Bladder Moulding

[IthonEng]

Afternoon All,

This is my first thread here but I have been reading up on and off over the years. A great source of information!

I have a fair amount of experience with wet lay up and pre-preg composites using vacuum bag/oven techniques.

However I am working on a project that would benefit from bladder moulding. It is effectively a shelled component with one open end. It could me made by simply curing the 2 halves independently using vacuum bag and then joining together post cure. But, given I have not tried bladder moulding before and would like to build my understanding/knowledge of this technique for future projects, it seems a nice place to start.

A few points to note:

- I will be using cnc'd aluminium moulds
- The part is not structural. Therefore aesthetics are priority

I have read this forum and also searched a fair bit on google so have gained a reasonable amount of knowledge to be able to give it a go. However I still have a few questions:

1) is it still best practice to utilise a vacuum bag between the pre-preg and the bladder to reduce the effect of air bubbles

2) if the above is true, how best to incorporate the vacuum valve/line and the bladder valve line into the mould

3) if no vacuum is required, does a bladder require a release film (will likely look at latex bladder)

4) I have read up a number of cases where designers have utilised a heated mandrel in the centre of the bladder. what is the reason for this?

5) lastly do anyone know of any manufacturers in the UK that can produce one off/low volume bladders

I appreciate its a few questions but any help would be much appreciated on my journey. If you know of any good guides/literature I would welcome any links.

Thanks in advance!

 

[zgzomb]

Sounds similar to the hollow stringer cavities on current composite commercial a/c shells (e.g. 787) which trap inflatable elastomer bladders between interior vacuum bags with exterior cauls. Scrap rates are very low. It is a good practice used with autoclave, but out of autoclave will be more difficult and, if you use a hollow bladder, you should have good control of interior pressure. Most likely some trials will be required to set a useful bladder pressure. To connect the bladder inlet port into your particular mold, a quick connect fitting can usually be molded into the bladder, but it's best to contact a manufacturer like Rubbercraft for specific guidance.

Have you considered whether a solid, high expansion elastomer bladder system, like some of the Mosites materials, can provide what you need? Experience says that approach can cost far less than the inflatable types. Mosites has a UK distributor listed in their contact page (Aerovac). They also have a decent release agent.

 

[CompoMan]

Hi IthonEng
One company in UK I've used who's good with bladder moulding (e.g. propellers)is Rockwood Composite in Newton Abbot