Carbon fiber tubes

[GL-P]

This is my first attempt at carbon fibre tubes. The mandrell I am using now is aluminum 29mm with 5 layers of premium auto wax. I'm using a CF sleeve and West System 24 hr epoxy. I have a rotisserie motor setup to smooth the surface. It should be dry by luch time tommorrow. I'll post pics then.

 

[GL-P]

First pic still drying:

 

[DynaSoar]

No mylar break-away? Cool. I'm waiting to see how it works out. Our 38mm mandrel is phenolic, so we need the mylar. A rotor is definitely the way to go. What did you use for smoothing, just gloves?

 

[Stymye]

try the small foam rollers they are great for getting a nice smooth even coating,, too much ? just roll over it and the foam soaks it back in

no more wet ,dry or uneven areas,, great for glassing tubes as well.

 

[Stymye]

try the pic again

 

[rocketsonly]

styme, I do not see a picture

 

[GL-P]

No mylar break-away? Cool. I'm waiting to see how it works out. Our 38mm mandrel is phenolic, so we need the mylar. A rotor is definitely the way to go. What did you use for smoothing, just gloves?

We'll see how well the tubes comes off. It didn't seem like any wax was on there but when I tried an epoxy test, it came off relatively easily.

I've used cheap plastic drywall scrapers to smooth the epoxy. I also got a set of official epoxy spreaders that are made of a plastic that epoxy doesn't stick to (and too expensive for a mandrel ) . So the epoxy just snaps off them.

The gloves were used to apply the epoxy to get a better absorption and the scrapers were used to smooth out the mess.

 

[GL-P]

We're having technical difficulties...
(the dang thing won't come off)

Ideas:

-freezer
-heat gun
-a hammer (with a piece of wood in between of course)

Anything else I could try?

 

[ResearchWorm]

GL-P:

Nice setup for the mandrel, but..

Please tell me you didn't air-cure that beautiful 45/45/90 fabric, especially since you were using West 24hr (which is one of West's best products, by the way). There are some better epoxies to use, but price vs. performance of the West 24hr puts it among the best available on the general market.

Looks like you did a fantastic job keeping the fabric from moving around while you were adding the resin. Trust me, that's hard to do.

You didn't say how many layers (wraps?) of fabric you used. I'm guessing two? Any finish layers (fiberglass cloth for protection) involved?

I've done a little work using C/FRP (Carbon/Fibre Reinforced Plastics), so I guess I should probably inject a little of what I know into this thread.

- Vacuum bagging allows you to remove excess resin (by squeegee) and also encourages a higher fibre/resin contact ratio. Pros: Results in a stronger and lighter(!) tube. Cons: Requires a vacuum pump, heavy plastic sheeting, cotton batting.

- If you can't vacuum bag (no pump, etc), wrap with a layer of plastic and squeegee excess resin in one direction. You'll know you've got it right when the fibre/resin viewable through the plastic is in sharp relief with no visible airpockets or dry spots.
Pros: Almost as good as Vaccum bagging. Cons: Not as good as Vacuum bagging.

- Some epoxies cure best under pressure. For small diameter stuff, try using low-temperature heat-shrink tubing slid over a tube that has been squeegee'd and then SLOWLY heat from the middle outward using a hair-dryer or heat gun set on low. Excess resin will be squeezed out the end. Pros: Slightly better than Vacuum bagging. Cons: More expensive, and easier to make a mistake with.

-If you're really insane, you can try making your own quasi-autoclave with a vacuum frame, a heat-gun, plywood and aluminized faced foam sheeting. It is embarrassing to admit I've used one, but it works. Pros: REALLY nice results, faster cure times, etc. Cons: Fire hazard. Can damage results if temperature is uncontrolled. Rather expensive to set up.

Here's a couple of links. I apologize for their sources, but they were the only ones that I could come up with that showed fabrication steps from beginning to end. I am sure someone else can find better ones.

https://superstreetonline.com/techarticles/54702/ <- Good pictures. Waste of good fibre though. Doesn't show vacuum bagging.

https://www.sheldonbrown.com/rinard/howibuil.htm <-- Small pictures on a bicycle site (click for larger ones) , but shows vacuum bagging.

