I wanted to discuss to separate aspects that are somewhat related.
I was wondering what the pros and cons are for two different processes and how would you go about doing these different processes.
Less assume we have a male mold that is a 3.5" diameter tube. Coated and all that good stuff pre lay up.
filament wound section:
-Would you use filament wound carbon fiber? Do they make a filament wound c/f in that diameter? what about kevlar, fiberglass, and the others?
Would you be able to use multiple layers of a filament wound cloth to build thickness? I find this to be difficult because it would be like putting multiple pairs of socks on the same foot. the more you layer the harder it gets.
Non filament wound
-When try to build a part that has several layers of thickness (also called plies) would you firt spray tac the cloth layers to each other than wrap your male mold? or would you wrap the layers of cloth one at a time around your mold?
Which is structurally stronger? Which would yield a better appearance?
Which method would be best when working with large radii?
If you need simple CF tube, then it may well be available ready made in the diameter you are looking for, which would save a lot of work and probably be less costly than making it yourself.
I’m sure they make filament wound tubes that size. You would have to find a winder that would do that. You can also find a braider and make socks (braider.com, et al). Anything can be filament wound.
Yes, a useful tube will be multiple layers, not just one (even though one “layer” of a 45deg wind will be MANY overlaping tows, even though there may be some air spaces.
Look at a CF motorcycle muffler, or a Canonndale bike Lefty shock (not really a fork, since there is only ONE side). Many of them use winding for their tubes.
To wind, it involves basically, a lathe, and a bobbin. Tow is fed into the bobbin, and it is computer controlled to move back and forth, as a computer controlled lathe spins the mold, building up many layers until it’s done. You can easily make 2" thick walls…
Non filament wound
-When try to build a part that has several layers of thickness (also called plies) would you firt spray tac the cloth layers to each other than wrap your male mold? or would you wrap the layers of cloth one at a time around your mold?
I have not done dry fabric before, but I would imagine that figure out how many layers, and cut that ammount off the fabric roll. You wet it out, and wrap the mold like you are rolling up wrapping paper back onto the roll. Be as TIGHT as you can.
You then take an elastic tape, or coated plastic tape, and tightly wrap the entire mold, like you were heat-wrapping a muffler pipe. Over lapping each layer of tape. This compresses the resin the fabric. You can poke holes in the tape to let the extra resin leach out.
Same thing with braided socks. Place one sock on the mold, wet it out, place the next one on, etc etc. Then wrap with tape, as mentioned above.
I used to do pre-preg wrapped tubes, both plainweave and unidirectional. I just lay out the pre-preg, and start sticking one side of the fabric on the tube, pushing down as I roll up the fabric. I then wrap the tube with a release coated heatshrink tape (Dunstone), and cook per the pre-preg calls for.
Which is structurally stronger? Which would yield a better appearance?
Which method would be best when working with large radii?
Filament wound, depending on your testing, will be the way to get a strong part. It can yield ANY apperence you like, which all depends on the angle of wind. you can wind something that looks like the fiber is going at 90deg, or a weave look. You can also do many styles of wind in one tube. You can start with a 45deg wind, stop, put some longitudel unidirectional on for strength, and then wrap again with a pretty weave.
Radii. Well THEN you have issues.
You will need a bladder mold of some sort. You can possibly wind that on a multi-axis winder (the bobbin would be like a robot arm to move the filament around the bends), OR you can hand layup several styles of fabric around the straight parts, and other layers around the bends.
Either way, once you wrap the carbon around a bend or anything, you can not pull the mold back out!! bladder mandrels let you deflate the soft mold, and wiggle it out. There are also heat set inflatable bladders that you match with a female mold. When cool, the mandrel is solid. You wrap it, stick it in the female mold, clamp, and heat to cure the resin, while injecting air into the mandrel. When heated, the mandrel is soft, and when cured, you can pull it out. (Smart Mandrel?)
so would filiment winding be as strong for lengthwise bending as using uni that runs the lengthwise direction of the tubing? I would expect that since Uni is strongest in the direction it is oriented in, you would assume filiment winding would be less effective even though it has superior wet out and such…
Filament winding is better, because you can customize the weave pattern to that YOU want. If you want extra length support, you add some low angles. Want strength from crushing, add hoop winding. Torque also plays a part in many tubes.
As for uni, yeah. But if you have ALL length uni (0 deg), the tube will split open with any pressure on the tube surface. That is why you add hoop or angles.
BUT, most people don’t have a winder in their basement.
Some great info from all. Thank you very much. I like when i see nothing but positive post.
This seems to be a much more complicated process than i had anticipated. I bet this would get so much more complicated with a tube that had some radii’, even if the radii were large. I really want to try this out.
Werksberg: Where do you buy your prepreg from? I want to start purchasing some scrap prepreg from the local shops.
Like I said before, if you have radii in your part, you would need a multi (3-5? i forget)-axis one…it can be done I think.
Pre-preg: Newport, Bryte, are the ones I got my stuff from.
check out http://compositesworld.com/sb/browse/1 under “Prepreg - Thermoset”
Standard resin would be under “Epoxy” or “Epoxy 250f cure”
but, it gives you the list of everything.
A few thousand for a basic one. it’s more than just a lathe with a bobbin you move back and forth. Yes, for simple tubes you don’t plan on using for critical parts maybe…but they are computer controled to get exactly what you want, every time, perfectly. That way you won’t have fiber gaps, etc.
I check out this site u sent me, but it seems to be a maze of links taking you all over the place. I found a company similar to the one u mentioned above but not the exact name.
well, it takes you to the list of epoxies available in thermoset prepreg. Pick what you want, and it shows you the companies that supply the product.
Like when clicking on Epoxy 250f cure, I personally know that lewcott, newport, hexcel, cytec and ten cate sell 250f cure pre-preg. Some even sell “room temp” cure pre-pregs which normally only need 140-180f cure temps.
You can find anything you will ever need in composites in the Composites World Sourcebook.
