I have been using .25" reclaimed chopped carbon fiber in a project. The issue is that the fibers are still grouped with many others as if a tow was simply cut down. I’m looking for a much efficient way to further separate the fibers so they can be mixed much more thoroughly without removing the sizing and what not.
You can buy bags of ready chopped and sized carbon fiber. To me, that’s preferable to using the recycled stuff. My experience has been that the recycled carbon produces a significantly more brittle part than using fresh chopped strands.
The only practical use I have found for the recycled cf is mixing layers of it with regular woven material to lower costs when I make a carbon fiber mold.
I actually prefer to chop my own cf strands when I need them. I save all those odds and ends of the CF fabric that would otherwise be wasteage. I don’t find the need for exact sizing. I just make sure to cut some extra short bits for areas of fine detail. The length doesn’t seem to matter for the rest of it (within reason).
For volume work I would buy it ready done though, in bags sold by the pound.
It’s not recycled, it’s reclaimed. The difference is just like you mentioned, the odds and ends of projects so the actual fibers are still virgin while recycled has been used already. The problem is they’re still grouped too heavily w the other fibers in tow lines from these past projects and do not separate Much when mixed. I need better distribution for strength purposes of course.
You have two options. One is to buy milled cf strands in bags - ready seperated. The other is to cut your own like I do.
Even if the strands are separated, they will still clump together when mixed with resin and form a sticky, difficult to handle mesh. The strands being clumped together won’t reduce strength. It would probably increase it as long as they aren’t all still in the same direction (as they were when woven).
Is that the issue? I.e. You are looking for multi-directional strength and the threads you have are still somewhat bound in the direction of their original weave pattern? If so, chop it up finer with a pair of scissors.
I buy the cheapest $10/ yard plain weave cf off ebay, add my leftovers and spend an evening cutting it into strands. I then mix with heat cure resin and run it through my cold roll laminator sandwiched between two release liners to make my sheet molding compound. It works well and produces very strong parts.
Do you mind if I ask what you are making with it?
I’m making a cylindrical blank that I can machine. I would do the scissors option except I’m doing over 1000g of this at a time so to sit there and cut all the strands in half again would be unrealistic. The clumping issue we are discussing I feel like is still different things maybe. Yes it clumps either way but the way it clumps further separated v stock (how i get it still in a .25 cut tow form) has definitely effected the strength of piece especially since I’m machining this with some detail. I have found the more separated they are the less imperfections there are and the easier it is to machine. Right now I’m throwing them in a blender with grinded down blades so it beats them apart but I’m worried that is damaging the fibers and it’s also still not that fast. Hope that makes sense.
It does. The part I was missing was that you were milling it after curing. I push the mix of cf strands and epoxy directly into a mold in the final shape, so no further milling is needed.
If you are curing it under pressure and still getting imperfections, there are other things you could try but the obvious one is to go to eBay and buy 1/4" chopped cf strands in ready made up bags. Problem solved (if you don’t get the imperfections with uniform 1/4" strands).
Still think we are on different pages. The fibres are already the proper length and uniform. The imperfection does not lie within the fiber itself. It’s the fact that the these quarter inch cut fibers are still in their 24k tow or 10k tow even when cut down to the perfect length. I want to further separate these 1/4" pieces so my molded piece has less imperfections because the more finely they are sperated the better they adhere in the matrix. Since I’m doing a higher detail piece this all is necessary. Even in eBay listings the chopped groupings hold too many fibers per 1/4" segment.
Contact Quantum Composites, they specialize in carbon SMC (What Lamborghini uses)
You’re correct. I wasn’t understanding your issue properly. I only know what you meant now because the last lot of chopped cf I received came in thick 1/4" tubes. They felt almost rigid and I wasn’t even sure it was real cf until I separated a few strands with my fingers. I thought you meant that the individual strands were stuck together.
I think the answer might be to change suppliers and ask what tow was used to make the chopped strands. You need a thinner one as the starting point like a 3k.
I can’t think of any way of separating the thick 1/4" chopped strands any further without a long labor intensive process. Maybe grinding them between two sanding blocks.
I haven’t had this issue before with the chopped cf I have used. It has always produced a solid jet black surface with no imperfections (as long as I removed the trapped air).
If you bought them from the same eBay seller as I did, I would avoid them in future. My first thought was “no wonder they are half the price of everyone else”. …