The next two links are to small project I was involved with. 900 odd lbs at max weight, monocoque carbon fibre construction with a mix of hand-layed up and honeycomb carbon fibre sheet.

https://vri.etec.wwu.edu/viking_xx_photo.htm <- I'm in one of these pics, but I ain't saying which.

https://vri.etec.wwu.edu/viking_xx.htm

Hope this helps. Keep up the good work, that looks like the start of a very nice fabrication system.

Harm none,

ResearchWorm

 

[GL-P]

Thanks ResearchWorm!!!

I'm air curing it. I should've put a heat lamp on it.

I have been using a CF sleeve sold by this company: https://www.sollerpaddles.com/light-sleeves-sock.html
(It's the 1.5 inch diameter one)

I used only one layer of CF sleeve but it has 2 layers of epoxy to smooth the rough outer surface.

I'm staying away from a vacuum setup because of the equipment setup. I just use drywall scrapers to spread and remove excess epoxy.

The carbon fibre looks dry. There was no super wet spots after the first layer.

I have some window film that is heat applied and is even epoxy resistant. I should've tried it this time.

Any ideas for emergency removal of a tube?

 

[ResearchWorm]

I have some good news, and I have some bad news. The good news is I know how to rescue your carbon fibre tube. The bad news is you're going to have to lose the mandrel (for rescueing the tube, that is). All I can say is thankfully you chose the right material to make the mandrel out of. If you had used steel I would suggest you start making Javelins, or Lawn Darts (Anyone remember that fun game that got liability lawsuited out of existence?)

If you can easily get another mandrel (and mandrel we are concerned with is hollow!), and you desperately need the tube, do the following, only as a last resort:

1. Disassemble your jig (remove the frames, etc) once the tube is cured.
2. Plug one end of the tube with silicone caulking (white, black, clear, it doesn't matter. Just seal the end of the tube, making sure to go at least 1 inch up the surface of the carbon fibre surface.
3. While you're at the DIY store to get the caulking, go down the swimming pool chemicals aisle and pick up a jug of Muratic Acid. Contrary to labeling, this is fairly pure Hydrochloric Acid. You may have to sign a waiver saying "this is not for making crystal meth" or something similar. Oh, wait a sec, that's only in the United States of Paranoia. Also pick up a pair of safety goggles, a face shield, some acid-proof gloves, and an acid-proof apron. Oh, you'll also need a turkey baster or kerosene tank sqeeze pump (pump-siphon with a check valve).
4. Stand tube (and mandrel) vertically up in a 12 liter bucket full of sand outside. Preferably about 50 meters from anything. If sand does not completely cover tube, get a bigger bucket, garbage can, refuse bin, or rubbish bin. A Ford Pinto Gremlin also works.
5. Verify that you are wearing the appropriate protective equipment and that there are no open flames within 20 meters of you. This includes pilot lights, smokers getting nicotine fixes, idiots with cigars, etc.
6. You are now looking at a small bomb waiting to detonate. Proceed carefully. Extremely carefully. Vapour/Steam propelled acid explosions are not user-friendly.
7. Pour a very small amount (<5cc) of muratic acid into open end of tube, making sure that you are not looking down the mouth, and that all bodily parts are clear of the nozzle throat.
8. Back away rapidly.
9. Wait until gas/steam/smoke stops pouring out of tube. I suggest watching from 10 meters away, from cover.
10. Approach carefully, and listen for boiling noises, if you hear any, goto step 9.
11. Return to step seven until mandrel tube is dissolved by filling tube entirely with HCL acid.
12. Use a Turkey Baster or Kerosene Siphon Pump to remove liquid from tube and into an acid resistant bucket.
12. Dispose of waste in appropriate manner.
- Neutralize acid by slowly adding Sodium Bicarbonate ("Baking Soda") in extremely small quantities to top of tube. Collect all run off.
- Wash all surfaces, materials with water mixed with Sodium Bicarbonate. Collect all run off.
- Let run off stand until water evaporates. Dispose of residue at household toxic waste facility. Aluminum Chloride isn't poisonous, but the other stuff in non-pure aluminum is.

