Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2002-04-02
2004-07-20
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
C384S492000, C384S571000
Reexamination Certificate
active
06764219
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
None
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
This invention relates in general to antifriction bearings and more particularly to full complement antifriction bearings.
Antifriction bearings, often referred to as rolling element bearings, find widespread use in a variety of machinery generally to support one machine component on another such that the one can rotate relative to the other. The typical antifriction bearing includes an inner race or ring provided with a raceway that is presented outwardly away from the axis of the bearing, an outer ring or race provided with a raceway that is presented inwardly toward the axis and toward the raceway on the inner race, and rolling elements arranged in a circular row between the raceways of the two races. The rolling elements may take the form of balls, tapered rollers, cylindrical rollers, spherical rollers or even so-called “needles”. Most antifriction bearings also include a retainer or cage to maintain a uniform separation between the rollers and with some types of bearings to further keep the rolling elements oriented properly between the raceways. Most cages contain pockets, although in some bearings containing rollers, the cages may have pins that project into the rollers where they serve as a spindle about which the rollers rotate. A pocket-type cage, which is usually formed from pressed steel, must of necessity spread the rolling elements apart to fit between them, and this reduces the load-carrying capacity of the bearing. The pin-type cages, since the pins do not pass between the rollers but instead project through them, enable the rollers to be organized with less spacing between them, so a bearing equipped with such a cage will have greater capacity than one equipped with a pocket-type cage. However, pin-type cages are not as durable as pocket-type cages, and furthermore cannot be used with some types of rolling elements.
Full complement antifriction bearings have no cages whatsoever and thus can hold the maximum number of rolling elements—a full complement, in other words. Without a cage to separate the rolling elements, adjacent rolling elements in a full complement bearing can and actually do contact each other during the operation of the bearing and also while the bearing is at rest. Indeed, when the bearing is not in operation, the contact between adjacent rolling elements can produce an adhesive wear condition known as fretting. Basically, fretting occurs when the asperities along contacting surfaces of adjacent rolling elements cold weld together. Microscopic motion between the contacting surfaces, which motion may be generated by vibrations, causes the welds to break, and this, if repeated over time, results in a deterioration of the surfaces.
Adhesive wear can also occur along contacting surfaces of adjacent rolling elements when the bearing is in operation. Normally, a hydrodynamic lubrication film exists between the rolling elements and the raceway along which they roll, and thus inhibits adhesive wear between these contacting surfaces. The same does not hold true with regard to contacting rolling elements at the point or line of contact between adjacent rolling elements. According to Dowson's equations, the thickness of the lubricant film along contacting surfaces in a rolling element bearing is:
h
=
K
D
{
a
0.54
R
0
.43
(
μ
0
V
)
0.7
W
0
.13
}
where K
D
is a constant containing the modulus of elasticity, &mgr;
0
is the lubricant viscosity, V is the entrainment velocity, &agr; is the lubricant pressure viscosity coefficient, W is the load per unit length, and R is an equivalent radius. Since at the contact point or line between the rolling elements in a full complement bearing the tangential velocities for each element are of equal magnitude but opposite direction, the entrainment velocity at that contact is zero, and the thickness h of the hydrodynamic lubrication is likewise zero. This exposes the rolling elements to adhesive wear.
Of course, frictional or abrasive wear also occurs where adjacent rolling elements contact each other with the bearing in operation.
BRIEF SUMMARY OF THE INVENTION
The present invention resides in an antifriction bearing including first and second races provided with raceways and rolling elements located between the races and contacting the raceways along the raceways. The rolling elements are arranged such that adjacent rolling elements contact each other, and at least some of the rolling elements are covered with a tribological coating.
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T. Lunow, R.Kocis, G. Leonhardt, and R. Wilberg, Surface & Coatings Technology 76-77, 579 (1995).
The Guide to More Reliable Precision Components, (The Balzers Company, Balzers, Liechtenstein, 1996) p. 24-25.
The Tapered Roller Bearing Guide (The Timken Company, Canton, Ohio 1994), p. 107.
Doll Gary L.
Fox Gerald P.
Footland Lenard A.
Polster Lieder Woodruff & Lucchesi L.C.
The Timken Company
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