I have made a CF tube on a steel tube. I used the grease and tape method so that it will slide off but for the life of me I cant get this beautiful CF tube off the mandrel.
I have read that dry ice down the tube may provide enough thermal shrinkage on the steel to allow it to come off but just checking to see if anyone has any better ideas.
The first one i made came off but it was only about 5' in length, this one is 80", it has moved about a foot but seems to be really stuck now!

What are you pulling or pushing on it with? Do you have some for the lugs that you can grip it with? I tried the same thing last summer to make a carbon boom around a steel tube. Ultimately I was unsuccessful in separating them. It seemed like the carbon really needed a sacrificial place to yank on it from with a winch or come along.

Your tape has probably bunched up...this could be a terminal problem for your tube....I'm sorry for your loss. :-(

I saw Alan do a neat trick with a tube by putting in strips of plastic before laminating the tube. He would then pull the plastic strips out one by one to reduce the inside diameter enough to slide the tube off. I don't know if this would work on something that long (might want to try strips of latex?) but it might be worth a shot.



I think the only way you are going to get that to remove from a mandrel that long is to use nothing but a spray mold release between the steel and the carbon and heat it considerably while it's curing so the steel expands. You'll probably still need some sort of mechanical means to pop it loose.

The guys making one-piece hiking sticks use mandrels that have a very slight taper to them and some are aluminum to take better advantage of heat expansion.

Ideally, you need to push it off - it will act a bit like chinese fingercuffs if you try to pull it.

Dave,

The first carbon tube I ever made I did what you have done. I separated the tube and mandrel with two vehicles. I got them apart but broke the tube in half in the process.

Since then I have made quite long carbon tubes of various diameters over mandrels and had no problem removing them, but I coat the mandrel in candle wax. Just melt a candle and apply the wax with a brush and use a wide flat metal scraper that I heat to smooth out the wax out.
(Usually set up a way of spinning the mandrel with a cordless drill on very low speed to apply the wax.) When it is time to separate just poor boiling water down the mandrel tube, the wax melts and the tube slides out easy. Only issue is the wax will shoot out the ends when the boiling water melts it and if you want to bond the tube to something else you need to protect it from getting covered in the melted wax.

What is the diameter? It is just that I have also made a collapsible mandrel recently that worked well also.
I have also made them by inflating a bag inside the laminate inside a pipe that has been split and held together with hose clamps. It all depends on what I want to use the tube for in the end.

would certain vibration frequencies allow the metal to vibrate differently than the carbon and possibly break free?

Yes, if by "vibration" you mean a sledge hammer.

exactly

I forgot that around 12 months ago I had another attempt using that method, I got them apart, but the tube was quite short. The way I got them apart was to drill a hole in one end of the metal mandrel tube so I could fit a shackle. Got some flat bar big enough to dril a hole just the size of the mandrel. Bent it into a "U" shape and drilled hole in each end for shackles
to attach a line. The single shackle was tied to a post on my carport at ground level.The other two shackles were tied to a winch that went to another post and managed to winch them apart without damage. This way the tube is being pushed not pulled so it is just a matter of a big enough winch. I used a chain driven engine winch that lifts 1 ton. I'm not sure how this would go for you but work giving a try.

Sorry for this :
Carbon and steel, have nearly the same expansion rate
to about 300-deg ! And just for a referencing ; so does
cement. It's one of those things builders found out when
they started using steel re-bar to strengthen cement buildings.

For a straight taper :
Next time out ; undersize your mandrel by 1/8", and use a foam or wax
to bring it up to full diameter. The foam can be removed
with acetone ; the wax with heat, but use a Low-temp wax,
or lower max-temp than that of your epoxy.

Bille

Another point of interest is that steel pipes are not all round and the same diameter over their full length.
They looked perfect until you put them in a lathe.
Wrap them in carbon and with a little shrinkage as the resin cures and small differences can become a real problem.
I have recently had the need for perfectly round and true pipes. I had to turn them down on my lathe to get them that way.

