I learned this from Ray Goodson when he used to use a helical vacuum mixer.
Whe dropping the bowl after the course AP was mixed the propellant was like
peanut butter stuck to the mixer blades. Seemingly counterintuitively he
then added the fines and after a brief mixing he dropped the bowl again and
the propellant just ran off of the mixing helix. I forever learned an
important lesson in particle distribution physics.
Vacuum mixing is important too for the best physical properties with the
highest solids loading.
Ken
On Sat, Apr 29, 2023 at 7:02 AM Terry McCreary <prfesser@xxxxxxxxxxx> wrote:
It did. In one batch I used 200 um AP that had caked and needed to be
rubbed through a screen. The resulting mixture should have been fairly
stiff, for packing. The fines created by rubbing made the mix more like
peanut butter; sticky and hard to pack. Got it packed but the fines also
increased the burn rate significantly, with a rather high peak in the test
runs.
------------------------------
*From:* arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> on
behalf of roxanna Mason <rocketmaster.ken@xxxxxxxxx>
*Sent:* Friday, April 28, 2023 9:39 PM
*To:* arocket@xxxxxxxxxxxxx <arocket@xxxxxxxxxxxxx>
*Subject:* [AR] Re: APCP properties, was Re: Re: starship abort?
A little fines really makes a difference in viscosity, as I discovered to
my dismay. Tests did not go well.
Can you elaborate?
The right size and amount of fines should have lowered the viscosity like
putting BB's in a jar full of golf balls and marbles. It will displace the
binder out of the voids into the rest of the mix matrix.
Ken
On Fri, Apr 28, 2023 at 4:57 PM Terry McCreary <prfesser@xxxxxxxxxxx>
wrote:
The sizes that seem to be available to amateurs are 400, 200, and 90 um. A
little fines really makes a difference in viscosity, as I discovered to my
dismay. Tests did not go well.
------------------------------
*From:* arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> on
behalf of roxanna Mason <rocketmaster.ken@xxxxxxxxx>
*Sent:* Friday, April 28, 2023 1:40 PM
*To:* arocket@xxxxxxxxxxxxx <arocket@xxxxxxxxxxxxx>
*Subject:* [AR] Re: APCP properties, was Re: Re: starship abort?
They don't say what the AP size was, just "coarse" and "fine", but the
professionals usually consider fines to be on the order of 10 micron or
less,
Isn't 20-25u considered an explosive ass far as DOT? The finest sold on
FireFox is or at least was 90u.
At Edwards we used a trimodal mix containing 200/90/25u.
Ken
On Fri, Apr 28, 2023 at 8:51 AM Terry McCreary <prfesser@xxxxxxxxxxx>
wrote:
Thank you, Hagen. That kind of work is something I'd avoid with extreme
prejudice. They don't say what the AP size was, just "coarse" and "fine",
but the professionals usually consider fines to be on the order of 10
micron or less, often purchased as a suspension in HTPB to avoid the
researchers having to handle such fine material. Coarse might be 200 micron
or it could be finer than that. And they do mention the fracture of AP as
being a possible reason for some of the behavior.
Reproducibility was a concern of the authors. Three runs with an 8.8mm
nozzle throat gave peak pressures from about 270 to 325 kg/cm^2. Not good.
An exponent of 0.845, and dramatic changes in burn rate with 0.1mm (0.004"
for us 'muricans) changes in the nozzle throat diameter...and one of the
references mentions studies that showed an exponent of 1.05.....oh no, no
thank you. I already know a number of ways to dismember this body, I don't
need any more. 🙂
Terry
------------------------------
*From:* arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> on
behalf of Hagen Hübner <hagen.huebner@xxxxxx>
*Sent:* Friday, April 28, 2023 10:07 AM
*To:* arocket@xxxxxxxxxxxxx <arocket@xxxxxxxxxxxxx>
*Subject:* [AR] Re: APCP properties, was Re: Re: starship abort?
Terry, speaking of the library... work was done up to 15000 psi - with
interesting results:
https://www.eucass.eu/component/docindexer/?task=download&id=4434
(notice: 1kg/cm^2 = 0,981 bar = 14,2 psi)
Hagen
------ Originalnachricht ------
Von "Terry McCreary" <prfesser@xxxxxxxxxxx>
An "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
Datum 28.04.2023 14:32:41
Betreff [AR] Re: APCP properties, was Re: Re: starship abort?
Kevin, I apologize for my earlier post. It was snide and uncalled for.
Now, to address your question: Aerotech has/had, somewhere on the web,
properties of their propellants. Some of them were extremely high
performance, highly aluminized mixes intended for commercial/military use.
You might check the propellant "sticks" they sell on rocketmotorparts.com,
see if properties are described there. However...
From earlier posts it sounds as though you want to work at extremely high
pressures, ten to thirty times those normally used in APCP motors. The
coefficient, exponent, etc. around 1000 psi is surely going to be very
different from those values at 30,000 psi. There may be some plateau
burning or some regions where the exponent decreases (ok) or jumps
dramatically (very bad), I don't know.
Moreover, there is a well-known problem with propellants containing a
large amount of 400 micron AP. Apparently at pressures around (I think)
1000psi or a bit higher, the 400 micron can crack, exposing more surface
area and leading to a rapid unscheduled disassembly. I hypothesize that the
same thing would occur to 200 micron (which makes up most of the usual
APCP) and even 90 micron, which is as fine as the amateur can obtain
without grinding, at the kind of pressures you're considering. There's also
the issue of the binder; that which works well at 1000 psi is unlikely to
be satisfactory at 10-30 times that pressure.
There's an old tongue-in-cheek saying that my own research students have
heard: Six months in the laboratory will save you six hours in the library.
I don't know whether the professionals have done work with APCP at very
high pressures...but before attempting such work it would be wise to find
out what has already been done, and with what kind of success.
Unfortunately such work may be behind a paywall; that's how most
professional journals do it these days.
Before expending a single dollar or hour on propellant/motor making it
would be wise to find out if the kind of work you're considering is even
possible. There is some reason to think that it may not be.
------------------------------
*From:* arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> on
behalf of kevin ward <kevinward46@xxxxxxxxx>
*Sent:* Thursday, April 27, 2023 11:17 PM
*To:* arocket@xxxxxxxxxxxxx <arocket@xxxxxxxxxxxxx>
*Subject:* [AR] Re: APCP properties, was Re: Re: starship abort?
Ap\htpb\+al (294isp, 70\13\12 ?)
I'm asking for any and all stats re open rocket
Ty kindly