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Bearing
Life
In a broad sense, bearing life is the period during which bearings
continue to operate and satisfy their required function. More specifically,
bearing life may be limited by noise life, abrasion life, grease
life or rolling fatigue - depending on which of these causes loss
of bearing service.
Rolling
fatigue life
Rolling fatigue life - also called "fatigue life" -- is
defined by the number of revolutions before the bearing surface
begins to flake due to stress.
Even seemingly identical bearings - those that are of the same type,
size, and materials, and that have received the same heat treatment
and other processing - can vary greatly in rolling fatigue life,
even in identical operating conditions. This variation occurs because
flaking of materials due to fatigue is also subject to many other
variables. Consequently, the term "rated fatigue life"
as a definition of actual rolling fatigue life is based on statistical
analysis of rolling fatigue life.
Example: A number of bearings of the same type are operated individually
under the same conditions. After a certain period of time, 10% of
them fail as a result of flaking caused by rolling fatigue. The
total number of revolutions in that operational time is defined
as the "rated fatigue life,' or, if the speed is constant,
the rated fatigue life is often expressed by the total number of
completed operation hours when 10% of the bearings become disabled
by flaking.
Basic rated life
The "basic rated life" is the 90%-reliable life of a single
bearing or of a group of apparently identical bearings operating
in identical conditions. Basic rated life is listed as "L10"
(millions of revolutions) or "l10h" (operating hours).
For radial ball bearings
L10 = (Cr/Pr)3
Where L10 is basic-rated life in millions of revolutions, Cr is
radial basic-rated dynamic load (N), and Pr is radial equivalent
dynamic load (N).
Basic-rated dynamic load is defined as the constant load that can
be can endured by inner rings on bearings with non-moving outer
rings and a rating life of one-million revolutions. The basic-rated
dynamic load is expressed as constant direction and magnitude. The
radial basic-rated dynamic load "Cr" is listed in bearing
tables.
For bearings operating at a constant speed, the basic-rated life,
expressed in operating hours, can be calculated by the equation.
L10 = 106 /60n (Cr/Pr) 3
where n is rotational speed, r/min
Calculations determining bearing size must be based on the rated
life that corresponds to the purpose of operation. These calculations
usually depend on the type and service life of machinery, and the
requirements for operational safety.
Rated Static Loading and Equivalent Static Load
For low speeds, low vibration movement or static use, radial static
loading (Cor) should be considered. According to ISO76 (GB/T4662),
radial-rated static loading (Cor) is defined as the radial static
load that produces a corresponding calculated contact stress in
the center of the contact area between the most heavily loaded rolling
element and the raceway.
A stress of 4200Mpa (deep groove ball bearings) produces a complete
and permanent deformation that is 0.0001 times the diameter of the
rolling element and raceway.The radial equivalent static loading
(Por) is the radial static loading that produces a contact stress
in the center of the contact area between the most heavily loaded
rolling element and the raceway that is equal to the stress under
actual load conditions.
The radial equivalent static loading on radial ball bearings should
be equal to the greater of two values calculated in the following
equations:
Por = XoFr + YoFa
Por = Fr
where Por is radial equivalent static load, Fr is radial load (N),
Fa is axial load (N), Xo is a factor of radial static load (0.6),
and Yo is a factor of axial static load (0.5)
The allowed radial equivalent static loading on bearings varies,
depending on the basic-rated static loading and on the specific
application and operating conditions.
Limiting Speed
The values of limiting speeds are listed in the bearing tables.
They are applicable to standard-design bearings that are subjected
to normal loads (c/p > or = 12 and Fa/Fr < or =0.2). The limiting
speeds for oil lubrication listed in the bearing tables are usually
for oil-bath lubrication. When speeds are greater than 70% of the
listed limiting speed, lubricating oil or grease with high-speed
characteristics must be used.
Inner Ring Shield Groove
| Bearing
Type (RS/ZZ) |
Groove |
Legend |
|
607,
608, 609,
626, 627, 628, 629
|
105?/div>
|
|
|
6000-6007
6200-6206
6300-6305
R8-R12
1616-1635
|
V
|
|
|
606,
625 & folowing series
R6 & following series
1614 & following series
68, 69 series
|
UG
|
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