When a girth gear fails, the wear pattern is a confession. Reading it correctly tells you whether to blame installation, maintenance — or the gear itself.
Misalignment damage
Contact concentrated at one tooth end, often with diagonal pitting bands, means the gear and pinion axes are not parallel — usually foundation settlement or thermal distortion of the mill shell. No gear survives sustained edge loading; re-alignment is the fix, not a harder gear.
Pitting and scuffing
Uniform micro-pitting across the face is normal run-in; progressive macro-pitting signals overload or lubricant film breakdown. Scuffing (scoring along the slide direction) is almost always lubrication failure — spray timing, viscosity or contamination.
Tooth-root and rim cracks
These are the failures that trace to manufacturing. Cracks initiating at subsurface inclusions or shrinkage porosity in the rim mean the casting shipped with defects that UT should have caught. This is precisely why 100% ultrasonic coverage of rim and tooth zones — with documented acceptance criteria — belongs in every girth gear purchase specification.
Joint problems
Fretting, bolt loosening or steps at segment joints point to machining accuracy or assembly torque procedure. Insist on joint-face flatness records and witnessed trial assembly at the foundry before shipment.