This might be of interest to Europa builders, Gary is Shell Chemical epoxy
expert.
Graham
Message text written by "Hunter GA (Gary) at MSXSCC"
>[The Canard Aviators's Mailing list]
where near cure. I thought the pot life was 2hrs@ 77F and tack free was
8hrs. The temp in the shop is about 65F. How warm does the shop have to
be to get the resin to cure? Is this a problem or is the shop to cold?
>>
Short and simple - Epoxies do not cure very well below 70F. It is best
to heat your shop to at least 70F and better yet - 75 to 80F.
The published gel of 2 hrs @ 77F is for a 100 gram mass (about 8 oz) in
a paper coffee cup type container. If the quantity you tested is
anything less than that, it will lengthen the gel time SIGNIFICANTLY.
Then you must consider the following.
The reaction rate for an epoxy/curing agent combo doubles every 10C -
Thus, an epoxy/curing agent combination that has a published gel time of
2 hrs. @ 77F (25C) will gel in 1 hr @ 95F (35C). Conversely, the gel
time should be about 4 hrs @ 59F (15C). This temperature / reaction rate
relationship is fairly constant as the temperature increases above 77F
(25C). HOWEVER, as the temperature decreases the relationship is not
so constant and for many resin systems, they simply will not cure at all
below 65F (18C).
Please - control the temperature in your shop. Think of it as
controlling the flame on your welding torch. It needs to be just right
for consistent results. Temperature is also important from a viscosity
point of view. The colder the resin, the harder it is to work with in
terms of air release and wet out. Additionally, it is more difficult
obtaining minimum resin content in the lay up.
To be certain your situation is not related to a bad batch of curing
agent, I suggest you redo your test at 77F.
Gary Hunter
EAA Technical Counselor
Shell's Epoxy Guru....
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