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What is FAG bearing creep and its influencing factors

wallpapers Low Carbon 2020-08-27
Creep is a common form of FAG bearings damage. We need to distinguish the damaged bearings according to the specific damage of a specific bearings and determine how to handle the bearing.
 
1. What is bearing creep?
Bearing creep refers to the relative sliding between the mating surfaces when a gap is generated on the mating surfaces of the bearing. The wriggling mating surface shows a mirror-like bright or dark surface, which sometimes gets stuck and worn.
The creep of FAG bearing mainly includes inner ring and outer ring.
FAG bearing inner ring creep means that the bearing inner ring and the shaft are fixed by an interference fit to prevent the inner ring from sliding relative to the shaft. However, once proper interference cannot be maintained, there will be a gap between the mating surfaces of the inner ring and the shaft, and the inner ring will slide relative to the shaft. This phenomenon is called inner ring creep.
FAG bearing outer ring creep refers to the phenomenon that the outer ring rotates slowly relative to the bearing seat when rolling bearings are used, which is called outer ring creep. Creep of the outer ring will cause the bearing seat or outer ring to wear, and cause particles to wear into the bearing, which can lead to bearing damage.
 
(1) Factors affecting creep of FAG bearing inner ring:
In the initial stage of inner ring creep, no sharp temperature rise is found in the bearing, and there is no direct relationship between the temperature rise of the bearing and the creep speed of the inner ring. At the same time, when the creep speed of the inner ring increases to the rotating state, the wear of the inner ring mating surface of the shaft will increase. It can be understood that the bearing rotating in this state will cause the bearing temperature to rise due to the internal damage of the bearing, the aging of the lubrication state and the misalignment of the bearing centerline.
Although the temperature of the bearing does not rise rapidly at the initial stage of the inner ring creep, data may be recorded when the inner ring reaches a rotating state as the creep progresses. Therefore, to prevent creep, it is very important to maintain a proper amount of interference between the bearing inner ring and the shaft. At the same time, in order to prevent the bearing from being damaged by heat, the bearing temperature monitoring system must be equipped with high reliability.
 
(2) Factors affecting the creep of FAG bearing outer ring:
 
A. The influence of fit clearance
When the fit clearance decreases, the bat variable torque decreases, and the occurrence of creep becomes difficult.
B. The influence of the number of rolling elements
The creep torque decreases as the number of rolling elements increases. This is because the increase in the number of rolling elements reduces the load of the rolling elements, thereby suppressing local deformation of the outer ring.
C. Influence of outer ring wall thickness
Consider increasing the stiffness of the outer ring to suppress the occurrence of creep. The effect of the wall thickness of the outer ring (ratio to the diameter of the rolling elements) is that as the wall thickness of the outer ring increases, the creep torque decreases and it is difficult to creep. 2. Factors affecting creep
(1) Temperature, temperature rise, steady state creep rate increases,
(2) Stress, the steady-state creep rate increases with the increase of stress,
(3) The influence of microstructure, creep is a performance index that is more sensitive to microstructure. The porosity and particle size equal to the glass have a great influence on the creep performance.
 
3. The continuous creep of the bearing over time is roughly divided into three stages:
(1) Initial creep or transitional creep, the strain increases with time, but the increasing speed gradually slows down;
(2) For steady-state creep or steady-state creep, the strain increases uniformly with time, and this stage is longer;
(3) Creep accelerates, strain increases with time and reaches the breaking point. The greater the stress, the shorter the total time for creep. The smaller the stress, the longer the total creep time.
However, every material has a minimum stress value. When the stress is lower than this value, no matter how long time passes, the stress will not break, or the creep time is unlimited. This stress value is called the long-term strength of the material.

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