As Peter and Tom said, it’s very much the epoxy that’s your killer. You need a
binder that won’t melt especially at low temperatures ie. a polymer instead of
melting will sublimate or ablate or char at its decomposition point eg phenolic
or some kind of Phenol formaldehyde resin. Even a wood bonding product such as
the one Carl recently suggested for ablative chambers would be far preferable.
If you can’t find any such product available in your region – and they are
becoming increasingly scarce – then you ‘ll need to improvise with something
like a ceramic or maybe (depending on duration) you might *just* get away with
high temp JB weld filled to the max with more high temperature fillers and post
cured at the highest possible temperatures allowable. In terms of ceramics, you
could *perhaps* try a sodium silicate based muffler putty ie. the type that are
good for 1000deg C cont. Whichever way, you need to max out the fibre
reinforcement that provides most of the structural and thermal support.
If you can find something like this anywhere, then you’re free to worry about
other things.
www.propulsionlabs.com.au/Phenolic_Resin/Resinox_Resin.pdf
<http://www.propulsionlabs.com.au/Phenolic_Resin/Resinox_Resin.pdf>
Troy
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Hagen Hübner
Sent: Thursday, 22 April 2021 5:17 PM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] nozzle problem - problem nozzle...
Hello everyone,
a few days ago we (Forschungsgemeinschaft Alternative Raumfahrt - FAR e.V.)
tested an O-motor with a nitrate-based fuel. The part of the nozzle near the
combustion chamber was made of graphite and withstood the high temperatures and
the abrasive exhaust without any problems. The nozzle extension - for weight
reasons made of carbon fiber reinforced epoxy resin (tempered, but otherwise
standard resin), material thickness 3 - 7 mm - however, failed after about one
second of burning time (see attached photos).
Question(s): What can be improved to prevent the extension from burning through
in the future? Is there any chance at all chance to make a weight-saving nozzle
extension made of composite, designed for a burn time of 5 - 10 seconds? Which
more temperature-resistant resin should I use? Which reinforcing fibers are
(more) useful? Do basalt fibers have a significant advantage over carbon fibers?
Regards,
Hagen