johncarman
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| posted on 1/2/10 at 02:09 PM |
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Air bubbles in Carbon Fibre
I have recently been trying to make some parts in carbon fibre, starting out with a simple flat piece to be used on my dash, but I was hoping to do
cycle wings etc. I have attempted 4 or 5 pieces now but I can't get rid of the air bubbles in the first layer of resin (the top coat once
released from the mold).
I have tried using the heat gun trick on the carbon mods video and this helps, but I have to heat it for so long to remove all the bubbles it has
cured before I have finished ! I have tried both West and Carbon mods Resin, I have the same issue with both.
I am wondering if the problem could be the conditions I am working in, I have a small heater in the workshop, but how cold it's been outside, it
doesn't get that warm in there. I have noticed the epoxy goes runny the warmer it gets, is this the problem, do I need to do this somewhere
warmer ??
Has anyone else had the same problem, or got any advise ??
[Edited on 1/2/10 by johncarman]
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Richard Quinn
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| posted on 1/2/10 at 02:21 PM |
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Is it small air bubbles where the tow's cross each other or are you getting larger patches? Is this just on flat pieces and are you just doing a
wet lay-up or are you applying any vacuum or pressure to consolidate the part?
[Edited on 1/2/10 by Richard Quinn]
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Steve Hignett
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| posted on 1/2/10 at 02:32 PM |
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Have you used any release agents on the glass?
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Werner Van Loock
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| posted on 1/2/10 at 02:38 PM |
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are you using clear gelcoat as first layer? This might do the trick.
And yes, epoxy resin likes a warm environment so start heating or wait till summer.
And what are the steps you take to make up the piece?
eg first release agent, then clear gelcoat, then epoxy resin rolled on, then epoxy resin rolled into the first layer of CF, then place the CF on the
gelcoat/resin etc...
http://www.clubstylus.be
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bodger
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| posted on 1/2/10 at 02:46 PM |
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Clairetoo is an expert on carbon.
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smart51
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| posted on 1/2/10 at 02:47 PM |
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Whenever I've tried to use epoxy resin, I get air bubbles just by stirring the 2 parts together. I've never managed to get the bubbles
out so I ended up with pin holes in the gaps between the weaves. I'd always guessed that vacuum bagging removed these.
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Richard Quinn
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| posted on 1/2/10 at 02:48 PM |
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quote:
Originally posted by Werner Van Loock
are you using clear gelcoat as first layer? This might do the trick.
And yes, epoxy resin likes a warm environment so start heating or wait till summer.
And what are the steps you take to make up the piece?
eg first release agent, then clear gelcoat, then epoxy resin rolled on, then epoxy resin rolled into the first layer of CF, then place the CF on the
gelcoat/resin etc...
It's unusual to have a gelcoat with an epoxy resin system. Also, if you are using a fairly light (e.g. ~ 200gsm)
twill then using a roller can drag the cloth. Careful stippling is the only way. Use a slow hardener and warm the lay up with a gentle heat gun and
you should really see the resin start to "wick" into the cloth. A really slow hardener should allow you to apply a reasonable bit of heat
before the resin starts to go off.
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blakep82
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| posted on 1/2/10 at 03:00 PM |
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using rollers is supposed to help with bubbles too.
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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Steve Hignett
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| posted on 1/2/10 at 03:14 PM |
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IMO the gel needs to be rollered onto the glass, you could try a different type of gel (spray gel?).
Also IMO, you need to roll the CF after you've brushed the resin on, but you need a specific roller for best results...
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Richard Quinn
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| posted on 1/2/10 at 04:03 PM |
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IMHO 2x2 twill, inexperience and a roller may do away with some of the bubbles but it will end up with the twill all over the place!
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twybrow
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| posted on 1/2/10 at 04:21 PM |
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Paint the resin on neat as the first coat. Not too thick, and use a paintbrush, which will help release any trapped air bubbles. Let that go tacky, or
completely off before you carry on and put the fibre down...
If you want to get real technical, you could place the unmixed resin under vacuum before using it, which will remove dissoved voltatiles, but this is
massive overkill to achieve a good finish.
Any hand layup type process will be prone to air bubbles, hence the need to paint the resin on first as a nice clear coat, that can be sanded/polsihed
as required to produce the surface finsih you desire.
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Richard Quinn
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| posted on 1/2/10 at 06:41 PM |
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If it's epoxy, don't let the first coat cure completely. Sure, let it tack and then lay up onto that but if it cures you get an amine
"blush" which won't allow the 2nd coat to bond properly.
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johncarman
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| posted on 1/2/10 at 07:33 PM |
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Thanks everyone for the advise, here is a bit more info to clear up some of the questions...
I am not using any Gel Coat, the first layer is epoxy straight onto the mould (covered with release agent). I let this go tacky, then lay up my first
layer of fabric which I use a roller on to ensure it is well pressed into the resin. I find without the roller I was getting air where the
tow's cross, between the first layer and the fabric, but now the air I have is actually in the first layer of epoxy. as Smart51 mentions, the
bubbles are there as soon as you start mixing the epoxy and the hardener, and I don't mean the odd bubble, I mean it's like the head on a
pint of beer !! Is this normal ??
I am suspecting this must just be down to the conditions I am working in as I seem to be following most of the advise out there short of using a
vacuum and I still have a problem.
John
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Steve Hignett
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| posted on 1/2/10 at 07:57 PM |
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How are you applying the first layer of epoxy to the glass/mould surface then?
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johncarman
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| posted on 1/2/10 at 09:39 PM |
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I am just brushing the first layer onto the sheet of glass (my mould), which has been covered in a PVA release agent.
