What Are the Key Considerations for Regular Maintenance of FAG Bearings​

Key Maintenance Precautions for FAG Bearings in Regular Overhauls

Regular overhauls are the most direct way to extend the service life of FAG bearings and prevent costly unplanned downtime. The following precautions, grouped under bold sub-headings, summarize what maintenance teams should do before, during and after a scheduled outage. The word bearing appears in every sub-heading to keep the focus firmly on the component itself.

1. Bearing pre-overhaul data review

Collect at least three months of trending data—vibration, temperature, acoustic emission and lubricant condition—before the machine is stopped. Compare the values with FAG’s alarm limits published for the exact bearing designation. A sudden 10 °C rise or a 20 % increase in overall vibration often indicates that the rolling elements have already entered the fatigue spall initiation phase.

Print or export the spectra: they will guide the physical inspection and help decide whether the bearing can remain in service or must be replaced.

2. Bearing shutdown and lock-out sequence

Never stop the machine abruptly. Reduce load gradually and allow the bearing to cool below 50 °C before cutting power. Lock the shaft so that it cannot rotate when maintenance personnel remove guards or couplings. A hot bearing contracts on the shaft; attempting removal while still hot will score both the journal and the inner ring raceway.

3. Bearing cleanliness during removal

Clean the external housing with lint-free cloths and a neutral detergent. Remove all grease fittings and plugs, then collect the used grease in a sealed container for later analysis. When the bearing is lifted, label the orientation (“drive side, outer ring top mark”) so that any wear pattern can be correlated to the operating geometry. Never apply force through the rolling elements; use FAG-approved mechanical or hydraulic pullers that grip the strong inner ring back face.

4. Bearing visual and tactile inspection

Leave the bearing in its lubricated state—do not wash it yet. Rotate the rings slowly by hand and feel for roughness, binding or excessive clearance. Record every finding photographically: discoloration, smearing, frosting, brinelling, cage wear and seal damage. A uniform brown-blue heat tint around the entire circumference of the outer ring usually points to global overheating, whereas local blue patches indicate micro-slip and inadequate axial clamping.

5. Bearing dimensional check

Measure the internal clearance with a feeler gauge while the bearing is still intact. Compare the value with the FAG catalogue initial clearance and the permissible post-service reduction. If the radial clearance has vanished or gone negative, the bearing has been subjected to excessive interference fits or thermal expansion beyond design limits. Next, measure roundness and taper of the shaft seat and housing bore; out-of-roundness above half the IT5 tolerance calls for re-machining or sleeve installation.

6. Bearing lubricant laboratory test

Send a 50 g grease sample to an accredited lab. Request tests for contamination level (ISO 4406), water content (Karl Fischer), ferrous wear debris (PQ index) and additive depletion (FTIR). A spike in silicon combined with normal iron may indicate external dust ingress, meaning the bearing seals are no longer effective. Conversely, high chromium or molybdenum implies cage or roller wear inside the bearing.

7. Bearing cleaning and re-lubrication

If the inspection shows the bearing is re-usable, clean it at room temperature in a mineral-spirit bath equipped with an ultrasonic stage. Dry with filtered compressed air, then weigh the exact grease quantity prescribed for the bearing size and speed factor. FAG Arcanol greases are filled to 30 % of the internal free volume for horizontal shafts and 40 % for vertical arrangements. Avoid hand-packing; use a grease cartridge and follow the FAG four-quadrant method to ensure even distribution.

8. Bearing installation and alignment

Mount the bearing with an induction heater set to 110 °C maximum; higher temperatures degrade the martensitic structure and the retained austenite ratio. Slip the bearing onto the shaft in one continuous motion and hold it against the abutment shoulder until it cools below 50 °C. Check the labyrinth gap: radial seals must have 0,3–0,5 mm clearance to the housing cover to avoid preload and seal lip wear. Use feeler gauges at four 90° positions; any deviation above 0,05 mm requires re-alignment of the entire bearing cartridge.

9. Bearing run-in and post-overhaul monitoring

Start the machine at 25 % rated load for 30 min, then increase in 25 % steps every 20 min while logging temperature and vibration. A properly mounted bearing should stabilise below 60 °C and show vibration velocity under 2.8 mm/s RMS. Continue trending for the first 168 h; any sudden rise is a red flag that the overhaul did not correct the root cause .

10. Bearing storage for spares

Store replacement bearing units horizontally in their original, vapour-proof wrapping, on shelves at least 30 cm above floor level. Keep relative humidity below 60 % and avoid temperature swings that create condensation. Rotate the bearing stock every three years; the grease inside ages even when the bearing is idle.

By integrating these ten checkpoints into the standard work package, maintenance teams turn the regular overhaul into a predictive exercise rather than a reactive repair. The bearing receives exactly the attention it needs, when it needs it, ensuring that FAG’s design reliability is translated into real-world uptime.

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