PTFE — Frequently Asked Questions
Answers to the questions that come up most often when specifying PTFE parts, written for engineers and buyers rather than as marketing copy.
What temperature can PTFE actually take?
The usual figure quoted is −200 °C to +260 °C, and that is a fair working band. The nuance is that mechanical properties fall away long before the upper limit: PTFE softens progressively, and creep accelerates sharply with temperature. A part that is dimensionally stable at 20 °C under load may not be at 200 °C under the same load. Treat 260 °C as a material ceiling, not a design condition.
What attacks PTFE?
Very little. The practical exceptions are molten alkali metals, elemental fluorine, and some fluorinating agents at temperature. For almost every industrial acid, alkali and solvent, unfilled PTFE is unaffected.
The catch is that filled grades are only as resistant as their filler. A bronze-filled part fails in acid that virgin PTFE would ignore. If chemical resistance is the reason you chose PTFE, check the filler, not the base polymer.
Why does PTFE creep, and what can be done about it?
PTFE cold-flows — it deforms permanently under sustained load, even at room temperature. This is the material’s main design limitation and the reason most fillers exist. Glass, carbon and bronze filling all reduce creep substantially. Where a joint must hold load long-term, either specify a filled grade, energise the seal mechanically, or design the joint so it can be retightened.
Virgin or filled — how do I decide?
Choose virgin when chemical resistance and the lowest friction lead, and load is modest. Choose filled when the part carries sustained load, wears, or must hold dimension. Then choose the filler by what the duty needs: glass for creep, bronze for load and heat, carbon for wet and anti-static service, graphite for protecting a soft counterface.
Is PTFE food safe?
The resin can be. FDA 21 CFR 177.1550 lists PTFE for food contact, and food-grade parts are moulded from listed resin. That is a property of the material, and the material certificate traces the resin lot. Filled grades are generally not food-contact suitable unless the filler is specifically approved.
Why is PTFE compression moulded rather than injection moulded?
PTFE has an extremely high melt viscosity and does not flow like a thermoplastic. It is compacted as a powder into a preform, then sintered above about 327 °C so the particles coalesce. This is why PTFE tooling and PTFE presses look nothing like injection moulding equipment.
How much does PTFE shrink during sintering?
Enough that it must be designed for — the tool is cut oversize and the shrinkage allowance depends on the grade, the section and the sintering cycle. Filled grades shrink less than virgin. This is why a supplier will want the finished dimension and tolerance rather than the mould dimension.
What should I send with an enquiry?
Drawing or sample, grade if you know it, quantity, and the duty — media, temperature, pressure and whether the load is sustained. The duty matters more than the grade: if you send the conditions, the grade discussion can happen against your actual application.
Related pages
Terms used above are defined in the PTFE glossary. For grade selection see virgin PTFE, glass-filled PTFE and bronze-filled PTFE. For the process side, see PTFE powder compaction behaviour. Send a drawing to HEMSUN for a scoped quote.