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Slewing Bearing Failure Analysis
- Oct 16, 2018 -

Gear material in slewing bearings is literally a real old topic. actually it is  “solid particle contamination” or “hard particle contamination,” which people kept complaining, that is a kind of fine “solid” particle.

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we know — they aren’t “that” large; but what we are talking about are particles that will create a small stress riser in the surface — which can lead to spall. These particles create dents that are large enough to see on the surface of slewing bearing. normally it would be around 50 microns. Some even well over 200-300 microns. This type of denting usually comes from something else actually failing. That “something” is often another bearing or some type of external contamination. The debris created by a gear mesh is much finer than this. Gear wear particles are closer to 10-30 microns. Those can still be troublesome if they are in heavy enough concentration, but unlike this visible denting, small debris creates a wear mechanism. Certain wear mechanisms can be a problem for some ball bearing applications, particularly for angular contact slewing bearings that are preloaded and under heavy loads. The particles tend to concentrate in the center of the raceway and can eventually start degrading the surface and lead to premature failures.

You will not find any shortage of information meticulously breaking down the specific amount of contamination to slewing bearing life degradation; use some caution with that. I have found many instances where new oil had more contamination than the recommended operating condition. All you can really do is run it and see how it does. If you are finding denting on raceways of slewing bearing, then you are likely generating a lot of particles. But that in itself doesn’t mean your system is doomed to failure. The good news is that aluminum is very soft compared to bearing steel and other common wear mechanisms we see in our systems such as gear steel and external contaminants. In the unlikely event that you do start seeing early failures of the slewing bearing, almost all of the top slewing bearing companies offer some sort of debris resistant bearings. These usually involve some sort of additional surface hardening. There is quite a difference in performance/contamination between a typical 60 HRC slewing bearing and a premium 65 HRC slewing bearing.