Poly Expansion is Useful

From: 	Thomas McGahee[SMTP:tom_mcgahee-at-sigmais-dot-com]
Sent: 	Tuesday, December 09, 1997 6:50 AM
To: 	Tesla List
Subject: 	Poly Expansion is Useful

> From: 	baumann-at-proton.llumc.edu[SMTP:baumann-at-proton.llumc.edu]
> Reply To: 	baumann-at-proton.llumc.edu
> Sent: 	Monday, December 08, 1997 4:58 AM
> To: 	tesla-2-at-emachine-dot-com; tesla-at-pupman-dot-com
> Subject: 	Poly surprise
> This is a heads up, for all those that are building poly caps. I got 
> a nasty little surprise this weekend. I had built a flat-plate cap,
> 0.006 mf, made from *lots* of sheets of 6 mil poly. 430+ to be more
> precise. Because I wanted to ensure that the plates were as tight as
> possible, I made tie-straps across the tops and sides of the plate.
> Each individual cap was approximately 10x7x1.5".
> [the plates are between slabs of 3/8" polycarb, you use what you have.]
> I filled it with oil, and and put it away for a few days. when I pulled
> it out, all of my tie-straps had been broken off.
> Why? Because the poly apparenly absorbed some of the oil, and expanded.
> Less than 5%, but for 10", that amounts to 1/2" exapansion, more than
> enough to be a problem. I've reworked the tiedowns, but thought I would
> warn others, as I have not seen this mentioned in any of the
> documentaion for capacitor constrution.  I was using Diala-AX for the
> oil.
> I hope to fire this at full power by the weekend [currently firing
> at about 40%, but not seeing the bubbles I was told to expect, could
> I have all the air out already? I did fill it very slowly, so that
> the oil was always rising via capillary action faster than the oil 
> was coming in [ I used a siphon through IV line, it took 7 hours to 
> siphon the 1 gallon, I did not plan it that way.. it just worked out
> that way] no other way to fill it without a vacuum pump.
> - 
> --
> Michael Baumann  Optivus Technology Inc.|Loma Linda University Medical Center
> San Bernardino, California. (909)799-8308 |Internet: baumann-at-llumc.edu
The poly expansion HAS been mentioned a few times on this list, but
it is always good to have frequent reminders of these things. By the
way, you can actually put this poly expansion to good use :)

If the poly and plates are initially assembled either dry or
with a thin layer of oil applied inside a rigid container such as
one made of polycarbonate, and the container then secured shut, 
with the entire assembly just snug inside the casing and then
filled with oil very slowly as in your case, then eventually the
poly tries to swell 5% and THAT acts as the final *compression* that
we want! That final compression will drive out the bubbles, if
there are any present.  The case, of course, must be able to
take these compressive forces without bulging or leaking. Oil can
be introduced through a hole in the frame of the case. The hole
will need to be plugged after all oil is introduced and
expansion has levelled off.

Fr. Tom McGahee