Wear Failure

Polishing

Slow process of wear causing a very smooth surface to develop on the gear teeth.

Cause: Lubricant is too thin, gears are operating near lubrication borderline.

Solutions: Polish gears, use a higher viscosity lubricant or lower lubricant temperature, reduce load or increase speed to help oil flint.

Moderate Wear

Metal is being removed from both the addendum and dedendum tooth surfaces.The pitch line remains as a continuous line.

Cause: Lubrication contamination, using a splash fed system.

Solutions: Increase oil film thickness, use a higher viscosity lubricant, increase speed, reduce load, use a filtered positive‑spray system. Changing materials or hardness.

Extreme Wear

Same wear pattern as moderate `near but occurring at a much faster rate. Pitch line may also show signs of pitting.

Cause: Lubrication film too thin for tooth load, lubrication contamination, extreme vibratory load

Solutions: Replace or install shaft seals and air filters, lower oil temperature, higher viscosity, run gears faster, reduce vibration.

Abrasive Wear

Radial scratches or grooves showing rip as a lapped surface oil the tooth contact surfaces.

Cause: Usually from the lubrication being contaminated. Metal particles from the gears, hearing, sand, dirt, etc.

Solutions: Regular lubricant changes, use a circulating system with filters, thicker oil film, cleaning gearbox.

Corrosive Wear

Gear surfaces show signs of deterioration & pitting.

Cause: Lubricant breaks down and corrosive elements attack gear surfaces.

Solutions: Regular lubricant changes, using lubricants with higher anti‑wear additives, although these also need to be observed carefully because of chemical activity. Sealing gear units from exposure may be necessary.

Scoring

Metal is torn away from gear surfaces, and/or alternately metal is welded into itself.

Cause: Lubricant failure, misalignment, deflection and uneven loads or temperatures.

Solutions: Reduce the mesh area temperature, reduce load, gear speed, reduce oil temperature, use extreme‑pressure additives, or synthetic fluids with anti‑scuff additives, gearing may need to be redesigned.

Surface Fatigue

Pitting

Metal is removed forming small and/or larger cavities. Pitting may occur over the entire tooth profile or, if severe, in the dedendum section of the gear teeth.

Cause: Overload conditions whereby material is pushed beyond endurance limits.

Solutions: With small pitting the gears will redistribute material removing high contact spots and, over time, polish itself and improve the overall contact pattern. With severe pitting the gear load should be reduced or the material needs to be hardened.

Spalling

Similar to pitting, pits are usually larger.

Cause: Excessive high‑contact stress levels.

Solutions: reduce contact stress and/or harden the material to increase surface strength. Gear redesign may be necessary.

Case Crushing

may appear similar to pitting, material may chip away from the core, also may appear as cracks on the surface of teeth.

Cause: High stress on gear. Occurs on material where the case is substantially harder than the core. Endurance limits are exceeded.

Solutions: Increase depth of case hardening and possibly the core hardness, change materials.

Other Causes

Heat Treating Cracks

Improper quenching or cooling during heat treatment. Cracks may not show up until after gears are in production. Procedures should be reviewed to prevent this problem.

Overload Breakage

Overloading of stress which exceeds endurance limits. Load needs to be lowered, material used for application should be reviewed.

Grinding Cracks

Occurs during the grinding process due to excessive heat being generated while the gear is being ground. Improper heat treating may contribute to this problem. Lowering speeds and feeds during grinding may eliminate problem. A review of the material and heat treating process may also be considered.