Laying up carbon fibre, resin, what's needed etc. The process?

Without any particular project in mind - but say dash clock surrounds - I was just pondering how you'd go about getting a professional finish when laying up a carbon fibre sheet.

I got hold of a few offcuts of carbon weave, which is a bit tacky to the touch (presume this is pre-preg?) so it would be rude not to at least try..

The aim would be to:

1) soak the weave full of some sort of epoxy, for the main strength of the sheet. No idea what epoxy you need btw. Ideas?
2) And then somehow, haven't a clue how, put laquer on it for a mirror perfect finish...

Any ideas? Got to be similar in theory to fibreglass moulding, and I assume pre-preg means no autoclaves required at all, ever (thank Gaawwd )

 

The technique I've been told from the bloke I bought some uni-directional carbon from (not pre-preg) told me to do it this way...

"...if you want a really good finish you wont to lay it on a plate of glass, if you do it this way, you only wont 1 layer of wax as a release agent but it must be buffed up really well. I have used glass with no release agent on it but there is a knack to it. You paint a layer of polyester resin on the glass then then lay the cloth, stipple more resin on top of the cloth, then lay another layer of cloth 90 degrees to the first layer then apply resin to the surface of that cloth. Make sure you use a roller to force the resin into the fibres.

Use polyester resin, any make is ok.

Use a Wax with no silicones in it eg simomize wax (as used to polish car body work)."

The glass is used to make flat panels, the smoother you can get the surface and the more resin you use, the outcome should hopefully be a deep gloss finish, no need for lacquer.

Pre-preg carbon fibre will need to be cured in an oven, the non-pre-preg carbon cures in ambient air. I can give you some details of the bloke I got my CF from if you need any.

 

Nice info.

Ah, right - I was thinking glass or flat laminate surfaces (kitchen - no, not really!) with a release agent, but then I couldn't figure how the top surface can cure.

So effectively it's all done using another smooth surface - nice.

Hmmm. Cogs whirring...

So polyester resin - any trade names to hand? I would't know where to look.

Just on the pre-preg, non-pre-preg point, what actually is curing? The polyester resin dries/cures, and the sheet is rigid and usable, but it needs an oven to cure the fibres and whatever is impregnated into them?

Is there an obvious visual difference between pre-preg and non to help identify?

 

I think you might just have some pre-preg,meaning you do need an autoclave! i think you could use the oven if the part is small enough though but i'm not sure what finish you'd get without it being vacum-packed in a mould
I looked into this a while ago,like you say wet lay is like fibreglass (i have some and its not stick at all,just woven cloth) the finish you get depends on the finish of the mould.
ie highly polished,then a gel coat is applyed to that 1st (which becomes the shiny outer layer) then the weave and so on.....
If you want flat carbon some told be to use 2 bits of polished glass! (very flat and smooth)
But you must always use a mould release agent or you'll just bond it all together
Sorry i can't be of more help but i was a few years ago
I'd give it another try but remember the epoxy likes heat to set (a nice hot day) and this time of year is not ideal.
what ever you want you'll need some type of mould and you will have to make it! fibreglass is ideal and is cheap to experiment with before you try the carbon.You can get F/G kits for less than 20 at most car spare shops to start you off but there is a load of info on the web about it. I lost all mine on an old computer otherwise i'd point you in the right direction.
Keep it simple at 1st (small & flat) think about "shrinkage" and remember that shards and carbon dust is dangerous (a tiny shard can work its way right through your hand in time)
Good luck.

 

All good info too.

Let's assume flat carbon sheets to keep mould complications out of it.

I've got some carbon, like you say, which is woven cloth. Tacky to the touch - that's all I know about it.

So 2 pieces of glass inplies carbon sandwich I take it? Usually one side can be left rough though, so one bit of glass should do for a small sheet, say 10cm x 10cm (as an initial effort).

You mention a release agent, so this goes on the glass after the Simoniz wax polish on the glass which Mk1 Driver mentioned? Or is that the alternative release method?

