By carboncactus - 9/5/2013 10:03:57 AM
I've only had this twice. First time I ignored it as a random oddity. But its happened again. Ive had "print through" (if you want to call it that) from the backing layer through to the surface. Its not print through as in the carbon fibres showing through the resin, but the patching of backing shwing through. I know I could just use a single layer of backing, but the offcuts need to be used somewhere!
Im guessing its the difference in clarity between the two resin systems. Where the backing layers overlap, the part is slightly thicker there, creating a resin build-up. Another part was cooked at the same time alongside it with the same layup yet that one doesn't show this effect.
Forgot what the cooking times were the first time. This time it was 65 for 1 hour, 75 for 10 hours. Using VTF261 and PRF 464.
I've edited the photos by upping the contrast to highlight the effect. In real life its a bit less noticeable.
You can clearly see the corresponding lines that came through from the backing:
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By Dravis - 9/12/2013 11:23:20 AM
I Guess this is a prepreg part??
My guess is that the overlaying parts in the backing "patches" simply creates a slightly greater pressure in the "double layer" areas, causing a very slight deformation of the top layer into the outer coating.. What you see is the change in reflective properties in the thinner areas.
You may minimize the effect simply by using an extra layer of "non-patchwork" backing, but otherwise --- only do "patchwork" in a nice looking "pattern" and tell the customers that it is done on purpose to create a stronger part 
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