Bearing Low Friction Coatings - No More Oil Or Grease
September 24th 2008
Bearing low friction coatings used instead of oil or grease? Absolutely. And in many cases, the use of dry film lubricants or vapor deposition coatings are the better way to go. That is right. Friction can be reduced below that of oil-lubricated systems! Accept the idea that oil or grease serves as a boundary between two moving surfaces, and you will soon see what I mean.
On a microscopic level, mated metal surfaces will appear rough, more like “peaks” and “valleys.” If these surfaces come in contact with each other, slide across one another, significant friction and heat is produced. So much so that the two surfaces may melt and temporarily fuse together. This phenomenon is called micro-weld adhesion. Soon, though, bearings are moving, welds break, and material is stripped away from one of the surfaces. This is known as adhesive wear.
Of course, hydrocarbon lubricants will smooth out bearing surfaces. Oil or grease can fill in the valleys to keep the peaks from contacting each other. Keep in mind, though, it takes only the smallest of non lubricated areas, the tiniest of metal surfaces exposed, to create catastrophic failure. What may be a force of less than a few pounds can translate into literally millions of pounds of pressure per square inch.
What is the answer? That’s easy. Depending on service parameters and environment, such as temperature, load, ambient or atmosphere, choices can include Teflon, PTFE (polytetrafluoroethylene) or graphite. Of course there are other products, inorganic forms of lubrication, including thin film coatings of ceramic nitrides, MoS2 (molybdenum disulfide) or WS2 (tungsten disulfide).
Physical vapor deposition (PVD) and other related advanced processes enable ultra-thin coatings less than a micrometer thick. This is good news for bearings constrained dimensionally. Other products, too, like diamond-like coatings (DLC) can offer increased resistance to wear, protection from corrosion, heat stability, higher strength and negligible outgasing.
So, who needs oil or grease? When you can add low friction coatings to your bearing.
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William Gunnar, a degreed scientist, researcher, engineer, and friend, has helped thousands of ‘best of class’ product designers and equipment manufacturers — for nearly 20 years now — surface engineer with coatings for success.
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