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Hello, My fatherand I are avid kitesurfers and have recently gotten into making our own boards.Our first board was made out of mahogany and is 6mm thick at the thinnest part.This has so far proven to be structurally sound but a bit too heavy, so werelooking into reducing the thickness and reinforcing with carbon fiber or fiberglass.
My question is, is carbon fiber skinning a good choice for this? Can Iapply multiple layers for skinning and if so do you have any recommendation asto how many layers would be needed to maintain the strength if I were to reducethe wood thickness by half? Also it needs to be slightly flexible to absorbimpact and would the clearcoat stand up against salt water conditions or wouldI want to apply a layer of something else on top?
Thanks much
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A question for Matt: I've seen people suggest bagging to 65% vacuum, or 30% vacuum, etc. We just chuck it in and switch on the pump, but we are now looking for a gauge and regulator to control the vacuum. Can you explain how the % vacuum affects carbon fibre, and how we would select the ideal vacuum strength? Is there potential to go to vacuum infusion for this?
Hi Aka,
The reason people vacuum bag at less than 100% vacuum (which we too suggest people should do) is because vacuum bagging, when done at 100% vacuum, often bleeds too much resin out of the laminate which can leave it with a pin-holed or pitted surface, or even fully dry patches. Not only does this affect the surface finish (meaning that lacquering, gel coating or other reparation is necessary) but it will also result in a weaker laminate. This would never happen with infusion (or pre-preg) they are more like a closed system.
To prevent this bleed-off you can reduce the amount of perforation in the perforated release film, abandon it altogether or reduce the level of vacuum (or a combination of these). With the right level of vacuum and perforation, you should be able to get a pretty good surface finish on your laminate; it's not an exact science though and we have less less 'first time success' with vacuum bagging than any other process.
I think you could move over to pre-preg, with the right planning.
All the best, Matt
Matt StathamEasy Composites / Carbon Mods - Technical Sales
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Thanks for your reply Matt, Our reservation with pre-pregs stems from a reluctance to introduce an oven. Can we make our own "pre-pregs" for the carbon outer layers that do not need to go in an oven? Our kiteboards are approx 1.4 x 0.4m in plan. A finished board is max 15mm thick in the middle down to 5mm around the edges, with approx 50mm curvature introduced after bagging onto the bottom mould. Most recently we have waxed our bottom mould, put our board consisting of a 5-layer sandwich of; wetted carbon fibre, 1.5mm plywood sheet, resin/shaped foam core/resin, 1.5mm ply and top layer of wetted carbon fibre onto the mould, placed a waxed sheet of 3mm MDF board on top and vacuum bagged at full vacuum. We will try this again with, say, 40% vacuum. We are achieving good strength, lightness, flex and (apart from occasional airbubbles) finish, which we hope to avoid by reducing the vacuum. The top sheet of waxed MDF means instead of a peel-ply top finish (where you can feel the texture of the fabric, which some of us like, but others want the supersmooth, off-form finish we are getting for the bottom) we are now getting an off-form, perfectly smooth finish both top and bottom. Our development efforts are now tweaking the finishes, but mainly focussing on how to minimize the labour/time to lay up another board. Is there a way we can use infusion technology to achieve top and bottom off-form surfaces in a single bagging process? Regarding graphics: we have succesfully laid individual plastic lettering onto the carbon fibre, and it's turned out perfectly, but it's a bit fiddly. Is there a standard method (I'm thinking surfboards) of having graphics prepared on a film, that we can then lay onto the carbon fibre, or face down onto a first coat of clear resin that we apply directly to the waxed mould? If we wanted to cover much of the surface with broad bands of a single opaque colour, could this be done? What about digital or photographic images? Will the resin/epoxy bond sufficiently to the film/plastic?
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You're welcome Aka, Our reservation with pre-pregs stems from a reluctance to introduce an oven. Can we make our own "pre-pregs" for the carbon outer layers that do not need to go in an oven? Not really. If you did make your own 'pre-pregs' then by their very nature you would still need to cure them in an oven. If you don't cure them in an oven then it's not pre-preg in the conventional meaning of the work (although it could be some other technique for pre-wetting out your reinforcement). Is there a way we can use infusion technology to achieve top and bottom off-form surfaces in a single bagging process? To use Resin Infusion to achieve a double-A sided finish you would need to use an internal flow media that would facilitate the resin through through the laminate in place of the infusion mesh. Lantor Soric SF is a simple version of an internal flow media/infusion core but there are others. Of course the internal flow media/core remains in the finished laminate and so you would need something that has the performance characteristics that you're looking for but there are different options out there and something might fit the bill just right. You could then use RTV Silicone Rubber to make a reusuable vacuum bag with a smooth finish moulded into the top. If we wanted to cover much of the surface with broad bands of a single opaque colour, could this be done? What about digital or photographic images? Will the resin/epoxy bond sufficiently to the film/plastic? The surfboard manufacturers tend to have graphics screen printed onto paper or even glass tissue and then infuse/laminate them in. The epoxy does a nice job of encapsulating the pigments. I would steer clear of embedding plastics as many would be difficult for the epoxy to bond to but on this more experimental side only testing will reveal the best combinations.
Matt StathamEasy Composites / Carbon Mods - Technical Sales
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