The basic chemistry: Aluminum + HCL = Aluminum Chloride (a salt), Water, Heat, and Hydrogen gas atmospheric pressure. Hydrogen + Oxygen at atmospheric pressure + spark (or flame, or excessive heat) = BOOM. Fuel/Air explosion. Not pretty.

Again, do this ONLY if you absolutely have to have that carbon fibre tube.

For future tubes:
If you absolutely must use an aluminum mandrel: Multiple coats of Turtle Wax (tm), three coats of Poly Vinyl Alcohol (liquid mold release agent), then wrap with kraft paper, and then a layer of mylar. Over this layer your carbon fibre, resin and plastic (for vacuum packing or squeegeeing). This may not release entirely.

Better mandrel materials:
Cardboard tubes coated with candlewax.. water dissolvable.
Sacrificial Stryrofoam plug - Chippable / Acetone dissolvable (WD-40 also?)

There's a few other ways, but they are expensive and used at the professional level (Pneumatic Rubber Tube Mandrels, etc). Personally I'd suggest the Sacrifical Styrofoam Plug first, the Cardboard tube second, and the Aluminum Mandrel last.

Hope this helps.

Hrm.. Would it be helpful if I put together a thread on composite mold making/use?

Harm none,

ResearchWorm

 

[DynaSoar]

Originally posted by GL-P
We're having technical difficulties...
(the dang thing won't come off)

Ideas:

-freezer
-heat gun
-a hammer (with a piece of wood in between of course)

Anything else I could try?

Try this:

3 (or more) vice grips (or other clamps) and a hammer.

Put it along the edge of a table/workbench with the end sticking over. Place two (or more) slats of wood over the tube and place two vice grips/clamps them and under the table (the wood prevents biting at those points). Grab the end of the mandrel tightly with vice grips. Start banging on the end of the mandrel while turning it with the vice grips. The turning will help it continue breaking free and sliding once it starts, and the banging should help break it free and get it started. If you can just get the mandrel to slide some you can tap it out the rest of the way.

Just guessing here, but I think the thermal expansion of aluminium is greater than that of carbon and epoxy. If so, freezing it might help. Heating would be the wrong thing to do, unless you heated it to expand the tube some by forcing the mandrel to expand against it, then froze it to shrink the mandrel away from it. Just don't exceed the heat limit of the epoxy you used.

 

[GL-P]

It was suggested that for metal mandrels, you use heat.

I'll check the max heat for the epoxy.

ResearchWorm: I don't want the mandrel that badly, heck I could make a little sounding rocket out of it.

 

[GL-P]

R. Worm, could you start a mold making thread?

 

[ResearchWorm]

I'll see what I can do about putting one together. Should be able to get something hammered together before Friday or so.

Harm none,

ResearchWorm

 

[GL-P]

Update:

I'm trying again on a 24mm mandrel. Using a GOOD release film this time. Will try to update with pics tomorrow

 

[r1dermon]

sorry man, the DIY store no longer sells muriatic acid in the US. or, at least in RI MA, NH, or CT. i can't find it at any hardware or home depot store any more. muriatic acid is also 33% conc HCl, not uber powerful, but definately will hurt you. i found this other stuff at home depot, however, i can't get a conc % on it, its called ZEP, patio cleaner. labeled as HCl and other additives. but i can't find the conc% of HCl. but i do agree, if you could hit up a chem supply store that would sell you muriatic acid, or HCl(dont buy this at any more than 50% conc, or you're asking for 3rd degree burns or worse) then that would work very nicely on a mandrel. make sure you have a double filtered gas mask and you do this outside away from trees and such. animals...all those good things. lol.

 

[GL-P]

Don't worry r1dermon, my new tube came off the mandrel beautifully. It just needs some epoxy touch up.

The release film I used was the window film that is also a heat shrink tubing. I put down a layer of newspaper and then wrapped 2 layers of film around the mandrel. Came off beautifully!