PTFE flattening characteristics
PTFE flattening characteristics
(OP)
I am a manufacturing engineer trying to come up with a standard for determining the proper o-ring configuration for seals we use. I have no formal plastics training, but I am a mechanical engineer so I understand most of the physics behind what is going on. Can someone tell me if there isan easy way to determine how much a PTFE o-ring will flatten under a given pressure? How much does the cross section of the o-ring change the results. Thanks





RE: PTFE flattening characteristics
PTFE "O" rings usually have a core of Viton or similar elastomer and just a thin layer of PTFE.
To answer your question, PTFE will flatten indefinitely.
Cheers
Harry
RE: PTFE flattening characteristics
RE: PTFE flattening characteristics
Realistically, the deformation is slow but constant.
I am sure DuPont will publish a co-efficient for creep or provide graphs for creep, time, temperature and load for various grades of PTFE.
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RE: PTFE flattening characteristics
PTFE is very nearly a true plastic, except for some strangeness having to do with it being sintered from powder.
To give you an example of the plastic deformation that's possible, I once worked on a line of small ball valves. When you take them apart, the ball seals have spherical surfaces that mate perfectly with the ball, or did before you took it apart. But they're not molded that way; they're cut from round bars in the form of square section rings, and crushed against the ball as the housing is assembled around it (with a big wrench). I.e., the strain is very large, but they survive it.
Of course, just like a rubber o-ring, they're not compressible; you can change the shape of the cavity they're in, drastically, but you can't reduce its volume below the plastic's volume; something else will break. In the case of my ball valves, when the tolerances drifted the wrong way, the brass housing would split on assembly.
Mike Halloran
Pembroke Pines, FL, USA
RE: PTFE flattening characteristics
RE: PTFE flattening characteristics
FEP teflon can be made leakproof to superfluid helium using flat ended cylinder (1.5" diameter with 0.020 flat) to flat surface. long term effects not known (RSI sept 72)