If you’re using most urethane cross-linking chemistries, you want to dry
everything and that means everything including things that may not be obvious
at first. Additives such as super fine iron and aluminum oxide for example may
not absorb water chemically but a gram of material can have a square meter or
more of surface area to attract H2O which is enough to scavenge all kinds of
functionality and blow the intended reaction. You can easily end up with a fuel
grain with a matrix resembling cold peanut butter just because your inert
ballistic modifier happened to pick up water molecules by surface attraction.
Keep your rubber and plasticizers sealed and under dry nitrogen as well.
Certain HTPB plasticizers such as isodecyl pelargonate are especially notorious
for picking up moisture. Once it’s been contaminated, you might get lucky by
applying a molecular sieve or better still, toss it.
Did somebody mention that air can also be a problem?
Anthony J. Cesaroni
President/CEO
Cesaroni Technology/Cesaroni Aerospace
<http://www.cesaronitech.com/> http://www.cesaronitech.com/
(941) 360-3100 x101 Sarasota
(905) 887-2370 x222 Toronto
From: arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> On Behalf Of
Troy Prideaux
Sent: Sunday, July 7, 2019 6:53 PM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Vacuum processing of solid propellant
This is why I do all my mixing and casting under vac. Normally NCO will favour
H2O over OH in terms of reactivity although OH groups do some in various
different reactivities.
Troy
From: arocket-bounce@xxxxxxxxxxxxx <mailto:arocket-bounce@xxxxxxxxxxxxx>
[mailto:arocket-bounce@xxxxxxxxxxxxx] On Behalf Of 1bcjolly
Sent: Monday, 8 July 2019 5:09 AM
To: arocket@xxxxxxxxxxxxx <mailto:arocket@xxxxxxxxxxxxx>
Subject: [AR] Re: Vacuum processing of solid propellant
Some suggestions:
1) Do you dry your AP? I have found that AP contains moisture, supposedly
from absorption from the atmosphere. This water can be driven off by drying at
a temperature of 240 F. Drying the AP before mixing should also help the cure
if you are using OH/NCO chemistry since moisture contamination uses up NCO
functional groups.
2) Use slow mix speed. Baking type mixers on almost any speed will introduce
air into the mix.
Barry C
Sent from my Sprint Tablet.
-------- Original message --------
From: Anthony Cesaroni <anthony@xxxxxxxxxxx <mailto:anthony@xxxxxxxxxxx> >
Date: 7/7/19 14:43 (GMT-05:00)
To: arocket@xxxxxxxxxxxxx <mailto:arocket@xxxxxxxxxxxxx>
Subject: [AR] Re: Vacuum processing of solid propellant
Discharge machine extra.:-)
Anthony J. Cesaroni
President/CEO
Cesaroni Technology/Cesaroni Aerospace
<http://www.cesaronitech.com/> http://www.cesaronitech.com/
(941) 360-3100 x101 Sarasota
(905) 887-2370 x222 Toronto
From: arocket-bounce@xxxxxxxxxxxxx <mailto:arocket-bounce@xxxxxxxxxxxxx>
<arocket-bounce@xxxxxxxxxxxxx <mailto:arocket-bounce@xxxxxxxxxxxxx> > On Behalf
Of William Claybaugh
Sent: Sunday, July 7, 2019 12:40 PM
To: arocket@xxxxxxxxxxxxx <mailto:arocket@xxxxxxxxxxxxx>
Subject: [AR] Vacuum processing of solid propellant
I ran some static tests recently using a modified version of the standard RRS
composite propellant (10% Al rather than 7%). Those tests included applying
vacuum to the fully processed mix ahead of casting (5 minutes); the mix was
still outgassing when we repressurized
This resulted in an about 5.6 % increase in density, of which 0.9% is
attributable to the increased Al loading.
Given that full mixing under vacuum is not viable given the processing
equipment available at the MTA, is there another vacuum schedule that might
provide still higher density?
Does degassing the liquid components before mixing help or does the subsequent
mixing just reintroduce air? Any recommendations on degassing time after
mixing (recognizing that the catalyst is in the mix at this point).
Two static tests, one at 390 psia average and the other at 760 psia average
showed a decreased burn rate and a slightly higher ISP as compared to the
original mix, as expected.
Bill
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