I would really like to find out the dia of the tube that you are trying to make. Collapsible mandrels are easy to make for larger dia tubes.

1" OD steel tube, I tried the dry ice last night with little success. I have maybe 18"s of tube removed in 2 nights of fighting with it. Maybe in a month or 2 it will finally come off!
I have it in a vice on a pretty solid table, but still have to have my wife hold the table while my 2 boys and I twist and pull, Im sure the neighbors are amused.
I read the candle wax trick and a Mylar wrap technique on a model rocketry site, seems this has been a common problem. I used the CF sleeve that acts like a Chinese handcuff and may have stretched it too tight.
Not willing to give up on it yet....its way too pretty, and BTW it is the beginning of a paddle shaft for my SUP

The epoxy will keep shrinking, until full-cure is achieved, so
your part will continue to get smaller with time.


Easy solution for this one ; cut it full-length, on one side
and slide it off. Then add one more layer of carbon biaxial
sleeve , to cover up the cut. Perhaps super-glue the cut first, to keep the sides perfectly aligned.

Bille

Dave,
I don't think you will be able to apply anything like the amount of force required the way you are trying to move it.
You may get it with the winch method I described but the sooner the better. The tubes I have made are usually quite pliable for a day or so after the resin is applied so they have to be laid flat when first off the mandrel but after a couple days they are as stiff as can be. I think you may have been able to winch it off while in the pliable state but that time may have passed.

Do you have more carbon. It may save a lot of time if you get to work on MK2. The candle wax method works like a dream when you want to get the carbon off the mandrel.

If we now are talking "terminal suggestions"?

How about bonding some ears to the tube and rigging a 4ton hydraulic jack to the pipe. Then apply pressure?

If that is not enough. Anchor pipe to a solid object with chain (big oak or similiar). Secure tube to towing hitch on a heavy 4wd vehicle and apply pressure?
When the above does not work. Build speed and "rip" the tube off.. Make sure to film as it might be a Kodak moment.

What would happen with the tube afterwards if the now carbon reinforced pipe was heated to to 80-100degC to soften the epoxy. Try to pull the tube off while the epoxy is "soft"?


I went through the same story with a 30cm tube once. Ended up cutting the tube and making MK2.

Unlikely to have worked, its much like removing seized nuts from bolts, if you only apply a single change of heat alteration your doomed from the start...
You need to apply 2 temperature variations in rapid succession to get a complete freeing clearance.

IE:
heat the nut till its red hot, then quench it in cold water, it will release its grip instantly....
how it works-> as the heat is applied, the heat in the nut slowly transfers to the bolt, the nut may be red hot but the bolt should not show any signs of the heat, once its quenched the nut shrinks rapidly onto the still expanding bolt and then the bolt shrinks down in size leaving a greater clearance.
Simplified -> your compressing the nut onto an expanded bolt

You need to apply the same principles to your stuck carbon.......


somehow.... apply heat to the carbon and dry ice to the pipe

Hotwater from the service could almost be enough if you crank it to MAX, the trick will be making it so it is constantly receiving a new supply of hotwater .... perhaps by placing your carbon into a larger PVC storm-water pipe with an end capped off bar for a dribble that the service can maintain the loss rate.

I'm sure you'll work it out

Just think of the stories you'll have when people ask where you got your CF paddle for you SUP.

Tired of fighting, just cut it lengthwise and will rewrap. The tape had bunched up at the end I was pulling toward, at least that was part of the problem. It cut pretty clean so not real worried about that, it probably needed another wrap of CF anyway for added strength.
$17 steel tube 10'
$27 CF sleeve(have enough for 2nd wrap)
~$5 CF 6 oz under the sleeve
~$10 CF for paddle blade
~$10 resin
Total price $69
Any decent CF SUP paddle $250-$450
I think Im still good!

I was going to say weld the pipe to something solid so you could mount it to something else more solid, then take a strap and wrap it around the carbon and try and apply some twist to it. Long enough lever, should get you something. It'd be tough to get something that won't slip on the carbon though.

How are you going to make the blade of the paddle? Any pics?