wrinkles from vacuum bagging

General Composites Discussions Composites Talk
#1

Hello,
I am getting wrinkles from the vac. bag where the two sides of the bag meet the joint. It appears that as vacuum is increased, the two sides of the bag come together and pinch the laminate causing a wrinkle along that line.
My joint is layed up using prepreg and then heat cured w/ vacuum. I am also using a layer of peel ply and breather/bleader. All other areas of the joint are well compacted.

I’ve even tried adding a rolled up piece of breather material along the area where the two sides of the bag meet. The hope was that the two sides of the bag would pinch the rolled up breather instead of the laminate. It definitely helps but I still have wrinkles. I can sand down the wrinkles but then the structural integrity of the joint would be compromised.

One solution would be to create some sort of tool that would encompass the laminate so that that when vacuum is drawn, the bag would press down on the “tool” and the tool would provide even compaction around the joint, thus preventing any sort of pinching of the laminate.

Can anyone suggest ways on how to create this outside “tool”?

I’d like to attach some pictures of the joint but can’t figure out where the attach option is.

#2

without seeing a photo its hard to tell, but making a caul plate would probably be the best solution. Usually sheetwax is used simulate laminate thickness, then you would make the caulplate the same way you made your hi-temp tool. If its a flat area you can make the caul plate on glass then cut to shape.

#3

how do I attach pictures?
Essentially my joint consists of two carbon fiber tubes that have been coped, joined with adhesive and wrapped with carbon.
It’s a complex joint with 360deg contours so a flat caul plate is not an option.
Is sheet wax flexible enough whereby I can wrap it around the joint.

#4

I’d use heat shrink tape wrapped round the whole joint in this situation

#5

I’m not sure I follow. Do you apply heat shrink tape around the joint after peel ply and breather/bleader have been applied? How does heat shrink tape help prevent bridging?
I’d love to post some pictures of my part but don’t see an option here to post a pic.

#6

The tape goes around the pregreg like a bandage directly on the carbon. Then lay the rest of the stack on the layup. Vac bag it all and apply more direct heat to the taped area

Again is hard to say without pics.

Try hosting your pics on photobucket or something. The will then give you a URL that you can paste in when you hit the insert pic icon.

#7

I uploaded some pics to photobucket.com.
http://s1106.photobucket.com/albums/h365/ptandon1/test%20joint/
You can see an area around the radius of the joint where the wrinkle is. I sanded through the wrinkle in an effort to smooth out the joint. That worked great but I’m afraid I compromised the structural integrity of the joint.

#8

I got ya. The shrink tape I have does not conform well around corners. It works great around round tubes but not around contours like the fillet radius of the joint.
Here is the link to some pics I put on photobucket.com
http://s1106.photobucket.com/albums/h365/ptandon1/test%20joint/
I sanded through the high spots on the wrinkles. Looks ugly and also my joint strength is compromised after removing all that material.

#9

Aha a bike head tube. I see what you mean. Integrity wil be compromised with sanding it down due to cutting, what should be continuos fibre. I’ll be the same as having a join but in this case it wouldnt be bonded correctly.

How wide is you tape? It should conform when it shrinks. Try slicing in down it length

A 2 peice outer mould would also work to clamp it but again would run the risk of the CF being crimped at a join

#10

Yea, the two piece mould idea would work to remove wrinkles in the joint but may cause pinching at the point where the moulds come together. I think I’m going to give it a shot and see how it turns out.
The shrink tape I have is 1" wide. It doesn’t bend around the radius of the joint. If I could get some stretchy shrink tape that had the consistency of electrical tape that would be much better. Do you know of any shrink tape that is pretty stretchy?

#11

If you wrap the heat shrink tape directly over the carbon how well will it release?

Also if you wrap it directly over the carbon how will any excess resin and air get out of the laminate?

Nice project btw.

#12

Sorry i dont know of any stretchy shrink tape. But wouldn’t it being stretchy defeat the object of it shrinking?
So long as the tape overlaps where is doesnt conform it should be ok as the vac bag will then compress it down. I’d also narrow it down to about .5".

#13

1: check this video http://www.compositescentral.com/showthread.php?t=6539
2: heat shrink tape MIGHT not be the best thing for compound curves like the headtube area. However, some have release on one side. you just wrap it tightly around the composite, and heate it up to shrink and cure.
Might help to debulk EACH layer, but i really like having a mold system like in that video.

#14

Interesting how Parlee compresses the laminate. I guess this is the sort of thing I was refering to as a possible solution to my problem. How would one go about making the right diameter mould after a stack of prepreg has already been wrapped around the tubes? I assume they figure out the thickness of the laminate stack beforehand and then prepare the mould to match the geometry accordingly. So if I’m building custom bikes that each as a unique geometry, I’d have to have a silicone mould for each bike geometry? Sounds like a lot of extra work.
The heat shrink tape I have as a release coating on one side and is performated as well. However, it does not conform to the joint radii so I’m afraid that when I do heat up the tape it’ll not give me even compaction around the joint.

#15

> Katmandu. Where did you find the heat shrink tape you have? Love to hear a report of a test after you try it.

#16

here is the manufacturer of the shrink tape
http://www.shrinktape.com/products/hi-shrink-tape/perforated.aspx

Try ACP
http://www.acp-composites.com/product.php?productid=17510