|
|
Marvin Kaye wrote:
The other reason I'd go for the EZ-Lam is the viscosity... 5000cps is still pretty high, but given the long pot life, and if you vacuum bag, you might be able to get the resin content down to 50-60%. (Aerospace hi-temp pre-pregs cert at 39% +/-1%). The 562N has a mixed viscosity of 8500cps... that's sort of like molasses... even with carbon fiber, wetout will be a trick. (I've used some 10,000cps material and couldn't wet out standard 7781 e-glass without raising the application temps to 120F+.)
Great points, Marvin. Frankly I think Alex is going to find it difficult to properly wet out the fibers with EITHER epoxy system without vacuum bagging, and Alex, correct me if I'm wrong but you're not doing that at this time (or perhaps not ever), right?
High-heat application does help, and some composite builders swear by heat guns to apply local heat where you're stippling at the moment. I've never needed one for my plane construction (MGS wets out anything with no trouble) but it would definitely help here.
Also, these other systems REQUIRE a post-cure in an oven.
Alex, if the intake is running over even 350F aren't we going to be worried more about detonation INSIDE the intake than having the epoxy melt or catch fire? I think we need a reasonable limit for this search. If you've established that 210F is a good upper limit, you'd probably be better off with a lower-viscosity and 250-280 just gives you margin. Why not go with a lower temperature setup? To set the "ideal" end of the scale, a good fiberglass layup resin will have a viscosity in the 500-1,000 range. Doubling it you can get away with, but quintupling it is going to get frustrating for manual layup techniques.
I'm wondering if we might not be able to find a compromise. I looked at all of the aircraft laminating epoxies and they're all designed for room-temperature cure without an oven post-cure. You have a trade-off to make - their highest Tg is 230F (MGS-285, special conditions - that DOES require a post-cure).
But what about something like this?
http://www.freemansupply.com/RenRP4005RRP1500HU.htm
It can go up to 300F, not as high as the others but its viscosity is only 1900cps so it'll be easier to work with. It DOES require a post-cure, but so did the other two you mentioned. As a general rule, any epoxy is going to require a post cure within the range of temperature it's designed to tolerate.
Is heat shielding an alternative? Under proper conditions you can get MGS-285 up to 230F, and that's spitting distance. If a reflective coating could be sprayed on, or other methods of insulation explored (SS shield?), and your mounting flange can provide some insulation from conducted heat, you might get away with the MGS-285. I suppose you could even duct some cooling air over the intake to keep it cool, but won't the fuel vaporization provide a natural cooling effect as well?
So, how's that post-cure oven? =)
Regards,
Chad
|
|