My idea on a different way to vacuum bag.

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#1

Great forum guys, had to sign up, way to much good knowledge to waste.

Anyway this is my idea for vacuum bagging without a bag. Would it be possible to build a solid air tight box, probably out of metal, then stick your part in there which already is wetted out and then remove the air. My question is, will this result in the fiberglass, carbon to sandwich itself against the mold from the negative pressure? Since the box is solid it wont deform and all you would have to do is release the vacuum and pull your part out. Am I thinking outside the box here guys, has this been done already?

#2

Why would you need negative pressure? Wouldnt posative presure push the laminate up against the mould. In that case its same princaple as a auto clave?

#3

it would degass the layup but you would get no consolidating pressure.

#4

Welcome to the forum!
It sounds like you want to make a large degas chamber. They only remove air from your resin and don’t compact your plys. If you are just vacuum bagging you need ambient air to create the positive pressure on the vacuum bag which compacts the plys. That’s why it’s important to pleat your vacuum bag so the bag can compact all areas. When you don’t pleat you get bridging. Bridging are areas under vacuum but because the bag isn’t touching or “compacting” the plys you end up with a air bubble, the vacuum bag basically creates a bridge over the area it’s supposed to compact hence the name.

#5

Rotor gotcha, What about using positive pressure? Increase the pressure inside the box to a certain PSI, but from rotor’s explanation the bag is essentially pushing the layers together right so positive pressure wont work?

#6

Using positive pressure would be like an autoclave which is what Brainstorm was talking about. You would still need a bag because you need a difference in pressure to create compaction. The only way to go without a bag is closed mold tooling or compression molding.

#7

^^ this.
part only in neg or pos pressure will only degas, or dissolve the bubbles. Add a BAG to the part, vent to atmosphere, and add vacuum, your bag will balloon out. Add post. pressure, and you will force the bag against the mold.