More basic Carbon fiber questions.

General Composites Discussions Composites Talk
#1

If your not tired of my thirst for knowledge, then could you answer some of my very stupid questions.

  1. whats does 2 x 2 twill mean?
  2. How many layers of carbon fiber + epoxy will it take to make a 40cm x 20 cm, 4mm thick part?
  3. I want to make a male mold, for a molded RC car carbon fiber/ kevlar chassis.

I plan to do something similar to this

My mold is going to be more complex, with corners in the design, but can i use the same theory? Whats that plastic sheet called?

Also, can i sandwich kevlar fabric between carbon fiber, during lay-up?

Finally, if I don’t use plastic sheet on the mold, what can i use to coat my mold?

Thanks for your help, and sorry for the interrogation :smiley:

#2

Since I’m bored at work due to Newport being gits…and my vacuum pump ready to commit suicide, i’ll pop a few answers.

  1. whats does 2 x 2 twill mean?

2 over 2 under. It is the style of the fabric weave. Plain Weave is one over, one under, like a normal…well…plain weave pattern. There are many many more. Harness, Satin, Crowfoot. it all depends on how each tow (strand of Carbon fibers) is weaved.

  1. How many layers of carbon fiber + epoxy will it take to make a 40cm x 20 cm, 4mm thick part?

Well, for thickness. Um. I dunno. For a 5oz plain weave pre-preg (meaning the epoxy is already on the fabric, ready to lay up and cook) is is about 10 plys.

  1. I want to make a male mold, for a molded RC car carbon fiber/ kevlar chassis.

My mold is going to be more complex, with corners in the design, but can i use the same theory? Whats that plastic sheet called?

Like, screwing a few 2x4’s on the sides, etc? It is possible yes. Just remember, what you put on, has to come off when it’s hard, so you can’t wrap a 2x4 completely, and expect to pull it right off. We used a truck to do that the other day, to pull a split 2x4 off a tube. (don’t get me started on what became of THAT project…)

The plastic sheet can be many kinds. Vacuum bagging I think is either nylon or some sort of poly. I hear trashbags work.
That picture I’m sure has a bag wrapped around the wood, and then another one stretched on top, to compact all the layers of carbon fiber. One can also put it in a sealed bag, and vacuum out the air with a good pump.

Also, can i sandwich kevlar fabric between carbon fiber, during lay-up?

Yup. as far as I know. I think kevlar is hard to wet-out with epoxy, or might not stick well…someone else can answer this.

Finally, if I don’t use plastic sheet on the mold, what can i use to coat my mold?

You can seal the wood with a sealer. Sand down until perfectly smooth and seal. I’m sure you can coat it with a polyurethane coat to make it shiny.
Then, you must either: wax the mold a few times, or use some sort of mold release agent. Frekote, or PVA. There are many kinds of perm, and semi-perm mold releases.

#3

WOW.

Thankyou sooooooooo much, this has really helped me again. Thankyou.

Can I ask where I can buy some polyurethane coat from please.

Thanks again, so helpful, this forum is a saviour.

#4

Home despot, or lowes or any hardware store…
Yup, everyone on this forum rocks!!!

#5

thanks again. You rock :wink:

#6

Ok thanks, I think I now have knowledge to order my carbon stuff, after I make the mold.
I am going to do a write up about this.
I know I am only a noob. However, I feel that if I create something strong, and use the methods you outline, I can describe it in a very easy to understand manner.

I found it quite complex at first to get into my head all the terminology, and processes, however, I have been helped by the best. :smiley: :smiley:

#7

Can you post a pic of what you want to do?

#8

Something similar to this

I have another question.

Could I cut those small slots ( that fit batteries, whilst I lay-it-up, or do I need to machine them?

#9

you rc guys kill me! I love how fierce you guys get with those things.

Those notches were machined after the fact. I doubt youll be able to have such concentric and perfect notches in a panel without doing it after demoulding the part.

Id love to make a carbon fiber badass RC boat…but its pointless…Im in the desert.

#10

haha, so true…:smiley: :smiley:

Cant you make your own lake for the boat? OR a small pond at least?

#11

90% of the construction of the parts shown are glass fibre,hence they are white in the cross section…the same as a huge amount of ‘carbon’ parts…

#12

I can’t see any white in those parts…they look exactly like the thickwalled carbon bits I do.
Of course, what the hell do I do with a .27" thick 2x2 90deg bracket.
anyways

Yeah, as long as the wood block u use as a mold is machined how you want it, it should be easy to do that. Even if you somehow machine those pockets, or glue on small bits of wood blocks, it should work out. Not as perfect as a post-machined part…
Definatly, you would want to seal the wood well, and sand it smooth. Seal again, and then apply lots of mold release.
I would say that vac. bagging would be the best way to do it though, since you have many corners to deal with…stretching plastic over it would not compress the inside corners.

#13

If you are trying to make U shape items, then you need draft angles in the plug too…

#14

I just got an idea.

Basically in RC cars, we use rechargeable Sub-C cell packs.

They cost around $60 per pack, so I need them secure. I always find in ‘machined’ battery slots cut into the battery, actually damaging them.

But If I stuck beveled blocks on like you say, then I could get a nice smooth, and angled edge to hold my cells. Then they would’nt be damaged, and would site a few mm’s lower.

Thanks for the help.

Another question, haha.

Could I use this bag, as vacuum bag?

It basically has the power to shrink a folded duvet to about 3 inch thick pack of fabric for storage. It works by th vacuum sucking air out the pack, and shrinking the plastic.

http://www.jmldirect.com/product.php?cid=7&pid=49

Thanks.

#15

or that.

Hmm. Whilst I would say no, it all depends on what exactly you need to do. Most vac. pumps can be run for hours. I don’t know if something like that can be run for that long without over heating. They aren’t meant to be run more than 60 seconds at a time.
Cure time for your resin can be anywhere between 2 hours or 24 hours. It all depends on what you use.
Also, it will not get a powerful vacuum anyway. though…it MIGHT be good enough for what you need…IF it could run as long as the resin is curing…

#16

The beauty of those bags…

You suck the air out, then you can seal it up, it holds that pressure, and stays compressed.

Also, Wekrsberg mention a draft.

Does that mean I must angle the edges so it is shaped for easy removal? I cant remember the term, is it convex?

#17

Yes, draft angle allows the removal of the cured part. 2 to 5 degrees can work.

That bag is Nylon (should release ok but still wrap other peel ply or release films too) so it may work but you will get stronger parts by using reg. vac. bagging supplies and pumps.

#18

Ok, thanks everyone. I have put together my wish list, which has totalled $300 :eek: :smiley:

Will be ordering in ‘stages’

Thanks for the help, I found this video super helpful
http://video.google.co.uk/videoplay?docid=8801536764731290932&q=carbon+fiber

#19

yup…that happens…this ain’t a cheap hobby!

just do a search for videos on youtube…there are a few.

#20

thanks,

Donty worry, after buggin everyone one here, it is my duty to dish out the money,…

i just need to get it round my ‘accountants’ :smiley: