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GEAR FAILURES
2.0 Tooth pitting
| Click on photograph to enlarge | |
 | Figure 2a Pitting in the dedendum of a helical gear |
 | Figure 2b
- Initial or corrective pitting of gear teeth. If there are surface profile errors in gears the pitting will tend to occur at any high spots. One typical error which arises on unhardened gears, due to tooth cutting with a non concentric hob, is split marking, where the teeth have bedding bands in the addendum and dedendum on one side and near the pitch line on the other Click photo to get additional pictures |
| Main Characteristics | The operating surfaces of gear teeth suffer pitting when subject to excessive contact stress. With unhardened gears pitting often occurs as a bedding in action and provides a corrective process for misalignment and minor profile errors. Such pitting often heals and the gear teeth can become smooth again after further running. Pitting of this nature will tend to start during the first few hundred hours of running. If it is monitored at regular intervals its incidence can be followed. Initial pitting of this kind will decrease eventually with running time, while more serious progressive pitting, associated with continuous overloading will become steadily worse and probably lead eventually to tooth breakage. Because of the relative directions of surface sliding and movement of the contact load in gear teeth, which affects surface crack direction and propagation, pitting occurs preferentially in the dedendum of the teeth of both driving and driven gears. |
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| Possible Confusion with Other Types of Damage | |
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