Gear Wear, Failure and Lubrication

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The most critical function provided by lubricants is to minimize friction and wear to extend equipment service life. Gear failures can be traced to mechanical problems or lubricant failure. Lubricant-related failures are usually traced to contamination, oil film collapse, additive depletion, and use of improper lubricant for the application. The most common failures are due to particle contamination of the lubricant Dust particles are highly abrasive and can penetrate through the oil film, causing plowing wear or ridging on metal surfaces. Water contamination can cause rust on working surfaces of the gears and eventually destroy metal integrity.

To prevent premature failure, gear selection requires careful consideration of the following: gear tooth geometry, tooth action, tooth pressures, construction materials and surface characteristics, lubricant characteristics, and operating environment.

Gear Distress & Failure Classifications

Distress or failure of gears may be classified into four categories:

1 – surface fatigue (pitting),
2 – wear,
3 – plastic flow
4 – breakage.

The appearance of the various distress and failure modes can differ between gears that have through hardened teeth and those that have surface hardened teeth. These differences result from the different physical characteristics and properties and from the residual stress characteristics associated with the surface hardened gearing.