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How thick can I lay carbon fiber?

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opie
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How thick can I lay carbon fiber?

Postby opie » Sun Feb 25, 2018 11:24 pm

I have a mold for a mast that is .75 inches/2 cm thick. It's made of PLA plastic that softens around 150 f / 70 c. I am thinking if I lay it all at once it'll exotherm and melt the plastic. Is this a valid concern?
Thanks.
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mast mold.jpg

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Re: How thick can I lay carbon fiber?

Postby thewindego » Sun Feb 25, 2018 11:30 pm

Depends on the epoxy and hardener combo you are using but I think it is a concern for sure. I decided to move to the 3d printed plug and make fiberglass mold from the plug as others have suggested to avoid this issue. However by doing your layup in 2 stages I think you can win here.

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downunder
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Re: How thick can I lay carbon fiber?

Postby downunder » Mon Feb 26, 2018 2:48 am

Heh,

sometimes I'm post curing on 80C. Last time went over...

2 halfs yes, it's possible. But than, I would make only skins and wrap them after. Wrapping is what mast gives strength, me thinks. Plus stringers, etc. The board 'plug' is, I think, almost always premade, hence you just build the straight mast and 'embed' it into a plug after. With your mold, you'll have a problem of laying a carbon around that area (at least I did).

Good luck.

PS, make a small vid when laying up, speed it up and I would be interested to see it :) Remember, wrapping the mast is fast, everything else takes heaps more time, me thinks:
https://youtu.be/qaj0SMtY8CA

opie
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Re: How thick can I lay carbon fiber?

Postby opie » Mon Feb 26, 2018 5:30 am

:)
thewindego wrote:
Sun Feb 25, 2018 11:30 pm
I decided to move to the 3d printed plug and make fiberglass mold from the plug as others have suggested to avoid this issue.
I've actually got my second (failed) attempt at a fiberglass wing mold drying in the garage right now. I am trying every method I half way understand and learning as I go.
downunder wrote: The board 'plug' is, I think, almost always premade, hence you just build the straight mast and 'embed' it into a plug after. With your mold, you'll have a problem of laying a carbon around that area (at least I did).
I haven't figured out that part yet. Originally I tried to make the end of the mold fit a K-F box. I don't think it will, but decided to keep going, mainly to learn if a PLA mold can be made to work. Now my goal is to not destroy the mold with my first attempt. :)

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Re: How thick can I lay carbon fiber?

Postby kostantin » Mon Feb 26, 2018 5:36 am

opie wrote:
Mon Feb 26, 2018 5:30 am
:)
thewindego wrote:
Sun Feb 25, 2018 11:30 pm
I decided to move to the 3d printed plug and make fiberglass mold from the plug as others have suggested to avoid this issue.
I've actually got my second (failed) attempt at a fiberglass wing mold drying in the garage right now. I am trying every method I half way understand and learning as I go.
downunder wrote: The board 'plug' is, I think, almost always premade, hence you just build the straight mast and 'embed' it into a plug after. With your mold, you'll have a problem of laying a carbon around that area (at least I did).
I haven't figured out that part yet. Originally I tried to make the end of the mold fit a K-F box. I don't think it will, but decided to keep going, mainly to learn if a PLA mold can be made to work. Now my goal is to not destroy the mold with my first attempt. :)
Greetings,

what happened ? If you provide details, I might be able to help.

tks

Kosta

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downunder
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Re: How thick can I lay carbon fiber?

Postby downunder » Mon Feb 26, 2018 5:59 am

opie wrote:
Mon Feb 26, 2018 5:30 am
:)
thewindego wrote:
Sun Feb 25, 2018 11:30 pm
I decided to move to the 3d printed plug and make fiberglass mold from the plug as others have suggested to avoid this issue.
I've actually got my second (failed) attempt at a fiberglass wing mold drying in the garage right now. I am trying every method I half way understand and learning as I go.
downunder wrote: The board 'plug' is, I think, almost always premade, hence you just build the straight mast and 'embed' it into a plug after. With your mold, you'll have a problem of laying a carbon around that area (at least I did).
I haven't figured out that part yet. Originally I tried to make the end of the mold fit a K-F box. I don't think it will, but decided to keep going, mainly to learn if a PLA mold can be made to work. Now my goal is to not destroy the mold with my first attempt. :)
To build the mold is 'easy'. To actually use it right is not so. I've got at least 4 FG molds, all discarded...

