Rolling bearing

Details Rolling bearing Rolling bearing

1994-10-31

1996-11-19

Hannon, Thomas R.

Bearings

Rotary bearing

Antifriction bearing

3849071, F16C 3356

Patent

active

055755712

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to rolling bearings and more particularly to rolling bearings wherein a rolling element, alternatively, a rolling element and a race are prepared from a ceramic material of silicon nitride.


BACKGROUND ART

As rolling bearings to be used under severe conditions such as high temperature, corrosive environment, vacuum or non-lubricant atmosphere in which normal metallic material cannot be used, there can mention so-called ceramic bearings wherein at least a rolling element (and more preferably, a rolling element and a race) is/are made of a ceramic material.
Such ceramic material preferred to use are those prepared by sintering a sintering material containing particles of silicon nitride(Si.sub.3 N.sub.4) because they are excellent in heat resistance and wear resistance.
Silicon nitride itself is, however, relatively poor in sintering properties. Therefore, to a sintering material, a variety of sintering assistants which improve sintering properties of the silicon nitride are generally added in each desired amount.
Examples of conventional sintering assistants include rare earth oxide such as yttrium oxide(Y.sub.2 O.sub.3), aluminum oxide (Al.sub.2 O.sub.3) and aluminum nitride(AlN), among others.
As exemplary sintering material of silicone nitride containing the sintering assistants as described, those of Si.sub.3 N.sub.4 --Y.sub.2 O.sub.3 --Al.sub.2 O.sub.3 or Si.sub.3 N.sub.4 --Y.sub.2 O.sub.3 --Al.sub.2 O.sub.3 --AlN are known in the art.
In the ceramic bearings prepared from the sintering material of silicon nitride, however, particularly sintering assistants and more particularly yttrium oxide is corroded when used in a corrosive atmosphere such as a strong acid atmosphere and a strong alkali atmosphere, reducing bonding strength between silicon nitride particles. This has been causing the problem that the strength of a ceramic bearing significantly reduces so that breakage occur before its design life.
It is accordingly the object of this invention to provide rolling bearings of a long service life, which are excellent in corrosion resistance when used under a corrosive atmosphere, as well as heat resistance and wear resistance.


DISCLOSURE OF THE INVENTION

The rolling bearing of this invention includes a pair of races and a plurality of rolling elements disposed between both races, at least the races being made of a ceramic material prepared by sintering a sintering material of silicon nitride containing an MgAl.sub.2 O.sub.4 of spinel structure and at least silicon oxide selected between silicon oxide and silicon carbide, as a sintering assistant.
The rolling element, alternatively, the rolling element and the races both comprising such a ceramic material, are excellent in durability in a corrosive atmosphere, as well as heat resistance and wear resistance.
Thus this invention can provide rolling bearings being excellent in wear resistance, corrosion resistance in a corrosive atmosphere, and of a long service life.


BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) is a perspective view illustrating appearance of a disc test piece for thrust test, which was prepared from a sintering material (Samples Nos. 1-3), in order to evaluate properties of the ceramic material for the rolling bearings of this invention and those of ceramic material for conventional ceramic bearings (Samples Nos. 4-5).
FIG. 1(b) is a perspective view illustrating appearance of a stick test piece for strength test, which was prepared from a sintering material out of Samples Nos. 1-5.
FIG. 2 is a graph illustrating weight lapse rate (%) of the disc test piece when conducting an acid dipping test wherein the disc test piece was dipped in acid to make it be corroded.
FIG. 3 is a graph illustrating the transition of flexural strength before and after conducting the acid dipping test for the stick test piece.
FIG. 4(a) is a sectional view illustrating the outline of a device used in a rolling life test for the disc test piece.
FIG. 4(b) is a graph illustrating the load transition when conducting the

REFERENCES:
patent: 4522453 (1985-06-01), Lammer et al.
patent: 4792244 (1988-12-01), Yamashita et al.
patent: 5102239 (1992-04-01), Momose et al.

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