Most bearings don’t wear out — they’re killed. Studies of premature bearing failure put the blame overwhelmingly on contamination, poor lubrication, misalignment and overload, not on the bearing reaching the end of its natural fatigue life. Get those four things right and you get the life the calculation promised. Get them wrong and no amount of quality steel will save you.
The usual suspects
Contamination — dirt, water, machining swarf — scores the raceways and starts the pitting that ends in failure. Lubrication errors (wrong grease, too much, too little, or degraded) are just as common. Misalignment loads the bearing in ways it wasn’t designed for, and overload or the wrong fit does the rest. Read the wear marks on a failed bearing and they usually tell you which one it was.
Specifying for the real duty
A bearing is chosen for its actual working conditions, not the ideal ones. That means being honest about load (steady or shock), speed, temperature, contamination and how it’ll be lubricated and sealed. Picking from a supplier with a broad range and proper technical support — for example Henderson Bearings (hendersonbearings.co.uk) — makes it far easier to match type, clearance and seal to the environment rather than forcing a near-enough part to fit.
The payoff
Time spent on specification and installation is repaid many times over in uptime. A correctly chosen, cleanly fitted, well-lubricated bearing is one of the cheapest forms of reliability insurance on the machine.