Then poly resin, then carbon layers, then roller, as before.

 

I'll try and get a name for the polyester resin from the same chap.

Pre-preg already has the correct ratio of resin pregnated into it (it'll be like a heavy cloth that wont fall apart, unlike carbon cloth which is quite delicate around the edges as the weave can fall apart, very light), on these F1 programmes you'll see pre-preg and technicians applying resin to bond layers together. When the CF is exposed to the heat (125C) and pressure (around 100psi) and vacuum, the resin flows between the fibres and cures.

Non pre-preg is quite similar apart from not requiring the (high) heat and pressure, the only downside is that it is a little tricky to determine how much resin you need, too much or too little can make the CF heavier or weaker (if it's for a panel gauge, door cards, this wont matter too much). You will need to be careful in keeping all the weave together when stippling the resin into the cloth, as you may end up with a pattern all over the place.

As mentioned above though, if the part is small enough you could put the pre-preg in an oven (kitchen!) but I'm not sure of the result you will get (or the reaction from your missus) without it vacuum packed and under pressure but I'm sure some guides I have seen, the pre-preg has gone straight into an oven with still a good result.

 

Tacky to touch must be pre-preg, the cloth I have is like this, where you can see all the strands at the edges (and if the weave breaks up, you'll be able to see through it).



Yes, one piece of glass if you want one surface smooth.

+ Glass sheet
+ Release agent or car body wax with no silicones in it (eg simomize wax)
+ Layer of polyester resin
+ Lay carbon cloth
+ Stipple more resin carefully to that layer
+ Another layer of carbon 90 degrees to the first
+ More resin and use a roller to force the resin through
+ Leave to cure (warm room required)

That is the basics to the 'wet layup' technique (not for pre-preg).

More resin on top of the release agent/wax will give the deeper gloss look. A highly polished piece of glass will also go towards this.

 

Sooper dooper info

I think I've got some pre-preg, because the fibres are tacky and they don't want to fall apart.

So, it's going in the oven . What temp? Gasmark ???

Surely because a weave is at 90 degrees to opposite weaves within the same sheet, this makes little difference - it's just a layer.

How does the lay up differ for pre-preg? As far as I can tell, the resin in the fibres isn't enough to cover the resin you'd use on non pre-preg, so I presume it still needs more resin?

Oh, and where to buy a roller of the type needed? Seems almost art-shop like...

 

This is a good thread (and getting me thinking about it all again)

Yes only 1 side has to look good meaning the 1st layer on top of any gel coat is the important one to get right the rest can look like cr*p.
I heard PVA could be used as a relese agent! i'm not too convinced about this my self but mabe its the easiest way to start experimenting. just coat 1 piece of glass in it put the other over the top and squeeze the 2 together a little to get rid of any air bubbles and make it nice and flat/thin the wait a while to see what the result is like!!

TBH i think the wax polish is a better idea just polish the glass 1st then give it at least 3 coats to make sure its a non stick surface
I also think you have pre-preg so you don't need any resin,just cure whats in the fibres,this will leave a less shiny but more authentic finish

Wonder how long it needs on gas mark "5" ?????? lol

 

How does the lay up differ for pre-preg? As far as I can tell, the resin in the fibres isn't enough to cover the resin you'd use on non pre-preg, so I presume it still needs more resin?


I think this i why pre-preg is both lighter and stronger!

There is an even covering using just enough and taking any guess work out of the equasion,surly some of it will "melt" 1st before the cure!

 

Exactly. 15 mins, 20 mins, or 40. What to do? Or maybe it can go in the microwave for 3 minutes?

Wax polish sounds easy - and it's in Halfrauds, which keeps this simple.

I've got some finished off cured CF, which has a poor finish on the rear face, so I know this is the 'done' thing.

PVA's a glue, no?

Judging from the amount of resin in this pre-preg, I don't think there's enough for it to seep through and form a sealed front-face.

See what Mk1 Driver says about pre-preg...

