By chriscnf - 5/7/2022 10:38:27 PM
I reckon this is about the hardest subject to get decent information on and I would love to see easy composites do a video.
I have an old mold just for bladder making, its got appropriate layers of carbon cloth laid into it to reduce the bladder size.
It's a three part mold its tricky but doable, I just use Dragon Skin 30 thickened with Thi Vex to prevent runoff and paint in multiple layers until I'm happy then apply a bead of thickened silicon and bolt it together.
My bladders are quite thick and almost stand alone, that allows me to dust with a talc and wrap the bladder in cling wrap before it goes into the work.
That way there is no resin contact and the bladder in theory should last indefinitely but that's a work in progress. A little cling wrap can get left in the piece but it weighs nothing so that's ok and the talc helps massively removing the bladder.
To get a good join I have thin mdf templates that bolt onto my mold flanges, they overhang the mold surfaces about 5mm and allow me to paint up under the overhang creating 5mm wide flat silicone surface to join, work brilliantly and makes the job super easy. The join faces will be 5 hours old when I join the bladder but it adheres nicely.
I just inflate with a bike pump thru a tube valve and that works fine for me. The carbon is hand laid and B Stage before I add joining cloth so the bladder is just holding that in place under pressure. Using prepreg would be demanding higher pressures but I don't think it would work on sone very tight radiuses in my molds.
The only hassle I'm having is air pushing past the silicone off stainless tube the bike valve is set into so i cable tie as a backup but that's far from ideal because as it exits the mold there is a vulnerable point which wouldn't hold under high pressures I would love to see how other guys get air into their bladders in a way that can cope with high pressure.
Cheers...Chris
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By Warren (Staff) - 5/9/2022 10:03:52 AM
Its not something we generally tend to use. In our experience, often bladder moulds can be unreliable and difficult to use. Sure for some specific applications they do have their uses but in our experience it is not that common in most hobby/DIY composite fabrication and certainly not common enough for us to stock a bladder system or specific set of equipment. A lot of situations using bladders can also be done with clever use of different size tubular bagging films under vacuum.
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