Another thermoset matrix which is showing promising results in ablative
applications is benzoxazine. Huntsman Araldite MT 35700 CH is one common
formulation. A bit tricky to process and the jury is still out on the
performance.
Good luck.
Anthony J. Cesaroni
President/CEO
Cesaroni Technology/Cesaroni Aerospace
http://www.cesaronitech.com/
(941) 360-3100 x1004 Sarasota
(905) 887-2370 x222 Toronto
From: arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> On Behalf Of
Hagen Hübner
Sent: Tuesday, April 27, 2021 5:10 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: nozzle problem - problem nozzle...
Thank you very much for your very helpful comments and suggestions!
Next time we will use a stainless steel nozzle - and at the same time continue
to try to construct a working composite nozzle.
There are some limitations, for example phenolic resin isn't available here (as
are AP and HTPB, but that's another story). We will therefore use resorcinol
resin and basalt
fibers for the next attempt. Weight / mass is in fact an important aspect.
Hagen
------ Originalnachricht ------
Von: "Anthony Cesaroni" <acesaroni@xxxxxxxxxxxx<mailto:acesaroni@xxxxxxxxxxxx>>
An: arocket@xxxxxxxxxxxxx<mailto:arocket@xxxxxxxxxxxxx>
Gesendet: 23.04.2021 00:20:14
Betreff: [AR] Re: nozzle problem - problem nozzle...
Wrong carbon probably as well. PAN and pitch-based carbon are conductive and
will tunnel the matrix rapidly. Rayon based carbon such as Enka and C2 is what
is used in nozzles and ablative structures. It’s not thermally conductive.
Epoxy/PAN-based carbon will not work for this application at all. Epoxy will
not pyrolyze like phenolic or retain char at the appropriate level.
There is only one manufacturer remaining in the US that produces rayon-based
carbon, National Electrical Carbon Products that I’m aware of. The market was
so small that Enka bailed a few years back leaving many including NASA in a
panic. Park Electrochemical et al outsource it and compound it as prepreg. In
the case of C2, under exclusive agreement with Arian. Expect to pay over
$100/lb. for plain weave, rayon carbon fabric and $250/lb. compounded with
SC-1008 phenolic. Silica or quartz phenolic prepreg is only slightly less
expensive to purchase. If you want to try making your own product with silica
and SC-1008, you can save money but keep in mind that single part resole
phenolics have to be molded and cross-linked under at least 50 psi. and
preferably 100 psi or more. It is possible to vacuum bag cure the laminate, but
you will have higher porosity and lower density than optimum. An autoclave,
compression mold or silicone bladder, pressure molding is typically employed.
Two part catalyzed phenolic is available and can be used for hand lay-up but
its performance doesn’t come close to SC-1008 under nozzle conditions.
Anthony J. Cesaroni
President/CEO
Cesaroni Technology/Cesaroni Aerospace
http://www.cesaronitech.com/
(941) 360-3100 x1004 Sarasota
(905) 887-2370 x222 Toronto
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From: arocket-bounce@xxxxxxxxxxxxx<mailto:arocket-bounce@xxxxxxxxxxxxx>
<arocket-bounce@xxxxxxxxxxxxx<mailto:arocket-bounce@xxxxxxxxxxxxx>> On Behalf
Of JAMES ROSSON
Sent: Thursday, April 22, 2021 12:38 PM
To: arocket@xxxxxxxxxxxxx<mailto:arocket@xxxxxxxxxxxxx>
Subject: [AR] Re: nozzle problem - problem nozzle...
+1 Wrong resin
Need to be using a oven cured phenolic novolac or resol based resin system.
The novalac are solid at room temp and molded at high temp/pressure. The resol
based are available as liquid system.
IMHO - There are several aspects of the nozzle that are improperly designed
beyond resin:
Nozzle design requires careful combination of ablative materials, insulation
materials, and structural materials. Most common old school, long burn time
nozzle fairing is produced via filament winding various layers of materials.
The often contain 2+ layers of different materials wound on same mandrel.
There is an ablative layer in contact with flame front. There is middle
insulation layer. And last a structural layer to support the pressures, and
mounting. Look up the designs on AMARM or HARP motors for examples. Even the
venerable shuttle motor is excellent teaching aid in the challenges of rocket
motor nozzles, and documentation is easy to find.
Use of graphite fabric is not good. Graphite fabric conducts heat almost as
well as metal. So as soon as the surfaces sees 2000°, so does the resin, and
the adhesive becomes Jello. Graphite fabric is last thing you want near flame
front. For rocket nozzle fibers, the lowest temp fibers you can get away with
are Kevlar (polyamide) materials. But even these polyamide fibers melt above
700-800°. What you really want is silicate based ceramic fibers.
We amateurs tend to use solid graphite as; thick section acts like an
insulator, and has low erosion rate. The nozzle exit pressure is supported by
casing. But these can be heavy when mass fraction is important. Amateurs
worry way to much about mass fraction, for all wrong reasons. Did you run an
FEA simulation on how many bolts you needed on end closures? My guess is used
to much hardware, that could be eliminated and the mass used for nozzle. LOL
Achieving highest mass fraction tends to be very expensive. Very few folks are
willing to spend hundreds of hours engineering the best nozzle, or the extra
1000's of $$ it takes to achieve lowest mass fraction.
Have flown several "O"/"P" class motors using graphite throat, and machined
fiberglass exit cone. The exit cone had a flange, and acted like the nozzle
insulation washer too. For small 1-2 second burn motors, have used a
stainless steel exit cone. :)
One of the newer technologies used in medium burn time nozzles is stainless
steel or titanium cone, spray coated with thick ceramic coating.
Last but not least: Need to pay careful attention to propellant chemistry, and
more temperatures/pressures. A motor with large amounts of metal has higher
exit temperatures, which needs more insulation and suffers more erosion.
Nitrate based propellants tend to generate complex ceramic oxides that can be
more abrasive than aluminum oxide found in AP/Al motors.
Another design element is chamber and exit pressure. Running higher pressure
and flow rates tends to reduce the exposure time of erosive particles on exit
area. If you really want to understand, try using FEA to model the
heat/pressure exposure of the mass flow.
PS - The suggestion for JB weld is not going to help. JB weld is filled with
aluminum. It conducts heat, and you want an epoxy with filler that insulates,
like silica glass or phenolic micro-balloons.