CF tube Removal

[GL-P]

I have a problem:

I have a beautiful CF tube that I can't get off the mandrel.

Any ideas???

(If I can't get it off, it can become a rocket with a permanent hybrid casing

or a structural pen holder.)

 

[Stones]

Is the mandrel a tube(hollow) or solid stock?
If it's a tube, you could try putting ice in it to cause it to "shrink".

 

[GL-P]

It's a tube but metals are less likely to shrink than a composite would. I heard that heat is the best.

 

[DPatell]

I had the same problem with a 38mm Fiberglass tube on a hollow aluminum mandrel. You're screwed, plain and simple.

I did it last winter in the really cold months. I put it in the freezer for days on end, no joy. Left it outside for days on end, packed with ice. No joy. Froze it good, then beat it with a mallet. I'd get partial separation, but not even close to joy. The aluminum and fiberglass seem to expand and contract almost exactly the same magnitude. You definately need mylar to get good separation, and also the mylar adds a tolerance so that the motor or couplers will slide in much better. I managed to get one tube off once, and it was incredibly tight on the motor casings.

https://www.aeroconsystems.com/tips/cloud_FG_tubes.htm
^The road to success in composite tube making.

 

[Elapid]

anyone ever try dissolving the mandrel?


to see if you can do it with differential expansion/contraction, try using dry ice and rubbing alcohol in a slurry. be VERY careful, temps of such a slurry are dangerously cold and will damage your skin if you aren't careful.

 

[GL-P]

I'm going to give the tube a ot water bath and hope the wax melts

 

[GL-P]

The hot water trick didn't work. We'll have to get physical.

 

[bobkrech]

Metals shrink more than composites.

If the tube is hollow, it can be plugged at the bottom and filled with dry ice or liquid nitrogen. This should shrink the mandril enough to get the carbon tube off. Wear thermal gloves and a ace shield when you do this.

Next time use lots of mold release, and a non stick layer over the mandril.

Bob Krech

 

[DynaSoar]

Originally posted by bobkrech
Metals shrink more than composites.

If the tube is hollow, it can be plugged at the bottom and filled with dry ice or liquid nitrogen. This should shrink the mandril enough to get the carbon tube off. Wear thermal gloves and a ace shield when you do this.

Next time use lots of mold release, and a non stick layer over the mandril.

Bob Krech

yup yup, that's what I was saying. greater thermal expansion coefficient. Heat them to stretch the CF by expanding the mandrel under it, then freeze it to make the mandrel smaller. THEN start whacking on it. If it was already heated, no need to do that again.

LN2? Nononono. That'd make the aluminium brittle.

CO2, now that's the ticket. Take the divergent nozzle off a CO2 fire extinguisher and run the hose down the mandrel. Then let it rip. Instant -150 F.

 

[Manwithbeers]

I've made tubes such as this on a steel mandrel. My mandrel is made so that I can clamp one end into a vise and then use channel lock pliars to clamp down on the composite tube and give it a twist. That will break it free. but it's still hard to pull off and the process of clamping and twisting does damage the sacrificial end of the composite which is cut away latter.

My fear in your case is that you may not be able to clamp the AL tube tightly enough without damaging it. but this is still worth trying. Maybe after the cold CO2 Bath...

I've put on 30 some coats of wax on my mandrel and now I also wrap it with wax paper. Easy off!

Good Luck.

Layne

 

[bobkrech]

In theory, the CF composite is stiffer than the aluminum. If you heat it, you won't stretch the CF as much as you will expand the aluminum. You could, in principal, fail the CF tube.

USE EXTREME CAUTION. Liquid nitrogen and dry ice are very cold, and you will get extreme frostbite if you get your skin in contact with the cryogens or anything in contact with the cryogens. Protective clothing and a face shield is required. If you are not willing to use them, then cut off the CF tube and start over. It not worth loosing fingers which could happen if you are not careful.

Also do this outside. Both LN2 and CO2 displace oxygen, and you could suffocate if you do this in a poorly ventalated room.

It is much easier to use the liquid nitrogen and the aluminum will not get brittle. Simply plug one end of the aluminum tube, place vertically in wooden stand and fill with LN2. After the tube is filled with liquid, wait 30 seconds, dump out liquid, and see if the CF tube can be pulled off with a well gloved hand and a bath towel around the CF tube. (Use oven mits as outer gloves and knit gloves as inner gloves and work quickly. If you feel your fingers getting cold stop immediately. Regardless wheter it comes apart or not, do not touch anything with bare hands until all the frost has melted.

If you can't get liquid nitrogen, you will need powdered dry ice. (A CO2 extinguisher is unlikely to cool the alumium down to a temperature low enough to do any good.) Pack the tube and waith till it cools and try to pull the CF tube of the mandrel.

Bob Krech

 

[GL-P]

I'm not that desperate for the tube. Serves me right. I have found a release film that's cheaper than mylar and reusable. Its clear wind foam that shrinks when heated. I've used it to make composite fins already with great success. I plan to try on some fibreglass before hand and then try it on a CF tube

My dad's gonna try brute force to get it off. The mandrel is worth more than the tube. (cheap CF sleeve)

 

[ResearchWorm]

GL-P:

Well, if you're unsuccessful in getting that mandrel free, you may have to resort to chipping and scraping the epoxy resin and the carbon fiber off the metal. Rubber mallet, flat side of a chisel, gloves, lung, and eye-protection.

* Beats self with a clue-stick * Okay, I admit it, I am offically a senile old geezer. Gotta love those CRS situations. We're talking single layer composites, and if I remember correctly, 29mm in diameter here.

Wear heavy gloves to protect your hands from sharp fragments, and safety goggles to protect your eyes. Long sleeve shirt and a dust mask is mandatory. CF slivers are NOT fun, and are not covered under the "easy to remove" section of any first aid kit. Took me several hours to get a piece out of my arm once. Epoxy fragments are even less fun. So be careful.

Try this. Take a utility knife (Stanley (tm) type) and a lot of spare blades. Spray the blades with Silicone Spray Lubricant (Yet another DIY store trip) and polish them dry with a peice of paper towel. This not only gives you sharp blades (and keeps the ones you don't use from rusting), but also reduces the amount of surface area the epoxy can grab against as you're cutting (Silicone Spray will fill in the rough surface area of the steel, etc, ad nauseum). Then, using multiple light passes and a straight edge or steel rule [taped in place] to guide the blade, slice through the carbon/epoxy matrix along the mandrel (end to end). It'll probably take you 30 to 40 passes, and several blades. This will take you a while, but it'll save the mandrel. Once you get through the epoxy, try lifting one of the edges of the cut with the razor blade, wedging it open as you go, with toothpicks or dull utility knife blades at first. Assuming that you waxed the mandrel before laying up your fiber and epoxy, you should be able to peel the majority of it off. A single layer of cured carbon fiber (you did say 5.7oz, right?) isn't as stiff as most people think. It'll probably be about as hard to bend as heavy cardboard, crabshell (Crawfish?) or lobster shell.

Most people look at carbon fiber as being a very strong material, but it is actually a two-dimensional fabric of strings (err. most of it is 2-D anyway) that is only strong in tension. Like thin sheet metal (think car door panels, body work, etc), most of its strength and rigidity comes from the shape it is formed into. Once you cut a string under tension, it no longer supports anything.

Harm none,

ResearchWorm

 

[GL-P]

I'll see how successful dad is tonight. If he isn't successful, we'll try to save the mandrel and try again with a better release agent.

I'll try cutting it if my dad can't get it off. My dad's at a machine shop so if the industrial equipment can't get it off and nor can the cutting, I 'll just make another mandrel.