Teflon, a tradename of DuPont, is most closely associated with the fluoropolymer, polytetrafluoroethylene (PTFE). With its exceptional release (non stick), low friction or dry lubrication, PTFE is one of the most widely recognized compounds used throughout the world. In fact, its uses are almost endless.
Formed by free radical vinyl polymerization of tetrafluoroethylene (TFE), PTFE is recognized for its high thermal stability. Continuous service temperatures of 500 F are typical, though higher temperatures can be satisfactorily sustained for shorter duration.
Mechanical properties include flexibility at low (cryogenic) temperatures, abrasion resistance and mechanical toughness. Keep in mind that wear factors can be dramatically improved by internal or external material reinforcements. This is especially true using PTFE dispersions.
Non-lubricated mechanical systems have reported coefficients of friction as low as 0.02-0.04. Even at higher dynamic PV limits, (8,000 to 10,000) coefficients of friction of 0.10 or less are attainable. Results will vary with load, rates of travel, distance, surface finish, temperature, and other system-dependent parameters. PTFE resins exhibit exceptionally low friction (in otherwise non-lubricated environments), at lower surface velocities, pressures greater than 5 pounds per square inch. Curiously, friction actually increases with sliding speed up to 100 feet per minute, under all pressure conditions. But it's this phenomenon that prevents 'stick-slip' tendencies. Other benefits include 'anti-squeak' or 'no noise' even at the highest speeds. Above 150 feet per minute, for example, 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 combination of pressure and rub-velocity that materials can operate continuously without lubrication. PV limits for PTFE approach zero at temperatures between 550F and 600 F. Useful PV limits must take into account the composition's wear characteristics and allowable wear for the application. When considering Dupont products such as PTFE for dry lubrication, low friction, you must consider 'creep' or '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 defined as 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.
So 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.
Much of this information pertains to PTFE in a pure (homogeneous) state. So, keep in mind the information presented here doesn't account for composites of PTFE available today. Various reinforcements to create PTFE composites can include 'internal' binders, co-polymers or fillers. Of course there are 'external' forms of PTFE reinforcements, too, including anodize, plating, thermal spray, or other advanced coating processes.
So, understand the capabilities of PTFE. And soon you'll be on your way to surface engineering with Teflon non stick coatings.
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