Three factors in bearing selection

Choosing bearing grease is essentially balancing speed, load and temperature. There is no universal grease, only the one that best matches the operating conditions.

1. Speed

• High speed (small bearings, micromotors): use soft grease (NLGI 1 or 0) with low-viscosity base oil to reduce churning resistance and heat;
• Low speed: NLGI 2 or even grade 3 is acceptable.

Speed can be roughly judged by the ndm value (speed × bearing pitch diameter): the higher the ndm, the lower the base oil viscosity should be.

2. Load

• Light load: ordinary lithium grease is enough;
• Medium/heavy or shock load: use grease with extreme-pressure (EP) additives and a high four-ball PB value.

3. Temperature

• Normal (−20°C to 80°C): lithium grease is sufficient;
• High temperature (above 120°C): synthetic base oil + polyurea or lithium-complex thickener;
• Low temperature (below −40°C): PAO or ester synthetic oil.

Fill amount (important)

The grease fill should be 1/3 to 1/2 of the bearing's free space:

• Too little → insufficient lubrication, fast wear;
• Too much → churning heat, grease pushed out, even seal failure.

Recommendations by scenario

Conclusion

First check speed (decides base oil viscosity and NLGI softness), then load (decides whether EP is needed), finally temperature (decides base oil and thickener type). Keep fill at 1/3–1/2 — don't overfill.