Don’t forget about PVC Plastisol. ARC used it exclusively for the ARCAS
sounding rocket IIRC. It’s fussy about the precursor grade of PVC powder used
but it’s still available.
Anthony J. Cesaroni
President/CEO
Cesaroni Technology/Cesaroni Aerospace
<http://www.cesaronitech.com/> http://www.cesaronitech.com/
(941) 360-3100 x1004 Sarasota
(905) 887-2370 x222 Toronto
From: arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> On Behalf Of
William Claybaugh
Sent: Friday, July 10, 2020 3:24 PM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Amateur thermoplastic binder solids
Ben:
The professional literature typically describes a mix of styrene and other
plastics, waxes, and or oils. (Anthony has a nice patent on one class of
thermoplastic binders.) The other obvious possibility is the thermoplastic used
for “run flat” bicycle tires which could even be obtained by remelting used
copes of same and does have some nice elastic properties.
Your comment about Mojave summers seems to me germane: an issue with these
binders is that they can become soft at high ambient temperatures and can pass
to a glass phase at relatively high lower temperatures. The other issue is they
tend toward a thicker melt layer than HTPB (which typically has little or none)
which can flow with the gas flow, increasing burning rate.
I’m still thinking about it but I’m not yet ready to start building the
required GSE.
Bill
On Thu, Jul 9, 2020 at 6:13 PM Ben Brockert <wikkit@xxxxxxxxx
<mailto:wikkit@xxxxxxxxx> > wrote:
Bill,
I googled around a bit but didn't find many plastics that are higher
than Mojave in summer temperature but lower than 100 C. PEG 8000 is
about as close as I got, https://amzn.to/2ZbzHNc
Melts at 160-165 deg F, sg 1.111. Have not put it into pypropep to see
what it does.
Independent of the "thermoplastic APCP" use case, it seems like an
interesting addition to try in KNSB motors. KNSB is melted and cast,
but is fairly brittle and stiff and can't generally be case bonded.
PEG is specifically used as an additive to other plastics to make them
more flexible. It is fairly water soluble, but then so is KN and SB so
it doesn't change that aspect of the motors.
Agreed that hands-off melting and casting seems like a good idea, but
from Troy it sounds like that is fairly well sorted out already.
On Wed, Jul 8, 2020 at 1:01 PM William Claybaugh <wclaybaugh2@xxxxxxxxx
<mailto:wclaybaugh2@xxxxxxxxx> > wrote:
Ben:
The RRI (circa 1968) use to melt tar in an electrically heated pot and then
mix in Potassium Perchlorate so there is an existence proof that a “low”
melting point binder can be mixed with oxidizer w/o ignition.
My sources say AP ignites a little above 400 degrees F so a binder that forms
a low viscosity fluid at around the BP of water will in theory work fine if
there is no possibility of hot spots.
If I were going in that direction I would want to automate the mixing rather
than stand over an open pot of hot binder, AP, and Al, stirring. I would
also expect that the casting process would require starting with a heated
motor / mandrel and then cooling it, presumably from bottom to top, assuming
a vertical pour. Again, I would not be willing to be standing next to this
setup during pour.
I’m thinking of putting it on the to-do list but I’m cautious.
Bill
On Wed, Jul 8, 2020 at 12:36 PM Ben Brockert <wikkit@xxxxxxxxx
<mailto:wikkit@xxxxxxxxx> > wrote:
In the "sugar" world where dry mixing and melting is common, they did
some basic sensitivity tests of putting the propellant on the skillet
or whatever and seeing how much excess heating it takes to set it off.
It turns out that it's usually quite a lot, though it's a proof test
that should be redone when things like catalysts are added.
I don't know how AP mixes compare for autoginition or decomposition
temperatures. But you can run the process with an inert oxidizer
stand-in, to look for hot spots and see how the viscosity works out at
a given dry proportion to melted.
Supposedly the big "hybrid" of doom has (or had) some oxidizer mixed
into the fuel grain to increase performance, so there's probably
someone out there who would really like to talk about casting a ton of
thermoplastic nylon with oxidizer.
On Wed, Jul 8, 2020 at 8:13 AM William Claybaugh <wclaybaugh2@xxxxxxxxx
<mailto:wclaybaugh2@xxxxxxxxx> > wrote:
There are today plenty of “rubbery” thermoplastics available. If we accept
somewhat lower performance then a professional propellant, it seems—in
principle—that making and casting solid propellant using a thermoplastic
binder should be relatively simple, as previous RRI experience w/ asphalt
suggests.
The problem for me has been figuring out a relatively safe process:
Dry mixing the ingredients and then melting seems—again, to me—too sporty.
Dry mixing the Al and binder seems safe enough; melting that and breaking
into pellets for later processing also seems safe up to the point that AP
is added.
Any thoughts as to how to cast a thermoplastic grain w/o having to mix dry
fuel and oxidizer before melting?
Bill