Drawing a vaccuum on a pressurized mold?

Lets say you wanted to lay up a fiberglass sphere inside a female mold. You could lay up glass over an air bladder, assemble the halves of the mold around the bladder and fiberglass, and then inflate the bladder inside the mold to press the fiberglass into the mold halves. We’ll say you want to pressurize the bladder to 2 atmospheres, or about 30psi. If you then vacuum-bag the entire mold and draw a complete vacuum, can you effectively reduce the stress on the female mold to one atm?

How might one mold a sphere otherwise?

Lets use this analogy to a one-piece motorcycle tail. I want to mold a tail. How do I get the fiberglass into all the nooks and crannies without using an access hatch? I want the tail to be structural so to me, just having 3 or 4 layers isn’t strong enough without a corresponding structure on the backside…Thoughts?

Thanks,
Matt

yea i cant see why that would not work, going to be quite a mission with the bags etc

what is the max dia of the mold ? 1 bar is quite a bit inside a mold, its only when you have small diameters that you need to go to higher pressure …

but glassing over the bladder is wrong , or at least very difficult , rather layup in the mold and let the material extend a bit past the mold on the one mold half. The other half will be trimmed flush with the mold. insert bladder, close molds, inflate. this way you have a wet seem that makes a nice join line

I second Blackrat’s idea

that’s exactly how we do it on our bladder parts and they come out perfectly. The trickiest part is closing the mold and keeping the overlapped side in place, without distorting the plys. But, it’s not that bad. The mold seam is pretty much non existent. We apply something like 150psi to the bladder, no vacuum. The parts are cured in a press.

Having some complex geometry will make things more difficult but, not impossible.

but wouldn’t be vacuum from outside good to degase the resin abd blader form inside for better consolidation ?

It’s prepreg so there isn’t need to degass. You would however, follow normal debulk procedures to minimize any entrapped air and ensure good consolidation. Honesty the pressures exerted by the bladder or silicone intensifier is so high, the parts come out with autoclave like quality.

In my opinion, this is one of the best manufacturing methods for it’s ease of quality and consistency.

considering that with vacuum you’ll get max about 14.7psi, 150psi is 10x the pressure exerted.