Infusing 6-8mm thick carbon fiber wing mast.

[svquintana]

I have a technical question, and would appreciate it if only those with experience submit answers. Conjecture will not help me.

I've built our 50 foot Catamaran using epoxy resin infusion, and am considering building our mast, bow tube, and boom as well. The mast will be 6-8mm thick, and I'll be infusing it with MAS infures/infucure CP of 160.

I have infused two test pieces of 5mm (bow tube and boom are 5mm) but can only get 9 inches of flow, without media. That should work for me if I feed from the middle, but I'd rather feed from the edge. I have not yet infused a test piece of the mast layup.

My question is, which flow media do you use for thick carbon fiber infusions.

Thanks in advance.
Paul.

 

[groper]

Hi Paul,

Flow media is risky on this type of laminate. Resin can flow over the top but the bottom laminate lags a long way behind due to the tight packing and slow wet out of the unidirectional carbon fibres (wet out in the through thickness direction). If you do use a flow media, it needs to be very slow.

It's not a question that can be clear cut answered. The entire process must be detailed to arrive at a solution, right down to the type, brand, tow size and fabric stitching - which all change the wet out character. Particularly the stitching of the uni, allows flow in the through thickness direction.

Something else you may wish to investigate, is an intra laminate flow enhancer such as CFM in the center of the laminate. This is a continuous glass fiber mat which aids flow similar to a typical flow media. Placed in the center of the laminate, it becomes a permanent part of the mast obviously, and it should effectively reduce the top to bottom lag and behave more like an infusion of half the laminate thickness. It would certainly be worth a test piece.

 

[svquintana]

Hi Groper, thanks for your input.
I know using flow media can make things complicated, which is why I wanted to know exactly what media folks are using.

I have used glass uni at 90 degrees to the carbon to help the flow, and have done other tests too. I'm at the point where it would be helpful to me to hear from someone who has actually infused thick carbon, and to know how they get the resin to flow over longer distances.

Lots of guys in my neighborhood have suggestions, but none have experience.

I don't want someone to tell me how to infuse my stack; I'd like to know how they infuse their own stack, esp if they're getting their resin to travel say 700mm, which is roughly the distance I want my resin to flow.

Cheers.
Paul.

 

[svquintana]

Have to bump this, any takers on infusing thick Carbon stacks?

 

[AndrewK]

Paul, there is no way to infuse a 5 - 10mm laminate over a 700mm distance with no infusion media. With thick leminates you need to keep the over the top media ~50mm short of the laminate edge at the vacum side when feeding from one edge, or both edges when centre fed. For 10mm glass laminates I have used 30% shade cloth and Delstar very fine clear mesh (~3mm diamonds) as well as their red mesh (~6mm diamonds). All 3 are relatively slow, I could try and find their product numbers if you like.
You need to do more tests with your materials.
Keep me informed as I am still to do my forebeam,
If you incorporate CFM into the laminates then you would need to consider the effect on the laminate properties as well.

 

[svquintana]

I'm happy to use flow media. I'd simply like to know what type of media others are using for 5-8mm thick carbon infusions.

As far as glass infusions go, my entire boat is infused, so I'm fine with that process. 10mm glass is easily infused, but carbon has me a little nervous.

Thanks for your input.

Paul.

 

[JosephT]

For masts & poles you're probably a lot better off going with filament winding. If you closely control the process to ensure equal plies, and have a female clamshell mold you can get a good smooth finish. Without the female mold you'll have to use a sandable filler to achieve a smooth finish.

All in all though the filament winding method is the way to go. Did a quick search and here's a link that shows some info. Much like spinning a carbon fiber fishing rod.

http://www.ancker-yachting.de/pdf/Selden_Carbon_Masten.pdf

Key tools:

-Rotating, disposable foam mandrel for the mast
-Carbon tow
-Female mold (for post-wind compression...gives smoother finish). Else, fill surface imperfections with a good sandable filler (e.g. West 405).

About 15 years ago I help spin a jet aircraft fuselage. We spun the entire thing in carbon...took about 21 hours. As I recall we set a speed record for building a fuselage!

