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° |
|
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 |
|
*Ask our technical support for more information about our newer design!
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