The #1 Cause of Premature Bearing Failure
Industry studies consistently show that over 50% of bearing failures are lubrication-related. That's either too little, too much, the wrong type, or contamination of the lubricant.
Getting lubrication right is the single highest-impact maintenance action you can take.
Choosing the Right Grease
Grease selection depends on three factors:
- Base oil viscosity — must match the bearing's speed and load. High-speed bearings need low-viscosity oil; heavy-load bearings need high-viscosity.
- Thickener type — lithium complex is the most versatile all-rounder. Polyurea is excellent for long-life sealed bearings. Calcium sulphonate excels in wet environments.
- NLGI consistency number — Grade 2 is standard. Grade 3 is stiffer for vertical shafts; Grade 1 is softer for low-temperature starts.
Calculating Re-Lubrication Intervals
The re-lubrication interval depends on bearing size, speed, operating temperature and grease type. As a rule of thumb:
- Small bearings (<100mm bore) at moderate speed: every 6–12 months
- Medium bearings (100–200mm): every 1–3 months
- Large or high-speed bearings: every 2–4 weeks
Reduce intervals by 50% for every 15°C above 70°C operating temperature.
The Over-Greasing Trap
More grease is NOT better. Over-greasing causes:
- Excessive heat from churning resistance
- Seal blowout and grease leakage
- Increased energy consumption
- Accelerated lubricant breakdown
The correct replenishment quantity is roughly:
**Q = 0.005 × D × B** (where D = bore diameter in mm, B = bearing width in mm)
Common Mistakes to Avoid
- **Mixing incompatible greases** — lithium and polyurea thickeners can react and soften, causing grease to run out.
- **Ignoring the purge** — when re-greasing, let the old grease purge out through the relief valve. If it doesn't come out, the cavity is over-pressured.
- **Re-greasing a sealed bearing** — 2RS bearings are greased for life. Adding grease through the seal damages it.
- **Using the same grease for all bearings** — a high-speed spindle bearing and a slow conveyor bearing have very different needs.
