Trouble Shooter

Published:  04 February, 2015

The answer to this month’s trouble shooter is provided by SKF.

Q

What is bearing smearing?

A

Bearing smearing, in the simplest terms, is when two metal surfaces slide against each other under load, transferring material from one surface to the other, causing surfaces to become scored. Indeed, when smearing occurs, the friction caused by roller and raceway sliding can generate temperatures that heat surfaces to such a degree that the contact area melts and subsequently re-hardens. As a result, localised stress concentrations can lead to surface cracking or flaking.

Smearing usually occurs suddenly, rather than being an accumulated wear process, and is particularly common in lightly loaded large bearings and in bearings subjected to high acceleration or rapid speed changes, typically found in wind turbine gearbox bearings. It is primarily caused by inadequate or inappropriate lubrication and the ingress of contamination.

Perhaps the most effective means of preventing and overcoming smearing is by ensuring that bearings are lubricated properly with grease with good oil film characteristics. Other ways of eliminating the problem include improving the preloading and bearing clearance, as well as enhancing sealing mechanisms.

Equally, the latest hybrid bearings overcome the problem as they have been designed to last much longer in applications operating under severe dynamic conditions or lubrication conditions with low operating viscosity.

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