lr64
Well-Known Member
I must have missed it. I thought he was going to use a commercially available bio-epoxy, but that it hadn't been selected yet. I got the impression that different bio-epoxies had different thermal ratings.Brendan is trying to build with bio materials, including a specific bio epoxy, so JB is out of the question. Also, it's pretty thick stuff that I doubt would wet out fabric at all without being massaged in.
Substituting refractory cement for JB Weld to save weight? I don't think you thought that through; you're too smart to seriously suggest that.
Waterglass is neat stuff, though I only know that in principal. (A water soluble silicate? That's just bizarre and cool.) I've been meaning to try some stuff with it. I don't see how it could possibly not be brittle.
In any case, JB, waterglass, cements, fiberglass batts, and so forth are all off the approved materials list, so all of this is moot.
@BrendanH69, have I gathered correctly that you plan to use Aerotech SU motors? Those have thrust rings, so you don't need an engine block at the forward end of the MMT. In point of fact, you could leave out the MMT completely, and that would make this epoxy temperature problem go away. A tube for the motor is a great convenience, but you really don't need it. Make your wooden CRs with their ID to go with the case diameter so they hold the motor directly. It makes lining up the motor to load it a bit of a pain, and installing the CRs a challenge, and those are really the only problems. (Tack each ring to an motor case with a single drop of CA. The case is a carrier to glue the rings to the inside of the BT. Once the glue is fully cured, give the motor a twist; CA sucks in sheer, so the case will come right out.)
The refractory cement wasn't to save weight, it was to resist high temperatures.
People do things with waterglass and various kinds of clay, etc. Maybe one of them isn't particularly brittle. And waterglass isn't some exotic material with fancy organic synthesis, solvents, etc. Nor is cement. I had not been suggesting fiberglass batts, though I did mention ceramic fibers. BTW, natural isn't the same as safe. When I was a kid, I had an asbestos rock that I could peel fibers off of. Fortunately, I didn't do much of that.
BTW, I ran across someone on the web who said they made paper tubes with waterglass as an adhesive. Perhaps they'd be more temperature resistant tubes than any of the more ordinary epoxies.