Graphite Low Friction Coatings – Surface Engineers, Learn When To Choose

Graphite low friction coatings are more widely recognized today as dry film lubricants. Certainly, they have their similarities to dichalcogenides, like molybdenum powder disulfide (MoS2) or tungsten disulfide (WS2): All have a layered lattice, a hexagonal structure, bonds stronger internally than with neighboring molecular planes.

But unlike the others, carbon graphite is not intrinsically lubricated. It is moisture or other condensate vapor, such as hydrocarbons, that gives graphite its surface lubrication. Consequently, performance is exceptional in a normal air atmosphere, but not at high altitudes or in vacuum. And once temperatures are high enough to create desorption, except when relevant oxides are available, dry graphite will result in higher friction.

So, why choose graphite?

Because, at service temperatures over 700 (F) for MoS2 or 550-600 (F) for Teflon (PTFE), these compounds will decompose. Whereas with graphite, though CO2 oxidation products begin to form above 900 (F), lubrication is still feasible. In fact, service temperatures to 1200 (F) are realistic.

And while friction will vary with humidity, sliding condition, and other parameters, friction coefficients of 0.02-0.04 are quite realistic. Especially with higher loads (up to 50,000 psi), faster surface speed, or combinations of both, whereas plastic compounds like PTFE will cold-flow.

Graphite can be applied in a number of economic ways. These include a simple rubbing or burnishing, dipping (colloidal dispersion), impact or impingement (powdered graphite). Thickness can vary from less than 0.0001 inch, in pure form, to 0.0005 inch and up, as resin-bonded or ceramic-based lubricants.

So, you have decided on graphite . Now, though, you would like to know which surfaces to coat.

While differences may prove negligible, consider this: Better performance versus longer wear life. Generally, coating both surfaces will increase your wear life. But coating one surface only will yield greater performance from your graphite low friction coating.

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