Bearing Brinelling in Ball Bearings: What is it all about?

Blog | March 5th, 2019

Brinelling takes place on a bearing when its internal surfaces accumulate indentation damage. What causes the raceway dents? As with most mechanically caused problems, there are unmanageable mechanical stresses acting on the bearing parts and materials. A system overload smacks a rolling element hard, it deforms the raceway, and the brinelling effect amasses. Bearing contaminants are another culprit here, so there are at least two different brinelling factors in play.

Bearings Are Slightly Ductile

The raceways and rolling elements are made from hardened alloys, naturally enough. Indeed, the balls speeding down the internal surfaces of a bearings’ twin rings are heat treated so that they’re extra-hard. In this way, when a heavy shaft or mounting load is applied, the spheroids maintain their form. The ring surfaces, while almost as durable, do exhibit a finite quantity of elasticity. Case-carburized and fatigue-resistant, that tiny amount of ductility leeway doesn’t affect bearing performance, not unless there’s an overload force striking the rolling parts as they spin down their raceways. Now, with the load energy threatening to deform the bearing parts, the rolling elements leave indents behind. They’re still holding their shape, at least for the moment, but the internal ring surfaces are in trouble.

Identifying Brinelling Causes

Again, the raceway’s elastic limit is being forced past its design threshold. A transient load or cyclic force is wreaking havoc on the bearing rings, so brinel marks are accumulating. Or perhaps the apparatus is poorly mounted and installed? In this case, thrust forces and misalignment errors are working in concert to undermine the way in which the raceways handle different axial forces. So far so good, then, a new bearing will be mounted and the misalignment error eliminated. If there are overload conditions in motion, they’ll fall under a troubleshooter’s wary eye. They’ll be identified and addressed so that a new bearing maintains its polished, unblemished raceway surfaces. And, assuming the causative factors have identified a contaminant, the source of that foreign matter will be tracked down so that the bearing runs clean.

Like a criminal’s fingerprints, there are clues left behind when differently shaped brinel marks are discovered on bearing rings. For lines of on-again-off-again dents, transient loads and/or misalignment errors are the clear suspects. If the brinel lines are finer, the surface scoring thinner, then machine vibration could be a problem. Just by tracking down the causes, the equipment vibrations, contaminants and transient loading effects, we can correct the issue at its source. Now the problem won’t reoccur, and the rolling elements won’t cause any more raceway indentations.

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