Tip: If you carve an x-grid approx 1 centimeter or so into your foam core before spinning (e.g. carefully by hand or with NC router) this adds a lot of strength to the structure. Many rocket casings are built this way (and they hold up well in high winds I might add ).

Regards,

Joseph

 

[UNCIVILIZED]

Have you completely ruled out wet preg, or pre-preg? I ask as this project sounds like a HIGH $ project, for the first time trying out new techniques. Not that the ones which I suggested are zero risk either, but...

 

[svquintana]

We have quite a bit of experience with infusion, so I'd prefer to build that way.
Pre preg is expensive, and complicated with post cure temps being somewhat higher than infusion post cure temps. So I'd have to build a special oven for the mast, also more expensive.

Hand layup, to me, leaves too much to chance. I can't do it alone, so will have to recruit helpers. And since I can't be everywhere at once, I'm afraid of having an incomplete wetout. Also, I dislike the time constraints with vacuum bagging. It's a stressful endeavour.

I'm accustomed to infusion, and it's stress free layup time. Very little stress.

Cheers.
Paul.

 

[groper]

Paul, the people who have done this successfully are the professionals, and most of these guys will be using prepreg and ovens rather than infusion. The infusion guys, are not going to give away their propriety processes on a public forum. So this explains the lack of information you seek.

Personally, I've thought about the process of infusing a large carbon mast for many hours over many months, and combined with my infusion experience, similar to yours, I believe I have a workable solution to the problem which reduces tooling costs and should be reasonably foolproof. however I cannot say that it works until I've actually done it. It doesn't cost much to make a few flat test panels and test the theory tho. I would simply use a very slow media such as the stuff andrew k mentioned earlier. Half of the laminate would go under this, followed by a central layer of CFM, then the mirror image of the first half of the laminate under that. The CFM will only act as flow media, remaining in the center of the stack similar to a very thin core material. It should not have a significant negative effect on the structure as all the compressive stress will be taken by the carbon. Similarly, one could also use a layer of 1mm soric in place of the CFM. This also acts like an intra laminate flow media. It also thickens the laminate so you get the local buckling stiffness which is accounted for in the engineering.

Depending on the section size, quite often the compression and global buckling can be satisfied and the wall thickness for local buckling cannot. So the laminate is increased in thickness to satisfy it, or sometimes a core material is specified to do the same.

Have you had this mast engineered yet? If so, ask the engineer if any of the above applies to your section and solutions can be worked around which also solve the flow problem such as using a core material to enhance flow characteristics and effectively half your laminate thickness.

 

[UNCIVILIZED]

It might help to talk to a few multihull designers (and or builders) and ask who they work with for trick/tricky projects. And pick the brains of all of the afore mentioned folks.
In addition to possibly seeing about hiring them to look over your setup, and or have them on site, to help you with both the prep/setup, & the actual build/infusion.
Unless they're spectacularly busy, I would think that you could find a well qualified spar builder or three, who wouldn't mind having a little bit of extra coin in his pockets. And such would likely give you a bit more peace of mind, before you go adding resin to a several thousand $ of carbon fiber.
A good friend of mine who was a rigger used to do plenty of after hours work, to help keep Cheerios & such on the table.

If memory serves, in his builder's blog, Kurt Hughes mentions a guy that he/they use when there's a tricky spar to be built. I can't say that it's in his blog for sure. But odds are, you could find out with a phone call. And also, I think that he will still fly out on a builder's dime, to assist with tricky bits of construction.
Kind of a hired gun, like folks used to do with me & some of my mates when we were doing a lot of high end racing. AKA, if you dig, you can find a guy or three who'd do the same for your spar. Perhaps try Eric Goetz's shop as well, & if they aren't able to help, I'd place a large wager that they'll know someone who can.

A few hundred $ for a pro is cheap compared to fudging several thousand $ in materials, by taking on too big of a DIY project solo.


PS: You might try running this project by Eric Sponberg. He's on here quite a lot, & Definitely seems to know both his Naval Architecture/Engineering, as well as how to build things right.

 

[groper]

Picture this Paul,

Cut some temp frames from cheap ply or similar, that have the leading edge profile of the mast radius to the thickest part of the section, then becomes a parrallel slot thereafter.

Set these up on a strong back so the leading edge of the mast is facing the floor. They will look like a series of U frames.

