Two branches of gear grease selection
First identify whether the gear is metal or plastic — the selection logic is completely different.
Metal gears
Focus on extreme-pressure (EP) anti-wear and adhesion:
- Low-speed heavy load, shock load → use EP-additive grease with high four-ball PB/PD values to prevent pitting and scuffing;
- High-speed light load → prioritize adhesion, anti-fling and noise reduction;
- Open gears → use highly adhesive, water-resistant grease to avoid centrifugal loss.
Plastic gears
Focus on material compatibility (the most overlooked factor):
- The grease must be compatible with POM, nylon, PC and other plastics, otherwise the gear swells, cracks or embrittles;
- Use synthetic oil (e.g. PAO) that does not corrode or swell plastics and rubbers;
- EP additives commonly used for metal gears may attack plastics and must not be reused directly.
Key metrics
- Four-ball PB/PD: extreme-pressure load capacity;
- Adhesion / anti-fling: no loss under high-speed centrifugal force;
- Noise and vibration reduction: key to gearbox quietness;
- Material compatibility: a must-test for plastic gears.
Recommendations by scenario
| Scenario | Recommendation |
|---|---|
| Geared motors, stepper motor gearboxes | Noise-reducing grease, metal/plastic compatible |
| Heavy-duty industrial gears | EP lithium-complex / aluminum-complex grease |
| Power tool gearboxes | High anti-wear, high-temperature grease |
| Plastic gears | PAO-based, plastic-compatible |
Conclusion
Metal gears prioritize EP and adhesion; plastic gears prioritize material compatibility and noise reduction. Never use metal-gear grease with corrosive EP agents on plastic gears.