As you see on my vid, working with that many carbon layers is time limited. Time is of essence, hence 70mins of pot life is not bad to have. But, 70 mins of pot life needs post curing or loooong room curing (weeks, months in winter?).

Also, where the mold is joined, you'll need to isolate this somehow, if not, the epoxy might flow out there under vacuum and carbon might be dry. That, you can't fix after. This is also where the mold might slightly bend under the vac. No vac? Well than the result might not be that great.

The KF plug can be a separate mold, you have the printer so why not. This means longer mast mold (make it extra long), to accommodate for a 'plug'. I think that plug is almost always a hard PU since it takes cylindrical brass inserts (or you risk carbon-brass corrosion), for SS bolts.

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Re: How thick can I lay carbon fiber?

Postby rynhardt » Mon Feb 26, 2018 10:53 am

opie wrote:
Sun Feb 25, 2018 11:24 pm
I have a mold for a mast that is .75 inches/2 cm thick. It's made of PLA plastic that softens around 150 f / 70 c. I am thinking if I lay it all at once it'll exotherm and melt the plastic. Is this a valid concern?
Thanks.
Short answer is yes, it is a valid concern. Once you start getting into the 5mm thickness range on a wet layup, it'll generate a fair amount of heat.
You can mitigate this by waiting for the previous layer to get to the tacky stage before doing the next layer, but this is obviously very time consuming and you need to time the window period right. Tricky.

A better solution might be to use a core.

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Re: How thick can I lay carbon fiber?

Postby opie » Mon Feb 26, 2018 7:04 pm

kostantin wrote:
Mon Feb 26, 2018 5:36 am

what happened ? If you provide details, I might be able to help.

tks

Kosta
Mistakes were result of me

learning to use composites. On one I made a taco around the plug, pulled the plug and tried to fill with pour foam. I weighted it in the middle to keep the top and bottom skins from separating but one wingtip where I did not have weight still bulged. When I get more foam I'll try again. The other fiberglass mold looked good but when I transferred it under an electric blanket I apparently added a couple wrinkles that were bad enough that I think I'll just start over. Thanks.

" plug is almost always a hard PU" ... What is a "hard PU"?


rynhardt wrote:
opie wrote:
Sun Feb 25, 2018 11:24 pm
I have a mold for a mast that is .75 inches/2 cm thick. It's made of PLA plastic that softens around 150 f / 70 c. I am thinking if I lay it all at once it'll exotherm and melt the plastic. Is this a valid concern?
Thanks.
Short answer is yes, it is a valid concern. Once you start getting into the 5mm thickness range on a wet layup, it'll generate a fair amount of heat.
You can mitigate this by waiting for the previous layer to get to the tacky stage before doing the next layer, but this is obviously very time consuming and you need to time the window period right. Tricky.

A better solution might be to use a core.
Do you mean use a core with the mold, so that I am not using so much carbon? I've considered this, do you think I could just print one? It would not help at all with strength, I think, but maybe the carbon could be enough. My other idea is to print a another complete (smaller) mold for the core and use pour foam.

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Re: How thick can I lay carbon fiber?

Postby rynhardt » Mon Feb 26, 2018 8:24 pm

opie wrote:
Mon Feb 26, 2018 7:04 pm
Do you mean use a core with the mold, so that I am not using so much carbon? I've considered this, do you think I could just print one? It would not help at all with strength, I think, but maybe the carbon could be enough. My other idea is to print a another complete (smaller) mold for the core and use pour foam.
Yes. Use a core within the mould, with just a few layers of carbon on the outside. The core needs to handle compression and shear force and bond well with the reinforcement. A printed core might work, if it's as strong as a good foam or wood core.
My approach was to pour the foam in exactly the same mould and then sand approx 1mm off. You don't need to be super precise if you can flood the mould with epoxy to fill in the missing half mm here or there.

Do the carbon layup on the insides of the mould, let it set a bit until tacky, then insert the core with a generous amount of epoxy.
Clamp the mould halves together and squeeze the excess epoxy out. You can mix some cotton flocks or glass spheres to increase the viscosity for this step.

The video below is not for a HF mast, but another structural beam, but I think the same principles will apply.


opie
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Re: How thick can I lay carbon fiber?

Postby opie » Tue Feb 27, 2018 6:48 am

rynhardt wrote:
Mon Feb 26, 2018 8:24 pm

My approach was to pour the foam in exactly the same mould and then sand approx 1mm off. You don't need to be super precise if you can flood the mould with epoxy to fill in the missing half mm here or there.

That's a good idea. I am going to try that. Thanks. :)

P.S. Cool video.


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