I am working on a custom cylindrical pole/handle CF application that will use a 2 part negative mold with an air bladder and vacuum drawn resin.
The vacuum will be used both to drop the pressure and inflate the partially inflated bladder and to draw the resin into bi-axial CF sleeve.
My Question: For the mold I am considering either fiberglass/resin for the rigidity or using a 40A hardness silicone mold.
I like the fiberglass for the rigidity & “hardness”
I like silicone for the clearness & ability to see whats going on inside. Note the silicone will be reinforced with a fiberglass or abs plastic ‘spine’ to increase the rigidity and maintain the integrity of the shape and, of course, offers better release characteristics than fiberglass (less need for PVA, wax…)
I will need to reuse this mold several dozen times.
Ultimately, which is a better choice Fiberglass or reinforced silicone?
Silicone can have the tendancy to leave a print from the fabric if you over pressurize the bladder. What you described will work so long your resin is very thin. I have made a similar setup. You can also leave the resin in the degas chamber with the resin feed going through the lid. Apply pressure inside the chamber to force the resin in 15psi makes a huge difference.
I suggest using composite tooling with a silicone bladder. Allow for enough time to work out the bugs.
How many layers of fabric do you intend to use?
I am planning on using 3 layers of fabric sleeve. I think without the pressure it should be able to get through the 36" mold under 29mm of vacuum. Your thoughts?
The resin will run along the edges of the mold and make it hard to judge when it’s infused. Edges meaning where your mold mate.
I had to use added pressure to resin to make a glob and let it run. Distorted the fabric but once pressure is added to the bladder it ran it’s course as normal. The fabric did distort at one end.
Bladders are tricky but I was also Laminating a bigger stack and did not have the choice of a very thin resin.
I think 3 layers will laminate just fine.
We did think a textured surface on the silicone at resin end would help with a consistent initial resin path. Sort of like a flow media texture incorporated into the silicone. But hindsight is 20 20.
Good luck. And if you have the ability to add extra length do so at resin feed end.
Getting silicone bladder and silicone moulds to join with decent vacuum integrity can be a pig.
My choice would probably be composite tooling on the outside, perhaps with clear gelcoat to be able to see what is going on.
The bladder I would probably make from gusseted nylon film (Airtech). I have no idea of the diameter, but for larger diameters a flow medium on the inside could be used.
You need to be careful with braid as if you stretch it when handling, it comes down in diameter and causes all sorts of problems when you pressurize the bladder. It may expand but probably not and just restrict the bladder or it pulls in from the ends. For me, pre-preg, bladder and composite or aluminium tooling, so simple, don’t have to worry about vacuum leaks.