Noobie looking to make a 3/8" x 3/4" hollow rectangular tube

General Composites Discussions Composites Talk
#1

Hi all,

New to the forum and composite construction. So far, I’ve made a flat square sheet and two 3/8" x 3/4" hollow rectangular tubes. None of these parts were really good, they all have flaws, but they were useful. I made what I wanted and learned a lot about composites. All work thus far was hand lay up.

The flat plate was made between 2 pieces of glass, with a weight on top. The first rectangular tube was wrapped around an aluminium bar and left cure on a piece of glass. I failed to remove the aluminium bar. My second rectangular tube was formed over a styrofoam blank. When cured, I used acetone to remove the foam.

In a couple of days from now, I’m going to attempt the layup over an aluminium bar again. This time I will be using vacuum and I think I’ve studied up on it enough to pull this off, but I’d like advice on it…

I plan to sand the aluminium bar up to 1000 grit paper, clean it, wax it with partall #2 paste and polish, repeating a 5 times. (this is where I think I failed before) Then using a coverall film mold release on the bar. Wrap the bar with the carbon fiber as I wet it down. Wrap perforated peel ply around that, then some breather material over top. I have 18" wide vinyl vacuum bag that I will place the lay up in, with breather material running from the hose to the part’s breather material. Then turn on the vacuum pump.

That’s what I plan to do, but would like any advice that might help me.

Would packing tape over the bar be easier than wax/polish/mold release?

Thanks for any tips,
Randy

#2

Hi randy.

I’ve done this multiple times , and due to the shrink of epoxy it’s almost impossible to get the laminate off the aluminium doesn’t matter what release I’ve used.

I followed target technique and work 100% every time.

I just use steel mandrel

Hope this helps

Tim

http://www.rcgroups.com/forums/showthread.php?t=632908

#3

Hi Tim,

Thanks for the link to that technique, looks interesting. The only thing I wonder about is with the inside dimension being 1/4" x 5/8", would there be enough room to remove the paper & tape from the inside?

Also, forgot to mention, when I wrap the carbon fiber around the aluminum bar, I plan on allowing about 2 inches of carbon fiber extend past the end of the bar. This way, once cured, I can drill a hole thru the carbon fiber at one end, and a hole thru the aluminum bar at the other end. This should allow me to mechanically separate the parts.

So I’m unsure which way to go, might try both ways and see what happens…

Thanks,
Randy

#4

fiber glast sells braided carbon fiber sleeve that way you will not have a seam line, good if part needs to be perfect cosmetically.

#5

Yes I use sock for mine as well.

I’ve never done a small dia like that so I guess only one way to find out :smiley:

Tim

#6

The chances of removing the aluminum tube will be increased if you heat the tube during the cure cycle. When you want to remove the tube put it in a freezer. This will use the difference in cte between the materials to give a bit of clearance.

#7

freeze spray is also a great tool for demolding

#8

Thanks for all the tips thus far!

I’ve seen the braided CF sleeves, indeed worth trying. I’ll keep that one in mind!!

I like the idea of heat and expanding the aluminium during cure, then cooling to shrink the aluminium. That was actually my first attempt at this, but I didn’t go about it right.

I had read on a bicycle forum someone was making CF tubes by wrapping aluminium pipes, then once cured, they placed them in a cooler with dry ice. Dry ice shrinks the aluminium, and is removed. I laid up my part on a 90 F day and chilled to -10 F, the aluminium loosened, but I couldn’t remove it. I had no way to securely grab the parts.

I see I need to make the aluminium hotter during cure and colder during removal, a bigger temperature swing than I had first time around.

I’m using west systems 105 resin & 206 slow hardener, If I’m looking to cure at 200 F, do I need to be looking for a different resin/hardener? One for high temps?

Thanks a lot for your help,
Randy