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Hanaldo - 12/16/2020 1:11:36 AM

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Marco Todeschini - 12/15/2020 9:31:35 AM

Hanaldo I think it makes sense, even if the channel is microscopic: I'm much more experienced in woodworking than in composites and I can tell you that there is a drastic difference in color between woods finished with finishes that soak the grain in depth (like oil based ones) and woods finished with finishes that penetrate less deep. In both cases "deep" and "less deep" refear to microscopic measures. I think it could work in a similar way.

Anyway: new day, new experiment, new failure : yestarday I tried to come back to the good old disposable vaccum bag (the last experiments were all done with silicone bags). The infusion came very badly, probably a leak at the entrance of the resin, BUT something interesting happened: all around the part damaged by the bubbles the color is light. 
In that area a bridge was formed, where the air from the leak was then collected, which perhaps compressed the laminate less (returning to the thesis of less compression = lighter color).
I absolutely have to do a test by adjusting the vacuum level:
1) Do you have any advice on the lowest (but working) vacuum level to keep?
2) In my limitate experience I've always heard that infusion needs the absolute absence of leaks to work. The vacuum regulator works by entering a small controlled  leak, right? How do the 2 things get along?

Sure, but composites lamination is very different to coating wood, even if the natural fibres have similarities.

What we are really suggesting here is that the fibres do not wet out properly when hand laminating. That has massive consequences on the finished laminate, not just colour difference. Do you notice any differences otherwise; does it feel a bit dry to cut, is it a bit lightweight, is it flimsier than the infused panels?

I think it is important to understand that hand lamination, unless done very poorly, doesn't effect how wet out the fibres are. A hand lamination resin will have very good fibre penetration, and unless you go very lean and don't apply enough resin then it will wet out the fibres. The only difference should be in void content and fibre consolidation, a hand laminated panel will include significantly more air in the layup than an infused panel and the fibres should be pressed tighter together with less space for resin (and voids) between the fibres. The actual centre of the fibre itself, if that can be wet out when infused then it should also be wet out when wet-laid.

I feel the fibre compaction is the more likely explanation. Theoretically the infused laminates should have a higher density per cubic mm than the hand laid laminates. Less space for resin and voids would also mean less space for light refraction I would think. 

The caveat - we are still kind of ignoring the fact we have both had lighter coloured results from infusion. Perhaps hand laminated seems to always result in a light coloured part, but infused does not always result in a dark coloured part. So what changes between those samples? If I had a bit more time I would do some experiments myself. Maybe on the weekend I will get a chance.