Anodizing Low Friction Coatings
Anodize aluminum (which includes the process known as ‘hardcoat’) is most recognized in the finishing industry for its ability to increase hardness or reduce wear. But, did you know these coating structures, which are made up of alumina oxide, can be modified for low friction?
Imagine outermost coating layers porous, stacked somewhat like hollowed, parallel tubes that extend downward, inward, toward the original barrier layers of the coating.
These cellular structures make for excellent absorptive processes. For example, structures of hard anodize can be supplemented with a variety of materials to promote low friction, including Teflon (PTFE), waxes, oils, and other compounds. And because these compounds can infiltrate the ceramic, their contribution to real surface growth is oftentimes negligible.
Material choices and processing methods for penetration vary. Be sure your service provider fully understands your performance requirements.
Generally, anodizing low friction coatings will be further enhanced with surface finish. Polishing should not be overlooked, especially prior to coating since, depending on the original finish, surface ‘roughness’ can increase by 10 to 30 micro inch (Ra).
While friction is a highly system-dependent parameter, values less between 0.05 and 0.10 are attainable. Of course, performance will be based on surface finish, load, travel distance, mated surface, temperature, and other considerations. But the benefit of achieving frictional characteristics of virgin lubricants, as ceramic coatings, can be enormous.
Keep in mind this coating process will likely result in coating all surfaces. Unless, that is, masking is performed. Be sure, too, that your work-piece is free of dissimilar metal, steel for example, which is incompatible with the coating process.
A variety of coating thickness is attainable, from 0.0001 to 0.003 inch. Just be sure you are clear of the performance benefits you really need. Since these coating processes are conformal in nature, they have little leveling capability. Do consider this when choosing your material and specifying your finish. Generally, highly polished finishes can be ‘roughened’ ten to twenty micro-inch, on average. So, over-polishing may be required of the virgin metal, or post-polishing of the coating.