GlossaryKind of term: Manufacturing termPTFE
What is PTFE?
PTFE is a soft fluoropolymer with very low friction and broad chemical resistance; it creeps under load and expands strongly with temperature.
PTFE, polytetrafluoroethylene, is a fluoropolymer that resists almost all chemicals, has very low friction and tolerates high service temperatures. Typical uses are seals, insulators, sliding elements and parts for chemical and food plant. Because PTFE cannot be extruded or injection moulded like an ordinary thermoplastic, stock shapes are compression moulded and sintered, or ram extruded. Besides virgin PTFE there are grades filled with glass, carbon, graphite or bronze.
How does PTFE behave in clamping, machining and measuring?
PTFE is soft and creeps: under a sustained load, clamping force included, it keeps deforming slowly. It expands strongly with temperature, and close to room temperature it has crystal transitions: one at about 19 °C with a step in volume, and a second near 30 °C. A dimension therefore depends noticeably on the temperature at measurement, right around the reference temperature. Fillers reduce creep and wear but make the material more abrasive on tools, and carbon or bronze changes its electrical insulation.
How does PTFE work in practice?
Holding size in PTFE calls for light clamping over a large contact area, for example in soft jaws, sharp tools with a positive rake and light cuts that generate little heat. Tight tolerances often add roughing and resting or stress relieving, and measuring at an agreed temperature once the part has reached it. How much time that takes, and whether the tolerance is achievable, depends on shape, wall thickness, grade and requirement.
What is PTFE often confused with?
PTFE is not UHMW-PE: both slide well, but PTFE takes higher temperatures and more aggressive media, while UHMW-PE resists abrasive wear far better and costs less. Nor is filled PTFE the same as virgin PTFE: the filler changes creep, wear, friction and electrical properties.
Frequently asked questions
Why is a tight dimension in PTFE hard to hold?
PTFE creeps under clamping and cutting force, expands strongly with heat and has a transition near room temperature that steps its size. Light clamping, cool cutting and measuring at an agreed temperature help; whether it is achievable depends on shape and requirement.
How do you clamp PTFE without deforming it?
With a large, soft contact area, such as soft jaws or a vacuum table, and as little clamping force as the cut allows. Hard clamping gives a part that springs back after release or stays deformed.
When do you choose filled PTFE over virgin PTFE?
When the part must creep less, carry more load or wear less. A glass, carbon or bronze filler makes it stiffer, but wears your tools faster and can change electrical and chemical properties.