Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Mon, 21 Oct 2002 15:23:35 -0400
Message-ID: <redirect-1841524@logan.com>
Reply-To: <DAP@DParsons.com>
From: "Don Parsons" <DAP@DParsons.com>
Subject: RE: [LML] Post curing wet layups
MIME-Version: 1.0
Content-Type: text/plain;
	charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Importance: Normal
In-Reply-To: <list-1841423@logan.com>

Dan,

There are several variables involved that effect the answer to your
question. I will gear most of my answer toward Jeffco 1307-LV resin with
either Jeffco 3102 or 3156 hardener combinations to lock down some of the
variables. The data sheet from Jeffco for those product combinations specify
a cure schedule of "Gel at ambient + 2 hours at 212 degrees F, or 7 days at
77 degrees F". You can use temperature/time combinations in between. As
temperature is adjusted down, time should be adjusted up correspondingly.
Some important points to keep in mind...

- It is possible to post cure too hot. However, as long as you are within an
acceptable temperature range, you don't hurt anything by going longer than
needed.
- Bring the heat up and back down slowly.
- Heat the part evenly.
- As the temperature you use increases, the importance of providing support
for the part also increases to make sure it does not loose shape as it
reaches higher temperatures. Given this point, it may be better to shoot for
temperatures in the 120 to 150 degree F range than the higher possible
temperatures. Higher temperatures will likely need some sort of active
heating source, and it may be difficult to have consistent temperatures over
larger parts.
- DO NOT POST CURE your aircraft composite parts IN DIRECT SUN LIGHT! You
can put parts inside an enclosure that are heated by the sun though. Just
make sure UV light is not shining on the part. Your garage attic is a
potentially good "post cure enclosure". Sun heated enclosures naturally heat
and cool slowly.
- When determining the temperature you will use, make sure that it is not
too hot for the core material in the part. With the Nomex core we are using,
this is not a problem. However, if you are using a foam core, this will
likely substantially lower the possible maximum temperature.

Given some of the points above, using a heat gun would not be a good
solution for a couple of reasons. First, you likely won't be holding it in
position long enough to make much of a difference. Second, it would be
difficult to keep from over heating the part. Third, it would also be
difficult to maintain temperature consistency over the part.

The resin/hardener combination is a very important variable. The times &
temperatures can drastically change if either are changed. So... if you are
using some other resin/hardener combo, the principles of what I included
above still apply, but the 2 hr @ 212 or 7 days @ 77 are no longer valid.

Don Parsons
Super ES
Houston, TX