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Manufacturing of PAX-3 High Explosive
Authors: Sean Swaszek, Phil Samuels, Dr. Paul Anderson, Katherine Guraini
Abstract
The manufacturing methods of processing controls of explosives play an important role
in maintaining the quality of explosive formulations. PAX-3 is an explosive formulation that is of
interest to the Army for use in gun launch munitions and grenades. PAX-3 shows improved
shock and Insensitive Munition (IM) response as compared with traditional explosive fills.
ARDEC developed the explosive formulation PAX-3 utilizing a twin screw extrusion mixing
method. This is a continuous process in which a two part mixture is fed into the extruder, which
uses high shear mixing to produce PAX-3. Currently, ARDEC is also pursuing an alternate
formulation process of PAX-3 production in a single batch 500 gallon slurry coating process.
Efforts for qualification of explosives often requires a significant amount of resources to
complete all required testing. ARDEC is evaluating the material produced from these two
methods to assess PAX-3 safety, long-term aging, and maintaining similar sensitivity and
performance characteristics according to AOP-7. Cost and acquisition time are also responses
of interest.
Background
The explosive composition PAX-3 is a high blast explosive that maintains metal pushing
capability for applications. The formulation is composed of HMX, aluminum, binder, and
plasticizer. In processing the material, the HMX and aluminum is coated in the polymer binder.
The PAX-3 molding powder is pressed into items achieving high densities for specific
applications. Efforts to produce and qualify PAX-3 molding powder using a slurry coating is
being pursued by ARDEC. The ingredients such as final granule particle size and composition
for the PAX-3 remains the same between both processes. Standards such as AOP-7 dictate
that undergoing any process change may cause for requiring a requalification of a process.
The method of twin screw extrusion was pursued as a larger scale manufacturing method
to produce PAX-3 high explosive. Early laboratory studies had shown the capability to produce
PAX-3 using twin screw extrusion process using a non-aluminized analogous formulation and
Aluminum. This is a 2 step process in which the non-aluminized analogous formulation is first
produced using a slurry coating process and then used as part of a feed mix with aluminum in the
twin screw. The twin screw extrusion process is a continuous method in which the ingredients are
fed at a constant rate to produce the final product. This allows for flexibility to produce variant
formulations containing different ratios of constituent materials. Efforts to transition the twin screw
technology to larger scale manufacturing was funded under the ManTech program in 2009. Using
a 19mm die twin screw extruder at Milan AAP, PAX-3 was produced in large scale quantities and
used for characterization testing at ARDEC. This batch of material was used for qualification
efforts and is now an accepted process to produce PAX-3.
Recently, work was pursued to produce PAX-3 using the slurry coating in a one-step single
batch process. BAE Holston developed a process to produce 500gallon batches of PAX-3 using
this method. Slurry coating is a process in which a binder-lacquer is dissolved in a solvent.
