Making silicone bladder for composite molding

[ingear]

I've seen several good posts on composite bladder molding, but I'm wondering if anyone has some specific recommendations for:

1) Silicone materials, sources, methods to use to make the bladders
2) Wall thickness of the bladder

FYI we can't used a trapped solid rubber mandrel since it would be trapped in the mold due to the bends in the part.

Thanks

 

[bellx1]

I once saw a college club use a bicycle tube as their bladder. It was for a one off part but it worked quite effectively, squeezing out a decent amount of resin. What is the diameter of the part you're trying to make?

http://www.compositescentral.net

 

[ingear]

Thanks, I've heard about that. My part is about 0.75" in diameter, but varies.

I suppose was post was a little vague, but I was just wondering if there are rules of thumb for building bladders. We'll experiment with some silicone molds.

 

[bellx1]

One important thing is to make sure that your bladder is more or less circular when inflated. Uneven shape = uneven pressure = uneven resin content. You can try getting a inner bladder that about the same size as the outside tube but then you run the risk of folds in your material. If you can try picking a bladder that stretches some so you can vary the pressure and have nice flat surface

http://www.compositescentral.net

 

[bellx1]

and still have a nice flat surface*

http://www.compositescentral.net

 

[MotoMike]

Ingear,

Try the silicone from Smooth-On. They are at

http://www.smooth-on.com.

I have used the silicone that they specify for moulding as well as their dragon skins 10 minute. The ten minute is colorless and quite elastic but does run a little bit. The material for mould making is green and more stiff. Either of these can be sprayed or brushed as well as injected into a mould using an epoxy gun to make a tube. I have used with epoxy and polyester, vinyl ester and they work fine.

Good Luck

Mike