It's worth mentioning with the 2nd point I was making there is there are
various types of "Teflon" to suit various applications. PTFE can't be
injection moldable or extrudable but some other grades of Teflon can be. So,
(for example) if you to embark on ... say... a cryogenically compatible
composite vessel project, you might want to look pretty seriously in the
Teflon direction (you might not want to too) and the chances are that PTFE's
processing properties would automatically render "Teflon" out of the
question, but perhaps there are other grades of Telfon that actually provide
a viable option.
Troy
-----Original Message-----
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On
Behalf Of Troy Prideaux
Sent: Tuesday, 26 April 2016 8:59 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Portland State Aerospace Society
Henry said:
The bigger issue is the one Ben mentioned: make sure the materials are
okay for cryo use. In particular, ordinary steel is flat out unacceptable
for anything that *might* get cryo cold, because it goes brittle. Brass,
bronze, stainless, nickel alloys are all generally okay. And most
elastomers stop being elastic at cryo temperatures, so things like seals
generally need to be Teflon aka PTFE (which retains some flexibility).
Good advice, however, I'm not sure I'd call anything "flexible" at LOX
temperatures. From my understanding, PTFE is quite hard at those temps, but
does retain some toughness ie doesn't suffer the same brittleness that other
room temperature plastics and rubbers suffer.
Minor point: Telfon (a trade name) is aka (commonly) PTFE, but it's also
important to point out there are many different materials that fall under
the tradename of "Teflon" of which PTFE is only one of and there's also a
multitude of materials that aren't labelled as "Teflon" but have similar
properties to that family - eg. PCTFE which is also used in cryogenic
sealing applications.
Troy.
