- This topic has 12 replies, 5 voices, and was last updated 13 years, 8 months ago by
Warren B. Musselman.
Warren B. Musselman.-
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Tom Martin
So I just got finished building a curing oven, and laying up my first fiber glass tube. For my first try it was a good learning experience. I used a length of coupler tube as a mandrel and wrapped with mylar. I then did my glass wraps and finished with peel ply. Once it was ready I placed the whole thing in the oven and cured for 2 hours. The finished tube was OK and will get cut and used.
I have a few questions though. What is a good temp / procedure for curing and heat treating the Aeropoxy? Also, If I wish to use heat shrink tape, would I be better off letting the oven shrink the tape or preshrink with a heat gun and then put things in the oven?
Adrian
You should cure Aeropoxy at a temperature that is close to the service temperature you’re planning to use, if you want it to have full strength when it’s hot. I have post-cured Aeropoxy to 225 in my kitchen oven for a couple of hours, with good results. The fins on my 32,000 foot, Mach 2 L shot in October were treated that way and came back without a scratch.
As a side note, if you’re going to be laying up your own composite anyway, you may find that carbon fiber is actually cheaper and faster than fiberglass, since you need less of it for the same strength. Sollar composites is a great resource there.
Tom Martin
Thanks. I actually cured this first tube at about 200F. I used an on / off temp switch that turned the heat off at about 200 and back on again at 185 so it would sit and cycle in this range. I got some redish discoloration on the end that was closest to my heat source, and was worried that this may be a sign of over heating during cure.
Adrian
What are you using for a heat source, and do you have a fan in your oven? I’m building an oven now, myself, and I’m working on rigging up an external motor that turns an internal fan blade.
Tom Martin
I have 3 75W light bulbs for a heat source that are turned on and off via a temp switch. I then have small 3 inch muffin fan that runs off 120V AC that is on all the time. The oven is 1′ by 1′ by 6′ and this length may mean that my temperatures are not as even as I would wish with a single fan. I have the temp switch and candy thermometer mounted about half way along the length of the part in the oven. I may not be convecting all the way to the far end of the oven, or my heat source is just too hot. Any idea if that discoloration I was asking about is a bad thing?
Adrian
Mine will be similar, at 18″x18″x6′. I’m concerned about not having enough convection for mine, too. You may want to do an experiment with the thermometer at different places. Where did you get your temp switch?
If your epoxy isn’t crumbly or chalky I wouldn’t be too worried about using it.
Tom Martin
Found it on Amazon. It came from a soldering company called Isotip I think. Less than $20. This limits me to single temp range use but was cheap to get things going. Dave Triano over at Shadow Aero is selling a fairly low cost adjustable controller but was out of stock and was waiting for more from his supplier. I am waiting for an E-mail from him and will likely order one for the flexability. My fan was from Amazon as well and was also cheap. It has held up to the heat in the oven fine so far. I guess we’ll see how long it lasts.
Warren B. Musselman
I did a multitude of experiments with a curing oven back in the early 2000’s when I was trying to make decent tubing on my own. The oven was basically 2″ Polyisocyanurate foil faced foam with a sort of rotisserie rig inside (I had hoped to rotate the tubing as it cured to keep drips and runs from happening). The bottom of the box had 4 x 100W regular lightbulbs in sockets underneath a foil-covered plywood baffle. At each end I had a 110VAC 4″ muffin fan to circulate air within the oven. In the main oven compartment, I had an LM35 extended range temp sensor that connected to a BASIC Stamp microcontroller that in turn controlled a Triac to control the light bulbs.
It worked great until I got into vacuum bagging and the whole rotisserie idea went out the window. It wasn’t possible to build a vacuum-tight oven box and there was no way to deal with the twisting of the vacuum hose. So, I gave up on heat-cured epoxies and went back to West Systems which I had a lot of experience with from boat building.
For most projects, you don’t need heat cured epoxies or anything fancy – primarily you just need an epoxy runny enough to properly wet-out the fabric. Except in cases of extreme minimum diameter projects with long burn larger motors, heat soak damage is either non-existent or so minimal that there is no need to go with heat-cured epoxies except for the fun of it. The one exception I make to that is for fin root joints (not fillets) and motor mounts (on non-MD projects) – there I use Cotronix (too expensive) or JD Weld.
Dave Smith
Warren,
Are you saying that JB Weld is more appropriate on the fin root (fin-to-motor mount) than just regular old epoxy that I get at the hardware store?
and what does “MD” mean in regards to your post?
thanks,
Doug Gerrard
It worked great until I got into vacuum bagging and the whole rotisserie idea went out the window. It wasn’t possible to build a vacuum-tight oven box and there was no way to deal with the twisting of the vacuum hose. So, I gave up on heat-cured epoxies and went back to West Systems which I had a lot of experience with from boat building.
You don’t need a rotisserie if you are curing a tube in a vacuum bag. I built my oven so the tube stands vertically. Don’t have to worry about the tube curing in an out-of-round state and it can still be in a vacuum bag. I too have a circulating fan (motor outside the oven box) that forces air up through the tube and then back down the out sides. It is about 2′ x 2′ and can handle about a 7′ long tube. It is intended to cure the entire fin can after the fins are installed.
Doug
(I’m sure Warren means minimum diameter…)
Tom Martin
Adrian
Warren B. Musselman
Dave Smith
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