 

Yes but it dries to a rubberish sort of barrier ( i'm still not convinced either)

You might need a "gel coat" on the finished side to get a glossy finish, not sure if you do this at the same time or after though

(edited just to sort the quotes out - CE)

 

Cure temp will depend on properties of the CF, by the sounds of what's on the web, most new pre-preg material require less heat. I have also seen 90-150C mentioned too. (and for that F1 extract of 125C, 100psi and vacuum, it said 2 hours)

The weave is not quite square from memory but what I have is uni-directional, so the strength runs in only one direction, a new layer laid at a different angle to the first will create further strength. One or two layers may still be very thin once you have compressed the cloth and resin.

I have just read that you use the wax and a release agent, but then this was for a mould where it would be more difficult to get the CF out after curing. Either way you have to make sure that the release agent is upto the temperatures of which the pre-preg requires.

Pre-preg has the correct ratio of resin, much more so than what you could achieve yourself wet layup. The amount of resin you need for wet layup I would guess comes with practice.

I think the method to take with pre-preg in making a flat panel is...

+ Polished piece of glass
+ Release agent on top (suited to cure temp)
+ Layer of resin (suited to cure temp again)
+ Layer of pre-preg
+ A little more resin (with a roller)
+ Another layer of pre-preg 90 degrees to the first
+ More resin with a roller
(+ Maybe another piece of glass with release agent applied to create a little pressure on top)

+ Place in oven with, by the looks of it, somewhere around 125C for an hour maybe?

(Or you may simply just need; glass, release agent, pre-preg, oven, done.)

It really will depend on exactly what the properties are of the pre-preg carbon you have and the resins you will need for high temp curing. All of this I'm not sure about as I've only ever looked at wet layups, your best bet might be to try and get some info on the pre-preg and contact a composites company for the exact process to cure it.

 

Yep, so pre-preg still needs some resin to help form the shiny face, so that solves that query.

Interesting about the direction of the weaves, so useful again. I guess for something non-structural, you can just take liberties with the weaves, and layers - add or take away. More or less do what you want after a bit of practice in effect.

The real function of the vacuum (I sense) is to drag air out from the composite layers and resin, mostly for structural reasons and secondly for aesthetic reasons (eg removing bubbles from the shiny face). So again, non-structural work can justify bypassing the vacuum stage (and let's face it, at this level, it's all non structural).

Which leaves the glass layup surface. My guess is some sort of toughened glass is required if wanting to put some in the oven. Bog standard window panes are next to useless (too thin, will crack), and old car windows, whilst toughened, are curved, so again useless. Thoughts?

Excellent. Finally found a proper use for the oven. Knew it was there for a reason!

 

Found a bit of info, here and a forum with cheeky crib and maybe some more info here

 

Heres a link on how to make a carbon plate;

http://www.racingcomposites.net/unt?id=11

Also someone making a home made door;

http://www.turbomustangs.com/techarticles/PBcarbonfiber.php

 

Fantastic - a $4 throwaway picture and frame . Cue one sheet of glass.

Edit: that guide is awesome!

 

Correct on both those main points you mentioned in post #14 Chris.

Both great finds g60racing, a quick glase over, neither of them are using ovens to cure? Is that right? And they look as though they are pre-preg sheets? Unless it's the rather nice twill weave putting me off! (didn't know you could get this as a non pre-preg cloth)

If so that is really quite interesting but surely the whole idea of pre-preg is that it does require heat to cure, not layers of resin top, middle and bottom to simply bond pre-preg sheets together.

 

Cheers for clarifying. I'm going to have to read the rest of those links later, so I am skim reading... but...

I thought resin was needed, as per below?

 

I know someone who make carbon components for a living, the process they use is all the layer are put down with tacky CF then put in oven (very basically) as I understand it.

I told him I found this stuff on the net, he says that the way described in the articles would not be as strong or as light.

I dont relly understand too much but the process I linked to looks pretty simple even with the vacuum..

Have to try scrounge some offcuts and have a go.