Reading failed bearings
Corrosion and electrical damage: photo guide
Rust at roller pitch means moisture while stationary. Pits and flutes mean current. Both leave patterns you can read at a glance.
Corrosion
Bearings pulled from a machine rust quickly, so protect them with oil, grease or rust inhibitor straight away. Corrosion can also occur in service, especially while the machine is shut down: static corrosion or black acid etching.
Electrical damage
Current through a bearing damages it in two ways. Large currents, such as from arc welding while the bearing is stationary, make large local pits. Small currents over a long period while the bearing rotates make many small pits, often lined up in axial bands called fluting.
- Weld on a machine with the earth clamp as close to the weld as possible and never across the bearing.
- On VFD-driven motors consider insulated bearings or shaft grounding.
- Look for grey frosted tracks in the bearing grease; dark discoloured grease is another sign.
Takeaway. Corrosion and current leave regular patterns; wear and fatigue are irregular. A repeating pattern is a clue to the external source.
Put it to work in the tool