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

Chris I mean that those in the two links are not (what it looks like) using heat to cure the layers of pre-preg (if it is that) carbon.

I've always thought that pre-preg needs heat to cure (which finishes off the process on my little how-to list), you still need the resin to bond the layers correctly, the heat is the final step.

 

2 fantastic links G60 racing



I think they're using wet layup not pre-preg though as pre still has to go in an autoclave when vacumed

Makes me want to have another go but its a bit cold this time of year [:^(]

 

i can try and get you some info from work if you like chris

 

Let me know which day, and I'll hire a lorry

 

chris, i work at the same place as mr Gill.. done a bit of CF work whilst there.


For pre preg...
Pre preg requires no seperate resin but is harder to get a good shiny finish with without the use of laquer, can't really be laid up on to glass as it has to be baked at approx 130 degrees C, (unless you've got some low bake stuff which cures at about 90).

The process goes something along the lines of...

Find a nice flat item that can go in your oven (possibly a stainless oven tray )
Lay out a piece of plastic sheeting,
then a layer of cloth to absorb the spare resin,
then the layers of CF in whatever orientation you want (i.e. 0, 90, 0, 90)
as these are laid down roller them flat to remove any air pockets or you'll get de-lamination causing a major weak spot in your CF.
once you have sufficient layers for what you need place a seperate layer of cloth on the top.

This is then vac bagged down flat on to the flat surface, and placed in the oven for approx 3hrs (depending on the type of pre preg you have.


For wet layup........

Find a suitable flat piece of glass (gives a reasonably shiny finish without the need for laquering).
Get some car polish and polish the living daylights out of it (this will allow you to peel it off when it's set),
apply a small layer of resin to the glass,
lay your first piece of CF on to the glass, apply resin over this and dab through so it penetrates,
repeat above step to the number of layers you want. (remembering to roller it flat in between to remove air pockets). and in the orientation you want.
Once you have done this apply a layer of cloth to absorb resin, a layer of fine cotton wool sheet (to absorb more of the excess (as it's wet and not pre preg),
then vac bag it all down and leave in a warm room over night (airing cupboard if you're at home).

Hope that helps a bit. Pre preg is good but not nearly as plyable for moulded shapes. wet layup is very simple to use (same as fibreglass basically) and you can get some quite nice results.

here's a sample of a practice i did on a 20v cam cover with wet layup

 

Nice!

What sort of sheeting? Thick plastic or other?

How can this be removed once in the sandwich once all absorbed?

It this removed pre curing?

So any trade names for the lacquer and the resin? And are the rollers the little 6inch wide things from art class? Metal, plastic or rubber wheel?

What sort of pressure is required from the roller? Assume it would be quite easy to compress the front face lacquer or resin too much?

 

What sort of sheeting? Thick plastic or other?

yea thick plastic (make sure you stick it down to avoid wrinkles etc on the face of your CF)

How can this be removed once in the sandwich once all absorbed?

Once the pre preg is baked the plastic shouldn't be stuck to the job, the cloth will peel off, it isn't easy to come off but with a good tug it'll peel away in one complete piece.

Is this removed pre curing?

The final layer of cloth is removed after curing (the resin won't stick properly and become fluid until it reaches the CF curing temp (dependant on what you have).


The rollers are the art type that you mention, pressure isn't really important as pre preg won't compress very much (more critical on wet layups where you apply the quantity of resin) and a small item won't really need much rolling as you should be able to get it pretty well compressed as you lay it out. (just make sure you use a nice clean roller to avoid getting contaminets on the CF).

I will try and find out the trade name for the cloth etc for you next week.

Hope this helps a bit.

 

Chris the 90 degree thing is to give striffness in a number of planes, imagine the fibres like a bunch of drinking straws, can only take loads in certain directions, rotate the layers like plywood and suddenly you have a reasonable structure on your hands

 

What sort of thickess, say? The sort of plastic from a signwriting place, maybe?

But surely the cloth contours will ruin the finish on the tidy side of the CF laminate?

Ok, sure. I was picturing a situation with cloth stuck to epoxy. Hmmm. Lost!!

So a metal wheel roller, or rubber, or (surely not?) plastic?

Indeed!

Sure Prof - I was just puzzled since the fibres criss-cross at 90-degrees within a single sheet anyway, but I'll leave it there! It's more than I need to be asking about !!

 

you have to pin the cloth down as flat as possible, it's normally not too difficult where the pre preg is slightly sticky.

at work we have plastic rollers, but any would do the job really.

Alot of companys that produce carbon panels use a wet layup as it's a lot easier to ply into contours and get a good finish with without the use of a laquer.

Some carbon has trace lines in to help with the layup of different orientations. Not really needed tbh unless you plan on making large panels (e.g. bonnets/tailgates) where flexing is a possibility.

I've just started to make up some big flat sheets to make some rear door cards for my mk2.. will keep you updated when i get to the layup stage (got to fit some D-zeus recepticals into the car first )

 

Sounds like you're our composite guru Chris, what's best to cut Carbon sheet, got some pre preg 0.8mm sheet from GPR at Silverstone the other day to make a switch panel mount.

Just wondering what to use to cut the stuff before I feck it up.

 

I gather it's fine to drill it, saw it etc.

The pros use Dremel-type trimmers and sander wheels - and breathing equipment...

Best to cut roughly first and then trim with the finer tools.

(Pre-preg cuts fine with scissors when uncured btw).

 

Very nice indeed! Keep us updated.

 

You can cut it *roughly* with a jigsaw + fibreglass blade, will need to find something that'll cut so it looks neat

Was 19.50 for the 300 (maybe more) x150 sheet so not toooooo bad.

 

You can cut it with a hacksaw, just take it easy and use a new blade. Then use a bit of 300 grit to dress the cut edge.
And the most important of all, seal the cut edge with some resin. If you don't do this moisture will seep into the edge and then it'll either look crap or fall off your car.

 

Thanks for the tips!

 

GVK, if you need any help with carbon fibre give me a shout, i'm just down the road in bristol.

 

as said easy to cut same as you would with fibreglass.

hacksaw/dremel... bandsaw if you have one is very good as it doesn't tend to cause any fraying/de-lamination.

for cleaning up and fine work you can use a file, emery paper etc. (just make sure you're wearing a dust mask!).

Note for anyone who is interested in more info i should be starting back in the composite area in the next few weeks so i can get more info on Companies that can provide cloths and CF itself.

Gary if you ever need small bits of CF again drop me a PM.

 

Cool, I'll bear that in mind thanks

 

Will do Chris, ta!