Micropitting and macropitting - Gear defects

Micropitting and macropitting - Gear defects - Other defects

Figure 1: Bearing inner-race micropitting. The inner race of a planet gear’s two-row cylindrical roller bearing failed first due to micropitting, which is the dull gray frosted area at the center of the bottom raceway. Deterioration then progressed to macropitting (spalling) seen at the upper edge of the micropitted area.

Defect name: Micropitting, macropitting
Record No.: 2018
Type of defect (Internal/Surface): Surface
Defect classification: Gear defects, other defects
Steel name: Steel
Steel composition in weight %: No data.
Note: Wind-turbine gearboxes. Even with continued improvements, however, there are still a few issues that result in accelerated component wear and early failure. Early recognition of these failure modes will help reduce downtime for turbines even further. It will also cut maintenance costs by heading off problems before secondary damage, usually from debris, increases repair expenses. Addressing these issues with manufacturers prior to purchasing turbines will increase gearbox life and reliability. Here’s a brief look at the common wear and failure modes we continue to see in the field today.

Bearing inner-race micropitting. Fatigue failure of a race’s metal surface leads to micropitting. It is characterized by a dull gray frosted appearance, and under magnification the surface appears to be covered by very fine and shallow pits. Micropitting often progresses to macropitting (spalling) as shown in the accompanying photo of the inner race of a roller bearing from a planet gear.
Reference: Not shown in this demonstration version.