Vacuum Bagging Problems

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#1

I have attempted vacuum bagging for the first time. The overall result was good but there was a small problem. The inside surface of the part, the side with the breather material, contained a lot less resin than the outside. It is still bonded together fully but you can feel the fibres if you run your hand over it. I know the inside surface finish will not be as good as the outside one but is seemed like too much resin had been absorbed by the breather material. Also when you hold the part up to the light you can see very small pinholes.

I would appreciate any suggestions to help solve these issues. I was thinking of using a thinner layer of breather material, would this help. Also the pressure I used was just over 29 inches Hg. I know this is on the high side but have no way of adjusting the strength of the pump.

many thanks, Ralf

#2

Did you use peel ply or release film?
Also I doubt less breather is going to fix your problem. The vacuum squeezes the epoxy out, the breather doesn’t suck it out. I would go as far to say that more breather creates less pressure on your part. As for your pressure put a valve inline with the pump. When you reach the desired pressure quickly close the valve and then let the part sit. This requires a perfect seal on your part but it’s doable.

#3

Perforated release film between the part and breather will control the resin a bit more. However, yes breather will suck out resin, since it is a voidy dry layer. It will want to contain as much resin as the rest of the fabric in the bag.
Your mold also matters. I can infuse on a metal plate, and a polypropylene plate, same method, same everything. The PP plate part will seem like the fabric is dry on the tool side, and you can feel the fibers if you scrape it. Not sure why (maybe the fibers push into the plastic, creating a micro conformable surface).
Start with the release if you don’t use it, then try using a thinner breather.

#4

I usually use breather over peel ply when doing a wet lay up/vacuum bagged. The backside always wets out for me. Just have to calculate how much resin and add anywhere from 1/2 ounce to 10 ounces more resin … like Riff said the breather is there just to absorb excess resin. One layer of breather is plenty.

#5

use less breather. one layer only, and even if you get dry spots then, try even reducing the coverage of the breather.