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> 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>
wrote:
accept somewhat lower performance then a professional propellant, it
There are today plenty of “rubbery” thermoplastics available. If we
seems—in principle—that making and casting solid propellant using a
thermoplastic binder should be relatively simple, as previous RRI
experience w/ asphalt suggests.
sporty.
The problem for me has been figuring out a relatively safe process:
Dry mixing the ingredients and then melting seems—again, to me—too
breaking into pellets for later processing also seems safe up to the point
Dry mixing the Al and binder seems safe enough; melting that and
that AP is added.
dry fuel and oxidizer before melting?
Any thoughts as to how to cast a thermoplastic grain w/o having to mix
Bill