|1)||Bearing service life|
bearings rotate under load, material flakes from the surfaces of inner and
outer rings or rolling elements by fatigue arising from repeated contact
stress (ref.A144). This phenomenon is called flaking. The total number of
bearing rotations until flaking occurs is regarded as the bearing"(fatigue)service
life". "(Fatigue) service life" differs greatly depending upon bearing structures,
dimensions, materials, and processing methods. Since this phenomenon results
from fatigue distribution in bearing materials themselves,differences in
bearing service life should be statistically considered. When a group of
identical bearings are rotated under the same conditions,the total number
of revolutions until 90% of the bearings are left without flaking (i.e.
a service life of 90% reliability) is defined as the basic rating life.
In operation at a constant speed, the basic rating life can be expressed
in terms of time.
In actual operation, a bearing fails not only because of fatigue, but other factors as well, such as wear, seizure, creep, fretting, brinelling, cracking etc (ref.A144,16. Examples of bearing failures). These bearing failures can be minimized by selecting the proper mounting method and lubricant, as well as the bearing most suitable for the application.
|2)||Basic dynamic load rating|
|The basic dynamic load rating is either pure radial (for radial bearings) or central axial load (for thrust bearings) of constant magnitude in a constant direction, under which the basic rating life of 1 million revolutions can be obtained, when the inner ring rotates while the outer ring is stationary, or vice versa. The basic dynamic load rating, which represents the capacity of a bearing under rolling fatigue, is specified as the basic dynamic radial load rating(Cr) for radial bearings, and basic dynamic axial load rating(Ca) for thrust bearings. These load ratings are listed in the specification table.|
|3)||Dynamic equivalent load|
|Bearings are used under various operating conditions; however, in most cases, bearings receive radial and axial load combined, while the load magnitude fluctuates during operation. The two are compared by replacing the load applied to the shaet center with one of a constant magnitude and in a specific direction, that yields the same bearing service life as under actual load and rotation speed. This theorical load is refered to as the dynamic equivalent load, can be obtained using the equivalent load equation.|
|4)||Basic rating life|
| The basic rating
life in relation to the basic dynamic load rating and dynamic equivalent
load can be expressed using equation (3-1). It is convenient to express
the basic rating life in terms of time, using equation (3-2), when a bearing
is used for operation at a constant speed; and, in terms of traveling distance
(km), using equation (3-3), when a bearing is used in railway rolling stock
|5)||Correction of calculated service life|
|When the bearing is used
under heat, adjust the service life by multiplying the basic dynamic load
rating indicated in the Bearing Specification Tables by the temperature
Also, adjust the rating life by using reliability factor a1, bearing characteristic factor a2, and operating condition factor a3.
|For applications where more than one bearing is used, calculate the service life of the entire bearing system.|
Equation for Calculation of Service Life of Entire System
|Also, adjust the rating life by using reliability factor a1, bearing characteristic factor a2, and operating condition factor a3.|