How many layers of CF to sandwich PVC core?

General Composites Discussions Composites Talk
#1

After several test parts, failures and successes, and help from folks here, I was able to infuse my first “real” part, a 50" long by 12" ID cylinder, and it was complete success!

I am starting on another cylinder, but a bit larger, 75" long by 21" ID.

:confused: Can I /Should I add additional layers into the stack to increase stiffness?
:confused: If yes, how many could I add before it could create a problem with infusion resin flow?
:confused: Would I add more twill OR biaxial layers?

I used the Pro-Set INF 114 infusion epoxy (viscosity spec 100-200 cPa) and the infusion took about 20 minutes and was completely wet out WITHOUT voids or bubbles. :cool:

The previous stack from inside to out:

Mylar (to seal mandrel)
Peelply
1 layer, 6K 2x2 Twill 11.0oz/sq. yrd
1 layer, 6K 45deg biaxial 11.0oz/sq. yrd
1 layer, 6K 2x2 Twill 11.0oz/sq. yrd
1/4" Divinycell (perforated with 1/16" drill every 2" in a grid and scored across perforations)
1 layer, 6K 2x2 Twill 11.0oz/sq. yrd
1 layer, 6K 45deg biaxial 11.0oz/sq. yrd
1 layer, 6K 2x2 Twill 11.0oz/sq. yrd
peelply
red mesh
MTI hose/MTI Valve
vacuum bag
The approach was to use MTI hose to wrap each end of the tube at the resin break, connected by a single run along the top of the cylinder joining each end (one long piece of MTI hose) and infuse from the under side. I have pictures and video of the setup/process somewhere…

#2

Are these tubes for a telescope by any chance?

How much stiffness you need is up to you. We can’t guess what your requirements are. The best way to increase stiffness in the axial direction is to add uni. If you are looking for axial stiffness, I would add a layer of uni between each layer of twill and biaxial in the longitudinal direction and you should have no issues infusing. Unless you need hoop strength, then go around the cylinder with uni. If you need both, go one layer in one direction, and another layer in the other direction.

The tubes you made aren’t stiff enough? Or are you just worried about the bigger tube not being stiff enough?

Please do put up pics/video so we can see how you are approaching this.

On Edit: I forgot to add that increasing your core thickness will dramatically increase your tube stiffness.

#3

Yay! I can reply. :smiley:
The 12" ID tubes I have crafted are indeed stiff enough.
My curiosity lies in how many layers on either side of the core COULD be added before infusion becomes a problem?
images forthcoming…

#4

Pictures worth a 1000 words, right? A few more wrinkles than I cared for. I assume that these can be worked out before bagging.

I am not super concerned with cosmetics, but is there a means of getting less of the mesh imprint on the outside?
How about a peelply that produces a smoother end result?

#5

Out of interest, if you aren’t concerned with cosmetics then why go to the trouble of infusion?

Surely, the best way to make a cylinder would be either filament winding or bladder molding. Just a thought.

#6

Hi Zebra. :slight_smile:
My main goal is light, stiff cylinders. After researching the cost and availability of “large” diameter composite tubes, for which I was told the cost of reusable mandrels is high, I’d try building a few tubes myself, just a few, not mass production. I have some experience with fiberglass and polyester resin from automotive and marine work. For mandrels, I’ve used mostly materials I already had around the house. I already owned a vacuum pump and used existing woodworking tools for fabrication. I built a simple, relatively inexpensive, electronically controlled curing oven and began experimenting with simple, flat, hand layups using nomex honeycomb and vacuum bagging over glass caul plates. After several experiments and a few prototypes I built two different size tubes using wet/hand layup, but I needed help (extra hands) for the process, so I kept researching and found that infusion seemed to be the next logical step. I can do it myself, I didn’t need a bunch of additional material or equipment, its not as messy and layup is all done “dry” without the time constraints of wet layup.

I’ve seen filament winding on the web, but it appears to require proper machinery.

I also looked into reusable bladders, but again the required mandrels appear to be cost prohibitive and most of what I read involves pre-preg which my oven was not designed for.

So for now, Infusion is my method of choice. I was simply hoping to gain more insight from others’ experience regarding number of layers before having to do additional experiments