Dupont Teflon, a trademarked name, is also available in polytetrafluoroethylene (PTFE).
This fluoropolymer, also manufactured by others, is one of the most widely recognized compounds used throughout the world. Its applications are near endless.
Dupont PTFE is a product formed by free radical vinyl polymerization of tetrafluoroethylene (TFE) and is known to have a continuous service temperature of 500 F. Much higher temperatures can be satisfactorily sustained for shorter exposures.
Mechanical properties include, but are not limited to, flexibility at low temperatures, stability at high temperatures, and low coefficient of friction. Understand, too, that the information below does not take into account wear factors, which can be dramatically improved upon by internal or external material reinforcements of PTFE dispersion.
There have been many practical non-lubricated mechanical systems developed with coefficient of friction as low as 0.05-0.08. Even at higher dynamic P-V (a pressure, rub-velocity combination of 8,000 to 10,000) a coefficient of friction around 0.10 is feasible.
These resins exhibit exceptionally low friction in non-lubricated environments, especially at low surface velocities and pressures higher than 5 pounds per square inch. The coefficient of friction actually increases with sliding speed up to 100 feet per minute, under all pressure conditions. It is this phenomenon that prevents ‘stick-slip’ tendencies. In addition, no ‘squeaking’ or noise occurs, even at the highest speeds. Above 150 feet per minute, sliding velocity has little effect (on friction) at combinations of pressure and velocity below the composition’s PV limit. Static friction of Dupont Teflon PTFE resins decrease with increasing pressure.
PV limits define the maximum combinations of pressure and velocity at which these materials will operate continuously 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) for PTFE in dry lubrication, low friction applications, you must consider creep and cold flow.
Generally, a plastic material subjected to continuous load experiences a continued deformation with time 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 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.