Mandrel for carbon mast

[Andy]

Has anyone ever used PVC tubing (I was thinking of 68mm PVC down-pipe which comes in 4m lengths) as a mandrel for laminating a carbon fibre mast? It seems to be a lot cheaper and easier to get hold of than aluminium....

[casavecchia]

I often use a PVC product as a flexible mould for small carbon masts
In Italy it is possible to buy a very cheap PVC gutter sold in 4 meters lenght, that can be easily deformed into a nice airfoil section.
Rub a mold release inside, use a slow setting epoxy, laminate carbon inside,step taper as you wish, uni,+/- 45°, 0/90°, peel ply, bleeder,close the bag, start vacuum, deform the mold to the desired shape, let cure and pop the part off.
After you can close the section with carbon tape or with a trapezoidal wooden stringer at the back. Exterior surface is flawless, you can use Kevlar as a local reinforcement to avoid stress cracks propagation at hounds and gooseneck ,you can put inside cores in way of butt and top of mast and you can even create a bit of taper in the top part.
Marco

[D'ARTOIS]

Andy, it is not advised to use carbon in connection with aluminium: tboth materials do bite each other.
Casavecchia's idea looks much sounder to me......

[casavecchia]

Well, yes. I was assuming that being a mandrel, this have to be extracted from the laminate.
Carbon and aluminium don’t go together well, in a marine ambient especially.
In fact I use PVC tubing as a mandrel for laminating carbon tubes up to 1,5 meters long , never tried anything longer. Make a very thin saw kerf along the whole length of the PVC tube. This cut will stay close because of the inner tension in the material. Make sure to cure the part at 40 degree at least. When cured, cool both mandrel and laminate, than a few raps with a hammer along where the kerf is will free the PVC tube from the carbon. Use a good mold release agent and when cooling you will hear small noises from the part indicating that mandrel is already separating from the laminate.
Marco.

[gggGuest]

Originally Posted by Andy

Has anyone ever used PVC tubing (I was thinking of 68mm PVC down-pipe which comes in 4m lengths) as a mandrel for laminating a carbon fibre mast?

Keeping it straight and taper are the main challenges

[casavecchia]

True. Working on a tight cable between two strong posts can help but you will still need some intermediate supports when the laminate is curing. A female mould is always better.
You can laminate the carbon on a flat mylar strip, than fold it in two lengthwise and insert the whole mess in a relatively simple mould. Of course you must use vacuum.
Marco.