Hey guys,

So i tried my first prepreg carbon mould. I used an 8inch ID piece of steel tube and laid up the sheets on the inner surface.

Basically what i discovered was a very effective way to adhere carbon fibre to a steel tube. I just used some silicone mould release i had lying around and think this might be the problem.

Anyway, basically what im wondering is what would be the best way to make large 8 inch (and larger) cylinders from prepreg?

Thanks.

The best way would be filament winding, or towpreg winding.

Laying up fabric on the inside of a tube is difficult. It's better to wrap it on the outside, applying a certain amount of tension.

You don't need chemical release agents and waxes etc. if you use certain tricks. If they can be used depends on what kind of surface quality you require on the inside. Of course you could dip the mandrel into heated wax and let it cool... should work, but there are other ways.

Without going into the delicious details, let's just say packaging tape sticks to paper, but paper doesn't adhere to metal. Then again epoxy doesn't stick to packaging tape, right? Twice no adhesion whatsoever and once stickiness means easy separation, if used in the right order...

Your method of using a single piece of steel tube may not work even with the right release agent. Once the part is cooked the steel tube mould will contract and clamp tight around the carbon which is same size as the tube mould when it was hot and expanded.

If you must have a moulded finish on the outside then you need split moulds.

Many composite tubes are moulded the other way where the laminates are placed over a tubular mould, this way the expansion works in your favour as the internal steel/metal mould will shrink when cooling and release away from the new carbon tube. Then the carbon tube will need surface work to get the finish you want.