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Steve Hignett
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| posted on 1/2/10 at 09:48 PM |
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I would strongly suggest rollering it on! (pour it out of the jug onto the surface in a cross hatch (think sauce on bread!) then roller it horiz. and
vertic. until it's as flat and even as you can get it)
Also, (and I know this is going to be imposible to gauge over t'internet, but) how are you applying the PVA, and how thick have you got it?
Have you sealed the glass? How many times have you used this "mould"?
[Edited on 1/2/10 by Steve Hignett]
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johncarman
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| posted on 1/2/10 at 09:52 PM |
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I have started with a fresh mould, I am not really sure how much release agent I should be using, I just pour about a cap full onto a rag and wipe it
over, I am frightened of putting too much on, I didn't know if it would effect the surface finish of the part.
When you say roll it on, you mean roll the epoxy on instead of brushing it ??
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Steve Hignett
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| posted on 1/2/10 at 10:30 PM |
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The performance of a mould is better after a few releases, so that could b playing a small part.
Yes I do mean to roller the epoxy on...
I'm sure the PVA is prob being done right else your part wouldn't be releasing in some areas potentially. The trick to it is, to put on as
little as possible, but you can't wipe/buff it over to thin it out or it will remove what you've put down instead. Work v quickly and
smoothly to get a perfectly even thin coat.
You never mentioned whether you've "sealed" the new mould yet either?
[Edited on 1/2/10 by Steve Hignett]
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Richard Quinn
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| posted on 1/2/10 at 11:21 PM |
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I probably wouldn't even use pva on glass. I would just use about 10 coats of silicone free wax polish (even colron wax will do)
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Steve Hignett
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| posted on 1/2/10 at 11:24 PM |
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quote:
Originally posted by Richard Quinn
I probably wouldn't even use pva on glass. I would just use about 10 coats of silicone free wax polish (even colron wax will do)
Was thinking that myself, but wasn't sure to suggest it in case that's all he had!!!
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twybrow
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| posted on 1/2/10 at 11:52 PM |
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PVA put on too thick will make a dodgy surface finish, but not air bubbles so much as a crazing type effect (although I guess it would depend on just
how much PVA you did apply!?).
Your resin shouldn't froth like a pint of beer. Some bubbles sure, but not super frothy! Is the froth only there when you mix the components?
Can you see signs within either individual component of the air? Are you being careful with your mix ratio - epoxy is not tolerant of poorly measured
mixes?!
Is the problem uniformly distributed all over your part, or just in very localised points?
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Benonymous
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| posted on 4/2/10 at 05:26 AM |
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I have just finished making some big parts in moulds and I'd actually avoid putting epoxy onto the mould to begin with. When you see racing car
(F 1) parts you're looking at stuff that's made from pre-impregnated fabric, put in moulds and then autoclaved at fairly high temperatures
in a near vacuum. No wet layup will ever approach this level of finish. The problem you're describing is practically unavoidable.
I have been doing my layups in a female mould using 450GSM twill with very wide tows. My method is to lay the cloth in the mould then wet out by
pouring the epoxy in and using a squeegee to move it around. Once I have wet the cloth out, I use a metal roller to consolidate and ensure the cloth
is wet through. I alternate between a roller with a sort of really coarse knurl and a paddle roller with corrugations that go across the roller.
The trick to the "glassy" carbon look is actually to use a high fill clear coat and buff it. I vacuum bag my parts at around 20 to 30
inches of mercury and not even that will give you a top surface free of pits in the crosses of the tows.
With any composite, you're trying to get the correct resin to reinforcement ratio for maximum strength. If you drown the carbon in resin to
get the top surface so thick that the weave isn't showing through you've got way too much resin and the part will be brittle.
If you want a good surface, vacuum bagging is the way to go.
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phelpsa
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| posted on 4/2/10 at 09:04 AM |
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quote:
Originally posted by Benonymous
I have just finished making some big parts in moulds and I'd actually avoid putting epoxy onto the mould to begin with. When you see racing car
(F 1) parts you're looking at stuff that's made from pre-impregnated fabric, put in moulds and then autoclaved at fairly high temperatures
in a near vacuum. No wet layup will ever approach this level of finish. The problem you're describing is practically unavoidable.
I have been doing my layups in a female mould using 450GSM twill with very wide tows. My method is to lay the cloth in the mould then wet out by
pouring the epoxy in and using a squeegee to move it around. Once I have wet the cloth out, I use a metal roller to consolidate and ensure the cloth
is wet through. I alternate between a roller with a sort of really coarse knurl and a paddle roller with corrugations that go across the roller.
The trick to the "glassy" carbon look is actually to use a high fill clear coat and buff it. I vacuum bag my parts at around 20 to 30
inches of mercury and not even that will give you a top surface free of pits in the crosses of the tows.
With any composite, you're trying to get the correct resin to reinforcement ratio for maximum strength. If you drown the carbon in resin to
get the top surface so thick that the weave isn't showing through you've got way too much resin and the part will be brittle.
If you want a good surface, vacuum bagging is the way to go.
The autoclave applies very high pressure, not vacuum 
I was going to suggest a thick coat of lacquer and buff it back. Its not cheating, its a trick used by many carbon fibre manufactures, even on prepreg
if you have a dry weave or a dull finish.
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johncarman
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| posted on 14/3/10 at 09:58 PM |
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Thanks everyone, some great advice here. Given up on CF at the moment, was taking up all my time and was getting no other winter mods done, I will
revisit over summer.
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RK
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| posted on 15/3/10 at 01:14 PM |
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As a mortal who's tried it many times, i gave up too. It is VERY Temperature dependant, and I never got rid of the small holes. They
wouldn't fill afterwards either, no matter what I did, because the release agent stops the new stuff from sticking to the epoxy, even when
dried. Obviously, it is possible to do, I am convinced, but I want an expert to show me first hand the next time!
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