Gear Tooth Failure

Gear Tooth Failure on a Triple Reduction Gearbox

Specimen
Two fractured gear teeth with 185mm face width.

Background
A triple reduction gearbox had failed after two years of service. The gearbox has an input of 700 HP at 1780rpm on the expeller and is one of many other similar gear-boxes in use. An analysis was performed to determine the root cause for the gear failure and to provide information about whether a gear failure in the other gear-boxes may be imminent.

Service Life
Approximately two years.

Findings
Microscopic examinations of cross-sections of the gear teeth show the presence of subsurface cracking at the location of the pitch circle where the initial point contact occurs between meshing gears. Subsurface cracking is indicative of excessive loading. The presence of subsurface cracking is a characteristic of rolling contact fatigue. The gear teeth were not able to transmit a load of 700 HP. Consequently, other gear-boxes in service should be inspected for early stages of rolling contact failure of the gear teeth.