Does the Type of Gear Action Affect the Appearance of Micro-Pitting and Gear Life?


Early results from testing conducted have raised questions concerning the role of gear action with the appearance of micropitting as well as surface fatigue (macropitting). Comparisons between similar gear sets with the same loads, speeds, and lubrication but operated either as speed increasers or as speed reducers have yielded strikingly different propensities for wear. Further, these observations are not limited to lubrication based failures such as micropitting, but, so far, have applied to traditional surface fatigue failures (macropitting) as well.
Findings point to an increase in the presence of micropitting on gearing operated as speed reducers. All components are operating at the same speed and load, yet wear is greatly reduced for the driven components.
Perhaps more intriguing is that to date all macropitting failures have occurred to the driving pinions of gear sets operated as speed reducers. While the number of samples is decidedly small, the length of life for these components is much less than would be anticipated under smooth load circumstances. The other gear sets (operated as speed increasers) do not show any fatigue wear.
In addition to how gear action affects micropitting in gearing is the question of how the gear action affects fatigue life. Current gear rating standards are based upon statistical analysis of real-world experience and mathematical stress-versus-cycle calculations. If gear action affects how gearing fails in fatigue, there may be significant ramifications in the industry. However, before any such conclusion may be made, additional testing is necessary.
ISBN: 978-1-55589-971-4 Pages: 30
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