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Each bearing must be ensured a proper fit for the bearing on its inner race and the outer race. Proper fit is stressed because it carries a lot of importance for the proper working of the bearing. There are two important types of failures that occur due to improper mounting i.e. without the proper fit. The first one in that is Failure of Bearings due to Loose Fits.
By loose fits, we mean to say that the bearing is either loosely fitted on the inner race i.e. on the shaft or on the outer race i.e. onto the housing. This can occur under the following conditions.
1. The size of the shaft is lesser that the bearing inner race bore diameter. This difference between the diameter of the shaft and the diameter of the bearing bore can be as less as 0.03 mm.
2. The size of the bore of the housing is larger than the outer race diameter of the bearing. The difference between the outer race diameter and the bore diameter of the housing can be as less as 0.02 mm.
So what happens if the above two point happen? The failure of the bearing due to loose fits occurs. This has a characteristic indication. The bearing can be easily removed (just by hand) without any external aid. The visual indications could be as follows:
· Discoloration and scoring on the surface which has been free from any fit. The discoloration is mainly due to the temperature raise cause due to the running in of the bearing as a whole. To put in simple words, in this condition the bearing does not work like a bearing and instead works as a scraper scraping the housing bores or the shaft diameter journals.
· This also leads to Fretting. Fretting is a process of generation of fine metal particles which oxidize and leave a distinct brownish mark on the surface. Moreover the fine particles are abrasive in nature and can cause further damage to the bearing and the areas on which the bearing is mounted upon.
The ultimate result of this will cause the bearing to run on the loose surface causing further wear and tear. A characteristic point to be noted during running of a bearing with looseness is that is tends to produce more noise and runs with a run out.
The best remedy or precaution for this would be to ensure a proper fit is available before assembly of the bearing on the corresponding location whether it is a shaft or a bore.
We will look on the other types of bearing failure in the next article.
Failure modes of Rolling Bearings - Part 7
Bearings are normally designed and selected to last for a life time. Any failure occurring in it needs to be identified properly. This article will help you in determining the various causes and the type of failure the causes tend to induce on the bearing.