AGMA 11FTM16

Micropitting is a type of fatigue failure occurring on hardenedtooth flanks of highly loaded gears. This failure consists of verysmall cracks and pores on the surface of tooth flanks. Micropittinglooks greyish and causes material loss and a change in the profileform of the tooth flanks, which can lead to pitting and breakdownof the gears. The formation of micropitting depends on differentinfluences. Besides material, surface roughness, and geometry ofthe tooth flanks, the lubricant and the operating conditions show amain influence on micropitting formation. The micropittingload-carrying capacity of gears can be calculated according toISO/TR 15144-1, where the influence of lubricant, operatingconditions, and surface roughness is considered with the specificlubricant film thickness. For this purpose, the specific lubricantfilm thickness of a practical gear is compared with a minimumrequired specific lubricant film thickness. The latter is thespecific film thickness where no micropitting risk is given for alubricant and can be determined by performing a micropitting testaccording to FVA 54/7. This test procedure consists of a load stagetest and an endurance test. Lubricants with a high micropittingload-carrying capacity reach the failure criterion of a profileform deviation of 7.5 ?m due to micropitting in load stage greaterthan or equal to LS 10 of the load stage test. In the endurancetest, a stagnation of micropitting formation compared with themicropitting area at the end of the load stage test is preferredbut not required. In field applications, micropitting formation isoften reported even though industrial gear oils with a highmicropitting load-carrying capacity are used. Such oils offer agood micropitting protection determined in the load stage test, butwith a low micropitting performance in the endurance test. The aimof research is therefore the investigation whether a change from anoil with low micropitting performance in the endurance test to anoil with high micropitting performance in the endurance test canstop the micropitting formation.

Edition:

11

Published:

10/01/2011

Number of Pages:

11

File Size:

1 file , 1.1 MB