Post cure heat treatment after long time

[sherif]

Given that epoxy characteristics are greatly improved with post heat treatment, I want to ask if I can post cure after a long time (maybe weeks, months?)
I'd like to finish a batch of parts (a couple of chapters) then group these parts and post cure them in a local composites oven. I will guarantee the first 48hrs of room temp cure to be higher than 75F, but after that the temperature can fluctuate a lot (between 100F and 50F in winter days)

would anyone happen to know how that affects post heat treatment outcome? datasheets do not specify time periods between room temp curing and heated curing, my basic understanding of chemistry tells me that it shouldn't matter much since the initial curing has occurred, the high temperature cross-linking should continue when parts are set in the oven

thanks in advance!

Edited July 3, 2024 by sherif

[Kent Ashton]

The Canard Pushers only talk about post-curing one time, in CP-15.   http://www.cozybuilders.org/Canard_Pusher/CPs_1_to_82_Sections.txt  After that it isn't mentioned.  Most EZs and Cozys are not post-cured.  In my opinion, you'd just be wasting your time and high temps in a professional post cure oven might damage the foam.

I have built stuff in my cool basement,  maybe it took a few hours more to cure but that airplane has been flying 20 years and I have seen no problems.

Google "Gary Hunter post cure" and  you will see some pertinent discussions about post curing.

[Voidhawk9]

I have post-cured my fuselage tub. It wasn't hard to do as I had already built a frame that clips onto my workbench that I can cover with a tarp and heat the inside to accelerate curing, which also enables layups in otherwise off-nominal temperatures.
I post-cured to 70C (158F), but this was just the tub. As Kent mentioned, beware of the temperature limits of blue wing foam.

I am no epoxy expert, but my understanding is this: Post-curing is merely a continuation of the chemical process. As such, it really doesn't matter if there is a period of time between initial cure and post-cure - if there is still a reaction possible at higher temps, the post-cure will accomplish it.

Side-note: When the above is generally true, I am also using a non-standard epoxy, as the commonly-used ones are not available in this country - except West, which has the worst properties of those deemed acceptable. I have better options available here, and they were chosen with much research, discussion with experts, and subsequently with inspection by experienced builders including a former Scaled employee. All were satisfied with what I have.