AGMA 13FTM16

Visual examination of a compressor box revealed that the LowSpeed (LS) Pinion exhibited pitting type defects on each of itsforty seven (47) helical teeth. Review of the failed componentrevealed a somewhat repetitive type of damage at one end of theteeth only. Each tooth showed what appeared to be one defect at asimilar location 3600 around the Pinion. Each defect was locatedwithin ~0.5 inch of the end of the helical tooth. It was noted thateach tooth defect was observed on the coast side of the teeth only.Visual examination of the mating gear revealed no evidence ofsimilar damage. While of and by itself, this pitting may not because for alarm, debris from the pitting can adversely affect othercomponents in the gearbox, especially the bearings, and the stressconcentration effect of the pitting, even though it is on the coastflank, could lead to partial tooth fracture in the region of thedistress.

This paper presents a discussion of the causation, diagnosis andmetallurgical failure investigation of this lubrication erosionfailure. Our effort was aimed at identifying the nature of thepitting and providing recommendations to avoid repeat instances ofthis failure in this specific application and in other futuredesigns for similar applications.

The subject is presented by way of the discussion of detaileddestructive metallurgical evaluations of this specific lubricationerosion failure which the authors have conducted in order toanalyze and characterize the failures. Lubrication erosion isgenerally limited to helical gears but the authors have also foundthis type of distress when evaluating damage to carburized,hardened and hard finished spiral bevel gears as well when operatedunder the “right” circumstances. Lubrication erosion observed onhelical gears only, however, will be addressed in thispresentation. Although a specific failure “case” is used as thevehicle for presentation, information has been extracted andcondensed from several individual actual failure investigationsconducted by the authors so that a better understanding of thespecific conditions that lead to micropitting and the actualprogression from micropitting to fracture can be presented.

Edition:

13

Published:

09/01/2013

Number of Pages:

30

File Size:

1 file , 2.1 MB