hi,
do you have a cold trap between your vacuum pump and the bell jar? although liquid nitrogen would be the best coolant to use in your trap, we used isopropyl alcohol and dry ice. the oil in the pump also needs to be clean. it may go without saying, but i'll say it anyhow, i hope you have an implosion shield around your bell jar. this recommendation to cant off the bubbly part of the degassed resin mix sounds very hoky to me.
phil
-----Original Message-----
From: Hinners Hans Civ WRALC/LYPME [mailto:[log in to unmask]]
Sent: Wednesday, September 13, 2000 1:47 PM
To: [log in to unmask]
Subject: Re: [TN] Potting Compounds
Hi Phil N. Mary and Phil C.,
We mix in atmosphere and then placed it in a vintage bell jar vacuum system.
(And everybody knows when I say vintage I mean vintage.) The thought has
occurred to get a newer/smaller vacuum system - quicker, stronger pump, with
say a calibrated pressure gauge.
I've seen the "whipped cream" several times. The entire mixing cup gets
quite a head of foam. You bring it back up to 1 ATM, the foam head
collapses, and there are still lots of tiny bubbles.
We've been using PR-1592 successfully but in much larger batches 1000+ grams
versus 50 grams for this stuff. Desoto mentioned using much more than was
required and discard the more bubbly sections.
Thanks for the tips Mary, Phil C. - I'll check that site out tomorrow.
Hans
-----Original Message-----
From: Phil Nutting [mailto:[log in to unmask]]
Sent: Wednesday, September 13, 2000 3:42 PM
To: 'TechNet E-Mail Forum.'; 'Hinners Hans Civ WRALC/LYPME'
Subject: RE: [TN] Potting Compounds
Hans,
Are you mixing this material out on the bench or in a vacuum mixing system?
When mixed on the bench, even without trying, you can whip the stuff up like
whipped cream. With a 2 part potting epoxy we use we've had great results
when we mix in a vacuum and then pour into the molds while still in the
vacuum. But then we have a 3.5 hour cure cycle at 90°C.
Just one man's opinion. Of course there could be something wild going on
between the A & B materials... nah, that's two far out.
Regards,
Phil Nutting
-----Original Message-----
From: Hinners Hans Civ WRALC/LYPME [mailto:[log in to unmask]]
Sent: Wednesday, September 13, 2000 3:27 PM
To: [log in to unmask]
Subject: [TN] Potting Compounds
Hi All,
I have a rare treat! - I get to recommend a substitute potting compound for
a component we build. We pot several discrete components - it's not more
than 2 cm long x 1 cm wide x 1.5 cm tall.
The drawing called for a Courtaulds Aerospace (now PRC DeSoto) compound
PR-1660, but that was replaced by PR-1664-D. Even with several cycles in a
vacuum chamber we can't get the bubbles out of the mixed compound before it
sets up (15 - 20 minutes). Part A pours like honey even before you start
mixing with Part B. We plan to use an injection mold or a simpler pour
mold. I plan to talk to PRC Desoto later today but I seek words of wisdom
from the Group.
So, does anyone know of a honey colored potting compound that doesn't
generate bubbles as it cures? Oh yeah, something approved by an IPC or an
old Mil Spec would be an added bonus.
Thanks Gang!
Hans
~~~~~~~~~~~~~~~~~~~
Hans M. Hinners
Materials Engineer (Process & Manufacturing)
Warner Robins Air Logistics Center
Avionics Production Division
Precision Attack/ Radar/Manufacturing Branch
Engineering Section
380 Second Street, Suite 104
Building: 640, Mail Stop: LYPME
Robins AFB, GA 31098-1638
Voice: (478) 926 - 1970 Fax: (478) 926 - 7164
mailto:[log in to unmask]
http://www.robins.af.mil
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