The failure that announces itself well before it arrives
The SKF Group estimates that bearing failures account for approximately 40 percent of all rotating machinery failures in industrial applications. NEMA found that bearing failure is the leading cause of electric motor failure in manufacturing environments, accounting for 47 percent of motor failures. These failures are not sudden events. They progress through predictable stages over weeks or months — and most plants are only detecting them at stage three or four, when the options are limited.
The same principle applies to electric motor faults more broadly — most motor failures have a detectable precursor that a systematic monitoring programme would catch. Bearing failure is the most common of those precursors.
The four stages — and what each one feels and sounds like
Stage one produces high-frequency stress waves detectable only by specialised ultrasound instruments. No human-perceptible symptoms. Stage two produces sub-harmonic vibrations detectable by accelerometer — an experienced technician may feel slight roughness when rotating the shaft by hand. Stage three produces audible noise — a cyclic roughness or grinding sensation distinct from normal machine noise, with temperature beginning to rise at the bearing housing. Stage four is catastrophic: metal fatigue, spalling, or seizure.
The Mobius Institute reports that vibration analysis can detect bearing faults at stage two — six to twelve weeks before stage four failure — in 85 to 90 percent of cases when measurements are taken at correct intervals and locations.
Why replacing a failed bearing is only half the job
Replacing a failed bearing without understanding why it failed leads to recurrence at predictable intervals. SKF's bearing failure analysis guide identifies lubrication failure as the cause of 36 percent of premature bearing failures, overloading as 34 percent, contamination as 14 percent, and incorrect fitting as 16 percent. Each leaves specific physical evidence on the bearing surfaces.
Lubrication failure shows blue or brown discolouration from heat and a hardened layer on internal surfaces where the lubricant film broke down. Contamination leaves characteristic denting on the raceway — small indentations where hard particles were pressed into the bearing steel. Incorrect fitting shows as fretting corrosion on mating surfaces, or raceway spalling concentrated at specific angular positions.
This is exactly the kind of root cause analysis that should be captured in every work order. When the same bearing position fails three times in 18 months, the work order history should tell you why — if the resolution notes are detailed enough. See our guide on what makes a CMMS actually useful for why most plants' work order records don't capture this.
Temperature as a practical early warning tool
A bearing operating within its design parameters stabilises at a fixed temperature differential above ambient — typically 40 to 70 degrees Celsius above ambient for most industrial applications. SKF specifies a maximum outer ring temperature of 120 degrees Celsius for standard bearing types. Beyond this, lubricant degradation accelerates and failure progression compresses from weeks to hours. A bearing temperature trending upward between successive checks warrants investigation before the audible stage begins.
YAFEX helps maintenance teams document and search bearing fault history across all rotating equipment. Talk to us.
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