Jeremy Davey wrote:
> Rule 1: if you heat an initially cured laminate to x degrees and then let it
> cool, in future it will remain hard until heated to approximately x+5
> degrees, at which point it will go soft.
I don't think you can have a simple rule, nor is 5-degrees realistic in
any case. The difference between cure temp and glass transition temp
varies all over the place by product, and increases over X number of
days. For Aeropoxy at only 77F cure, it's plus 119F degrees. As I
hinted in another post, for SP Systems it's at least plus 70F degrees
the next day. With moderate-temp postcure, it's still about plus 50;
thence even less if postcured hot enough to worry about the blue foam!
IOW look at the spec sheets for whatever resin you're using. There is
also a difference between heat deflection temp and glass transition
temp. Former I think is where the test piece begins to bend, by some
testing method I can't find. Latter is higher and where the
cross-linked molecules begin to unlink. It is determined on fancy
thermal equipment, as a small but rapid temperature spike occurs when
they unlink, the exotherm effect I guess.
Best,
Fred F.
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