Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2001-11-20
2004-06-08
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
Reexamination Certificate
active
06746157
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rolling bearing having self-lubricating and a retainer using therefor.
2. Description of the Related Art
When used in an environment where a clean atmosphere is required, such as clean room, semiconductor producing apparatus, liquid crystal panel producing apparatus and hard disc producing apparatus and in a liquid or an environment where a mist or spray of liquid is present, such as various cleaning apparatus and food processing machines, a rolling bearing cannot be lubricated by any lubricant or grease. Therefore, a self-lubricating rolling bearing which doesn't need to be lubricated by lubricant or grease has heretofore been proposed.
As such a self-lubricating rolling bearing, there is disclosed in Japanese Patent No. 2,709,119 a rolling bearing comprising inner and outer rings made of stainless steel, a retainer prepared only by forming a tetrafluoroethylene-ethylene copolymer (ETFE) comprising a potassium titanate whisker short fiber having a diameter of not more than 2 &mgr;m incorporated therein and a rolling body made of hard carbon. This bearing is arranged such that when the retainer and the rolling body come in frictional contact with each other, ETFE constituting the retainer is partially transferred to the rolling body and the inner and outer rings to form a thin film of ETFE thereon.
JP-A-4-331819 (The term “JP-A” as used herein means an “unexamined Japanese patent publication (kokai)”) discloses that a retainer is formed by a perfluoroalkoxy resin (PFA) comprising a heat-resistant fiber incorporated therein.
The retainers disclosed in the above cited publications can be produced by melt molding and thus have a higher productivity than retainers made of polytetrafluoroethylene (PTFE), which cannot be melt-molded. However, since ETFE and PFA have a relatively low elastic modulus, retainers made of these materials are liable to deformation during use under a high load or at high rotary speed. Further, these retainers can easily generate heat at contact points due to friction. This can result in the locking of the bearing or the development of abnormal abrasion in the retainers. Accordingly, rolling bearings comprising the retainers disclosed in the above cited patents may exhibit a shortened life under a high load or at high rotary speed.
Further, for the production of these retainers made of FTFE or PFA, the mold temperature or resin temperature at which these materials are melt-molded needs to be raised because these materials have a high melting point (melting point of ETFE: 260° C.-270° C.; melting point of PFA: 300° C.-310° C.). The higher the resin temperature is, the more easily can be produced a corrosive fluorine-based gas. The heat thus generated and the corrosion by fluorine-based gas shorten the life of the mold.
A rolling bearing comprises an inner ring having a groove on the outer periphery thereof, an outer ring having a groove on the inner wall thereof, a plurality of rolling bodies rollably disposed between the groove on the inner ring and the outer ring, and a retainer in which the plurality of rolling bodies are retained in such an arrangement that they are guided through the gap between the groove on the inner ring and the outer ring.
In general, a rolling bearing is lubricated by circulative supply of lubricant or grease into the bearing or incorporation of lubricant or grease in the interior of the bearing. However, when operated at elevated temperatures or in vacuum, a rolling bearing is liable to the scattering of lubricant or grease to the exterior of the bearing or the evaporation of lubricant or grease accompanied by the release of gas that can stain the external atmosphere of the bearing. Thus, no lubricants or greases can be used in the case where a pure atmosphere is required, e.g., in clean room, semiconductor element producing apparatus, liquid crystal panel producing apparatus, hard disc producing apparatus, and in other atmospheres, e.g., at elevated temperatures, in vacuum, in a special atmosphere, at extremely low temperatures, under irradiation.
Thus, as a method for lubricating rolling bearing there has heretofore been proposed a method free from lubricant or grease. For example, JP-A-55-57717 and JP-A-61-55410 disclose an approach involving the formation of a thin lubricating film made of molybdenum disulfide, graphite, silver, lead or the like on a part or the whole of the surface of inner ring, outer ring, retainer and rolling body by sputtering, ion plating, sintering, etc.
Further, JP-A-62-151539 and JP-A-64-79418 disclose the formation of a rolling bearing retainer by a sintered alloy obtained by sintering a material having a metal powder mixed with a solid lubricant such as molybdenum disulfide, graphite and hexagonal boron nitride. Moreover, JP-A-2-245514 and JP-A-4-102718 disclose an approach involving the formation of a rolling bearing retainer by a material comprising a resin composition having a solid lubricant incorporated in a plastic. In these rolling bearings, when the retainer and the rolling body come in frictional contact with each other, the material constituting the retainer is somewhat transferred to the rolling body, inner ring and outer ring to form thereon a thin lubricating film of the solid lubricant contained in the retainer material.
With the enhancement of the properties of devices and the production yield thereof, the temperature at which these devices are produced has been raised more and more, and the pressure under which these devices are produced has been reduced more and more. Under these circumstances, there is a growing demand for rolling bearings which can operate while scattering little particles to the exterior thereof in a severe atmosphere, e.g., at higher temperatures or under higher vacuum, over an extended period of time.
However, the approaches disclosed in these patents have the following disadvantages.
In other words, the approaches disclosed in JP-A-55-57717 and JP-A-61-55410 are disadvantageous in that the frictional force developed on the contact surface upon the operation of the bearing causes the thin lubricating film which has previously been formed on the surface of the grooves to be abraded to disappearance. The disappearance of the lubricating film causes the elimination of the lubricating effect. This results in the cohesion and seizing of the base metal (matrix). In general, accordingly, a rolling bearing which is thus lubricated can hardly operate over an extended period of time.
The retainer made of a sintered metal disclosed in JP-A-62-151539 and JP-A-64-79418 is disadvantageous in that it is very expensive. This is because a sintered metal cannot be formed into a complicated shape by molding and a rod or ring molded product of sintered metal must be machined to obtain a retainer having a desired shape. Further, a sintered metal normally exhibits an excellent heat resistance but shows a low mechanical strength and is brittle. Thus, a sintered metal can be cracked on the surface thereof when machined. As a result, a sintered metal must be slowly machined and thus shows a poor machinability.
Moreover, the approaches disclosed in JP-A-2-245514 and JP-A-4-102718 are disadvantageous in that if the plastic used as matrix of the retainer material has an insufficient lubricity, its lubricating effect is lost early during the operation of the bearing, causing rapid rise in the generation of abrasion particles. As a result, a large amount of particles are scattered from the bearing to the exterior of the bearing. Further, the resulting torque rise can terminate the life of the bearing. As the plastic having a high lubricity employable as matrix there may be used polytetrafluoroethylene (PFTE) resin. However, this resin cannot be melt-molded (melt molding is a method which comprises heating a resin to a temperature higher than its melting point, and then allowing the fluid resin to be cured in a desired shape in a mold) and thus needs to be machined to form a retainer similarly to t
Uchiyama Takahiko
Yamamoto Toyohisa
Footland Lenard A.
NSK Ltd.
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