Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2000-08-08
2002-03-19
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
Reexamination Certificate
active
06357924
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a rolling bearing used under high temperature conditions and, more in particular, it relates to a rolling bearing suitable to engine auxiliaries such as alternators, solenoid clutches, intermediate pulleys, compressors for vehicle air conditioners and water pumps.
BACKGROUND ART
Along with downsizing and weight reduction of automobiles in recent years, higher performance and higher power as well as down-sizing and weight reduction have been demanded also for the engine auxiliaries. For example, during operation of an engine, high temperature, large vibrations and heavy load (about 4G to 20G as gravitational acceleration) caused by high speed rotation exert simultaneously by way of a belt to bearings for use in an alternator. As a result, flaking occurs in an early stage to the rolling bearing, particularly, to an outer ring as a fixed ring and this tends to shorten the bearing life.
The prior art intended for the improvement of the life of bearings used under large vibrations and heavy load includes, for example, Japanese Examined Patent Publication No. Hei 7-72556 (hereinafter also referred to as prior art 1), Japanese Patent No. 2724019 (hereinafter also referred to as prior art 2), Japanese Unexamined Patent Publication No. Sho 62-218542 (hereinafter also referred to as prior art 3) and Japanese Unexamined Patent Publication No. Hei 2-190615 (hereinafter also referred to as prior art 4). Among them, the prior art 1 discloses that plastic deformation due to the decomposition of residual austenite under the raceway surface can be prevented by defining the amount of residual austenite in the outer ring of the bearing to 0.05% or more and 6% or less at least on the side of load input, that is, on the side of the pulley. Further, the prior art 2 discloses a heat resistant bearing steel of a composition comprising 0.8 to 1.5% C, 0.8 to 2.0% Si, 0.3 to 2.0% Mn, 1.3 to 1.98% Cr and 0.3 to 1.0% Mo, the total of Si and Mo being within a range of satisfying 1.0% or more, and the residue of Fe and impurities. Further, the prior art 3 discloses that the bearing ring contains 0.95 to 1.10% C, 1 to 2% Si, 1.15% or less of Mn, 0.90 to 1.50% Cr, and 8% or less of the amount of residual austenite, and has a surface hardness HRC of 60 or more. Further, the prior art 4 discloses a grease-sealed bearing having grease sealed in the bearing, in which an oxide layer of 0.1 to 2.5 &mgr;m thickness is formed on the rolling surface of the bearing ring of the bearing.
By the way, as a countermeasure for preventing early flaking in a bearing used under high temperature, large vibrations and heavy load caused by high speed rotation, [SAE Technical Paper: SAE 950944 (held in Feb. 27-Mar. 2, 1995)] describes in first to 14th sections that early flaking can be prevented by analyzing the fatigue mechanism of the bearing for use in the alternator, and replacing the sealing grease from E grease to M grease having a higher damper effect thereby absorbing large vibrations, heavy load and moderating metal contacting.
For the early flaking phenomenon, it is considered that water contained in a lubricant (sometimes contained, for example, usually by about 0.1% in grease) is decomposed and created hydrogen ions are adsorbed to the raceway surface, and accumulated as hydrogen atoms to a high strain area (near the maximum shearing stress position), which lead to stress corrosion cracking flaking. Further, for the cause of the formation of the water contained in the bearing, it is considered that since the auxiliary is heated to a high temperature during operation of an engine and cooled to an atmospheric temperature after stopping the engine, air presenting in a slight space of the bearing is condensed.
On the contrary, it is disclosed in the prior art 1 that tempering (at 250 to 380° C.) is conducted such that the mount of residual austenite at least in the outer ring on the side of the pulley is from 0.05 to 6%. However, mere decreasing in the amount of residual austenite can provide an effect for the improvement of the dimensional stability under a high temperature circumstance but this can only suppress the plastic deformation under the raceway surface for the flaking resistance and since sliding of the rolling element increases under large vibration, heavy load, the effect of prolonging the life is not recognized in a circumstance where hydrogen intrudes from the raceway surface.
Further, the prior art 2 also discloses that a hardness capable of withstanding the rolling contact fatigue can be maintained even during use at high temperature by adding an element of increasing the resistance to temper softening such as Si or Mo but macro carbide precipitates such as C—Cr tend to be formed to remarkably worsen the crack extension characteristic since C is contained up to 1.5% and Cr is contained by 1.3 to 1.98%. Further, no life extend effect can be expected by merely adding Mo by a small amount as 0.1 to 1.0%, since this can not precipitate fine Mo type carbides for improving the lower limit amplitude value of stress intensity factor.
Further, in the prior art 3, since the amount of residual austenite is decreased to 8% or less by high temperature tempering with addition of an element of improving the resistance to temper softening of steel such as Si or Al, a bearing ring with less dimensional aging change under a high temperature circumstance can be provided. However, for the flaking resistance, since sliding of a rolling element increases under large vibration, heavy load, the effect of prolonging the life can not be recognized under a circumstance where hydrogen intrudes from the raceway surface.
Further, in the prior art 4 since a troublesome treatment of dipping a bearing ring in an aqueous solution of sodium hydroxide under heating at a low temperature is necessary for forming a tri-iron tetroxide layer (generally referred to as a black coating) and, further, a treatment of corroding the rolling surface to such an extent as causing coloration in an aqueous oxidizing solution such as alcohol sulfate, hydrochloric acid or sulfuric acid as other solvent it involves problems, for example, in view of the facility or the processing time. Further, as shown in “Pretext for Conference of Japan Triopology (Tokyo, 1995-5) p 551-554”, in a bearing for use in engine auxiliaries used under large vibrations/heavy load, since auto-rotation slip is caused at the inlet of a fixed ring, oxide layers capable of providing a damper effect are ruptured and a load exerts directly on the outer ring frequently suffering from early flaking, so that it is actually difficult to prevent early flaking in the fixed ring.
Further, when a bearing is heated in air without controlling the temperature, scales of several &mgr;m (skins) are formed on the surface of the material by oxidation. Unevenness of the scales causes loss of metal to possibly form initiation points for pits. Further, when the bearing is merely left in atmospheric air, it may be considered that steels react with moisture in air to possibly cause atmospheric corrosion.
Further, the rolling contact fatigue is a phenomenon caused by shearing stress and vertical compressive stress synthesized under the rolling surface, and cracks are extended also in a synthesized mode of a tensile crack extension mode (mode I) and a shearing crack extension mode (mode II). Accordingly, for determining crack extension characteristic data for bearing materials, a study on bearing materials excellent in crack extension resistance characteristic has also been conducted, for example, by conducting a crack extension test using a compression/tensile (CT) test piece by a test method according to ASTM E 647-83.
The present invention has been developed in order to solve the foregoing problems and it is an object thereof to provide a rolling bearing used under a high temperature circumstance at 150° C. or higher, preferably, 180° C. or higher as in engine auxiliaries, by dispersingly precipitating Mo type or Ti type carbides of 50 to 300 nm finely
Murakami Yasuo
Sekino Kazuo
Takemura Hiromichi
Crowell & Moring LLP
Footland Lenard A.
NSK Ltd.
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