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Re: Linseed Oil/Mylar Cap
Tesla List wrote:
>
> Original Poster: twftesla-at-uswest-dot-net
>
> In a message dated 5/29/1999 1:17:21 AM Pacific Daylight Time,
> tesla-request-at-pupman-dot-com writes:
> X-Sender: twftesla-at-pop.dnvr.uswest-dot-net
> X-Mailer: QUALCOMM Windows Eudora Pro Version 4.1
> Date: Sat, 29 May 1999 20:51:53 -0600
> To: tesla-at-pupman-dot-com
> From: BillEaver-at-aol-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
> Subject: Linseed Oil
> Mime-Version: 1.0
> Content-Type: text/plain; charset="us-ascii"
>
> A very nice way of saving lives from heavy burns and electrocution you folks
> have here at this "ring" . My hat is off to you people...For a long time now
> I have been reading many posts from the other experimenters trying to get the
> info I need so as to not waste time asking a question that was answered
> already. Well I have not seen
> any other zany person making a poly cap out of old aircraft blue prints (made
> of some tuff type of plasic that they call "mylars") and use linseed oil as
> the air barrier that I could buy on sale 5gal for $30.00. . Now...the reason
> I ask is my life...I have found that linseed oil is a sure fire way to set
> your garage on fire if you leave it on a rag... in fact on T.V. they show a
> lady soak a rag in linseed oil, wrap it in a foil ball,
> put it in a foam cooler and 12 minutes later the thing bursts into
> flame...spontaneous
> combustion in a bad sort of way...Now at my work they use linseed oil to coat
> the inside of pipe type structures on aircraft of every kind so it won't
> corrode. My guess
> is that if there is no porous matter to feed the oxygen to it your not going
> to flame-on. The oil container/cap is a home made fiberglass box with a 1/2
> inch glass plate for the bottom. So that is my question, can I make a cap
> without making a cap/bomb ? I looked up linseed oil in the dielectric
> constant table and it says 3.2-3.5
> Thanks for any help...
> Denis Despins KC6TRW
Denis,
I really wouldn't recommend going this route for several reasons. Mylar
(polyester) will rapidly heat up inside your capacitor because it's very
lossy at RF frequencies. A "polyester" cap is NOT the same as a "poly
cap" on this list - "poly" designates a low or high density polyethylene
(LDPE, HDPE), or polyproylene (PP) dielectric. If your capacitor should
happen to overheat and/or break down internally, you may rupture the
container. Hot linseed oil leaking from your cap may then represent a
significant fire hazard once it hits the oxygen in the air. It also
turns out that linseed oil also has some other undesireable electrical
and physical properties (from "Insulating Materials for Design and
Engineering Practice", by Frank Clark, John Wiley & Sons, 1962)
Linseed oil is a lousy dielectric oil for RF and other AC capacitors. If
permitted, it will absorb up to 25% of its weight in oxygen, forming an
elastic solid called linoxyn, and this effect is increased in the
presence of ultraviolet light (such as from corona...). It also
polymerizes over time in the presence of heat (such as from higher
dielectric losses). Linseed oil is about 10X as lossy as mineral oil at
RF frequencies, and worse yet, this loss tends to increase over time in
service.
Mineral oil typically sells for $25-45 for a 5-gallon pail, and it does
NOT self-combust. Polyproplylene or polyethylene is comparatively
inexpensive (much less expensive than Mylar unless you're getting the
Mylar for free). If you DO decide to go the mylar-linseed oil route,
you'll basically create a poorly-performing, potentially dangerous tank
cap that will only further degrade in performance with time. And I
surely wouldn't "fire it up" indoors... :^)
Safe cappin' to you!
-- Bert --