Get some coiled 0.55mm colour bond sheet metal cut- the stuff they use for rolling into corrugated roofing iron, enough lengths to do the length of the mast, probably need 2 or 3 so the lengths are manageable. Push this gently down into the U frames, and join each piece together with tacky tape for a vacuum seal. This will become our female mold in due course.

After mold release etc lay the infusion stack perform. Apply the tacky tape to the top edge of the sheet metal and seal the vacuum bag to it. Eveything still looks like a long U section at this point.

Pull a light vacuum, around 10%, to hold things in place but not compress the laminate. Now take a second set of ply frames, which this time has the rear half of the foil cross section cut out of them. They will look like a an upside down V more or less. Lower these down over the existing preform and as they are being lowered, coax the sheet metal into the upside down V frames so the top edges of the sheet metal are brought closer together gradually you will get them all down and everything aligned etc. Stop when the sheet metal edges are about 1.5inches from touching each other, and fix the upper and lower frames together so it won't move. We will make the trailing edge and sail track as another piece and bond it into place later which will close out the mast section.

Now pull the full vacuum and proceed with the infusion as per normal with the extra care of doing a few debulking cycles first and then using degassed resin.

As the preform is pressed between the sheet metal and vacuum bag, the radius of the preform gets larger as the thickness of the preform reduces. This is important to prevent fiber crimping and a loss in mechanical properties and is a major reason I would not attempt a thick infusion over a male mold or mandrel.

The open slot in the back of the mast also allows easy stripping of the consumables and resin feed line which I'd place down the center of the leading edge. Also, as this is effectively female molding, the outside surface of the mast will not require fairing, it should come out looking really nice as the colour bond sheet metal has a very nice surface.

I'd setup a small apparatus to show you but I'm really pressed for time at the moment, way too much on my plate right now... but its simply an extension of what i did with my hull shoes when i infused the laminate against a 3mm "sign writing foam" surface held in place in temporary frames - i didnt want to use sheet metal back then as there was compound curvature so i chose the 3mm foam vertically strip planked;

Minimal tooling costs, and the time to make the mold would only be a few hours...

If any of this needs clarification - shoot...

Any questions, shoot...

 

[svquintana]

Thanks to you both for your suggestions.

Uncivilised: I live in a rather remote area (regards skilled infusion or spar builders) so flying someone out would be counter productive, regards saving any money on the mast build.

Groper: Clever idea. I'll be using two female moulds (left and right); that way I can keep the resin travel to within my present capabilities. I had thought of a similar method to yours, if I could get the resin to travel further. But your method would require a 45cm resin travel, whereas building in two halves requires only 22cm, which I have been doing easily, on my test pieces.

My present thoughts are to abandon the mast and bow tube build (to save time on the overall build) and just build my 6 metre "bow sprit". I think we'll buy an aluminum mast and bow tube, but build the sprit ourselves. The sprit has the same laminate as the mast, so it'll be interesting to build, and a good experience if we eventually do build a mast. Plus, I already have 60 metres ( by 1.3m) of carbon uni, so I have to build something! hehe.

Cheers.
Paul.

 

[groper]

You can always add another set of resin feeds, close the first then open the second pair. This would half the required flow distance.

I also have a neat method of infusing a round spar using a PVC pipe as a female mold. I adapted the idea from a pro builder who was vacuum bagging prodder spars like this. Was a simple modification to infuse it, it's effectively a female split mold. Inner bag is a tube, or sausage, it gets sealed to the outer bag which envelops the whole setup with the ends of the bags open to atmosphere but sealed to each other. Upon appliing the vacuum, the Inner bag presses outwards, pressing the laminate against the PVC pipe, the outer bag provides the opposite. A few wraps of packing tape holds things together until you get the vacuum on and another length of conduit to wrap things around in the middle. This wrapping conduit can be removed after you get the vacuum on. There's a few tricks involved in streamlining the process, but you get the general idea...

 

[JosephT]

One other thought on the carbon mast...lightning strikes. The carbon masts are not good conductors as compared to Aluminum. Lightning strikes can do some serious damage. You may want to read up on that topic if you're intent on a carbon mast.

Fair winds /)