Being in Florida in a hot barn I never have done a heater post cure on the stock
XS E glass aircraft, during the summer, but on the carbon fiber spar work in
the winter, I did as the Gurit literature states to do a post cure to achieve
proper cure of its slower hardeners.
Never lay a freshly cured aileron flat between supports, it will sag. Always
allow
a component to cure above 75F-80F for 8-12 hours minimum. Even Gurit medium
hardener cures fully at these temperatures. To get a bit more stiffness one
should post cure Ampreg 20 series epoxy used in thin components laid up with
thin glass over foam. Aeropoxy 2032/PH3660 fully cures at room temp in 8-12
hours and for those very thin components exposed to desert sun, a heat cure to
120 F is recommended. Paint the component any color you want as long as it
is white and you won't have issues with the glass parts deforming. Dark colored
painted surfaces should be heat cured in a well supported mold or surface
to preserve their final shape before heat curing in an oven (normally heated
to about 140-150F) as the surface temperature will be quite hot for a dark blue
painted surface, but a white painted surface will be cool to the touch even
in direct sunlight, therefore high temp heat cure is not necessary for white
finished
Aeropoxy parts.
In Florida my metal building in the hot sun post cures even Ampreg 20 series
within
one day at roughly 100-110F for 8 hours. Over a few weeks at these temps
it really hardens the cure. For those in a hurry Gurit says 50C or 120F for
16 hours is sufficient for slow cure hardener (which really stays sticky for a
long time and does not deep cure without heat ((NASTY). Dark painted surfaces
should be cured at a slightly higher temp for about 8 hours. The Gurit rep
I contacted was comfortable with a room temp layup and cure of their medium
hardener
if the temps throughout the layup time and cure was accomplished over a
few days at this warm room temp. But even if post cured at 50C, the thin glass
structures like an aileron will not be stiff enough to be stored only supported
on its ends in a horizontal position if stored in high heat. He suggested
that thin parts be stored long axis horizontal with the parts either vertical
(TE down or up) if supported only on its ends or just stack it vertical leaning
against the wall perfectly vertical.
PTW Aeropoxy preferred all components be supported fully if stored at high
temperatures
(like dessert sun in a hot metal building) even if heat cured to 120
F.
Gurit has declared their Ampreg 20 series epoxy laminating systems obsolete.
Their
new 3X series fully cures at a warm room temp 20C like Aeropoxy 2030. Post
curing the laminate will greatly increase mechanical/thermal properties. The
system will achieve similar properties with a cure of 5 hours at 70 - 80C or
16 hours at 50C. The latter temperature is easily achievable with low cost
heating
and insulation techniques.
The post cure need not be carried out immediately after laminating. It is
possible
to assemble several composite components and post-cure the
entire assembly together. It is recommended, however, that elevated temperature
curing should be completed before any further painting /
finishing operations. Furthermore, care should be taken to adequately support
the
laminate if it is to be post cured after demoulding, and the
laminate must be allowed to cool before the support is removed.
Bottom line: Properly support your components while curing, post curing, and in
storage.
Best Regards,
Bud Yerly
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