Hi all:
We are studying how to make carbon tubes. Light, stiff, about 1 1/2" diameter by 2 feet.
We are thinking about wrapping as it seem to be not imposible with lower Budget.
BUT I’m not sure if the final quality reached by wrapping will be similar to vacuum.
Does anybody know what’s the pressure reached by wrapping? In terms op comparation to vaccum, I mean… 50%? 60%?
Is the final quality similar in terms of stiffness, weight, etc ?
Thanks by your answers, Z.
I guess by wrapping you mean covering the wet layup with some kind of foil to keep it in place?
Perfect vacuum creates 1kg/cm², I’m not familiar with wrapping but it will be nowhere near that, talking like 5% at best. It will also be difficult to create even pressure using foil like that, which will create an uneven finish.
It seems harder to do than vacuum, and it doesn’t really pay of. I would go vacuum all the way.
Could you offer more details about your tube making technique? I’m investigating something similar for a hobby project.
Shrink tape wrapped done the correct way is as good as vacuum bagging especially on round tubing.
Yes, shrink tape, and even elastic mylar tape that is wrapped around the tube with tension can out-do vacuum. The problems you have with wet-layup wrapping and any sort of consolidation (vac, tape, etc) is wrinkles you get.
Unless you have a way to keep the fabric tight, while wet, and wrap the fabric around the tube. Such as attaching the fabric to the mandrel, and putting pressure on the table as it rolls across the wet fabric, rolling up the part. Or between 2 pressure plates like in prepregging.
I believe that wrapping tube laminates with the heavy type shrink tapes are equivalent to kind of pressures you get with autoclaves, so approx. 90psi. That’s over 600% more than using vacuum alone that is just 14psi…
Many years ago I heard of someone making tubes for a sailing dinghy. This was before pre pregs become as readily available. Wet lay up carbon laminate wrapped over a fluorescent light tube (with release coating, maybe they used waxed paper?) and then wrapped with wide peel ply tapes in a spiral manner. Once cured you just give it a good enough knock to smash the tube and there you have a tube!
Cool!
Yes the shrink wrap tape adds considerably greater pressure than vacuum bagging normally; only difference is trickier air removal (ie has to slide through the tape in this method as opposed to perforated film in vac bagging for example. Wet lay-up tubes can certainly be done but are harder to maintain fabric tension during wrapping and therefore more wrinkles normally as already mentioned; even trickier when multiple fibre angles are used to.I reckon theres notably greater porosity levels too.
It is worth using a cello-wrap machine or something to wrap the tubes if you plan on making a lot as the surface finish is much better and more repeatable.
The other thing to be considered with wet lay-tubes is the curing temperature of the resin. The easiest method of mandrel removal is curing at higher temps and then removing the lay-up from the oven, dunking in ice water and then sliding the mandrel out. It can be harder if using room temp curing wet lay resins and then trying to remove the mandrel due to the minimal CTE differences that are normally relied on for easy mandrel removal. Doesnt mean it cant be done - its just tricker!
Hi and thanks to all.
I guess the process is enough explained now. The shrink tape is thermo retráctil. Wrapped around the laminate and then temperature applied that both, shrinks the tape and cures the resin.
A pressure is created by shrinkage, but couldn’t make an idea of how much.
Many masts, booms and poles are home made for smll boats. Also professionaly, of course, but the method allows to make hollow profiles by an small Budget for tools.
I´ll go back to it !