Hello Larry:
Actually, the main aerospace criteria for the wider use of Tefzel has to do
with the overall weight and ampacity of the wiring system. The Tefzel
dielectric permits thinner walls, with higher continuous voltage ratings,
which translate to lower weight. A conductor insulated with a 6 mil wall of
ETFE will have a continuous voltage rating of 600 Vrms. A conductor
insulated with a 6 mil wall of TFE will have a continuous voltage rating of
250 Vrms (350 VDC). Most of the Tefzel in aerospace is probably irradiated
as well, with very tough cross linked bonding. This improves the cut thru
resistance of the insulation, and enables the bundles to avoid abrasion
damage from cable clamps, and where the bundles pass thru bulkhead fittings.
These aerospace applications require really high reliability, due to
environment considerations of vibration, temperature, thermal shock, fluid
compatibility, notch sensitivity, abrasion resistance, etc.
The cut thru resistance of TFE is rated as only FAIR, while Tefzel is rated
as EXCELLENT.
For use in really high current applications, Teflon may still be used, in
circuit sizes such as 10 and 12 AWG. Generally, to improve the abrasion
resistance of these circuits, a mineral filler is used along with the
lubricant during the mixing of the Teflon paste, for ram extrusion under
very high pressure.
Lower cost also enters into the picture, with Tefzel capable of being high
speed extruded in long lengths, rather than the slow high pressure ram
extrusion process required for Teflon systems. TFE requires the use of
either silver or nickel plated conductors, due to the high sintering
temperatures used to cure the TFE paste. Tefzel insulation may be extruded
over lower cost tin plated conductors because of the high speed melt
extrusion process, carried out at lower temperatures.
Due to the differences in densities, again Tefzel has an advantage in lower
weight. TFE has a density of 2.20 and Tefzel has a density of 1.70 gm/cc.
The greater thermal stability of the Fluropolymers, permits the use of
higher metallic conductor temperatures, and hence, greatly increased
ampacity for the wiring system. Higher ampacity and small metallic
conductor sizes, again translates to lower weight, the driving force in
aerospace wiring. Very small sizes carry large currents in commercial
applications, and even smaller sizes carry high current in military
applications using copper alloys.
The main copper conductor used with Tefzel for most airframe and engine
harness wire is 19 strands of 34 AWG. With a tin plated conductor, this
single wire circuit in an ambient environment of less than 30 degrees C,
will hold 14 amperes in free air, and would be derated for use in a bundle
from there. Silver plating will increase the ampacity to about 17 amperes.
73 and Happy DXing,
Mike
W2AJI
----- Original Message -----
From: "Larry Benko" <xxw0qe@comcast.net>
To: "Harold Mandel" <hmandel@barantelecom.com>
Cc: <amps@contesting.com>; "Rich Schmuke" <rdj@wildblue.net>
Sent: Monday, July 28, 2008 11:18 AM
Subject: Re: [Amps] Wire
> I had responded to Rich last week but I guess he either didn't like my
> answer or just wanted more opinions.
>
> Look at
>
http://www.welchfluorocarbon.com/techdata.htm#Table1FluoropolymerSelectionGuide
>
>
> for more than you probably want to know. I measured some 20 or 22 gauge
> twisted Teflon and Tefzel wire a few years ago and couldn't see any
> difference other than Tefzel has a slightly higher dielectric constant
> (2.6 vs 2.2). Tefzel is not rated to quite as high temperature but both
> are plenty high enough. :)
>
> Also in may last job we used only Tefzel wire in aircraft products. I
> think it is becoming more common that Teflon insulated wire. Also the
> breakdown voltage is higher than Teflon and the material is harder which
> is good for wire that is wound against a surface. Both Teflon and
> Tefzel are DuPont registered trademarks.
>
> 73, Larry W0QE
>
>
> Harold Mandel wrote:
> > Rich
> >
> > [snip]
> > Does any know a reason why TefzelR ETFE insulated wire would not be as
> > good or better because the dielectric strength is even higher...
> > [snip]
> >
> > A balun will generate heat.
> >
> > Manufacturers of popular baluns realized
> > stations would attempt to load RF into
> > huge mismatches and because they wanted
> > to reduce warranty claims, went for the
> > cheapest solution that would withstand
> > heated wires the longest.
> >
> > While PTFE insulated wire is a common
> > choice for commercial balun products there
> > are always upgrades in quality.
> >
> > Why not build such a device and test it
> > using your ETFE stuff? Mismatch it
> > and report on its ability to handle
> > high temperatures.
> >
> > I for one would be very interested in
> > insulation that would surpass PTFE.
> >
> > Hal Mandel
> > W4HBM
> >
> >
> > _______________________________________________
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> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
> >
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