Talk Composites - The Forum for Advanced Composites

Silicone RTV mould for carbon fibre?

http://www.talkcomposites.com/Topic3393.aspx

By John200 - 11/16/2012 2:27:34 AM

First I've got to compliment you guys on a great website, loads of brilliant information, products and support!

I'm about to venture into using composites to create some interesting artwork based loosely around the human torso.  I'm aiming for very low production runs (3 maximum) of carbon fibre / carbon kevlar, etc.  The surface finish / visible pattern from the cloth is the most important thing, strength & weight are much less of an issue.

I'm familiar with using RTV silicone with plaster bandage support shells for creating resin and wax items.

My first question is: Would it be possible to use a flexible RTV mould (with a rigid support shell) for the vacuum infusion process I've seen on the tutorial video?
The plug I will be taking the mould from has some undercuts, so it would be much easier and less time consuming to create a supported skin mould, than a multi-part rigid mould.  I would also hope that this method would reduce the final finishing process as there won't be moulding lines to polish out around the undercuts.

My second question is: Bearing in mind that the final products are going to have small production runs, and 100% accuracy is not critical (98% would be ok), is the vacuum infusion process over-kill?  I already have a vacuum pump, degass chamber etc, so it would be a relatively low setup cost.  But are there better suited products for this kind of project?

Thanks in advance & wish me luck with my learning curve.
By Matt (Staff) - 11/19/2012 5:00:54 PM

Hi John,

Sorry, I didn't get a chance to reply on Friday. Regarding the reinforcement staying in position, the way I've imagined the 'torso' is that it's a cylinder with some complicated contours. If you're working on it with the cylinder pointing up then you could potentially 'hang' the reinforcement from the top of the moulding but if the whole thing is made of silicone then I really don't know how you're going to stick down the top edge in order to hang it down; and arranging it into the more compound contours would be very difficult indeed. In its dry state, carbon fabric is not possible to 'shape beforehand' really (this is why I was asking about ovens, I thought that pre-preg might be the way forward but it's not an option).

You need the reinforcement to be pretty much in the right place before you pull the bag down otherwise you're likely to end up with a lot of 'voids' where the reinforcment has bridged the corners. My opinion in still that a rigid tool would be the way to go but I'll never stop anyone from trying something that they think might work (you know your piece better than I do).
All the best, Matt