PTFE Rod, Reprocessed

Reprocessed PTFE rod in natural, cut to length and sold by the foot.

This is reprocessed PTFE - ASTM D1710 and D3294 Grade 2, which is the standards-defined designation for stock made using reprocessed resin rather than virgin. That is a real grade with a formal definition, not a euphemism for off-spec material, and it is the economical way to buy PTFE for general industrial work.

What it keeps is everything that comes from the polymer itself: the chemical resistance, the low friction, the non-stick surface, the 500F continuous service rating, the cryogenic low end. For a bushing, a wear pad, a backing ring, a gasket or a slide strip, those are the properties you are buying and they are unchanged.

What it gives up is mechanical and electrical headroom. Published tensile strength runs 19 to 50 percent below virgin depending on whose figures you read, elongation at break is down anywhere from 7 to 63 percent - that is the biggest single loss and it matters most for seals and gaskets that have to stretch - and dielectric strength falls 7 to 54 percent. Hardness actually goes up slightly. Neither standard imposes a porosity requirement on reprocessed material.

And here is the line, stated plainly because it is the part that matters: this material is not supplied as FDA food-contact material, not 3-A Dairy (the dairy standard allows virgin material or a mill's own clean in-process scrap, but not bought-in reprocessed resin), not medical grade, and not for premium electrical insulation. Nobody can create those statuses for reprocessed stock by asserting them. If you need food contact, purity, traceability or dielectric performance, buy the virgin grade - we stock it in the same sizes.

It is for seals, gaskets, bushings, wear pads, backing and guide rings, slide strips, spacers and general machined industrial parts where PTFE's chemistry and friction are the point and the paperwork is not.

Cold flow is the thing to understand before you specify it. Under about 2,000 psi for 24 hours at 73F, virgin PTFE deforms 10 to 13 percent, and when you take the load off it recovers only about half - 6 to 7.5 percent is permanent (ASTM D621). That is at room temperature; raise the temperature and it gets dramatically worse. No other common engineering plastic behaves this way at ambient. If your part has to hold a dimension under sustained load, design to the compressive strength at 1 percent deformation - about 995 psi for virgin PTFE - and not to compressive strength at yield. Anything approaching 2,000 psi sustained will cold-flow by double figures. Where that is a problem, a filled grade is the answer: 25 percent carbon-filled cuts deformation under load to 5 to 7 percent.

One quirk that causes more tolerance arguments than anything else in this material: PTFE passes through a transition near room temperature that changes its volume by 1 to 1.5 percent - roughly 0.3 to 0.5 percent on a linear dimension. A part measured in a 65F inspection room is genuinely a different size in a 75F process. For critical dimensions, measure at service temperature or compensate for it.

Thermal expansion is high - roughly ten times that of metals - and it rises with temperature, so a single published figure is wrong at every temperature but one. Published values run 7.5 to 8.9 x 10^-5 in/in/F at room temperature and climb 50 to 75 percent by 480F. Parts sized at room temperature will not meet spec hot, and the reverse holds too.

Temperature: 500F continuous is unanimous across every source, and PTFE stays useful down to -328F (-200C), with some sources citing -400F. Heat deflection is 250F at 66 psi but only 132F at 264 psi - read the load with the number, because PTFE softens early under load. It is UL 94 V-0.

It machines easily with sharp tools and good chip clearance, but it is soft and it moves, so it will not hold a tolerance the way acetal does. Heat concentrated at the cut makes it swell locally, which is how you get overcuts, undercuts and tapered holes. For close work, rough it out, leave 0.015 to 0.030 inch, stress relieve, then finish cut.

There is no adhesive and no solvent that will bond untreated PTFE - that is the point of the material. Parts are mechanically fastened, or the PTFE surface is chemically etched first, after which it bonds normally with transfer adhesive, epoxy or a liquid adhesive. We stock etched plate for exactly that. PTFE also cannot be melt welded in the usual way, since it has no conventional melt-processing window - it is compressed and sintered into billets, which is why stock shapes are molded or ram-extruded rather than injection molded.

Thermal decomposition - worth reading even if you have worked with PTFE for years. Continuous service is 500F; above roughly 625F PTFE may give off hazardous fumes, and at 840F and above it can form toxic fumes including hydrogen fluoride and carbonyl fluoride, with perfluoroisobutylene above 890F. That leaves only about 125F between the top of the service range and the start of fume evolution. Inhaling decomposition products causes polymer fume fever, a temporary flu-like illness with fever, chills and cough that normally clears in 24 to 48 hours. Do not overheat it, use local exhaust when machining or grinding, and use coolant. And the one everybody leaves out: do not smoke or use tobacco where PTFE is machined or handled - PTFE residue transferred to tobacco and then burned is a documented cause of polymer fume fever. Exposure limits for the particulate are an OSHA PEL of 15 mg/m3 total and 5 respirable; ACGIH TLV-TWA 10 and 3. Ask us for the Safety Data Sheet.