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Everything you should know about the causes of bearing cage damage
If the cage is found to be damaged when inspecting a failed bearing, it can be difficult to determine the cause in many cases. Often, other parts of the bearing are also damaged, making it difficult to find the cause of the failure. However, based on than 20 years of manufacturing experience, AUB concluded that there are certain main reasons for cage failure.
Lubricating oil or grease is dry and not added in time (maintenance). Incorrect oil or grease used. Cage wear can be caused by insufficient lubrication or abrasive particles. Rolling bearings keep running, of course avoiding sliding friction. However, as far as the cage is concerned, slippage cannot be avoided in contact with other parts of the bearing. This explains why the cage is the first component to be affected when there is insufficient lubrication. The cage is made of a softer material than the rest of the bearing, so it wears out relatively quickly. This leads to an increase in the size of the cage, thereby degrading the performance of guiding the rolling elements. However, the cage is always in the center state, and the resultant force will “tear” the cage in a short time, causing the cage to fail.
Jam
Fragments of water, flake material or other hard particles can become wedged between the cage and the rolling elements, causing a “traffic jam”, preventing the latter from rotating about their own axis. This can lead to cage failure.
Shock loads on bearings
The severe vibration in the shock load produces the impact of the rolling elements on the cage.
Installation problem
If the bearing is installed incorrectly, the cage will be damaged during installation.
Bearing Creep Phenomenon
Creep refers to the sliding phenomenon of the ferrule. When the interference of the mating surface is insufficient, the load point moves to the surrounding direction due to sliding, resulting in the phenomenon that the ferrule deviates from the shaft or the housing in the circumferential direction.
Abnormal load on bearing cage
Improper installation, inclination, excessive interference, etc. will easily reduce the gap, increase frictional heat, soften the surface, and cause premature abnormal peeling. As the peeling expands, foreign matter will enter the pocket of the cage, causing the cage to be blocked and additional loads will be generated, which will aggravate the wear of the cage. This cyclical deterioration may cause the cage to rupture.
Bearing cage material defects
Cracks, large foreign matter metal inclusions, shrinkage cavities, air bubbles and riveting defects, missing nails, pad nails or gaps between the two halves of the cage, severe riveting, etc. may cause the cage to break.
Intrusion of hard foreign matter into the bearing
The intrusion of foreign hard foreign matter or other impurities aggravates the wear of the cage. Solve the above reasons, the life of the bearing will be very long. The cause of many bearing damages is not the life of the bearing itself, but many external environments, such as insufficient lubrication, dust ingress, improper installation, excessive load, high temperature, poor coupling, etc.
Vibration
When the bearing is subjected to vibration, due to the potentially large inertial forces, fatigue cracks will form in the cage material after a period of time, and these cracks will sooner or later cause the cage to break.
Too fast
If the bearing is operated at speeds exceeding the design speed of the cage, the cage is subjected to heavy inertial forces that can cause fracture. Often, when very high speeds are involved, bearings with specially designed cages can be selected.
Other Causes of Cage Damage
If the rings of a deep groove ball bearing are not aligned with each other, the orbits of the balls are elliptical. If the cage is centered on the ball, it has to change shape every revolution. Fatigue cracks then form in the material, which sooner or later lead to fracture.
The situation is similar when thrust ball bearings are assembled with radial plain bearings. If there is play in the plain bearing, the washers of the thrust bearing will shift relative to each other. This way the balls don’t follow their normal path and a lot of stress can build up in the cage. Bearing cages subjected to severe accelerations and decelerations and speed fluctuations are subject to inertial forces. These create considerable pressure between the contacting surfaces,
When the bearing is working, it will or less cause a certain degree of damage and wear due to friction, especially when it is running at high temperature, it will even damage the bearing cage.
The cage is a part of the bearing structure, which means that if the cage is damaged, the bearing will not operate normally. There are many reasons for bearing damage. It is necessary to judge the degree of damage to the bearing cage according to the situation, find out the most fundamental reason, and finally take corresponding measures to prevent repeated damage.
Bearing cage damage degree:
The first stage of bearing cage damage: the embryonic stage of bearing failure. At this time, the temperature is normal, the noise is normal, the total amount of vibration velocity and frequency spectrum are normal, but the total amount of peak energy and frequency spectrum show signs, reflecting the initial stage of bearing failure. At this time, the real bearing fault frequency appears in the range of about 20-60khz in the ultrasonic band.
The second level of damage to the bearing cage: the temperature is normal, the noise is slightly increased, the total vibration speed is slightly increased, the vibration spectrum does not change much, but the peak energy increases sharply, and the spectrum is prominent. At this time, the frequency of bearing failure appears in the range of about 500hz-2khz.
The third level of bearing cage damage: the temperature rises slightly, the ear can hear the noise, the total vibration velocity increases greatly, and the bearing fault frequency and its harmonics and sidebands are clearly visible on the vibration velocity spectrum. The noise level on the spectrum increases significantly, the total amount of peak energy becomes larger than in the second stage, and the spectrum becomes prominent. At this time, the frequency of bearing failure appears in the range of about 0-1khz. It is advisable to replace the bearings at the end of the third stage, when the signs of rolling bearing failure such as visible wear should have appeared.
The fourth level of damage to the bearing cage: the temperature rises significantly, the noise intensity changes significantly, and the vibration speed and total vibration displacement increase significantly. The frequency of bearing faults on the vibration velocity spectrum starts to disappear and increases with a larger random broadband. Changed frequency noise levels; peak energy totals increase rapidly, with some erratic variations possible. Bearings should never be allowed to operate in the fourth stage of fault development, or catastrophic damage could occur.
Case of cage damage
Cage Damage 1
Part: Cage of a deep groove ball bearing
Symptom: Fracture of pressed-steel cage pocket
Cage Damage 2
Part: Cage of an angular contact ball bearing
Symptom: Pocket pillar Fractures of a cast iron machined cage
Cause: Abnormal load action on cage due to misaligned mounting between inner and outer rings
Cage Damage 3
Part: Cage of an angular contact ball bearing
Symptom: Fracture of machined high-tension brass cage
Cage Damage 4
Part: Cage of a tapered roller bearing
Symptom: Pillar Fractures of pressed-steel cage
Cage Damage 5
Part: Cage of an angular contact ball bearing
Symptom: Pressed-steel cage deformation
Cause: Shock load due to poor handling
Cage Damage 6
Part: Cage of a cylindrical roller bearing
Symptom: Deformation of the side face of machined high-tension brass cage
Cause: Large shock during mounting
Cage Damage 7
Part: Cage of a cylindrical roller bearing
Symptom: Deformation and Wear of machined high-tension brass cage
Cage Damage 8
Part: Cage of an angular contact ball bearing
Symptom: Stepped Wear on the outside surface and pocket surface of machined high-tension brass cage
