PTFE under load at elevated temperature? 2

[hobbs101]

I'm designing some PTFE mounts. These mounts will be under a compressive load of 0.6 MPa and will be at a temperature of 150degC. Knowing that PTFE has a 'deflection temperature', the PTFE will compress more due to the elevated temperature.

My supplier of the material tells me -

"We don’t have any figures on compressive strength at 150°C, but we assume that even at this temperature with involved loads, there should not be any problems also with the unfilled grade of PTFE. According to values in literature, at 100°C, PTFE deforms of approx 1%, if we apply a constant load of 1.4 Mpa for 100 hours"

What I'm worried about is the '100 hrs'. In my design, the PTFE will be under load and at temperature for many 1000's of hrs. Will it continue to deflect until it is flat as a pancake?!

Thanks.

 

[Demon3]

I typed "creep of PTFE" into Google and the first hit is the PTFE Handbook

http://www.rjchase.com/ptfe_handbook.pdf

which is by DuPont.

Page 16 gives the information you need and a recommendation to use 40% fiber filled PTFE for temperatures over 149C.

As PTFE is used in gaskets this has been well studied.

Dr. Chris DeArmitt

Plastics consultant to the Fortune 500:

http://www.phantomplastics.com

Webinars on plastics, fillers & impact modification:

http://www.plastictraining.com

 

[CoryPad]

Yes, the part will continue deform.

 

[hobbs101]

Thanks, the PTFE handbook is really useful. I suspect that's where my supplier got his information.

From figure 8b on page 20, it seems as though the PTFE mounts will continue to compress (creep) as time goes on. The design life is about 30000 hrs, so from this graph I can expect somewhere in the region of 3% strain.

One aspect of the design I haven't yet mentioned is that the load is applied to the mounts for about 200 hrs and is then removed for about 30 hrs. During the 30 hrs the temperature will also return to ambient. (This cycle then repeats over the course of 4 yrs). Will the mounts have chance to recover from this compression, or is the creep permanent?

Thanks

 

[IRstuff]

Page 16 of that handbook seems to be relevant; the question unanswered is how long it takes to recover.

TTFN
faq731-376

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[Compositepro]

Creep is not recoverable, and is distinct from elastic deformation, which is recoverable.