I have worked a little with teflon as a machinist. It is hard to hold in a chuck
of course and drills weirder than most plastics. You should try tapping a hole
in it. I wish I had known about these differences then as I would have looked for
differences in their machinability.
Anyway my question is to Henry. How do the two Teflon's compare as RF
insulators? And what would be a simple test for telling the two apart?
Henry Spencer wrote:
> On Tue, 9 Jul 2002, John Carmack wrote:
> > ...Mark Henry (ex Beal propulsion engineer) had mentioned to us once
> > that not all Teflon is completely peroxide compatible, and this seems to be
> > an example of that...
>
> Hmm, yes, definitely noteworthy...
>
> Yes, there are different kinds of Teflon, partly because they're made by
> different processes, partly because there is some custom tailoring of the
> polymer for specific properties. The two flavors most likely to be seen
> in ordinary contexts are Teflon PTFE and Teflon FEP.
>
> Teflon PTFE is the original Teflon, as stubbornly chemically inert as any
> solid material can be (unless you heat it too far). PTFE is Poly Tetra
> Fluoro Ethylene -- you make CF2=CF2 first (easier said than done because
> the fluorine really wants to add to that double bond to make CF3-CF3), and
> then polymerize it.
>
> Teflon FEP is easier to make and almost as good. And as we all know,
> "almost" means "not". FEP is Fluorinated Ethylene Polymer, i.e. they take
> polyethylene and try to replace all the hydrogens with fluorines. I'm not
> sure whether the problem is that they don't entirely succeed, or that they
> weaken the polymer in the process of succeeding, or both or neither. It's
> pretty good but not the equal of PTFE.
>
> My guess would be that the usual valve hardware is Teflon FEP, and what
> you want for long-term peroxide compatibility is Teflon PTFE. (It's also
> possible that the valve hardware is some slightly-modified variant, custom
> cooked to reduce problems with cold flow. Teflon is notorious for trying
> to ooze out when put under pressure.)
>
> > Unfortunately, industrial suppliers don't make a distinction.
>
> Lab-equipment suppliers do -- that's where I first ran into it -- but
> whether you can find an industrial valve supplier who does (specialist
> chemical-industry suppliers?) is another question.
>
> Henry Spencer
> [EMAIL PROTECTED]
>
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