How To Bag A Tube and Avoid Wrinkles?

General Composites Discussions Composites Talk
#1

Hey Guys,
So, I am attempting to make something quite simple.
Basically, I have a tube that I need to make a sleeve for. So, the tube serves as a mandrel/tool in this case and all is fine and easy so far.

One side (yeah, a circle has no sides…;-)) of the sleeve will be open (the sleeve doesn’t go all around the mandrel, but I am kinda asking for best practice on how to bag this?

Reason is, first try out of the bag showed a nasty wrinkle along the top of the sleeve. I think the bag pulled the laminate up into it’s own wrinkle.
I had placed the mandrel in the middle of the bag which led the bag to wrinkle in two places: The top where the laminate wrinkled too and the bottom which has no laminate so no problem there. (Not sure “wrinkle” is the right word for what the bag does. I mean, it’s the two places where the bag after having wrapped itself around the tube meets itself and flattens against the other side of the bag).

Is the solution to wrap the bag tightly around the mandrel so as to only have one wrinkle at the bottom, where the is no laminate? Is it this simple?

Any other tricks? Do you guys pull a low vac first and then “massage” the bag around and hopefully stretch back any laminate wrinkles the bag might have induced?

Thanks all, I’m on a few other forums (for other stuff) and this place rates very highly in manners, but most of all, genuine helpfulness!:slight_smile:

#2

I think it could be difficult to avoid since the compaction from vacuum will do this. Especially if the laminate is thick or done with wet layup.

Best tip I can think is to maybe apply some of the laminate (1" wide cloth tape?) in a tight spiral wrapped fashion so that you are compacting as you go. Then apply a vacuum bag?

Can you apply a final cosmetic layer just to hide the pinched part?

#3

Why not use shrink wrap/tape?

#4

Hey guys,
Thanks for the input.

I thought leaving out a piece of info would make it easier to explain what I was trying to do. But, I shouldn’t have. My fault.

See, the bottom where the sleeve is open, it’s not just open, it goes into a kinda of flange.

Quick sketch here shows mandrel in red and laminate (sleeve) in black. So, spiralling tight or wrapping with tape wont do.

I think I am just gonna do one more where I try not to have any bag fold on the top of the tube, but just stretched nicely around it.

Sorry for the missing piece of the puzzle but thanks, still!:slight_smile:

#5

you should be able to bag without creating wrinkles in the laminate. You need enough excess bag to be able to have pleats to releieve any stress of the bag when you pull vacuum. You’re going to need pleats, you always do. Round parts are even more tricky and need many pleats. Not sure how big this thing is? But I’ve seen nose cones for planes and such similarly round parts and the bagging is pretty involved with many pleats. The pleats should help you avoid pulling the carbon up and creating a defect.

Like you said, you’ll bag it sort of get it all in place, then pull some vacuum to suck out the air and then work the pleats/bag until you’re satisfied with it, then suck it all the way down. Peel ply would help give a more even surface if you’re worried about the pleats creating any surface defects.

If you’re trying to get a ‘perfect’ gloss surface for cosmetic reasons, then you’re going to have to probably do a good amount of finish work. If this is a structural layup, then you could probably just add a sacrificial ply and sand it down some to even the surface if it has issues. Though sanding on a round part is also another fun thing to do.

#6

Hey Sammy,
Thanks for the elaborate reply!:slight_smile:

The part is pretty small. Mandrel is 2 inches in diameter and just a feet long, so plenty of bag material to play with.

It’s not tapered which is why I thought I could do without pleats, but I see what you are saying.
Although it is mostly a structural part, I wouldn’t mind if it looked OK, but that’s not super important.

But I was using perf ply, to that effect, which meant little with the crease in the laminate.

Yup, might have to sand down and put cosmetic layer on, if I don’t succeed.

Next try will be more pleats or the idea of no pleats around the tube part at all and all pleats at the bottom, if possible.

Will see if I have time to do one more tonight.

#7

Ah I see. To be honest, I don’t think you will be able to get a perfect result. You might minimise the wrinkling, but I doubt you will ever get it exactly the way you want it. Is there a reason you don’t want to make a mould? On such a small part it wouldn’t cost much to make.

#8

Gotcha, it’s just gonna be as good as it can get, no worries for this part.
No mould (for now) as inner diameter is the more critical one, outside less so. Also, the sleeve will fit around a tube which I already have and am using as mandrel. Also, just need a few of these small sleeves, so if I succeed in making an acceptable foot-long sleeve, I can cut that one in smaller sleeves as each one just needs to be 2 inches.

Thanks a lot guys:-)

#9

some guys use an old video tape to wrap the mandrel first

#10

Is there a reason you need to make this with vacuum bag?

Maybe just do a wet laid job with a peel ply on top?

#11

Nope, no valid reason at all - other than wanting to get into it and this was a part I needed to make right about now;-)

But honestly, as it came out, my first thought was indeed that I could have done it better wet laid, haha.

I’ll do one more and if I can’t get it to work, then wet is good:p

#12

One more too is to bring the vacuum on very slowly. When you initially pull the vacuum you want it to be the bare minimum so you can make sure the layers don’t shift and if they do you should still be able to smooth them out if they have. Once you feel like it is all good you can slowly start ramping up the vacuum making sure wrinkles don’t develop. You might also find that using breather mesh instead of fluff will make it easier to keep the wrinkles out and see when the are developing.