Bearing members making sliding motions can be classified into those making a rolling motion and those making a sliding motion. A rolling bearing making the former rolling motion can be to a ball bearing, for example. This ball bearing generally in a complicated structure. Bearings making the latter sliding motion include contact type bearings (metal bush bearing and oil retaining bearing) and non-contact bearings (oil bearing, air bearing and magnetic bearing). These bearings have extremely simple structures as compared with the former rolling bearing.
A slide bearing is widely used as a mechanical component, since its structure is simple. However, with increases in machine speed, problems of seizure and durability arise in a conventional slide bearing made of bearing steel. For this reason, ceramics have been carefully considered as a material for a slide member which is required to be wear-resistant under high-speed sliding. Furthermore, in office automation products or the like, it has become increasingly required to use oil-free bearings to reduce the requirement for cleaning. Also in this field, ceramics has been watched with interest as a material for a slide member. As to such ceramics, Al.sub.2 O.sub.3, ZrO.sub.2, SiC, Si.sub.3 N.sub.4 and the like are now being developed. In situations of oil-free high-speed sliding exceeding 1 m/sec., however, an impactive knock wear phenomenon is caused by contact between bearing members. In a conventional bearing body made of ceramics, therefore, it has been difficult to withstand such sliding.
On the other hand, a slide bearing body is also incorporated in a sliding part of a compressor of a refrigerator, a freezer or a car air conditioner. In this case, the sliding part of the bearing body is placed in a cooling medium. A chlorofluorocarbon (CFC), which is one of the fluorocarbons, has been employed as the cooling medium. In particular, a typical cooling medium of such a chlorofluorocarbon is CFC12. Chlorine (Cl) is included in molecules of this CFC12. This chlorine prevents adhesion and reaction of the slide member on a sliding surface. Namely, the chlorine prevents seizure between sliding surfaces or the like as an extreme pressure additive. Therefore, the CFC12 containing this chlorine itself serves as an extremely effective lubricant. Under a fluorocarbon atmosphere of CFC12 or the like containing chlorine, therefore, the sliding part of the slide member rarely seizes or causes abnormal wear. In general, therefore, a metal member of cast iron or the like has been used as a sliding part of a compressor of a refrigerator or the like, which is used in an atmosphere of a cooling medium. Under a fluorocarbon atmosphere containing chlorine, as hereinabove described, neither seizure nor abnormal wear of the sliding part has been caused even if a metal member of cast iron or the like is used as the sliding part.
In recent years, however, employment of chlorofluorocarbons, which are represented by CFC12, has been regulated to address the problem of destruction of the ozone layer in the stratosphere. This is because chlorine contained in the chlorofluorocarbons is one of the factors destroying the ozone layer. HFC134a containing no chlorine in its molecules, for example, is now expected to be used as a substitute for these chlorofluorocarbons. Thus, studies are now being conducted to investigate the use of fluorocarbons containing no chlorine as a cooling medium. In such a fluorocarbon containing no chlorine, however, no lubricating effect by chlorine can be expected. Thus, the problem arises that a metal such as cast iron used as a sliding part of a compressor or the like seizes to another metal or causes abnormal wear.
USPTO Backgrounds
USPTO Backgrounds