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Thin Section Bearings

WD thin section bearings: deep groove ball bearings, four-point contact ball bearings, angular contact ball bearings
 
WD thin section bearings have high precision, are very quiet and have high load carrying capacity. These ball bearings are available in three different designs and have an extremely small, predominantly square cross-section. Within each series, the cross-section remains constant even for larger shaft diameters and housing bores. The bearings are therefore also described as Constant Section. This special feature distinguishes thin section bearings from conventional bearings as standardised in ISO series.
It is therefore possible to select a larger cross-section and thus use a bearing with higher load carrying capacity without the need to change the shaft diameter as well. WD thin section bearings allow designs to be achieved that are extremely light and require little space.
 

Deep groove ball bearings, four point contact bearings,angular contact ball bearings

Thin section bearings are available as deep groove ball bearings (C), four point contact bearings (X) and angular contact ball bearings (E). Each of these designs is available in various series. The series correspond to the cross-section sizes. The balls are matched to the series.
Deep groove ball bearings can support axial loads from both directions as well as radial loads.
Four point contact bearings can support axial loads from both directions as well as radial loads; they thus act in the same way as double row angular contact ball bearings.
Angular contact ball bearings can be filled with an optimised number of balls and have a contact angle of 30°. They can support considerably higher radial loads than deep groove ball bearings or four point contact bearings are can support axial loads from one direction. For special requirements, angular contact ball bearings are also available as matched bearings. These combinations then have a significantly higher rigidity and load carrying capacity than single bearing solutions.
 
Load Rating and Life
Effective Life：
Even bearings are operated under normal conditions, the surfaces of the raceway and rolling elements are constantly being subjected to repeated compressive stresses which causes flaking of these surfaces to occur.This flaking is due to material fatigue and will eventually cause the bearings to fall. The effective life of a bearing is usually defined in terms of the total number of revolutions a bearing can undergo before flaking of either the raceway surface or the rolling element surfaces occurs.
Other causes of bearing failure are often attributed to problems such as seizing, abrasions, cracking, chipping, scuffing, rust, ect.However, these so called“causes”of bearing failure are usually themselves caused by improper installation, in sufficient or improper lubrication, faulty sealing or inaccurate bearing selection. Since the above mentioned “causes”of bearing failure can be avoided by taking the proper precautions, and are not simply caused by material fatigue, they are considered separately from the flaking aspect.
 
Basic rating life and basic dynamic load rating
A group of seemingly identical bearings when subjected to identical load and operating conditions will exhibit a wide diversity in their durability. This “life”disparity can be accounted for by the difference in the fatigue of the bearing material itself. This disparity is considered statistically when calculating bearing life,and the basic rating life is defined as follows.
The basic rating life is based on a 90% statistical model which is expressed as the total number of revolutions of the bearings in an identical group of bearings subjected to identical operating conditions will attain or surpass operating due to material fatigue occurs. For bearings operating at fixed constant speeds,the basic rating life(90% reliability) is expressed in the total number of hours of operation.
Basic dynamic load rating expresses a rolling bearing's capacity to support a dynamic load.The basic dynamic load rating is the load under which the basic rating life of the bearing is 1 million revolutions.This is expressed as pure radial load for radial bearings and pure axial load for thrust bearings.
 
Basic static load rating
When stationary rolling bearings are subjected to static loads,they suffer from partial permanent deformation of the contact surfaces at the contact point between the rolling elements and the raceway.The amount of deformity increases as the load increases,and if this increase in load exceeds certain limits,the subsequent smooth operation of the bearings is impaired.
It has been found through experience that a permanent deformity of 0.0001 times the diameter of the rolling element,occurring at the most heavity stressed contact point between the raceway and the rolling elements,can be tolerated without any impairment in running effciency.
The basic static load rating refers to a fixed static load limit at which a specified amount of permanent deformation occurs.It applies to pure radial loads for radial bearings and to pure axial loads for thrust bearings.
 
Equivalent load
Dynamic equivalent load
When both dynamic radial loads and dynamic axial loads act on a bearing at the same time, the hypothetical load acting on the center of the bearing which gives the bearings the same life as if they had only a radial load or only an axial load is called the dynamic equivalent load.
For radial bearings,the load is expressed as pure radial load and is called the dynamic radial load. For thrust bearings,it is expressed as pure axial load,and is called the dynamic eduivalent axial load.
 
Dynamic equivalent radial load
The dynamic equivalent radial load is expressed by formula
    Pr=XFr+YFa
Where,
    Pr: Dynamic equivalent radial load N
   Fr: Actual radial load N
    Fa: Actual axial load N
   X: Radial load factor
    Y: Axial load factor
The values for X and Y are listed in the bearing tables.
 
Dynamic equivalent axial load
As a rule,standard thrust bearings with a contact angle of 90° cannot carry radail loads. However,self-aligning thrust roller bearing can accept some radial load.The dynamic equivalent axial load for these bearings is given in formula.
    Pa=Fa+1.2Fr
Where,
    Pa: Dynamic equivalent axial load N
    Fr: Actual radial load N
    Fa: Actual axial load N
Provided that Fr/Fa 0.55 only

 

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