Jim:
Thanks, that is a very interesting post.
Just FYI, some solid rocket makers have tried purchasing foreign AP, the
incumbent manufacturer has gone to DOD and the Hill to stop it on the
grounds that it is a national security issue....
Bill
On Sun, Aug 5, 2018 at 1:07 AM Jim Rosson <jmrosson@xxxxxxx> wrote:
Bill:
Anthony nailed it.
There is no one perfect blend of 400/200/90 in APCP. You must consider
ALL solid particles used in formula greater than 1-2% of total. Optimizing
particle size blend is a complex statistical probability equation, best
visualized with CAD or 3D solids modeling tool. The Katz book is good
starting point.
IMHO - The ISP differences between bi-modal and tri-modal AP for amateur
HPR are not worth the hype wrapped around them. Most of the tri-modal
blends I used where only Tri-modal to help adjust burn rate, or increase
mix viscosity to eliminate particle size settling/stratification. BTW –
One size AP can be also used with bi-modal metal powders in highly
metalized APCP. Think about it…J
Oh look a rabbit hole appeared? J
To make APCP particle sizing even more complex, a perfect packed size
blend is horrible to mix as there is no extra space in matrix for movement.
You almost do not want a perfect 100% packing density matrix, as you get
reduced shear thinning. Processing a perfect blend successfully requires
complex vacuum blending/casting equipment, and usually entails processing
aids to reduce friction during mixing. It is quite common for formulator
to design max packing density, and then look for best way to keep energy
density high, and improve processing with adjusted size mix.
As Chuck Rogers noted: AP particle sizing is not as simple as it seems.
:o)
Something called 200um AP is actually a range of particle sizes with
statistic average near 200um. There is even an allowable percentage of
particles that are well outside of a ‘200um’’ range, depending on purchase
specification! Have seen bottom of a surplus 200um AP drum that had 20%+
broken AP fines in it due to rough transportation. These size variations
will wreak havoc on your packing density and propellant characteristics.
You ALWAYS want to re-characterize your formula with each and every new
batch of raw materials. It is only way to ensure that raw materials are
making same thing every time.
If you look up the government sourcing documents on AP (remember one was
MIL 822667 as it plastered on every drum?), they are probably best
definition for what is expected inside a drum of 200um AP as government
buys more than anyone else.
If you want to climb further down AP size rabbit hole:
Not sure if still true, as I am out of HPR game now, but; Majority of AP
bought and sold by amateur community used to be government surplus (or
surplus from a contractor working for government/aerospace contracts)?
In 20+ years I made HPR motors, personally inspected and processed
hundreds drums/totes of surplus AP. Everyone of small lot chemical
distributors that HPR folks use are all buying surplus AP from same (2)
chemical brokers that buy/sell AP in USA, or they have cash to buy large
lots directly from exact same government surplus auctions.
Back when my partner was alive, AMW used to split lots with one of
brokers occasionally. We had so much in inventory at times, one particular
Florida hurricane flooded 2 shipping containers holding 35,000+ pounds of
AP, destroying most all of it. L When a crazy dude (who has repeatedly
threaten to kill me) started funding AP buys with my partner and broker
buying large lots to supply amateur crowd, I stopped participating in
surplus purchase process and sort of lost track of it. I hear he actually
resorted to buying directly from the mfg at one point, as surplus market
has disappeared? Good for community.
One problem with surplus AP market that you need to watch out for: What
is really in the drum?
AP was sold ”surplus” for a reason.
Much of surplus AP is sold as remnants left over after a contract is
completed, years later. When Thiokol shuttle booster program used to sell
surplus lots, it was typically 50+ drum lots. When smaller missile
programs sold surplus it was 2-3 drums, or less. Reason being, they
always buy enough to finish contract from same mfg lot to keep same
performance.
Another (scary) reason AP is surplus; because it failed to met particle
size specifications. This size failure could be as shipped from mfg, or
could be due excess/poor storage conditions that allowed excess clumping or
particle size changes. Chemicals are not “fun” to return to mfg nor cheap
to dispose of properly; so many times these out of specification materials
get sold in surplus chemical market “AS IS” for alternate uses.
Believe it not, when surplus AP was really cheap in 90’s due bi-annual
Thiokol AP surplus sales; one ammunition company would buy every AP lot
listed below their trigger price. They would separate AP into perchlorate
acid and ammonia. The separated perchlorate was cheaper than buying it new
from mfg, and ammonia was sold for fertilizer. We could always tell then
perchlorate acid pricing was lower than re-processed surplus AP, as there
was less competitive bidding on surplus lots. J
As Anthony noted: AP in USA is mfg by one monopoly mfg. L I hear
pricing has gone crazy lately?
Maybe this will help?
AP is also produced in China in large quantities. “Surplus” pricing
became available from China ~2010. I am aware of at least one of the high
volume fireworks folks have imported full containers of oxidizers from
China that included AP due US pricing increases. The material I saw was
high quality with tight particle size distributions, and performed like any
other AP I used before?
The challenge with China sourcing is not transportation costs, but
logistics. If you are not routinely shipping containers from China, it is
very hard to find a reliable broker to consolidate, generate customs
paperwork in quintuplicate , and watch over a successful shipment.
Everyone in process has hand outstretched to help you move faster through
the system for higher cost. Most of the big fireworks operations actually
have a sourcing person in China for many weeks at a time, that manages
broker(s) & suppliers; to deal with crazy international logistics issues.
For anyone who needs large volumes of AP, it might be time to call some
fellow danger lovers from PGI, and see if they can help with lower cost
China AP sourcing? Just an idea from an old man. Ignore me please.
OK, rabbit hole is probably too deep. Thanks for reading some ancient
history.
YMMV, Stay safe, and Cheers!
*From:* arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx]
*On Behalf Of *Anthony Cesaroni
*Sent:* Saturday, August 04, 2018 9:51 AM
*To:* arocket@xxxxxxxxxxxxx
*Subject:* [AR] Re: Trimodal AP
This is very dependent on the size, distribution and quantity of other
solids in the formulation such as aluminum powder as well as ballistic
modifiers such as SSFO, ALO2, Guignet green etc. If you are using a
surfactant, that also comes into play. Most APCP is more than bi-modal or
trimodal in terms of solids. Only oxidizers seem to be referred to in this
regard.
Most workhorse commercial propellants are bi-modal as far as oxidizers are
concerned BTW. This is primarily for mechanical properties, ballistics and
economics. 200 mu is the baseline feedstock with everything else being site
milled from that. 90 and 400 have expensive surcharges. Those sizes are
sometimes used in specialty formulations such as 90/10/1 for example or in
the case of 400, gas generators, slower burn rate propellants, delays etc.
Until a few years ago, 600 mu and 50 mu varieties were also produced. AP
was also FDA approved for use in cattle feed. It causes thyrosis so the
bovine fattens up quicker for market but I digress.
A good but expensive reference is “ The Handbook of Fillers for Plastics”
by Harry S. Katz. One method I experimented with many years ago to
formulate multi-modal start points was CAD believe it or not. It worked
surprisingly well.
Best.
Anthony J. Cesaroni
President/CEO
Cesaroni Technology/Cesaroni Aerospace
http://www.cesaronitech.com/
(941) 360-3100 x101 Sarasota
(905) 887-2370 x222 Toronto
*From:* arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> *On
Behalf Of *William Claybaugh
*Sent:* Friday, August 3, 2018 11:51 AM
*To:* arocket@xxxxxxxxxxxxx
*Subject:* [AR] Trimodal AP
Any one know the optimum mix of 400 micron, 200 micron, and 90 micron AP?
Bill