Creep is a common form of damage of NSK bearings. We need to distinguish the damaged bearings according to the specific damage of the specific bearings and determine how the bearings should be dealt with. Based on the knowledge of the bearings, Eric Bearing Limited will share the relevant information today. Detailed knowledge of bearing creep is introduced.
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 creeping mating surface shows a mirror-like bright or dark surface, sometimes with jamming and abrasion.
NSK bearing creep mainly includes inner ring creep and outer ring creep.
NSK bearing inner ring creep means that the bearing inner ring and the axle are fixed by interference fit to prevent the inner ring from sliding relative to the axle. However, once the proper interference cannot be maintained, there will be a gap between the mating surface of the inner ring and the axle, and the inner ring will slide relative to the axle. This phenomenon is called inner ring creep.
NSK bearing outer ring creep refers to the phenomenon that the outer ring rotates slowly relative to the bearing seat during the use of rolling bearings, which is called outer ring creep. Creep of the outer ring will cause wear of the bearing seat or outer ring and wear particles into the bearing, resulting in bearing defects.
(1) Factors affecting the creep of the inner ring of NSK bearings:
In the initial stage of the creep of the inner ring, no sharp temperature rise was 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 is 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 center line of the bearing.
Although the bearing temperature will not rise rapidly at the initial stage of inner ring creep, data may be burnt 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, to prevent bearing heat damage, it is also essential to equip the bearing temperature monitoring system with high reliability.
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(2) Factors affecting the creep of NSK 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 rolling element load, thereby suppressing local deformation of the outer ring.
c. The influence of outer ring wall thickness
Consider increasing the rigidity of the outer ring to suppress the occurrence of creep. The effect of the outer ring wall thickness (ratio to the diameter of the rolling element) is that as the outer ring wall thickness increases, the creep torque decreases and the occurrence of creep becomes difficult.
2. Factors affecting creep
(1) Temperature, temperature rise, steady state creep rate increases,
(2) Stress, the steady-state creep rate increases with increasing stress,
(3) The influence of microstructure, creep is a performance index that is more sensitive to microstructure. Porosity and grain size equal to glass have a great influence on creep performance.
3. The continuation of bearing creep over time is roughly divided into 3 stages:
(1) Initial creep or transitional creep, the strain increases with time, but the increasing speed gradually slows down;
(2) Steady-state creep or steady creep, the strain increases uniformly with time, this stage is longer;
(3) Accelerated creep, the strain increases with time and reaches the point of rupture. The greater the stress, the shorter the total time for creep; the smaller the stress, the longer the total time for creep.
However, each material has a minimum stress value. When the stress is lower than this value, no matter how long it goes through, it will not break, or the creep time is infinite. This stress value is called the long-term strength of the material.