well as because the material of the rolling element differs from the material of a bearing ring (steel-made), the effect of preventing sticking by coagulation of them by the inferior lubricant can be obtained.
As described above, the formation of rolling elements with a ceramic material is effective for improving the acoustic characteristics of a ball bearing but by the inventor's further investigations. It has been found that there remains the following point to be solved.
That is, when a rolling element is formed with a ceramic, because the rigidity of the rolling element is increased and the rolling element is hard to deform, the contact area of the rolling element and the bearing ring becomes small and the stress applied to the orbital surface becomes large. Accordingly, when the bearing ring is formed with a conventional ball bearing steel wherein the residual austenite amount is about 10%, the contact portion with the bearing element is liable to cause a permanent deformation and impressions form to generate vibrations and noises to deteriorate the caustic characteristics. Also, when a stress applied to the orbital surface becomes large, there is a problem that austenite is liable to cause a martensite transformation. Furthermore, in the case of using a ball bearing steel wherein the residual austenite amount is about 10%, there is a problem that the amount of the generated heat by the martensite transformation caused at raising the bearing temperature becomes large.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a rolling bearing excellent in the caustic characteristics such as vibrations, noises, etc.
Other object of the present invention is to provide a rolling bearing capable of stably and continuously giving excellent caustic characteristics for a long period of time even under the circumstances of severe lubricating condition.
Still other objects, the features, and the merits of the present invention will become clear from the following descriptions.
That is, a 1st aspect of the present invention is a rolling bearing comprising a bearing ring formed with a steel material and a rolling element formed with a ceramic material, wherein the residual austenite amount of the steel material forming the bearing ring is not more than 8%.
Furthermore, a 2nd aspect of the present invention in a preferred embodiment is a rolling bearing of the 1st aspect wherein the residual austenite amount of the steel material forming the bearing ring is from 0.05% to 6%.
In addition, if the residual austenite amount (&ggr;
R
) is less than 0.05%, the crack proceeding speed becomes fast caused by greatly lowering the tenacity to lower the life. On the other hand, if the residual austenite amount exceeds 8%, the permanent deformation amount of the orbital surface by a load (a static load and an impact load) from outside is increased and scratches and impressions are liable to form. From the view point, the critical value of the residual austenite (&ggr;
R
) is specified as described above.


REFERENCES:
patent: 5228786 (1993-07-01), Tanimoto et al.
patent: 5413643 (1995-05-01), Murakami et al.
patent: 5639168 (1997-06-01), Noguchi et al.

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