Manufacturing Explosives

The majority of military explosives are solid compounds which are manufactured in
granular/crystalline form, and which have bulk densities of less than 1 g/cc. Then these
compounds are mixed with other explosive or inert additives to give explosive formulations
which have densities which are between 1.5 and 1.7 g/cc. Then the explosive formulation
is cast, pressed or extruded to its final form.


Making explosives for implosion systems can be quite a difficult task, and strict quality
control is necessary. Many explosive components have complex shapes, the majority need
narrow dimensional tolerances, and for all a strongly uniform product is necessary.
Detonation velocity variations cannot be greater than a few percent. In order to achieve a
strong degree of uniformity attentive control of many factors is needed, including
composition, purity, particle size, crystal structure, curing time and curing temperature.

Casting

Casting was the first method which was used to manufacture implosion components
because a homogenous product can be produced in quite complex shapes. Essentially
casting means heating the explosive composition until it melts, then pouring it into a
container mold and leaving it to cool and solidify.

However, the most desirable explosives do not melt, which makes casting of the pure
explosive impossible. Generally explosive formulations which are processed by casting
contain TNT, which has a relatively low melting temperature in comparison with its ignition
temperature.

Typically Composition B, which was the first explosive which was employed in a nuclear
device, consisted of 63% Hexogen, 36% TNT, and 1% wax. It is necessary to act with great
care to ensure that the slurry of solid explosive and melted TNT is uniform because settling
occurs. It is necessary to pay great attention to control the particle size of the solid
explosive, and to monitor the casting, cooling, and curing processes.

Pressing

Often the pressing technique is applied to load powdered explosive formulations in small
containers. It does not need very high temperatures and it can be carried out under vacuum.
It is possible to press the explosive compositions directly into a container mold, and to eject
them as pellets.

It is possible to press plastic explosives (which are soft, pliable explosives) into uniform
complex shapes quite easily. However their insufficient strength makes them unattractive
for the majority of practical weapon designs.

For PBXs, explosive crystals are mixed with the polymeric binder and formed by pressing.
Usually machining of the billet follows.

Normally the explosive and polymer binder are processed together to form a granulated
material which is called a molding powder. This powder forms as a result of hot pressing
with the use of molds under vacuum. The formed material can represent the final
component, but normally additional machining to final specifications is needed.

PBXs have a bigger proportion of the desired explosive, have greater structural strength, and
also do not melt. These last two properties make them easier to machine to final
dimensions. Polymer bonding is very important in insensitive high explosives (IHEs), because
mixing the insensitive explosives with the more sensitive TNT would defeat the objective for
their use.