Teflon Low Friction Coatings
Teflon low friction coatings can be an excellent means to create low friction surfaces. Compounds that incorporate PTFE (polytetrafluoroethylene) are widely recognized for their performance.
PTFE, formed by free radical vinyl polymerization of tetrafluoroethylene (TFE), is known for its high heat stability. Service temperatures from cryogenic to to 550 F are attainable.
This provides a large ‘window’ of applications requiring low friction.
Teflon low friction coatings have reported coefficients of friction as low as 0.05-0.08. Of course, friction being a system-dependent parameter, must take into account load, distance of displacement, frequency of travel, surface finish, temperature, mated material characteristics, and other factors.
Generally, under higher dynamic PV (8,000 to 10,000) conditions, a coefficient of friction less than 0.10 is attainable.
Teflon low friction coatings exhibit exceptional performance in otherwise non-lubricated environments. This is especially evident at low surface velocities, pressures greater than 5 pounds per square inch. With sliding speeds up to 100 feet per minute, the coefficient of friction actually increases under all pressure conditions. It is this phenomenon that gives Teflon its characteristic ‘stick-slip’ tendencies.
Even at higher speeds, no noise will occur. For example, over 150 feet per minute, at various combination of increasing pressure and sliding velocity, below its PV limit, there will be little effect on friction. Other characteristics that make DuPont Teflon, PTFE, unique is that static friction will decrease with increasing pressure.
PV limits define the maximum combination of pressure and velocity at which these materials will operate continuously for low friction, without lubrication. PV limits for PTFE approach zero at temperatures between 550F and 600 F. However, useful PV limits must take into account the composition’s wear characteristics and allowable wear for the application.
When considering Dupont products (or other manufacturers) based on PTFE, in dry lubrication, low friction environments, you must consider creep and cold flow.
A plastic material subjected to continuous load, experiencing a continued deformation with time, is called creep or cold flow. Deformation can be significant, even at room temperature or below; hence, the name "cold flow".
Creep is the total deformation under stress after a specified time in a given environment beyond that instantaneous strain which occurs immediately upon loading. Independent variables affecting creep are time under load, temperature, and load or stress level.
As long as the stress level is below the elastic limit of the material, performance of Teflon low friction coatings is sustainable. And beyond a certain point, creep is small and may be neglected for many applications. In many cases, too, there is compressive recovery from various percentages of strain. Nearly complete where the original strain does not exceed the yield strain.
Again, keep in mind the information presented here for Teflon doesn’t account for forms of reinforcement available today. ‘Internal’ reinforcements such as an array of binders and fillers, and ‘external’ forms of reinforcement that can include plating, anodizing, thermal spray, or other composite coating processes developed.