I found this rather interesting and a good idea:
[ame=“http://www.youtube.com/watch?v=9_tDQTgdsCg&feature=related”]YouTube - DIY Carbon Fiber Prepreg. How to Make Your Own Pre Preg Carbon Fiber[/ame]
What are everyone’s thoughts?
-Andrew
I thought the benefit prepreg was very precise ratios of resin to fiber, which this doesn’t give you. I’m sure this method could work, but I don’t know that I would call it better than proper prepreg. It would certainly be harder to monitor you’re resin content.
As a side note, did you notice that he was using a Coke cup? I’m pretty sure those are wax coated, which I though was a no no?
there was this discussion a few months ago about this same guy:http://www.compositescentral.net/showthread.php?t=4482
never noticed that!!! yeah, it’s a bad thing.
but prob the amount of wax that gets scraped off in a large sheet of selfpreg isn’t overly bad. Then again, it’s for an aircraft.
Besides having an exact fiber volume fraction prepreg is really easy to layup since you don’t have to force resin into corners. The tackiness also helps it stay in place. Poor man’s prepreg gives you those advantages as well.
I was also wondering what effect the freezing has on the epoxy. I know it’s the best thing for unmixed products, but I wonder what it does once it’s been mixed? Does it have an effect on ultimate strength?
I’m guessing if you told an expoxy manufacturer that you were going to freeze b stage product and reuse, they wouldn’t condone it.
What is this resin that they are using? does this go like proprietry pregreg after it is frozen then thawed out or is it like regular epoxy once thawed ie runny and very messy?
if you use the right hardner it works almost the same.i use a really slow harder and once it is frozen it has the same rigid feel that true pre preg has.you have to use a little heat to get it to take the shape of the mold.the only thing i need to figure out is where to buy the embossed sheet…i have spent a bit of time looking and i still havent found a source where i wouldnt need to buy a 1000 yard roll.the other issue im not crazy about is the higher cure temp for this resin/hardener combo.i use mainly frp molds.
this guy in the video has this process pretty well figured out.he uses a richer pre preg for the first few plies.then a leaner pre preg for the last few plies.from what i remember reading.his reasons for not liking commercial pre preg.it was not very consistant.i like going this route because i also like having very good control over my resin ratios.if i could only find that embossed sheet.
What is the embossed sheet that you need? Do you have a link to some so I can see what it is?
^ http://catalogue.airtech.lu/product.php?product_id=470&lang=EN
I have wanted some for awhile but like KMT said nobody needs a full roll. If enough people wanted some maybe we could all split the cost?
How much could a full roll cost?
this place looks promising.its a big outfit so im not sure how much luck i would have.its worth a try though.
http://www.bloomerplastics.com/products_composites.html
its what comes on pre preg.in all the searching ive done.i havent seen pics.i have used pre preg before.so i know what it looks like.but i havent seen a pic i could post for you.its just a thin plastic sheet that has a pattern embossed in it.
What benefit does the embossing give? Do you have a peice of the film that you could send me?
the embossing keeps the sheets from sticking to the resin.i use 1mil painters plastic.if the resin starts to firm up.it is a hassle to remove.its been awhile since i worked with pre preg.so i dont have any of the sheet.some folks here that do work with it regularly would have some.it gets chucked out when you do a layup.
reckon that there is a lesser amount of surface area that is in contact with the resin in the prepreg, so it’s easier to come off, but still protects the entire surface. besides that, NO idea why prepreggers use embossed film.
Also, maybe when you are debulking, and you leave the top layer on, it provides an airflow through the stack…just a guess on that one too.
the surface provides better air flow than a nontexture backing
Solution based prepreg is made by running the fabric through a bath of resin diluted with solvent. Most of the solvent is removed as the prepreg is B-staged in ovens. Residual solvent can change the flow properties of the matrix (viscosity vs temp) and can also increase void content. I’d imagine the embossed film helps with the removal of that solvent. The channels are not filled with resin, so vapors can flow out.
There seems to be some confusion/misunderstanding from watching only the video, so I’m quoting the article by David Algie that can be found on Woodward Aerospace’s website:
"All you really need to make your own carbon fiber prepreg is the right prepreg plastic embossed sheet. You can use just flat plastic but it gets an airlock of sorts and is almost impossible to pull off the carbon fiber.
I make an 8’ by 4’ table at a time by just spreading the correct amount out on the fiber and then putting the top sheet of plastic on it, and then cut the parts right there and then and put the lot in the freezer.
Over time and experience I have formulated the right amount of epoxy to use for first layers and then less for the next layers, you always want a richer layer on the tool surface. I tried blending different hardeners to get the cure temp and time I needed but have had the best results with the high temp hardeners, this gives you a wider B stage time so with the low pressures that a vacuum gives (as opposed to an autoclave cure) you need enough time to bleed out gasses and general resin flow. The hardener I use needs about 7 hours at 180F, or about 2 hours at 250F. I tried using B staged prepreg with vacuum like you have to with autoclaved parts but the low pressure doesen’t work well with that, so all my vacuum prepreg is A stage stuff. Finished parts I generally get a 40% resin content, and autoclave parts under 20%. With a vacuum I can get very close to a pinhole free surface, and with B staged fiber in an autoclave the parts are pinhole free. You generally need to look at the back side of any layup to check it’s quality, this is where you see the usual overuse of resin, giving a typical fluid lock as too much resin is impossible to bleed out, with a fluid lock like that the fiber isn’t really interlocking over each other and you give up a lot of part stiffness, and add a lot more weight that the vehicle has to carry around for life.
Prepreg always has either plastic on both sides, or plastic and waxed paper, leave off one of those and your cutting table or patterns are somewhat gooey…
I don’t know what the viscosity of this resin is, but I heat it slightly to get it thin enough, bit thick as it is cold.
I just use a spreader to spread the resin out, a Bondo spreader to be exact. I do it in quarters of the table and measure the poured amount to get it even.
Believe me, don’t use flat plastic to make your own carbon fiber prepreg, especially if you make a very rich batch. All types of fiber, be it 3K 2x2 carbon, 7544 fiberglass (my favourite for moulds) or 6K uni carbon needs a different amount of resin. Carbon first layers I use 600 grams of base resin, before adding hardener, 450 for layers after that. This is lean enough that the plastic will almost fall off itself, and for the autoclave stuff it does fall off, and you would swear that there is NO resin in that carbon."
interesting… most of my experience with carbon fiber has been with using low temperature cure prepreg from ACG and they don’t use embossed plastic film. One side is a sort of paper with a glossy side against the prepreg and the other side is a flat plastic sheet (with no embossing). It is somewhat a pain to get the plastic sheet off sometimes, but you get pretty good at it after a while and it is no where near “impossible”.
I have only been speedreading this thread, and did not even see the video, but I can say 2 things:
-I can ask for embossed film at Airtech in smaller rolls. I will need to take a full roll, but I am prepared to do so. (same for high temp (426C, 800F vacuum film).
-For the European people here: Use Sicomin SR8500 resin and KTA21 hardener. This is specifically made for prepregs. Wide B stage, low viscosity after heating.