bearing-failure-analysis

name	bearing-failure-analysis
description	Bearing failure analysis — fatigue spalling, wear, overheating, corrosion, misalignment, false brinelling, creep, root cause identification, corrective actions.
metadata	{"priority":7,"promptSignals":{"phrases":["bearing failure","bearing spalling","bearing damage","bearing wear","bearing overheating","false brinelling","fretting bearing"],"minScore":3}}

Bearing Failure Analysis — Complete Skill

Failure Classification

~95% of bearings are replaced before failure; but when failure occurs:

Category	Frequency	Examples
Lubrication	36%	Starvation, wrong viscosity, contamination
Mounting	16%	Over-force, wrong fit, misalignment
Contamination	14%	Dirt, water, metallic particles
Overload	11%	Shock, overload, vibration
Fatigue (design life)	34%	Subsurface crack propagation to surface

Failure Modes and Identification

1. Rolling Contact Fatigue (Spalling)

Appearance: flaked surface, pitting, rough raceway Cause: subsurface shear stress cycle → crack nucleation → propagation → spall L10 life exhausted or material defects, high load, poor lubrication (low κ) Pattern: sub-surface origin → random pattern; surface origin → lines of pitting

2. Smearing/Scuffing

Appearance: directional tearing, metal transfer, shiny rough areas Cause: insufficient EHD film → metal-to-metal contact under sliding Low-speed high-load starts; inadequate viscosity κ < 0.5 Prevention: higher viscosity oil, EP additives, speed up slowly

3. Brinelling (True)

Appearance: indentations at ball pitch spacing on raceway Cause: static overload (single event); load > static capacity C_0 Hertz contact stress > 4200 MPa creates plastic impression Prevention: increase bearing size; add vibration dampening during transport

4. False Brinelling

Appearance: dull depressions at ball pitch spacing; red-brown debris (goethite) Cause: oscillation at small angle under load (vibration) → fretting → wear Occurs during: transport, vibration from adjacent machinery, idle equipment Distinguish from true brinelling: false has flat depressions + rust debris; true has no debris initially Prevention: EP grease, preload, periodic slow rotation during storage

5. Electrical Pitting (Fluting)

Appearance: washboard/corrugated pattern on raceways; regular channels parallel to rotation Cause: stray electrical current flowing through bearing (VFD drives, welding) Mechanism: arcing melts micro-spots of raceway → periodic pattern as bearing rotates Prevention: insulated bearings (ceramic coating on OD/ID); hybrid bearings (ceramic balls); earthing brushes

6. Corrosion

Appearance: reddish-brown discoloration; pitting after moisture exposure Types: fretting corrosion (relative motion + oxygen = goethite Fe₂O₃), moisture corrosion Prevention: corrosion-resistant grease, sealed bearings, anti-corrosion coating

7. Overheating/Seizure

Appearance: blue/brown discoloration of steel; smeared or melted cage; welded surfaces Cause: starvation, excessive preload, over-greasing (churning), bearing cage failure Temperature indicator: steel turns blue >220°C; bronze cage softens ~250°C Prevention: proper lubrication quantity, verify preload, temperature monitoring

8. Cage Failure

Appearance: fragments, cracked or broken cage Cause: over-speed, shock loading, incorrect lubricant, cage-guided vs. race-guided selection Polymer cages more vulnerable to: chemical attack, high temperature, impact Prevention: correct cage material, speed verification, adequate lubrication

9. Misalignment Damage

Appearance: diagonal stress bands at approximately 45° across raceways Cause: angular misalignment between inner/outer ring; shaft deflection Pattern: in ball bearings — contact ellipses visible at angles Prevention: self-aligning bearings, proper alignment procedures, reduce shaft deflection

10. Creep (Ring Fretting)

Appearance: fretting marks/scoring on bore or OD of bearing ring; loose fit Cause: insufficient interference; rotating ring with loose fit → microslip → fretting wear Prevention: correct interference fit; replace shaft/housing if out-of-tolerance

Root Cause Investigation Procedure

1. Note operating history: load, speed, temperature, lubricant, interval
2. Examine bearing visually: raceway pattern, cage condition, surface color
3. Identify failure mode from classification above
4. Check: Was life calculation adequate? Was installation correct?
5. Measure fits: check shaft/housing diameters against specification
6. Examine lubricant: viscosity, contamination level (ISO particle count), water content
7. Review maintenance records: re-greasing schedule adherence

Corrective Actions

Root Cause	Corrective Action
Low viscosity	Use higher VG oil or heavier grease; check temperature
Over-greasing	Reduce quantity; use correct NLGI grade; add relief fitting
Wrong fit	Re-machine shaft/housing; verify tolerances
Contamination	Better seals; filtration; more frequent change
Electrical fluting	Insulated bearing; hybrid; shaft earthing
False brinelling	Periodic rotation during storage; EP grease; preload
Misalignment	Realign; check bearing supports; reduce span
Overload	Larger bearing; load analysis; reduce external forces

Output

Provide: failure mode classification, damage pattern description, probable root cause, supporting evidence from visual/measurement data, corrective action, prevention recommendation.