PTFE Plate

PTFE plate in natural, cut to size and sold by the square foot.

PTFE - polytetrafluoroethylene - is the material people reach for when nothing else will survive the chemistry. It resists very nearly everything: strong acids, strong alkalis, solvents, oxidizers, chlorine. It has the lowest coefficient of friction of any solid, nothing sticks to it, it insulates to over 10^18 ohm-cm, and it works from cryogenic temperatures up to 500F continuously. No other thermoplastic covers that span.

What you give up is mechanical. PTFE is soft, it is not stiff - flexural modulus around 72,000 psi against acetal's 420,000 - and it creeps under load at room temperature. It is a chemical and thermal material, not a structural one, and most PTFE that fails in service fails because it was asked to hold a load.

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.

Food contact: available in grades compliant with FDA 21 CFR 177.1550, perfluorocarbon resins. Two things worth knowing about that. The regulation controls by melt viscosity, thermal instability index and extractives - properties of a specific lot from a specific mill, not of "PTFE" generically - and paragraph (e) attaches an actual extraction test to any molded article over 100 square inches and 1.27 mm thick, which covers most plate. So compliance is the mill's dated declaration, which we will pass on to you; it is not something a distributor can originate. We do not claim NSF listing, and USDA does not approve materials at all - it requires finished articles be made of FDA-compliant ones.

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.

The governing specification for molded PTFE sheet is ASTM D3294. Type is the property level: I premium, II general purpose, III mechanical, IV utility with no electrical requirement at all. Grade is resin origin: 1 virgin, 2 reprocessed. Class is thermal dimensional change: A is the tight class at 0.5 percent, B is 5 percent, C has no requirement. One trap worth flagging, because it catches people who buy both rod and plate: the Class letters run in opposite directions in the two standards. On rod, Class B is the tighter class; on plate, Class A is. Also note that only Type I sheet carries a porosity requirement, and sheet for tank lining must be Type I at specific gravity 2.19 to 2.22.

It goes into chemical-resistant seals, gaskets and diaphragms, valve and pump components, manifolds and fittings, semiconductor process parts, laboratory and scientific equipment, high-temperature insulators and bushings, slide plates and bearing pads, release surfaces, and electrical insulation for wire, cable and circuit boards.

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.