Double Bagged Infusion - Why does it work?

[Matvd]

Pressure on the laminate will be determined by the pressure within bag number 1 only, bag 2 does not contribute any more consolidation. Two bags are better than one for vacuum integrity reasons.

Exactly, Its is all about vacuum integrity!

Have to disagree about having the same VF as using prepreg in a clave, some of the PrePreg systems that we use are Just 35% resin content, we could never dream of such low resin content from infusion.

[DDCompound]

You can reach a VF of 65% by infusion, but thats nit really good. Same in prepreg, such a high VF can be used for very light covers. For dynamic load parts this VF is not recommended.

[JIGGER]

So, after reading the whole thread as carefully as I could my final conclusion would be that double bagging due to the relatively counterintuitive physics involved: would do nothing or practically nothing to provide a more compacted laminate when compared to single bag practise, and that if more compaction is needed all that can be done is to suck resin on both ends of the infusion bag, the vacuum hose and the resin inlet hose applying vaccum or gravity force by lowering the resin pot one meter, it seems that if instead of this the resin inlet is closed before the part gets fully wet some compaction could be achieved as well, so the double bag should be considered mainly as a mean to guarantee vacuum integrity … amazing how the couinterintuitive matter of the double bag beast could lead so many composites prefessionals into fooling themselves … Am I right with my conclusion ???

[DDCompound]

You are right.

[Worldwealth]

From what I understand Double bagging for most people is indeed for vacuum integrity, but something I read… trying to remember where I read the article but it had to to with Boeing’s double bagging method.

I remember reading the double bag method also prevented the swimming effect that the infusion method has when resin is infused to the laminate. Usually you can see this at your inlet area. The second bag was supposed to compact the laminate to prevent the swimming effect. I cant remember if they said the second bag was compacted all at the same time or if full vacuum to the second bag was applied after the part was infused.

I have basically been applying light vacuum to the inlet hose once the part is fully infused. Ive been getting very good results so far with this method.

How long is your infusion taking and how long before your resin begins B-staging ?